Drug resistance and apoptosis in cancer treatment: development of new apoptosis-inducing agents active in drug resistant malignancies.

Modulation of multidrug resistance (MDR) has been extensively studied in vitro and in vivo. However, several clinical trials have failed to show any important benefits in terms of response to chemotherapy or the length of survival using MDR reversing agents. This may be due to the expression or co-expression of other drug resistance mechanisms in malignant cells. Several studies have shown that most, if not all, chemotherapeutic agents exert their anticancer activity by inducing apoptosis; therefore, resistance to apoptosis may be a major factor limiting the effectiveness of anticancer therapy. In the last few years, effort has been made to understand the biochemical alterations of apoptotic pathways in cancer. Many of these alterations confer a multidrug resistant phenotype to malignant cells. In this context, the new recently developed anticancer therapies based on drugs that modulate apoptosis may have importance for the treatment of tumors that are scarcely responsive to the conventional anticancer chemotherapy. In this review, we discuss the current knowledge about drug resistance, apoptosis and cancer and report the recently developed apoptosis modulating strategies that have potential therapeutic implications for the drug resistant tumors.