Cross-resistance to alternative second-line Apalutamide treatment in Castration Resistance Prostate Cancer cellular models

Abstract Background/Objectives: The treatment of choice for prostate cancer is androgen deprivation (ADT) and novel hormonal agents such as abiraterone, Enzalutamide or Apalutamide. Initially, this therapy is highly effective, but a significant challenge arises as most patients eventually develop resistance, resulting in castration-resistant prostate cancer (CRPC). Furthermore, the sequential use of these drugs can lead to cross-resistance, diminishing their efficacy. Tumor heterogeneity plays a pivotal role in the development of resistance to different treatments. This study utilized cellular models of CRPC to assess the response to Apalutamide when it is administered as a second- or third-line treatment. Methods: Functional and genetic analyses were conducted in various CRPC cell models exposed to Apalutamide. These analyses included real-time cell monitoring assays, flow cytometry, clonogenicity assays, and RT-qPCR. Results: CRPC cell models were capable of continued proliferation, maintained cell cycle profiles similar to those of untreated cells, and retained their clonogenic potential. Cross-resistance to Apalutamide in models of ADT, ADT plus Enzalutamide, or Abiraterone resistance did not correlate with the expression levels of AR-V7 and AR-V9 variants. Gene expression analysis of resistant prostate cancer cell lines revealed that treatment with Apalutamide induced the emergence of more aggressive phenotypes, including cancer stem cells or neuroendocrine differentiation profiles. Conclusions: Most CRPC cell models develop cross-resistance to Apalutamide and are able to proliferate and retain their clonogenic capability. Apalutamide resistance is not linked to the expression of AR-V7 or AR-V9 variants but is instead associated to the emergence of more aggressive expression profiles.