Ewing\#8217;s sarcoma is a childhood malignancy that occurs in bones and soft tissues. Current therapies for Ewing\#8217;s sarcoma are mostly ineffective and thus new therapies are urgently needed. We examined the efficacy of the retinoid N-(4-hydroxyphenyl) retinamide (4-HPR) and the flavonoid genistein (GST) alone and in combination for controlling the growth of Ewing\#8217;s sarcoma SK-N-MC cells in culture as well as in xenografts in athymic nude mice. A strategy involving treatment with 0.5 µM 4-HPR for 3 days and then 100 µM GST for 24 h produced significant amounts of apoptosis in SK-N-MC cells. Flow cytometric analyses showed accumulation of significant amount of apoptotic cells following combination therapy. Combination of 4-HPR and GST activated extrinsic pathway of apoptosis as Western blot analyses showed activation of caspase-8 and cleavage of Bid to tBid. Also, combination therapy activated intrinsic pathway increasing Bax:Bcl-2 ratio, calpain and caspase-3 expression, and their activities that cleaved 270 kD \#945;-spectrin at specific sites to generate 145 kD spectrin break down products (SBDP) and 120 kD SBDP, respectively. The efficacy of this combination of 4-HPR and GNT was subsequently evaluated in the SK-N-MC xenografts in athymic nude mice. For xenotransplantation of Ewing\#8217;s sarcoma, 6-week old nude mice (about 20-22 g each) were subcutaneously (sc) injected with a (1:1) mixture of exponentially growing SK-N-MC cells (6x106 cells/mouse) and Matrigel and allowed to develop the tumors. Animals with the 3-week old xenografts were randomly assigned to 4 different groups: control, 4-HPR alone, GST alone, and 4-HPR plus GST. Animals in control group did not receive any therapy. Each animal in other group received intraperitoneal (ip) injection of a daily dose of 4-HPR (20 µg/kg/day), GST (1 mg/kg/day), or 4-HPR (20 µg/kg/day) plus 4 h later GST (1 mg/kg/day) for 8 days before tumors from all groups were collected for evaluation of therapeutic outcomes. The combination of 4-HPR plus GST showed the highest efficacy in regression of the tumor volume. Histopathological examination of tumor sections following H&E staining showed that tumors of control group maintained characteristic growth of Ewing\#8217;s sarcoma, treatment with 4-HPR alone caused differentiation of tumor cells, GST alone induced apoptosis, and treatment with 4-HPR plus GST produced significant amount of apoptosis in the tumors. In situ TUNEL and double immunofluorescent labelings of tumor sections demonstrated occurrence of apoptosis with upregulation of calpain, caspase-12, caspase-3, and also apoptosis-inducing factor (AIF) that could contribute to caspase-independent apoptosis. Results showed that treatment with combination of 4-HPR and GST could be highly effective for controlling growth of Ewing\#8217;s sarcoma. This work was supported in part by the R01 grants (NS-57811 and CA-91460).

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4595.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO