Induction of autoantibodies to murine P-glycoprotein: Consequences on drug sensitivity in MDR cancer cells and on the expression of mdr genes in organs

Cytotoxicity and apoptosis induced by alfalfa (Medicago sativa) leaf extracts in sensitive and multidrug-resistant tumor cells

Alfalfa (Medicago sativa) has been used to cure a wide variety of ailments. However, only a few studies have reported its anticancer effects. In this study, extracts were obtained from alfalfa leaves and their cytotoxic effects were assessed on several sensitive and multidrug-resistant tumor cells lines. Using the mouse leukaemia P388 cell line and its doxorubicin-resistant counterpart (P388/DOX), we showed that the inhibition of cell growth induced by alfalfa leaf extracts was mediated through the induction of apoptosis, as evidenced by DNA fragmentation analysis. The execution of programmed cell death was achieved via the activation of caspase-3, leading to PARP cleavage. Fractionation of toluene extract (To-1), the most active extract obtained from crude extract, led to the identification of 3 terpene derivatives and 5 flavonoids. Among them, (-)-medicarpin, (-)-melilotocarpan E, millepurpan, tricin, and chrysoeriol showed cytotoxic effects in P388 as well as P388/DOX cells. These results demonstrate that alfalfa leaf extract may have interesting potential in cancer chemoprevention and therapy.

Resveratrol induces cell-cycle disruption and apoptosis in chemoresistant B16 melanoma

Resveratrol, a naturally occurring polyphenol, has been shown to possess chemopreventive activities. In this study, we show that resveratrol (0-500 microM) inhibits the growth of a doxorubicin-resistant B16 melanoma cell subline (B16/DOX) (IC(50) = 25 microM after 72 h, P < 0.05). This was accomplished by imposing an artificial checkpoint at the G(1)-S phase transition, as demonstrated by cell-cycle analysis and down-regulation of cyclin D1/cdk4 and increased of p53 expression level. The G(1)-phase arrest of cell cycle in resveratrol-treated (10-100 microM) B16/DOX cells was followed by the induction of apoptosis, which was revealed by pyknotic nuclei and fragmented DNA. Resveratrol also potentiated at subtoxic dose (25 microM for 24 h) doxorubicin cytotoxicity in the chemoresistant B16 melanoma (P < 0.01). When administered to mice, resveratrol (12.5 mg/kg) reduced the growth of an established B16/DOX melanoma and prolonged survival (32% compared to untreated mice). All these data support a potential use of resveratrol alone or in combination with other chemotherapeutic agents in the management of chemoresistant tumors.