Mechanisms of Anthracycline-Enhanced Reactive Oxygen Metabolism in Tumor Cells

Table 4

Effect of inhibitors of NADPH:cytochrome p-450 reductase on superoxide formation in tumor microsomes. NADPH:cytochrome P-450 reductase was assayed at 30°C as described in Materials and Methods using nonacetylated cytochrome c and 200 μg of microsomal protein per ml. Reactions were initiated with 100 nmol of NADPH. Where indicated, the reaction mixtures were preincubated with DTNB or NADP⁺ for 2 min prior to the initiation of cytochrome c reduction. In these experiments, superoxide production was assessed as described in Table 2 except that the NADPH concentration was 100 μM rather than 1 mM.

Experimental system	NADPH:cytochrome P-450 reductase activity (nmol/min/mg)	Superoxide production (nmol/min/mg)
Control	(3)^a
+DTNB (100 μM)	(3)^b
+NADP^+ (1 mM)	(3)^b
Doxorubicin (135 μM)		(3)
+DTNB (100 μM)		(3)^b
+NADP^+ (1 mM)		(3)^b

^a; numbers in parentheses are numbers of experiments; ^bsignificantly different from samples without inhibitor present ().