of chemotherapy drugs
the use of powerful medicines to kill cancer cells. However, all chemotherapy agents do not act the
same way. Some chemotherapy drugs affect the behavior of cancer cells without directly attacking them; and some
directly attack the DNA of the cells, preventing them from multiplying. Others do not act directly; they target
the molecular abnormality in certain types of cancer. Depending on their biochemical mode of action,
chemotherapy drugs (also called antineoplastic or cytotoxic drugs which means toxic to cells or cell-killing)
are grouped into different therapeutic classes: Alkylating agents (also called DNA damaging agents),
anti-metabolites, plant alkaloids and terpenoids, podophyllotoxin, taxanes, topoisomerase inhibitors, antitumour
antibiotics, hormones, and monoclonal antibodies.
Alkylating agents (also called DNA damaging agents): alkylating agents are molecules that
form chemical bonds. In other words, they are able to establish covalent bonds with the DNA of all cells (normal
or cancerous), but mainly cells that reproduce rapidly which is the main characteristic of cancer cells.
Alkylating agents stop tumor growth by establishing a cross-linking in the double helix in the DNA of cancer
cells and, unfortunately, some normal cells that multiply rapidly. This process prevents the cells from
replicating their DNA, and become unable to divide.
Alkylating agents include several
drugs, the most common are: cisplatin, carboplatin (Paraplatin), ifosfamide, chlorambucil, busulfan, and
These anticancer agents
work by inhibiting the synthesis of nucleic acids (DNA, RNA), a necessary process in cell multiplication. In
nature, cancer cells divide more frequently than normal cells; and therefore any halt in cell division affect
cancer cells more than healthy cells. Antimetabolites fight cancer by interfering with DNA of cancerous cells,
which stops or slows the growth of the tumor.
The antimetabolites are among the
oldest chemical agents used in chemotherapy. It is thought that they have been used in the fight against cancer
since the late 1940s. Today, they are widely prescribed for the treatment of cancers in children and adults. Depending on their therapeutic action, anti-metabolites are
divided into three groups:
analogues - those molecules are found
mainly in nitrogenous bases making up the molecules of DNA and RNA. Pyrimidines and purines (see antipurine
below) are nucleotides that form the building blocks of nucleic acids. One of the anti pyrimidines agents
is 5-fluorouracil (5FU), a drug used in the treatment of many cancers principally colorectal cancer and
- they are substances that inhibit enzyme which are very active during cell replication: DNA polymerase, DNA
primase and DNA ligase I. Among drugs that are classed purine analogues include Fludarabine
phosphate or Fludara)
, a chemotherapeutic drug used to treat chronic lymphocytic leukemia.
- Antifolates –
chemotherapy drugs act in the action of synthesis of folate. In other words, antifolates
impair the function
of folic acids,
substances essential for the biosynthesis of nucleic acids. One of the most common of antifolates is
t acts by inhibiting dihydrofolate reductase, an enzyme essential for synthesis of purines and pyrimidines.
Plant alkaloids and
lkaloids are organic
substances of vegetable origin (caffeine, mescaline, nicotine, caffeine, etc...) that have therapeutic
properties. They are used in the production of cancer drugs. The alkaloids act by preventing the formation of
(cellular) spindle, the structure which allows the chromatic
separation of chromosomes during cell division (mitosis or division of a "mother cell" into two "daughter
cells"). The process causes the cells to remain blocked at the stage of mitosis and unable to
common alkaloids include vincristine, vinblastine, vinorelbine, paclitaxel and docetaxel. They are used to treat
a variety of cancers, including but not limited to:
are a class of drugs widely used in chemotherapy to fight cancer. Their main function is to halt cell
Cancer cells multiply
in an anarchic way; by blocking cell division, the taxanes make it difficult for the tumor to grow.
Although can be used in the treatment
of other cancerous conditions, the taxanes are used mainly to treat advanced stages of breast cancer, lung
cancer and metastatic ovarian cancers. The
taxanes include paclitaxel and docetaxel.
topoisomerases are essential enzymes that maintain the topology of DNA: replication, transcription and
recombination. They control and modify the
topological states of cells DNA. There are two forms of DNA topoisomerases: topoisomerase I, which cut and
link complementary rings of single-stranded DNA into double-stranded rings; and
topoisomerase II, which cuts both the two strands of DNA and link them in a different conformation after
modification of its torsion.
The topoisomerase inhibitors interfere
with both transcription and cell replication by inhibiting the relegation of DNA fragments. Among this class of
chemotherapy drugs include amsacrine, anthracyclines, camptothecin derivative (Irinotecan), and
epipodophyllotoxin derivatives (etoposide and teniposide). The topoisomerase inhibitors are used to treat
several types of cancers including colorectal cancers that have been treated unsuccessfully with
5-fluoro-uracil/acid folic (folinic acid combined with 5-fluorouracil).
Antitumour antibiotics: a
ntitumour antibiotics are a class of chemotherapy drugs used to treat certain malignancies such as acute myeloid
leukemia, breast cancer, and non-small cell lung cancer. These drugs act by preventing cell division in both
cancerous cells and healthy cells that multiply rapidly.
The most common antitumour antibiotics include:
Hormones: hormone-dependent or hormone sensitive
cancers (prostate cancer and breast cancer for example) feed on hormones;
their cells need hormones to grow and reproduce. For example, estrogen produced by the ovaries may contribute to
the development of certain cancers of breast and uterus; androgens, hormones produced by the testes, can be
involved in the development of prostate cancer. Hormone therapy is used to block hormonal stimulation, thus
stopping or slowing tumor growth.
In the fight against cancer, hormone
can act different manner; for example:
- In the treatment of prostate
cancer, finasteride selectively inhibits 5-alpha reductase, an enzyme that catalyzes the conversion of
testosterone into dihydrotestosterone (DHT).
This causes a discontinuity of production of 5-hydroxytestosterone, which results in inhibition of cell growth
of prostate cancer.
Aromatase inhibitors and tamoxifen are used to treat breast cancers that are either ER-positive (ER or estrogen
receptor) or PR-positive (PR or progesterone receptor). These drugs act by inhibiting the production of
estrogen and/or progesterone.
- Gonadotropin-releasing hormone
agonists (GnRH agonist) are used to treat hormonally sensitive cancers such as
prostate cancer and breast cancer. GnRH
such as Goserelin work by impairing the function of the hypophysis (also called pituitary
gland), a pea-sized gland located in the frontal portion of your brain that controls the functions of the other
Monoclonal antibodies: Our body has a natural defense called
immune system. One of the properties of the immune system is to produce antibodies against bacteria, viruses and
other pathogenic attacks. Having a weak immune system, the body becomes a gateway to several illnesses. To boost
weakened immune system, scientists have produced industrially very pure antibodies called monoclonal antibodies.
Monoclonal antibodies directed against antigens carried by tumor cells to specifically destroy them.
Unlike other chemotherapy drugs which attack both healthy cells and cancer cells, monoclonal antibodies primarily
target diseased cells and causing fewer side effects. In other words, monoclonal antibodies are substances that
deprive cancer cells of their growth opportunities, and cause them to commit suicide. Among drugs classed as
monoclonal antibodies include:
used in the treatment of breast cancer
used to treat lymphoma