Phenothiazines and related
antipsychotics were reported to have an antiproliferative effect in several tissue cultures. The aims of this study were: a) to screen in vitro, the potential anti-
cancer activity of
phenothiazines in wild-type and multi-drug resistant (MDR) B16 mouse
melanoma cell lines; and b) to determine the in vivo anti-
tumor effect of an in vitro selected highly potent
phenothiazine (
thioridazine) in a murine
melanoma model. The following
phenothiazines were evaluated:
perphenazine,
fluphenazine,
thioridazine trifluoperazine and
chlorpromazine. All agents induced a dose-dependent decrease in cell viability in wild-type and in MDR
B16 melanoma cells.
Thioridazine displayed the highest antiproliferative activity. Flow cytometric analyses of 24-h treated
B16 melanoma cells revealed an increase in fragmented
DNA (16.3 vs 71.3% and 87.2% in controls, 25 microM and 50 microM
thioridazine-treated, respectively). Apoptosis was confirmed by co-staining of
thioridazine-treated B16 cells (12.5 microM) with
propidium iodide and
Hoechst 33342 reagents.
Caspase-3 expression, a typical mediator of apoptosis, was markedly increased following a 4-h exposure of B16 cells to
thioridazine (25 microM and 50 microM). This increase could be blocked by a specific
caspase-3 inhibitor. In vivo studies were performed using female C57/Bl mice. Animals were inoculated with wild-type B16 cells by i.v. injection into the tail vein. Mice were treated with
thioridazine (10 and 15 mg/kg x3/week i.p. or 15, and 25 mg/kg/day p.o.) and control animals received saline. Mice were monitored for 21-30 days.
Body weight was recorded. After autopsy, the lung weight and number of pulmonary
melanoma colonies were determined.
Thioridazine administration (i.p. or p.o.) resulted in the reduction of lung
tumor burden and an increase in mice survival. In conclusion, several
phenothiazines, and particularly
thioridazine, induced apoptosis of
B16 melanoma cells and demonstrated in vivo anti-
tumor activity.