Cutaneous melanoma is not an unusual finding in horses, especially in individuals with grey-colored hair coats. In humans, melanoma is aggressive and life-threatening, whereas this cancer is slower growing in horses and generally local and well encapsulated.
An attempt to find possible treatments for human melanoma led Brazilian researchers to investigate in vivo treatment with Amblyomin-X protein that “selectively leads to the death of tumor cells via apoptosis.” This compound is derived from saliva of the Amblyomma sculptum tick [Lichtenstein, F.; Iqbal, A.; de Lima, Will S.E.A.; et al. Modulation of stress and immune response by Amblyomin-X results in tumor cell death in a horse melanoma model. Scientific Reports 2020, vol. 10:6388; doi.org/10.1038/s41598-020-63275-2].
The study evaluated intra-tumoral injection of Amblyomin-X at 1 mg/kg of tumor mass on each third day over 28 days. Tumors treated were on the ventral tail of five horses, each affected with multiple tumors. The tumor volume and clinical signs of each horse, including controls, were monitored for five months. All treated horses achieved at least 75% reduction in tumor volume within the initial month, and some achieved remission up two months following the end of treatment. This was in contrast to the controls, which had either no change or an increase in volume over the study period.
The researchers summarized: “Amblyomin-X is an anti-tumor molecule because it acts on multiple cellular targets to induce tumor cell death. It selectively enters only cancer cells via endocytosis, binding to the external membrane attracted by phosphatidylserine affinity, and thereafter, inside the cell modulates its microenvironment. Amblyomin-X activates the Endoplasmic Reticulum and mitochondria-stress pathways followed by apoptosis and survival responses.”
Also observed was activation of innate immune pathways inducing pro-inflammatory cytokines and chemokines within six hours of intra-tumoral injection.
At this time, the study is focused on potential treatment of human melanoma; however, there could be clinical application for equine melanoma with adjuvant therapy following further studies and outcomes.