Drugs used in oncology

Drugs used in oncology

Malignant disorders, also called cancers, are an important group of disorders. They constitute a substantial proportion of non-communicable diseases and affect all regions of the world. Cancers, such as of prostate, lung, colon and breast are an important cause of high mortality despite heavy cost. Although with advancement in medical sciences, better treatment options are being devised leading to improved survival rates among patients but their morbidity and mortality still remains high. There are a number of challenges while treating cancers, such as, disease stage at the time of diagnosis, disease behavior, patient characteristics, limited treatment options, expensive treatment, resistance to treatment, potentially lethal adverse effects and disease recurrence. Topics in this module include the drugs used in treating cancer including their mechanisms of action and adverse effects, and general principles of their use.

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Introduction to antineoplastics

Cancer chemotherapy has changed dramatically and advances in our understanding of cancer biology is facilitating development of drugs that produce cures.

Chemotherapy may be indicated as a primary treatment or as adjuvant or neoadjuvant therapy. The former is used when there are no other effective treatment approaches. Adjuvant therapy is used to eradicate micrometastatic disease following localized treatments such as surgery or radiation or both. Neoadjuvant chemotherapy is used to make other treatment modalities more effective by reducing tumor burden and to destroy micrometastases.

Despite the high cure rates of previously lethal cancers, the use of these drugs is associated with significant harmful effects. Thus, a thorough understanding of the pharmacology of the antineoplastics is important for their safe and effective use in clinical practice.

The compounds used in cancer chemotherapy are varied in structure and mechanism of action, including alkylating agents; antimetabolite analogs; natural products; hormones and hormone antagonists; and a variety of agents directed at specific molecular targets.

  • Alkylating drugs and platinum compounds: These drugs are the classical cytotoxic drugs which chemically bind with macromolecules such as DNA and disrupt cell dynamics, growth and differentiation.
  • Anthracyclines: These drugs disrupt DNA replication and transcription by DNA intercalation, a type of physical binding. Ultimately, they shift the balance in favor of cancer cell apoptosis.
  • Antimetabolites: These drugs disrupt the metabolism inside the cells by inhibiting folate metabolism and/or DNA synthesis.
  • Topoisomerase inhibitors: inhibit the release of supercoils during DNA replication and transcription and thus disrupt DNA dynamics.
  • Antimitotic Drugs (Vinca alkaloids and Taxanes): Inhibit the dynamic instability of microtubules and thus arrests the cell cycle in mitosis.
  • Protein kinase inhibitors and Antibodies: These are relatively new group of drugs which target specific growth receptors and thus help control cell growth and differentiation.

The biological targets of anticancer therapy are present throughout the cell, from cell membrane to nucleus. The cell cycle specificity is an important attribute and it determines the selection of drug regimen, among other factors. Likewise, ability to eradicate cancer cells can be judged with log-kill hypothesis.

Dr Nasir Afsar

This 42-minute video introduces the concept of chemotherapy for cancer. In addition to a short description of the log kill hypothesis, the mechanisms of action of the main classes of antineoplastic drugs are described. These include the cytotoxic drugs (e.g. alkylating agents), hormones, and immunoglobulins and tyrosine kinase inhibitors. The video concludes with a general overview of the general principles of chemotherapy and adverse effects. This video would be appropriate for learners as they begin their study of antineoplastic drugs. Presentation created and contributed by Dr Nasir Afsad, Alfaisal University College of Medicine, Riyadh, Saudi Arabia.

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