Abstract 2250: Cytototoxicity and mode of action of extract from of two lichens, Tuckermannopsis ciliaria (Ach.) Gyelnik and Xanthoparmelia chlorochroa (Tuck.) Hale against Burkitt's Lymphoma (Raji) cells and the Human colon cancer (HT-29) cell line.
Authors: Shrestha Gajendra , El-Naggar Atif M. , Derenthal Sean C. , Boswell Michael R. , Weagel Evita , St. Clair Larry L. , Robison Richard , O'Neill Kim L. 
Published: August 2014

Natural products from various plants, microorganisms, fungi etc. have provided considerable value to the pharmaceutical industry over the past half century. But there still remains a vast potential reservoir of possible useful therapeutics, yet to be identifed. Among them, lichens (symbiotic associations between a fungus and an alga and/or a cyanobacterium), which produce more than a 1000 secondary chemicals. The United States is home to a diverse assemblage of lichen species. Lichens play many biological roles; however, their full potential as a source of anticancer drugs has been largely unexplored. To examine the possible anticancer role of several lichen species, we assessed the cytotoxic activity of 17 species collected from various parts of the US. Secondary compounds of these lichens were extracted with acetone and screened against Burkitt's Lymphoma cells (Raji) and the human colon cancer cell line (HT-29). Based on the cytotoxcity of these lichen extracts we selected two species Tuckermannopsis ciliaris and Xanthoparmelia chlorochroa for further testing. IC50 values for these two species showed particular promise - 28.8 and 28.6 μg/ml for Raji cells and 60 and 40 μg/ml for HT-29 cells respectively. The viability and cell growth of both cell lines was significantly reduced by the extracts from these two lichens but these extracts did not affect the viability and growth of normal lymphocytes. We performed morphological detection of apoptosis using Acridine orange and Propidium Iodide. Extracts from both lichens were found to induce apoptosis in both cancer cell lines when treated with the concentrations equivalent to the IC50. Cell proliferation of Raji and HT-29 cells, as measured by 3H-thymidine incorporation, was significantly reduced in treated cells (P &lt;0.05) over 24 hours as compared with controls. To further investigate apoptosis we measured DNA fragmentation using gel electrophoresis. Within 24 hours of treatment, there was partial DNA degradation. Using flow cytometry, it was discovered that extracts from both lichens arrested cell-cycle progression in S phase. Using RT-PCR, it was found that the p53 gene was up-regulated in the treated cells during G1 phase while the DNA repair enzyme Thymidine kinase 1 (TK1) was down regulated.

In conclusion, extracts from T. ciliaris and X. chlorochroa were both cytotoxic and induced apoptosis in cancer cells but not in normal cells. Hence extracts from these two lichens could hold potential as a non-toxic anticancer therapy. However, more research is required to further elucidate the molecular mechanisms behind these preliminary findings.

Citation Format: Gajendra Shrestha, Atif M. El-Naggar, Sean C. Derenthal, Michael R. Boswell, Evita Weagel, Larry L. St. Clair, Richard Robison, Kim L. O'Neill. Cytototoxicity and mode of action of extract from of two lichens, Tuckermannopsis ciliaria (Ach.) Gyelnik and Xanthoparmelia chlorochroa (Tuck.) Hale against Burkitt's Lymphoma (Raji) cells and the Human colon cancer (HT-29) cell line. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2250. doi:10.1158/1538-7445.AM2013-2250