Anticancer drugs chemotherapy resistance

Methotrexate remains an anticancer drug of major importance for "combination chemotherapy." A number of mechanisms by which cancer cells gain resistance to methotrexate have been identified. 

Efforts to promote medical applications of liposomes have permitted the development of several new drug formulations applicable to a broad range of therapeutics. One of the main areas of liposomes application is cancer therapy, A great number of scientists worldwide have focused their work on drug discovery or the improvement of the efficacy and reduction of the toxicity of known drugs. Two of the main problems in cancer chemotherapy are the toxicity of the known anticancer drugs and the multi drug resistance of certain cancer cells. 

There are very few tumor types in which the use of chemotherapy can bring about prolonged survival, and possibly cure, for individual patients. The most common reason for this is the development of drug resistance within tumor cells. The laboratory study of resistance to anticancer drugs has resulted in the discovery of numerous mechanisms present within tumor cells that act to reduce their cytotoxic effects. However, the failure to translate this basic laboratory research into improved clinical outcome for patients remains one of the most pressing problems in contemporary cancer research. 

A few years after the introduction of Taxol in 1996, further phytogenic anticancer drugs were launched to treat advanced cancers. Topotecan, marketed by Smith Kline Beecham under the trade name of Hycamtin, was approved by the FDA to treat ovarian cancers that have resisted other chemotherapy drugs. Furthermore, irinotecan was introduced by Pharmacia Upjohn under the trade name of Camptosar for the treatment of metastatic cancer of the colon or rectum. Both compounds are derivatives of camptothecin which was isolated from the Chinese tree Camptotheca acuminata, well known in Chinese Traditional Medicine for anticancer treatment [65]. Isolation of the bioactive principle camptothecin and its structure elucidation had already been performed in 1966... 

Many conventional anticancer drugs display relatively poor selectivity for neoplastic cells, and solid tumors are particularly resistant both to radiation and to chemotherapy. 

C. Resistance to Anticancer Drugs Drug resistance is a major problem in cancer chemotherapy. Mechanisms of resistance include the following. 

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