Safety and Preliminary Efficacy of SA53-OS in Patients With Locally Advanced or Metastatic Solid Tumors

This is a phase 1/2a, open-label, dose escalation study conducted in adult participants with p53 wild-type refractory solid tumors. The study will assess the safety, efficacy, and pharmacokinetics of SA53-OS a novel MDM2 inhibitor capable of selective activation of p53. This enables the p53 tumor suppressor protein to selectively facilitate tumor cell death and growth inhibition.

The study drug, SA53-OS, will be administered for 3 consecutive days every 3 weeks as an oral solution. Phase 1 will consist of a dose escalation study to establish a candidate recommended phase 2 dose (RP2D). Phase 2a will enroll 2 expansion cohorts to establish any preliminary efficacy of SA53-OS in participants with dedifferentiated liposarcoma (DD LPS) with MDM2 amplifications and other p53 wild-type solid tumors as a single agent.

Phase 1 dose escalation:

Escalating doses of SA53-OS will be provided to participants with p53 wild-type refractory solid tumors to determine the RP2D. The MTD is the highest dose of a drug or treatment that does not cause unacceptable side effects in the first cycle. The RP2D considers all available safety, pharmacokinetics, and efficacy data including, the frequency, severity, and manageability of toxicities occurring after Cycle 1.

Phase 1 of the study will start with dose escalation by 2-fold (i.e., 2x preceding dose level) in cohorts of a single participant until Grade 2 or greater toxicity is observed.

When a single Grade 2 or higher toxicity is observed, 3+3 multi-participant cohorts will be treated at the dose in which the Grade 2 or higher toxicity was observed by enrolling another 2 participants at this dose. The 3+3 multi-participant cohorts will follow the standard 3+3 paradigm based on occurrence of any DLT with 50% dose escalation until the MTD is identified.

Phase 2a dose expansion:

The purpose of Phase 2a of the study is to describe any preliminary evidence of efficacy from SA53-OS monotherapy in participants with DD LPS or other p53 wild-type or MDM2 amplified solid tumors. Phase 2a will also be used to confirm the safety and tolerability of the candidate RP2D of SA53-OS determined in Phase 1 of the study, to further describe the toxicity and pharmacokinetics profiles of SA53-OS, and to assess potential biomarkers of sensitivity resistance, and toxicity.

Participants will continue to receive study treatment until either: 1) disease progression; 2) occurrence of unacceptable treatment-related toxicity as per participant or Investigator discretion; 3) the maximum of 2 years of treatment has been reached; or 4) other reason(s) for study treatment discontinuation. In the case of complete response, treatment should be continued for at least 6 months if no other stopping criteria are met, and further treatment can be recommended at the investigator's discretion.