Researchers have identified three possible mechanisms that trigger cancerous growth in cells and the most common hypotheses point to cellular DNA damage as the main culprit. This results in cells that have altered DNA, and hence, altered properties and have the potential to grow at a higher rate. Different factors such as excessive exposure to certain chemicals such as steroids or chemicals in asbestos, exposure to high doses of radiation or hormonal stress have been explained as the cause of the change in DNA composition. These factors can result in activation (or expression) of growth inducing oncogenes, alterations of genes that regulate apoptosis (programmed cell death), or inactivate tumor suppressor genes.
Since the 20th century, treatment options for malignant tumors have broadened from surgery (surgical removal of tumors), to chemodrugtherapy (use of anticancer drugs, often intravenously, to kill cancerous cells or reduce symptoms), and radiotherapy (application of gamma radiation to affective areas to destroy tumor cells) – and in some cases, all three of these options are combined.
The term chemotherapy was used as early as the first decade of the 20th century by the renowned microbiologist and physician, Paul Ehrlich. Originally an antimicrobial procedure, chemo drug therapy is now widely used to treat cancers. Chemotherapy for cancer treatment was carried out in the 1940s when some patients suffering from lymphoma were intravenously given sulfur mustard to observe its effect on their white blood cell count. The patients showed temporary recovery, which was considered a breakthrough and this promoted researchers to look for new chemical agents. Mustine (mechlorethamine) was subsequently discovered in 1942.
It is also worth mentioning that cancer chemo drug therapy can involve a combination of drugs (a cocktail of drugs). The original purpose of chemotherapy was to kill cancer cells through the use of cytotoxic drugs. This is called classical chemotherapy. Non-classical chemotherapy involves the use of antibodies that bind to specific proteins or biochemical factors that are either expressed by tumor cells or essential to their growth, or both.
This article will summarize the types of drugs used in chemotherapy (chemo drugs or anticancer drugs). Such drugs can be classified on the basis of chemical structure/action or on the basis of biological role/function. We will use the most commonly recognized categories (based on both properties).
The first class of anticancer drugs to be discovered was alkylating compounds which have the ability to add alkyl groups to DNA and RNA strands. Alkylated strands tend to break during processes of DNA repair and eventually trigger apoptosis. Therefore these drugs are inherently cytotoxic in nature. Alkylating agents are also not cell cycle specific, ie. they will kill both dividing cells and resting cells. Because of these properties, alkylating agents have severe side effects including emesis, suppression of bone marrow growth, alopecia (hair loss) and reduced gonadal activity. Long term use can result in permanent infertility and in rare cases, acute leukemia can also occur. Examples of Alkylating agents include Cyclophosphamide (Cytoxan), chlorambucil (Leukeran) and busulfan (Myleran). Some Alkylating agents are nutrosoreas, such as Steptozocin and these are useful for treating brain tumors as they can cross the blood brain barrier. These drugs have to be administtrered in controlled doses, as high doses result in a lot of cells (both normal and abnormal) dying.
Some newer alkylating agents are also useful for treating cancers that resist other alkylating agents such as altretamine which is used to treat alkylation resistant ovarian cancer.
This class of chemo drugs is normally comprised of structural analogues of metabolic products of cancer cells and relies on increased susceptibility of such cells to its actions.Most antimetabolites interfere with normal metabolite synthesis including nucleic acid synthesis (DNA) or nucleotide synthesis.
Antimentabolites have been successfully used to combat many types of cancers including leukemias, carcinomas and sarcomas. One of the most well-known antimetabolites includes, methotrexate, a folic acid antagonist which acts on dihydrofolatereductase. Methotrexate, however does have dermatologic and gastrointestinal (GI) side effects. Other anitmetabolites include pyrimidine and purine antagonists such as thiopurines and fluorouracil. These compounds, are however, capable of severe myelosuppression, in addition to GI and neurotoxic effects.
Antibiotic chemotherapy drugs are derived from species of the bacterium Streptomyces. These compounds normal inhibit DNA synthesis by intercalation between DNA base pairs. These can be broadly divided into two categories: anthracyclines and small peptides.
Clinically significant anthracyclines include doxorubicin anddaunorubicin which are topoisomerase inhibitors. These Weed kaufen online have been used effectively in chemotherapy for several types of cancers. Doxorubicin is preferred in solid tumors such as those found in carcinomas of the breast, uterus, lung, gonads and thyroids glands. It is also useful as an adjuvant chemotherapeutic agent in osteosarcoma and rhabdomyosarcoma.
Daunorubicin is more effective in hematological cancers. The most dangerous side effect of this class of drugs is potentially irreversible cardiotoxicity and therefore, physicians need to carefully monitor cardiac activity of patients who are administered these drugs.