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.

Tumor cell cholesterol depletion and V-ATPase inhibition as an inhibitory mechanism to prevent cell migration and invasiveness in melanoma.

BACKGROUND: V-ATPase interactions with cholesterol enriched membrane microdomains have been related to metastasis in a variety of cancers, but the underlying mechanism remains at its beginnings. It has recently been reported that the inhibition of this H+ pump affects cholesterol mobilization to the plasma membrane. METHODS: Inhibition of melanoma cell migration and invasiveness was assessed by wound healing and Transwell assays in murine cell lines (B16F10 and Melan-A). V-ATPase activity was measured in vitro by ATP hydrolysis and H+ transport in membrane vesicles, and intact cell H+ fluxes were measured by using a non-invasive Scanning Ion-selective Electrode Technique (SIET). RESULTS: Cholesterol depletion by 5mM MßCD was found to be inhibitory to the hydrolytic and H+ pumping activities of the V-ATPase of melanoma cell lines, as well as to the migration and invasiveness capacities of these cells. Nearly the same effects were obtained using concanamycin A, a specific inhibitor of V-ATPase, which also promoted a decrease of the H+ efflux in live cells at the same extent of MßCD. CONCLUSIONS: We found that cholesterol depletion significantly affects the V-ATPase activity and the initial metastatic processes following a profile similar to those observed in the presence of the V-ATPase specific inhibitor, concanamycin. GENERAL SIGNIFICANCE: The results shed new light on the functional role of the interactions between V-ATPases and cholesterol-enriched microdomains of cell membranes that contribute with malignant phenotypes in melanoma.