TP53 loss-of-function causes vulnerability to autophagy inhibition in aggressive prostate cancer.

Objectives: TP53 loss-of-function is commonly found in aggressive prostate cancer. However, a highly-efficient therapy for this tumor subtype is still lacking. In this study, we investigated the relationship between TP53 mutation status and autophagy in prostate cancer and assessed the efficacy of autophagy inhibitors on TP53-deficient tumors.

Methods: We first evaluated the expression patterns of p53 and autophagy-related proteins, namely LC3B, ULK1 and BECLIN1, as well as their relationship in treatment-naïve and castration-resistant prostate cancer specimens through immunohistochemistry. Subsequently, we generated a Trp53-deleted genetically-engineered mouse model, established prostate tumor organoid lines from the mice and assessed the efficacy of autophagy inhibitors in overcoming Enzalutamide resistance in the tumor organoid model. We also investigated the impact of TP53 re-expression in modulating responses to autophagy inhibitors using LNCaP cell line, which harbored a TP53 missense mutation. Lastly, we attempted to identify potential autophagy-related genes that were crucial for TP53-deficient tumor maintenance.

Results: TP53 loss-of-function was associated with increased levels of autophagy-related proteins in aggressive prostate cancers and Trp53-deleted genetically-engineered mouse-derived tumors. Moreover, the generated androgen receptor-independent tumor organoids were highly vulnerable to autophagy inhibition. Upon TP53 re-expression, not only did the surviving LNCaP cells demonstrate resistance, but they also showed growth advantage in response to autophagy inhibition. Lastly, PEX14, an important peroxisomal regulator was differentially upregulated in aggressive tumors with TP53 loss-of-function mutations, thus implying the importance of peroxisome turnover in this tumor subtype.

Conclusion: Our results support the potential use of autophagy inhibitors in prostate cancers that contain TP53 loss-of-function mutations.