ATP Dependent Efflux Transporters ABCB1 and ABCG2 Are Unlikely to Impact the Efficacy, or Mediate Resistance to the Tyrosine Kinase Inhibitor, Ponatinib

Abstract Abstract 2745 Ponatinib is a potent pan-BCR-ABL tyrosine kinase inhibitor (TKI) currently in a pivotal phase 2 clinical trial. Ponatinib (PON) was specifically designed to target both native and all mutant forms of BCR-ABL, including T315I. The phase I study of oral ponatinib in patients with refractory CML/ALL or other hematologic malignancies recently reported that 66% and 53% of patients with CP-CML achieved MCyR and CCyR respectively (Cortes et al., ASH 2011 abstract #210). While extensive modelling experiments in BaF3 cells have been performed characterising in vitro response to ponatinib, little is known about the interactions of this drug and drug transporters that impact the response of other tyrosine kinase inhibitors (TKIs). To explore this we have examined both the degree of in vitro kinase inhibition mediated by ponatinib in BCR-ABL+ cell lines, and the intracellular uptake and retention (IUR) of ponatinib achieved. The IC50 was determined by assessing the reduction in %p-Crkl in response to increasing concentrations of ponatinib in vitro. The IUR assay was performed as previously using [14-C]-ponatinib. To determine the role of ABCB1 and ABCG2, both previously implicated in the transport of other TKIs, IC50 analysis was performed on K562 cells, and variants; ABCB1 overexpressing K562-DOX and ABCG2 overexpressing K562-ABCG2. As shown in Table 1, in contrast to the results previously observed with imatinib (IM), nilotinib (NIL) and dasatinib (DAS) there was no significant difference in the IC50ponatinib between these three cell lines, suggesting neither ABCB1 nor ABCG2 play a major role in ponatinib transport. Furthermore, the addition of either the ABCB1 and ABCG2 inhibitor pantoprazole, or the multidrug resistance (MDR) inhibitor cyclosporin did not result in a significant change in the IC50ponatinib in any of the cell lines tested. In contrast the addition of either pantoprazole or cyclosporin resulted in a significant reduction in IC50IM, IC50NIL. and IC50DAS of K562-DOX cells, supporting the notion that these TKIs interact with ABCB1.Table 1:The IC50 of ponatinib (compared to IM, NIL and DAS) in K562 cells and the over-expressing variants DOX and ABCG2 in the presence of the ABC inhibitors pantoprazole and cyclosporin. n=5. *p<0.05IC50% reduction in IC50+ pantoprazole+ cyclosporinPON (nM)IM (μM)NIL (nM)DAS (nM)PONIMNILDASPONIMNILDASK5627.793751111544*NA−107NA2DOX7.919*598*100*1018*63*1655*88*ABCG26.4730025*6NA To further examine the effect of ABC transporters on ponatinib efflux we have determined the IUR of [14-C]-ponatinib in K562, DOX and ABCG2 cell lines. We demonstrate no significant difference in the IUR between these cell lines at 37°C (n=6) (K562 vs DOX p=0.6; K562 vs ABCG2 p=0.37 and DOX vs ABCG2 p=0.667 at 2uM respectively). Temperature dependent IUR experiments reveal a significant reduction in the ponatinib IUR at 4°C compared to 37°C in K562 cells (n=6) (p=0.008), DOX cells (p=0.004) and ABCG2 cells (p=0.002) supporting the likely involvement of an ATP/temperature dependent, and yet to be determined, component of ponatinib influx. There was no significant difference in the IUR between these cell lines at 4°C (p=0.824, p=0.7 and p=0.803 respectively). Importantly, these data are consistent with the IC50ponatinib findings. If ATP dependent efflux pumps (ABCB1 and ABCG2) were actively transporting ponatinib, a significant decrease in IUR in DOX and ABCG2 at 37°C compared to K562 cells would be expected, but is not observed here. Analysis of ponatinib IUR in the prototypic ABCB1 over-expressing CEM-VBL100 cells, and their parental, ABCB1 null counterparts (CCRF-CEM) further confirmed these findings. The IUR in VBL100 cells was significantly higher than that observed in CEM's (p<0.001; n=5), providing further evidence that ponatinib was not being exported from the cell actively via ABCB1. These data suggest that the transport of ponatinib is, at least in part, temperature-dependent indicating a yet to be determined ATP transporter may be involved in the transport of ponatinib into leukaemic cells. Importantly, this data suggests that ponatinib is unlikely to be susceptible to resistance via the major ATP efflux transporters (ABCB1 or ABCG2) that have been previously demonstrated to significantly impact the transport of, and mediate resistance to other clinically available TKIs. Disclosures: White: BMS: Honoraria, Research Funding; Novartis Pharmaceuticals: Honoraria, Research Funding. Clackson:ARIAD: Employment. Hughes:Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; ARIAD: Honoraria, Membership on an entity's Board of Directors or advisory committees.

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Differential Activity of Pazopanib and Imatinib Against PDGFRA-Related MPN and AML

Blood ◽

10.1182/blood.v118.21.5153.5153 ◽

2011 ◽

Vol 118 (21) ◽

pp. 5153-5153

Author(s):

Steffen Koschmieder ◽

Mirle Schemionek ◽

Christian Elling ◽

Utz Krug ◽

Torsten Kessler ◽

...

Keyword(s):

Cell Growth ◽

Tyrosine Kinase Inhibitor ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Kinase Inhibitor ◽

Point Mutations ◽

Differential Sensitivity ◽

Advisory Committees

Abstract Abstract 5153 Introduction: Pazopanib is a tyrosine kinase inhibitor with proven activity against metastatic renal cancer. Due to its target spectrum of kinases (PDGFR, KIT, and VEGFR), we sought to investigate its activity against myeloid malignancies. Methods: 32D cells transduced with FIP1L1-PDGFRA or several activating PDGFRA point mutations as well as AML cell lines were analyzed for the effects of pazopanib vs. imatinib on cell growth, MTS activity, 7-AAD positivity, and clonogenic growth. Pazopanib and imatinib were purchased from LC Laboratories Woburn, MA, USA. Results: Pazopanib was found to decrease the growth of FIP1L1-PDGFRA transduced cell lines at low nanomolar concentrations (10 nM). 1000 nM doses were equally effective as 1000 nM of the PDGFR tyrosine kinase inhibitor imatinib. MTS assays confirmed that at 10 nM, pazopanib reduced cell proliferation to 28% of that of vehicle-treated control cells (DMSO 0.05%), while 100 nM of pazopanib completely abolished cell growth and suppressed MTS activity. Analysis of 7-AAD positivity using flow cytometry showed that reduction in cell growth and MTS activity was due to induction of apoptosis (17+/−0.6%, 63+/−0.5%, and 87+/−0.5%, 86+/−0.1% for 10, 100, and 1000 nM of pazopanib and 1000 nM of imatinib, respectively). Interestingly, while two PDGFRA activating point mutations (H650Q and R748G) recently identified in patients with idiopathic hypereosinophilic syndrome-type myeloproliferative neoplasms (MPN) were equally sensitive against pazopanib and imatinib, two other such point mutations showed differential sensitivity, with Y849S being more sensitive to imatinib and N659S being more sensitive to pazopanib. When evaluating the effect of pazopanib on acute myeloid leukemia cell lines, we found that imatinib inhibited the cell growth and reduced colony forming units of Kasumi-1 and BCR-ABL positive K562 but not MV4-11 or NB-4 cells, while Kasumi-1, MV4-11, and NB-4 cells were sensitive towards pazopanib treatment. Moreover, while the clonogenic growth of bone marrow-derived cells from two control patients (lymphoma or AML in remission) were only reduced to 75% of control with pazopanib treatment in vitro (100 nM), 100 nM pazopanib decreased colony growth to 18% in another patient with AML at diagnosis. Conclusion: Our data suggest that pazopanib may be active against a variety of myeloid neoplasms and that clinical studies assessing its efficacy are warranted. Also, cells may show differential sensitivity against the PDGFR and KIT inhibitors pazopanib and imatinib. Disclosures: Koschmieder: GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Off Label Use: Data on in vitro activity of pazopanib and imatinib in MPN and AML discussed. Krug:MedA Pharma: Honoraria; Novartis: Honoraria; Alexion: Honoraria; Boehringer Ingelheim: Research Funding; Sunesis: Honoraria. Müller-Tidow:Novartis: Research Funding.

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The ABCC6 Transporter Plays a Significant Role in the Efflux of Nilotinib and Dasatinib, and May Contribute to Tyrosine Kinase Inhibitor Resistance

Blood ◽

10.1182/blood.v128.22.4237.4237 ◽

2016 ◽

Vol 128 (22) ◽

pp. 4237-4237

Author(s):

Laura N Eadie ◽

Jarrad M Goyne ◽

Timothy P. Hughes ◽

Deborah L White

Keyword(s):

Mrna Expression ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

K562 Cells ◽

Mrna Levels ◽

Advisory Committees ◽

Ku812 Cells

Abstract Efflux transporters ABCB1 and ABCG2 interact with tyrosine kinase inhibitors (TKIs) and mediate drug resistance, however, evidence of the interaction of other potentially relevant drug transporters with TKIs is lacking. We investigated the involvement of the closely related transporter ABCC6, in imatinib (IM), nilotinib (NIL) and dasatinib (DAS) transport and also the role of ABCC6 in NIL resistance. The impact of short-term (overnight) exposure to NIL on mRNA expression of ABC transporters in three BCR-ABL1+ cell lines was assessed by Taqman transporter array: K562, K562-Dox and KU812 cells. Several transporters of interest were identified, including ABCC6, based on alterations in mRNA expression. In order to elucidate the importance of ABCC6 in the development of NIL resistance, ABCC6 mRNA levels were determined by RT-PCR in K562 and K562-Dox NIL-resistant lines generated in vitro and compared with ABCC6 mRNA levels in respective parental control cells. ABCC6 protein expression was confirmed by western blot. p-Crkl dependent IC50 experiments in the absence and presence of three ABCC6 inhibitors (indomethacin, INDO; probenecid, PRO; pantoprazole, PP) were performed in patient mononuclear cells (MNCs) and BCR-ABL1+ cell lines to assess the role of ABCC6 in NIL, IM and DAS transport. A marked increase in ABCC6 mRNA expression in response to short-term in vitro NIL exposure occurred: in K562 and KU812 cells ABCC6 mRNA levels increased 9.5- and 9.7-fold in response to overnight NIL exposure respectively. Increased expression of ABCC6 was also observed in cells subjected to long-term NIL exposure during development of NIL resistance in vitro. NIL-resistant K562 cells demonstrated up to 57-fold higher levels of ABCC6 mRNA compared with control cells (p=0.002). Analogous results were observed in NIL-resistant K562-Dox cells (up to 33-fold higher levels of ABCC6 mRNA p=0.002). In order to determine the relevance of ABCC6 in patient cells, p-Crkl dependent IC50 experiments were performed in MNCs from de novo CML patients in the absence and presence of ABCC6 inhibition. Results demonstrated a significant reduction in IC50NIL in the presence of all three ABCC6 inhibitors compared with IC50NIL in the absence of inhibitors. Similar results were observed for IC50DAS but not IC50IM. Experiments in three parental BCR-ABL1+ cell lines confirmed these findings (Table 1). Notably, comparison of IC50 values in the absence of ABCC6 inhibition in KU812 vs. K562 cells revealed that KU812 cells demonstrated increased IC50NIL (307 vs. 257 nM, p=0.0493) and IC50DAS (14 vs 8 nM, p=0.0005). This was unexpected given both cell lines demonstrate negligible expression of ABCB1 (a transporter known to interact with both NIL and DAS). However, assessment of ABCC6 protein levels by western blotting revealed KU812 cells have greater levels of ABCC6 when compared with K562 cells: 53% in KU812 vs. 24% in K562 (ABCC6 normalised to β-actin). A greater %reduction in IC50NIL and IC50DAS in the presence of ABCC6 inhibition was also observed in KU812 cells compared with K562 cells confirming the role of ABCC6 in the transport of NIL and DAS. Combined, these studies highlight the importance of ABCC6 in the export of NIL and DAS from patient MNCs and BCR-ABL1+ cell lines. This is the first report of ABCC6 involvement in TKI transport and results suggest ABCC6 overexpression may also contribute to NIL resistance. The addition of ABCC6 inhibitors to NIL and DAS therapy may enhance the efficacy of these TKIs in the treatment of CML. Disclosures Hughes: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Australasian Leukaemia and Lymphoma Group (ALLG): Other: Chair of the CML/MPN Disease Group. White:Ariad: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding.

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Increasing Expression Of The Efflux Transporter ABCB1 May Predispose CML Cells To Overt TKI Resistance

Blood ◽

10.1182/blood.v122.21.5157.5157 ◽

2013 ◽

Vol 122 (21) ◽

pp. 5157-5157

Author(s):

Laura Eadie ◽

Timothy P. Hughes ◽

Deborah L. White

Keyword(s):

Disease Progression ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Resistance Mechanisms ◽

Molecular Response ◽

Advisory Committees ◽

Tki Resistance ◽

Additional Resistance

Abstract Tyrosine kinase inhibitors (TKIs) result in excellent responses in most Chronic Myeloid Leukemia (CML) patients. However, up to 35% of patients treated with imatinib (IM) exhibit resistance and more recently nilotinib (NIL) and dasatinib (DAS) resistance have also been observed. Mutations in the BCR-ABL kinase domain (KD) are the main cause of secondary TKI resistance. Other mechanisms include overexpression of BCR-ABL, LYN and ABCB1. Predicting patients with susceptibility to mutation development and disease progression is crucial, thus we investigated the kinetics of TKI resistance emergence in vitro and in vivo. ABCB1 is implicated in TKI efflux hence we postulated that overexpression of ABCB1 leads to reduced intracellular TKI concentrations, resulting in inferior inhibition of Bcr-Abl predisposing cells to resistance development. Accordingly, 3 CML blast crisis (BC) cell lines (K562, K562-Dox, KU812) were cultured in increasing concentrations of IM to 2 μM, NIL to 2 μM and DAS to 200 nM until we observed overt resistance defined as a significant increase in survival in cytotoxicity assays and p-Crkl dependent IC50. Mechanisms of resistance were investigated in cell line intermediates: BCR-ABL, ABCB1 and LYN mRNA expression levels were determined by RT-PCR and KD mutation sequencing was performed. In our TKI resistant cell lines (Table 1), an increase in ABCB1 mRNA was the initial change observed prior to the development of additional resistance mechanisms (KD mutations, ABCB1 BCR-ABL and LYN overexpression). Interestingly, in 4/6 cells lines ABCB1 mRNA reduced to basal levels or below following establishment of these additional resistance mechanisms. ABCB1 levels were assessed in 37 de novo CML patients treated with IM who achieved major molecular response (MMR) compared with patients who progressed to BC, lost MMR or developed KD mutations. ABCB1 levels were determined in blood at diagnosis and following therapy (selected patients summarized in Table 2). A sustained >2 fold rise in ABCB1 was observed prior to disease progression in 3/3 patients and in 13/16 patients who did not achieve MMR. Importantly, the same was not observed in patients who achieved MMR (1/6 patients). The fold change of ABCB1 mRNA at day 22 vs diagnosis in patients achieving MMR was significantly different to that in patients not achieving MMR (p=0.004). ABCB1 increased by >2 fold post therapy and decreased following mutation development in 3/12 patients, confirming observations made in vitro, while 6/12 patients demonstrated sustained increase in ABCB1 post mutation similar to results observed in progression patients. ABCB1 mRNA did not change during therapy in 3/12 patients with mutations. While we recognize the majority of cells present in patients who achieve MMR are normal rather than leukemic, it is important to note that in patients who do not achieve MMR, ABCB1 expression increases in the remaining leukemic cells. We conclude ABCB1 overexpression acts as an initial mediator of resistance, providing a favorable environment for development of further resistance. Sustained increased levels of ABCB1 may contribute to disease progression and lack of response to IM. Additionally, ABCB1 may serve as a prognostic indicator (eg: level at day 22) and potentially assist in development of treatment strategies using TKIs in combination with other medications to enhance intracellular TKI concentration. Disclosures: Hughes: Ariad: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; Novartis: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding; CSL: Research Funding. White:Novartis: Research Funding; BMS: Research Funding, Speakers Bureau; Ariad: Research Funding; CSL: Research Funding.

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The Genomic Landscape of Childhood and Adult Acute Erythroid Leukemia

Blood ◽

10.1182/blood.v128.22.39.39 ◽

2016 ◽

Vol 128 (22) ◽

pp. 39-39 ◽

Cited By ~ 2

Author(s):

Ilaria Iacobucci ◽

Ji Wen ◽

Manja Meggendorfer ◽

Catherine Carmichael ◽

John K Choi ◽

...

Keyword(s):

Dna Methylation ◽

Tyrosine Kinase ◽

Board Of Directors ◽

Transcription Regulation ◽

Research Funding ◽

Complex Karyotype ◽

Advisory Committees ◽

Nih3t3 Cells ◽

Genomic Landscape

Abstract Introduction: The genetic basis of several acute myeloid leukemia (AML) subtypes remains poorly characterized, such as that of acute erythroid leukemia (AEL, AML M6) which is currently subclassified by morphology alone, and is associated with poor outcome. Here we sought to perform a definitive genomic analysis of AEL and translate these findings into faithful experimental models and novel therapeutic approaches. Methods: We studied 151 AEL cases (19.2% pediatric, 4.6% young adult, 21.9% adult and 54.3% older adult). Diagnosis of AEL was centrally confirmed and subclassified according to WHO 2008 and revised 2016 criteria. Whole exome and/or genome sequencing, RNA-sequencing and SNP array analysis were performed on all cases and in 2 AEL cell lines (TF-1 and Hel). Genomic data were compared to those from non-M6 childhood and adult AML from TARGET (n=192) and TCGA (n=197) studies. The functional effects of fusion transcripts and mutated genes were examined in IL-3 dependent Ba/F3 cells, NIH3T3 cells for focus formation assays and/or mouse lineage negative hematopoietic stem cells (lin- HSC) for colony forming and transplantation assays. Avatars of human AEL were established in immunocompromised NSGS and MISTRG mice for preclinical studies. Results: a) Genomic landscape of AEL. We identified 2,250 non-synonymous clonal and subclonal somatic mutations in 1,723 genes with a mean of 16.4 per case (range 2-88) and with missense and frameshift mutations accounting for 47.1% and 22.5% of all mutations, respectively. 78 genes were recurrently mutated in at least 3 cases. In frame fusions were detected in 31% of childhood and 27.5% of adult cases, and were more frequent in cases with complex karyotype. 124 potential driver genes were identified by statistical analysis or known pathogenic role in cancer, 9 of which were recurrent novel targets of mutation, most commonly involving chromatin modification (60.3%), cell cycle/tumor suppression (TP53, 33.8%), DNA methylation (28.5%), transcription regulation (26.5%), splicing (15.9%), NPM1 (11.9%), Ras (11.3%), JAK-STAT signaling (9.9%), the cohesin complex (8.6%), ALK/NTRK1 (4.6%) and PI3K signaling (3.3%). Overall, 33% of cases harbored a mutation in signaling genes amenable to inhibition by tyrosine kinase/Ras inhibitors. Mutations in TP53 and DNA methylation genes were significantly more frequent in adults while mutations in transcription regulators and Ras pathway were more frequent in children. Splicing mutations correlated with MDS phenotype and PI3K alterations with therapy-related AEL. Based on the co-occurrence and exclusivity of mutations 7 main distinct AEL genetic subtypes were defined: 1) pediatric AEL with NUP98-rearrangements (3.3% of all cases); 2) adult complex karyotype AEL with TP53 mutations (33.8%); 3) AEL with MLL-rearrangements (12.6%); 4) NPM1-mutated AEL (11.9%); 5) DNA-methylation/splicing mutated AEL (17.8%); 6) splicing/Ras/transcription regulation mutated AEL (21.2%) and 7) Other (8.6%) (Fig.1A). Mutations of chromatin modifiers occurred independently of karyotype, age and subtype (Fig.1B). NUP98-fusions and mutations in PTPN11, UBTF and GATA1 were more frequent in pediatric AEL compared to non-M6 AML. Among adults, mutations in TP53 and MLL were more frequent in AEL while FLT3, NPM1, DNMT3A and IDH1 were more in frequent in non-M6 subtypes. A complex karyotype, therapy-related AEL, TP53 mutations and NUP98-rearrangements were associated with poor outcome. b) Functional AEL modeling and therapeutic translations. Expression of NUP98-JARID1A in lin- HSC resulted in sustained self-renewal and development of an aggressive transplantable leukemia. At least three classes of signaling pathway mutations are targetable in AEL. ALK mutations in the extracellular MAM domain transformed Ba/F3 cells which were sensitive to crizotinib in vitro. Mutations in the tyrosine kinase domain of NTRK1 transformed NIH3T3 cells and were sensitive to entrectinib in vitro. Targeting of JAK-STAT, mTOR and PI3K pathways were examined in xenografts and sensitivity to JAK2 inhibitor ruxolitinib was confirmed in vivo. Conclusions: We provided the first comprehensive landscape of genomic alterations in AEL and defined distinct genomic groups with unique patterns of mutation occurrence compared to non-M6 AML. Finally, we showed that several pathogenic pathways are amenable to inhibition by approved targeted compounds. Disclosures Meggendorfer: MLL Munich Leukemia Laboratory: Employment. Wei:Novartis: Honoraria, Research Funding. Loh:Abbvie: Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Mullighan:Amgen: Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees; Loxo Oncology: Research Funding.

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The 3-Drug Combination Treatment ART838, ABT199 Plus Sorafenib Is Effective Against AML Xenografts, Possibly Via Cooperative Targeting of MCL1

Blood ◽

10.1182/blood-2018-99-113040 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 4044-4044

Author(s):

Blake S Moses ◽

Jennifer Fox ◽

Xiaochun Chen ◽

Samantha McCullough ◽

Sang Ngoc Tran ◽

...

Keyword(s):

Acute Leukemia ◽

Board Of Directors ◽

Cell Lines ◽

Drug Combination ◽

Research Funding ◽

Leukemia Cell ◽

Advisory Committees ◽

Leukemia Cell Lines ◽

Equity Ownership

Abstract Antimalarial artemisinins have broad antineoplastic activity in vitro, are well tolerated and inexpensive, and can be parenterally or orally administered in humans. Artemisinin-derived trioxane diphenylphosphate dimer 838 (ART838; a potent artemisinin-derivative) inhibited acute leukemia growth in vivo and in vitro, at doses where normal human CD34+ hematopoietic stem-progenitor cell clonogenicity was essentially unaffected (Fox et al, Oncotarget 2016, PMID: 26771236). In our focused drug combination screen for drugs that synergize with ART838, the only BCL2 inhibitors in the screen library of 111 emerging antineoplastic compounds, navitoclax (ABT737) and venetoclax (ABT199; FDA-approved), were identified as 2 of the top 3 candidates. Synergies between ART838 and BCL2 inhibitors were validated in multiple acute leukemia cell lines and primary cases. This ART838-BCL2 inhibitor synergy may be due to reduced levels of MCL1 protein that we and others have observed in multiple acute leukemia cell lines and primary cases treated with artemisinins (Budhraja et al, Clin Cancer Res 2017, PMID: 28974549). Treatment of acute leukemia xenografts with the ART838 plus ABT199 combination reduced leukemia growth rates and prolonged survivals, compared to vehicle or either ART838 or ABT199 alone. To add to the efficacy of this ART838 plus ABT199 treatment regimen, we sought to rationally add a third low-toxicity active antileukemic agent. Sorafenib (SOR; FDA-approved) inhibits multiple kinases which may mediate its antileukemic activity, with the importance of the targets varying from case to case; e.g. FLT3 is an important target in many AMLs. In addition, several reports have found that SOR reduces MCL1 protein stability and translation through inhibition of the ERK and PI3K pathways (Wang et al, Clin Cancer Res 2016, PMID: 26459180; Huber et al, Leukemia 2011, PMID: 21293487). In all acute leukemia cell lines tested, we observed large reductions in MCL1 protein levels with SOR treatment, which may further rationalize the addition of SOR to our ART838 plus ABT199 antileukemic regimen. We had previously observed strong in vitro synergy between ART838 and SOR (PMID: 26771236). Treatment of acute leukemia xenografts with the ART838 plus SOR combination reduced leukemia xenograft growth rates and prolonged survivals, compared to single drugs. Mice bearing luciferase-labelled acute leukemia xenografts were treated (PO daily x5) with single drug or 2-drug or 3-drug combinations of ART838, ABT199, and SOR, each at their individual maximally tolerated doses. Treatment with this 3-drug combination caused rapid regression of luciferase-labelled MV4;11 AML xenografts (Fig 1A). The 5-day treatment cycles were repeated every other week, and mice receiving this 3-drug combination survived >4 times longer than vehicle-treated mice (Fig 1B). Mouse body weights were stable during treatment. Although myelosuppression is the human clinical dose-limiting toxicity of each of these 3 drugs, mouse blood cell counts during 3-drug combination treatment were in the normal range. Treatment of a luciferase-labelled primary AML leukemia xenograft with this 3-drug combination reduced leukemia growth more than the single drugs or 2-drug combinations (Fig 1C). Assessment of efficacy and pharmacokinetics-pharmacodynamics against diverse acute leukemia xenografts will test this combination of ART838, ABT199 plus SOR as a rational low-toxicity drug triad for treatment of acute leukemias and potentially other cancers. Disclosures Fox: Intrexon Corporation: Employment. Tyner:Genentech: Research Funding; Janssen: Research Funding; AstraZeneca: Research Funding; Gilead: Research Funding; Incyte: Research Funding; Constellation: Research Funding; Array: Research Funding; Takeda: Research Funding; Vivid Biosciences: Membership on an entity's Board of Directors or advisory committees; Aptose: Research Funding. Civin:ConverGene LLC: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Research Funding; GPB Scientific LLC: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; 3DBioWorks Inc: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; BD (Becton Dickinson): Honoraria.

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For Patients with Sustained MR4-MR4.5, Less Frequent Molecular Monitoring during the First 12 Months after Tyrosine Kinase Inhibitor Cessation Is Viable for Timely Detection of Loss of MMR

Blood ◽

10.1182/blood.v128.22.1890.1890 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1890-1890

Author(s):

Naranie Shanmuganathan ◽

Susan Branford ◽

Jodi Braley ◽

Devendra Hiwase ◽

David T. Yeung ◽

...

Keyword(s):

Tyrosine Kinase ◽

Tyrosine Kinase Inhibitor ◽

Board Of Directors ◽

Median Time ◽

Research Funding ◽

Kinase Inhibitor ◽

Molecular Response ◽

Monitoring Strategy ◽

Molecular Monitoring ◽

Advisory Committees

Abstract Background: Discontinuation of tyrosine kinase inhibitor (TKI) treatment for chronic myeloid leukaemia (CML) patients in stable deep molecular response leads to treatment-free remission (TFR) in approximately 50% of cases. In most studies, monthly PCRs was performed for 12 months followed by 2-3 monthly testing thereafter. Around 80% of molecular relapses occur within the first 6 months after TKI cessation. The current recommendation for TKI recommencement is a single BCR-ABL1 value ≥0.1% IS (International scale), indicating loss of major molecular response (MMR). Not all institutions can offer monthly PCR monitoring due to financial constraints, particularly relevant in developing countries. For some patients, remaining on TKI is a cheaper alternative. Aim: To assess the safety of less frequent BCR-ABL1 monitoring for detection of loss of MMR for CML patients attempting TFR. Methods: We monitored 85 patients who ceased TKI with the aim of achieving TFR. Patients had a minimum of 24 months of sustained MR4 (n=3) or MR4.5 (n=82) prior to TKI cessation. At the time of TKI cessation, 64 patients were on imatinib (75%), 17 on nilotinib (20%) and 4 on dasatinib (5%). Forty of the patients were enrolled in the TWISTER study where the criteria for TKI recommencement was loss of MMR or 2 consecutively rising BCR-ABL1 positive values. The remaining patients were on a registry study and the trigger for TKI recommencement was loss of MMR. Results: TKI recommencement occurred in 49 of 85 patients. Median time to TKI recommencement was 4 months (range 2-28 months) at a median BCR-ABL1 value of 0.27% on the International Scale (IS), range 0.002-24% IS. Thirty-six of the 49 patients (73%) lost MMR prior to TKI recommencement; the median time to loss of MMR was 3 months (range 1 to 10 months). One patient lost MMR within the first month. Figure A demonstrates the time to loss of MMR in the 36 patients with PCR values ≥ 0.1%. Eighteen of the 36 patients (50%) lost MMR by the 3 month BCR-ABL1 assessment and 35 of 36 patients (97%) lost MMR by 6 months. The latest loss of MMR was at 10 months. Fourteen patients recommenced TKI at a BCR-ABL1 value of >1% and 1 recommenced at a value >10%. Clinician delay in TKI recommencement of 1 month resulted in a BCR-ABL1 rise from 0.84% to 24% with associated loss of complete hematological response. We propose monthly BCR-ABL1 testing between 2 and 6 months post TKI cessation followed by 2 monthly testing. Detection of a BCR-ABL1 value of ≥0.1% would trigger TKI recommencement. In the presence of a rising BCR-ABL1, which remains ≤0.1%, monthly monitoring should ensue in order to avoid hematological relapse. If this strategy were employed in this cohort of patients, only 1 patient would have had the trigger for TKI recommencement delayed by 1 month (estimated BCR-ABL1 at recommencement ~2.5%). This patient had loss of MMR in the first month post TKI cessation. If this molecular monitoring strategy was applied to patients in our cohort who had not lost MMR at TKI recommencement, we estimate that 1 other patient would have had TKI recommencement delayed by 1 month based on the average BCR-ABL1 doubling time of 1 log per month. A proportion of patients maintain low levels of BCR-ABL1 after TKI cessation and do not lose MMR. There were 2 such patients in our cohort. Conclusion: The critical time for molecular monitoring to trigger TKI recommencement is the first 6 months. A monthly monitoring strategy beginning 2 months after cessation would capture the majority of patients at loss of MMR. The data suggest that after 6 months, 2-monthly monitoring could follow. Monthly BCR-ABL1 testing can be re-introduced in the event of a positive result in those that ceased TKI with undetectable BCR-ABL1 or if there is a BCR-ABL1 result higher than the cessation value. This approach would reduce BCR-ABL1 testing by approximately 33% in the majority of cases while minimizing hematological relapse. Therefore this strategy would reduce the cost and inconvenience of molecular monitoring for a trial of TKI cessation, making the option of TFR available to some patients for whom it is otherwise not feasible. Disclosures Branford: Qiagen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Cepheid: Consultancy; Ariad: Research Funding; Bristol Myers Squibb: Research Funding; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Yeung:BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Research Funding. Ross:Novartis Pharmaceuticals: Honoraria, Research Funding; BMS: Honoraria. Hughes:Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Ariad: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Australasian Leukaemia and Lymphoma Group (ALLG): Other: Chair of the CML/MPN Disease Group.

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Targeting Wnt/β-Catenin and BCL-2, Two Critical Survival Factors, Synergistically Induces Apoptosis in AML Via Rac1-Mediated MCL-1 Inhibition

Blood ◽

10.1182/blood-2018-99-118367 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 1442-1442

Author(s):

Xiangmeng Wang ◽

Po Yee Mak ◽

Wencai Ma ◽

Xiaoping Su ◽

Hong Mu ◽

...

Keyword(s):

Progenitor Cells ◽

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Single Agent ◽

Advisory Committees ◽

Equity Ownership ◽

Critical Survival

Abstract Wnt/β-catenin signaling regulates self-renewal and proliferation of AML cells and is critical in AML initiation and progression. Overexpression of β-catenin is associated with poor prognosis. We previously reported that inhibition of Wnt/β-catenin signaling by C-82, a selective inhibitor of β-catenin/CBP, exerts anti-leukemia activity and synergistically potentiates FLT3 inhibitors in FLT3-mutated AML cells and stem/progenitor cells in vitro and in vivo (Jiang X et al., Clin Cancer Res, 2018, 24:2417). BCL-2 is a critical survival factor for AML cells and stem/progenitor cells and ABT-199 (Venetoclax), a selective BCL-2 inhibitor, has shown clinical activity in various hematological malignancies. However, when used alone, its efficacy in AML is limited. We and others have reported that ABT-199 can induce drug resistance by upregulating MCL-1, another key survival protein for AML stem/progenitor cells (Pan R et al., Cancer Cell 2017, 32:748; Lin KH et al, Sci Rep. 2016, 6:27696). We performed RNA Microarrays in OCI-AML3 cells treated with C-82, ABT-199, or the combination and found that both C-82 and the combination downregulated multiple genes, including Rac1. It was recently reported that inhibition of Rac1 by the pharmacological Rac1 inhibitor ZINC69391 decreased MCL-1 expression in AML cell line HL-60 cells (Cabrera M et al, Oncotarget. 2017, 8:98509). We therefore hypothesized that inhibiting β-catenin by C-82 may potentiate BCL-2 inhibitor ABT-199 via downregulating Rac1/MCL-1. To investigate the effects of simultaneously targeting β-catenin and BCL-2, we treated AML cell lines and primary patient samples with C-82 and ABT-199 and found that inhibition of Wnt/β-catenin signaling significantly enhanced the potency of ABT-199 in AML cell lines, even when AML cells were co-cultured with mesenchymal stromal cells (MSCs). The combination of C-82 and ABT-199 also synergistically killed primary AML cells (P<0.001 vs control, C-82, and ABT-199) in 10 out of 11 samples (CI=0.394±0.063, n=10). This synergy was also shown when AML cells were co-cultured with MSCs (P<0.001 vs control, C-82, and ABT-199) in all 11 samples (CI=0.390±0.065, n=11). Importantly, the combination also synergistically killed CD34+ AML stem/progenitor cells cultured alone or co-cultured with MSCs. To examine the effect of C-82 and ABT-199 combination in vivo, we generated a patient-derived xenograft (PDX) model from an AML patient who had mutations in NPM1, FLT3 (FLT3-ITD), TET2, DNMT3A, and WT1 genes and a complex karyotype. The combination synergistically killed the PDX cells in vitro even under MSC co-culture conditions. After PDX cells had engrafted in NSG (NOD-SCID IL2Rgnull) mice, the mice were randomized into 4 groups (n=10/group) and treated with vehicle, C-82 (80 mg/kg, daily i.p injection), ABT-199 (100 mg/kg, daily oral gavage), or the combination for 30 days. Results showed that all treatments decreased circulating blasts (P=0.009 for C-82, P<0.0001 for ABT-199 and the combination) and that the combination was more effective than each single agent (P<0.001 vs C-82 or ABT-199) at 2 weeks of therapy. The combination also significantly decreased the leukemia burden in mouse spleens compared with controls (P=0.0046) and single agent treated groups (P=0.032 or P=0.020 vs C-82 or ABT-199, respectively) at the end of the treatment. However, the combination did not prolong survival time, likely in part due to toxicity. Dose modifications are ongoing. These results suggest that targeting Wnt/β-catenin and BCL-2, both essential for AML cell and stem cell survival, has synergistic activity via Rac1-mediated MCL-1 inhibition and could be developed into a novel combinatorial therapy for AML. Disclosures Andreeff: SentiBio: Equity Ownership; Oncolyze: Equity Ownership; Oncoceutics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Jazz Pharma: Consultancy; Amgen: Consultancy, Research Funding; Eutropics: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo: Consultancy, Patents & Royalties: MDM2 inhibitor activity patent, Research Funding; Aptose: Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Reata: Equity Ownership; Astra Zeneca: Research Funding; Celgene: Consultancy; United Therapeutics: Patents & Royalties: GD2 inhibition in breast cancer . Carter:novartis: Research Funding; AstraZeneca: Research Funding.

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Expression and in Vitro Binding of Protease Activated Receptor1 (PAR1) with Novel Anti-PAR1 Molecules: Data on Fresh Myeloma Marrow Plasma Cells and Human Myeloma Cell Lines

Blood ◽

10.1182/blood.v126.23.4440.4440 ◽

2015 ◽

Vol 126 (23) ◽

pp. 4440-4440

Author(s):

Meral Beksac ◽

Pinar Ataca ◽

Berna Atesagaoglu ◽

Klara Dalva ◽

Andry Nur Hidayat ◽

...

Keyword(s):

Board Of Directors ◽

Cell Lines ◽

Research Funding ◽

Plasma Cells ◽

Myeloma Cell ◽

Lower Percentage ◽

Advisory Committees ◽

In Silico Docking ◽

Human Myeloma Cell

Abstract Introduction and Aim: Myeloma plasma cells are dependent on stromal support which is mediated through cell adhesion. Heparanase activity has been shown to be associated with aggressive behavior or Bortezomib resistance and can lead to increased levels of proteases as well as shedding of heparan sulfate proteoglycan syndecan-1(CD138) from myeloma cells. We have recently published in vivo anti-myeloma effects of low molecular weight heparin (Beksac et al Acta Haematol 2015). Protease activated Receptor (PAR1) is a thrombin receptor. PAR1 gene and antigen expression on myeloma patient samples and cell lines (HMCL) has been recently reported by University of Arkansas (UAMS) group (Tian et al ASH 2011). They were able to find HMCLs H929, U266, JJN3 to express PAR1. Also expression was found to be highest among patients with 5q amplification where the PAR1 gene is located. Patients and Methods: We analyzed PAR1 expression (WEDE15 PE, Beckman Coulter) by flow cytometry, on CD38+CD138+/-CD27+/- cells obtained from fresh patient bone marrow samples obtained either at diagnosis (n: 84)(NDMM) or relapse (n: 54)(RRMM) and were compared with marrow samples taken from patients without MM (n: 43). Our group in Ankara University had previously synthesized and published novel benzamide and phenyl acetamide derivatives. We performed an in silico docking analysis on these molecules, and eleven (TD10,TD12,TD12A,TD12B,TD13,TD14,TD14B,XT2,XT2B,XT5,XT11) were found to bind to PAR1. These molecules were screened using 72 hour MTT assay on primary and refractory cell lines (U266BR ,U266, JJN3BR, JJN3, H929R, OPM2, OPM2R, KMS28PE). Results: PAR1 expression was highest on platelets followed by myeloma plasma cells (0-81.9%) and did not correlate with ISS. PAR1 expression (Threshold: >2.5 % or >5%) could be detected in NDMM (35 % or 14%) and RRMM (31% or 19%) of patients (Table1). PAR1+CD38+138+ cells were more frequent among patients with lower percentage of plasma cells in RRMM group (2,98 ± 4,5 vs 1,93 ± 3,96, P=0.028) but not NDMM. PAR1 was similarly highly expressed on HCML. Two of the novel PAR1 binding molecules (XT5 and XT2B) were found to have the lowest IC50. The IC50 were similar for all HMCLs, primary and refractory, with XT5. With XT2B the IC50 was less (U266) or higher (JJN3) or similar (OPM2) for refractory compared to the primary HMCL. PAR1 expression and anti-myeloma IC50 values of cell lines are summarized in Table 2. Conclusion: PAR1 expression is detectable at very low or very high percentages on CD138+plasma cells. Expression is higher on cells with CD27 expression (patient samples) or lacking CD27 (HMCL). Inverse correlation between PAR1 expression and plasma cell percentage among myeloma patients is detected among RRMM but not on NDMM samples. This finding may point to expression of PAR1 on quiescent plasma progenitors as suggested by Tian et al previously. The intensity or frequency of PAR1 expression on HMCL did not influence the anti-myeloma effects of these novel molecules. PAR1 binding molecules, in particular XT5, are promising as they are effective even on Bortezomib refractory HCML. However their mechanism of action and the role of PAR1 require further investigations. This study has been supported by a research grant from Turkish Academy of Sciences. Table 1. Frequency of PAR1 expression (> 2.5 %) on total plasma cells (CD38+138+) and on quiescent plasma cells (CD38+138+27+) Control (n=43) NDMM (n=84) RRMM (n=54) P CD38+138+ (%) 0,56± 0,66 4,48 ± 7,67 5,44 ± 12,13 0,007 PAR1+ among CD38+138 (%) 6,18 ± 13,14 4,14 ± 11,00 3,42 ± 8,81 0,394 PAR1+ among CD38+138+27+(%) 5,44 ± 12,13 3,42 ± 8,81 3,58 ± 8,57 0,207 Table 1. Comparison of Flow Cytometric PAR1 expression and IC50 (in uM after 72 hours)of the two novel molecules on three Human Myeloma Cell Lines. H929 RPMI8221 U266 IC50 XT2B 33.9 >100 34.3 IC50 XT5 8.12 5.45 9.77 CD38+138+ (total%) 85 % 75 % 80 % PAR1% and (MFI) within CD38+138+ 83 %(13,6) 90 % (2,1) 85 % (2,1) Disclosures Beksac: Celgene: Consultancy, Speakers Bureau; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen-Cilag: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Off Label Use: Elotuzumab is an investigational agent being studied for the treatment of multiple myeloma.. Usmani:Millennium: Honoraria, Speakers Bureau; Sanofi: Honoraria, Research Funding; Onyx: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Array BioPharma: Honoraria, Research Funding; Pharmacyclics: Research Funding; Janssen Oncology: Honoraria, Research Funding. Tian:University of Arkansas for Medical Sciecnes: Employment.

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The FLT3 F691L Gatekeeper Mutation Promotes Clinical Resistance to Gilteritinib + Venetoclax (GILT + VEN) in AML

Blood ◽

10.1182/blood-2021-145762 ◽

2021 ◽

Vol 138 (Supplement 1) ◽

pp. 2235-2235

Author(s):

Setareh Sharzehi ◽

Sunil K Joshi ◽

Janét Pittsenbarger ◽

Jeffrey W. Tyner ◽

Elie Traer

Keyword(s):

Tyrosine Kinase ◽

Board Of Directors ◽

Research Funding ◽

Immunoblot Analysis ◽

Tyrosine Kinase Domain ◽

Resistance Mutations ◽

Advisory Committees ◽

Mechanism Of Resistance ◽

Clinical Resistance

Abstract Background: FMS-like tyrosine kinase (FLT3) is one the most frequently mutated genes in AML and is associated with poor prognosis. FLT3 internal tandem duplication (ITD) and tyrosine kinase domain (TKD) mutations occur in up to 30% and 5-10% of AML, respectively. Several small molecule FLT3 inhibitors (FLT3i) have been developed but their use as single agents is limited due to the development of drug resistance. Our lab developed a two-step model of early and late resistance to FLT3i that recapitulates resistance in AML patients (Traer et al. Cancer Res. 2016; Joshi et al. Cancer Cell 2021). Early resistance, also known as AML persistence, is the stage when residual AML cells are dependent upon the marrow microenvironment for survival and patients are clinically responding. Late resistance to GILT was characterized by expansion of intrinsic mutations, with NRAS mutations being the most frequent mutation, in addition to a few gatekeeper FLT3 mutations. Current therapies are looking at combinations to overcome GILT resistance, including chemotherapy, hypomethylating agents (HMAs), and venetoclax (VEN) +/- HMAs. GILT+VEN, in particular, has shown good initial activity in relapsed/refractory FLT3 AML patients (Daver et al. ASH 2020), however the mechanism of resistance to this combination is unknown. Results: Early resistance cell cultures to GILT+VEN were created by exposing MOLM14 cells to GILT 25nM + VEN 25nM alone or supplemented with microenvironmental ligands FGF2 or FLT3 ligand (FL; N=3/group). Media, drugs, and ligands were replenished twice weekly. After 25 weeks, only the cultures exposed to ligand resumed growth (N=1 for FGF2 and N=3 for FL). Ligands were then removed from these early resistant cultures to induce late resistance. There was an initial drop in cell viability but cells resumed growth after only 3.5 weeks (Fig. 1). In contrast, the time to develop early and late resistance to GILT monotherapy was 8 and 15 weeks, respectively. Immunoblot analysis of GILT + VEN early and late resistant cultures demonstrated restoration of FLT3 signaling, as well as phosphorylation of downstream AKT/MAPK pathways. These results also contrasted to late GILT monotherapy resistant cultures, which had downstream AKT/MAPK activation via outgrowth of NRAS mutations. Since FLT3 appeared to be functionally active, we sequenced FLT3 and found that all early and late GILT + VEN resistance cultures had gatekeeper FLT3 F691L mutations. F691L accounted for only in a minority of resistance cultures to GILT monotherapy. To test if FLT3 signaling was important for resistance, we exposed parental cells to higher concentrations of gilteritinib, which have been shown to partly overcome F691L, as well as the FLT3i FF-10101, which binds FLT3 at a different site and is not affected by the F691L mutation. Both of these approaches restored sensitivity to FLT3i in vitro. As expected, the F691L mutation provided broad resistance to most FLT3i (Fig. 2). To validate this mechanism of resistance in patients, we identified a relapsed FLT3-ITD patient who was treated with GILT monotherapy for 5 months, followed by GILT + HMA for 4 cycles, and then GILT + VEN for resistant proliferative disease. After an initial response to GILT + VEN, the leukemia cells began to increase again in the peripheral blood. A repeat genetic test was ordered and the patient was found to have developed a FLT3 F691L mutation at a high variant allele frequency (Fig. 3). Conclusion: We have developed a robust cell line model of early and late resistance to FLT3i that mimics the timing and expansion of resistance mutations in the clinic. Our model of early and late resistance to GILT combinations can prospectively predict mechanisms of resistance. Although uncommon as a mechanism of resistance to GILT monotherapy, our model and early patient data predicts that F691L mutations are more important for GILT + VEN resistance. Figure 1 Figure 1. Disclosures Tyner: Seattle Genetics: Research Funding; Astrazeneca: Research Funding; Array: Research Funding; Janssen: Research Funding; Takeda: Research Funding; Gilead: Research Funding; Incyte: Research Funding; Petra: Research Funding; Constellation: Research Funding; Genentech: Research Funding; Agios: Research Funding; Schrodinger: Research Funding. Traer: ImmunoGen: Membership on an entity's Board of Directors or advisory committees; Schrodinger: Research Funding; Genentech: Membership on an entity's Board of Directors or advisory committees; Servier/Agios: Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Research Funding; Astellas: Consultancy, Membership on an entity's Board of Directors or advisory committees.

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In Vitro and inVivo Activity of Melflufen in Amyloidosis

Blood ◽

10.1182/blood-2019-125952 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 3100-3100 ◽

Cited By ~ 2

Author(s):

Ken Flanagan ◽

Muntasir M Majumder ◽

Romika Kumari ◽

Juho Miettinen ◽

Ana Slipicevic ◽

...

Keyword(s):

Board Of Directors ◽

Cell Lines ◽

Plasma Cell ◽

Light Chain ◽

Research Funding ◽

Plasma Cells ◽

Al Amyloidosis ◽

Advisory Committees

Background: Immunoglobulin light-chain (AL) amyloidosis is a rare disease caused by plasma cell secretion of misfolded light chains that assemble as amyloid fibrils and deposit on vital organs including the heart and kidneys, causing organ dysfunction. Plasma cell directed therapeutics, aimed at preferentially eliminating the clonal population of amyloidogenic cells in bone marrow are expected to reduce production of toxic light chain and alleviate deposition of amyloid thereby restoring healthy organ function. Melphalan flufenamide ethyl ester, melflufen, is a peptidase potentiated alkylating agent with potent toxicity in myeloma cells. Melflufen is highly lipophilic, permitting rapid cellular uptake, and is subsequently enzymatically cleaved by aminopeptidases within cells resulting in augmented intracellular concentrations of toxic molecules, providing a more targeted and localized treatment. Previous data demonstrating multiple myeloma plasma cell sensitivity for melflufen suggests that the drug might be useful to directly eliminate amyloidogenic plasma cells, thereby reducing the amyloid load in patients. Furthermore, the increased intracellular concentrations of melflufen in myeloma cells indicates a potential reduction in systemic toxicity in patients, an important factor in the fragile amyloidosis patient population. To assess potential efficacy in amyloidosis patients and to explore the mechanism of action, we examined effects of melflufen on amyloidogenic plasma cells invitro and invivo. Methods: Cellular toxicity and apoptosis were measured in response to either melflufen or melphalan in multiple malignant human plasma cell lines, including the amyloidosis patient derived light chain secreting ALMC-1 and ALMC-2 cells, as well as primary bone marrow cells from AL amyloidosis patients, using annexin V and live/dead cell staining by multicolor flow cytometry, and measurement of cleaved caspases. Lambda light chain was measured in supernatant by ELISA, and intracellular levels were detected by flow cytometry. To assess efficacy of melflufen in vivo, the light chain secreting human myeloma cell line, JJN3, was transduced with luciferase and adoptively transferred into NSG mice. Cell death in response to melflufen or melphalan was measured by in vivo bioluminescence, and serum light chain was monitored. Results: Melflufen demonstrated increased potency against multiple myeloma cell lines compared to melphalan, inducing malignant plasma cell death at lower doses on established light chain secreting plasma cell lines. While ALMC-1 cells were sensitive to both melphalan and melflufen, the IC50 for melphalan at 960 nM was approximately 3-fold higher than melflufen (334 nM). However, ALMC-2 cells were relatively insensitive to melphalan (12600 nM), but maintained a 100-fold increase in sensitivity to melflufen (121 nM). Furthermore, while 40% of primary CD138+ plasma cells from patients with diagnosed AL amyloidosis responded to melflufen treatment in vitro, only 20% responded to melphalan with consistently superior IC50 values for melflufen (Figure 1). Light chain secreting cell lines and AL amyloidosis patient samples were further analyzed by single cell sequencing. We further examined differential effects on apoptosis and the unfolded protein response in vitro in response to either melflufen or melphalan. This is of particular interest in amyloidosis, where malignant antibody producing plasma cells possess an increased requirement for mechanisms to cope with the amplified load of unfolded protein and associated ER stress. As AL amyloidosis is ultimately a disease mediated by secretion of toxic immunoglobulin, we assessed the effects of melflufen on the production of light chain invitro, measuring a decrease in production of light chain in response to melflufen treatment. Finally, we took advantage of a recently described adoptive transfer mouse model of amyloidosis to assess the efficacy of melflufen and melphalan in eliminating amyloidogenic clones and reducing the levels of toxic serum light chain in vivo. Conclusions: These findings provide evidence that melflufen mediated toxicity, previously described in myeloma cells, extends to amyloidogenic plasma cells and further affects the ability of these cells to produce and secrete toxic light chain. This data supports the rationale for the evaluation of melflufen in patients with AL amyloidosis. Figure 1 Disclosures Flanagan: Oncopeptides AB: Employment. Slipicevic:Oncopeptides AB: Employment. Holstein:Celgene: Consultancy; Takeda: Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy; Genentech: Membership on an entity's Board of Directors or advisory committees; Sorrento: Consultancy. Lehmann:Oncopeptides AB: Employment. Nupponen:Oncopeptides AB: Employment. Heckman:Celgene: Research Funding; Novartis: Research Funding; Oncopeptides: Research Funding; Orion Pharma: Research Funding.

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