PHORBOL ESTER AND OKADAIC ACID-RESISTANT CELLS - THE CROSSROADS OF SIGNAL-TRANSDUCTION AND DRUG-RESISTANCE

Many factors are involved in the development of drug resistance for an ticancer drugs. The drugs should pharmacokinetically attain the approp riate concentration. They should be metabolized to the active forms. T umor cells should have sensitivity to them. Several molecular and bioc hemical mechanisms that may explain cellular drug resistance have been identified. The contribution of protein phosphorylation and dephospho rylation for drug resistance is demonstrated in phorbol ester and okad aic-acid-resistant cells. The modulation of drug resistance by substan ces that affect the signal transduction pathway is an important issue in the development of an effective method for overcoming drug resistan ce.