A phase I, pharmacokinetic and pharmacodynamic study of sorafenib (S), a multi-targeted kinase inhibitor in combination with temsirolimus (T), an mTOR inhibitor in patients with advanced solid malignancies

2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 3512-3512 ◽  
Author(s):  
A. Patnaik ◽  
A. Ricart ◽  
J. Cooper ◽  
K. Papadopoulos ◽  
M. Beeram ◽  
...  

3512 Background: The combination of S and T is hypothesized to maximize pathway inhibition by concurrently targeting parallel signaling mechanisms and will abrogate potential resistance mechanisms directed towards the MAPK pathway through increased signaling via the survival pathway involving PI3K/Akt. Methods: Eligible patients (pts) were treated with escalating continuous oral doses of S (200 and 400 mg BID) and weekly T IV (15 mg, 25 mg). S began on day 8 of course 1 to permit PK evaluations of T. PD studies in PBMCs were performed serially in pts. Results: To date, 24 evaluable pts have received 85 courses [median 3;range1–12] in the following S/T dose cohorts; cohort 1: 200 mg/15 mg (n=6), cohort 2: 400 mg/15 mg (n=11), cohort 3: 400 mg/25 mg (n=6), and cohort 4: 200 mg/25 mg (n=1). Patients demographics were males/female 11/13, median age 54.5 [range 27–71] and PS of 0/1/2 : n=9/13/2. Dose limiting toxicities (DLT) were grade 3 typhlitis in 1/6 pts in cohort 1, and mucositis in 1/6 pts in cohort 2. Expansion of cohort 2 to 11 patients resulted in 4 additional DLTs (hand foot syndrome (HFS) x 2 pts, thrombycytopenia/rash x 1 pt, creatinine elevation x 1 pt). 3 of 6 pts in cohort 3 experienced DLT (HFS x 2 pts, thrombocytopenia x 1 pt). PK analyses show no evidence of S effect on T kinetics while Css,min values of S are consistent with those reported in single-agent studies (S 200mg BID median Css,min 4.42 μg/mL [SD 3.05], S 400 mg BID median Css,min 5.11 μg/mL [SD 4.35]). Apparent downregulation of 4E-BP1 and activated forms of p70S6 kinase and ERK was observed in some patients following treatment. Partial responses have occurred in NHL (1 pt) and papillary thyroid cancer (1 pt) and prolonged SD (> 12 mo) has been observed in RCC (1 pt). Conclusions: The combination of S and T demonstrate significant mucocutaneous toxicity at full doses of S, however preliminary PK analyses show no evidence of drug-drug interactions. Characterization of an intermediate dose of S 200 mg BID/T 25 mg IV is ongoing. [Table: see text]

2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 5101-5101 ◽  
Author(s):  
G. V. Kondagunta ◽  
G. R. Hudes ◽  
R. Figlin ◽  
G. Wilding ◽  
S. Hariharan ◽  
...  

5101 Background: Sunitinib malate is an oral, multitargeted tyrosine kinase inhibitor of VEGFRs and PDGFRs with anti-tumor activity in mRCC patients previously treated with cytokines (JAMA, 2006;295:2516). A phase 3 randomized trial showed superiority for SU over IFN in first-line mRCC (PROC ASCO 24,18S, 2006). Dose and safety for SU combined with IFN was investigated in this phase I trial. Methods: Patients (pts) with previously untreated clear-cell mRCC received SU in repeated 6-week cycles of 50 or 37.5 mg/day orally for 4 weeks, followed by 2 weeks off treatment. IFN was given continuously, starting at 3 MU SC 3x/week with intrapatient dose escalation weekly as tolerated, to a maximum of 9 MU. Pts not tolerating a dose combination received lower doses of SU or IFN, or had dose interruptions. Doses of SU plus IFN were considered tolerable if = 4/6 pts completed 2 cycles without dose reduction or interruption. Results: 25 pts were enrolled; 19 are evaluable for safety/response. 6 pts who started treatment at 37.5 SU and 3 MU IFN are too early. The median age of the 19 pts (16 M: 3 F) was 63 years (range 45–77). MSKCC risk group (JCO 20:289–96, 2002) was 37% good and 63% intermediate. 12 pts started treatment with SU 50 mg and dose escalated IFN to 6 or 9 MU TIW. 13 pts started treatment with SU 37.5 mg and dose escalated IFN at 3 MU or to 6 MU TIW. 4 of 19 pts tolerated two cycles. 68% of pts had dose interruptions of SU; 90% of pts had dose interruptions of IFN. 15/19 pts had grade 3 toxicity, 1 pt had grade 4 hypertension and 1 pt grade 5 toxicity (myocardial infarction). Most common grade 3 toxicities were neutropenia (26%), fatigue (26%), and hand-foot syndrome (16%). Although response was not a primary endpoint, at a median of 3 cycles, there were 2 PR, 14 SD, 2 PD and 1 pt was not evaluable. Conclusions: The adverse events seen with combination SU and IFN in mRCC, neutropenia and fatigue, were similar to those seen with single agent SU and IFN, and resulted in frequent dose modifications and interruptions. The safety and efficacy of 37.5 mg sunitinib and 3 MU IFN is being evaluated. No significant financial relationships to disclose.


2017 ◽  
Vol 35 (15_suppl) ◽  
pp. 5524-5524 ◽  
Author(s):  
Neesha C. Dhani ◽  
Hal W. Hirte ◽  
Julia V. Burnier ◽  
Angela Jain ◽  
Marcus O. Butler ◽  
...  

5524 Background: Recurrent/metastatic EC has a poor prognosis with no standard 2ndline therapy. Cabo is a multi-targeted kinase inhibitor of MET, VEGFR, TIE2, AXL & KIT, relevant in epithelial-stromal cross-talk. The role of MET/HGF in aggressive EC biology, where transient benefit of VEGF-targeting is due to MET/HGF, TIE2 & AXL, provides rationale for MET targeting in EC. Methods: PHL86 (NCI#9322/NCT01935934) is a multi-centre, phase II trial of cabo (60mg oral daily dose) in pts with EC recurring within a year of adjuvant chemotherapy (ctx), or with progression after 1 line of ctx for metastatic disease. Experimental (E) cohort was stratified by histology (serous (SER) vs endometroid (END)) in a Simon two-stage design for co-primary endpoints of response rate ( > 30%) & 12-week progression-free-survival (PFS) ( > 55%). Activity was defined as > 7 partial responses (PRs) or > 15 instances of 12 wk-PFS in 36 pts. Pts with rare histology EC were treated in a parallel exploratory (Ex) cohort. Results: From May 2013 to Nov 2016, 102 pts (E: 71; Ex: 31) have been treated with cabo after prior radiation (59) and/or ctx (no. lines: 1(77); 2(22)). Cabo was well tolerated with common toxicities of fatigue, nausea, diarrhea & hand-foot syndrome. Most frequent Grade 3/4 toxicity was hypertension (32/101 pts). Fistula/perforation occurred in 4 of 71 SER/END pts & 4 of 31 Ex pts; no risk factors were identified. In 33 END pts, 6 PRs & 24 instances of > 12-wk PFS were observed; median PFS is 4.8 mths (95% CI: 4.4 – 6.4) with estimated 6-mth PFS of 43% (95% CI: 27 to 59%). In 34 SER pts, 4 PRs & 20 instances of > 12-wk PFS were observed; median PFS is 4.0 mths (95% CI: 2.7 – 4.7) with estimated 6-mth PFS of 30% (95% CI: 15 to 46%). 4 pts have had PFS > 12 mths, 1 SER pt remains on study after 25mths. Mutational analysis demonstrated presence of KRAS with PTEN or PIK3CA mutations in 9 (SER/END) pts, of whom 8/9 pts met 12-wk PFS endpoint, with a median PFS 5.9 mth (4.1 to 15.4). Conclusions: Cabo has single agent activity in END and SER EC with durable disease control. Concurrent mutation in KRAS/PTEN/PIK3CA may enrich for response. The current data support further evaluation of cabo in EC. Clinical trial information: NCT01935934.


eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Vidhu Sharma ◽  
Lisa Young ◽  
Miguel Cavadas ◽  
Kate Owen ◽  

The Reproducibility Project: Cancer Biology seeks to address growing concerns about reproducibility in scientific research by conducting replications of selected experiments from a number of high-profile papers in the field of cancer biology. The papers, which were published between 2010 and 2012, were selected on the basis of citations and Altmetric scores (<xref ref-type="bibr" rid="bib4">Errington et al., 2014</xref>). This Registered Report describes the proposed replication plan of key experiments from “COT drives resistance to RAF inhibition through MAPK pathway reactivation” by Johannessen and colleagues, published in Nature in 2010 (<xref ref-type="bibr" rid="bib10">Johannessen et al., 2010</xref>). The key experiments to be replicated are those reported in Figures 3B, 3D-E, 3I, and 4E-F. In Figures 3B, D-E, RPMI-7951 and OUMS023 cells were reported to exhibit robust ERK/MEK activity concomitant with reduced growth sensitivity in the presence of the BRAF inhibitor PLX4720. MAP3K8 (COT/TPL2) directly regulated MEK/ERK phosphorylation, as the treatment of RPMI-7951 cells with a MAP3K8 kinase inhibitor resulted in a dose-dependent suppression of MEK/ERK activity (Figure 3I). In contrast, MAP3K8-deficient A375 cells remained sensitive to BRAF inhibition, exhibiting reduced growth and MEK/ERK activity during inhibitor treatment. To determine if RAF and MEK inhibitors together can overcome single-agent resistance, MAP3K8-expressing A375 cells treated with PLX4720 along with MEK inhibitors significantly inhibited both cell viability and ERK activation compared to treatment with PLX4720 alone, as reported in Figures 4E-F. The Reproducibility Project: Cancer Biology is collaboration between the Center for Open Science and Science Exchange and the results of the replications will be published in eLife.


2019 ◽  
Vol 20 (6) ◽  
pp. 1483 ◽  
Author(s):  
Paola Savoia ◽  
Paolo Fava ◽  
Filippo Casoni ◽  
Ottavio Cremona

The discovery of the role of the RAS/RAF/MEK/ERK pathway in melanomagenesis and its progression have opened a new era in the treatment of this tumor. Vemurafenib was the first specific kinase inhibitor approved for therapy of advanced melanomas harboring BRAF-activating mutations, followed by dabrafenib and encorafenib. However, despite the excellent results of first-generation kinase inhibitors in terms of response rate, the average duration of the response was short, due to the onset of genetic and epigenetic resistance mechanisms. The combination therapy with MEK inhibitors is an excellent strategy to circumvent drug resistance, with the additional advantage of reducing side effects due to the paradoxical reactivation of the MAPK pathway. The recent development of RAS and extracellular signal-related kinases (ERK) inhibitors promises to add new players for the ultimate suppression of this signaling pathway and the control of pathway-related drug resistance. In this review, we analyze the pharmacological, preclinical, and clinical trial data of the various MAPK pathway inhibitors, with a keen interest for their clinical applicability in the management of advanced melanoma.


2013 ◽  
Vol 31 (11) ◽  
pp. 1405-1414 ◽  
Author(s):  
Athanassios Argiris ◽  
Musie Ghebremichael ◽  
Jill Gilbert ◽  
Ju-Whei Lee ◽  
Kamakshi Sachidanandam ◽  
...  

Purpose We hypothesized that the addition of gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, to docetaxel would enhance therapeutic efficacy in squamous cell carcinoma of the head and neck (SCCHN). Patients and Methods Patients with recurrent or metastatic SCCHN with Eastern Cooperative Oncology Group (ECOG) performance status of 2, or patients with ECOG performance status of 0 to 2 but were previously treated with chemotherapy, were randomly assigned to receive weekly docetaxel plus either placebo (arm A) or gefitinib 250 mg/d, orally (arm B) until disease progression. At the time of progression, patients in the placebo arm could receive single-agent gefitinib. EGFR, c-MET, and KRAS mutations and polymorphisms in drug metabolizing enzymes and transporters were evaluated by pyrosequencing. Results Two hundred seventy patients were enrolled before the study was closed early at interim analysis (arm A, n = 136; arm B, n = 134). Median overall survival was 6.0 months in arm A versus 7.3 months in arm B (hazard ratio, 0.93; 95% CI, 0.72 to 1.21; P = .60). An unplanned subset analysis showed that gefitinib improved survival in patients younger than 65 years (median 7.6 v 5.2 months; P = .04). Also, there was a trend for improved survival in patients with c-MET wild-type (5.7 v 3.6 months; P = .09) regardless of treatment. Grade 3/4 toxicities were comparable between the two arms except that grade 3/4 diarrhea was more common with docetaxel/gefitinib. Of 18 eligible patients who received gefitinib after disease progression in arm A, one patient had a partial response. Conclusion The addition of gefitinib to docetaxel was well tolerated but did not improve outcomes in poor prognosis but otherwise unselected patients with SCCHN.


2006 ◽  
Vol 24 (18_suppl) ◽  
pp. 4529-4529 ◽  
Author(s):  
P. H. De Mulder ◽  
J. Roigas ◽  
S. Gillessen ◽  
S. Srinivas ◽  
P. Pisa ◽  
...  

4529 Background: Renal cell carcinomas are known for their vascularity and production of high levels of VEGF. Sunitinib malate (SU11248), an oral, multitargeted tyrosine kinase inhibitor of multiple receptors including VEGFR, PDGFR, KIT, RET, and FLT3, has previously demonstrated significant efficacy in 168 patients (pts) with mRCC, with a 42% objective response rate (ORR) at 50 mg/day in 6-week (wk) cycles of 4 wks on treatment followed by 2 wks off. This study sought to determine the efficacy and safety of single-agent sunitinib in mRCC when administered in a continuous 37.5 mg/day regimen. Methods: Pts with histologically proven mRCC, refractory to a cytokine-based regimen, were enrolled in this open-label, multicenter, phase II study. Eligibility criteria included measurable disease, ECOG PS 0/1, and adequate organ function. Pts were randomized to receive sunitinib in the morning (AM) or in the evening (PM) at a dose of 37.5 mg/day, with individual doses subsequently titrated based on tolerability. The primary endpoint was RECIST-defined ORR. Secondary endpoints includedprogression-free survival, adverse events (AEs) and quality of life measures. Results: A total of 88/100 planned pts have been randomized to date: AM (43) and PM (45), and enrollment will be completed by end January 2006. 44 pts have been on continuous sunitinib treatment at 37.5 mg/day for >16 wks (3), >12 wks (9), >8 wks (12), and >4 wks (20). 2 pts (2.3%) discontinued (colon perforation and renal insufficiency) and 9 (10.2%) dose reduced to 25 mg/day due to grade 2/3 AEs: mucositis (2), hand-foot syndrome (2), thrombocytopenia (2), asthenia (1), nausea/diarrhea (1), and neutropenia (1). Preliminary efficacy data show some tumor shrinkage in the majority of patients evaluated at 4 wks, with 3 initial partial responses. There has been no significant difference between pts who received AM or PM doses. The most commonly reported AEs were mucositis, fatigue, hair/skin discoloration, and hand-foot syndrome. Conclusions: Sunitinib administered at a continuous dose of 37.5 mg/day was generally well tolerated; only a few patients required treatment breaks and/or dose reduction. Preliminary efficacy data are encouraging. Mature data will be presented. [Table: see text]


2006 ◽  
Vol 24 (18_suppl) ◽  
pp. 3006-3006 ◽  
Author(s):  
J. Baselga ◽  
P. Schöffski ◽  
F. Rojo ◽  
H. Dumez ◽  
F. J. Ramos ◽  
...  

3006 Background: C and G are two anti-EGFR agents with different mechanisms of action. We had previously shown a synergistic effect combining the two agents in preclinical models (Matar et al, Clin Cancer Res 2004). This study aims to explore safety, PK and PD changes in tumor and skin at different doses of C/G to define the recommended dose (RD) for further development. Methods: pts were treated at the RD of weekly iv C (400 mg/m2 initial dose, 250 mg/m2 weekly) and oral daily G (250 mg/d) as single agents (5 pts each) and in successive cohorts of combined C/G (3–6 pts each): C (320/200) / G (100), C (400/250) / G (100), C (400/250) / G (250), C (320/200) / G (500) & C (400/250) / G (500) (ongoing). Dose escalation depended on dose limiting toxicity (DLT) rate during the first 28 d. Pre- & on-treatment steady-state (14 d) tumor & skin biopsies were obtained and have been evaluated by IHC for total (t) and phospho (p)-EGFR, p-MAPK, p-Akt, proliferation (Ki67), p27 expression and apoptosis by TUNEL. Gene profiling analysis is ongoing. Results: 35 pts have been treated so far: 20 CRC, 13 HNC & 2 NSCLC; median KI 90 % (70–100); median age 60 years (38–80); 24 males, 11 females. DLTs occurred in 3 pts: 1 pt with G alone with reversible ILD; 1 pt with G (250) / C (400/250) with reversible deafness & 1 pt with G (500) / C (320/200) with grade 3 anorexia and nausea. There were 1 CR (HNC) and 5 PRs (CRC) in the C/G cohorts, and 1 PR (CRC) in the C cohort. Overall, 5 out of 9 (56%) pts with CRC treated in the C/G cohorts presented a PR. PD studies show superior inhibition of p-EGFR, p-MAPK and p-Akt, reduction of proliferation and increased apoptosis (all p values <0.05) in the tumors of pts treated with C/G compared with the single agent cohorts. PK evaluation shows no PK interactions with the 2 drugs. Conclusions: This combination of an anti-EGFR MAb (C) and a TKI (G) is feasible at the RD of both agents. Our findings show encouraging clinical activity, especially in CRC, and superior PD signaling inhibition with the combination without any significant PK interaction. Combined anti-EGFR therapy deserves further evaluation. [Table: see text]


2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 1003-1003 ◽  
Author(s):  
H. S. Rugo ◽  
A. Stopeck ◽  
A. A. Joy ◽  
S. Chan ◽  
S. Verma ◽  
...  

1003 Background: Single-agent DOC is commonly used to treat MBC. Axitinib (AG) is a potent TKI of VEGFRs. A phase I lead-in study identified 80 mg/m2 q3wks of DOC in combination with 5 mg BID of AG as the recommended phase 2 dose. The primary objective was to determine whether the time to progression (TTP) of AG+DOC arm is superior to DOC+PL. Methods: Pts with no prior chemotherapy for MBC and =12 mos from adjuvant chemotherapy (aCT), measurable disease, ECOG performance status (PS) of 0–2, and no uncontrolled brain metastases were randomly assigned (2:1) to receive treatment with either DOC+AG or DOC+PL without prophylactic growth factor in cycle 1. Tumor measurements were performed q9wks. Pts were stratified according to estrogen receptor (ER) status, prior aCT and PS (0–1 or 2). Results: A total of 168 pts were randomized. 92 pts had received prior aCT, 27 of whom received a prior taxane. Treatment arms were well balanced for prior adjuvant and taxane therapy. A median of 7 cycles of AG+DOC (range: 1–18) and 7 cycles of DOC+PL (range: 1–23) were administered. The most common non-hematologic adverse events observed in the AG+DOC arm included diarrhea (60%), nausea (53%), alopecia (51%), fatigue (49%), stomatitis (44%) and vomiting (40%). Grade 3/4 adverse events that were increased with AG+DOC vs DOC included febrile neutropenia (16 vs 7%), fatigue (13 vs 5%), stomatitis (13 vs 2%), diarrhea (11 vs 0%) and hypertension (5 vs 2%). Other grade 3/4 hematologic toxicities were similar in both arms. The median TTP (by RECIST) was 8.2 mo with AG+DOC arm and 7 mo with DOC+PL arm with a hazard ratio of 0.73 (prespecified, one-sided p=0.052). The overall response rate (ORR) was 40% for AG+DOC arm and 23% for DOC+PL arm (p=0.038). In a hypothesis-generating subgroup analysis, the median TTP in patients receiving prior aCT was 9.0 mo with AG+DOC arm and 6.3 mo with DOC+PL arm with a hazard ratio of 0.54 (p=0.012). Within this stratum, ORR was 45% for AG+DOC arm and 13% for DOC+PL arm (p=0.003). Conclusions: The anti-angiogenic TKI AG combined with DOC (80 mg/m2 q3wks) as first line therapy for MBC has an acceptable safety profile and promising anti-tumor activity. No significant financial relationships to disclose.


2007 ◽  
Vol 25 (18_suppl) ◽  
pp. 3549-3549 ◽  
Author(s):  
D. S. Hong ◽  
L. Camacho ◽  
C. Ng ◽  
J. Wright ◽  
R. A. Newman ◽  
...  

3549 Background: The Ras and Raf kinases are sequential signaling proteins in the MAPK pathway and inhibition of both targets may confer synergistic effects, particularly in tumors with activation of either kinase through mutation or other mechanisms. Therefore, we sought to combine sorafenib, a multikinase inhibitor (Raf, VEGFR, PDGFR) and tipifarnib an inhibitor of farnesyltransferase that is critical for Ras activity in a phase I study to determine the safety, pharmacokinetics (PK), and tumor response. Methods: The trial was a phase I trial of advanced cancer patients(pts) with a conventional dose escalation design. Each cycle consisted of 28 days of sorafenib and 21 days of tipifarnib. Dose levels are listed in the table . Results: To date, a total of 27 pts have been enrolled (median age 54.5 yrs, M:F 1:1. 3 RCC, 3 breast, 4 sarcoma, 4 melanoma, 3 CRC, 4 thyroid, 2 H&N, one thymic, one adrenal cortical, one SCC of the lung, and one unknown primary SCC). Two pts developed grade 3 DLT-skin rash on the first dosing level (tipifarnib at 100 mg po BID and sorafenib at 400 mg po BID). Dose escalation was modified as per table below. At dose level 4, 2/5 pts entered experienced a DLT of grade 3 rash and grade 3 drug fever, therefore MTD has been determined to be tipifarnib 100 mg BID, sorafenib 400 mg qam, 200 mg qpm. The most common treatment related toxicities included lymphopenia (18), hyperglycemia (17), and skin rash (14). Currently, 19 of the 27 pts are evaluable; 13 pts had SD (8–44 weeks); 2 RCC pts for 32 weeks, an adrenal cortical ca pt for 32 weeks, one melanoma pt for 44 weeks. PK analysis suggested findings similar to single agent PK profiles, no PK interactions were apparent. Conclusions: Significant toxicity with the combination of these two agents, even doses well below single agent maximum levels were observed. The MTD was determined to be tipifarnib at 100 mg BID, sorafenib at 400 mg qam, 200 mg qpm. PK analysis, to date show,no pharmacokinetic interaction between tipifarnib and sorafenib. [Table: see text] [Table: see text]


2009 ◽  
Vol 27 (15_suppl) ◽  
pp. 10534-10534 ◽  
Author(s):  
P. Schoffski ◽  
G. Floris ◽  
R. Sciot ◽  
C. Stefan ◽  
A. Wozniak ◽  
...  

10534 Background: Inhibition of HSP90 is a new strategy for treatment of GIST. IPI-504 is a potent i.v. HSP90 inhibitor. We assessed the activity of IPI-504 in imatinib-sensitive GIST xenografts, alone/combined with the TKI. Methods: Human GIST882 cells (KIT exon 13 mut.) were grafted in 43 nude mice, who were randomized to 4 groups: A (n=13; control); B (n=18; IPI-504 100 mg/kg 3x/wk p.o.); C (n=8; imatinib 50 mg/kg 2x/d p.o.); D (n=4; IPI-504+imatinib, dose/schedule as above) for 2 weeks. Histopathological assessment was done by H&E and KIT immunostaining, histological response (HR) was defined by magnitude of necrosis and myxoid degeneration [grade 1 (0–10%), 2 (>10% - ≤ 50%), 3 (> 50% - ≤90%), 4 (>90%)]. Expression/activation of KIT and its signaling (AKT, S6, MAPK) was assessed by Western blot. Results: IPI-504 alone significantly reduced tumor volume (41%) at day 14, further enhanced by adding imatinib (58%). Imatinib alone led to only a 5% reduction. IPI-504 induced grade 2 HR in 17/36 tumors, while the majority of tumors (13/15) treated with imatinib showed grade 1 HR. Grade 3/4 HRs were only seen with the combination. Mitosis decreased 3.3-fold, apoptosis increased 1.3-fold with IPI-504. Despite substantial reduction in mitotic activity in C and D (8.2- and 82-fold), apoptosis was virtually unaffected. In the IPI-504 arm, KIT levels were partially downregulated. Imatinib alone had no effect on KIT expression, while the combination produced a marked suppression of total KIT, accompanied by complete downregulation of the signaling. Loss of KIT in the combination arm was confirmed by immunostaining. Although KIT was not completely degraded with IPI-504, measurable effects on activation of AKT, S6 and MAPK were observed. Conclusions: IPI-504 has consistent antitumor effects in GIST xenografts, both histologically and on the molecular level. Combining IPI-504 with imatinib substantially enhances anti-tumor activity, providing a strong rationale for clinical trials of IPI-504 in GIST as single agent and in combination. [Table: see text]


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