Preclinical Activity of the MPS1 Inhibitor S81694 in Acute Lymphoblastic Leukemia (ALL)

Introduction: The dual-specificity protein kinase, monopolar spindle 1 (Mps1) is one the main kinases of the spindle assembly checkpoint (SAC) critical for accurate segregation of sister chromatids during mitosis. A hallmark of cancer cells is chromosomal instability caused by deregulated cell cycle checkpoints and SAC dysfunction. Mps1 is known to be overexpressed in several solid tumors including triple negative breast cancer. Thus, Mps1 seems to be a promising target and small molecules targeting Mps1 entered clinical trials in solid tumors. ALL originates from malignant transformation of B-and T-lineage lymphoid precursors with a variety of genetic aberrations including chromosome translocations, mutations, and aneuploidies in genes responsible for cell cycle regulation and lymphoid cell development. While outcome is excellent for pediatric patients and younger adults, relapsed and refractory disease still remain a clinical challenge for elder patients. Here, we demonstrate for the first time preclinical efficacy of the small molecule Mps1 inhibitor (Mps1i) S81694 in T- and B- ALL cells including BCR-ABL1+-driven B-ALL. Materials and Methods: Expression of Mps1 was determined by RT-qPCR and WB in JURKAT, RS4-11 and BCR-ABL1+ cells (BV-173 and TOM-1). A small molecule Mps1i (S81694) was tested alone (0 to 1000nM) or in combination with imatinib, dasatinib, nilotinib and ponatinib in BCR-ABL1+ ALL cell lines. Cell viability and IC50 was assessed by MTS assays after exposure to Mps1i for 72h. In combination experiments, compounds were added simultaneously and relative cell numbers were determined at 72h with MTS assays and combination index (CI) values were calculated according to the Bliss model. Induction of apoptosis was evaluated by annexin-V exposure and PI incorporation at 72h with increasing doses of Mps1i. Cell-cycle distribution was determined by cytofluorometric analysis detecting nuclear propidium iodide (PI) intercalation at 48h. Phosphorylation of Mps1 was detected in synchronized (by nocodazole and MG-132) cells by immunofluorescence using an anti phospho-Mps1 antibody detecting Thr33/Ser37 residues. Time-lapse microscopy was used in cell lines in presence or absence of S81694 to determine mitosis duration. Bone marrow (BM) nucleated patient cells were obtained after informed consent and incubated in methylcellulose with cytokines with or without Mps1i for 2 weeks to determine colony growth. Results: Expression of Mps1 could be detected by RT-qPCR and at the protein level by WB in all cell lines (Figure 1A and B ). IC50 after Mps1i exposure alone was 126nM in JURKAT cells, 51nM in RS4-11 cells, 75nM in BV-173 cells and 83nM in TOM-1. Significant apoptosis as detected by phosphatidylserine exposure and PI incorporation in all cell lines with BCR-ABL1+ cell lines BV-173 and TOM-1 cells being the most sensitive (80% and 60% apoptotic cells respectively)(Figure 1C). Upon Mps1i exposure we observed targeted inhibition of Mps1 phosphorylation at Thr33/Ser37 residues indicating the specific on target effect of S81694 by inhibiting Mps1 autophosphorylation (Figure 1D and E). Cell cycle profile was generally lost after treatment with S81694 in all cell lines indicating aberrant 2n/4n distribution due to SAC abrogation (Figure 1F). Furthermore, we demonstrated that S81694 exposure accelerated significantly mitosis in BV-173 cell line from 36 minutes to 19 minutes indicating effective inhibition of SAC function (Figure 1G). Interestingly, S81694 induced significant apoptosis (70%) in the imatinib resistant BV173 cell line bearing the E255K-BCR-ABL1-mutation. Combination of S81694 with TKI imatinib, dasatinib and nilotinib (but not ponatinib) was strongly synergistic in BCR-ABL1+ cells (Figure 1H). Finally, we observed inhibition of colony formation in a patient with BCR-ABL1+ B-ALL after exposure to 100nM and 250nM S81694 (reduction of 85% and 100% respectively)(Figure 1I). Conclusion: Mps1i S81694 yields significant preclinical activity in T-and B-cell ALL including BCR-ABL1+ models. Interestingly S81694 was efficacious in a TKI resistant cell line. Disclosures Kaci: Institut de Recherches Internationales Servier (IRIS): Employment. Garrido:Institut de Recherches Internationales Servier (IRIS): Employment. Burbridge:Institut de Recherches Internationales Servier (IRIS): Employment. Dombret:AGIOS: Honoraria; CELGENE: Consultancy, Honoraria; Institut de Recherches Internationales Servier (IRIS): Research Funding. Braun:Institut de Recherches Internationales Servier (IRIS): Research Funding.

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CYC065, a Potent Derivative of Seliciclib Is Active In Multiple Myeloma In Preclinical Studies

Blood ◽

10.1182/blood.v116.21.2999.2999 ◽

2010 ◽

Vol 116 (21) ◽

pp. 2999-2999 ◽

Cited By ~ 1

Author(s):

Samantha Pozzi ◽

Diana Cirstea ◽

Loredana Santo ◽

Doris M Nabikejje ◽

Kishan Patel ◽

...

Keyword(s):

Cell Cycle ◽

Multiple Myeloma ◽

Cell Line ◽

Board Of Directors ◽

Cell Lines ◽

Preliminary Data ◽

Research Funding ◽

Preclinical Studies ◽

Dependent Manner ◽

Advisory Committees

Abstract Abstract 2999 Multiple myeloma (MM) is a treatable but incurable hematological malignancy and novel targeted therapies are under investigation. MM is characterized by dysregulation of the cell cycle, consequent to the overexpression of cyclins and their related kinases, the cyclins dependent kinases (CDK), a group of Ser/Thr proteine kinases. CDKs represent a promising therapeutic target, and inhibitors have been developed for anticancer treatment. We have previously studied seliciclib in the context of MM. CYC065, a second generation CDK inhibitor is the more potent derivative of seliciclib. It is mainly active on CDK 2, 5 and 9, involved in progression of the cell cycle and protein transcription. It has already shown promising results in preclinical studies in breast cancer and acute leukemia. We tested CYC065 in in vitro experiments in MM. Our preliminary data in 7 MM cell lines showed cytotoxicity of CYC065, both in MM cell lines sensitive as well as resistant to conventional chemotherapy, with an IC50 ranging between 0.06 and 2μ M, at 24 and 48h. Tritiated thymidine uptake assay confirmed the antiproliferative effects of CYC065 in MM, and its ability to overcome the growth advantage conferred by co-culture with bone marrow stromal cells derived from MM patients, and cytokines like interleukin 6 (10ng/ml) and insulin like growth factor-1 (50ng/ml). The anti-proliferative effect was evident both at 24 and 48h, starting at concentrations as low as 0.015μ M. The AnnexinV/PI assay in the MM1.s cell line confirmed CYC065's ability to induce apoptosis in a time dependent manner starting at 9 hours of treatment, at a concentration of 0.125 μ M, inducing 82% of apoptosis after 48h of exposure. Cell cycle analysis in the same MM1.s cell line showed an increase of subG1 phase, starting at 9 hours of treatment, at 0.125 μ M of CYC065. Preliminary results of western blot analysis confirmed the apoptotic effect of CYC065 in the MM1s cell line, highlighted by the cleavage of caspase 3, 8, 9 and PARP. The compound was tested in primary CD138+ cells isolated from three refractory MM patients, confirming its efficacy at 0.125 μ M, both at 24 and 48h. Comparative analysis in PBMCs from normal donors, for the evaluation of the drug toxicity is ongoing and will be presented. In conclusion our preliminary data confirm the efficacy of CYC065 in MM cell lines and primary MM cells, at nanomolar concentrations. Ongoing mechanistic and in vivo studies will delineate its role in the now increasing spectrum of CDK inhibitors in MM and better define its potential for clinical development in MM. Disclosures: Green: Cyclacel: Employment. Anderson:Millennium Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Scadden:Fate Therapeutics: Consultancy, Equity Ownership, Patents & Royalties. Raje:Celgene: Membership on an entity's Board of Directors or advisory committees; Astra Zeneca: Research Funding; Acetylon: Research Funding.

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Preclinical Evaluation of the BET-Bromodomain (BET-BRD) Inhibitor OTX015 in Leukemia Cell Lines Harboring the JAK2 V617F Mutation

Blood ◽

10.1182/blood.v124.21.873.873 ◽

2014 ◽

Vol 124 (21) ◽

pp. 873-873

Author(s):

Maria Eugenia Riveiro ◽

Lucile Astorgues-Xerri ◽

Charlotte Canet-jourdan ◽

Mohamed Bekradda ◽

Esteban Cvitkovic ◽

...

Keyword(s):

Cell Cycle ◽

Cell Line ◽

Cell Lines ◽

Research Funding ◽

Leukemia Cell ◽

Jak2 V617f ◽

Jak2 V617f Mutation ◽

Mrna Levels ◽

Protein Levels ◽

V617f Mutation

Abstract Background: Exposure of cancer cells to BET-BRD protein inhibitors has been associated with a significant downregulation of C-MYC expression, leading to suppression of the transcriptional program linked to proliferation and survival. C-MYC mRNA expression, mediated by STAT5 activation, is induced by the JAK2 (V617F) mutation (JAK2mu) in transfected BA/F3 cells (Funakoshi-Tago, et al. 2013). We selected JAK2mu leukemia-derived cell lines for preclinical evaluation of OTX015 (Oncoethix, Switzerland), a selective orally-bioavailable inhibitor of BET-BRD proteins with promising early results in an ongoing phase I study in hematologic malignancies (Herait et al, AACR 2014, NCT01713582). Material and Methods: Antiproliferative effects of OTX015 and JQ1 were evaluated in three established JAK2mu human myeloid leukemia cell lines (SET2, MUTZ8, HEL 92.1.7). GI50 (OTX015 concentration inducing 50% growth inhibition) and Emax (% cell proliferation at 6 µM OTX015) values were determined by MTT assay after 72h exposure. Protein levels were analyzed by Western blot, and RT-PCR was performed with Fast SYBR Green Master Mix on a StepOnePlus Real-Time PCR System. For cell cycle analysis, cells were stained with propidium iodide and analyzed with a FACScan flow cytometer. Induction of apoptosis was evaluated by Annexin-V. Simultaneous schedules of OTX015 combined with ruxolitinib, a JAK2 inhibitor, were evaluated. Combination index (CI) was determined using the Chou & Talalay method; CI<1 reflects synergy, CI=1 additivity and CI>1 antagonism. Results: After 72h exposure, SET2 was the most sensitive cell line (GI50=0.12 µM and Emax=15%), and HEL92.1.7 cells had a GI50=1.9 µM with an Emax=23%. MUTZ8 was the most resistant cell line with an Emax=61%. Similar GI50 and Emax values are observed with JQ1. A significant increase in the fraction of apoptotic cells was observed in SET2 cells after 72h 500 nM OTX015 exposure. Non-significant increases in Annexin-positive cells were seen in HEL92.1.7 and MUTZ8 cells. Cell cycle analysis revealed a significant increase in the percentage of SET2 cells in subG0/G1 after 24, 48, and 72h 500 nM OTX015, correlating with the increase in apoptosis. Conversely, an increase in the percent cells in the G1 phase was observed in HEL 92.1.7 cells. After 4h 500 nM OTX015, BRD2 mRNA levels were significantly increased in all three cell lines, whereas BRD3 levels were not modified. BRD4 mRNA levels increased significantly after 48h in SET2 cells. OTX015 treatment induced a transitory reduction of C-MYC mRNA levels after 4h with an increase at 24h in all cell lines. At the protein level, C-MYC decreased substantially in SET2 cells after 4h, with complete disappearance after 48h without recovery, while in the less sensitive MUTZ8 cell line, the decrease in C-MYC protein levels was transitory. Conversely, this proto-oncogene was not modified in HEL92.1.7 cells. In addition, p-STAT5 protein was downregulated by OTX015 in SET2 cells, but was increased in MUTZ8 cells after longer exposure time. Furthermore, BCL2 mRNA and protein levels decreased in SET2 cells, correlating with the apoptosis induction seen with OTX015 treatment. In HEL92.1.7 cells, P21 mRNA levels and cyclin D1 protein levels increased after 4h and 48h OTX015 treatment, respectively. Moreover, concomitant combination of OTX015 with ruxolitinib showed a highly antagonist effect (CI>7) in SET2 cells, the most sensitive cell line to both agents. On the other hand, very strong synergy was observed in HEL92.1.7 (CI=0.19) and MUTZ8 (CI=0.41), despite their low sensitivity to single agent OTX015. Conclusions. Our findings demonstrate that OTX015 exhibits potent activity against cultured leukemic cells expressing the JAK2 V617F mutation, inducing apoptosis or cell cycle arrest at submicromolar concentrations. This activity correlates with modulation of C-MYC, p-STAT5, BCL2, P21 and cyclin D1 mRNA and protein levels following OTX015 treatment. Our study highlights the novel and synergistic activity of the combination of a BRD antagonist and a JAK inhibitor in human leukemic cells harboring the JAK2 V617 F mutation, supporting the rationale for in vivo testing of OTX015 in combination with JAK inhibitors in leukemic JAK2mu models. Disclosures Riveiro: Oncoethix SA: Research Funding. Astorgues-Xerri:Oncoethix SA: Research Funding. Canet-jourdan:Oncoethix SA: Research Funding. Bekradda:Oncoethix SA: Research Funding. Cvitkovic:Oncoethix SA: Membership on an entity's Board of Directors or advisory committees, Shareholder and CSO Other. Herait:Oncoethix SA: CMO and Shareholder Other. Raymond:Oncoethix SA: Membership on an entity's Board of Directors or advisory committees, Research Funding.

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Establishment and characterization of a chordoma cell line from the tissue of a patient with dedifferentiated-type chordoma

Journal of Neurosurgery Spine ◽

10.3171/2016.3.spine151077 ◽

2016 ◽

Vol 25 (5) ◽

pp. 626-635 ◽

Cited By ~ 1

Author(s):

Jeong-Yub Kim ◽

Jongsun Lee ◽

Jae-Soo Koh ◽

Myung-Jin Park ◽

Ung-Kyu Chang

Keyword(s):

Cell Cycle ◽

Cell Line ◽

Cell Lines ◽

Nude Mice ◽

Surface Expression ◽

Cell Surface Expression ◽

Wide Resection ◽

Cell Cycle Distribution ◽

Facs Analysis ◽

Mesenchymal Transition

OBJECTIVE Chordoma is a rare bone tumor of the axial skeleton believed to originate from the remnants of the embryonic notochord. The available tumor cells are characteristically physaliferous and express brachyury, a transcription factor critical for mesoderm specification. Although chordomas are histologically not malignant, treatments remain challenging because they are resistant to radiation therapy and because wide resection is impossible in most cases. Therefore, a better understanding of the biology of chordomas using established cell lines may lead to the advancement of effective treatment strategies. The authors undertook a study to obtain this insight. METHODS Chordoma cells were isolated from the tissue of a patient with dedifferentiated-type chordoma (DTC) that had recurred. Cells were cultured with DMEM/F12 containing 10% fetal bovine serum and antibiotics (penicillin and streptomycin). Cell proliferation rate was measured by MTS assay. Cell-cycle distribution and cell surface expression of proteins were analyzed by fluorescence-activated cell sorting (FACS) analysis. Expression of proteins was analyzed by Western blot and immunocytochemistry. Radiation resistance was measured by clonogenic survival assay. Tumor formation was examined by injection of chordoma cells at hindlimb of nude mice. RESULTS The putative (DTC) cells were polygonal and did not have the conventional physaliferous characteristic seen in the U-CH1 cell line. The DTC cells exhibited similar growth rate and cell-cycle distribution, but they exhibited higher clonogenic activity in soft agar than U-CH1 cells. The DTC cells expressed high levels of platelet-derived growth factor receptor–β and a low level of brachyury and cytokeratins; they showed higher expression of stemness-related and epithelial to mesenchymal transition–related proteins than the U-CH1 cells. Intriguingly, FACS analysis revealed that DTC cells exhibited marginal surface expression of CD24 and CD44 and high surface expression of CXCR4 in comparison to U-CH1 cells. In addition, blockade of CXCR4 with its antagonist AMD3100 effectively suppressed the growth of both cell lines. The DTC cells were more resistant to paclitaxel, cisplatin, etoposide, and ionizing radiation than the U-CH1 cells. Injection of DTC cells into the hindlimb region of nude mice resulted in the efficient formation of tumors, and the histology of xenograft tumors was very similar to that of the original patient tumor. CONCLUSIONS The use of the established DTC cells along with preestablished cell lines of chordoma may help bring about greater understanding of the mechanisms underlying the chordoma that will lead to therapeutic strategies targeting chordomas.

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A CXCL10/CXCR3 Driven Thymic Epithelium-Leukemia Cell Crosstalk Augments T Cell Acute Lymphoblastic Leukemia Notch1 Signalling

Blood ◽

10.1182/blood-2019-125331 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 2537-2537

Author(s):

Ashwini M Patil ◽

Stefanie Kesper ◽

Vishal Khairnar ◽

Marco Luciani ◽

Michael Möllmann ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Mouse Model ◽

Cell Line ◽

Cell Lines ◽

Research Funding ◽

Lymphoblastic Leukemia ◽

Thymic Epithelial Cells ◽

Hematopoietic Organ ◽

Notch1 Mutations

Introduction: The thymus is a specialized hematopoietic organ, which is responsible for the generation of T cells. The central thymic cell type controlling T cell development are thymic epithelial cells (TECs). Based on their specific function and anatomic location TECs are separated into cortical and medullary subsets (cTECs and mTECs). cTECs express pivotal NOTCH-ligands such as DLL4 controlling T cell lineage commitment while mTECs play a central role in negative selection of developing T cells. Acquisition of NOTCH1 gain-of-function mutations play a central role in acute T cell lymphoblastic leukemia (T-ALL) development. During T-ALL leukemogenesis aberrant expression of transcription factors such as SCL/TAL1 and LMO1 block T cell differentiation and increase self-renewal while NOTCH1 mutations promote survival and proliferation. Since most acquired NOTCH1 mutations still require ligand binding to exert augmented signaling we propose DLL4-expressing TECs playing a critical role during T-ALL leukemogenesis. Methods: In the present study, we used a Scl/Lmo1 T-ALL transgenic mouse model, murine ANV and TE71 TEC cell lines and human T-ALL cell lines (Jurkat, ALL-SIL, DND-41, and HPB-ALL) to investigate TEC dynamics and function in the T-ALL context. Results: First, we demonstrated T-ALL supporting potential of TEC cell lines in vitro, which was comparable to the mesenchymal cell line OP9. Next, we showed in the Scl/Lmo1 T-ALL mouse model which had a mean survival rate of 90 days that preleukemic thymocytes displayed a striking upregulation of Notch1 target genes. Interestingly, fluorescence microscopy revealed a relative expansion of cortical and a relative reduction of the medullary thymic areas in Scl/Lmo1 thymi (Fig. 1A). Correspondingly, absolute numbers of cTECs expanded while mTEC numbers declined (Fig. 1B). Gene expression profiling of sorted preleukemic Scl/Lmo1 cTECs revealed upregulation of the chemokine CXCL10 (Fig. 1C). Moreover, increased CXCL10 chemokine concentrations were detected in Scl/Lmo1 thymic interstitial fluid (Fig.1D). Strikingly, we demonstrated T-ALL dependence of TEC Cxcl10 upregulation. We showed that Cxcl10 upregulation in TEC cell lines was only induced by direct cellular contact with Scl/Lmo1 thymocytes while wild-type control thymocytes did not alter TEC cell line Cxcl10 expression (Fig. 1E). Next, a high proportion of the CXCL10 receptor CXCR3 expressing cells was revealed in Scl/Lmo1 thymi (Fig. 1F) and by human T-ALL cell lines. Finally, we demonstrated a CXCL10 dependent pro-survival effect within cultured SCL/LMO1 thymocytes (Fig. 1G), which was associated with the activation of NOTCH1 signaling (Fig. 1H). Conclusions: In summary, the data support a novel T-ALL-promoting regulatory circuit in which emerging T-ALL lymphoblasts induce CXCL10 in expanding TECs which positively feeds back to T-ALL cells via the CXCL10 receptor CXCR3. Disclosures Dührsen: Celgene: Research Funding; Takeda: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding; Teva: Honoraria; Novartis: Consultancy, Honoraria; Alexion: Honoraria; Roche: Honoraria, Research Funding; CPT: Consultancy, Honoraria; Janssen: Honoraria. Göthert:Proteros Biostructures: Consultancy; Novartis: Consultancy, Honoraria, Other: Travel support; Pfizer: Consultancy, Honoraria; Incyte: Consultancy, Honoraria, Other: Travel support; Bristol-Myers Squibb: Consultancy, Honoraria, Other: Travel support; AOP Orphan Pharmaceuticals: Honoraria, Other: Travel support.

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ARF Loss, a Negative Prognostic Factor in Philadelphia-Positive Acute Lymphoblastic Leukemia, May Be Efficiently Overcome by the Small Molecule MDM2 Antagonist RG7112

Blood ◽

10.1182/blood.v118.21.2574.2574 ◽

2011 ◽

Vol 118 (21) ◽

pp. 2574-2574

Author(s):

Ilaria Iacobucci ◽

Federica Cattina ◽

Silvia Pomella ◽

Annalisa Lonetti ◽

Anna Ferrari ◽

...

Keyword(s):

Cell Cycle ◽

Acute Lymphoblastic Leukemia ◽

Cell Viability ◽

Cell Line ◽

Cell Lines ◽

Lymphoblastic Leukemia ◽

Prognostic Impact ◽

Wild Type ◽

Mdm2 Antagonist ◽

Wild Type P53

Abstract Abstract 2574 Recently, using genome-wide single nucleotide polymorphism arrays and gene candidate deep exon sequencing, we identified lesions in CDKN2A gene, encoding p16/INK4A and p14/ARF tumor suppressors, in 27% (32/117) adult newly diagnosed Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) patients and in 47% (14/30) relapsed cases. Clinically, in our cohort CDKN2A deletions were associated by univariate analysis to a worse outcome in terms of overall survival (OS), disease-free survival (DFS) and cumulative incidence of relapse (CIR) (OS: 27.7 vs 38.2 months, p = 0.0206; DFS: 10.1 vs. 56.1 months, p = 0.0010; CIR: 73.3 vs 38.1, p = 0.0014). Noteworthy, the negative prognostic impact of CDKN2A deletion on DFS was also confirmed by the multivariate analysis (p = 0.0051). These results showed that there are genetically distinct Ph+ ALL patients with a different risk of leukemia relapse and that testing for CDKN2A alterations at diagnosis may help in risk stratification. Furthermore, since the loss of CDKN2A eliminates the critical tumor surveillance mechanism and allows proliferation and tumor cell growth by the action of MDM2, a negative regulator of p53, we investigated the preclinical activity of the MDM2 antagonist RG7112 in primary B-ALL patient samples and leukemic cell line models. BV-173, SUPB-15 and K562 Ph+ cell lines were incubated with increasing concentration of RG7112 (0.5–10 μM) and its inactive enantiomer for 24, 48 and 72 hours (hrs). MDM2 inhibition by RG7112 resulted in a dose and time-dependent cytotoxicity with IC50 (24 hrs) of 2 μM for BV-173 and SUPB-15 which harbor homozygous deletion of CDKN2A but wild-type p53. No significant changes in cell viability were observed in K562 p53-null cell line after incubation with RG7112. The time and dose-dependent reduction in cell viability were confirmed in primary blast cells from a Ph+ ALL patient with the T315I Bcr-Abl kinase domain mutation found to be insensitive to the available tyrosine kinase inhibitors and from a t(4;11)-positive ALL patient (IC50 at 24 hrs equal to 2 μM). Consistent with the results of cell viability, Annexin V/Propidium Iodide analysis showed a significant increase in apoptosis after 24 hrs in BV-173, SUPB-15 and in primary leukemia blasts, whereas no apoptosis was observed in K562 cells. To examine the possible mechanisms underlying RG7112-mediated cell death, western blot analysis was performed. Protein levels of p53, p21 (an important mediator of p53-dependent cell cycle arrest), cleaved caspase-3 and caspase-9 proteins increased upon treatment with RG7112 after 24 hrs of incubation with concentrations equal to the IC50. These data demonstrate the ability of RG7112 to activate the intrinsic apoptotic pathway by a p53-dependent mechanism. In order to better elucidate the implications of p53 activation and to identify biomarkers of clinical activity, gene expression profiling analysis (Affymetrix GeneChip Human Gene 1.0 ST) was next performed, comparing sensitive cell lines (BV-173 and SUPB-15) after 24 hrs exposure to 2 μM RG7112 and their untreated counterparts (DMSO 0.1%). A total of 621 genes (48% down-regulated vs 52% up-regulated) were differentially expressed (p < 0.05). They include genes involved in cell cycle and apoptosis control (e.g. Histone H1, TOP2, GAS41, H2AFZ) and in the down-regulation of the Hedgehog signaling (e.g. BMI1, BMP7, CDKN1C, POU3F1, CTNNB1, PTCH2) with a strong repression of stemness genes and re-activation of INK4/ARF as illustrated in Figure 1. Actually, both GAS41 (growth-arrest specific 1 gene) and BMI1 (a polycomb ring-finger oncogene) are repressors of INK4/ARF and p21 and their aberrant expression has found to contribute to stem cell state in tumor cells. In our data they were strongly down-regulated (fold-change −1.35 and −1.11, respectively; p-value 0.02 and 0.03, respectively) after in vitro treatment as compared to control cells, suggesting that these genes have a potential as new biomarkers of activity. In conclusion, inhibition of the p53–MDM2 interaction by RG7112 can activate the p53 pathway, resulting in apoptosis and inhibition of stemness genes in B-ALL with wild-type p53. Our findings provide a strong rational for further clinical investigation of RG7112 in Ph+ ALL. Supported by: ELN, AIL, AIRC, Fondazione Del Monte di Bologna e Ravenna, FIRB 2006, Ateneo RFO grants, Project of integrated program, Programma di Ricerca Regione–Università 2007–2009. Disclosures: Baccarani: Novartis: Consultancy; Bristol Myers Squibb: Consultancy; Novartis: Honoraria; Bristol Myers Squibb: Honoraria; Pfizer: Honoraria; Ariad: Honoraria. Martinelli:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Pfizer: Consultancy.

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The Potent PI3K-δ,γ Inhibitor, IPI-145, Exhibits Preclinical Activity In Murine and Human T-Cell Acute Lymphoblastic Leukemia

Blood ◽

10.1182/blood.v122.21.1438.1438 ◽

2013 ◽

Vol 122 (21) ◽

pp. 1438-1438 ◽

Cited By ~ 1

Author(s):

Xiaoyan Huang ◽

Jennifer Proctor ◽

Yaling Yang ◽

Xiuhua Gao ◽

Weihong Zhang ◽

...

Keyword(s):

Growth Inhibition ◽

Cell Line ◽

Cell Lines ◽

Research Funding ◽

Lymphoblastic Leukemia ◽

Annexin V ◽

Pi3k Pathway ◽

Down Regulation ◽

Cell Acute Lymphoblastic Leukemia

Abstract Phosphoinositide-3 kinases (PI3Ks) are key cellular signaling proteins that act as a central node for relaying signals from cell surface receptors to downstream mediators, such as AKT. The PI3K-δ and PI3K-γ isoforms are preferentially expressed in normal and malignant leukocytes where they play critical roles in cell differentiation, migration, and proliferation. Constitutive activity of the PI3K pathway is common in T-cell acute lymphoblastic leukemia (T-ALL) and frequently involves the deletion of PTEN, the phosphatase that negatively regulates the PI3K pathway. An important role for the PI3K-δ and PI3K-γ isoforms has been demonstrated in the Pten-deleted genetically engineered murine model of T-ALL in conjunction with PI3K-δ and/or PI3K-γ gene knock outs (Subramanian et al, Cancer Cell, 2012). IPI-145 is a potent inhibitor of PI3K-δ and PI3K-γ currently being studied in a Phase 1 trial (IPI-145-02) in patients with advanced hematologic malignancies, including T-ALL (ClinicalTrials.gov NCT01476657). We performed in vitro studies to address the sensitivity of human and murine T-ALL cell lines to IPI-145 and to additional PI3K inhibitors with defined isoform selectivity. The human T-ALL cells examined were from cell lines that lack PTEN protein expression (Loucy, MOLT-4, CCRF-CEM, CEM/C2, p12 Ichikawa, and Karpas-45) and cell lines that express PTEN protein (MOLT13 and MOLT16). In addition, two murine cell lines derived from a Pten-deleted model of T-ALL (LPN049 and LPN236) were studied. The expression levels of class I PI3K isoforms were determined by western blotting and quantitative RT-PCR, which revealed varying levels of protein and RNA expression across the cell lines. In vitro treatment of human T-ALL cells with IPI-145 resulted in variable degrees of growth inhibition, with the PTEN-deficient Loucy cell line demonstrating the greatest sensitivity with an IC50 of 245 nM. In the cell lines tested, growth inhibition to IPI-145 was only seen in PTEN-deficient human cell lines, whereas all PTEN-expressing human T-ALL cell lines were resistant to IPI-145 (IC50 > 10 uM). However, not all PTEN-deficient human T-ALL cells demonstrated sensitivity to IPI-145 (e.g., CEM/C2), indicating that loss of PTEN does not confer sensitivity to PI3K inhibition in all settings. Inhibition of phospho-AKT (pAKT) correlated with growth inhibition, with an IC50 of 286 nM in the Loucy cell line. Studies to evaluate the mechanism of growth inhibition revealed that IPI-145 treatment resulted in apoptosis of sensitive cells as measured by 7-AAD and Annexin V staining. Cell lines derived from the Pten-deleted murine T-ALL model were also sensitive to IPI-145 with IC50s in the 300-600 nM range as measured by MTT assay. In addition, IPI-145 led to apoptosis, as measured by cleaved Caspase 3 and 7-AAD/Annexin V. Interestingly, Pten-deleted murine T-ALL cell lines showed down-regulation of pAKT and c-MYC expression with IPI-145 in a dose responsive manner that corresponded with increasing activated Caspase-3 expression. In NOTCH1-expressing murine T-ALL cell lines, down regulation of NOTCH1 and activated NOTCH1 was also observed in parallel with c-MYC down-regulation. To explore further the individual contributions of the varying PI3K isoforms on T-ALL cell growth, the effect of IPI-145 on tumor cell growth was compared with PI3K-δ, PI3K-δ,γ, and PI3K-β selective compounds in the Loucy PTEN-deficient T-ALL cell line. These experiments support an anti-leukemic effect for both PI3K-δ and PI3K-γ inhibition and indicate that the greatest effect is seen with combined PI3K-δ and PI3K-γ inhibition. A role for PI3K-β in T-ALL cell survival was not observed. Evaluation of the in vivo activity of IPI-145 on Loucy xenografts, as well as PTEN-expressing MOLT-13 xenografts, is ongoing. Together, these data provide a strong rationale for combined targeted inhibition of PI3K-δ and PI3K-γ in T-ALL. Disclosures: Huang: Infinity Pharmaceuticals, Inc.: Research Funding. Proctor:Infinity Pharmaceuticals, Inc.: Employment. Yang:Infinity Pharmaceuticals, Inc.: Research Funding. Gao:Infinity Pharmaceuticals, Inc.: Research Funding. Zhang:Infinity Pharmaceuticals, Inc.: Research Funding. Huang:Infinity Pharmaceuticals, Inc.: Research Funding. Changelian:Infinity Pharmaceuticals, Inc.: Employment. Kutok:Infinity Pharmaceuticals, Inc.: Employment. McGovern:Infinity Pharmaceuticals, Inc.: Employment. You:Infinity Pharmaceuticals, Inc.: Research Funding.

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An Evaluation of the Cytotoxic Effect of the Natural Product Aaptamine Against t(4;11) Leukemias

Blood ◽

10.1182/blood.v128.22.1624.1624 ◽

2016 ◽

Vol 128 (22) ◽

pp. 1624-1624 ◽

Cited By ~ 1

Author(s):

Chandrima Sinha ◽

John Bowling ◽

Aman Seth ◽

Bensheng Ju ◽

Bhaskar Kahali ◽

...

Keyword(s):

Cell Cycle ◽

Cell Line ◽

Cell Lines ◽

Leukemia Cell ◽

Treated Group ◽

Jurkat Cells ◽

G1 Arrest ◽

Thp1 Cell ◽

Rb Phosphorylation

Abstract The marine environment has been shown to be a rich source of pharmacologically-active secondary metabolites. Three marine- compounds have FDA approval for cancer indications. Aaptamine is a sponge-derived alkaloid that exhibits multiple pharmacological activities including proapoptotic/antiproliferative effects on leukemia cell lines. The effect of the aaptamine class has not been previously studied for high risk leukemias with mixed-lineage leukemia (MLL) gene rearrangements. Using the CellTiter-Glo cell viability assay we evaluated the cytotoxic effect of aaptamine against a panel of leukemia cell lines. We observed that cell lines containing t(4;11) are the most sensitive to aaptamine. Translocation (4;11) is associated with mixed-lineage leukemia and responsible for a very aggressive and refractory pediatric leukemia. Specifically, infants less than one year with t(4;11) have poor survival rates (≈ 19%) and new therapies are urgently needed. Interestingly other MLL cell lines that contain t(9;11) are comparatively less susceptible to aaptamine-mediated cytotoxicity. Jurkat cells overexpressing MLL-AF4 fusion protein are also more sensitive to aaptamine-induced cytotoxicity than wild type or MLL-AF9 overexpressing Jurkat cells indicating the specificity of aaptamine for t(4;11). To further confirm the specificity we conducted a flow based apoptosis assay and observed that aaptamine induces significant apoptosis and necrosis in RS4;11 and MV4;11 cell lines starting at 10µM but not in the t(9;11) containing THP1 cell line. We also found that aaptamine treatment induced G0/G1 arrest specifically in t(4;11) containing cell lines but not in THP1. Additionally we observed that aaptamine did not induce any resistance to the sensitive cell lines after 27 days of chronic exposure. Importantly the compound was well tolerated by healthy activated PBMCs and mice at high concentrations. In order to decipher the mechanism of specificity, we conducted a global proteomic study with treated and untreated RS4;11 and THP1 cell lines. Our proteomic data revealed a significant upregulation of p21 and p27 in aaptamine treated RS4;11 cells but not in THP1. In agreement with the proteomic data, we observed a dose-dependent upregulation of p21 and p27 in both protein and mRNA levels in RS4;11 and MV4;11 cells but not in resistant THP1 cells. Using p21 and p27 promoter-driven luciferase reporter constructs, we observed a significant upregulation of luminescence signal in the RS4;11 cell line at much lower concentration of aaptamine (1µM) whereas the THP1 cell line required 50µM of aaptamine for significant increase in luminescence signal. Cyclin-dependent kinase regulates the G1/S cell cycle transition by phosphorylating retinoblastoma protein (RB). Upregulation of cyclin-dependent kinase inhibitors, such as p27 and p21, promote RB hypophosphorylation and induce G0/G1 arrest. To confirm that this molecular mechanism is responsible for aaptamine induced G0/G1 arrest, we investigated the effect of aaptamine on Rb phosphorylation. We observed a dose dependent downregulation of Rb phosphorylation by aaptamine in sensitive cell lines and predicted it as a major cause of cell cycle arrest. Previous studies have shown that translocation (4;11) is associated with p27 upregulation; thus we hypothesize by further upregulating p27, aaptamine may induce G0/G1 arrest specifically in t(4;11) containing cell lines. To validate the efficacy of aaptamine in vivo, we xenografted 10 NSG mice with 1 million luciferase expressing RS4;11 cells. Four days after leukemia induction we treated half of the mice with subcutaneous injection of aaptamine (100mg/kg, daily) and the other half received vehicle treatment. Bioluminescence imaging (BLI) data revealed a significantly lower disease (p< 0.03) burden in the aaptamine treated group compared to vehicle treated group after 2 weeks. These findings are being confirmed in patient samples. Additional aaptamine analogs are being designed and will be evaluated for improved therapeutic efficacy. Together our in vitro and in vivo findings suggest that by inducing p21 and p27 aaptamine can induce cell cycle arrest and eventually apoptosis specifically in leukemia cells that contain t(4;11) with relatively low toxicity . Therefore the aaptamine class of drug may provide additional therapeutic options for t(4;11) containing high-risk MLL leukemia patients. Disclosures No relevant conflicts of interest to declare.

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Small Molecule ONC201/TIC10 Induces Caspase-Dependent Apoptosis in Acute Lymphoblastic Leukemia Cells Via Modulation of Bcl-2 and IAP Family Proteins

Blood ◽

10.1182/blood.v124.21.5237.5237 ◽

2014 ◽

Vol 124 (21) ◽

pp. 5237-5237 ◽

Cited By ~ 1

Author(s):

Varun Vijay Prabhu ◽

Amriti R. Lulla ◽

Jessica M Wagner ◽

Liz J. Hernandez-Borrero ◽

Mala K. Talekar ◽

...

Keyword(s):

Acute Lymphoblastic Leukemia ◽

Cell Viability ◽

Solid Tumors ◽

Cell Lines ◽

Small Molecule ◽

Lymphoblastic Leukemia ◽

Parp Cleavage ◽

Dependent Manner ◽

Equity Ownership ◽

The Impact

Abstract ONC201/TIC10 is a potent small molecule anti-tumor agent in several types of solid tumors and lymphomas. ONC201/TIC10 is on track to enter clinical trials for patients with advanced cancer in 2014, with IND issued by the FDA in March, 2014. Early trials will evaluate the safety and efficacy of ONC201/TIC10 as a monoagent in hematological malignancies. In the current study, we evaluated the anti-cancer effects of the small molecule in Acute Lymphoblastic Leukemia (ALL). Analysis of cell viability by the CellTiter-Glo method revealed that ONC201/TIC10 treatment reduces the viability of three ALL cell lines (Reh, Jurkat, MOLT-4) in a dose- (2.5/5/10 μM) and time-dependent manner (24/48/72 h). We have previously reported that ONC201/TIC10-mediated reduction in cell viability and apoptosis in various types of solid tumors occurs at 60/72 h. Interestingly, ONC201/TIC10 reduces the viability of ALL cell lines within 24/48 h at the indicated doses. An inactive TIC10 isomer compound synthesized by Medkoo Biosciences with a structure related to the active ONC201/TIC10 compound does not reduce the viability of ALL cells. Sub-G1 analysis indicated that ONC201/TIC10 induces apoptosis in ALL cells and a pan-caspase inhibitor reduces ONC201/TIC10-mediated apoptosis. Western blot analysis was used to further investigate the mechanism of ONC201/TIC10-mediated apoptosis. ONC201/TIC10-mediated apoptosis involves PARP cleavage and caspase-9 activation. Anti-apoptotic Bcl-2 family members Bcl-2 and Bcl-xl are downregulated while the pro-apoptotic Bcl-2 family member Bim is upregulated in response to ONC201/TIC10 treatment. ONC201/TIC10 also downregulates the inhibitor of apoptosis (IAP) family proteins cIAP1 and cIAP2. We have previously shown that the anti-tumor effect of ONC201/TIC10 involves inhibition Akt and ERK phosphorylation resulting in Foxo3a activation and TRAIL-gene transcription. We observed inhibition of Akt phosphorylation upon ONC201/TIC10 treatment of ALL cells. Thus, ONC201/TIC10 holds promise as a novel agent for the treatment of ALL based on its robust activity in preclinical models of the disease. Our ongoing studies are evaluating the impact of this novel therapy on ALL cells with different translocations, and are introducing combination therapy with ONC201/TIC10 for ALL. Figure 1 Figure 1. Disclosures Allen: Oncoceutics: Employment, Equity Ownership, Patents & Royalties. El-Deiry:Oncoceutics, Inc.: Equity Ownership, Patents & Royalties.

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BRD4 Proteolysis Targeting Chimera (PROTAC) ARV-825 Targets Both NOTCH1-MYC Regulatory Circuit and Leukemia-Microenvironment in T-ALL

Blood ◽

10.1182/blood.v130.suppl_1.716.716 ◽

2017 ◽

Vol 130 (Suppl_1) ◽

pp. 716-716

Author(s):

Sujan Piya ◽

Hong Mu ◽

Seemana Bhattacharya ◽

Teresa McQueen ◽

Richard E Davis ◽

...

Keyword(s):

Cell Cycle ◽

Acute Lymphoblastic Leukemia ◽

T Cell ◽

Cell Lines ◽

Research Funding ◽

Lymphoblastic Leukemia ◽

New Haven ◽

Down Regulation ◽

Regulatory Circuit ◽

Cell Acute Lymphoblastic Leukemia

Abstract Background: Salvage options for patients with relapsed T cell acute lymphoblastic leukemia (T-ALL) are limited, with less than 25% of these patients achieving second remission 1, 2. 70% of T-ALL cases have activating mutations of the NOTCH1 pathway, which transcriptionally activates MYC by binding to its `superenhancer' region 3, 4. Other deregulated oncogenic pathways in T-ALL include PI3K/Akt, the anti-apoptotic Bcl-2 family, and CDKN2A/2B cell cycle regulators 5, 6. The NOTCH1-MYC regulatory circuit is an attractive therapeutic target, but clinical development of gamma-secretase inhibitors (GSI) to target NOTCH1 has been limited by 'on target' toxicities. A better target may be BRD4, a critical component of superenhancer complexes that binds to acetylated histone (3 and 4) and drives NOTCH1 mediated MYC transcription7. ARV-825 is a hetero-bifunctional PROteolysis TArgeting Chimera (PROTAC) that has 3 components: a thienodiazepine-based BRD4 ligand, a linker arm, and a cereblon-binding ligand. ARV-825 recruits BRD4 to the E3 ubiquitin ligase cereblon and leads to efficient and sustained degradation of BRD4, resulting in down-regulation of MYC. Methods: We investigated the effectiveness of ARV-825 against T-ALL cell lines, including GSI-resistant lines. Since microenvironmental signals are critical for the survival of T-ALL, we specifically tested the impact of BRD4 degradation on CD44/CD44v, which integrates cell-extrinsic microenvironmental signals and is part of cysteine transporter that maintains low intra-cellular reactive oxygen species (ROS), necessary for T-ALL survival and the persistence of disease. We also examined the anti-leukemic effect of ARV-825 in a T-ALL patient-derived xenograft (PDX) mouse model of disseminated leukemia with a constitutively active NOTCH1 mutation. Results: The IC50s for all tested T-ALL cell lines at 72 hours were in the low nanomolar range (< 50 nM). ARV-825 leads to sustained degradation of BRD4 and down-regulation of its transcriptional targets MYC, Bcl-2 and Bcl-XL and inhibits cell proliferation and induces apoptosis in GSI-sensitive (HPB-ALL, KOPT1) and GSI-resistant (MOLT4, SUPT1) cell lines. Mass cytometry based proteomic analysis (CyTOF) and immunoblotting showed that ARV-825 down-regulated cell intrinsic oncogenic molecules: transcription factors Myc and NFkB, cell cycle regulator CDK6, activated PI3K/Akt, and anti-apoptotic Bcl2 family proteins. In addition ARV-825 down regulated two key molecules involved in leukemia-stroma interaction; CD44 (Fig. 1), and CD98, a component of amino acid transporters xCT, LAT1 and 2, both essential in regulation of oxidative stress. Quantitative PCR and immunoblotting analysis confirmed the transcriptional down regulation of total CD44 and CD44 variants 8-10 (2-fold change treated vs . untreated). As a functional correlate of down-regulation of CD98/CD44/CD44v, flow cytometry confirmed increased intracellular ROS generation (Fig. 2). Finally, in a PDX mouse model of human T-ALL, ARV-825 treatment resulted in lower leukemia burden (confirmed by flow cytometry for human CD45+ cells in bone marrow) and better survival compared to vehicle-treated control mice (p=0.002) (Fig.3). Reference: 1. Marks DI, Rowntree C. Management of adults with T-cell lymphoblastic leukemia. Blood 2017; 129(9): 1134-1142. 2. Litzow MR, Ferrando AA. How I treat T-cell acute lymphoblastic leukemia in adults. Blood 2015; 126(7): 833-41. 3. Sanchez-Martin M, Ferrando A. The NOTCH1-MYC highway toward T-cell acute lymphoblastic leukemia. Blood 2017; 129(9): 1124-1133. 4. Demarest RM, Ratti F, Capobianco AJ. It's T-ALL about Notch. Oncogene 2008; 27(38): 5082-91. 5. Girardi T, Vicente C, Cools J, De Keersmaecker K. The genetics and molecular biology of T-ALL. Blood 2017; 129(9): 1113-1123. 6. Joshi I, Minter LM, Telfer J, Demarest RM, Capobianco AJ, Aster JC et al. Notch signaling mediates G1/S cell-cycle progression in T cells via cyclin D3 and its dependent kinases. Blood 2009; 113(8): 1689-98. 7. Loven J, Hoke HA, Lin CY, Lau A, Orlando DA, Vakoc CR et al. Selective inhibition of tumor oncogenes by disruption of super-enhancers. Cell 2013; 153(2): 320-34. Disclosures Qian: 4Arvinas, LLC. New Haven, CT: Employment. Raina: 4Arvinas, LLC. New Haven, CT: Employment. McKay: 6 ImmunoGen, Inc.Waltham, MA: Employment. Kantarjian: Novartis: Research Funding; Amgen: Research Funding; Delta-Fly Pharma: Research Funding; Bristol-Meyers Squibb: Research Funding; Pfizer: Research Funding; ARIAD: Research Funding. Andreeff: Daiichi Sankyo: Consultancy.

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Niche-Based Screening Identifies Novel Small Molecules That Overcome Stromal Effects in Multiple Myeloma

Blood ◽

10.1182/blood.v120.21.571.571 ◽

2012 ◽

Vol 120 (21) ◽

pp. 571-571

Author(s):

Shrikanta Chattopadhyay ◽

Alison L. Stewart ◽

Siddhartha Mukherjee ◽

Cherrie Huang ◽

Kimberly A. Hartwell ◽

...

Keyword(s):

Multiple Myeloma ◽

Bone Marrow ◽

Drug Discovery ◽

Small Molecules ◽

Cell Line ◽

Cell Lines ◽

Small Molecule ◽

Research Funding ◽

Small Molecule Inhibitors ◽

Novel Therapeutic

Abstract Abstract 571 Despite advances in the treatment of multiple myeloma (MM), this disease remains incurable and novel therapeutic strategies are urgently needed. Ideal strategies would overcome resistance factors from the bone-marrow microenvironment (niche) since a variety of inhibitors are rendered less effective by bone-marrow stromal cells (BMSCs) of the MM niche (McMillin et al., Nat Med. 2010 Apr;16(4):483–9). Drug discovery often entails a target-based approach but identifying targets in MM is challenging because of its complex genome and multiple niche interactions. We used a chemical biology approach in which small-molecule inhibitors of MM cells, grown within their niche, are first identified and then used to discover targets within MM or its niche. These compounds also serve as leads for future drug discovery. To model myeloma/niche interactions, we chose an MM cell line MOLP5 that has an obligate dependence on BMSCs to maintain viability. Small-molecule inhibitors were identified by screening ∼25,000 structurally diverse small molecules on GFP-labeled MOLP5 cells co-cultured with primary BMSCs derived from hip replacement samples. MOLP5 growth inhibition was measured by quantifying GFP(+) cells with automated high-throughput microscopy. About 800 hits were counter-screened on BMSCs alone to exclude non-specifically toxic compounds. The remaining 182 MOLP5-selective inhibitors were then tested on 2 other GFP-labeled MM cell-lines, MM1S and INA6, in the presence or absence of BMSCs to exclude compounds that are less effective in the presence of BMSCs. The 64 compounds that overcome BMSC resistance were tested on CD34+ human hematopoietic progenitors to prioritize compounds with selectivity between MM and normal blood cells. The 8 compounds that met these criteria fell into 3 categories: 1) compounds with equal activity in the presence or absence of BMSCs (overcome stromal resistance); 2) compounds with selectivity for BMSC-dependent MOLP5 cells (block stromal viability factors); and 3) compounds with increased activity in the presence of BMSCs (enhance stromal inhibitory factors). Because most efficacious clinical compounds like bortezomib act like compounds in category 1, compound BRD9876 was chosen from this category for mechanistic studies. Gene-expression profiling of BRD9876-treated MM1S cells suggested possible links to mitotic arrest and cell cycle analyses revealed a rapid accumulation of cells in the G2/M phase. Treated cells were stained for the mitotic spindle protein α-tubulin and found to exhibit an aberrant mono-astral mitotic phenotype, reminiscent of the kinesin-5 (Eg5; KIF11) inhibitor monastrol. This was encouraging because a kinesin-5 inhibitor ARRY-520 has shown promising durable responses in multiple myeloma (Shah et al, ASH Annual Meeting 2011; Abstract 1860). To determine if BRD9876 was a kinesin-5 inhibitor, a BRD9876-resistant sub-line of MM1S was developed and the kinesin-5 gene sequenced. BRD9876-resistant cells have a novel kinesin-5 mutation (Y104C) at a site that is distant from the monastrol-binding pocket. Most kinesin-5 inhibitors in clinical development bind the monastrol pocket, and the BRD9876-resistant cells were not cross-resistant to one such inhibitor, ispinesib, suggesting a distinct mode of kinesin-5 inhibition by BRD9876. To identify biomarkers of sensitivity to BRD9876, quantitative dose/response measurements in 98 genetically characterized cell lines (Schreiber & co-workers, submitted) comprising a subset of the Cancer Cell Line Encyclopedia (CCLE) were analyzed. Unbiased analyses correlating genetic features with sensitivity revealed that mutations in the mitotic regulator WEE1 were associated with sensitivity to BRD9876. Validation studies comparing WEE1 mutant to wild-type cell lines confirmed enhanced sensitivity of mutant cells to both BRD9876 and ispinesib suggesting that WEE1 mutations could be a useful biomarker for different kinesin-5 inhibitors. In contrast, co-treatment of WEE1 WT cells with sub-toxic concentrations of the WEE1 inhibitor MK1775 led to marked enhancement of BRD9876 activity but had little effect on ispinesib activity, suggesting a unique synergistic relationship between WEE1 inhibitors and BRD9876. In summary, niche-based screening in multiple myeloma has revealed a novel therapeutic candidate and can complement other drug-discovery approaches against this disease. Disclosures: Ebert: Celgene: Consultancy; Genoptix: Consultancy. Raje:Onyx: Consultancy; Celgene: Consultancy; Millennium: Consultancy; Acetylon: Research Funding; Amgen: Research Funding; Eli-Lilly: Research Funding.

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