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Advanced hormone-refractory prostate cancer remains a therapeutic challenge, because all available pharmaceutical concepts have been ineffective in improving cancer-specific survival. Failure of chemotherapy may be caused by multidrug resistance (MDR) mechanisms protecting cancer cells against cytotoxic drugs, and the question arises whether prostate cancer is also using MDR principles resulting in resistance against chemotherapeutic agents. In consequence, an array of diverse pathways known to lead to MDR such as MDR1, MRPs, glutathione, and apoptosis have been examined and partially established at varying degrees in hormone-refractory prostate cancer. Thus, evidence keeps accumulating for the involvement of some MDR mechanisms in the chemoresistance of prostate cancer in vitro and in vivo. For some of them, e.g. MRP1, functional expression appears to be probable. This lends credit to the idea that reversal, circumvention, or overcoming of MDR pathways in advanced prostate cancer may be feasible and will lead to new avenues with improved treatment efficacy in otherwise intractable disease., (Copyright 2003 S. Karger GmbH, Freiburg)

Chemotherapy is the principal strategy to systemically challenge metastasized cancers of genitourinary origin. Unfortunately, the efficacy of chemotherapy is often hampered by multidrug resistance, the resistance to a variety of structurally and functionally distinct cytotoxic agents. Multidrug resistance can be either intrinsic or acquired, and can be caused by several mechanisms. The so-called classical multidrug resistance, mediated by the MDR1 gene product P-glycoprotein, has been held mainly responsible for inferring the multidrug resistance phenotype on urologic malignancies. However, several other multidrug resistance pathways have been identified. Multidrug resistance can be caused by the membrane-bound multidrug-resistance-associated protein, the detoxifying glutathione metabolism, the antiapoptotic protein BCL2, and changes in levels or activity of the topoisomerase enzymes. Strategies to overcome multidrug resistance of genitourinary tumors have arisen from the better understanding of the biologic and molecular mechanisms of multidrug resistance, and have been studied in experimental and clinical settings. However, attempts to modulate multidrug resistance in clinical renal cell, bladder, prostate, and testicular cancer have not been very rewarding so far, despite the optimism that had arisen from experimental data. Nevertheless, application of novel therapies to reverse multidrug resistance and to increase efficacy of chemotherapy for urologic cancers should be further pursued, within the setting of controlled clinical trials, to improve on current strategies.