The role of reduced nicotinamide adenine dinucleotide phosphate in glucose- and temperature-dependent doxorubicin cytotoxicity

Abstract

The mechanism of doxorubicin resistance induced by glucose deprivation was examined using an L929 cell system. Resistance developed even when the synthesis of glucose-regulated proteins was suppressed by supplementing glucose-deprived cultures with uridine. Resistance was also not correlated with pyruvate availability, with DNA strand breaks, or with intracellular drug or nucleotide levels. However, intracellular concentrations of reduced nicotinamide adenine dinucleotide phosphate (NADPH) decreased to undetectable levels in glucose-deprived cells with or without uridine supplementation. NADPH depletion induced by treating glucose-fed cells with low concentrations of methylene blue afforded the same degree of protection as glucose deprivation, and normal sensitivity could be restored to glucose-deprived cells by adding NADPH to the culture medium. These results suggest that decreased NADPH availability is responsible for the doxorubicin resistance induced by glucose deprivation. Although drug uptake and NADPH production increased with temperature, these effects could not fully account for the > 1000-fold decrease in clonogenic survival observed over the 25 degrees-37 degrees C temperature range. Similarly, manipulation of NADPH levels confirmed a role for drug bioreduction in the cytotoxic mechanism but did not suggest that NADPH availability was rate-limiting for this process at any temperature employed.

Synthesis of texaphyrin conjugates

“…Doxorubicin (adriamycin) is one of the most important chemotherapeutic agents currently in use. While its mode of action is not thought to be related to electron-transfer processes per se, the fact that it contains easy-to-reduce quinone functionality, could be important in terms of its dose-limiting cardiomyopathy; capture of an electron by this subunit (from, e.g., NAD(P)H) followed by production of reactive oxygen species may trigger a cytotoxic reaction at sites other than within the cancerous tissues [24][25][26][27][28][29][30][31][32][33][34]. The possibility that this kind of chemical process could occur, led to studies wherein doxorubicin was administered in conjunction with MGd, 1 [35].…”

Photodynamic enhancement of doxorubicin cytotoxicity

“…Figure 7 shows that either enzyme was capable of completely abolishing the increase in cytotoxicity produced by laser irradiation, i.e., exposure of cultures to doxorubicin followed by enzyme was the same in the presence or absence of irradiation. It should be noted that enzyme treatment did not completely block doxorubicin cytotoxicity since drug and enzyme were not applied simultaneously [3].…”