Cancer is one of the most dreaded diseases to haunt mankind in the world today. It is one of the leading causes of death worldwide. Although overall cancer incidence rates in the developing countries are half of those seen in the developed world in both sexes, the overall cancer mortality rates are generally similar. 1− 3 Breast cancer is the most frequently diagnosed and the foremost reason for cancer deaths among females, accounting for almost 23% of the total cancer cases and 14% of the cancer deaths every year, while lung is the leading cancer site among males, comprising 17% of the total new cancer cases and 23% of the total cancer deaths. The approach used to treat depends upon the specific type, location, and stage of the cancer. There are several fundamental techniques available to treat cancer, which include surgery, radiation therapy, immunologic treatment, and chemical-based approaches, and each has its own merits and limits. Generally, a combination of these methods is used, and most of the therapeutic approaches to the treatment of cancer comprise a chemical component. 4, 5 Although cancer was recognized as a disease as early as 1500 BC and herbal management of cancer is recorded in many ancient medical writings, the use of drugs in cancer treatment was not seriously considered prior to the 1930s. Application of androgens and estrogens in the treatment of breast and prostatic cancers as well as other types of neoplastic growth, based on alteration of the hormonal status of the cancer patients, was initiated about a century ago. 6, 7 Shortly thereafter, the discovery of antileukemic activity of the nitrogen mustards and analogues of folic acid triggered the earnest search for cancer chemotherapeutic agents. 8− 11 Up to present, several thousand synthetic compounds and numerous natural products have been evaluated as anticancer agents. 12

Despite the availability of a large number of chemotherapeutic antineoplastic agents, the medical need remains still largely unmet. The main reasons behind the failure of chemotherapy include (i) the lack of selectivity of conventional drugs,(ii) the metastatic spreading of initial tumors,(iii) the heterogeneity of the disease, and (iv) multidrug resistance. These drawbacks prompt medicinal chemists to design and develop safer, targetspecific, and effective antineoplastic agents. 4 The basic approaches to cancer treatment are constantly changing. Clinical protocols are now exploring molecular targets, genetic therapies, manipulations of the immune system, stimulation of normal hematopoietic elements, induction of differentiation in tumor tissue, and inhibition of angiogenesis as appealing areas for cancer therapy. 13− 18 In the background of new available chemotherapeutic antineoplastic agents, cytotoxic drugs remain the mainstay of cancer therapy as they are highly specific to their targets. 19− 22 It is noteworthy that in the late 1980s the idea that cytotoxic drugs had substantially exhausted their potential and their development had reached a plateau was gaining ground. However, just in the nineties, important cytotoxic anticancer drugs such as taxanes and camptothecins entered the market and are still milestones in cancer treatment. 23 Most of the FDA (Food and Drug Administration)-approved drugs in the last two decades are either reintroduced after the patent expiry or analogues of the older cytotoxic drugs. Older drugs are constantly being reapproved for a wider use, and their analogues are approved for therapy resistant cancers. 24 On the basis of their targets, new anticancer drugs approved by the FDA in the past decade may be classified into three categories. The first group …