Table 2. dCK, TK2 and dCDA activities and dCK protein and mRNA expression in the human NSCLC cell line SW1573 and its doxorubicin MDR variants; 2R120 (MRP1) and 2R160 (P-gP).

Enzyme		SW1573	2R120	2R160
dCK	Activity	0.3±0.08	2.1±0.3***	1.3±0.7 NS
	Protein	0.3	2.0	0.6
	mRNA	0.5	3.1	2.8
TK2		0.2±0.2	0.2±0.3	0.1±0.2 NS
dCDA		37±3.0	13±3***	17±1***

Enzyme activities are means±s.d. of at least three experiments in nmol h⁻¹ per 10⁶ cells. For dCK and TK2 activity, dCyd was used as a substrate with or without thymidine to block TK2 activity. The difference in dCMP formation between dCyd as a substrate and dCyd and thymidine as a substrate was considered as TK2 activity. The protein content of SW1573, 2R120 and 2R160 cells was about 273±77, 442±152 and 210±8 μg per 10⁶ cells, respectively (means±s.d.). Protein and mRNA expression are means of two and three separate experiments in (OD mm⁻²) and (dCK/β-actin × 10⁻³), respectively. Statistically different from SW1573 by t-test (independent samples); NS=not significant.

^***P<0.001.