Introduction:
Chemotherapy is the administration of one or more cytotoxic antineoplastic medications (chemotherapeutic agents) as part of a predetermined schedule to treat cancer. Chemotherapy may be administered with the intention of curing a disease, extending life, or alleviating symptoms. It is frequently used in conjunction with other treatments, such as radiation, surgery, and/or hyperthermia therapy.
Chemotherapy might utilize a single medicine or multiple treatments at once. Chemoradiotherapy is the treatment that combines chemotherapy and radiation. Photo chemotherapy, also known as photodynamic therapy, is a type of chemotherapy that uses medicines that only convert to cytotoxic action when exposed to light.
The majority of chemotherapy is administered intravenously, while a few drugs can be given orally (for example, melphalan, busulfan, and capecitabine). Intrathecal chemotherapy may be used if the malignancy has spread to the central nervous system or is associated with meningeal disorders.
They are used for the following purpose:
- Preventive
- Curative
- Palliative
Mode of action:
Chemotherapeutic medications function by impairing mitosis (cell division), allowing them to target rapidly dividing cells. Cytotoxic medications are defined as those that cause cell harm. They prevent mitosis by a variety of ways, including DNA damage and inhibition of the cellular machinery that controls cell division. One idea for why these medications destroy cancer cells is because they cause a predetermined kind of cell death known as apoptosis.
Because chemotherapy impacts cell division, malignancies with a rapid growth rate (such as acute myelogenous leukaemia and aggressive lymphomas, including Hodgkin’s disease) are more sensitive to chemotherapy because a larger proportion of the targeted cells are undergoing cell division at all times.
Slow-growing cancers, such as indolent lymphomas, respond considerably more gently to chemotherapy.
Heterogenic cancers may also have varied sensitivity to chemotherapeutic drugs, depending on the sub clonal populations inside the tumour.
Classification:
- Cell cycle specific-destroy cells at specific phases of cell cycle.
- Cell cycle non-specific- prolonged effect on cells leading to cell death
Types:
Alkylating agents
Till date, alkylating agents are the oldest and mostly used chemotherapeutic agents. They are named for their ability to alkylate a wide spectrum of molecules, including proteins, RNA, and DNA, which can bond covalently due to their alkyl group.
Alkylating compounds can act at any stage of the cell cycle causing cell cycle arrest and triggers apoptosis (programmed cell death also DNA transcription.
Antitumour antibiotic
Anti-metabolites are a type of chemical that inhibits DNA and RNA synthesis that are basically derived from microorganisms (mostly Streptomyces species).
These medications work by either inhibiting the enzymes needed for DNA synthesis or incorporating into DNA or RNA also generated free radicals. Furthermore, it inhibits enzymes necessary for DNA synthesis, preventing mitosis.
E.g., Blenoxane (Bleomycin), Adriamycin (Doxorubicin).
Anti-metabolites
Drugs that interfere with RNA, DNA, and cellular metabolisms. When cells proliferate, anti-metabolites prevent the usage of a metabolite and disrupt essential biochemical process which is an important part of proper metabolism. They are frequently used to treat leukaemia, breast, ovarian, and intestinal cancers, as well as other forms of cancer.
Fluorouracil, methotrexate, and fludarabine are some examples.
Topoisomerase inhibitors
These class of drugs targets the activity of activity of enzyme topoisomerase I and topoisomerase II. This enzyme helps to reduce the topological strength develop due to unopened DNA winds supercoils during the DNA replication, DNA transcription, and DNA repair.
Plant alkaloids and natural products
Natural-based medicines that inhibit the capacity of cell to divide and form two cells, as well as repair cell damage. Examples include Vincristine, Paclitaxel, and Topotecan.
Mitotic inhibitors
A drug that inhibits mitosis by stopping cells from dividing to form new cells, disrupting microtubules that pull the cell apart when it divides. Microtubules are long thread like proteins that extend through the cell and move cellular components around.
They are used to treat a wide range of cancers, including breast, lung, myeloma, lymphomas, and leukaemia.
Corticosteroids
Corticosteroids, sometimes known as steroids, are natural hormones and hormone-like medications used to treat many cancers and other disorders. When these medications are used as part of cancer treatment, they are classified as chemotherapy drugs.
Treatment Strategies of chemotherapy:
Today, there are a numerous number of chemotherapeutic drugs that are applied under accurate strategies.
However, it is applied under the aim for curative intent or prolong life or palliate symptoms.
Induction chemotherapy
Induction chemotherapy represent the first line or initial phase of cancer treatment with a chemotherapeutic drug that is used for curative intent. The aim of induction chemotherapy is to destroy many cancer cells as possible that aim to improve survival rates for certain types of cancer.
Combined modality chemotherapy (CMT)
This is a type of treatment strategy where one or more type of therapy can be adopted at a time. There are several therapies such as radiation therapy, surgery, immunotherapy, and/or hyperthermia therapy can be adopted to enhance the overall treatment efficacy with an aim to improve both local and distant tumour.
However, it is highly recommended on depending on the type of disease type, the stage of cancer, and health status.
Consolidation chemotherapy
Consolidation chemotherapy is the second step in treatment and is typically administered after reduction to extend disease-free time and enhance survival.
Consolidation treatment is also known as post-remission therapy with an aim to kill any remaining cancer cells in the body and prevent from coming back in order to maintain the complete remission and prevent deterioration.
Intensification chemotherapy
This stage of treatment is identical to consolidation chemotherapy. However, the drugs introduced in the intensification chemotherapy will be different than the induction chemotherapy which is the first part of the treatment.
Neoadjuvant chemotherapy (NACT)
Neoadjuvant chemotherapy is the delivery of chemotherapy prior to a local treatment such as before surgery or radiation and is designed to shrink the primary tumour.
It is also given to cancers with a high risk of micro-metastatic disease to optimize main success rate of treatment.
Adjuvant chemotherapy
It is delivered after a local treatment (radiotherapy or surgery) to kill any remaining cancer cells in the specific area.
Generally, it is a cancer treatment given after the primary treatment in order to lower the risk that the cancer will come back with the intention of preventing relapse.
Maintenance chemotherapy
It is a promising strategy in the treatment of cancer that is refers to the administration of drugs relatively with less toxicity after the initial treatment with the aim of “maintaining” tumour complete remission.
Salvage chemotherapy
Salvage chemotherapy also known as rescue therapy is an intensive strategies of cancer treatment. Generally, it is administered after the initial, first or second line, therapy is not responded by the patients with an option for attempting to control the disease.
Palliative chemotherapy
Palliative chemotherapy is the treatment used for someone to live longer, more comfortably and improve quality of life that is introduced without curative intent. It is a non-curative cancer treatment which is introduced simply to decrease tumour load and increase life expectancy.