Mariathasan, Sanjeev

Abstract Abstract 3788 Poster Board III-724 Multiple myeloma (MM) is a malignancy characterized by clonal expansion and accumulation of long-lived plasma cells within the bone marrow. Phosphatidylinositol 3' kinase (PI3K) -mediated signaling is frequently dysregulated in cancer and controls fundamental cellular functions such as cell migration, growth, survival and development of drug resistance in many cancers, including MM, and therefore represents an attractive therapeutic target. Here, we demonstrate in vitro, that a potent and selective pan-isoform PI3Kinhibitor, GDC-0941, modulates the expected pharmacodynamic markers, inhibits cell-cycle progression and induces apoptosis; overcomes resistance to apoptosis in MM cells conferred by IGF-1 and IL-6; and is additive or synergistic with current standard of care drugs including dexamethasone, melphalan, lenolidamide and bortezomib. In cell lines we find sensitivity to GDC-0941 is positively correlated with pathway activation as determined by phospho-AKT-specific flow-cytometry and Western-blot analysis. Preliminary results indicate apoptosis of MM cells is correlated with increased expression of the proapoptotic BH3-only protein BIM; mechanisms of increased apoptosis in MM will be further explored and an update presented. We further extend these in vitro findings to show that GDC-0941 has activity as a single agent in vivo and combines well with standard of care agents in several murine xenograft models to delay tumor progression and prolong survival. Our results suggest that GDC-0941 may combine well with existing therapies, providing a framework for the clinical use of this agent, and a rational approach to improving the efficacy of myeloma treatment. Disclosures: Munugalavadla: Genentech: Employment, Patents & Royalties. Berry:Genentech: Employment, Patents & Royalties. Du:Genentech, Inc.: Employment, Equity Ownership. Mariathasan:Genentech: Employment, Patents & Royalties. Slaga:Genentech: Employment, Patents & Royalties. Sun:Genentech Inc.: Employment. Chesi:Genentech, Inc.: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Merck: Research Funding. Bergsagel:Genentech: Consultancy; Amgen: Consultancy; Celgene: Consultancy; Merck: Research Funding. Ebens:Genentech, Inc.: Employment, Equity Ownership, Patents & Royalties.

LBA4500 Background: Cisplatin-based chemo is a standard 1L treatment (tx) for mUC and the only tx that prolongs OS; however, age or comorbidities render many pts ineligible, and 30-50% receive no tx. Atezo (MPDL3280A) is active and well tolerated in platinum-treated mUC, justifying testing atezo as 1L tx in cisplatin-ineligible pts. Methods: Pts were chemo naive in the metastatic setting and cisplatin ineligible (renal [GFR > 30 but < 60 mL/min]/hearing impairment, ≥ G2 peripheral neuropathy [PN] or ≥ ECOG PS2). Atezo 1200 mg was given IV q3w until PD (RECIST v1.1). Centrally assessed PD-L1 on tumor infiltrating immune cells (IC; SP142 IHC assay) was scored IC2/3, 1 or 0. The primary efficacy endpoint was confirmed ORR assessed per RECIST v1.1 (central independent review facility) using a data cutoff of Sep 14, 2015. Results: 119 efficacy/safety-evaluable pts of any PD-L1 IC had a median age of 73 y: 21% ≥ 80 y. 18% had prior systemic tx (21% [neo]adjuvant); 10% had radiotherapy. 66% had visceral mets. 71% had CrCl < 60 mL/min; 13% had hearing loss ≥ 25 dB; 6% had prior PN ≥ G2; 20% had ECOG PS2. ORR was 19% (95% CI 13-28; 5% CR), and responses occurred in all IC subgroups (Table; includes DCR/PFS/OS) and in pts with poor prognostic factors. 22/23 responses were ongoing with mDOR not reached. Median follow-up was 8.5 mo (range 0.2-14.3); median tx duration was 15 wk. Atezo was generally well tolerated. Tx-related all-G and G3-4 AEs were seen in 64% and 12% of pts, respectively. Related all-G AEs ≥ 10% included fatigue, pruritus, diarrhea. 1 G5 related AE occurred (sepsis). 3% had a G3-4 immune-mediated AE. Conclusions: Atezo has clinically meaningful activity in 1L cisplatin-ineligible mUC pts, and preliminary OS is encouraging. The durable nature of response and favorable AE profile makes this an attractive alternative to chemo. NCT02108652. Clinical trial information: NCT02108652. [Table: see text]