Malignant melanoma, the most deadly form of
skin cancer, has a high propensity for metastatic spread and is notoriously
chemotherapy-resistant.
Metapristone is the primary metabolite of
mifepristone (
RU486) and shows biological activities similar to
RU486. In the present study, we comprehensively investigated the efficacy of
metapristone as a metastatic chemopreventive against
melanoma B16F10 cells in vitro and in vivo, and evaluated the safety profile of both drugs in mice.
Metapristone showed less
cytostatic effect in vitro and in vivo in comparison with
mifepristone. However,
metapristone interfered the adhesion of B16F10 cells to
fibronectin by down-regulating cellular expression of
integrin α4. Chemopreventive pretreatment followed by
oral administration of
metapristone and
mifepristone (2.5, 10, 50 mg/kg/day for 35 days) to
melanoma C57BL/6 mouse model showed significant attenuation of pulmonary metastatic development.
Oral administration of high doses of
metapristone and
mifepristone to normal mice for 35 days (25, 100, 250 mg/kg/day) resulted in a dose-dependent increase in mouse liver weight that was more severe with
mifepristone than
metapristone. The long-term toxicity study revealed more changes by
mifepristone in counts of erythrocytes, leukocytes and platelets than by
metapristone. In conclusion,
metapristone may fit into a new class of
cancer metastatic chemopreventive agents. It showed a safety and efficacy profile better than
mifepristone.