Novel indoloquinoline alkaloid glycosides from Cryptolepis sanguinolenta (Lindl.) Schltr

To explore the phytochemistry of the African ethnomedicinal plant Cryptolepis sanguinolenta (Lindl.) Schltr. (Apocynaceae) for rare indoloquinoline alkaloids, two novel indoloquinoline alkaloid glycosides, namely Cryptospirosanguine A (1) and B (2), were isolated from an ethanolic extract of the root. Their structures were elucidated based on spectral evidence. Furthermore, two known terpenoids were isolated from this plant for the first time.

Indoloquinoline-Mediated Targeted Downregulation of KRAS through Selective Stabilization of the Mid-Promoter G-Quadruplex Structure

KRAS is a well-validated anti-cancer therapeutic target, whose transcriptional downregulation has been demonstrated to be lethal to tumor cells with aberrant KRAS signaling. G-quadruplexes (G4s) are non-canonical nucleic acid structures that mediate central dogmatic events, such as DNA repair, telomere elongation, transcription and splicing events. G4s are attractive drug targets, as they are more globular than B-DNA, enabling more selective gene interactions. Moreover, their genomic prevalence is increased in oncogenic promoters, their formation is increased in human cancers, and they can be modulated with small molecules or targeted nucleic acids. The putative formation of multiple G4s has been described in the literature, but compounds with selectivity among these structures have not yet been able to distinguish between the biological contribution of the predominant structures. Using cell free screening techniques, synthesis of novel indoloquinoline compounds and cellular models of KRAS-dependent cancer cells, we describe compounds that choose between KRAS promoter G4_near and G4_mid, correlate compound cytotoxic activity with KRAS regulation, and highlight G4_mid as the lead molecular non-canonical structure for further targeting efforts.

A Label-Free Cellular Proteomics Approach to Decipher the Antifungal Action of DiMIQ, a Potent Indolo[2,3-b]Quinoline Agent, against Candida albicans Biofilms

Candida albicans forms extremely drug-resistant biofilms, which present a serious threat to public health globally. Biofilm-based infections are difficult to treat due to the lack of efficient antifungal therapeutics, resulting in an urgent demand for the development of novel antibiofilm strategies. In this study, the antibiofilm activity of DiMIQ (5,11-dimethyl-5H-indolo[2,3-b]quinoline) was evaluated against C. albicans biofilms. DiMIQ is a synthetic derivative of indoquinoline alkaloid neocryptolepine isolated from a medicinal African plant, Cryptolepis sanguinolenta. Antifungal activity of DiMIQ was determined using the XTT assay, followed by cell wall and extracellular matrix profiling and cellular proteomes. Here, we demonstrated that DiMIQ inhibited C. albicans biofilm formation and altered fungal cell walls and the extracellular matrix. Cellular proteomics revealed inhibitory action against numerous translation-involved ribosomal proteins, enzymes involved in general energy producing processes and select amino acid metabolic pathways including alanine, aspartate, glutamate, valine, leucine and isoleucine. DiMIQ also stimulated pathways of cellular oxidation, metabolism of carbohydrates, amino acids (glycine, serine, threonine, arginine, phenylalanine, tyrosine, tryptophan) and nucleic acids (aminoacyl-tRNA biosynthesis, RNA transport, nucleotide metabolism). Our findings suggest that DiMIQ inhibits C. albicans biofilms by arresting translation and multidirectional pathway reshaping of cellular metabolism. Overall, this agent may provide a potent alternative to treating biofilm-associated Candida infections.

Oncogene Expression Modulation in Cancer Cell Lines by DNA G-Quadruplex-Interactive Small Molecules

Nucleic acids are prone to structural polymorphism and a number of structures may be formed in addition to the well-known DNA double helix. Among these is a family of nucleic acid four-stranded structures known as G-quadruplexes (G4). These quadruplex structures can be formed by sequences containing repetitive guanine-rich tracks and the analysis of Non-B-DNA database indicated an enrichment of these sequences in genomic regions controlling cellular proliferation, such as for example in the promoter regions of c- MYC, k-RAS, c-KIT, HSP90 and VEGF among others. The broad concept of G4 targeting with small molecules is now generally accepted as a promising novel approach to anticancer therapy and several small molecules with antiproliferative activity in cancer cell lines have also been shown to stabilize these DNA structures, thus suggesting a potential application of G4-interactive small molecules as new anticancer drugs. Herein we review, by targeted oncogene and main chemical scaffold, those G4-interactive small molecules with reported gene expression modulatory activity in cancer cell lines. The data obtained so far are encouraging but further efforts are needed to validate G4 as drug targets and optimize the structure of G4- interactive small molecules into new anticancer drugs.

Ligand-Induced Dimerization of a Truncated Parallel MYC G-Quadruplex

Binding of an indoloquinoline derivative with an aminoalkyl side chain to a truncated sequence from the MYC promoter region was studied through isothermal titration calorimetry (ITC). The targeted MYC3 sequence lacks 3'-flanking nucleotides and forms a monomeric parallel quadruplex (G4) with a blunt-ended 3'-outer tetrad under the solution conditions employed. Analysis of ITC isotherms reveals multiple binding equilibria with the initial formation of a 1:2 ligand/quadruplex complex. Evaluation of electrophoretic mobilities as well as NMR spectral data confirm ligand-induced dimerization of MYC3 quadruplexes with the ligand sandwiched between the two 3'-outer tetrads. Additional ligand molecules in excess bind to the 5'-outer tetrads of the sandwich complex. Such a ligand-promoted G4 dimerization may be exploited for the controlled assembly or disassembly of G4 aggregates to expand on present quadruplex-based technologies.

Synthesis, G-quadruplex stabilisation, docking studies, and effect on cancer cells of indolo[3,2-b]quinolines with one, two, or three basic side chains

G-quadruplex (G4) DNA structures in telomeres and oncogenic promoter regions are potential targets for cancer therapy, and G4 ligands have been shown to modulate telomerase activity and oncogene transcription. Herein we report the synthesis and G4 thermal stabilisation effects, determined by FRET melting assays, of 20 indolo[3,2-b]quinolines mono-, di-, and trisubstituted with basic side chains. Molecular modelling studies were also performed in an attempt to rationalise the ligands' binding poses with G4. Overall, the results suggest that ligand binding and G4 DNA thermal stabilisation increase with an N5-methyl or a 7-carboxylate group and propylamine side chains, whereas selectivity between G4 and duplex DNA appears to be modulated by the number and relative position of basic side chains. From all the indoloquinoline derivatives studied, the novel trisubstituted compounds 3 d and 4 d, bearing a 7-(aminoalkyl)carboxylate side chain, stand out as the most promising compounds; they show high G4 thermal stabilisation (ΔTm values between 17 and 8 °C) with an inter-G4 ΔTm trend of Hsp90A>KRas21R≈F21T>c-Kit2, 10-fold selectivity for G4 over duplex DNA, and 100-fold selectivity for the HCT116 cancer cell line (IC50 and IC90: <10 μM) over primary rat hepatocytes. Compounds 3 d and 4 d also decreased protein expression levels of Hsp90 and KRas in HCT116 cancer cells.

Indolo[3,2-b]quinolines: synthesis, biological evaluation and structure activity-relationships

The tetracyclic indolo[3,2-b]quinoline ring system constitutes an important structural moiety in natural products exhibiting numerous biological activities. In particular, indolo [3, 2-b]quinoline, commonly known as linear quindoline is of particular interest, because of its rigid structure and scope of derivatization. Although the core linear quindoline skeleton shows little or no activity in several biological systems, introduction of a methyl group on the N-5 atom leading to cryptolepine induces remarkable activity against a broad spectrum of biological targets. A number of analogs of quindoline and cryptolepine have been synthesized, incorporating various functional groups on the core quindoline skeleton leading to improved biological activities. In this review, we describe various synthetic methodologies leading to the quindoline scaffold, the biological activities and the structure activity relationships (SAR) of quindoline derivatives toward different disease states to give a better picture of the importance of this moiety in medicinal chemistry.