Abstract #4683: Dendrogenin A, a promising therapy for metastatic melanoma, involving the secretion of exosomes, enriched in HSP70 and tyrosinase, and immunogenic cell death.

Malignant melanoma is the deadliest form of skin cancer. Treatment options include the surgical resection of metastases, therapy with dacarbazine or immunotherapy, however, the response rates of these treatments are weak (around 15-20 %). In order to develop new compounds with anti-melanoma activities, we studied the anti-tumor activity of a new aminosterol, Dendrogenin A (DDA), against B16F10, a very aggressive metastatic melanoma. We observed that DDA enhanced the secretion of exosomes from B16F10 cells in a concentration-dependent manner and for concentrations (10 nM to 1 µM) that induced an increase in cells in the G0/G1 phase of the cycle and characteristics of melanoma cell differentiation. Exosomes secreted from cells treated by DDA were characterized as bearing specific exosomal markers and particularly enriched in HSP70 and tyrosinase. At higher concentrations, we characterized that DDA induced apoptotic cell death associated with an increase in cell surface exposure of calreticulin, a key molecular determinant for immunogenic cancer cell death. Since DDA might activated the immune system by its cellular effects, we tested the anti-tumor effect of DDA against B16F10 tumors implanted on immunocompetente and athymic mice. After 4 weeks of treatment with low doses of DDA (sc, 0.5 µmole/Kg), mean DDA-treated tumor volumes were reduced by 90 %, while dacarbazine (57 µmole/Kg) had slight influence on tumor growth. At day 60, the survival of mice treated with DDA was 40 %, while it was null for the vehicle or dacarbazine-treated groups. In contrast, no tumor growth control was observed in athymic mice treated with DDA, suggesting a T cell-mediated immune response. To study the effect of DDA on metastases, B16F10 cells were injected into the tail vein of C57/BL6 mice. After two weeks of treatment with DDA (ip, 0.5 µmole/Kg), the number of lung metastasis was 75 % lower in animal treated with DDA than in the control group. To explore whether exosomes secreted by DDA treatment may contribute to the anti-tumor effect of DDA, exosomes from cells treated with DDA or the vehicle were collected, purified and injected intradermally into the flank of mice while B16F10 cells were injected subcutaneously into the opposite flank. A single injection of exosomes from cells treated with 1 µM DDA reduced significantly the growth of tumors and increased the survival of mice while exosomes from vehicle-treated cells did not display any anti-tumor activity. In conclusion, DDA displays an antitumor and antimetastatic activity against B16F10 melanoma and extends animal survival via an original mechanism involving secretion of exosomes particularly enriched in tyrosinase and HSP70. Together, these data indicate that DDA is a promising therapy against metastatic melanoma.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4683.