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Background: Crisaborole is a novel, topical nonsteroidal, anti-inflammatory, phosphodiesterase 4 (PDE4) inhibitor for the treatment of mild to moderate atopic dermatitis., Objective: As part of a nonclinical safety testing program, these 2-year studies tested the carcinogenic potential of crisaborole., Methods: Crisaborole ointment, 2%, 5%, or 7%, was applied once daily topically to mice, and crisaborole was administered orally to rats at doses of 30, 100, or 300mg/kg/day for up to 104 weeks. Systemic exposure to crisaborole and its metabolites, moribundity/death, clinical signs, and tumor formation were assessed in each study., Results: Crisaborole treatment was not tumorigenic in mice at any of the doses administered and did not increase the incidence of neoplastic or nonneoplastic microscopic lesions compared with controls. Oral administration of crisaborole at the high dose (300mg/kg/day) to female rats increased the incidence of treatment-related benign granular cell tumors in the distal reproductive tract (uterus with cervix and vagina) but did not cause moribundity/death., Conclusion: Crisaborole was well tolerated and not tumorigenic in mice. It was not tumorigenic in male rats at 300mg/kg/day at exposures that were 3× the human area under the concentration-time curve (AUC 24 ) and was nontumorigenic in female rats at 100mg/kg/day at exposures that were 1× the human AUC 24 ., (Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.)

Carboxamide pyrazinyloxy benzoxaboroles were investigated with the goal to identify a molecule with satisfactory antimalarial activity, physicochemical properties, pharmacokinetic profile, in vivo efficacy, and safety profile. This optimization effort discovered 46, which met our target candidate profile. Compound 46 had excellent activity against cultured Plasmodium falciparum, and in vivo against P. falciparum and P. berghei in infected mice. It exhibited good PK properties in mice, rats, and dogs. It was highly active against the other 11 P. falciparum strains, which are mostly resistant to chloroquine and pyrimethamine. The rapid parasite in vitro reduction and in vivo parasite clearance profile of 46 were similar to those of artemisinin and chloroquine, two rapid-acting antimalarials. It was nongenotoxic in an Ames assay, an in vitro micronucleus assay, and an in vivo rat micronucleus assay when dosed orally up to 2000 mg/kg. The combined properties of this novel benzoxaborole support its progression to preclinical development.

Tavaborole is a topical antifungal agent approved by the US Food and Drug Administration for the treatment of toenail onychomycosis. The effects of tavaborole on gestation, parturition (delivery, labor), offspring development, and survival during the perinatal and postnatal periods were assessed in mated female rats. Females (F0 generation) were administered single daily oral (gavage) doses of 15, 60, or 100 mg/kg/d from gestation day 6 through lactation day 20. The females were allowed to deliver naturally and rear their offspring until lactation day 21, at which time the F0 females were euthanized. One male and female from each litter were selected (F1 generation) and retained for assessments, including growth, neurobehavior, fertility, and their ability to produce an F2 generation. Reproductive and offspring parameters were determined for the F1 and F2 generations, as applicable. F1 females and F2 pups were euthanized on postnatal day 7. In the F0 females, decreased activity was observed in the 100 mg/kg/d dose group. Excess salivation was observed in the 60 and 100 mg/kg/d dose groups (slight to moderate), however, this finding was not considered adverse. There were no tavaborole-related effects on the growth, viability, development, neurobehavioral assessments, or reproductive performance of the F1 generation. Survivability and mean body weight of the F2 pups were unaffected. The no observed adverse effect level (NOAEL) for maternal toxicity (F0 generation) was 60 mg/kg/d, based on the decreased activity observed in the 100 mg/kg/d dose group. The NOAEL for the offspring effects was ≥100 mg/kg/d, based on the lack of test article-related changes., (© The Author(s) 2016.)

Tavaborole is a topical antifungal agent approved by the US Food and Drug Administration for the treatment of toenail onychomycosis. As part of the nonclinical development program, reproductive and developmental toxicity studies were conducted (rat oral fertility and early embryonic development, rat (oral) and rabbit (dermal) embryo-fetal development). There were no effects on fertility or reproductive performance at doses up to 300 mg/kg/d (107 times the maximum recommended human dose [MRHD] based on mean area under the plasma concentration-time curve comparisons). In the rat embryo-fetal development toxicity studies, teratogenicity was not observed at doses up to 100 mg/kg/d (29 times the MRHD). However, several treatment-related skeletal malformations and variations were observed at 300 mg/kg/d (570 times the MRHD). In rabbit embryo-fetal development toxicity studies dosed via oral or dermal administration, the no observable adverse effect level for maternal toxicity and embryo-fetal toxicity was 50 mg/kg/d (16 times the MRHD) and 5% (26 times the MRHD), respectively., (© The Author(s) 2016.)

Crisaborole topical ointment, 2% (formerly known as AN2728) is a benzoxaborole, nonsteroidal, topical, anti-inflammatory phosphodiesterase 4 (PDE4) inhibitor investigational compound that recently completed phase 3 studies for the treatment of mild to moderate atopic dermatitis (AD). The unique configuration of boron within the crisaborole molecule enables selective targeting and inhibition of PDE4, an enzyme that converts the intracellular second messenger 3'5'-cyclic adenosine monophosphate (cAMP) into the active metabolite adenosine monophosphate (AMP). By inhibiting PDE4 and thus increasing levels of cAMP, crisaborole controls inflammation. The use of boron chemistry enabled synthesis of a low-molecular-weight compound (251 daltons), thereby facilitating effective penetration of crisaborole through human skin. In vitro experiments showed that crisaborole inhibits cytokine production from peripheral blood mononuclear cells in a pattern similar to other PDE4 inhibitors and distinct from corticosteroids. Crisaborole also displayed topical anti-inflammatory activity in a skin inflammation model. Once crisaborole reaches systemic circulation after topical application, it is metabolized to inactive metabolites. This limits systemic exposure to crisaborole and systemic PDE4 inhibition. In phase 1 and 2 clinical studies, crisaborole ointment, 2% was generally well tolerated and improved AD disease severity scores, pruritus, and all other AD signs and symptoms. Two large, randomized, controlled, phase 3, pivotal clinical trials assessing the efficacy and safety of crisaborole topical ointment, 2% in children, adolescents, and adults with mild to moderate AD were recently completed with positive results.

Tavaborole, a cyclized boronic acid, has been approved by the Food and Drug Administration for the topical treatment of toenail onychomycosis. This novel, low-molecular-weight pharmaceutical compound has broad-spectrum antifungal activity against dermatophytes, yeasts, and molds responsible for the disease. Tavaborole was tested in 2-year carcinogenicity studies in mice (once daily dermal administration) and rats (once daily by oral gavage) as part of the extensive nonclinical safety program. There was no evidence of tavaborole-related neoplasms observed in either study. Based on the data gathered from these 2 carcinogenicity studies, tavaborole is considered noncarcinogenic., (© The Author(s) 2014.)

Boron-containing compounds are being studied as potential therapeutic agents. As part of the safety assessment of these therapeutic agents, a battery of genetic toxicology studies was conducted. The battery included a bacterial reverse mutation (Ames) assay, an in vitro chromosome aberration assay in peripheral human lymphocytes, and an in vivo rat micronucleus study. The following compounds represent some of the boron-containing compounds that have been advanced to human clinical trials in various therapeutic areas. The borinic picolinate, AN0128, is an antibacterial compound with anti-inflammatory activity that has been studied in clinical trials for acne and the treatment of mild to moderate atopic dermatitis. AN2690 (tavaborole) is a benzoxaborole in Phase 3 clinical trials for the topical treatment of onychomycosis, a fungal infection of the toenails and fingernails. Another benzoxaborole derivative, AN2728, a phosphodiesterase-4 (PDE4) inhibitor, is in Phase 2 clinical trials for the treatment of atopic dermatitis. AN2898, also a PDE4 inhibitor, has been studied in clinical trials for atopic dermatitis and psoriasis. AN3365 is a leucyl-tRNA synthetase inhibitor that has been in clinical development for the treatment of various Gram-negative bacterial infections. These five representative compounds were negative in the three genotoxicity assays. Furthermore, AN2690 has been studied in mouse and rat 2-year bioassays and was not found to have any carcinogenic potential. These results demonstrate that it is possible to design boron-based therapeutic agents with no genetic toxicology liabilities., (Copyright © 2013 Wiley Periodicals, Inc.)

There is an increasing interest in in vivo metabolite identification in early drug discovery in order to (i) give a more complete picture of metabolic profile in investigational animal models, (ii) propose phase I and phase II metabolites using the same pharmacokinetic/toxicokinetic study samples, (iii) expose metabolically labile groups where chemical modifications could improve stability, and (iv) enable early safety assessment of metabolites. In the early discovery stage of our anti-inflammatory program, one novel benzoxaborole, AN6414, exhibiting both PDE4 enzyme and TNFα inhibition activities, became our primary candidate for further investigation. The traditional metabolite identifications usually require high dosed samples with long data scans and analysis. In this study, we conducted quick and more selective core-structure related precursor scans followed by daughter ion scans and identified a total of 10 major phase I and phase II metabolites using rat plasma samples from a toxicokinetic study at an oral dosing of 30 mg/kg. Plasma samples were treated with solid phase extraction (SPE) prior to LC/MS/MS. An AB SCIEX API 4000 QTRAP mass spectrometer coupled with a Shimadzu LC system was used for LC/MS/MS analysis. We found the major metabolites of AN6414 to be oxidative deboronation, protodeboronation, oxidation products and their sulfate-conjugated species. This analysis drove analoging efforts which improved the pharmacokinetic profile, namely, lowering clearance and increasing exposure relative to AN6414. Toxicity predictions by the software program DEREK suggest the identified potential metabolites to be safe., (Copyright © 2012 Elsevier B.V. All rights reserved.)