ANTITUMOR EFFECTS OF PAK4-INHIBITION IN IN VIVO AND IN VITRO PROSTATE CANCER MODELS

Background: Prostate cancer represents 11% of all cancers and 9% of cancer-related deaths in European men (1, 2). The treatment of prostate cancer includes radical prostatectomy, radiations and hormonal therapy (3). To date, although the improvements of care and of outcome of the disease, further efforts must to be put in place for increase the efficacy of treatment and reduction of the relapse. So, in the last years have been identified different molecular targets in prostate cancer, useful for the generation of new therapeutic strategies (4, 5). Among these new targets PAK4 raised a great interest for its importance in prostate cancer progression and survival (6, 7). In our work we resumed the antitumor effects of PAK4 inhibition in four prostate cancer cells (PC3, DU145 and 22RV1) through in vivo and in vitro experiments. Materials and Methods: PC3, DU145, and 22RV1 prostate cancer cells were subcutaneously injected in the flank of nu/nu CD1 mice, treated with PAK4-inhibitor and monitored over the time for tumor growth rate respect to untreated animals. In parallel, the prostate cancer cells were cultured and treated for the evaluation of different properties, such as proliferation, cell death induction, autophagy, migration, through western blotting, FACS analysis, and wound healing repair assays. Results: In vivo experiments showed that KPT-8752 reduced cancer growth of about 25-60% in relation to the cell line, respect to the untreated group. Indeed, 22RV1 cell lines seemed to be the most sensitive, while the PC3 cell line resulted to be very less sensitive to the inhibitor. The in vitro results, defined that apoptosis occurred in 22RV1 and DU145 cells when KPT8752 was administered proven by caspase 3 cleaved appearance, while in PC3 cells the activation of the autophagy program was very clear, testified by the increase of Beclin1 and LC3IIb levels. In all the cell lines the wound healing repair assay showed a reduction of migratory capacity, in a dose-dependent way with the inhibitor. Discussion: Our results indicate that PAK4-inhibitor KPT-8752 delayed tumor growth in treated mice, respect to the control group. In association to this, the overall tumor weight in treated animals resulted to be lower in comparison to untreated animals. Regarding in vitro results, they showed that the three prostate cancer cells exhibited a different behavior when exposed to the PAK4-inhibitor. Indeed, by the evaluation of two important mechanisms related to cancer survival, such as apoptosis and autophagy, the different prostate cancer cell seemed to be undertaking different faith. This, could be explained by the different genetic asset own of the cells. Moreover, in all the three cell lines used is evident a reduction of the migration when compared to control cells, when KPT-8752 was administered. Conclusion: Our results, in agreement with previous studies, confirm that PAK4 is a suitable therapeutic target for prostate cancer. The role of PAK4 in tumorigenesis and sustenance of prostate cancer is well known and these results spur us to continue to investigate the implication of the inhibition of this marker and identify new strategies for counteract its functions in the disease.