Current Topics in Medicinal Chemistry - Volume 19, Issue 9, 2019

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), still remains an urgent global health issue, mainly due to the emergence of multi-drug resistant strains. Therefore, there is a pressing need to develop novel and more efficient drugs to control the disease. In this context, targeting the pathogen virulence factors, and particularly signal mechanisms, seems to be a promising approach. An important transmembrane signaling system in Mtb is represented by receptor-type Serine/ Threonine protein kinases (STPKs). Mtb has 11 different STPKs, two of them, PknA and PknB, are essential. By contrast PknG and PknH are involved in Mtb virulence and adaptation, and are fundamental for the pathogen growth in infection models. Therefore, STPKs represent a very interesting group of pharmacological targets in M. tuberculosis. In this work, the principal inhibitors of the mycobacterial STPKs will be presented and discussed. In particular, medicinal chemistry efforts have been focused on discovering new antimycobacterial compounds, targeting three of these kinases, namely PknA, PknB and PknG. Generally, the inhibitory effect on these enzymes do not correlate with a significant antimycobacterial action in whole-cell assays. However, compounds with activity in the low micromolar range have been obtained, demonstrating that targeting Mtb STPKs could be a new promising strategy for the development of drugs to treat TB infections.

Background: Hispolons are natural products known to possess cytoprotective, antioxidant and anti-cancer activities. We have found recently anti TB activity in these compounds. Efforts were made to optimize the structure with bioisosteric replacement of 1,3-diketo functional group with the corresponding pyrazole and isoxazole moieties. Objective: The goal of this paper is designing new hispolon isoxazole and pyrazole and the evaluation of their biological activities. Methods: The designed compounds were prepared using classical organic synthesis methods. The anti- TB activity was evaluated using the MABA method. Results: A total of 44 compounds were synthesized (1a- 1v and 2a-2v) and screened for anti TB activity and antibacterial activity. The compounds 1b and 1n showed the highest potency with MIC 1.6μg/mL against M. tuberculosis H37Rv. Conclusion: Bioisosteric replacement of 1,3-diketo functional group in hispolons with pyrazole or isoxazole rings have resulted in potent anti TB molecules. Docking simulations of these compounds on mtFabH enzyme resulted in a clear understanding of bioactivity profiles of these compounds. Docking scores are in good agreement with the anti TB activity obtained for these compounds. Computational studies and in vitro screening results indicate mtFabH as the probable target of these compounds.

Background and Introduction: Mefloquine, a drug used to prevent and treat malaria is described possessing activity against the Mycobacterium tuberculosis (Mtb) as well as against multidrugresistant tuberculosis (MDR) and other types of bacteria. Despite their importance, few compounds based on the Mefloquine nucleus have been synthesized and evaluated against TB. Materials and Methods: For the synthesis of all the compounds based on the Mefloquine nucleus we used a synthetic route which utilized the key derivative 4-methoxy-2,8-bis(trifluoromethyl)quinoline 2 as starting material. The compounds 3 (a-c), 4 (a-b) were synthesized after one step by reaction of 2 with appropriate amines substituted. The chloro derivatives 5 and 6 were obtained from compounds 4b and 4a by treatment with SOCl2 in CH2Cl2 at reflux in 75 and 80% yield, respectively. The analogue 6 was converted to 7 after treatment with ethanolamine under heating at 90oC in 64% yield and to the azido derivative 8 in 56% after reaction with sodium azide in MeOH at reflux for 2 h. The analogue 9 was obtained after reaction of 5 with ethanolamine at 90oC for 1 h in 90% yield. All the new compounds were identified by detailed spectral data, including 1H NMR, 13C NMR and high resolution mass spectra. All the compound were evaluated for their in vitro antibacterial activity against sensitive Mycobacterium tuberculosis ATCC 27294, using the microplate Alamar Blue assay (MABA). The more active compounds 3c, 7, and 9 were also evaluated against resistant strain SR 2571/0215 (resistant to Rifampicin and Isoniazid) by above method. All compounds were tested against three cancer cell lines: SF-295 (glioblastoma), HCT-116 (colon) and PC-3 (prostate) using the MTT assay. Results: All the planned ten compounds were synthetically obtained in good global yield, displaying activity against sensitive Mycobacterium tuberculosis in vitro, with exception of one, with MIC values between 37.2 and 154.8 μM. The compounds 3c (37.2 μM), 7 (68.1 μM) and 9 (65.6 μM) showed the highest activity in this series with MIC values similar when compare to the standard Mefloquine (30 – 60 μM), being 3c the most potent. The more active compounds 3c, 7, and 9 were also evaluated against resistant strain, displaying MIC of 37.2, 136.2 and 65.6 μM, respectively. All compounds were tested against three cancer cell lines and showed low cytotoxicity. Conclusion: All synthesized compounds, with the exception of 5, exhibited activity against the Mtb. Compound 3c was the most potent against resistant and sensitive Mtb in this series, with MIC value of 37.2 μM. All compounds showed low cytotoxicity. These findings could be considered a good model to develop possible lead compounds in the fight against TB based on Mefloquine nucleus.

Nitrogen mustards, a family of DNA alkylating agents, marked the start of cancer pharmacotherapy. While traditionally characterized by their dose-limiting toxic effects, nitrogen mustards have been the subject of intense research efforts, which have led to safer and more effective agents. Even though the alkylating prodrug mustards were first developed decades ago, active research on ways to improve their selectivity and cytotoxic efficacy is a currently active topic of research. This review addresses the historical development of the nitrogen mustards, outlining their mechanism of action, and discussing the improvements on their therapeutic profile made through rational structure modifications. A special emphasis is made on discussing the nitrogen mustard prodrug category, with Cyclophosphamide (CPA) serving as the main highlight. Selected insights on the latest developments on nitrogen mustards are then provided, limiting such information to agents that preserve the original nitrogen mustard mechanism as their primary mode of action. Additionally, future trends that might follow in the quest to optimize these invaluable chemotherapeutic medications are succinctly suggested.

DNA topoisomerases are enzymes that catalyze the alteration of DNA topology with transiently induced DNA strand breakage, essential for DNA replication. Topoisomerases are validated cancer chemotherapy targets. Anticancer agents targeting Topoisomerase I and II have been in clinical use and proven to be highly effective, though with significant side effects. There are tremendous efforts to develop new generation of topoisomerase inhibitors. Targeted delivery of topoisomerase inhibitors is another way to reduce the side effects. Conjugates of topoisomerases inhibitors with antibody, polymer, or small molecule are developed to target these inhibitors to tumor sites.

Inhibitors targeting human topoisomerase I and topoisomerase II alpha have provided a useful chemotherapy option for the treatment of many patients suffering from a variety of cancers. While the treatment can be effective in many patient cases, use of these human topoisomerase inhibitors is limited by side-effects that can be severe. A strategy of employing the topoisomerase inhibitors in combination with other treatments can potentially sensitize the cancer to increase the therapeutic efficacy and reduce resistance or adverse side effects. The combination strategies reviewed here include inhibitors of DNA repair, epigenetic modifications, signaling modulators and immunotherapy. The ongoing investigations on cellular response to topoisomerase inhibitors and newly initiated clinical trials may lead to adoption of novel cancer therapy regimens that can effectively stop the proliferation of cancer cells while limiting the development of resistance.

Background & Introduction: Pyrrolobenzodiazepine (PBD) dimers are highly potent DNA cross-linking agents used as warheads in Antibody Drug Conjugates (ADCs) for cancer therapy. We propose to investigate the correlation existing between the lipophilicity of those molecules and their activity (both in vitro and in vivo) as well as any effect observed during conjugation. Materials and Methods: Reaction progress was monitored by Thin-Layer Chromatography (TLC) using Merck Kieselgel 60 F254 silica gel, with a fluorescent indicator on aluminium plates. Visualisation of TLC was achieved with UV light or iodine vapour unless otherwise stated. Flash chromatography was performed using Merck Kieselgel 60 F254 silica gel. Results: We have successfully designed and synthesized a novel PBD warhead (SG3312) with enhanced physicochemical properties. The warhead also displayed increased potency in vitro. After overcoming some epimerization issues, the synthesis of enantiomerically pure payload was achieved (SG3259) and fulfilled our criteria for a simplified and more efficient conjugation. No addition of propylene glycol was required, and high DAR and excellent monomeric purity were achieved. Conclusion: The ADC (Herceptin-maia-SG3259) has been shown to release the active warhead (SG3312) upon exposure to Cathepsin B and demonstrated encouraging activity both in vitro and in vivo.