Diffuse large B-cell lymphoma (DLBCL) responds well to treatment with rituximab (RTX, an anti-CD20 antibody) based regimen, but a subset of patients still fail to achieve complete or durable responses and are not eligible for high-dose chemotherapy followed by autologous stem cell transplant. Therefore novel effective therapies with less toxicity for relapsed or refractory DLBCL patients are needed. Bendamustine (BEN) is a bifunctional alkylating agent for the treatment of multiple hematological tumors, including indolent and RTX-resistant NHL, and the combination of BEN with RTX showed clinical activity in patients with relapsed or refractory DLBCL in the Phase II study 1. Sepantronium bromide (YM155), a survivin suppressant, shows potent antitumor activities against a wide range of cancer cells, and NHL including DLBCL is one of the most sensitive tumor types to YM155. YM155 showed clinical activity when combined with RTX in patients with relapsed DLBCL 2. In the present study, we evaluated therapeutic potential of YM155, in combination with BEN or BEN and RTX using DLBCL models.
The combination of YM155 with BEN decreased cell viability to a greater extent than either single agent alone in DB, SU-DHL-8, and WSU-DLCL2 human DLBCL cell lines. Bliss additivism analysis revealed that the combined effects were synergistic. In addition The combination of YM155 with BEN induced a greater sub-G1 population, indicative of apoptosis, than either agent alone. The percentages of sub-G1 population induced by YM155, bendamustine, and combination of both were 5.9%, 6.5%, and 27% in DB cells; 19%, 32%, and 58% in SU-DHL-8 cells; and 46%, 30%, and 71% in WSU-DLCL2 cells, respectively. BEN induced γ-histone 2AX (γ-H2AX), a marker of DNA damage and phosphorylation of ATM substrates including p53, and check point kinase-2 (Chk2) which leads to phosphorylation of cdc2. Further BEN induced G2/M arrest associated with the increase of survivin. The combination of YM155 with BEN inhibited phosphorylation of p53, chk2, and cdc2 and accumulation of survivin at G2/M phase, and induced greater DNA damage and cleaved PARP than either single agent alone. In human DLBCL DB xenografts, 7-day continuous s.c. infusion of YM155 at 1 mg/kg/day enhanced antitumor activity of BEN at 50 mg/kg (i.v.) and induced complete regressions in 6 out of 8 mice without affecting body weight. Further, in an activated B-cell-like (ABC)-DLBCL disseminated xenograft model, the combination of YM155 with BEN and RTX significantly prolonged survival associated with the decrease in the FLT-PET signals in lymph node compare with either the combination of BEN with RTX and YM155 with RTX.
Our data indicates that YM155 enhances the antitumor activity of BEN against DLBCL models through inhibition of DNA damage responses as well as survivin accumulation at the G2/M phase. Further, triple combination of YM155 with BEN and RTX showed survival benefit in comparison with either BEN-RTX combination or YM155-RTX combination, supporting the further clinical investigation of this triple combination for the treatment of relapsed or refractory DLBCL.
1. Ohmachi et al. J Clin Oncol. 2013 Jun 10;31(17):2103-9
2. Papadopoulos et al. American Society of Hematology Annual meeting Abstract No. 2731. 2012.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.