FDA approved drugs with antiviral activity against SARS-CoV-2: From structure-based repurposing to host-specific mechanisms.

The continuing heavy toll of the COVID-19 pandemic necessitates development of therapeutic options. We adopted structure-based drug repurposing to screen FDA-approved drugs for inhibitory effects against main protease enzyme (Mpro) substrate-binding pocket of SARS-CoV-2 for non-covalent and covalent binding. Top candidates were screened against infectious SARS-CoV-2 in a cell-based viral replication assay. Promising candidates included atovaquone, mebendazole, ouabain, dronedarone, and entacapone, although atovaquone and mebendazole were the only two candidates with IC50s that fall within their therapeutic plasma concentration. Additionally, we performed Mpro assays on the top hits, which demonstrated inhibition of Mpro by dronedarone (IC50 18 µM), mebendazole (IC50 19 µM) and entacapone (IC50 9 µM). Atovaquone showed only modest Mpro inhibition, and thus we explored other potential mechanisms. Although atovaquone is Dihydroorotate dehydrogenase (DHODH) inhibitor, we did not observe inhibition of DHODH at the respective SARS-CoV-2 IC50. Metabolomic profiling of atovaquone treated cells showed dysregulation of purine metabolism pathway metabolite, where ecto-5'-nucleotidase (NT5E) was downregulated by atovaquone at concentrations equivalent to its antiviral IC50. Atovaquone and mebendazole are promising candidates with SARS-CoV-2 antiviral activity. While mebendazole does appear to target Mpro, atovaquone may inhibit SARS-CoV-2 viral replication by targeting host purine metabolism.

Radiosynthesis and in silico bioevaluation of 131 I-Sulfasalazine as a highly selective radiotracer for imaging of ulcerative colitis.

This study demonstrated the tracking of ulcerative colitis, which is considered a stressful immune disease. Although there are many ways to test for this disease including dependence on gases, dyes, and painful anal endoscopy, these treatment modalities have many disadvantages. Hence, it is the utmost need of time to discover new methods to detect this chronic immune disease and to avoid the defects of traditional methodologies. Sulfasalazine (SSD) was labeled with iodine-131 (half-life: 8 days, Energy: 971 keV) under optimum reaction conditions including the amount of reducing agent, pH factor, chloramine-T (Ch-T) amount, and incubation period. Characterization was performed using 1 H/ 13 C-NMR, ESI-MS, and HPLC (UV/ Radio) techniques. The biodistribution study was performed in normal and ulcerative mice models, and in silico molecular docking study was performed to evaluate the possible mechanism of action to target peroxisome proliferator-activated receptor gamma (PPARγ). The high radiolabeling yield of [131 I]-sulfasalazine ([131 I]-SSD) was achieved ≥90% through the direct labeling method with radioactive iodine-131 in the presence of chloramine-T (100 µg). The radiotracer [131 I]-SSD was observed to be stable in normal saline and freshly eluted serum up to 12 hr at ambient temperature (37℃ ± 2℃). The radiotracer [131 I]-SSD showed the highest uptake in the targeted organ (i.e., ulcerative colon) which was observed to be ≥75% injected dose per gram (% ID/g) organ for 24 hr postinjection (p.i). Furthermore, in silico data collected from molecular modeling analysis of SSD and [131 I]-SSD with antimicrobial protein (PDB code: 3KEG) and peroxisome proliferator-activated receptor gamma (PPARγ) (PDB code: 4XTA) showed azoreductase activity and high binding potential for PPAR-γ site, respectively. The results of biological studies obtained in this study enlighten the usefulness of radiotracer [131 I]-SSD as a potential imaging agent for ulcerative colitis.

Design and synthesis of a new class of indeno[1,2-b]pyridine thioglycosides.

This research reports a novel method for synthesizing a new class of indeno[1,2-b]pyridine thioglycosides. This series of indenopyridine thioglycosides was designed by the reaction of (E)-2-cyano-3-(furan/or thiophene-2-yl)prop-2-enethioamide 1a or 1b with 1-indanone 2 to give the corresponding 2-thiooxo-1H-indeno[1,2-b]pyridine-3-carbonitriles 3a,b. The latter compounds were treated with peracetylated sugar bromides 5 in KOH-acetone to give the corresponding indenopyridine thioglycosides 6a-h. Ammonolysis of the protected indenopyridine thioglycosides 6a-h gave the corresponding free indenopyridine thioglycosides 7a-h. The compounds have been characterized by 13C NMR, 1H NMR and IR spectra.

Design, synthesis, molecular docking and anti-hepatocellular carcinoma evaluation of novel acyclic pyridine thioglycosides.

A novel series of acyclic pyridine thioglycosides has been synthesized. Evaluation of the anti proliferative activity of these compounds against HEPG-2 cell lines (liver carcinoma cell lines) shows that most of the compounds have high anti-tumor activities especially 6b, 6c, 7b and 7c. Furthermore, in the modeling study, these compounds showed that they have high binding affinity with thymidylate synthase dihydrofolate reductase (TS-DHFR).

Design, synthesis, and biological evaluation of novel amide and hydrazide based thioether analogs targeting Histone deacteylase (HDAC) enzymes.

Development of HDAC inhibitors have become an ultimate need targeting different types of cancer. In silico virtual screening was applied to screen novel scaffolds via scaffold hopping strategy to develop different acrylamide and aryl/heteroaryl hydrazide based analogs merged with thioether moiety. The acrylamide based analogs showed significant hydrophobic interaction within binding pocket in addition to co-ordination with Zn+2 via carbonyl group, however the aryl/heteroaryl hydrazide based analogs showed binding towards Zn+2 via thiol moiety. Two classes (acrylamide and aryl/heteroaryl hydrazide based analogs) were synthesized to be screened along with 60 cancer cell lines panel to reveal that both of AHM-4 and AHM-5 showed significant inhibitory growth against HL-60 (Leukemia cell lines) at GI50 2.87 µM and 3.20 µM, respectively and MDA-MB-435 (Melanoma cell lines) cell lines at GI50 of 0.37 µM and 0.42 µM, respectively. AHM-4 and AHM-5 showed general inhibitory profile against class I HDAC enzymes with differential inhibitory activity towards HDAC 2 at IC50 32 nM and 20 nM, respectively via ELISA enzymatic assay, in addition to inhibiting activity for the expression of class I HDAC enzymes via real time PCR with differential selective inhibition against HDAC 2 up to 10 folds, compared to control. AHM4 and AHM5 showed cell cycle arrest action at G2/M phase along with induction of apoptosis via assessment of apoptotic parameters such as Caspase 3, 9, and γ- H2AX. The synthesized analogs offer novel scaffold to be further optimized for development of HDAC inhibitors.

Design, synthesis, and in vitro anti-hepatocellular carcinoma of novel thymine thioglycoside analogs as new antimetabolic agents.

A first reported direct method for preparation of thymine thioglycoside analogs utilizing novel pyrimidine-2(1H)-thiones and α-bromoglucose or α-bromogalactose tetraacetate as starting components is described. The synthetic potential of the method is demonstrated. The evaluation of antiproliferative activity against HepG-2 cell lines (Liver carcinoma cell lines) shows that most of the compounds have high antitumor activities especially 6b, 6e, 11b, and 12b. Moreover, molecular modelings of these compounds reveal that they have high binding affinity through hydrogen bond interaction with the binding pocket of thymidylate synthase dihydrofolate reductase (TS-DHFR).

Antimetabolites: Design, synthesis, and cytotoxic evaluation of novel dihydropyridine thioglycosides and pyridine thioglycosides.

A convenient synthesis of a novel series of dihydropyridine and pyridine thioglycosides was developed. The evaluation of anti-proliferative activity against HepG-2 cell lines (liver carcinoma cell lines) shows that most of the compounds have antitumor activity, especially 5b, 5f, 5j, 5n, 7b, 7f, 7j, 7n, 8b, 8f, and 8j. The results of molecular docking reveal that these compounds have high binding affinity by hydrogen bond formation with the binding pocket of thymidylate synthase dihydrofolate reductase (TS-DHFR).