Differential modulation of apoptosis-related proteins in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) preclinical model after treatment with enzalutamide and jaboticaba peel extract

Prostate cancer (PCa) is one of the most common cancers in men. In castration-resistant prostate cancer, therapeutic options remain limited. Enzalutamide, a nonsteroidal androgen receptor antagonist, inhibits its nuclear translocation and transcriptional activity. However, treatment resistance may be developed. In addition, natural compounds have been investigated as potential complementary therapeutic strategies. Thus, this study evaluated the effects of jaboticaba peel extract (JPE), administered alone or in combination with enzalutamide, on apoptosis-related proteins in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) preclinical model. At 16 weeks old, the animals were assigned to four groups and treated by oral gavage for six weeks: sham castration + vehicle (TC), sham castration + JPE (5.8 g/kg; TCJ), surgical castration + enzalutamide (10 mg/kg; TE), or surgical castration + combined treatment with JPE (5.8 g/kg) and enzalutamide (10 mg/kg; TEJ). The dorsolateral prostate lobes of animals without macroscopic tumors were collected for protein expression analysis by Western blotting and immunohistochemistry. Western blot analysis showed that JPE administered alone did not significantly alter the pro- and anti-apoptotic proteins evaluated compared with the TC group. Enzalutamide increased the expression of the pro-apoptotic proteins BAX and BAD and decreased the expression of the anti-apoptotic proteins BCL-2, BCL-XL, and MCL-1 compared with the TC group, indicating a molecular profile consistent with modulation of the intrinsic apoptotic pathway. And also, the qualitative immunohistochemical analysis was consistent with the alterations in BCL-XL and total caspase-3 expression observed by means of Western blotting. Despite the changes in BCL-2 family proteins, the caspase-9 expression was not significantly altered in the TE compared with the TC group. However, its expression was significantly higher in the TEJ than in the TCJ and TE groups. Caspase-8 expression decreased in the TE and TEJ groups compared with the TC and TCJ groups, respectively. Total caspase-3 expression also decreased in the TE and TEJ groups, with no significant changes in cleaved caspase-3 in the same comparisons. In conclusion, JPE administered alone did not significantly alter the apoptosis-related proteins evaluated. Enzalutamide modulated proteins primarily associated with the intrinsic apoptotic pathway, whereas combined treatment increased caspase-9 expression compared with the individual treatments. However, the absence of an increase in cleaved caspase-3 did not allow us to conclude that apoptosis was effectively activated. Further studies using different experimental models and earlier stages of disease could provide further insight into the effects of these treatments on cell death mechanisms. (SisGen - AB61OF; CEUA: 6070-1/2022). Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001, CNPq (Grants: 307314/2023-5; 404066/2025-9), FAPESP (Grants: 2022/10794-3; 2022/09692-1 and 2023/17076-1) and FAEPEX (Grants: 2576/22 and 3299/23).