Resistance to taxanes is induced by c-erbB-2 overexpression in human MCF-10A mammary epithelial cells and is blocked by combined treatment with an antisense oligonucleotide targeting type I protein kinase A

We have tested the sensitivity of human MCF-10A mammary epithelial cells an d of their transformed derivatives overexpressing an activated c-Ha-ras gen e (MCF-10A Ha-ras cells), the c-erbB-2 gene (MCF-10A c-erbB-2 cells) or bot h genes (MCF-IOA HE cells) to different cytotoxic drugs. As compared with p arental MCF-IOA cells, the transformed cells exhibited an increased sensiti vity to topoisomerase I-and topoisomerase Ii-inhibitors, and to platinum-de rivatives with a 2- to 10-fold reduction in IC50 values. A remarkable diffe rence in sensitivity was observed following treatment with taxanes, While M CF-IOA Ha-ras cells showed an increased sensitivity, MCF-I OA c-erbB-2 and MCF-I OA HE cells exhibited a relative resistance to taxol and taxotere, wi th an approximately 3.5- to 6.5-fold higher IC50 as compared with MCF-10A c ells suggesting that c-erbB-2 overexpression has a dominant effect compared with an activated c-Ha-ras gene. The type I cAMP-dependent protein kinase (PKAI) is overexpressed in cancer cells, Inhibition of PKAI by antisense ol igonucleotides targeting its Riot regulatory subunit results in cancer cell growth inhibition. To evaluate the effect of blocking PKAI on MCF-10A cell sensitivity to taxanes, we treated these cells with taxol or taxotere in c ombination with a PKAI antisense oligonucleotide. Treatment with this agent , but not with a control scramble sequence, was able to overcome the effect of c-erbB-2 overexpression on MCF-I OA cell sensitivity to taxol and taxot ere, with a 20- to 40-fold shift in the IC50 values for the 2 drugs. (C) 20 00 Wiley-Liss, Inc.