1341 Discovery and preclinical characterization of ALG-093940, a potent and orally bioavailable small molecule PD-L1 inhibitor for the treatment of cancer

<h3>Background</h3> 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 (irAEs) due to their long half-life and development of anti-drug antibodies. Recently, PD-L1 small molecule inhibitors have been developed, e.g., INCB086550 that demonstrated clinical responses in a phase I study.¹ Here, we report the discovery and preclinical characterization of ALG-093940, a potent and orally bioavailable small molecule PD-L1 inhibitor, that may overcome the limitations of PD-1/PD-L1 antibodies. <h3>Methods</h3> The biochemical interaction of PD-1/PD-L1 and PD-L1 dimerization was assessed by AlphaLISA®. Cellular activity was measured using a co-culture assay of PD-1 expressing Jurkat NFAT luciferase T cells with PD-L1 expressing CHO cells. <i>In vitro</i> ADME and the compound safety profile was established using standard assays. Pharmacokinetic (PK) studies were performed in mice, rat and cynomolgus monkey. <i>In vivo</i> inhibition of tumor growth, PD-L1 target occupancy and tumor infiltration of T-cells were assessed in a humanized-PD-L1 MC38 subcutaneous tumor mouse model. <h3>Results</h3> ALG-093940 inhibited PD-1/PD-L1 interaction with an IC₅₀ of 0.048 nM and induced PD-L1 dimerization with an EC₅₀ of 79 nM. ALG-093940 showed comparable T-cell activation potency to INCB086550. ALG-093940 demonstrated no <i>in vitro</i> liabilities for CYP-mediated drug-drug interactions, cardiovascular safety, or genotoxicity and exhibited low clearance (5.3 – 12 mL/minute/kg) and moderate to high oral bioavailability (58 - &gt;100%) in preclinical species, indicating its potential for once daily dosing in patients. In the <i>in vivo</i> humanized-PD-L1 MC38 mouse model, oral once daily dosing of ALG-093940 at 1.5, 15, 50 or 150 mg/kg demonstrated dose-dependent inhibition of tumor growth with tumor stasis and tumor regression observed in a subset of animals. At 24 hours post-final dose on day 21, PD-L1 target engagement demonstrated dose-dependent increases up to 98%. In addition, dose-dependent increases in tumor-infiltration of CD8⁺ T-cells and CD8⁺/CD4⁺ T-cell ratios were observed. All 21-day dosing regimens were well tolerated with body weight gains indistinguishable between ALG-093940 and vehicle treated animals. <h3>Conclusions</h3> ALG-093940 is a potent PD-L1 small molecule inhibitor, that shows similar T-cell activation potency to INCB086550. ALG-093940 demonstrated excellent, dose-dependent tumor growth inhibition, target engagement and tumor T-cell infiltration in a humanized PD-L1 MC38 subcutaneous mouse model. The properties of ALG-093940 warrant further development as a potential clinical candidate for the treatment of cancer. <h3>Reference</h3> Koblish HK, Wu L, Wang LS, <i>et al</i>. Characterization of INCB086550: a potent and novel small-molecule PD-L1 inhibitor. <i>Cancer Discov</i>. 2022;<b>12</b>(6):1482–1499.