A New Synthetic Spiroketal: Studies on Antitumor Activity on Murine Melanoma Model In Vivo and Mechanism of Action In Vitro.

BACKGROUND: In a previous study, we synthesised a new spiroketal derivative, inspired to natural products, that has shown high antiproliferative activity, potent telomerase inhibition and proapoptotic activity on several human cell lines. OBJECTIVE: This work focused on the study of in vivo antitumor effect of this synthetic spiroketal on a murine melanoma model. In order to shed additional light on the origin of the antitumor effect, in vitro studies were performed. METHODS: Spiroketal was administered to B16F10 melanoma mice at a dose of 5 mg/Kg body weight via intraperitoneum at alternate days for 15 days. Tumor volume measures were made every 2 days starting after 12 days from cells injection. The effects of the spiroketal on tumor growth inhibition, apoptosis induction, and cell cycle modification were investigated in vitro on B16 cells. HIF1α gene expression, the inhibition of cells migration and the changes induced in cytoskeleton conformation were evaluated. RESULTS: Spiroketal displayed proapoptotic activity and high antitumor activity in B16 cells with nanomolar IC50. Moreover it has shown to inhibit cell migration, to strongly reduce the HIF1α expression and to induce strongly deterioration of cytoskeleton structure. A potent dose-dependent antitumor efficacy in syngenic B16/C57BL/6J murine model of melanoma was observed with the suppression of tumor growth by an average of 90% at a dose of 5 mg/kg. CONCLUSION: The synthesized spiroketal shows high antitumor activity in the B16 cells in vitro at nM concentration and a dose-dependent antitumor efficacy in syngenic B16/C57BL/6J mice. The results suggest that this natural product inspired spiroketal may have a potential application in melanoma therapy.

Simvastatin inhibits the expression of stemness­related genes and the metastatic invasion of human cancer cells via destruction of the cytoskeleton.

Statins are a class of drugs that inhibit the rate-limiting steps in the cholesterol biosynthesis pathway. They act by inhibiting 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, which catalyzes the conversion of HMG-CoA to mevalonate. Blocking of mevalonate synthesis leads to inhibition of the farnesylation and geranylgeranylation of several functional proteins, such as RhoA and other small guanosine triphosphate-binding proteins, that are important in maintaining the undifferentiated status of the cells. In the present study, we hypothesized that simvastatin, likely through the inhibition of farnesylation and geranylgeranylation of Rac1, Cd42 and RhoA, induces a destruction/restructuration of the cytoskeleton that decreases mechanical strain transfer to the nuclei, inducing the loss of transmission of regulatory signals from the cytoskeleton to the nucleoskeleton. Although this remains at present a hypothesis and is not easy to define if the de-structuration of the cytoskeleton is a secondary effect of simvastatin treatment or the inhibition of post-translational protein modification have a precise role in the structuration of actin cytoskeleton, we speculate that these signal variations could inhibit the expression of certain stemness genes, which could therefore be considered nucleoskeleton-associated and mechanically regulated genes. On the other hand, the restructuration of the cytoskeleton inhibits the formation of lamellipodia and filopodia, which likely decreases the capability of cancer cells to invade the extracellular matrix, thereby modulating the equilibrium between proliferation, differentiation and metastatic invasion in human cancer cells. On the basis of our results we think that simvastatin, alone or in combination with conventional drugs, may have a possible role in cancer therapy.

Simvastatin reduces melanoma progression in a murine model.

Statins are a class of drugs that inhibit the rate-limiting step in the cholesterol biosynthetic pathway and show an anticancer effect, probably through the inhibition of cell proliferation. To date, the exact mechanism of cancer cell growth arrest induced by statins is not known. We report that simvastatin is able to induce apoptosis in melanoma cells but not in normal cells and also able to contrast the growth of tumor in an experimental melanoma murine model. We observed a delay in the tumor development in almost the 50% of the simvastatin administered animals and a strong reduction of the tumor volume with a differences of ~150% compared to the controls. Also the survival rate was significantly higher in mice that received the drug with a survival increase of ~130% compared to the controls. The tumor growth reduction in mice was supported by the results of cell migration assay, confirming that simvastatin clearly reduced cell migration. Moreover, simvastatin induced a strong downregulation of NonO gene expression, an important growth factor involved in the splicing regulation. This result could explain the decrease of melanoma cells proliferation, suggesting a possible action mechanism. The results derived from our experiments may sustain the many reports on the anticancer inhibitory property of statins and encourage new studies on this drug for a possible use in therapy, probably in combination with conventional chemotherapy.