Table II.

Stability and Reproducibility of P-gp Function in Parent and MDR1 _WT and MDR1 _GT1292-3TG Recombinant Cells

	Doxorubicin (percent of HEK host cells)
	HEK host cells	MDR1 wt (431 Cys)	MDR1 GT1292-3TG (431Leu)
Pre-banked cellsa	100 ± 2.3	61.8 ± 2.8	78.3 ± 3.9
37 days after thawingb	100 ± 7.5	62.9 ± 1.7	79.6 ± 1.7
61 days after thawingb	100 ± 4.4	61.7 ± 4.0	80.1 ± 3.7

The recombinant cells expressing MDR1 _wt or MDR1 _GT1292-3TG were exposed to 5 μM doxorubicin for 30 min at 37°C and the doxorubicin concentration were determined. These data were normalized for protein content and expressed as percentage of drug uptake in the HEK host cells. Data expressed were a mean ± SD for quadruplicate

^aCells were banked in 10% DMSO in DMEM + 10% FBS growth medium

^bCells were thawed and passaged following 4 months of storage in liquid N₂