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Introduction: Adenosine is an anti-inflammatory and immunosuppressive metabolite, that signals to diminish activation and proliferation of cytotoxic T-cells, impair activity of natural killer cells and CD4 + effector T-cells, and promote the expansion of immunosuppressive cell types. CD73, a cell surface ecto-5'-nucleotidase, is required to convert AMP to adenosine and is a major catalyst of adenosine generation in the tumor microenvironment. Overexpression of CD73 is observed in many tumors and correlates with unfavorable clinical outcome. Bone marrow (BM) aspirates from multiple myeloma (MM) patients have shown increased adenosine levels correspond with disease progression [Horenstein et al. Mol Med. 2016,22:694-704] In addition to the adenosine rich feature of MM, multiple cell types within the MM BM niche express the enzymes required for adenosine production from both NAD and ATP precursors, including CD38, CD203a, CD39 and CD73. Previously, we demonstrated that dysfunctional plasmacytoid dendritic cells (pDCs) predominantly found in the BM of MM patients contribute to MM cell growth, survival, and suppression of antitumor immunity [Chauhan et al, Cancer Cell 2009, 16:309-323; Ray et al, Leukemia 2015, 29:1441-1444]. We recently discovered that the interaction between pDCs and MM cells increased CD73 transcript and protein levels in both cell types, implicating a role for adenosine signaling via CD73 signaling axis in MM. Together, these MM disease features indicate that reducing the level of adenosine via inhibition of CD73 may represent a unique vulnerability and treatment strategy for MM. Methods: To understand the functional consequence of CD73 inhibition in MM, autologous ex vivo cell assays using freshly isolated BM aspirates from MM patients were used to detect changes in immune cell function and MM cell viability upon treatment with OP-5558, a potent and selective CD73 small molecule inhibitor which is an analog of the clinical candidate, ORIC-533. The majority of BM samples utilized were from patients with relapsed or refractory MM after at least three lines of therapy including immunomodulatory drugs, proteasome inhibitors, and anti-CD38 monoclonal antibodies, as well as a patient with relapsed MM post BCMA-CAR-T therapy. Results: In BM aspirates from MM patients with relapsed refractory MM, CD73 inhibition by OP-5558 triggered activation of MM pDCs, evidenced by increased expression of CD40/CD83/CD86 (1.2-1.5-fold, OP-5558-treated versus untreated; p < 0.05; n=3). This inhibition of CD73 reversed immunosuppression in MM BM. Specifically, CD73 inhibitor OP-5558 stimulated T-cell activation, associated with increased CD69 cell surface expression on CD3 + T-cells (CD69 MFI:20% increase, treated versus control; p = 0.0031; n = 3). Moreover, CD8 + T-cells from these co-cultures enhanced cytolytic activity against patient MM cells, significantly decreasing autologous MM cell viability (mean 42% decrease in viability; treated versus control; p=0.014; n=5). Of note, OP-5558 treatment did not directly affect viability of MM cells when treated in isolation, indicating that the observed decreased viability occurs via enhanced cytotoxic T-cell activity. Importantly, we show that OP-5558 triggered significant MM cell lysis even within autologous MM bone marrow mononuclear cell (BMNC) cultures, confirming that CD73 inhibition restores MM-specific cytolytic activity of autologous patient T-cells in the MM BM microenvironment. (mean 37% decrease in viability; treated versus control; p=0.009; n=3). Conclusions: This study therefore demonstrates that: 1. CD73-mediated adenosine activity suppresses the cytolytic activity of T-cells against tumor cells in the MM BM milieu; and 2. CD73 inhibition can overcome immune suppression and restore lysis of MM cells by autologous T-cells. A clinical trial of potent, selective, orally bioavailable CD73 inhibitor ORIC-533 will examine the utility of CD73 inhibition to improve outcome in patients with relapsed refractory MM. Disclosures Junttila: ORIC Pharmaceuticals: Current Employment. Sutimantanapi: ORIC Pharmaceuticals: Current Employment. Chen: ORIC Pharmaceuticals: Current Employment. Warne: ORIC Pharmaceuticals: Current Employment. Chang: ORIC Pharmaceuticals: Current Employment. Blank: ORIC Pharmaceuticals: Current Employment. Wu: ORIC Pharmaceuticals: Current Employment. Moore: ORIC Pharmaceuticals: Current Employment. Ndubaku: ORIC Pharmaceuticals: Current Employment. Zavorotinskaya: ORIC Pharmaceuticals: Current Employment. Nadeem: GSK: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Adaptive Biotechnologies: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees. Friedman: ORIC Pharmaceuticals: Current Employment. Chauhan: C4 Therapeutics: Current equity holder in publicly-traded company; Stemline Therapeutics, Inc: Consultancy. Anderson: Millenium-Takeda: Membership on an entity's Board of Directors or advisory committees; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Sanofi-Aventis: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Scientific Founder of Oncopep and C4 Therapeutics: Current equity holder in publicly-traded company, Current holder of individual stocks in a privately-held company; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Mana Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Abstract 2862 Chronic and juvenile myelomonocytic leukemias (CMML and JMML) are overlap myelodysplastic/myeloproliferative neoplasia (MDS/MPN) syndromes that respond poorly to conventional treatment regimens. Both diseases are characterized by aberrant N-Ras, K-Ras, Cbl, and SHP-2 proteins, which are not attractive drug target candidates. Focus has shifted to downstream effector pathways, which include Raf/MEK/ERK, phosphoinositide-3-OH kinase (PI3K)/Akt, and Ral-GDS/Ral-A cascades. However, it is unclear which pathways, if any, should be targeted. In part to address this question, we previously developed a mouse model of CMML and JMML by expressing a conditional “knock-in” KrasG12D oncogene in bone marrow. Our earlier studies showed that inhibition of MEK yields a significant reduction in disease burden in this model, including reduced leukocytosis, improved anemia and enhanced survival. Here, we interrogate the role of the PI3K/Akt pathway in KrasG12D driven MPN and further explore which specific pathways are responsible for leukemogenesis due to hyperactive Ras. We administered GDC-0941, a selective PI3K inhibitor, to Mx1-Cre, KrasG12D mutant mice Mice with well established MPN and wild-type (WT) littermates were randomly chosen to receive daily oral administration of GDC-0941 or a control vehicle. Treated mice exhibited dramatic corrections of leukocytosis and anemia as well as decrease in splenomegaly. Flow cytometry of bone marrow and peripheral populations also imply that GDC-0941 treatment corrects the aberrant proliferation, amends differentiation of bone marrow progenitors, and revives ineffective erythropoiesis found in KrasG12D mice. Treatment also resulted in markedly improved survival of KrasG12D mice; virtually all KrasG12Dmice in the treatment arm outlived their control counterparts. Our data suggest PI3K inhibition may play a role in suppressing hematologic dysfunction in JMML and CMML patients. Potential crosstalk between PI3K and MEK signaling further suggest that combinatorial activities of PI3K and MEK inhibition should be investigated. Disclosures: Friedman: Genentech, Inc.: Employment. Sampath:Genentech, Inc.: Employment.

Abstract 1839 The PIM kinases are a family of 3 growth factor- & cytokine-induced proteins hypothesized to have redundant survival and growth functions. Although PIM-1, -2 have been noted as highly expressed in multiple myeloma (MM) (Claudio JO et al., 2002), there are few data to support potential therapeutic utility of PIM inhibition in this indication. Here we show that the myeloma cell lines express all PIM protein isoforms to varying extents, and we describe the properties of a novel pan-PIM inhibitor GNE-652 with picomolar biochemical potency, an excellent selectivity profile, and favorable ADME properties. Myeloma cell lines and patient samples exhibit a striking prevalence of response to GNE-652 (23 of 25 lines with IC50 < 1 micromolar, median < 0.1 micromolar) and synergy in combination with the PI3K inhibitor GDC-0941 (mean combination index values ∼0.2 (n=25)). MM cells respond to this combination with cell cycle arrest and marked apoptosis in vitro. Conversely, a PIM-1, -3 selective inhibitor, GNE-568, failed to suppress MM cell growth and also failed to provide synergy in combination with PI3K inhibition, suggesting PIM-2 is a critical driver of MM cell growth & survival. Additional results suggest that PIM signaling converges on both TORC1 and AKT to generate differential synergies with PI3K/AKT/mTOR pathway inhibitors. PIM has been shown to potentially inactivate PRAS40, a negative regulator of TORC1 (Zhang et al., 2009). We demonstrate that PIM or PI3K inhibition caused a loss of phosphorylation on PRAS40 and resulted in a physical association of PRAS40 and TORC1 and a decrease in phosphorylated p70S6K and S6RP. These reductions were apparent in 7 of 7 cell lines assayed and enhanced by the combination of PI3K and PIM inhibition. Consistent with prior reports (Hammerman et al., 2005), we show that a second node of convergence between PIM and TORC1 is 4E-BP1. Both GDC-0941 and GNE-652 treatments reduced phosphorylation of 4E-BP1 in all the myeloma cell lines tested. Since dephosphorylated 4E-BP1 competes with eIF4G for the mRNA cap binding factor eIF4E, we assayed immunoprecipitates of eIF4E for the presence of eIF4G and 4E-BP1 and observed increased BP1 and decreased 4G. The combination treatment significantly enhanced the loss of 4G relative to either single agent, and importantly, even at 5 × IC50 concentrations for single agents, combination drug treatment achieved greater extent of effect than single agent treatment. It has been hypothesized that a subset of mRNAs are particularly sensitive to inhibition of cap-dependent translation, including a number of oncogenes such as cyclin D1. We noted across 7 different myeloma cell lines, strong decreases in levels of cyclin D1, and D3 that were further decreased by combination treatment of PIM and PI3K inhibition. In summary, we have identified several points at which PIM and PI3K/AKT/mTOR converge to provide synergy in multiple myeloma cell lines. As PIM isoforms are highly expressed in MM cells, we hypothesized that this could be due to proteosomal-mediated stability, and interestingly, MG132 and velcade each stabilized all PIM isoforms. It is commonly known that the JAK/STAT pathway regulates PIM transcription, but we show JAK inhibitors failed to abolish the expression of PIM in myeloma cells, suggesting a role for additional regulators. Recent genome sequencing studies from human myeloma samples (Chapman MA et al., 2011) confirmed the prevalence of NF-kB pathway activation, consistent with prior observations made in MM cell lines (Demchenko YN et al., 2010). The relationship of PIM and NF-kB is controversial in the literature (Hammerman PS et al., 2004 & Zhu N et al., 2002), with some groups placing PIM upstream of NF-kB and others the converse. Using an IκBα inhibitor, BMS-345541, we have examined the role for NF-kB in the regulation of PIM kinases. Here, we show that the BMS-345541 could preferentially suppress PIM2 expression in a dose dependent manner while PIM 1, 3 levels are modestly affected, suggesting that the high levels of PIM2 expression observed are partly driven by deregulation of the NF-kB pathway in MM. In conclusion, we provide pharmacological and biochemical evidence to suggest that PIM2 differentially regulate growth and survival of myeloma cells. Our results provide the rationale for further preclinical development of PIM inhibitors and the basis for a possible clinical development plan in multiple myeloma. Disclosures: Munugalavadla: Genentech: Employment. Berry:Genentech: Employment. Chang:Genentech: Employment. Rosario:Genentech: Employment. Drummond:Genentech: Employment. Du:Genentech: Employment. Fitzgerald:Genentech: Employment. Friedman:Genentech: Employment. Gould:Genentech: Employment. Maecker:Genentech: Employment. Moffat:Genentech: Employment. Slaga:Genentech: Employment. Xiaojing:Genentech: Employment. West:Genentech: Employment. Yu:Genentech: Employment. Ebens:Genentech: Employment.

Abstract 4084 Related work from our group has shown the therapeutic utility of PIM inhibition in multiple myeloma cell lines, xenografts, and primary patient samples (Ebens A. et al., ASH 2010 submitted abstr.). In this study we provide detailed mechanistic findings to show that PIM kinase inhibition co-regulates several important elements of the PI3K/AKT/mTOR pathway, resulting in significant synergy for combination drug treatments. The PIM kinases are a family of 3 ser/thr growth factor- & cytokine-induced proteins hypothesized to have redundant survival and growth functions. GNE-652 is a pan-PIM kinase inhibitor with picomolar biochemical potencies and an excellent kinase selectivity profile. Myeloma cell lines exhibit sensitivity to single agent PIM inhibition and a striking synergy in combination with the PI3K inhibitor GDC-0941. Cells respond to this combination with cell cycle arrest and marked apoptosis in vitro. We tested a panel of selective PI3K/AKT/mTOR inhibitors and found PI3K and AKT inhibitors showed the greatest extent of synergy with GNE-652, whereas mTOR inhibitors were synergistic to a lesser extent. These results suggest that PIM signaling converges on both TORC1 and AKT to generate these differential synergies. BAD is a negative regulator of both Bcl-2 and Bcl-XL, and we were able to confirm previous reports that AKT and PIM cooperate to inactivate BAD (Datt et al., 1997; Yan et al., 2003). Pim has been shown to potentially inactivate PRAS40, a negative regulator of TORC1 (Zhang et al., 2009). We demonstrate that PIM or PI3K inhibition caused a loss of phosphorylation on PRAS40 and results in a physical association of PRAS40 and TORC1 and a decrease in phosphorylated p70S6K and S6RP. These reductions were apparent in 7 of 7 cell lines assayed and enhanced by the combination of PI3K and PIM inhibition in these cell lines. Consistent with prior reports (Hammerman et al., 2005), we show that a second node of convergence between PIM and TORC1 is 4E-BP1. Both GDC-0941 and GNE-652 treatments reduced phosphorylation of 4E-BP1 in 7 of 7 myeloma cell lines. Since dephosphorylated 4E-BP1 competes with eIF4G for the mRNA cap binding factor eIF4E, we assayed immunoprecipitates of eIF4E for the presence of eIF4G and 4E-BP1 and observed increased BP1 and decreased 4G. The combination treatment significantly enhanced the loss of 4G relative to either single agent, and importantly, even at 5× the IC50 concentrations for single agents, combination drug treatment achieved greater extent of effect than single agent treatment. Thus PI3K and PIM pathways are redundant at the level of cap-dependent translational initiation mediated by eIF4E. It has been hypothesized a subset of mRNAs are particularly sensitive to inhibition of cap-dependent translation, and that this includes a number of oncogenes such as cyclin D1. We assayed global protein synthesis in MM1.s cells using 35S-methionine and as expected we observed only a modest ≂∼f20% decrease caused by either GNE-652 or GDC-0941 and this decrease was not enhanced by combination treatment. However, we noted across 7 different myeloma cell lines, strong decreases in levels of cyclin D1 that were enhanced by combination treatment. In summary, we have identified several points at which PIM and PI3K/AKT/mTOR converge to provide synergistic apoptosis in multiple myeloma cell lines. These results provide the rationale for further preclinical development of PIM inhibitors and provide the basis for a possible clinical development plan in multiple myeloma. Disclosures: Munugalavadla: Genentech: Employment, Equity Ownership. Berry:Genentech: Employment, Equity Ownership. Chen:Genentech: Employment, Equity Ownership. Deshmukh:Genentech: Employment, Equity Ownership. Drummond:Genentech: Employment, Equity Ownership. Du:Genentech: Employment, Equity Ownership. Eby:Genentech: Employment, Equity Ownership. Fitzgerald:Genentech: Employment, Equity Ownership. S.Friedman:Genentech: Employment, Equity Ownership. E.Gould:Genentech: Employment, Equity Ownership. Kenny:Genentech: Employment, Equity Ownership. Maecker:Genentech: Employment, Equity Ownership. Moffat:Genentech: Employment, Equity Ownership. Moskalenko:Genentech: Employment, Equity Ownership. Pacheco:Genentech: Employment, Equity Ownership. Saadat:Genentech: Employment, Equity Ownership. Slaga:Genentech: Employment, Equity Ownership. Sun:Genentech: Employment, Equity Ownership. Wang:Genentech: Employment, Equity Ownership. Yang:Genentech: Employment, Equity Ownership. Ebens:Genentech Inc: Employment, Equity Ownership.

Abstract 3001 PIM kinases co-regulate several important elements of the PI3K/AKT/mTOR pathway in myeloma cells (Munugalavadla V. et al., ASH 2010 submitted abstr.). In this study we show that pan-PIM inhibition suppresses growth in myeloma cell lines, xenografts, and primary patient samples, both as a single-agent as well acting synergistically in combination with PI3K, AKT, and mTOR inhibition. The PIM kinases are a family of 3 ser/thr growth factor- & cytokine-induced proteins hypothesized to have redundant survival and growth functions. Although PIM-1,2 have been noted as highly expressed in myeloma (Claudio et al., 2002), there are few data to support potential therapeutic utility of PIM inhibition in this indication. We show myeloma cell lines express all 6 PIM protein isoforms to varying extents, and we describe the properties of a novel pan-PIM inhibitor GNE-652 with picomolar biochemical potency, an excellent selectivity profile, and favorable ADME properties. Myeloma cell lines exhibit a striking prevalence of response to GNE-652 (23 of 25 lines with IC50 < 1 micromolar, median < 0.1 micromolar) and synergy in combination with the PI3K inhibitor GDC-0941 (mean combination index values ~0.2 (n=25)). We used an unrelated compound GNE-568 which has a PIM-1,3 selective profile to test the hypothesis that PIM-2 may have a non-redundant role in myeloma cells. GNE-568 while having cellular potency against PIM-1 and PIM-3, did not have single agent activity in myeloma cell lines nor did it act synergistically with GDC-0941 (n=10 cell lines). Interestingly, PI3K and AKT inhibitors showed the greatest extent of synergy with GNE-652, whereas mTOR-selective inhibitors were synergistic to a lesser extent. Standard of care agents dexamethasone, revlimid, velcade, and melphalan also combined well with GNE-652, but to a lesser extent and not as broadly. The synergistic anti-tumor activity of GNE-652 and PI3K inhibitor GDC-0941 on cell lines or on primary myeloma bone marrow aspirates in vitro was associated with cell-cycle arrest and marked apoptosis. In addition, we found 4 of 4 myeloma xenograft mouse models tested with GNE-562 and GDC-0941 showed excellent combination efficacy that correlated with modulation of the expected pharmacodynamic markers. These results provide the rationale for further preclinical development of PIM inhibitors and provide the basis for a possible clinical development plan in multiple myeloma. Disclosures: Ebens: Genentech: Employment, Equity Ownership. Berry:Genentech: Employment, Equity Ownership. Chen:Genentech: Employment, Equity Ownership. Deshmukh:Genentech: Employment, Equity Ownership. Drummond:Genentech: Employment, Equity Ownership. Du:Genentech: Employment, Equity Ownership. Eby:Genentech: Employment, Equity Ownership. Fitzgerald:Genentech: Employment, Equity Ownership. S. Friedman:Genentech: Employment, Equity Ownership. E. Gould:Genentech: Employment, Equity Ownership. Kenny:Genentech: Employment, Equity Ownership. Maecker:Genentech: Employment, Equity Ownership. Moffat:Genentech: Employment, Equity Ownership. Moskalenko:Genentech: Employment, Equity Ownership. Pacheco:Genentech: Employment, Equity Ownership. Saadat:Genentech: Employment, Equity Ownership. Slaga:Genentech: Employment, Equity Ownership. Sun:Genentech: Employment, Equity Ownership. Wang:Genentech: Employment, Equity Ownership. Yang:Genentech: Employment, Equity Ownership. Munugalavadla:Genentech: Employment, Equity Ownership.

Abstract 1057 Poster Board I-79 The PI3K-Akt signal transduction pathway plays a key role in the pathogenesis of many human cancers. In AML malignancy, deregulation of upstream receptor tyrosine kinases such as FLT3, c-Kit, and c-FMS or mutations in K-Ras, N-Ras, B-Raf and CEBPA genes lead to activation of PI3K-Akt signaling to promote cell survival and cell growth. A highly selective Class I PI3K inhibitor, GDC-0941, provides exciting therapeutic opportunities for targeting this pathway in AML. Here we show that GDC-0941 significantly inhibits the viability of the majority of a large panel of AML cell lines tested in vitro (80% or 19/24) at a concentration of < 1 uM. Because not all AML cell lines responded to GDC-0941, we show that PI3K-Akt pathway activation, evidenced by basal pAkt level, can serve as a potential predictive biomarker for GDC-0941 in AML in that sensitive cell lines displayed higher level of pAkt relative to resistant cell lines. Consistently, GDC-0941 treatment leads to decreased pAkt, and therefore the down-regulation of this important pro-survival signaling. Our further analysis shows that GDC-0941 treatment can induce apoptosis and/or cell cycle arrest. We also obtained fresh AML tumor samples to test whether GDC-0941 can similarly induces apoptosis in blast cells and showed that GDC-0941 treatment results in a down-regulation of pAkt level and increased apoptosis. Other PD biomarkers such as phospho-BAD level and Bim expression are both consistent with the observed apoptotic responses. Furthermore, the mammalian target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, synergizes with GDC-0941 to produce an increased amount of apoptosis in several AML cell lines tested. This is likely due to the fact that long-term treatment with rapamycin induces the sensitivity of the PI3K –Akt signaling pathway by releasing the negative feedback loop of mTORC1-S6K-IRS1/2 module. Importantly, in some AML cell lines we observe synergies between GDC-0941 and AraC. Interestingly, while AraC alone does not induce apoptosis in AML cell lines with PTEN loss or mutation, the synergy between AraC and GDC-0941 comes from increased apoptotic response, suggesting that GDC-0941 can synergize with chemo agents that induces S/G2 cell cycle arrest. Together, our preclinical data suggest that GDC-0941 may be used as a targeted therapy in AML patients as a single agent or in combination with other chemotherapies in clinic. Disclosures: Ma: Genentech Inc.: Employment. Du:Genentech, Inc.: Employment, Equity Ownership. Sun:Genentech Inc.: Employment. Shi:Genentech, Inc.: Employment, Equity Ownership. Friedman:Genentech Inc.: Employment. Dornan:Genentech, Inc.: Employment, Equity Ownership. Ebens:Genentech, Inc.: Employment, Equity Ownership, Patents & Royalties.