DESIGN, SYNTHESIS AND BIOLOGICAL EVALUATION OF ALKYLTHIO- AND ALKYLSELENO-IMIDOCARBAMATES AS ANTITUMOR AGENTS

Resumo

The public perception of selenium has changed significantly over the last decades. Originally mainly known for its high toxicity, it was later recognized as an essential trace element and is now (despite its narrow therapeutic window) almost being marketed as a lifestyle drug. Indeed, some clinical and preclinical studies suggest that selenium supplementation may be beneficial in a large number of clinical conditions. However, its mode of action is unresolved in most of these cases. At present, our main focus in the laboratory is the synthesis and evaluation of the cytotoxic activity of selenium-containing compounds. With the aim of develop new anticancer drugs and clarify its mechanisms of action and taking into account the results obtained in previous studies, twenty new derivatives that contain this trace element have been synthesized. All of them have been screened for their cytotoxic and antiproliferative activities against a panel of five human tumor cell lines: breast adenocarcinoma (MCF-7), colon carcinoma (HT-29), lymphocytic leukemia (K-562), hepatocarcinoma (Hep-G2) and prostate cancer (PC-3) as well as the non-malignant mammary gland cell line MCF-10A. These cell lines represent common cancer tumor types. Regardless of the type of tumor cell, several common features have been observed in the antiproliferative activity of the compounds. Among the cancer cell lines tested, MCF-7 and HT-29 are the most susceptible ones, with GI50 values in the nanomolar range. Comparison of the results with the cytotoxicity values for the standard drugs show that of the compounds had GI50 values lower than those found for doxorubicin, nine lower than those obtained for etoposide and lower than those observed for taxol in MCF-7 cells. The biological activities of the designed compounds confirm our hypothesis that molecular symmetry and the presence of a selenomethyl moiety is a valid approach to obtain potent new antitumor agents. A wide variety of biological assays have also been performed in order to elucidate a possible mechanism of action of some of the derivatives. These assays include in vitro studies, as the determination of the effects cell cycle distribution, apoptosis induction, protein kinases inhibitory activity, effects on selenoprotein expression, effects on cancer stem cells (CSCs) viability and maintennace; and in vivo studies, with the aim of finding new active drugs for cancer treatment. In summary, this study validates our initial strategy of designing organoselenium compounds with particular chemical characteristics that may therefore confer antitumor activity. The strategy of narrowing down a large number of potentially active compounds based on their biological properties have led to the identification of one organoselenium compound as the most active antitumor compound. This novel multikinase drug affects strongly PI3K/AKT/mTOR and MAPK pathways in human solid tumors, which probably would prevent the negative feedbackloops secondary to mTOR inhibition. We have demonstrated that it is an inducer of G0/G1 arrest, accompanied by an induction of both autophagy and apoptosis. Moreover, the lead compound of this series is one of the few identified compounds that targets the number, size and self-renewal capacity of CSCs grown in spheres and alters expression of ALDH, ABCG2, CD44 and CD133. This compound also exhibits promising single-agent antitumor activity in vivo in a molecularly relevant human prostate cancer model, without associated toxicity. Although the precise mechanism underlying the antitumor effect of this compound is not yet fully understood, our preclinical findings suggest that it could be a valuable compound in the treatment of patients displaying aberrant activation of PI3K/AKT/mTOR and MAPK signaling cascades.