Comparison of feline and human immunodeficiency virus reverse transcriptase enzymes through chemical screening and computational analysis.

Feline immunodeficiency virus (FIV) is a common infection found in domesticated and wild cats worldwide. Despite the wealth of therapeutic understanding of the disease in humans, considerably less information exists regarding the treatment of the disease in felines. Current treatment relies on drugs developed for the related human immunodeficiency virus (HIV) and includes compounds of the popular non-nucleotide reverse transcriptase (NNRTI) class. This is despite FIV-RT being only 67% similar to HIV-1 RT at the enzyme level, increasing to 88% for the allosteric pocket targeted by NNRTIs. The goal of this project was to try to quantify how well the more extensive pharmacological knowledge available for human disease translates to felines. To this end we screened known NNRTIs and 10 diverse pyrimidine analogs identified virtually. We use this chemo-centric probe approach to (a) assess the similarity between the two related RT targets based on the observed experimental inhibition values, (b) try to identify more potent inhibitors at FIV, and (c) gain a better appreciation of the structure-activity relationships (SAR). We found the correlation between IC50s at the two targets to be strong (r2 = 0.87) and identified compound 1 as the most potent inhibitor of FIV with IC50 of 0.030 µM ± 0.009. This compared to FIV IC50 values of 0.22 ± 0.17 µM, 0.040 ± 0.010 µM and >160 µM for known anti HIV-1 RT drugs Efavirenz, Rilpivirine, and Nevirapine, respectively. This knowledge, along with an understanding of the structural origin that give rise to any differences could improve the way HIV drugs are repurposed for FIV.

Computational design, synthesis and biological evaluation of PDE5 inhibitors based on N2,N4-diaminoquinazoline and N2,N6-diaminopurine scaffolds.

We report the synthesis, and characterization of twenty-nine new inhibitors of PDE5. Structure-based design was employed to modify to our previously reported 2,4-diaminoquinazoline series. Modification include scaffold hopping to 2,6-diaminopurine core as well as incorporation of ionizable groups to improve both activity and solubility. The prospective binding mode of the compounds was determined using 3D ligand-based similarity methods to inhibitors of known binding mode, combined with a PDE5 docking and molecular dynamics based-protocol, each of which pointed to the same binding mode. Chemical modifications were then designed to both increase potency and solubility as well as validate the binding mode prediction. Compounds containing a quinazoline core displayed IC50s ranging from 0.10 to 9.39 µM while those consisting of a purine scaffold ranging from 0.29 to 43.16 µM. We identified 25 with a PDE5 IC50 of 0.15 µM, and much improved solubility (1.77 mg/mL) over the starting lead. Furthermore, it was found that the predicted binding mode was consistent with the observed SAR validating our computationally driven approach.

Elucidation of Vasodilation Response and Structure Activity Relationships of N²,N4-Disubstituted Quinazoline 2,4-Diamines in a Rat Pulmonary Artery Model.

Pulmonary arterial hypertension (PAH) is a rare and progressive disease arising from various etiologies and pathogenesis. PAH decreases life expectancy due to pulmonary vascular remodeling, elevation of mean pulmonary arterial pressure, and ultimately progresses to heart failure. While clinical treatments are available to reduce the associated symptoms, a complete cure has yet to be found. Phosphodiesterase-5 (PDE-5) inhibition has been identified as a possible intervention point in PAH treatment. The functional vasodilation response to N²,N4-diamino quinazoline analogues with differing PDE-5 inhibitory activities and varying physicochemical properties were assessed in both endothelium-intact and denuded rat pulmonary arteries to gain greater insight into their mode of action. All analogues produced vasorelaxant effects with EC50s ranging from 0.58 ± 0.22 µM to ˃30 µM. It was observed that vasodilation response in intact vessels was highly correlated with that of denuded vessels. The ~10% drop in activity is consistent with a loss of the nitric oxide mediated cyclic guanosine monophosphate (NO/cGMP) pathway in the latter case. A moderate correlation between the vasodilation response and PDE-5 inhibitory activity in the intact vessels was observed. Experimental protocol using the alpha-adrenergic (α1) receptor agonist, phenylephrine (PE), was undertaken to assess whether quinazoline derivatives showed competitive behavior similar to the α1 receptor blocker, prazosin, itself a quinazoline derivative, or to the PDE-5 inhibitor, sildenafil. Competitive experiments with the α1-adrenergic receptor agonist point to quinazoline derivatives under investigation here act via PDE-5 inhibition and not the former. The pre-incubation of pulmonary arterial rings with quinazoline test compounds (10 µM) reduced the contractile response to PE around 40⁻60%. The most promising compound (9) possessed ~32 folds higher selectivity in terms of vasodilation to its mammalian A549 cell cytotoxicity. This study provides experi0 0mental basis for PDE-5 inhibition as the mode of action for vasodilation by N²,N4-diamino quinazoline analogues along with their safety studies that may be beneficial in the treatment of various cardiovascular pathologies.

Design, synthesis and evaluation of N2,N4-diaminoquinazoline based inhibitors of phosphodiesterase type 5.

We describe the design, synthesis and evaluation of a series of N2,N4-diaminoquinazoline analogs as PDE5 inhibitors. Twenty compounds were prepared and these were assessed in terms of their PDE5 and PDE6 activity, ex-vivo vasodilation response, mammalian cytotoxicity and aqueous solubility. Molecular docking was used to determine the binding mode of the series and this was demonstrated to be consistent with the observed SAR. Compound 15 was the most active PDE5 inhibitor (IC50 = 0.072 ±â€¯0.008 µM) and exhibited 4.6-fold selectivity over PDE6. Ex-vivo assessment of 15 and 22 in a rat pulmonary artery vasodilation model demonstrated EC50s of 1.63 ±â€¯0.72 µM and 2.28 ±â€¯0.74 µM respectively.

Synthesis, Plasmodium falciparum Inhibitory Activity, Cytotoxicity and Solubility of N2 ,N4 -Disubstituted Quinazoline-2,4-diamines.

BACKGROUND: Despite the development of extensive control strategies and treatment options, approximately 200 million malaria cases, leading to approximately 450,000 deaths, were reported in 2015. Due to issue of disease resistance, additional drug development efforts are needed to produce new, more effective treatments. Quinazoline-2,4-diamines were identified as antiparasitic compounds over three decades ago and have remained of interest to date in industry and academia. OBJECTIVE: An anti-malarial SAR evaluation of previously unreported N2 ,N4 -disubstituted quinazoline- 2,4-diamines have been undertaken in this study. We have synthesized and evaluated new derivatives against P. falciparum in our attempt to better characterize their biological activity and overall physical properties. METHODS: The synthesis of N2 ,N4 -disubstituted quinazoline-2,4-diamines inhibitors is reported along with activities in a radioactive labeled hypoxanthine incorporation assay against the f Plasmodium falciparum (Pf.) K1 strain. In addition, cytotoxicity was determined in the A549 and Vero cell lines using an MTT based. The aqueous solubility of key compounds was assessed at pH 7.4 using a shake flask-based approach. RESULTS: We identified compounds 1 and 6p as sub µM inhibitors of P. falciparum, having equivalent anti-malarial activity to Chloroquine. Compounds 1 and 6m are low µM inhibitors of P. falciparum with improved cytotoxicity profiles. Compound 6m displayed the best balance between P. falciparum Inhibitory activity (2 µM) and cytotoxicity, displaying >49 fold selectivity over A549 and Vero cell lines. CONCLUSION: Twenty one N2 ,N4 -Disubstituted Quinazoline-2,4-diamines have been prepared in our group and characterized in terms of their antimalarial activity, cytotoxicity and physical properties. Compounds with good activity and reasonable selectivity over mammalian cell lines have been identified. SAR analyses suggest further exploration is are necessary to improve the balance of P. falciparum Inhibitory activity, cytotoxicity and solubility.