Cell-cycle arrest and p53-independent induction of apoptosis in vitro by the new anticancer drugs 5-FdUrd-P-FdCydOct and dCydPam-P-FdUrd in DU-145 human prostate cancer cells

Purpose: Current therapies have limited impact on the progression of metast atic hormone-refractory prostate cancer. Therefore, we investigated the uti lity of now heterodinucleoside phosphate dimers of 5-fluorodeoxyuridine (5- FdUrd) in p53-mutated and androgen-independent DU-145 human prostate tumour cells. Methods: The effects of the dimers were assessed in vitro by a cell proliferation assay for cytotoxicity, flow cytometry for cell cycle distri bution, confocal laser scanning microscopy for the detection of apoptotic b odies, poly(ADP-ribose) polymerase cleavage for caspase 3 activity and by a thymidylate synthetase assay. Results: The new dimers N-4-palmitoyl-2'-deo xycytidylyl-(3'--> 5')-5-fluoro-2'-deoxyuridine (dCydPam-P-FdUrd) and 2'-de oxy-5-fluorouridylyl-(3'--> 5')-2'-deoxy-5-fluoro-N-4-octadecyclytidine (5- FdUrd-P-FdCydOct) caused marked cytotoxicity with IC50 values of 3-4 mu M. 5-FdUrd-P-FdCydOct at 200 mu M was capable of eradicating 100% of tumour ce lls whereas 10% of the cells were resistant to 5-FdUrd. Cytotoxicity was ca used by a dramatic S-phase arrest, resulting in an increase of this cell po pulation from 34% to 85% with 5-FdUrd-P-FdCydOct and to 81% with dCydPam-P- FdUrd. S-phase arrest was followed by apoptosis, as shown by 85% of the cel ls staining positive for Apo 2.7 antibody, a six- to eight-fold increased c aspase 3 activity and DNA fragmentation. Thymidylate synthase activity was inhibited by 50% at 0.6-0.7 mu M dimer concentration. The dimers were hydro lysed in vitro by phosphodiesterase I and human serum to the corresponding nucleosides and nucleoside monophosphates. Conclusions: The new dimers dCyd Pam-P-FdUrd and 5-FdUrd-P-FdCydOct are effective prodrugs of 5-FdUrd and ha ve potential value for the treatment of p53-mutated and hormone-independent human prostate carcinomas.