Investigating the anti-cancer potential of pyrimethamine analogues through a modern chemical biology lens.

Pharmacological inhibition of dihydrofolate reductase (DHFR) is an established approach for treating a variety of human diseases, including foreign infections and cancer. However, treatment with classic DHFR inhibitors, such as methotrexate (MTX), are associated with negative side-effects and resistance mechanisms that have prompted the search for alternatives. The DHFR inhibitor pyrimethamine (Pyr) has compelling anti-cancer activity in in vivo models, but lacks potency compared to MTX, thereby requiring higher concentrations to induce therapeutic responses. The purpose of this work was to investigate structural analogues of Pyr to improve its in vitro and cellular activity. A series of 36 Pyr analogues were synthesized and tested in a sequence of in vitro and cell-based assays to monitor their DHFR inhibitory activity, cellular target engagement, and impact on breast cancer cell viability. Ten top compounds were identified, two of which stood out as potential lead candidates, 32 and 34. These functionalized Pyr analogues potently engaged DHFR in cells, at concentrations as low as 1 nM and represent promising DHFR inhibitors that could be further explored as potential anti-cancer agents.

Ursane-Type Triterpenes, Phenolics and Phenolic Derivatives from Globimetula braunii Leaf.

Globimetula braunii is a hemi-parasitic plant used in African ethnomedicine for the management of microbial infections, rheumatic pain and tumors amongst others. We report the isolation and characterization of eight compounds with their antioxidant and antimicrobial activities. The air-dried powdered leaf was macerated in EtOH/H20 (4:1). The extract was solvent-partitioned into n-hexane, EtOAc, n-BuOH and aqueous fractions. The fractions were screened for their antioxidant properties, using DPPH, FRAP, TAC and FIC assays. Antimicrobial analysis was performed using the micro-broth dilution method. The active EtOAc fraction was purified for its putative compounds on a repeated silica gel column chromatography monitored with TLC-bioautography. The isolated compounds were characterized using spectroscopic methods of UV, FT-IR, NMR and MS. Eight compounds (1-8) were isolated and characterized as 13,27-cycloursane (1), phyllanthone (2), globraunone (3), three phenolics: methyl 3,5-dihydroxy-4-methoxybenzoate (4), methyl 3-methyl-4-hydroxybenzoate (5) and guaiacol (6), as well as two phenol derivatives: 4-formaldehyde phenone (7) and 6-methoxy-2H-inden-5-ol (8). The study identified 4 and 6 as natural antioxidant compounds with potential as antimicrobial agents.

Syntheses of L-Rhamnose-Linked Amino Glycerolipids and Their Cytotoxic Activities against Human Cancer Cells.

A major impediment to successful cancer treatment is the inability of clinically available drugs to kill drug-resistant cancer cells. We recently identified metabolically stable L-glucosamine-based glycosylated antitumor ether lipids (GAELs) that were cytotoxic to chemotherapy-resistant cancer cells. In the absence of commercially available L-glucosamine, many steps were needed to synthesize the compound and the overall yield was poor. To overcome this limitation, a facile synthetic procedure using commercially available L-sugars including L-rhamnose and L-glucose were developed and the L-GAELs tested for anticancer activity. The most potent analog synthesized, 3-amino-1-O-hexadecyloxy-2R-(O-α-L-rhamnopyranosyl)-sn- glycerol 3, demonstrated a potent antitumor effect against human cancer cell lines derived from breast, prostate, and pancreas. The activity observed was superior to that observed with clinical anticancer agents including cisplatin and chlorambucil. Moreover, like other GAELs, 3 induced cell death by a non-membranolytic caspase-independent pathway.

Development of a nebramine-cyclam conjugate as an antibacterial adjuvant to potentiate ß-lactam antibiotics against multidrug-resistant P. aeruginosa.

The ß-lactams are the most widely used class of antibiotics due to their safety, effectiveness, and spectrum of activity. As a result of their ubiquitous usage, there has been a steady rise in ß-lactam resistant Gram-negative bacteria, especially Pseudomonas aeruginosa, resulting in limited treatment options. P. aeruginosa can develop multidrug-resistant phenotypes using a multifaceted approach of ß-lactamase expression, decreased porin production and increased efflux. Current ß-lactamase inhibitors address drug hydrolyzing enzymes but may not be as effective in phenotypes with reduced permeability and/or overexpressed efflux pumps. Herein, we present the synthesis and biological evaluation of a nebramine-cyclam conjugate molecule that is able to potentiate ß-lactam antibiotics, as well as other legacy antibiotics, against P. aeruginosa in vitro. Combination studies show that this adjuvant is able to synergize with ß-lactams such as aztreonam and ceftazidime against multidrug-resistant and extremely drug-resistant clinical isolates through a hypothesized mechanism of outer membrane permeabilization. Importantly, the addition of low concentrations (8 µM) of the nontoxic nebramine-cyclam conjugate is able to further potentiate existing ß-lactam/ß-lactamase inhibitor combinations in ß-lactamase-harboring P. aeruginosa strains. These data support a potential application of the nebramine-cyclam conjugate as an adjuvant for treating infections caused by P. aeruginosa strains that utilize multiple mechanisms of resistance.

Potentiation of ß-lactam antibiotics and ß-lactam/ß-lactamase inhibitor combinations against MDR and XDR Pseudomonas aeruginosa using non-ribosomal tobramycin-cyclam conjugates.

OBJECTIVES: To develop a multifunctional adjuvant molecule that can rescue ß-lactam antibiotics and ß-lactam/ß-lactamase inhibitor combinations from resistance in carbapenem-resistant Pseudomonas aeruginosa clinical isolates. METHODS: Preparation of adjuvant was guided by structure-activity relationships, following standard protocols. Susceptibility and chequerboard studies were assessed using serial 2-fold dilution assays. Toxicity was evaluated against porcine erythrocytes, human embryonic kidney (HEK293) cells and liver carcinoma (HepG2) cells via MTS assay. Preliminary in vivo efficacy was evaluated using a Galleria mellonella infection model. RESULTS: Conjugation of tobramycin and cyclam abrogates the ribosomal effects of tobramycin but confers a potent adjuvant property that restores full antibiotic activity of meropenem and aztreonam against carbapenem-resistant P. aeruginosa. Therapeutic levels of susceptibility, as determined by CLSI susceptibility breakpoints, were attained in several MDR clinical isolates, and time-kill assays revealed a synergistic dose-dependent pharmacodynamic relationship. A triple combination of the adjuvant with ceftazidime/avibactam (approved), aztreonam/avibactam (Phase III) and meropenem/avibactam enhances the efficacies of ß-lactam/ß-lactamase inhibitors against recalcitrant strains, suggesting rapid access of the combination to their periplasmic targets. The newly developed adjuvants, and their combinations, were non-haemolytic and non-cytotoxic, and preliminary in vivo evaluation in G. mellonella suggests therapeutic potential for the double and triple combinations. CONCLUSIONS: Non-ribosomal tobramycin-cyclam conjugate mitigates the effect of OprD/OprF porin loss in P. aeruginosa and potentiates ß-lactam/ß-lactamase inhibitors against carbapenem-resistant clinical isolates, highlighting the complexity of resistance to ß-lactam antibiotics. Our strategy presents an avenue to further preserve the therapeutic utility of ß-lactam antibiotics.

Heterodimeric Rifampicin-Tobramycin conjugates break intrinsic resistance of Pseudomonas aeruginosa to doxycycline and chloramphenicol in vitro and in a Galleria mellonella in vivo model.

Intrinsic resistance in Pseudomonas aeruginosa, defined by chromosomally encoded low outer membrane permeability and constitutively over-expressed efflux pumps, is a major reason why the pathogen is refractory to many antibiotics. Herein, we report that heterodimeric rifampicin-tobramycin conjugates break this intrinsic resistance and sensitize multidrug and extensively drug-resistant P. aeruginosa to doxycycline and chloramphenicol in vitro and in vivo. Tetracyclines and chloramphenicol are model compounds for bacteriostatic effects, but when combined with rifampicin-tobramycin adjuvants, their effects became bactericidal at sub MIC levels. Potentiation of tetracyclines correlates with the SAR of this class of drugs and is consistent with outer membrane permeabilization and efflux pump inhibition. Overall, this strategy finds new uses for old drugs and presents an avenue to expand the therapeutic utility of legacy antibiotics to recalcitrant pathogens such as P. aeruginosa.

Ubiquitous Nature of Fluoroquinolones: The Oscillation between Antibacterial and Anticancer Activities.

Fluoroquinolones are synthetic antibacterial agents that stabilize the ternary complex of prokaryotic topoisomerase II enzymes (gyrase and Topo IV), leading to extensive DNA fragmentation and bacteria death. Despite the similar structural folds within the critical regions of prokaryotic and eukaryotic topoisomerases, clinically relevant fluoroquinolones display a remarkable selectivity for prokaryotic topoisomerase II, with excellent safety records in humans. Typical agents that target human topoisomerases (such as etoposide, doxorubicin and mitoxantrone) are associated with significant toxicities and secondary malignancies, whereas clinically relevant fluoroquinolones are not known to exhibit such propensities. Although many fluoroquinolones have been shown to display topoisomerase-independent antiproliferative effects against various human cancer cells, those that are significantly active against eukaryotic topoisomerase show the same DNA damaging properties as other topoisomerase poisons. Empirical models also show that fluoroquinolones mediate some unique immunomodulatory activities of suppressing pro-inflammatory cytokines and super-inducing interleukin-2. This article reviews the extended roles of fluoroquinolones and their prospects as lead for the unmet needs of "small and safe" multimodal-targeting drug scaffolds.

Amphiphilic Modulation of Glycosylated Antitumor Ether Lipids Results in a Potent Triamino Scaffold against Epithelial Cancer Cell Lines and BT474 Cancer Stem Cells.

The problems of resistance to apoptosis-inducing drugs, recurrence, and metastases that have bedeviled cancer treatment have been attributed to the presence of cancer stem cells (CSCs) in tumors, and there is currently no clinically indicated drug for their eradication. We previously reported that glycosylated antitumor ether lipids (GAELs) display potent activity against CSCs. Here, we show that by carefully modulating the amphiphilic nature of a monoamine-based GAEL, we can generate a potent triamino scaffold that is active against a panel of hard-to-kill epithelial cancer cell lines (including triple-negative breast) and BT474 CSCs. The most active compound of this set, which acts via a nonmembranolytic, nonapoptotic caspase-independent mechanism, is more effective than cisplatin and doxorubicin against these cell lines and more potent than salinomycin against BT474 CSCs. Understanding the combination of factors crucial for the enhanced cytotoxicity of GAELs opens new avenues to develop potent compounds against drug-resistant cancer cells and CSCs.

Replacing d-Glucosamine with Its l-Enantiomer in Glycosylated Antitumor Ether Lipids (GAELs) Retains Cytotoxic Effects against Epithelial Cancer Cells and Cancer Stem Cells.

We describe metabolically inert l-glucosamine-based glycosylated antitumor ether lipids (L-GAELs) that retain the cytotoxic effects of the D-GAELs including the ability to kill BT-474 breast cancer stem cells (CSCs). When compared to adriamycin, cisplatin, and the anti-CSC agent salinomycin, L-GAELs display superior activity to kill cancer stem cells (CSCs). Mode of action studies indicate that L-GAELs like the D-GAELs kill cells via an apoptosis-independent mechanism that was not due to membranolytic effects.

Design, synthesis and antitumor properties of glycosylated antitumor ether lipid (GAEL)- chlorambucil-hybrids.

Glycosylated antitumor ether lipids (GAELs) kill cancer cells and cancer stem cells via a novel, apoptosis-independent mechanism. In contrast, chlorambucil, a drug in clinical use for the treatment of chronic lymphocytic leukemia reacts with nucleophiles within the major groove of DNA, leading to apoptosis. We hypothesized that hybrid molecules that combine apoptosis-dependent and apoptosis-independent mode of actions in a single molecule may lead to enhanced antitumor activity. Here, we describe the antitumor activities of chlorambucil-linked glucosamine-derived glycerolipid hybrids and investigate the role of the chlorambucil moiety and the effect of cationic charge on the hybrid molecule. Three hybrids and two control GAELs were synthesized and their activities against breast (JIMT1, MDA-MB-231, BT474), pancreas (MiaPaCa2) and prostate (DU145, PC3) cancer cell lines were determined using MTS assay. Hybrid 3 displayed the most potent activity on DU145 at CC50 of 6.0 µM while hybrid 4 displayed the best activity on JIMT1 at 7.5 µM. Hybrid 5 exhibited no activity at the highest concentration tested (CC50 >20 µM), underscoring the significance of the cationic charge at C-2 position as previously reported. Although chlorambucil (2) itself showed very little activity against all the six cell lines (CC50 >150 µM), GAELs 6 and 7 which lack the chlorambucil moiety were consistently less active than 3 and 4, suggesting that the chlorambucil moiety contributes to the overall activity. The hybrids were however not as active as the parent GAEL 1 against MiaPaCa2 whereas 6 restored activity comparable to 1.