Anticancer Drug‐mediated Induction of Multidrug Resistance‐associated Genes and Protein Kinase C Isozymes in the T‐Lymphoblastoid Cell Line CCRF‐CEM and in Blasts from Patients with Acute Lymphoblastic Leukemias

The major determinants mediating drug resistance in acute lymphoblastic leukemias (ALL) unresponsive to chemotherapy, are still unclear. For example, it is still unknown whether selection or induction processes are responsible for drug resistance here or whether protein kinase C (PKC) isozymes contribute to the resistant phenotype. Therefore, inducibility of resistance factors or PKC isozymes genes was examined in CCRF‐CEM cells treated with diverse anticancer drugs‐ adriamycin, camptothecin, etoposide or vincristine‐at sublethal concentrations for 24 h. MDR1, MRP1, LRP and PKC isozyme α, β(1), β(2), ε, ι, η, θ, ζ gene expression was determined by cDNA‐PCR. We found significant dose‐dependent, mostly combined, induction of the MDR1, MRP1 and LRP genes. Significantly enhanced gene expression of the majority of PKC isozyme genes was found after treatment with camptothecin. PKCζ was upregulated throughout by each anticancer drug applied in this setting. A series of selected CCRF‐CEM‐derived multidrug resistance (MDR) sublines also showed enhanced expression of the PKC isozymes compared to the parental cell line. MDR1 and PKCη gene expression levels were correlated highly significantly. Blasts from two patients with ALL during the first week of monotherapy with steroids revealed combined induction of the MDR1, multidrug resistance‐associated protein 1 (MRP1), lung cancer resistance‐related protein (LRP) and most PKC isozymes, predominantly PKCζ. Another patient with T‐ALL, who failed to respond to four months of intensive chemotherapy, showed an enhanced MRP1 gene expression combined with markedly overexpression of PKCη and PKCθ. Furthermore, the camptothecin and etoposide‐mediated induction of resistance factors in the CCRF‐CEM cell line could be suppressed by staurosporine, a rather unspecific inhibitor of protein kinases. However, selective inhibitors of PKC isozymes (bisindolylmaleimide GÖ 6850, indolocarbazole GÖ 6976) produced no significant effects here. Therefore, the PKC isozymes η, θ and ζ are of interest as potential targets to overcome drug resistance in ALL.