Project summary/abstract This proposal advances the development of a novel therapeutic for p53 wild type sarcomas. Our team has identified a novel MDM2 inhibitor, SA53, with best-in-class potency, bioavailability and in vivo efficacy across a broad range of preclinical models. It has also undergone extensive safety and pharmacokinetic testing, suitable for support of an IND submission, with an identified starting dose in humans. SA53 has the potential to facilitate apoptosis in p53 wild-type cancers and to spare normal tissue. To drive proof of concept, we will conduct a first in human trial to 1) identify a safe dose for future clinical trials, 2) establish the pharmacokinetic profile and appropriate safety endpoints, 3) in an expansion cohort, establish feasibility and early indication of efficacy in treating p53 wild type soft tissue sarcoma. Our primary objective is to rapidly and efficiently advance SA53 through clinical trials to implement a novel and innovative treatment for p53 wild type soft tissue sarcoma. Our approach is first establishing the recommended phase 2 dose in a trial for p53 wild type refractory solid tumors, then to apply this novel therapy in an expansion cohort targeting a pre-surgical window in soft tissue sarcoma patients. To achieve these goals, we will complete the following specific aims: Aim 1: We will complete GMP manufacturing of the drug and formulated clinical product suitable to complete a phase 1 clinical trial. Aim 2: We will conduct a phase 1 clinical trial to establish the recommended dose for phase 2 and early indication of feasibility and efficacy in soft tissue sarcoma patients. At the completion of this proposal, we will have completed a phase 1 trial to have established safety and preliminary efficacy, which will serve as the foundation for registration directed studies. In light of our exceptional in vivo efficacy data, we further believe that this can be a breakthrough paradigm-changing therapy for cancer treatment.