Abstract 983: Effect of optically active Englerin A on global metabolism of A498 renal cell cancer: Impact on carnitine metabolism
Authors: Harsch Kelley , Roth Jordan , Koepf Britney , Wang Xinning , Yin Lihong , Heston Warren D.W. 
Published: June 2012

Introduction and Objectives: The Natural Products Branch of the National Cancer Institute examined extracts from a number of plants from South Africa. One extract in particularly, from the Phyllanthus engleri plant exhibited selective toxicity towards renal cancer cells in the NCI panel of 60 cell lines. The active ingredient from the plant extract has been recently isolated and identified as Englerin A (Beutler, J., et al). Renal cancers are notorious for their resistance to various therapies. Therefore, the potential for any agent that has selective anti-tumor activity is attractive. In additions, renal cancers are associated with a variety of metabolic changes, regardless of the tumors VHL status (wild type vs. mutant). Using the synthetic, optically active compound to Englerin A, we have examined its impact on global metabolism in the sensitive human renal carcinoma cell line A498.

Methods: Using the synthetic material of Englerin A (Applichem Co., Germany) and A498 renal cancer cell line (ATCC, Baltimore MD), we tested for cytotoxicity and growth inhibition using the CellTiter-Glo® assay (Promega). Cell Titer-Glo measures the number of viable cells in culture based on quantitation of the ATP present, an indicator of metabolically active cells. Cell cycle was determined with the aid of flow cytometry following propidium iodide staining. Global metabolism was determined by GC and LC/mass SPEC in the A498 cells receiving treatment with Englerin A (30nM and 150nM) at 0, 2, 4, 8 and 24 hour time points (Metabolon, Durham, N.C.). Statistical analysis of the 2,000 standard metabolites (and unknown metabolites) is compared between treated/non-treated cells, at the various time periods, utilizing the commercial package JMP (SAS). Following log transformation and samples in which the metabolite was detected within at least two/thirds of the specimens will be included in the analysis.

Results: In the A498 cells, we observed an IC50 of 3nM, comparable to reported studies for Englerin A. Flow cytometry data revealed a delayed cell cycle progression through S phase. In the metabolic studies, the most sensitive aspect of the Englerin A toxin was the alteration of carnitine metabolism.

Conclusion: Englerin A is a newly isolated molecule that has selective toxicity towards renal cancer cell lines, but also inhibits other types of tumor lines and cancers. Renal cell cancers are notorious for their insensitivity to treatment with a variety of therapies. The low dose of Englerin A required producing selective toxicity towards renal cell cancers, suggests that this newly identified toxin is likely to be impacting a novel signaling pathway. Identification of that signaling pathway may provide additional means for targeted tumor therapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 983. doi:10.1158/1538-7445.AM2011-983