Antitumor screening of Pterodon pubescens terpenic fraction indicates high sensitivity for lymphocytic leukemia cells

Cancer is the second leading cause of human mortality worldwide. Therefore, the search for new drugs or alternative therapy strategies has been required. Anticancer agents have been developed from plants since the 1950s and natural products still represent an important source of new and promising bioactive molecules. This work describes the cytotoxic effects of SF5 on tumor cells of high prevalence in the world and investigated some mechanisms of its antitumor action. The antitumor screening was performed with human lung carcinoma (A549), human breast (MCF-7) and prostate (PC-3) adenocarcinoma and chronic myeloid and acute lymphocytic leukemia cell lines. The acute lymphocytic leukemia Jurkat cells presented high sensitivity to the cytotoxic effects of SF5 (inhibition of 85-90%), compared with either the chronic myeloid leukemia K562 or solid tumor cell lines (lung, breast and prostate). SF5 arrested the cell cycle in G1 phase, which may be related with the observed downregulation of mRNA expression of c-Myc transcription factor at 24 h and 36 h. SF5 treatment induced cytochrome c release from mitochondria to cytosol, leading the Jurkat cells into apoptosis, which was evidenced by the internucleosomal fragmented DNA and increased number of annexin V-FITC positive cells. The SF5 showed high cytotoxicity for lymphocytic leukemia cells and low or none for solid tumor cells, without toxicity for peripheral mononuclear cells of healthy humans. SF5 altered gene expression, arrested the cell cycle and induced apoptosis via the mitochondrial pathway, similar to traditional antineoplastic chemotherapeutic drugs.