Synthesis and evaluation of 2-carboxy indole derivatives as potent and selective anti-leukemic agents

Despite the success achieved in the treatment of acute lymphoblastic leukemia (ALL), the search for new drugs featuring selectivity against leukemia cells and effectiveness to prevent relapsed ALL is still highly desirable. Here, we described the synthesis of several novel 3-substituted and 3,6-disubstituted-2-carboalkoxy indoles followed by the elucidation of their mechanism of action and in vivo anti-leukemia efficacy. The synthesis of 3-substituted-2-carboalkoxy indoles relied on two Heck arylations of methyl acrylate and methyl cinnamates respectively, to generate β,β-disubstituted acrylates followed by an efficient Cadogan-Sundberg reaction of these latter intermediates. The method developed led to the synthesis of twenty-one novel functionalized indoles. Of these, indole 20 showed selective cytotoxicity against leukemia cells at the nanomolar scale, and, therefore, it was selected for the investigation of its mechanism of action. Indole 20 was found to target tubulin leading to G2/M cell cycle arrest, DNA damage and apoptosis. Indole 20 decreased β-tubulin protein in leukemia cells in a time-dependent manner and induced depolymerization of the microtubule network in Hela cells, thus fully characterizing its microtubule destabilizer activity. The connectivity map analysis of HL60 promyelocytic leukemia cells treated with indole 20 revealed a transcriptional profile similar to that of cells treated with prostaglandins, apparently due to the induction of cellular differentiation as addressed by the expression of CD11 and CD14 markers. Finally, indole 20 given intraperitoneally, at 10 mg/kg, 5x/week significantly prolonged the overall survival of NOD/SCID mice transplanted with RS4; 11 B-ALL cells.