Involvement of esterases in the pulmonary metabolism of beclomethasone dipropionate and the potential influence of cannabis use

Beclomethasone dipropionate (BDP) is an inhaled glucocorticoid used for maintenance treatment of asthma in adults and children. BDP is a prodrug activated in lung when hydrolyzed to its major active metabolite beclomethasone-17-monopropionate (17-BMP), which can be further deactivated to beclomethasone (BOH). The specific hydrolases contributing to these processes have not been identified which warrants an investigation to enable a better assessment of the drug-drug interaction (DDI) liability and a better management of drug efficacy and systemic toxicity. In the present study, the pulmonary metabolism of BDP was investigated using both human lung S9 (HLuS9) and recombinant carboxylesterase 1 (CES1) S9. By employing the relative activity approach, we tested the hypothesis of CES1 being the major enzyme involved. Assessment of other hydrolases were conducted in an assay with selective esterase inhibitors. In addition, the DDI potentials between BDP and Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) were evaluated due to the increasing use of inhaled cannabis both recreationally and medically. The mechanism of DDI was conducted in an in vitro time-dependent inhibition assay, and further interpreted utilizing a proposed model. In HLuS9, BDP was efficiently metabolized almost completely to 17-BMP, which was then converted to BOH at a much lower rate. CES1 was found as a minor contributor accounting for only 1.4% of BDP metabolism in HLuS9, while arylacetamide deacetylase might be the main enzyme involved. Both THC and CBD inhibited the HLuS9 mediated BDP hydrolysis in a reversible manner, with reported IC50 values estimated as 8.98 and 36.8 μM, respectively. Our proposed model suggested a moderately decreased 17-BMP exposure in lung by concomitant THC from a cannabis cigarette, while the effects from orally administered CBD was expected to be of no clinical relevance.