isocryptolepine and Malaria

Indoloquinoline (IQ) is an important class of naturally occurring antimalarial alkaloids, mainly represented by cryptolepine, isocryptolepine, and neocryptolepine. The IQ structural framework consists of four isomeric ring systems differing via the linkage of indole with quinoline as [3,2-b], [3,2-c], [2,3-c], and [2,3-b]. Structurally, IQs are planar and thus they bind strongly to the DNA which largely contributes to their biological properties. The structural rigidity and associated nonspecific cellular toxicity is a key shortcoming of the IQ structural framework for preclinical development. Thus, the lead optimization efforts were aimed at improving the therapeutic window and ADME properties of IQs. The structural modifications mainly involved attaching the basic aminoalkyl chains that positively modulates the vital physicochemical and topological parameters, thereby improves biological activity. Our analysis has found that the aminoalkylation consistently improved the selectivity index and provided acceptable in-vivo antimalarial/anticancer activity. Herein, we critically review the role of aminoalkylation in deciphering the antimalarial and cytotoxic activity of IQs.

Topics: Alkaloids; Antimalarials; Antineoplastic Agents; Cell Proliferation; Indoles; Malaria; Molecular Structure; Neoplasms; Quinolines

Drug-resistant strains of malaria parasites have emerged for most of antimalarial medications. A new chemotherapeutic compound is needed for malarial therapy. Antimalarial activity against both drug-sensitive and drug-resistant P. falciparum has been reported for an isocryptolepine derivative, 8-bromo-2-fluoro-5-methyl-5H-indolo[3,2-c]quinoline (ICL-M), which also showed less toxicity to human cells. ICL-M has indoloquinoline as a core structure and its mode of action remains unclear. Here, we explored the mechanisms of ICL-M in P. falciparum by assessing the stage-specific activity, time-dependent effect, a proteomic analysis and morphology. Since human topo II activity inhibition has been reported as a function of isocryptolepine derivatives, malarial topo II activity inhibition of ICL-M was also examined in this study. The ICL-M exhibited antimalarial activity against both the ring and trophozoite stages of P. falciparum. Our proteomics analysis revealed that a total of 112 P. falciparum proteins were differentially expressed after ICL-M exposure; among these, 58 and 54 proteins were upregulated and downregulated, respectively. Proteins localized in the food vacuole, nucleus, and cytoplasm showed quantitative alterations after ICL-M treatment. A bioinformatic analysis revealed that pathways associated with ribosomes, proteasomes, metabolic pathways, amino acid biosynthesis, oxidative phosphorylation, and carbon metabolism were significantly different in P. falciparum treated with ICL-M. Moreover, a loss of ribosomes was clearly observed by transmission electron microscopy in the ICL-M-treated P. falciparum. This finding is in agreement with the proteomics data, which revealed downregulated levels of ribosomal proteins following ICL-M treatment. Our results provide important information about the mechanisms by which ICL-M affects the malaria parasite, which may facilitate the drug development of isocryptolepine derivatives.

Topics: Antimalarials; DNA Topoisomerases, Type II; Gene Expression Regulation; Humans; Indole Alkaloids; Malaria; Metabolic Networks and Pathways; Plasmodium falciparum; Proteomics; Protozoan Proteins; Quinolines; Ribosomes