BackgroundTuberculosis (TB) is still a leading cause of death worldwide. Almost a third of the world's population is infected with TB bacilli, and each year approximately 8 million people develop active TB and 2 million die as a result. Today's TB treatment, which dates back to the 1970s, is long and burdensome, requiring at least 6 mo of multidrug chemotherapy. The situation is further compounded by the emergence of multidrug-resistant TB (MDR-TB) and by the infection's lethal synergy with HIV/AIDS. Global health and philanthropic organizations are now pleading for new drug interventions that can address these unmet needs in TB treatment.Methods and FindingsHere we report OPC-67683, a nitro-dihydro-imidazooxazole derivative that was screened to help combat the unmet needs in TB treatment. The compound is a mycolic acid biosynthesis inhibitor found to be free of mutagenicity and to possess highly potent activity against TB, including MDR-TB, as shown by its exceptionally low minimum inhibitory concentration (MIC) range of 0.006–0.024 μg/ml in vitro and highly effective therapeutic activity at low doses in vivo. Additionally, the results of the post-antibiotic effect of OPC-67683 on intracellular Mycobacterium tuberculosis showed the agent to be highly and dose-dependently active also against intracellular M. tuberculosis H37Rv after a 4-h pulsed exposure, and this activity at a concentration of 0.1 μg/ml was similar to that of the first-line drug rifampicin (RFP) at a concentration of 3 μg/ml. The combination of OPC-67683 with RFP and pyrazinamide (PZA) exhibited a remarkably quicker eradication (by at least 2 mo) of viable TB bacilli in the lung in comparison with the standard regimen consisting of RFP, isoniazid (INH), ethambutol (EB), and PZA. Furthermore, OPC-67683 was not affected by nor did it affect the activity of liver microsome enzymes, suggesting the possibility for OPC-67683 to be used in combination with drugs, including anti-retrovirals, that induce or are metabolized by cytochrome P450 enzymes.ConclusionsWe concluded that based on these properties OPC-67683 has the potential to be used as a TB drug to help combat the unmet needs in TB treatment.

In an effort to develop potent new antituberculosis agents that would be effective against both drug-susceptible and drug-resistant strains of Mycobacterium tuberculosis, we prepared a novel series of optically active 6-nitro-2,3-dihydroimidazo[2,1-b]oxazoles substituted at the 2-position with various phenoxymethyl groups and a methyl group and investigated the in vitro and in vivo activity of these compounds. Several of these derivatives showed potent in vitro and in vivo activity, and compound 19 (OPC-67683) in particular displayed excellent in vitro activity against both drug-susceptible and drug-resistant strains of M. tuberculosis H37Rv (MIC = 0.006 microg/mL) and dose-dependent and significant in vivo efficacy at lower oral doses than rifampicin in mouse models infected with M. tuberculosis Kurono. The synthesis and structure-activity relationships of these new compounds are presented.

The efficacy and safety of topical OPA‐15406, a new phosphodiesterase 4 inhibitor, were examined in Japanese patients aged 15–70 years with atopic dermatitis in a phase 2, randomized, double‐blind, vehicle‐controlled study. Two hundred patients were randomized to three treatment groups at a 1:1:1 ratio to receive OPA‐15406 0.3%, OPA‐15406 1% or vehicle ointment twice daily for 8 weeks. The OPA‐15406 1% group was superior to the vehicle group in terms of the incidence of success based on the Investigator Global Assessment score at week 4 (P = 0.0328), which was the primary end‐point, while the OPA‐15406 0.3% group showed a trend toward improvement in the primary end‐point. The mean Eczema Area and Severity Index total score and subscale (erythema, induration/papulation, excoriation and lichenification) scores, the Visual Analog Scale pruritus score and the Patient‐Oriented Eczema Measure score were significantly improved and the percentage of affected body surface area was significantly decreased in both OPA‐15406 groups relative to the vehicle group as early as week 1, and the improved scores and decreased percentages were generally maintained until week 8. No deaths or serious treatment‐emergent adverse events occurred in the OPA‐15406 treatment groups. Treatment‐emergent adverse events frequently observed across treatment groups were worsening of atopic dermatitis, viral upper respiratory tract infection and pruritus, all of which were mild or moderate in severity in the OPA‐15406 groups. OPA‐15406 1% ointment showed favorable efficacy and safety profiles, indicating a promising treatment option for patients with atopic dermatitis.

The safety and efficacy of OPA‐15406 (international non‐proprietary name, difamilast; also referred to as MM36), a new topical, selective phosphodiesterase type‐4 inhibitor, in Japanese pediatric patients with atopic dermatitis aged 2–14 years were evaluated in a phase 2, randomized, double‐blind, vehicle‐controlled, 4‐week study. Seventy‐three patients were randomized 1:1:1 to receive OPA‐15406 0.3%, OPA‐15406 1% or vehicle ointment twice daily for 4 weeks. The mean age of patients was similar across treatment groups. No deaths or serious treatment‐emergent adverse events were reported; all treatment‐emergent adverse events were mild or moderate in severity. The incidence of treatment‐emergent adverse events leading to treatment discontinuation was 4.2% (1/24) in the OPA‐15406 0.3% group, 4.0% (1/25) in the OPA‐15406 1% group and 16.7% (4/24) in the vehicle group, all of which were worsening of atopic dermatitis. Both OPA‐15406 groups demonstrated a higher incidence of success in the Investigator Global Assessment score compared with the vehicle group over the 4‐week study. The OPA‐15406 groups also showed greater improvements from baseline compared with the vehicle group in the Investigator Global Assessment score, Eczema Area and Severity Index overall score and subscale (erythema, induration/papulation, excoriation and lichenification) scores, Visual Analog Scale pruritus score, Patient‐Oriented Eczema Measure score, and percentage of affected body surface area over the 4‐week study. Topical OPA‐15406 twice daily for 4 weeks was considered a safe and effective treatment option in this phase 2 study in pediatric patients with atopic dermatitis, and phase 3 development is currently ongoing.

Conflicts of interestH.S. was the medical expert for the study and N.B. was the advisor. H.S. and N.B. have received fees for consultation from Otsuka Pharmaceutical Co., Ltd. K.I., D.Y. and H.T. are employees of Otsuka Pharmaceutical Co., Ltd. Data availabilityThe data that support the findings of this study are proprietary in nature and are not publicly available. However, the data are available from the corresponding author upon reasonable request.