Targeted MDM2 degradation for improved treatment for triple-negative breast cancer

Although significant progress in targeted and immunotherapies has been made in recent years, effective treatment of TNBC remains a challenge. Clinical studies of TNBC tumors have revealed that the overexpression of the oncogene MDM2 are positively associated with tumor stages and are an independent negative prognostic factor for TNBC patients, indicating that target MDM2 is a promising strategy for improved TNBC treatment. However, existing MDM2 inhibitors such as AMG-232 (KRT-232) only block the MDM2-p53 binding, dependent on wild-type p53 activation for their anticancer activity and with a risk of increasing MDM2 expression due to the p53-MDM2 negative feedback loop. Distinct from this mechanism, we recently discovered a novel class of MDM2 degraders binding to the MDM2 RING domain, with CH175 as the current lead compound, that induces tumor regressions in clinically relevant TNBC PDX models. Based on these preliminary studies, our central hypothesis is that the CH175 scaffold as a first-in-class MDM2 degrader can be further optimized, leading to a potential future clinical candidate for improved therapy outcomes in TNBC patients. Aim 1: Perform focused structure-based optimization of the CH175 scaffold to develop new analogs with increased binding to the MDM2 RING domain and increased anti-TNBC potency. Aim 1.1. Perform focused optimization of the CH175 scaffold to increase their binding to the MDM2 RING domain and drug-like properties. Aim 1.2. Screen new CH175 analogs using a panel of TNBC cell lines. Aim 1.3. Screen the selected CH175 analogs for their drug-like properties, and assess potential off-target effects for the selected analogs. Aim 2: Elucidate the molecular mechanisms by which CH175 and new analogs degrade MDM2, leading to strong anti-TNBC activity. Aim 2.1. Confirm CH175-MDM2 RING-domain binding, effects on E2, E3 ligase activity, and association with improved anti-TNBC activity. Aim 2.2. Demonstrate that the MDM2 is a critical target for CH175 and its best analogs. Aim 2.3. Demonstrate biological effects of CH175 and analogs on MDM2 downstream pathways using in vitro and in vivo biochemical and molecular biology technologies. Aim 3: Demonstrate in vivo efficacy and characterize the pharmacological and toxicological properties of CH175 and up to two best new analogs using clinically relevant TNBC PDX models. Aim 3.1. Determine Maximum Tolerance Dose (MTD) and Minimal effective concentration (MEC). Aim 3.2. Perform PK/PD correlation study to demonstrate the in vivo drug behavior and MDM2 targeting efficacy. Aim 3.3. Demonstrate in vivo efficacy in comparison with clinically used drugs and the best available MDM2 inhibitors. Aim 3.4. Perform initial in vitro and in vivo non-GLP toxicity screening following FDA guidelines. Impact: Existing MDM2 inhibitors depend on disrupting the MDM2-p53 binding and have not resulted in positive outcomes in clinical trials. The CH175 scaffold as a first-in-class MDM2 degrader has anticancer activity, regardless of p53 status. If successful, a novel MDM2 targeted therapy will be developed for TNBC treatment.