Nitrogen-containing heterocyclic rings are common structural components of marketed drugs. Among these heterocycles, imidazole/fused imidazole rings are present in a wide range of bioactive compounds. The unique properties of such structures, including high polarity and the ability to participate in hydrogen bonding and coordination chemistry, allow them to interact with a wide range of biomolecules, and imidazole-/fused imidazole-containing compounds are reported to have a broad spectrum of biological activities. This review summarizes recent reports of imidazole/fused imidazole derivatives as anticancer agents appearing in the peer-reviewed literature from 2018 through 2020. Such molecules have been shown to modulate various targets, including microtubules, tyrosine and serine-threonine kinases, histone deacetylases, p53-Murine Double Minute 2 (MDM2) protein, poly (ADP-ribose) polymerase (PARP), G-quadraplexes, and other targets. Imidazole-containing compounds that display anticancer activity by unknown/undefined mechanisms are also described, as well as key features of structure-activity relationships. This review is intended to provide an overview of recent advances in imidazole-based anticancer drug discovery and development, as well as inspire the design and synthesis of new anticancer molecules.

Analogs of the antimitotic herbicide oryzalin (3,5-dinitro-N4,N4-di-n-propylsulfanilamide) were recently prepared that were more potent in vitro than the parent compound against the kinetoplastid parasite Leishmania donovani (Bioorg Med Chem Lett 12:2395-2398, 2002). In the present work, we show that the most active molecule in the group, N1-phenyl-3,5-dinitro-N4,N4-di-n-propylsulfanilamide (GB-II-5), is a potent, selective antimitotic agent against kinetoplastid parasites. GB-II-5 possesses IC₅₀ values of 0.41 and 0.73 μM in vitro against two strains of the related parasite Trypanosoma brucei but is much less toxic to J774 murine macrophages and PC3 prostate cancer cells, exhibiting IC₅₀ values of 29 and 35 μM against these lines, respectively. Selectivity is also observed for GB-II-5 with purified leishmanial and mammalian tubulin. The assembly of 15 μM leishmanial tubulin is completely inhibited by 10 μM GB-II-5, whereas 40 μM GB-II-5 inhibits the assembly of 15 μM porcine brain tubulin by only 17%. In cultured L. donovani and T. brucei, treatment with 5 and 0.5 μM GB-II-5, respectively, causes a striking increase in the fraction of G₂M cells compared with control. Given the potency and selectivity of this agent against kinetoplastid tubulin, GB-II-5 emerges as an exciting new antitrypanosomal and antileishmanial lead compound.

Aromatic dicationic molecules possess impressive activity against a broad spectrum of microbial pathogens, including Pneumocystis carinii , Cryptosporidium parvum , and Candida albicans . In this work, 58 aromatic cations were examined for inhibitory activity against axenic amastigote-like Leishmania donovani parasites. In general, the most potent of the compounds were substituted diphenyl furan and thiophene dications. 2,5-Bis-(4-amidinophenyl)thiophene was the most active compound. This agent displayed a 50% inhibitory concentration (IC ₅₀ ) of 0.42 ± 0.08 μM against L. donovani and an in vitro antileishmanial potency 6.2-fold greater than that of the clinical antileishmanial dication pentamidine and was 155-fold more toxic to the parasites than to a mouse macrophage cell line. 2,4-Bis-(4-amidinopheny)furan was twice as active as pentamidine (IC ₅₀ , 1.30 ± 0.21 μM), while 2,5-bis-(4-amidinopheny)furan and pentamidine were essentially equipotent in our in vitro antileishmanial assay. Carbazoles, dibenzofurans, dibenzothiophenes, and benzimidazoles containing amidine or substituted amidine groups were generally less active than the diphenyl furans and thiophenes. In all cases, aromatic dications possessing strong antileishmanial activity were severalfold more toxic to the parasites than to a cultured mouse macrophage cell line. These structure-activity relationships demonstrate the potent antileishmanial activity of several aromatic dications and provide valuable information for the future design and synthesis of more potent antiparasitic agents.

Since tubulin is a known anticancer and anthelmintic drug target, the investigation of protozoal tubulin could lead to the development of new antiparasitic drugs. This review outlines the current state of knowledge concerning drug-mammalian tubulin interactions, the effects of antimicrotubule agents on parasites and parasite tubulin, and our current hypotheses regarding the development of selective ligands for protozoal tubulin as antiparasitic drug candidates.