The naturally occurring betulinic acid (BA) and its derivative NVX-207 show anticancer effects against equine malignant melanoma (EMM) cells and a potent permeation in isolated equine skin in vitro. The aim of the study was to determine the in vivo concentration profiles of BA and NVX-207 in equine skin and assess the compounds' local and systemic tolerability with the intent of developing a topical therapy against EMM. Eight horses were treated percutaneously in a crossover design with 1% BA, 1% NVX-207 or a placebo in a respective vehicle twice a day for seven consecutive days with a seven-day washout period between each formulation. Horses were treated at the neck and underneath the tail. Concentration profiles of the compounds were assessed by high-performance liquid chromatography in the cervical skin. Clinical and histopathological examinations and blood analyses were performed. Higher concentrations of NVX-207 were found in the skin compared to BA. Good systemic tolerability and only mild local adverse effects were observed in all three groups. This study substantiates the topical application of BA and NVX-207 in further clinical trials with horses suffering from EMM; however, penetration and permeation of the compounds may be altered in skin affected by tumors.
© 2020 The Authors. Journal of Veterinary Pharmacology and Therapeutics published by John Wiley & Sons Ltd.