Riboscience, LLC, today announced the first presentation of data from the ongoing Phase 1 clinical trial of the ENPP1 inhibitor RBS2418 that will be delivered by Dr. Thomas U. Marron, MD, PhD, from Mount Sinai, New York at the European Society for Medical Oncology (ESMO) Congress 2023 on October 21, 2023. RBS2418 is the first ENPP1 inhibitor in clinical development.

Clinical study RBS2418-1001 (NCT05270213) is a Phase 1, open-label, non-randomized study in adult patients with advanced, unresectable, recurrent or metastatic solid tumors, who have progressed on, or are ineligible for standard therapies. The dose escalation phase of the study follows a 3+3 design with increasing doses of RBS2418 given orally as monotherapy or in combination with Pembrolizumab.

Riboscience presents data from an ongoing Phase 1 trial of a new immunotherapy in patients with advanced cancers.

The ESMO presentation #1025MO summarizes the safety, PK and PD results and clinical outcomes of treatment with RBS2418 from the first 19 patients in the dose escalation phase of the study. There are 11 different cancer types represented and 84% of patients had failed 3 or more lines of prior treatment. The concentration of RBS2418 in plasma and in tumor samples exceeded the human serum EC90 of ENPP1 inhibition in all patients at all dose levels (100, 200, 400 mg) and at all time points tested. Median plasma Cmax and Ctrough levels of RBS2418 increased dose proportionally. No DLTs, no treatment-related SAEs or treatment-related AEs above grade 2 were observed for treatment durations up to 1 year. Immune activation and tumor infiltration of CD4 and CD8 cells was observed in patients who expressed ENPP1 and cGAS protein in baseline tumor samples, EG(+) phenotype. The EG(+) phenotype was present in 53% of the patients at baseline.

This phenotype predicted outcome with RBS2418 treatment, as 60% of treated EG(+) patients experienced stable disease as compared to 0% of patients who did not express ENPP1 or cGAS in the baseline tumor sample, EG(-) phenotype. Progression-free survival (PFS) was significantly increased in EG(+) vs EG(-) phenotypes (p=0.0013). Clinical benefit from RBS2418 was dependent on the presence of the drug target (ENPP1), indicating target-inhibition dependent clinical benefit with RBS2418 treatment, consistent with the PK/PD results that demonstrated full ENPP1 inhibition and cGAMP stabilization at all dose levels.

These results show a target-inhibition-dependent immune activation and significant clinical benefit of a well-tolerated oral RBS2418 treatment and support further clinical development of this novel first-in-class immunotherapy agent. The clinical study is proceeding into a dose-expansion phase.