Preclinical Characterization of ALG-094295, a highly potent and orally bioavailable small molecule PD-1/PD-L1 inhibitor targeting dimerization, internalization and degradation of PD-L1

Background: PD-1/PD-L1 antibody-based therapies have demonstrated tremendous success in the treatment of a variety of cancers. However, these antibody drugs are associated with several disadvantages, such as weak tumor penetration, immune-related adverse events and emergence of anti-drug antibodies. Here, we report the discovery and characterization of ALG-094295 as a highly potent and orally bioavailable small molecule PD-1/PD-L1 inhibitor that binds to PD-L1 and promotes PD-L1 dimerization, internalization and degradation, offering a different mechanism of action with potential advantages over PD-1/PD-L1 antibody therapeutics. Methods: The interaction of PD-1/PD-L1 and PD-L1 dimerization were assessed by AlphaLISA®. Cellular activity was measured using PD-1 expressing Jurkat NFAT luciferase T cells and CHO-hPD-L1 cells. In vivo PD-L1 target engagement, tumor growth inhibition and tumor infiltration of T-cells were assessed in a humanized-PD-L1 MC38 subcutaneous tumor mouse model. In vitro ADME tox profile was established using standard assays. Pharmacokinetic (PK) studies were performed with rat, dog and cynomolgus monkey. Results: ALG-094295 demonstrated inhibition of PD-1/PD-L1 interaction at sub-nanomolar concentrations and induced PD-L1 dimerization. In vitro studies showed that ALG-094295 activated T cells with approximately ten times greater potency compared to INCB086550, an orally administered small molecule PD-L1 inhibitor that has demonstrated clinical responses in a phase I trial. Furthermore, treatment of CHO-hPD-L1 cells with ALG-094295 resulted in internalization and reduction of PD-L1 protein levels. In ex vivo human PBMC assays, ALG-094295 demonstrated PD-L1 target engagement, T cell activation and immune cell mediated tumor cell killing. In a humanized PD-L1 MC38 mouse model, a single oral dose of ALG-094295 (5 mg/kg) achieved PD-L1 target engagement comparable to INCB086550 (150 mg/kg PO). Daily oral dosing of ALG-094295 (50 or 150 mg/kg) in humanized PD-L1 MC38 mice over 21 days resulted in tumor growth inhibition equivalent to twice-weekly administration of durvalumab (10 mg/kg IV), with tumor size correlating with increased CD8⁺ T-cell infiltration. ALG-094295 demonstrated no in vitro liabilities for CYP450 inhibition or induction mediated drug-drug interactions, off target toxicity, cardiovascular safety, or genotoxicity. Preclinical in vivo PK data suggests once-daily oral dosing is feasible in humans. Conclusion: ALG-094295 is a highly potent and orally bioavailable small molecule PD-1/PD-L1 inhibitor that promotes PD-L1 dimerization, internalization and degradation. ALG-094295 has the potential to overcome some limitations of antibody-based therapies due to potent PD-L1 blockade, oral delivery and novel mechanism of action.