Through in-vitro kinase assays and docking studies, we report the synthesis and biological evaluation of a phenothiazine analogue-J54 with potent TLK1 inhibitory activity for Prostate Cancer therapy. Most PCa deaths result from progressive failure in standard ADT, leading to metastatic castration-resistant PCa. Treatments that can suppress the conversion to mCRPC have high potential to be rapidly implemented in the clinics. ADT results in increased expression of TLK1B, a key kinase upstream of NEK1 and ATR and mediating the DDR that typically results in temporary cell cycle arrest of androgen responsive PCa cells, while its abrogation leads to apoptosis. We studied J54 as potent inhibitor of this axis and as mediator of apoptosis in-vitro and in LNCaP xenografts, which has potential for clinical investigation in combination with ADT. J54 has low affinity for the dopamine receptor in modelling and competition studies and weak detrimental behavioral effects in mice and C. elegans.