Myrtenal-induced V-ATPase inhibition - A toxicity mechanism behind tumor cell death and suppressed migration and invasion in melanoma.

Background: Metastatic tumor cells have acidic extracellular pH and differential electrochemical H gradients generated across their cell membranes by V-type H-ATPases. This study shows that inhibition of the V-ATPases by the plant-derived monoterpene Myrtenal results in tumor cell death and decreased metastatic dissemination in mice.

Methods: The Myrtenal anticancer toxicity was evaluated in vitro using murine (B16F0 and B16F10) and human (SkMel-5) melanoma cell lines, and in in vivo mouse metastatic dissemination model. Proton flux and extracellular acidification were directly evaluated at the surface of living cells using a non-invasive selective ion electrode approach.

Results: The inhibition of V-ATPases by 100 μM Myrtenal disrupted the electrochemical H gradient across the cell membranes, strongly induced cell death (4-5 fold), and decreased tumor cells migration and invasion in vitro. Myrtenal (15 mg/kg) also significantly reduced metastasis induced by B16F10 in vivo, further reinforcing that V-ATPase is a molecular target to halt the progression of cancers.

Conclusions: These data revealed the therapeutic potential of Myrtenal as inhibitor of melanoma progression proposing a mechanism of action by which once inhibited by this monoterpene the proton pumps fail to activate cancer-related differential electrochemical gradients and H fluxes across the tumor cell membranes, disrupting pH signatures inherent in tumor progression, resulting in reprogrammed cell death and metastasis inhibition.

General Significance: The work represents a new mechanistic strategy for contention of melanoma, the most aggressive and deadly form of cutaneous neoplasm, and highlights Myrtenal, other related monoterpenes and derivatives as promising proton pump inhibitors with high chemotherapeutic potential.