Oncolytic Reovirus Immune Priming: A Phase 1b Study Of Reolysin With Bortezomib And Dexamethasone In Patients With Relapsed/Refractory Multiple Myeloma

Background: While novel agents have improved the outcome for multiple myeloma (MM), the disease remains incurable. Our preclinical work has shown that MM cells from relapsed/refractory patients are very sensitive to the combination of Reolysin (a proprietary formulation of an oncolytic reovirus) and bortezomib (BZ), resulting in synergistic levels of endoplasmic reticulum (ER) stress. A pilot phase 1 study showed that Reolysin was well tolerated in relapsed/refractory MM patients and was associated with prolonged stable disease. Methods: Relapsed/refractory MM patients including patients refractory to BZ were included. This is a phase 1b study of 3 escalating doses of Reolysin (cohort 1; 3 x10 10 TCID 50 , cohort 2; 4.5 x10 10 TCID 50 , and cohort 3; 9 x10 10 TCID 50 ). Reolysin is given on days 1, 2, 8, 9, 15, and 16. Patients receive 40 mg dexamethasone and 1.5 mg/m 2 bortezomib on days 1, 8, and 15. Cycles are repeated every 28 days in the absence of disease progression or unacceptable toxicity. Results: Eight patients have been enrolled, seven were male and the median age was 55 (range, 33 - 66). The median number of prior therapies was 4 (range 1 to 6). All patients were previously exposed to BZ, and 6 patients were previously exposed to both an immunomodulatory agent and carfilzomib. Most patients had ISS stage I disease at study entry (n=5), 2 had stage II and 1 had stage III. The combination was well tolerated and most treatment-related toxicities were transient and easily managed with supportive care. The most common treatment-related toxicities were grade 1 diarrhea (n=4), grade 1 fatigue (n=4), grade 1 flu-like symptoms (n=5) and grade 1 headache (n=4). No dose limiting toxicities occurred in cohort 1 or 2. Three patients completed 1 cycle of treatment only, 2 completed 3 cycles, and 1 patient completed 4 cycles. One patient remains on treatment. Reasons for treatment discontinuation included disease progression (n=4), clinical deterioration (n=1) and patient withdrawal (n=2). Six patients were evaluable for response, 3 patients had stable disease lasting at least 3 cycles whereas 3 patients had progressive disease at the end of cycle 1. Ex vivo treatment of primary MM cells and MM cell lines (U266 and RPMI-8226) with Reolysin revealed a dramatic induction of PD-L1 expression as measured by qRT-PCR and flow cytometry. Furthermore, ex vivo treatment of MM patient mononuclear cells with Reolysin resulted in NK and T cell activation. These results suggest that the addition of an anti-PD-1 or anti-PD-L1 agent may augment the anti-MM activity of Reolysin. Conclusions: The combination of Reolysin, BZ and dexamethasone is well tolerated in a heavily pretreated MM patient population. Cohort 3 is currently enrolling at the 9 x10 10 TCID 50 dose level of Reolysin. The potential anti-MM effects of immune activation following Reolysin infusion may be mitigated by MM expression of PD-L1. Additional cohorts exploring the tolerability, efficacy and pharmacodynamics of the combination of Reolysin, BZ or carfilzomib, dexamethasone and an immune checkpoint inhibitor will be added following completion of cohort 3. Disclosures Kelly: Pharmacyclics: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Amgen: Consultancy, Membership on an entity9s Board of Directors or advisory committees. Coffey: Oncolytics Biotech: Employment. Gill: Oncolytics Biotech: Employment.