Melanomas are tumours of the pigment-producing melanocytes, and are among the most common equine tumours, occurring particularly in grey horses. Typically, they first appear as small, pigmented nodules, often under the tail. They usually grow slowly for years, but may infiltrate surrounding tissues, or appear elsewhere in the body.
Betulinic acid (BA) is a natural compound, found in the bark of several species of plants, such as the
white birch (Betula pubescens) after which it was named. It has been shown to have several potentially-useful pharmacological effects. Previous work has shown that BA can induce death (apoptosis) of melanocytes in cell culture.
Research conducted in Austria looked at whether topical treatment with betulinic acid, or NVX-207, (a betulinic acid derivative) could be used to treat early cases of melanoma.
Lisa A. Weber and colleagues conducted a small, pilot study involving eighteen Lipizzaner mares with cutaneous melanomas (all having a diameter of no more than 15mm).
The horses, on a stud farm in Austria, were divided into three treatment groups: placebo cream; 1% BA cream; and 1% NVX-207 cream.
The research team treated a maximum of two tumours per horse. After topical application of the cream, the melanomas were covered to prevent it being rubbed off. The study extended over 13 weeks.
The researchers assessed progress with clinical examinations, measuring the tumours, monitoring them and the surrounding clinically normal skin, assessing the horses’ behaviour during cream application, and monitoring haematologic and blood biochemistry profiles.
All horses tolerated the topical drug application well and did not object to it being applied. Two horses had mild colic during the study, which resolved with medical treatment. Both horses had a previous history of colic and the authors consider it very unlikely that the colic was related to the topical melanoma treatment.
The topical therapy resulted in part in clinically visible and measurable changes in small melanocytic lesions, which were reflected in skin depigmentation and reduction in tumour diameters and volumes.
The researchers found a beneficial effect after treatment with BA towards the end of the treatment period. A few tumours in the placebo group also showed a decrease in size.
They conclude: “The results presented in this pilot study indicate that topical treatment of early-stage equine melanoma with 1% BA and 1% NVX-207 twice a day over a period of 13 weeks is feasible and safe.”
“Especially after BA application, positive effects were observed toward the end of the treatment interval. This suggests that this approach might be a potential therapy for early-stage equine melanoma and, thus, reduce the health risks associated with the possible malignant degeneration of the tumours.”
However, the authors are unable to recommend the current treatment protocol for general use as the long treatment duration could lead to poor owner compliance. They suggest that modification of the pharmaceutical formulations may improve the clinical outcome and reduce treatment periods.
For more details, see:
Effects of Topically Applied Betulinic Acid and NVX-207 on Melanocytic Tumors in 18 Horses.
Weber, L.A.; Delarocque, J.; Feige, K.; Kietzmann, M.; Kalbitz, J.; Meißner, J.; Paschke, R.; Cavalleri, J.-M.V.
Animals 2021, 11, 3250.