A Phase 1 Trial Of Reolysin Alone In Patients With Refractory Or Relapsed Multiple Myeloma

In relapsed/refractory multiple myeloma, approximately 50% of patients have Ras-family (NRAS and KRAS) activating gene mutations. Reovirus Serotype 3 - Dearing Strain (Reolysin) is the infusible form of the RNA human reovirus associated with minor respiratory infections in humans. Reovirus has been shown to replicate specifically in, and be cytopathic to, transformed cells possessing an activated Ras-signaling pathway. The specificity of the reovirus for Ras-activated cells makes it an attractive anti-cancer therapy candidate.

For this phase 1 trial, patients were required to have relapsed or refractory myeloma with IMWG-defined measurable disease, ANC ≥ 1,000/uL, platelet count ≥ 50,000/uL, with no creatinine requirements. Reolysin was administered intravenously over 60 minutes on days 1 - 5 every 28 days to 12 patients. It was started at 3 x 10⁹ median tissue culture infective dose per day (TCID₅₀/day) for 3 patients and then escalated to 3 x 1010 TCID₅₀/day for the remaining 9 patients. In situ based methodologies were used to examine the distribution of CD138, p38, caspase-3, reoviral capsid protein, and reoviral RNA in bone marrow biopsies performed at screening and then on cycle 1 day 8. Neutralizing Anti-Reovirus Assay (NARA) was performed weekly during cycle 1.

Twelve patients were enrolled with a median age of 61 (range 48 - 77), median number of prior therapies at enrollment of 4 (range 1 - 10) and mean ISS stage of 1.9 (range 1 - 3). No DLT's were experienced and all patients reached 3 x 10¹⁰ TCID₅₀/day. Grade 2 toxicities included leukopenia, anemia and myalgias, and grade 3 toxicities (asymptomatic) included 3 patients with neutropenia and one patient each with thrombocytopenia and hypophosphatemia.

Reoviral protein and RNA were found in post-Reolysin bone marrow biopsies but not at baseline. Reoviral RNA stained within 20 - 100% of myeloma cells, but only rare reoviral protein and caspase-3 staining was seen. Patients with 1:1 reoviral RNA:CD138 staining showed the most reduction in the percent of myeloma cells with treatment (Table 1). All patients developed NARA responses with 8 patients having endpoint titers greater than 2000 at 3 weeks post-treatment.

Stable disease (SD) was evident in 5 (42%) patients (longest duration on treatment was 8 cycles). One patient had a minimal response after two cycles.

Treatment with single-agent Reolysin was well tolerated, reovirus infection of myeloma cells was proven in all patients, but there was minimal intracellular reoviral protein production. Patients with 100% co-expression of reoviral RNA and CD138 had the largest relative decrease in CD138+ cells suggesting an early cytotoxic T- or NK-cell antiviral effect. The lack of clinical response is expected because reoviral-induced oncolysis typically requires concomitant chemotherapy. Clinical experiments in solid tumors confirm the necessity of chemotherapy as a cellular stressor to induce viral protein production and subsequent apoptosis (Sei et al., Mol Cancer 2009). Given the preclinical synergy reported with bortezomib in myeloma cell lines, we are planning a phase 1b combination of Reolysin with Carfilzomib.

No relevant conflicts of interest to declare.