In Vivo Downregulation of Bcl-2 by G3139 (G) Enhances Rituximab (R) Anti-Tumor Activity: Effect of Sequential Versus Concurrent G3139 Administration on Survival in a Lymphoma-Bearing SCID Mouse Model.

Bcl-2 over expression has been associated with poor prognosis and chemoresistance in various hematologic and solid tumor malignancies. G, an antisense oligonucleotide (ASO) targeting Bcl-2, downregulates Bcl-2 expression favoring apoptosis in cancer cells. Previously, we have demonstrated that G enhances R anti-tumor activity in various lymphoma pre-clinical models. Clinical trials are being conducted to evaluate the safety and efficacy of G3139 combined with R in relapsed/refractory NHL patients. However, the optimal sequence of administration of G and R is unknown. Our main objective was to determine the optimal anti-tumor schedule to administer G in combination with R. Six 8-week old SCID mice were inoculated via tail vein injection with Raji cells (1 x 10⁶ on day 0). After five days, to allow for tumor engraftment, mice were assigned to receive placebo [P], G, R, R followed by G [R→G], G followed by R [G→R] or G preceding each dose of R [G+R]. In addition, other control groups consisted of lymphoma-bearing mice treated with G3622 (ASO control) [reverse sequence, RS], trastuzumab (isotype) [I] and R in combination with G3622 [R+RS]. Antibodies were administered vial tail vein injection at a dose of 10mg/kg/dose x 4 doses and ASO were administered intraperitoneally at 5mg/kg/dose x 8 doses. The end-point of the study was survival. Survival analysis was performed by Kaplan-Meier curves and p values calculated using log rank test. Differences in survival of lymphoma-bearing SCID mice were noted according to the schedule of G/R administration. Synergistic activity was observed in animals treated with [G+R]. A modest improvement in the mean survival was noted in animals treated with [G] (26 days) or [G→R] (28 days) when compared to control mice (20 days) (P < 0.001). Anti-tumor activity was observed in SCID mice treated with R (mean survival 34 days) and was improved by the sequential addition of G [R→G] (median survival 48 days, P = 0.038). Concomitant administration of G and R resulted in the highest anti-tumor activity as measured by the longest survival (mean 80 days, P < 0.001). Our data demonstrates differences in R/G anti-tumor activity depending on the schedule of administration of G and R. Sequential administration of R followed by G resulted in a better disease control than G followed by R. However, concurrent G and R administration was shown to be superior to sequential strategies in improving survival of lymphoma-bearing SCID mice. Our pre-clinical data suggest the importance of a concurrent administration of these agents in clinical trials whereby, down-regulation of Bcl-2 by G allows enhancement of rituximab-associated anti-tumor activity.