In this Phase 1a/b study, subjects must have received standard of care (SOC) therapy for their advanced/metastatic tumors and subjects must have received, have been intolerant to, have been ineligible for, or have declined all treatment known to confer significant clinical benefit. Subjects must also have at least 1 measurable lesion per Response Evaluation Criteria in Solid Tumors (RECIST1.1), an Eastern Cooperative Oncology Group (ECOG) performance score of 0, 1 or 2 and predicted life expectancy of greater than 3 months. An imaging scan is required at baseline, up to 28 days prior to treatment initiation. Subjects are required to provide an adequate tumor tissue sample (archival or fresh-tissue if no archival is available).~Approximately 24 - 64 subjects will be enrolled and will receive therapy as part of their respective treatment groups (ascending doses of RBS2418 of 100 mg, 200 mg, 400 mg and 800 mg BID as monotherapy or in combination with pembrolizumab 200 mg IV q3w). The study consists of two (2) phases. The first part of the study (Part A) is the dose escalation phase of the study and is planned to enroll up to 8 cohorts in total (3-6 subjects per cohort) to receive RBS2418 as monotherapy or in combination with pembrolizumab to identify the fixed dose to be evaluated further in the expansion phase of the study (Part B) (~20-40 subjects).~A 3+3 design will be used to establish dose limiting toxicities (DLT), the maximum tolerated dose and the dose level of RBS2418 corresponding to an optimal biologically active dose to aid in the selection of the fixed expansion cohort dose.~In all treatment arms, treatment will continue until progressive disease (PD), unacceptable adverse events (AEs), intercurrent illness that prevents further administration of treatment, investigator's decision to withdraw the subject, subject withdrawal of consent, pregnancy of the subject, noncompliance with study dosing or procedure requirements, subject receiving approximately 2 years of RBS2418 monotherapy or in combination with pembrolizumab, or administrative reasons requiring cessation of treatment.~After the last dose of study drug, each subject will be followed for 30 days for AE monitoring. Serious adverse events (SAEs) will be collected for 90 days after the end of treatment or for 30 days after the end of treatment, if the subject initiates new anticancer therapy, whichever is earlier
RBS2418 (investigational product) is a specific immune modulator, working through ectonucleotide pyrophosphatase/phosphodiesterase I (ENPP1), designed to lead to anti-tumor immunity by increasing endogenous 2'-3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) and adenosine triphosphate (ATP levels) and reducing adenosine production in the tumors. RBS2418 has the potential to be an important therapeutic option for subjects both as monotherapy and in combination with checkpoint blockade. This study is an open-label, multi-site Phase 1a/1b study of RBS2418, a selective ENPP1 inhibitor, in combination with pembrolizumab or as a monotherapy in subjects with advanced unresectable, recurrent or metastatic tumors.