CCX559 is a potent, orally-administered small molecule PD-L1 inhibitor that induces anti-tumor immunity.

The interaction of PD-L1 with PD-1 is a major immune checkpoint that limits effector T cell function against cancer cells; monoclonal antibodies that block this pathway have been approved in multiple tumor indications. As a next generation therapy, small molecule inhibitors of PD-L1 have inherent drug properties that may be advantageous for certain patient populations compared to antibody therapies. In this report we present the pharmacology of the orally-available, small molecule PD-L1 inhibitor CCX559 for cancer immunotherapy. CCX559 potently and selectively inhibited PD-L1 binding to PD-1 and CD80 in vitro, and increased activation of primary human T cells in a T cell receptor-dependent fashion. Oral administration of CCX559 demonstrated anti-tumor activity similar to an anti-human PD-L1 antibody in two murine tumor models. Treatment of cells with CCX559 induced PD-L1 dimer formation and internalization, which prevented interaction with PD-1. Cell surface PD-L1 expression recovered in MC38 tumors upon CCX559 clearance post dosing. In a cynomolgus monkey pharmacodynamic study, CCX559 increased plasma levels of soluble PD-L1. These results support the clinical development of CCX559 for solid tumors; CCX559 is currently in a Phase 1, first in patient, multicenter, open-label, dose-escalation study (ACTRN12621001342808).

Optimization of LpxC Inhibitors for Antibacterial Activity and Cardiovascular Safety.

UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a Zn2+ deacetylase that is essential for the survival of most pathogenic Gram-negative bacteria. ACHN-975 (N-((S)-3-amino-1-(hydroxyamino)-3-methyl-1-oxobutan-2-yl)-4-(((1R,2R)-2-(hydroxymethyl)cyclopropyl)buta-1,3-diyn-1-yl)benzamide) was the first LpxC inhibitor to reach human clinical testing and was discovered to have a dose-limiting cardiovascular toxicity of transient hypotension without compensatory tachycardia. Herein we report the effort beyond ACHN-975 to discover LpxC inhibitors optimized for enzyme potency, antibacterial activity, pharmacokinetics, and cardiovascular safety. Based on its overall profile, compound 26 (LPXC-516, (S)-N-(2-(hydroxyamino)-1-(3-methoxy-1,1-dioxidothietan-3-yl)-2-oxoethyl)-4-(6-hydroxyhexa-1,3-diyn-1-yl)benzamide) was chosen for further development. A phosphate prodrug of 26 was developed that provided a solubility of >30 mg mL-1 for parenteral administration and conversion into the active drug with a t1/2 of approximately two minutes. Unexpectedly, and despite our optimization efforts, the prodrug of 26 still possesses a therapeutic window insufficient to support further clinical development.