Acquired resistance to chemotherapy in lung cancer cells mediated by prolonged nitric oxide exposure

The effect of extended exposure of cancer cells to nitric oxide (NO), an endogenous mediator frequently found increased in tumors, is largely unknown. In the present study, the effect of long-term NO exposure on chemotherapeutic resistance was investigated in lung cancer cells.

The effect of long-term exposure of human lung cancer cells to NO on susceptibility to chemotherapeutic agents-induced apoptosis was analyzed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, co-staining of Hoechst 33342 and propidium iodide (PI), and Annexin V detection. The expression of survival-related proteins was analyzed by western blot. Gene manipulation was used for evaluation of the effect of expression proteins on susceptibility of the cells to chemotherapeutic agent-mediated death.

Long-term NO exposure for 7-14 days rendered the lung cancer cells resistant to cisplatin, doxorubicin, and etoposide dose- and time-dependently. The underlying mechanism was found to involve the adaptive responses of the cells, by increasing survival due to increase in the level of caveolin-1 (CAV1) and anti-apoptotic B-cell lymphoma-2 (BCL2), and up-regulation of activated protein kinase B (AKT). The gene manipulation study revealed that the increase of activated AKT and BCL2 was responsible for the resistance to all tested drugs, while the up-regulation of CAV1 only attenuated cell death mediated by doxorubicin and etoposide. Interestingly, NO-mediated drug resistance was found to be reversible when cells were further cultured in the absence of NO for five days.

These findings reveal the novel role of NO in the tumor environment, in attenuating chemotherapeutic susceptibility and this could be beneficial in contriving strategies to treat the disease.