Statins revert doxorubicin resistance via nitric oxide in malignant mesothelioma

Human malignant mesothelioma (HMM) is resistant to many anticancer drugs, including doxorubicin. Mevastatin and simvastatin, 2 inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, potentiated the intracellular accumulation and the cytotoxicity of doxorubicin in HMM cells constitutively expressing P-glycoprotein and multidrug resistance-associated protein 3. This effect of statins was nitric oxide (NO)-dependent, since it was reverted by either an NO synthase inhibitor or an NO scavenging system. The NO synthase up-regulation in HMM and other cells is known to be associated with the activation of the transcription factor NF-kappaB: in HMM cells statins increased the NF-kappaB translocation into the nucleus, decreased the level of the NF-kappaB inhibitor IkBalpha and increased the phosphorylation/activation of IkB kinase alpha (IKKalpha). IKKalpha is under the negative control exerted by RhoA in its prenylated (active) form: incubation of HMM cells with statins lowered the amount of active RhoA and the level of Rho-associated kinase activity. All statins' effects were reverted by mevalonic acid, thus suggesting that they were mediated by the inhibition of HMGCoA reductase and were likely to be subsequent to the reduced availability of precursor molecules for RhoA prenylation. Both the Rho kinase inhibitor Y27632 and the RhoA inhibitor toxin B (from Clostridium difficile) mimicked the statins' effects, enhancing doxorubicin accumulation, NO synthesis and IKKalpha phosphorylation and decreasing the amount of IkBalpha in HMM cells. Simvastatin, Y27632 and toxin B elicited tyrosine nitration in the P-glycoprotein, thus providing a likely mechanism by which NO reverts the doxorubicin resistance in HMM cells.