Pamela Cohen

Superior activity of the combination of histone deacetylase inhibitor LAQ824 and the FLT-3 kinase inhibitor PKC412 against human acute myelogenous leukemia cells with mutant FLT-3.

Purpose: Mutant FLT-3 receptor tyrosine kinase is a client protein of the molecular chaperone heat shock protein 90 and is commonly present and contributes to the leukemia phenotype in acute myelogenous leukemia (AML). LAQ824, a cinnamyl hydroxamate histone deacetylase inhibitor, is known to induce acetylation and inhibition of heat shock protein 90. Here, we determined the effects of LAQ824 and/or PKC412 (a FLT-3 kinase inhibitor) on the levels of mutant FLT-3 and its downstream signaling, as well as growth arrest and cell-death of cultured and primary human AML cells. Experimental Design: The effect of LAQ824 and/or PKC412 treatment was determined on the levels of FLT-3 and phosphorylated (p)-FLT-3, on downstream pro-growth and pro-survival effectors, e.g., p-STAT5, p-AKT, and p-extracellular signal-regulated kinase (ERK) 1/2, and on the cell cycle status and apoptosis in the cultured MV4–11 and primary AML cells with mutant FLT-3. Results: Treatment with LAQ824 promoted proteasomal degradation and attenuation of the levels of FLT-3 and p-FLT-3, associated with cell cycle G1-phase accumulation and apoptosis of MV4–11 cells. This was accompanied by attenuation of p-STAT5, p-AKT, and p-ERK1/2 levels. STAT-5 DNA-binding activity and the levels of c-Myc and oncostatin M were also down-regulated. Cotreatment with LAQ824 and PKC412 synergistically induced apoptosis of MV4–11 cells and induced more apoptosis of the primary AML cells expressing mutant FLT-3. This was also associated with more attenuation of p-FLT-3, p-AKT, p-ERK1/2, and p-STAT5. Conclusions: The combination of LAQ824 and PKC412 is highly active against human AML cells with mutant FLT-3, which merits in vivo studies of the combination against human AML.

Cotreatment with 17-allylamino-demethoxygeldanamycin and FLT-3 kinase inhibitor PKC412 is highly effective against human acute myelogenous leukemia cells with mutant FLT-3

Presence of the activating length mutation (LM) in the juxtamembrane domain or point mutation in the kinase domain of FMS-like tyrosine kinase-3 (FLT-3) mediates ligand-independent progrowth and prosurvival signaling in approximately one-third of acute myelogenous leukemia (AML). PKC412, an inhibitor of FLT-3 kinase activity, is being clinically evaluated in AML. Present studies demonstrate that treatment of human acute leukemia MV4-11 cells (containing a FLT-3 LM) with the heat shock protein 90 inhibitor 17-allylamino-demethoxy geldanamycin (17-AAG) attenuated the levels of FLT-3 by inhibiting its chaperone association with heat shock protein 90, which induced the poly-ubiquitylation and proteasomal degradation of FLT-3. Treatment with 17-AAG induced cell cycle G1 phase accumulation and apoptosis of MV4-11 cells. 17-AAG-mediated attenuation of FLT-3 and p-FLT-3 in MV4-11 cells was associated with decrease in the levels of p-AKT, p-ERK1/2, and p-STAT5, as well as attenuation of the DNA binding activity of STAT-5. Treatment with 17-AAG, downstream of STAT5, reduced the levels of c-Myc and oncostatin M, which are transactivated by STAT5. Cotreatment with 17-AAG and PKC412 markedly down-regulated the levels of FLT-3, p-FLT-3, p-AKT, p-ERK1/2, and p-STAT5, as well as induced more apoptosis of MV4-11 cells than either agent alone. Furthermore, the combination of 17-AAG and PKC412 exerted synergistic cytotoxic effects against MV4-11 cells. Importantly, 17-AAG and PKC412 induced more loss of cell viability of primary AML blasts containing FLT-3 LM, as compared with those that contained wild-type FLT-3. Collectively, these in vitro findings indicate that the combination of 17-AAG and PKC412 has high level of activity against AML cells with FLT-3 mutations.

Abstract 2435: Anticipating clinical resistance to SAR302503, a JAK2 inhibitor in clinical development for the treatment of myelofibrosis.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DCnnOne of the challenges of using kinase inhibitors in the clinic is the potential emergence of resistance mechanisms that render them inefficacious in patients who were previously responsive. Imatinib is one of the best examples of this phenomenon. Despite initially impressive clinical responses, a significant proportion of CML patients become unresponsive to imatinib primarily due to the emergence of secondary missense mutations. Identifying these mutations and understanding resistance mechanisms are key to the design of second-generation inhibitors capable of overcoming resistance and for predicting potential clinical resistance to novel drugs.nnSAR302503 is a JAK2 inhibitor currently in Phase III clinical development as a treatment for myelofibrosis. In a Phase I/II trial, prolonged treatment (>4 years) with SAR302503 has resulted in durable responses (Pardanani et al. ASH 2011; Gotlib et al. EHA 2012). Because of the frequent emergence of resistance with other kinase inhibitors, we wanted to anticipate and understand potential resistance to JAK2 inhibitors in general and SAR302503 in particular. Resistance to ruxolitinib in vitro has recently been associated with reactivation of the JAK/STAT pathway due to the formation of JAK1/JAK2 and TYK2/JAK2 heterodimers (Koppikar et al. Nature 2012). To study potential clinical resistance to SAR302503 in vitro, two approaches were used: selective pressure and ENU induced mutagenesis using JAK2V617F expressing patient derived (SET-2 and HEL) and engineered (Ba/F3.JAK2V617F) cell lines.nnThe results of these in vitro SAR302503 resistance screens indicate that: i) JAK2V617F cells are more prone to develop resistance to ruxolitinib than to SAR302503 after treatment with concentrations 4- or 10-fold over their respective IC50s; ii) resistance does not arise in cells treated with concentrations of SAR302503 above 3 μM even after a prolonged treatment (up to 12 weeks); iii) resistance to SAR302503 in the patient-derived cell lines SET-2 and HEL is accompanied by over-activation of the JAK/STAT pathway in the absence of JAK2 secondary mutations; and iv) resistance to SAR302503 in Ba/F3.JAK2V617F cells results from the mutation Y931C in all of the resistant clones analyzed. From these in vitro results and SAR302503 pharmacokinetic data in humans and preclinical species we can conclude: i) high-level resistance to SAR302503 in patients is unlikely because concentrations of free SAR302503 of approximately 6 μM are estimated to be reached and sustained in the tissues of myelofibrosis patients at a 500 mg daily dose level; ii) overactive JAK/STAT signaling in resistant clones can still be effectively inhibited by clinically achievable concentrations of SAR302503; and iii) clinical activity of SAR302503 may be less challenged than that of ruxolitinib in the event patients express the Y931C mutation.nnCitation Format: Raelene Hurley, Rita Greco, Fangxian Sun, Anlai Wang, Shih-Min A. Huang, Jenny Zhang, Claudia Lebedinsky, Pamela Cohen, Francisco Adrian. Anticipating clinical resistance to SAR302503, a JAK2 inhibitor in clinical development for the treatment of myelofibrosis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2435. doi:10.1158/1538-7445.AM2013-2435

Abstract LB-294: Determination of JAK2V617F allele burden in a phase II study of patients with myelofibrosis treated with SAR302503 using a sensitive and robust allele-specific qPCR assay.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DCnnJanus kinase-2 (JAK2)/STAT pathway activation is commonly observed in myeloproliferative neoplasms and plays an important role in disease development and progression. The V617F activating mutation in the JAK2 pseudokinase domain is found in 95% of patients with polycythemia vera (PV) and in 50-70% of patients with primary myelofibrosis (MF) or essential thrombocythemia (ET). Studies have shown the clinical efficacy of JAK2 inhibitors in treating MF in terms of a reduction in splenomegaly and relief of constitutional symptoms. A reduction in the JAK2V617F allele burden after treatment with a JAK2-targeted agent could be a surrogate for a disease-modifying effect of this therapy. To demonstrate this, a robust method that can accurately measure the JAK2V617F allele burden is required. Here, we report the development of a sensitive quantitative PCR (qPCR) assay to determine the JAK2V617F allele burden in patients treated with SAR302503, the validation of the assay in a Phase 0 clinical study and implementation in a phase II study using samples from patients with MF. The assay demonstrated robust performance, with high sensitivity (LLOD=0.05% and LLOQ=0.5%) and accuracy. A phase 0 study in MF, PV, and ET patients showed that (1) there was minimal intra-subject sampling variability in JAK2V617F allele burden, and (2) whole-blood samples are stable for at least 48 hours at ambient conditions for DNA preparation without a significant impact on JAK2V617F allele burden measurement.Of the 31 patients with intermediate-2 or high-risk MF enrolled in a phase II clinical study ([NCT01420770][1]), baseline samples were available for 29 patients and of these, 26 were JAK2V617F-positive using this assay. Of the 19/26 patients for whom samples were available at all 3 time points, the median allele burden was 93% at baseline, 87% at the end of Cycle 3, and 78% at the end of Cycle 6. Among the 24 patients who were JAK2V617F-positive and for whom spleen measurements were available at the end of Cycle 6, a total of 15 (63%) had a spleen response (≥ 35% reduction in spleen volume by MRI versus baseline). In contrast, two JAK2V617F-negative patients did not have a spleen response. Patients with baseline allele burden levels of 0 to <25%, 25% to 75%, and ≥75% showed spleen response rates of 50%, 44%, and 69%, respectively, at the end of Cycle 6. JAK2V617F allele burden will continue to be assessed every 3 cycles. Longer follow up is needed to determine the clinical effect of allele burden reduction.nnCitation Format: Feng Liu, Moshe Talpaz, Animesh Pardanani, Catriona Jamieson, Nashat Gabrail, Ayalew Tefferi, Tianlei Lei, Rita Greco, Francisco Adrian, Nikki Daskalakis, Claudia Lebedinsky, Pamela Cohen, Donald Bergstrom. Determination of JAK2 V617F allele burden in a phase II study of patients with myelofibrosis treated with SAR302503 using a sensitive and robust allele-specific qPCR assay. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-294. doi:10.1158/1538-7445.AM2013-LB-294nn [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01420770&atom=%2Fcanres%2F73%2F8_Supplement%2FLB-294.atom

Abstract 1796: SAR302503: A Jak2 inhibitor with antitumor activity in solid tumor models

Numerous studies have recognized the critical role of STAT3 in malignant transformation and tumor progression. Constitutive STAT3 activation is frequently found in cancer cell lines and tumor samples and it is usually linked to the presence of IL-6. Autocrine or paracrine IL-6 loops have been described to provide tumor cells with the ability to proliferate, survive, migrate and metastasize. At the molecular level, IL-6 binding to its receptor results in activation of Jak/STAT3 signaling and other signaling cascades, namely PI3K/Akt, MEK/ERK1-2, with a well established role in cancer. We have evaluated the ability of SAR302503, a selective Jak2 inhibitor entering a PhIII clinical trial in myelofibrosis patients, to block these pathways in a panel of ∼20 tumor cell lines representing different cancer types (prostate, breast, lung, colorectal, pancreas, hepatocellular, etc). A 45 minutes treatment with different concentrations of SAR302503 (0.1-10 µM) was sufficient to block both basal or IL-6 induced STAT3 phosphorylation in a dose dependent manner. Compound concentrations equal or greater than 0.1 µM were able to reduce the phosphorylation levels of STAT3 by an extent greater than 50% in all the cell lines included in the study. The impact of SAR302503 in tumor cell proliferation and survival was evaluated using different assays including clonogenic assays. Complete inhibition of colony formation was achieved at concentrations of SAR302503 below 1 µM in most of the cell lines. The antitumor activity of SAR302503 was evaluated in mice xenotransplanted subcutaneously with DU145 human prostate cancer cells. Oral administration of SAR302503 for 10 days resulted in significant dose dependent tumor growth inhibition, near to stasis at the highest dose (T/C=19% at 100 mg/kg, bid). In summary, we demonstrate that SAR302503 negatively impacts the proliferation and survival of different solid tumor cells and our data supports a role for a selective Jak2 inhibition in treating solid tumors with activated Jak/STAT signaling. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1796. doi:1538-7445.AM2012-1796