SYNTHESIS AND EVALUATION OF INDOLEAMINES AND INDOLEAMIDES AS ANTI-CANCER AGENTS TARGETING ISOPRENYLCYSTEINE CARBOXYL METHYLTRANSFERASE (ICMT)

Abstract

The enzyme isoprenylcysteine carboxyl methyltransferase (Icmt) plays an important role in the post-translational modification of proteins involved in the regulation of cell growth and oncogenesis. Biological studies on the 1st selective small molecule inhibitor of Icmt cysmethynil has provided convincing evidence that targeting Icmt selectively induces cancer cell death. The consequences of Icmt inhibition strongly support the potential of the enzyme as a novel therapeutic target for oncogenesis. In this thesis, structural modifications of cysmethynil were undertaken with the aim of identifying compounds that had favorable physicochemical profiles, were potent Icmt inhibitors and exhibited in vivo efficacy in xenograft bearing animals. It was hypothesized that previously identified indoleamines with Icmt inhibitory and antiproliferative activities were appropriate starting ¿leads¿ to achieve these objectives. Fifty nine novel compounds were synthesized and evaluated for antiproliferative activity on a human breast cancer cell line (MDA MB 231). Those with promising activities were shortlisted for evaluation of Icmt inhibitory activity. 5-(3-Diethylaminomethyl-1-octyl-1H-indol-5-yl)-pyrimidin-2-ylamine (4-12) emerged as a promising candidate with nanomolar IC50 for inhibition of Icmt, and low micromolar antiproliferative activities on a panel of malignant cells. The desirable activity profile of 4-12 highlighted the critical role of position 5 on the indoleamine scaffold in modulating activity. The antiproliferative activity of 4-12 arose from its ability to disrupt the transition of prostrate PC3 cells from G1 to G2/M phase in the cell cycle. 4-12 prevented colony formation of PC3 cells, suggesting that it curtailed reproductive capacity of these cells. Interestingly, it did not initiate apoptotic cell death but demonstrated the induction of autophagy in several malignant cell lines. There was also evidence that 4-12 restricted cell migration. These findings showed that 4-12 affected several processes that are critical in carcinogenesis, namely antiproliferation, disruption of cell cycle, induction of autophagy and cell migration. In spite of the diversity of these phenomena, the effects of 4-12 were observed over a narrow and recurring concentration range (1-5 µM). Compared to cysmethynil which also affected these processes in a qualitatively similar manner, 4-12 was more potent by at least a fold magnitude. The efficacy of 4-12 was demonstrated in vivo on xenografts induced in immunocompromised mice. Animals treated with 15mg/kg and 30 mg/kg of 4-12 demonstrated statistically significant reduction in tumor volumes with no overt weight loss or toxicity. A preliminary pharmacokinetic assessment in mice at the same dose range showed that 4-12 was widely distributed into tissues, rapidly cleared from the circulation and had a moderately short half-life (1.5 h). Taken together, the results presented in this thesis have contributed to a better understanding of functionalized indoleamines as Icmt inhibitors and the mechanistic basis of their antiproliferative activity. It has also highlighted the potential of one candidate compound (4-12) as an anticancer agent.