A Safety and Dose-finding Study of PRL-02 Depot in Men With Advanced Prostate Cancer

Medicines that reduce the amount of testosterone in the body are commonly used to treat prostate cancer. PRL-02 depot is a potential treatment for men with advanced prostate cancer. It is given by an injection into the muscle. Men with advanced prostate cancer can take part in this study. Their cancer has come back after previous cancer treatment, or the previous cancer treatment they had didn't work. The main aims of the study are: * to check the safety of PRL-02 depot given with and without another medicine called enzalutamide. * to check if the men can tolerate PRL-02 depot given with or without enzalutamide. * to find a suitable dose of PRL-02 depot. This study will be in 2 parts. In the first part, different small groups of men will receive lower to higher doses of PRL-02 depot together with other medicines. In the second part of the study, men who have previously taken a hormone therapy called abiraterone acetate or have previously taken 1 specific hormone therapy as part of their prostate cancer treatment can take part. Men in both parts of the study will receive injections of PRL-02 depot into a muscle once every 12 weeks. They will also take dexamethasone or prednisone, or enzalutamide once a day. The other medicines they take depend on which group and which part of the study they are in. During the study, the men will visit the clinic several times for health checks and scans. After the final visit, men whose cancer has not become worse will continue to have health checks and scans every few months.