A comprehensive overview of β-carbolines and its derivatives as anticancer agents

β-Carboline alkaloids are a family of natural and synthetic products with structural diversity and outstanding antitumor activities. This review summarizes research developments of β-carboline and its derivatives as anticancer agents, which focused on both natural and synthetic monomers as well as dimers. In addition, the structure-activity relationship (SAR) analysis of β-carboline monomers and dimers are summarized and mechanism of action of β-carboline and its derivatives are also presented. A few possible research directions, suggestions and clues for future work on the development of novel β-carboline-based anticancer agents with improved expected activities and lesser toxicity are also provided.

Molecular hybrid design, synthesis, in vitro and in vivo anticancer evaluation, and mechanism of action of N-acylhydrazone linked, heterobivalent β-carbolines

A series of N-acylhydrazone-linked, heterobivalent β-carboline derivatives was designed and synthesized from l-tryptophan in a nine-step reaction sequence. The effort resulted in the heterobivalent β-carbolines 10a-t in good yields. The target compounds were characterized by ¹H NMR, ¹³C NMR and high-resolution mass spectrometry (HRMS). The in vitro cytotoxic activity of the synthesized compounds was evaluated against normal EA.HY926 cells and five cancer cell lines: LLC (Lewis lung carcinoma), BGC-823 (gastric carcinoma), CT-26 (murine colon carcinoma), Bel-7402 (liver carcinoma), and MCF-7 (breast carcinoma). Compound 10e, with an IC₅₀ value of 2.41 μM against EA.HY926 cells, was the most potent inhibitor. It showed cytotoxicity against all five cancer cell lines of different origin - murine and human, with IC₅₀ values ranging from 4.2 ± 0.7 to 18.5 ± 3.1 μM. A study of structure-activity relationships indicated that the influence on cytotoxic activities of the substituent in the R₉'-position followed the tendency, 2,3,4,5,6-perfluorophenylmethyl > 4-fluorobenzyl > 3-phenylpropyl group. The antitumor efficacies of the selected compounds were also evaluated in mice. Compound 10e exhibited potent antitumor activity, with tumor inhibition of more than 40% for Sarcoma 180 and 36.7% for Lewis lung cancer. Furthermore, the pharmacological mechanisms showed that compound 10e has a certain impairment in the motility of LLC cells, which suggests the anti-metastatic potential. And compound 10e inhibited angiogenesis in chicken chorioallantoic membrane assay, and the anti-angiogenetic potency was more potent than the reference drug combretastatin A4-phosphate (CA4P) at a concentration 50 μM.

Bivalent AMPA receptor positive allosteric modulators of the bis(pyrimidine) series

The first example of a novel class of AMPA receptor positive allosteric modulators of the bis(pyrimidine) series having a hydroquinone linker has been obtained and showed a potency to increase kainate-induced currents at subnanomolar concentrations.

Design, Synthesis, and Biological Evaluation of Novel N-Acylhydrazone Bond Linked Heterobivalent β-Carbolines as Potential Anticancer Agents

Utilizing a pharmacophore hybridization approach, we have designed and synthesized a novel series of 28 new heterobivalent β-carbolines. The in vitro cytotoxic potential of each compound was evaluated against the five cancer cell lines (LLC, BGC-823, CT-26, Bel-7402, and MCF-7) of different origin—murine and human, with the aim of determining the potency and selectivity of the compounds. Compound 8z showed antitumor activities with half-maximal inhibitory concentration (IC₅₀) values of 9.9 ± 0.9, 8.6 ± 1.4, 6.2 ± 2.5, 9.9 ± 0.5, and 5.7 ± 1.2 µM against the tested five cancer cell lines. Moreover, the effect of compound 8z on the angiogenesis process was investigated using a chicken chorioallantoic membrane (CAM) in vivo model. At a concentration of 5 μM, compound 8z showed a positive effect on angiogenesis. The results of this study contribute to the further elucidation of the biological regulatory role of heterobivalent β-carbolines and provide helpful information on the development of vascular targeting antitumor drugs.

Synthesis and biological evaluation of novel N9-heterobivalent β-carbolines as angiogenesis inhibitors

A series of novel N⁹-heterobivalent β-carbolines has been synthesized. All the novel compounds were tested for their anticancer activity against six tumour cell lines in vitro. Among these molecules, compounds 5b, and 5w exhibited strong cytotoxic activities with IC₅₀ value of lower than 20 μM. Acute toxicities and antitumor efficacies of the selected compounds in mice were also evaluated, compounds 5b and 5w exhibited that tumour inhibition rate of over 40% in the Sarcoma 180 and Lewis lung cancer animal models. Preliminary structure-activity relationships (SARs) analysis indicated that: (1) C¹-methylation and C⁷-methoxylation were favorable for increased activities; (2) 3-Pyridyl or 2-thienyl group substituent into position-1 of the β-carboline core, and the aryl substituent into another β-carboline ring might be detrimental to cytotoxic effects of this class compounds. Investigation of the preliminary mechanism of action demonstrated that compound 5b had obvious angiogenesis inhibitory effects in the chicken chorioallantoic membrane (CAM) assay.

Synthesis and structure-activity relationships of asymmetric dimeric β-carboline derivatives as potential antitumor agents

A series of newly asymmetric dimeric β-carbolines with a spacer of 4-6 methylene units between the indole nitrogen and the harmine oxygen were synthesized. Structures of all the novel synthesized compounds were confirmed by their spectral and analytical studies. All of the synthesized compounds were screened for their in vitro cytotoxic activity against nine cancer cell lines. The results revealed that compounds 7c, 7o and 7s exhibited the highest cytotoxic activities with IC₅₀ values of less than 20 μM against the tumor cell lines tested. Acute toxicities and antitumor efficacies of the selected compounds in mice were also evaluated, and compound 7o exhibited potent antitumor activities with the tumor inhibition rate of over 40%. The wound healing assay displayed a specific impairment in the motility of the HT-29 cells, which suggested the anti-metastatic potential of compound 7o. Moreover, compound 7o had obvious angiogenesis inhibitory effects in the chicken chorioallantoic membrane (CAM) assay. Preliminary structure-activity relationship (SAR) analysis indicated that: (1) 3-phenylpropyl substituent at the N⁹-position of the indole ring was the most suitable group giving rise to potent cytotoxic agents; (2) the spacer length affected the antitumor potencies, and four methylene units were more favorable.