Synthesis and Biological Evaluation of Structurally Diverse Benzimidazole Scaffolds as Potential Chemotherapeutic Agents

Abstract

Background and Objective : Drug resistance and adverse effects are immense healthcare challenges in cancer therapy. Benzimidazole ring-based small molecules have been effective anticancer agents in drug development. In an effort to develop novel chemotherapeutics, we synthesized and assessed the anticancer and antibacterial activities of a small library of structurally unique benzimidazoles. Methods : The benzimidazoles were derived from indole, N-alkyl indole, fatty acid, and alpha-amino acid scaffolds providing a panel of diverse structures. The compounds were tested in three different cancer cell lines for cytotoxicity: HepG2 (human hepatocellular carcinoma), HeLa (human cervical carcinoma), and A549 (human lung carcinoma). Mechanism of cell death induced by benzimidazoles was evaluated using fluorescent dye-based apoptosis-necrosis assay, immunoblotting for active caspases, topoisomerase-II activity assay, and cell cycle assay. Results : Cell viability testing revealed that indole- and fatty acid-based benzimidazoles were most potent followed by the amino acid derivatives. Many compounds induced cytotoxicity in a concentration-dependent manner with cellular cytotoxicity (CC50) <20μM in the cell lines tested. Most compounds exhibited cytotoxicity via apoptosis through the intrinsic pathway. Inhibition of topoisomerase activity and cell cycle alterations were not the primary mechanisms of cytotoxicity. In addition, several compounds showed promising activity against S. aureus and S. epidermidis (Minimum Inhibitory Concentration (MIC) of as low as 0.04μmol/mL). Conclusion: The reported benzimidazole derivatives possess promising anticancer and antibacterial properties. Additionally, we discovered apoptosis to be the primary mechanism for cancer cell death induced by the tested benzimidazoles. Our findings suggest that further development of these scaffolds could provide drug leads towards new chemotherapeutics.

An Efficient Chemo‐Selective N‐Alkylation Methodology for the Structure Diversification of Indolylbenzimidazoles

“…[4][5][6] Nitrogen containing heterocyclic compounds, including indole, benzimidazole and indolylbenzimidazoles are an important class of bioactive scaffolds due to their broad spectrum of bioactivity. [7][8][9][10][11][12][13][14][15] Indolylbenzimidazoles are hybrid structures, composed of an indole unit and a benzimidazole motif, and are a key structural component within small molecules developed as chemotherapeutics. [13][14][15] More specifically, N-alkylated indolylbenzimidazole scaffolds with different N-alkylation patterns have been identified as highly effective reversible inhibitors of protein arginine deiminases (PADs).…”

“…[7][8][9][10][11][12][13][14][15] Indolylbenzimidazoles are hybrid structures, composed of an indole unit and a benzimidazole motif, and are a key structural component within small molecules developed as chemotherapeutics. [13][14][15] More specifically, N-alkylated indolylbenzimidazole scaffolds with different N-alkylation patterns have been identified as highly effective reversible inhibitors of protein arginine deiminases (PADs). [15] These enzymes are a family of hydrolases that catalyze the conversion of arginine into citrulline, and have been associated with cancer and various autoimmune diseases.…”

“…[15] Furthermore, N-alkylation of heterocycles, including indolylbenzimidazoles, provides an efficient and direct route to investigate their structure activity relationship (SAR) during medicinal chemistry efforts. [13][14][15][16][17][18] N-alkylation of indoles or benzimidazoles is typically performed under conditions or with reagents that cannot differentiate the reactivity of an indole, benzimidazole or any other reactive functional groups. [13,19] This reactivity profile makes it nearly impossible to chemo-selectively alkylate indolylbenzimidazoles.…”

“…[20][21][22][23] To the best of our knowledge, a direct and simple synthetic method to chemo-selectively alkylate indolylbenzimidazoles has not been reported to date. Due to an increased interest in developing indolylbenzimidazole-based drug leads, [13][14][15] a simple and chemo-selective method to N-alkylate indolylbenzimidazoles would tremendously benefit the scientific community. We hypothesized that the pKa differences between the indole nitrogen (pKa ∼ 21) and the benzimidazole nitrogen (pKa ∼ 16) would enable us to chemo-selectively alkylate these heterocycles.…”

“…We hypothesized that the pKa differences between the indole nitrogen (pKa ∼ 21) and the benzimidazole nitrogen (pKa ∼ 16) would enable us to chemo-selectively alkylate these heterocycles. As part of our continuing interest in benzimidazoles, [14,24] we have developed a simple, and chemo-selective N-alkylation method to modify 2-indolylbenzimidazoles with an excellent substrate scope, and remarkable selectivity profile. To our knowledge, this is the first example of a chemo-selective strategy to access N-alkylated analogs of this heterocyclic scaffold (Scheme 1).…”