Influence of Tumor pH on Therapeutic Response

Abstract

The intratumor microenvironment is intrinsically acidic due mainly to accumulation of lactic acid as a result of increased aerobic and anaerobic glycolysis by the tumor cells. In general, the extracellular pH (pHe) in human tumors is below 7.0, whereas the intracellular pH (pHi) is maintained at neutral range, i.e.,>7.0, by powerful pHi control mechanisms. The low pHe and the significant gradients between pHe and pHi affect markedly the response of tumors to various treatments such as chemotherapy, radiotherapy and hyperthermia. For instance, the acidic pHe increases the cellular uptake of weakly acidic drugs such as cyclophosphamide and cisplatin and thus increases the effect of the drugs, whereas the acidic pHe retards the uptake of weakly basic drug such as doxorubicin and vinblastine, thereby reducing the effect of the drugs. The radiationinduced apoptosis is suppressed by an acidic environment, whereas the hyperthermiainduced cell death is potentiated by an acidic environment. Better understanding of the control mechanisms of pHe and pHi in tumors may lead to device effective treatment strategy of human tumors.