That is why most conventional cytotoxic drugs work on DNA by either causing extensive DNA damage that will lead to apoptosis or block DNA synthesis.

The development of cytotoxic agents for cancer is one of the cornerstones of treatment of cancer in recent years [3,4]. There are three main treatments established for cancer: surgery, irradiation, and cytotoxic agents. For several types of cancer, especially, at the early stage of the disease, cytotoxic therapy provides either cure of the disease or prolong survival combined with other treatment modalities or alone. Also in the advanced or metastatic stage of the disease, it may be helpful in symptom control of the patient, which is another important aspect of cancer treatment. However, there are still some important limitations of cytotoxic drugs mainly because of the lack of understanding of the detailed mechanism of action and the rationale use of them in cancer treatment. Most of them have very narrow therapeutic indexes, resulting in severe toxic side effects. It is a well-known fact that most conventional cytotoxic drugs not only cause the death of the tumor cell but also may damage normal cells, especially cells that divide rapidly like bone marrow cells. Another limitation of the conventional cytotoxic treatment is the lack of its selectivity to different types of cancer. Each cancer has its own unique genetic pro le such as nger prints that differ among cancers. So new target molecules are being widely studied for cancer treatment, which will clearly result in improving therapeutic outcome and lessen the unwanted side effects. These side effects may sometimes be life threatening [2,4].