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Cutaneous leishmaniasis (CL) is caused by several species of the protozoan parasite Leishmania , affecting an estimated 10 million people worldwide. Previously reported strategies for the development of topical CL treatments have focused primarily on drug permeation and formulation optimization as the means to increase treatment efficacy. Our approach aims to identify compounds with antileishmanial activity and properties consistent with topical administration. Of the test compounds, five benzoxaboroles showed potent activity (50% effective concentration [EC 50 ] < 5 μM) against intracellular amastigotes of at least one Leishmania species and acceptable activity (20 μM < EC 50 < 30 μM) against two more species. Benzoxaborole compounds were further prioritized on the basis of the in vitro evaluation of progression criteria related to skin permeation, such as the partition coefficient and solubility. An MDCKII-hMDR1 cell assay showed overall good permeability and no significant interaction with the P-glycoprotein transporter for all substrates except LSH002 and LSH031. The benzoxaboroles were degraded, to some extent, by skin enzymes but had stability superior to that of para -hydroxybenzoate compounds, which are known skin esterase substrates. Evaluation of permeation through reconstructed human epidermis showed LSH002 to be the most permeant, followed by LSH003 and LSH001. Skin disposition studies following finite drug formulation application to mouse skin demonstrated the highest permeation for LSH001, followed by LSH003 and LSH002, with a significantly larger amount of LSH001 than the other compounds being retained in skin. Finally, the efficacy of the leads (LSH001, LSH002, and LSH003) against Leishmania major was tested in vivo LSH001 suppressed lesion growth upon topical application, and LSH003 reduced the lesion size following oral administration., (Copyright © 2018 American Society for Microbiology.)

The recent development and spread of extensively drug-resistant and totally drug-resistant resistant (TDR) strains of Mycobacterium tuberculosis highlight the need for new antitubercular drugs. Protein synthesis inhibitors have played an important role in the treatment of tuberculosis (TB) starting with the inclusion of streptomycin in the first combination therapies. Although parenteral aminoglycosides are a key component of therapy for multidrug-resistant TB, the oxazolidinone linezolid is the only orally available protein synthesis inhibitor that is effective against TB. Here, we show that small-molecule inhibitors of aminoacyl-tRNA synthetases (AARSs), which are known to be excellent antibacterial protein synthesis targets, are orally bioavailable and effective against M. tuberculosis in TB mouse infection models. We applied the oxaborole tRNA-trapping (OBORT) mechanism, which was first developed to target fungal cytoplasmic leucyl-tRNA synthetase (LeuRS), to M. tuberculosis LeuRS. X-ray crystallography was used to guide the design of LeuRS inhibitors that have good biochemical potency and excellent whole-cell activity against M. tuberculosis Importantly, their good oral bioavailability translates into in vivo efficacy in both the acute and chronic mouse models of TB with potency comparable to that of the frontline drug isoniazid., (Copyright © 2016 Palencia et al.)

Gram-negative bacteria cause approximately 70% of the infections in intensive care units. A growing number of bacterial isolates responsible for these infections are resistant to currently available antibiotics and to many in development. Most agents under development are modifications of existing drug classes, which only partially overcome existing resistance mechanisms. Therefore, new classes of Gram-negative antibacterials with truly novel modes of action are needed to circumvent these existing resistance mechanisms. We have previously identified a new a way to inhibit an aminoacyl-tRNA synthetase, leucyl-tRNA synthetase (LeuRS), in fungi via the oxaborole tRNA trapping (OBORT) mechanism. Herein, we show how we have modified the OBORT mechanism using a structure-guided approach to develop a new boron-based antibiotic class, the aminomethylbenzoxaboroles, which inhibit bacterial leucyl-tRNA synthetase and have activity against Gram-negative bacteria by largely evading the main efflux mechanisms in Escherichia coli and Pseudomonas aeruginosa. The lead analogue, AN3365, is active against Gram-negative bacteria, including Enterobacteriaceae bearing NDM-1 and KPC carbapenemases, as well as P. aeruginosa. This novel boron-based antibacterial, AN3365, has good mouse pharmacokinetics and was efficacious against E. coli and P. aeruginosa in murine thigh infection models, which suggest that this novel class of antibacterials has the potential to address this unmet medical need.

The valine at position 82 (Val 82) in the active site of the human immunodeficiency virus (HIV) protease mutates in response to therapy with the protease inhibitor ritonavir. By using the X-ray crystal structure of the complex of HIV protease and ritonavir, the potent protease inhibitor ABT-378, which has a diminished interaction with Val 82, was designed. ABT-378 potently inhibited wild-type and mutant HIV protease (Ki = 1.3 to 3.6 pM), blocked the replication of laboratory and clinical strains of HIV type 1 (50% effective concentration [EC50], 0.006 to 0.017 microM), and maintained high potency against mutant HIV selected by ritonavir in vivo (EC50, 50-fold after 8 h. In healthy human volunteers, coadministration of a single 400-mg dose of ABT-378 with 50 mg of ritonavir enhanced the area under the concentration curve of ABT-378 in plasma by 77-fold over that observed after dosing with ABT-378 alone, and mean concentrations of ABT-378 exceeded the EC50 for >24 h. These results demonstrate the potential utility of ABT-378 as a therapeutic intervention against AIDS.

Coadministration with the human immunodeficiency virus (HIV) protease inhibitor ritonavir was investigated as a method for enhancing the levels of other peptidomimetic HIV protease inhibitors in plasma. In rat and human liver microsomes, ritonavir potently inhibited the cytochrome P450 (CYP)-mediated metabolism of saquinavir, indinavir, nelfinavir, and VX-478. The structural features of ritonavir responsible for CYP binding and inhibition were examined. Coadministration of other protease inhibitors with ritonavir in rats and dogs produced elevated and sustained plasma drug levels 8 to 12 h after a single dose. Drug exposure in rats was elevated by 8- to 46-fold. A > 50-fold enhancement of the concentrations of saquinavir in plasma was observed in humans following a single codose of ritonavir (600 mg) and saquinavir (200 mg). These results indicate that ritonavir can favorably alter the pharmacokinetic profiles of other protease inhibitors. Combination regimens of ritonavir and other protease inhibitors may thus play a role in the treatment of HIV infection. Because of potentially substantial drug level increases, however, such combinations require further investigation to establish safe regimens for clinical use.

C2 symmetry-based human immunodeficiency virus (HIV) protease inhibitors were examined in vitro as single agents or in combination with 3'-azido-2',3'-dideoxythymidine (AZT) or 2',3'-dideoxyinosine for activity against HIV type 1 (HIV-1). Ten C2 symmetry-based or pseudo-C2 symmetry-based HIV protease inhibitors were active against a laboratory strain (HIV-1IIIB) in the HIV-1 cytopathic effect inhibition assay. Three inhibitors, A75925, A76928, and A77003, selected to represent a range of aqueous solubility and antiviral activity, were active against four different HIV-1 strains tested. These three inhibitors exhibited a significant inhibition of the cytopathic effect of HIV-1 against the CD4+ ATH8 cell line, with 90% inhibitory concentrations ranging from 0.1 to 4 microM. Cellular toxicity was negligible at up to 20 microM. Furthermore, they completely inhibited the replication of monocytotropic strain HIV-1Ba-L in purified monocytes and macrophages at 0.75 to 2 microM. Potent inhibitory activity against a primary HIV-1 isolate and an AZT-resistant HIV-1 variant was also observed for all three inhibitors in phytohemagglutinin-activated peripheral blood mononuclear cells. When these three HIV protease inhibitors and AZT or 2',3'-dideoxyinosine were used in combinations against a primary HIV isolate in phytohemagglutinin-activated peripheral blood mononuclear cells and the results were analyzed with the COMBO program package, their antiviral activities were identified to be synergistic in some cases and additive in others. The present data warrant further investigations of these compounds as potential antiviral agents for the therapy of HIV infections.

Two newly synthesized carbocyclic oxetanocin analogs, (+/-)-9-[(1 beta,2 alpha,3 beta)-2,3-bis(hydroxymethyl)-1-cyclobutyl]adenine (cyclobut-A) and (+/-)-9-[(1 beta,2 alpha,3 beta)-2,3-bis(hydroxymethyl)-1-cyclobutyl]guanine (cyclobut-G) were tested for activity against the infectivity of human immunodeficiency virus (HIV) in vitro. A number of other carbocyclic oxetanocin analogs failed to exert good antiretroviral effects. Both cyclobut-A and cyclobut-G protected CD4+ ATH8 cells against the infectivity and cytopathic effect of HIV type 1 (HIV-1) and suppressed proviral DNA synthesis in ATH8 cells exposed to HIV-1 in vitro at concentrations of 50 to 100 microM. These compounds also inhibited the in vitro infectivity of another human pathogenic retrovirus, HIV-2. Furthermore, both compounds completely suppressed the replication of a monocytotropic strain of HIV-1 in monocytes and macrophages at concentrations as low as 0.5 microM, as assessed by inhibition of HIV-1 p24 gag protein production. We also found that 2'-deoxyguanosine readily reversed the antiretroviral activity of cyclobut-G in our system, whereas the activity of cyclobut-A was hardly reversed by 2'-deoxyadenosine or 2'-deoxycytidine. We noted, however, that these compounds inhibited the proliferation of peripheral blood mononuclear cells at concentrations of greater than or equal to 100 microM in vitro. Although both cyclobut-A and cyclobut-G appear to have a certain level of in vitro toxicity, our observations may have theoretical and clinical implications in understanding the structure-activity relationships of antiretroviral agents active against HIV.