Abstract

Tumor hypoxia is accompanied by resistance to many damaging therapeutic effects. This effect is often attributed to the loss of the ability of normal and benign tumor cells to adapt their metabolism to hypoxia, whereas cancer cells, on the contrary, acquire the ability to survive and avoid an immune response under hypoxic conditions. Moreover, cancer cells use hypoxia to reprogram their metabolism and induce antioxidant protection, in particular by increasing the production of antioxidant molecules [NAD(P)H and glutathione], which protect hypoxic cancer cells from the damaging effects of free radicals. However, hypoxic cancer cells may differ one from another by the efficiency of protection against damage; an indicator is required to assess this efficiency. The goal of our work is the search for such a single-cell endogenous indicator. For this, we measured endogenous NAD(P)H fluorescence in single hypoxic cancer cells during their UV-induced damage [NAD(P)H photodegradation], as well as determined their ability to restore NAD(P)H fluorescence intensity after the damage/(photo)degradation. Most hypoxic cancer (but not normal) cells were experimentally found to be capable of partially restoring the damage with different efficiencies. Some hypoxic cancer cells possess increased resistance to UV-induced damage. Such cells retained the ability to partially restore NAD(P)H intensity even after 5-6 cycles of repeated damage. Our studies enable recommending the NAD(P)H regenerative response observed in hypoxic tumor cells as a prognostic indicator to assess their potential resistance to damage. This indicator can be useful in choosing new antitumor capabilities of specifically destroying cancer cells with increased resistance to damage.

Keywords:Cancer resistance; Hypoxia, Injury; NAD(P)H; Single-cell indicator