Three novel chemotypes inhibited phorbol ester-induced endogenous PKD1 activation (i.e., PKD Ser916 phosphorylation) in LNCaP prostate cancer cells and were structurally dissimilar to CID 755673, BKPDi and CRT5, revealing an expanded diversity of PKD1 small molecule inhibitors. This evidence concerns the gene PKD1 and prostate cancer.