Ab Initio Studies of Anti-Cancer Drugs

Cancer is an extraordinarily complicated group of diseases which are characterized by the loss of normal control of the maintenance of cellular organization in the tissues. It is still not completely understood how much of the disease is of genetic, viral, or environmental origin. The result, however, is that cancer cells possess growth advantages over normal cells, a reality which damages the host by local pressure effects, destruction of tissues, and secondary systemic effects. As such, a goal of cancer therapy is the destruction of cancer cells via chemotherapeutic agents or radiation. Since the late 1940s, when Farber treated leukemia with methotrexate, cancer therapy with cytotoxic drugs made enormous progress. Chemotherapy is usually integrated with other treatments such as surgery, radiotherapy, and immunotherapy, and it is clear that post-surgery, it is effective with solid tumors. This is due to the fact that only systemic therapy can attack micrometastases. The rationale for using chemotherapy is the control of tumor-cell populations via a killing mechanism. The major problem in this approach is the lack of selectivity of chemotherapeutic agents. Some agents indeed preferentially kill cancer cells, but no agents have been synthesized yet which kill only cancer cells and do not affect normal cells. Unfortunately, normal tissues are affected, giving rise to a multitude of side effects. In addition to drugs exhibiting cytotoxic activity, antiproliferative drugs are also formulated. According to their mode of action, anti-cancer drugs are divided into several classes. . . . alkylating agents antimetabolites DNA intercalators mitotic inhibitors lexitropsins drugs which bind covalently to DNA . . . Experimental studies of these molecules are complemented and enhanced by theoretical studies. Some of the theoretical studies use molecular mechanics methods while others apply ab initio or semi-empirical quantum-chemistry methods. Most of these molecules are large and besides their structures and properties it is important to investigate their interaction with DNA fragments (themselves large molecules). Ab initio calculations cannot always be applied to the whole system. Therefore, models are used and through a judicious choice of the entities investigated, the calculations can shed light on the problem and provide enough information to complement the experimental studies.