Collateral sensitivity to gemcitabine (2′,2′-difluorodeoxycytidine) and cytosine arabinoside of daunorubicin- and VM-26-resistant variants of human small cell lung cancer cell lines1 1 Abbreviations: ara-C,1-β-d-arabinofuranosylcytosine; dCDA, deoxycytidinedeaminase; dCK, deoxycytidine kinase; dCyd, deoxycytidine; dFdC,2′,2′-difluorodeoxycytidine; MDR, multidrug resistance; MRP,multidrug resistance-associated protein; P-gP, P-glycoprotein; SCLC,small cell lung carcinoma; TCA, trichloroacetic acid; TK, thymidinekinase; and VM-26, teniposide, epipodophyllotoxin 4′-demethyl-O-(4,6-O-2-thenylidene-β-d-glucopyranoside).