Prolidase-activated prodrug for cancer chemotherapy cytotoxic activity of proline analogue of chlorambucil in breast cancer MCF-7 cells.

Although prolidase [EC 3.4.13.9] is found in normal cells, substantially increased levels are found in some neoplastic tissues. Because prolidase possesses the ability to hydrolyse imido bonds of various low molecular weight compounds coupled to L-proline, we hypothesized that coupling of L-proline through an imido bond to anticancer drugs might create prodrugs which would be locally activated by tumour-associated prolidase and consequently would be less toxic to normal cells that evoke lower prolidase activity. To test this concept we have synthesized a conjugate of chlorambucil-proline (CH-pro) as a possible prodrug. Treatment of this prodrug with prolidase generated the L-proline and the free drug, demonstrating its substrate susceptibility to prolidase. We have compared several aspects of biological actions of chlorambucil (CH) and its prodrug in breast cancer MCF-7 cells. IC50 values for chlorambucil and for CH-pro in DNA synthesis were found to be 54 and 16 microM, respectively. CH-pro also exhibited a lesser ability to inhibit collagen biosynthesis in breast cancer MCF-7 cells compared to the free drug. The IC50 values for chlorambucil and for CH-pro in collagen biosynthesis were found to be about 32 and 80 microM, respectively. This suggests that the targeting of prolidase may serve as a potential strategy for converting antineoplastic prodrugs.