The Triple Combination of the CD20 Antibody Obinutuzumab with the Bcl-2 Inhibitor Venetoclax (GDC-199) and the MDM2 Inhibitor Idasanutlin Results in Superior Efficacy and Long Term Response in Wildtype p53 NHL Tumor Models

Introduction: Previous preclinical studies have shown that the CD20 antibody obinutuzumab achieved greater anti-tumor efficacy together with the Bcl-2 inhibitor venetoclax (GDC-199) (Sampath et al, Blood 122 (21), 4412), and the MDM2 inhibitor idasanutlin (RG7388) (Herting et al., Blood 124 (21), 1780). Clinical combination studies combining obinutuzumab with venetoclax (NCT01685892) or idasanutlin (NCT02624986) are currently ongoing. Based on the data we investigated whether the triple combination of obinutuzumab with venetoclax and idasanutlin can further improve outcome in two preclinical human wildtype p53 NHLtumor xenograft models.

Experimental Methods: The in vivo antitumor efficacy of the triple combination and the respective double combinations and monotherapies was evaluated in two different CD20 positive p53 wildtype xenograft models in female SCID beige mice bearing established s.c. human DoHH-2 diffuse large B cell lymphoma (DLBCL) or human Z-138 mantle cell lymphoma (MCL) tumors. In the DoHH-2 model, mice were treated when tumors reached 200 mm³ with vehicle control, obinutuzumab (ip, 10 mg/kg, q7d, days 13, 21, 27), idasanutlin (po, 30 mg/kg, days 13-17, 20-24, 27-29) or venetoclax (po, 100 mg/kg, days 13-29). One study group received the triple combination at the indicated days. In the Z-138 model, mice were treated when the tumors reached 500 mm³ with vehicle control, a sub-optimal dose of obinutuzumab (ip, 0.5 mg/kg, q7d, days 18, 25, 32), idasanutlin (po, 100 mg/kg, days 18-22, 80 mg/kg days 25-36) or venetoclax (po, 100 mg/kg, daily, days 18-36). In the combination groups, obinutuzumab, idasanutlin and venetoclax were administered at the same dosages and on the same days.

Results: In the DoHH-2 model all monotherapies resulted in significant anti-tumor efficacy with 56% tumor growth inhibition (TGI) for idasanutlin (npTCR 0.48, CI 0.33-0.68), 60% TGI for venetoclax (npTCR 0.43, CI 0.27-0.67) and a TGI of 90% for obinutuzumab (npTCR 0.17, CI 0.08-2.24). Superior efficacy compared to the respective monotherapies was observed for the triple combination group which induced tumor regression in 90% of the animals with 30% reaching complete tumor remission (npTCR 0.009, CI 0.00-0.02). In the Z-138 model monotherapy treatment using obinutuzumab, venetoclax or idasanutlin resulted in TGI of 47 % (npTCR 0.56, CI 0.42 - 0.76), 53% (npTCR 0.50, CI 0.40 - 0.64) or 67% (npTCR 0.43, CI 0.32 - 0.55), respectively. Combination of obinutuzumab with venetoclax or idasanutlin yielded a TGI of 85% (npTCR 0.26, CI 0.20 - 0.34) or 86% (npTCR 0.26, CI 0.19 - 0.35), respectively. Combination of idasanutlin with venetoclax and the triple combination showed tumor regression (TGI>100%) on day 32. To elucidate the long term effects a time-to-event (TTE) analysis was performed until study termination on day 125. Whereas, monotherapy with obinutuzumab at the suboptimal dose of 0.5 mg/kg resulted in 2/10 and the combination of idasanutlin and venetoclax in 5/10 tumor-free animals, the triple combination resulted in a complete tumor remission in 10/10 animals until study termination on day 125.

Conclusions: These preclinical data demonstrate a strong anti-tumoral efficacy of combining the CD20 antibody obinutuzumab with the Bcl-2 inhibitor venetoclax and the MDM2 inhibitor idasanutlin, in particular regarding complete tumor remissions and long term response, and support the clinical investigation of this triple combination for the treatment of B cell malignancies.