Abstract 255: Gross thymic extract induces cell cycle arrest and apoptosis in Ehrlich ascites carcinoma in vivo

Abstract

Abstract Objective. Gross thymic extract (GTE) obtained from pathogen-free pigs is composed of thymosin, thymomodulin, and other peptides. We have previously demonstrated that GTE induces apoptosis in human breast cancer cells in vitro. The present study was undertaken to examine the chemopreventive effect of GTE in mice bearing Ehrlich ascites mammary carcinoma (EAC) and to elucidate the mechanisms underlying its effect. Materials and Methods. Swiss albino mice were inoculated with EAC cells in the thigh to develop solid mass. Oral treatment with GTE (5.45mg/kg body weight) was started either 14 days prior to tumor cell inoculation or 9 days post inoculation. Tumor incidence and growth were monitored for 30 days. Cell cycle progression, apoptosis, and the expression of their related proteins were analyzed by flow cytometry and western blot. Mitochondrial membrane potential (MMP) and natural killer (NK) cell cytotoxicity were examined by flow cytometry. Molecular analysis of DNA fragmentation was analyzed by agarose gel electrophoresis. GTE was provided by YS Nature Company, Tokyo, Japan. Results. Pretreatment of mice with GTE markedly delayed tumor growth and reduced tumor incidence by 38.9% as recorded on day 30. Significant tumor growth inhibition reached 90.5% and 55.0% for pre-inoculation and post-inoculation cases, respectively. GTE treatment prior to tumor inoculation decreased tumor cell proliferation as indicated by marked suppression in the expression of PCNA, Ki-67, and Cyclin D1 in cancer cells with concomitant upregulation of p53 , p21 , and p27 expression relative to the untreated control. This was associated with significant G0/G1 phase arrest of the cell cycle accompanied by induction of apoptosis as indicated by the appearance of a significant sub-G0/G1 peak and confirmed by Annexin V/PI assay and DNA laddering pattern. Additionally, GTE decreased MMP, activated caspase-3, and increased Bax/Bcl-2 ratio by 2.4 fold in neoplastic cells, indicating that GTE induces apoptosis via an intrinsic pathway. Treatment with GTE markedly enhanced NK cell cytotoxicity by 5.8 fold relative to the untreated control. Data also showed the effectiveness of GTE treatment in post-inoculation cases but to a lesser extent than for pre-inoculation. Conclusion. Our data demonstrate that GTE intake results in profound tumor growth inhibition by a mechanism involving cell cycle arrest, apoptosis via a mitochondrial dependent pathway, and modulating the immune system via increased NK cell activity. GTE may represent a new class of adjuvants for the treatment of breast cancer. Citation Format: Nariman K. Badr El-Din, Azza I. Othman, Maggie E. Amer, Mamdooh Ghoneum. Gross thymic extract induces cell cycle arrest and apoptosis in Ehrlich ascites carcinoma in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 255.