Apogossypolone, a nonpeptidic small molecule inhibitor targeting Bcl-2 family proteins, effectively inhibits growth of diffuse large cell lymphoma cells in vitro and in vivo

Apogossypolone (ApoG2) is a semi-synthesized derivative of gossypol. The principal objective of this study was to compare stability and toxicity between ApoG2 and gossypol, and to evaluate anti-lymphoma activity of ApoG2 in vitro and in vivo. ApoG2 shows better stability when compared with a racemic gossypol and can be better tolerated by mice compared to gossypol. ApoG2 showed significant inhibition of cell proliferation of WSU-DLCL(2) and primary cells obtained from lymphoma patients, whereas it displayed no toxicity on normal peripheral blood lymphocytes. For a treatment of 72 h, the IC(50) of ApoG2 was determined to be 350 nM against WSU-DLCL2 cells. Treatment with ApoG2 at 600 mg/kg resulted in significant growth inhibition of WSU-DLCL(2) xenografts. When combined with CHOP, ApoG2 displayed even more complete inhibition of tumor growth. ApoG2 binds to purified recombinant Bcl-2, Mcl-1 and Bcl-X(L) proteins with high affinity and is shown to block the formation of heterodimers between Bcl-X(L) and Bim. For a treatment of 72 h, ApoG2 induced a maximum of 32% of apoptotic cell death. Western blot experiments showed that treatment with ApoG2 led to cleavage of caspase-3, caspase-9 and PARP. Moreover, pretreatment of DLCL(2) cells with caspase-3, -9 and broad spectrum caspase inhibitors significantly blocked growth inhibition induced by ApoG2. In conclusion, ApoG2 effectively inhibits growth of DLCL(2) cells at least partly by inducing apoptosis. It is an attractive small molecule inhibitor of the Bcl-2 family proteins to be developed further for the treatment of diffuse large cell lymphoma.