The Dual PI3K/mTOR Inhibitor PQR309 Has Synergistic Activity with Other Targeted Agents in Diffuse Large B Cell Lymphomas

Introduction. PQR309 is a novel oral dual PI3K/mTOR inhibitor (Cmiljanovic et al, AACR 2015), being now evaluated as single agent in a phase I study in patients with relapsed or refractory lymphomas (NCT02249429). We previously reported activity of PQR309 as single agent in a large panel of lymphoma cell lines, and early combination data in two diffuse large B-cell lymphoma (DLBCL) cell lines (Tarantelli et al, ASH 2014). Here, we present extended combination data that might enhance the anti-proliferative effect of the single drug.

Methods. A panel of DLBCL cell lines derived from activated B-cell like (ABC) or germinal center B (GCB) subtype, with or without BCL2 or MYC deregulation, were used: RIVA (ABC, BCL2 amplification), SU-DHL-2 (ABC), TMD8 (ABC) and U2932 (ABC, BCL2 amplification); DOHH2 (GCB, BCL2 and MYC translocations), SU-DHL-6 (GCB, BCL2 translocation), KARPAS422 (GCB, BCL2 translocation), OCI-LY18 (GCB, BCL2 and MYC translocations), SU-DHL-10 (GCB), OCI-LY1 (GCB, BCL2 translocation). Cell lines were exposed to increasing doses of PQR309 alone or in combination with increasing doses of other agents for 72h and synergism was assessed with the Chou-Talalay combination index (CI): <0.3, very strong synergism 0.3-0.9, synergism; 0.9-1.1 additive effect; >1.1, no benefit.

Results. The combination of PQR309 with the BCL2 inhibitor venetoclax (ABT199) gave positive results in 6/8 cell lines, with strong synergism in three (U2932, median CI=0.1, SU-DHL-6, 0.14, Karpas422, 0.14) and synergism in the remaining three (TMD8, 0.5, RIVA, 0.56, DOHH2, 0.65). No benefit was observed in SU-DHL-2 and OCI-LY18.

The combination of PQR309 with the BTK inhibitor ibrutinib was synergistic in 3/4 ABC-DLBCL (RIVA, 0.42; U2932, 0.6; TMD8, 0.57), while it was of no benefit in SU-DHL-2.

The combination of PQR309 with the immunomodulator lenalidomide was of benefit in 4/4 ABC-DLBCL: synergistic in three (RIVA, 0.38; U2932, 0.4; TMD8, 0.5) and additive effect SU-DHL-2 (1.01).

The combination of PQR309 with the HDAC-inhibitor Panobinostat was synergistic in 5/6 (KARPAS422, 0.21; U2932, 0.65; SU-DHL-6, 0.67; DOHH2, 0.8; SU-DHL-2, 0.83), but not in the TMD8 (1.14). In our models, synergism was observed in only 2/5 cell lines (TMD8, 0.6; DOHH2, 0.89) exposed to both PQR309 and anti-CD20 monoclonal antibody, while not in KARPAS422, SU-DHL-6, or U2932.

Finally, since we had previously observed an up-regulation of the PIM1 kinase after exposure to PQR309 (Tarantelli et al, ICML 2015), potentially acting as a mechanism of adaptive resistance, we evaluated the addition of the PIM inhibitor AZD1208 to PQR309 in four DLBCL cell lines. The combination showed synergism in two (OCI-LY1, 0.29; SU-DHL-10, 0.57), an additive effect in TMD8 (0.95) and no benefit in the SU-DHL-2 (1.15).

Conclusions. The novel dual PI3K/mTOR inhibitor PQR309 showed synergism when combined with additional targeted agents in different DLBCL models, including some derived from double hit lymphomas. In particular, the combination with the BCL2 inhibitor venetoclax showed very good results, especially in cell lines bearing BCL2 gene deregulation due to chromosomal translocation or genomic amplification, and the combination with a PIM inhibitor might overcome early adaptive resistance to PQR309. These data provide the basis for future pre-clinical and clinical studies.