Targeting the PI3K/mTOR Pathway in Lymphoma with PQR309 and PQR620: Single Agent Activity and Synergism with the BCL2 Inhibitor Venetoclax

Background. The PI3K/AKT/mTOR pathway is an important therapeutic target in lymphomas. PQR309 is a dual PI3K/mTOR inhibitor that has shown in vitroanti-lymphoma activity (Tarantelli et al, ASH2015) and is in phase 2 trial (NCT02249429, , NCT02723877, NCT02669511). PQR620 is a novel mTORC1/2 inhibitor that has shown preclinical activity in solid tumor models (Beaufils et al, AACR 2016).

Here, we present the in vitro and in vivo anti-lymphoma activity of PQR620 as single agent and also the in vivo results of PQR620 or PQR309 containing combinations with the BCL2 inhibitor venetoclax.

Materials and Methods. The drug concentration causing 50% inhibition of cell proliferation (IC50) was obtained in lymphoma cell lines [diffuse large B cell lymphoma (DLBCL), no.=26; mantle cell lymphoma (MCL), no.=8; anaplastic large T-cell lymphoma, no.=5; others, no=5] exposed to increasing doses of PQR620 for 72h using a Tecan D300e Digital Dispenser on 384well plates. For in vivo experiments, NOD-Scid (NOD.CB17-Prkdcscid/J) mice were subcutaneously inoculated with 10 x10⁶ (RIVA) or with 5 x10⁶(SU-DHL-6) cells.

Results. PQR620 had a median IC50 of 250 nM (95%CI, 200-269 nM) when tested on 44 lymphoma cell lines. Activity was higher in B cell (no.=36) than in T cell tumors (no.=8) (median IC50s: 250 nM vs 450 nM; P=0.002). At 72h, anti-tumor activityof PQR620 was mostly cytostatic and apoptosis induction was seen only in 6/44 cell lines (13%), Sensitivity to PQR620 or apoptosis induction did not differ between DLBCL and MCL, and they were not affected by the DLBCL cell of origin, by TP53 status or by the presence of MYC or BCL2 translocations.

The activity of PQR620 as single agent underwent in vivo evaluation in two DLBCL models, the germinal center B cell type DLBCL (GCB-DLBCL) SU-DHL-6 and the acivated B cell-like DLBCL (ABC-DLBCL) RIVA. Treatments with PQR620 (100mg/kg dose per day, Qdx7/w) started with 100-150 mm³ tumors and were carried for 14 (SU-DHL-6) or 21 days (RIVA). In both models, PQR620 determined a 2-fold decrease of the tumor volumes in comparison with control, with significant differences in both SU-DHL-6 (D7, D9, D11, D14; P < 0.005) and RIVA (D14, D16, D19, D21; P < 0.005).

Based on the previously reported synergy between the dual PI3K/mTOR inhibitor PQR309 and venetoclax (Tarantelli et al, ASH 2015), we evaluated the combination of the PQR620 or PQR309 with the BCL2 inhibitor venetoclax (100 mg/kg, Qdx7/w) in the SU-DHL-6 model. Both the venetoclax combination with the dual PI3K/mTOR inhibitor and the venetoclax combination with mTORC1/2 inhibitor were superior to the compounds given as single agents, leading to the eradication of the xenografts. The combination of PQR620 with venetoclax showed highly significant differences either versus control or single agents during all days of the experiment (D4, D7, D9, D11, D14; P < 0.001). Similarly, the combination of PQR309 with venetoclax showed highly significant differences versus venetoclax (D7, D9, D11, D14; P < 0.001) and PQR309 (D7, D9, D11; P < 0.005) alone.

Conclusions. The novel mTORC1/2 inhibitor PQR620 had in vitro and in vivo anti-lymphoma activity as single agent. In vivo experiments showed that both PQR620 and the dual PI3K/mTOR inhibitor PQR309 can strongly benefit from the combination with the BCL2 inhibitor venetoclax.