Comprehensive Profiling of OTSSP167 Action in Adrenocortical Carcinoma

PURPOSE: Adrenocortical carcinoma (ACC) is an aggressive malignancy with no approved targeted therapy and poor outcomes. METHODS: Using multiple patient and cell line derived xenograft (PDX/CDX) models, and a newly developed PDX model (CUACC9), we investigated the potential action of the multikinase inhibitor OTSSP167 for treatment of ACC. RESULTS: OTSSP167 effectively reduced tumor growth in wild type TP53 (CUACC1) and mutant TP53 (H295R, CUACC9) in vivo tumor models. Immunohistochemical (IHC) analysis of treated tumors verified apoptosis via caspase activation as a mechanism of OTSSP167 action. Further evaluation of downstream effectors via RNA-seq and a Reverse Phase Protein Array (RPPA), using ACC cell lines matching the in vivo genetic diversity, demonstrated that OTSSP167 impeded cell cycle via G2/M arrest independent of TP53 status. In TP53 mutant lines, OTSSP167 enhanced DNA damage and inhibited protein synthesis. RSK1 was identified as a direct target of OTSSP167 activity in vitro. OTSSP167 also induced the G2/M checkpoint protein, WEE1, activation in all models, indicating an early adaptive response. Combining the WEE1 inhibitor AZD1775 with OTSSP167 significantly enhanced cytotoxicity in TP53 mutant lines, and reduced tumor growth in a TP53 mutant ACC model. CONCLUSION: Together these findings establish the feasibility of using OTSSP167 in ACC, especially in TP53 mutant ACC tumors. In addition, this study demonstrates the possibility of targeting the early adaptive response subsequent to exposure to OTSSP167 treatment. Our findings provide strong rationale for a future phase I clinical trial in ACC.