Targeted therapy

Targeted therapy or molecularly targeted therapy is one of the major modalities of medical treatment (pharmacotherapy) for cancer, others being hormonal therapy and cytotoxic chemotherapy. As a form of molecular medicine, targeted therapy blocks the growth of cancer cells by interfering with specific targeted molecules needed for carcinogenesis and tumor growth,[1] rather than by simply interfering with all rapidly dividing cells (e.g. with traditional chemotherapy). Because most agents for targeted therapy are biopharmaceuticals, the term biologic therapy is sometimes synonymous with targeted therapy when used in the context of cancer therapy (and thus distinguished from chemotherapy, that is, cytotoxic therapy). However, the modalities can be combined; antibody-drug conjugates combine biologic and cytotoxic mechanisms into one targeted therapy.

Patients and their diseases are profiled in order to identify the most effective treatment for their specific case.

Another form of targeted therapy involves use of nanoengineered enzymes to bind to a tumor cell such that the body's natural cell degradation process can digest the cell, effectively eliminating it from the body.

Targeted cancer therapies are expected to be more effective than older forms of treatments and less harmful to normal cells. Many targeted therapies are examples of immunotherapy (using immune mechanisms for therapeutic goals) developed by the field of cancer immunology. Thus, as immunomodulators, they are one type of biological response modifiers.

The most successful targeted therapies are chemical entities that target or preferentially target a protein or enzyme that carries a mutation or other genetic alteration that is specific to cancer cells and not found in normal host tissue. One of the most successful molecular targeted therapeutic is Gleevec, which is a kinase inhibitor with exceptional affinity for the oncofusion protein BCR-Abl which is a strong driver of tumorigenesis in chronic myelogenous leukemia. Although employed in other indications, Gleevec is most effective targeting BCR-Abl. Other examples of molecular targeted therapeutics targeting mutated oncogenes, include PLX27892 which targets mutant B-raf in melanoma.

There are targeted therapies for lung cancer, colorectal cancer, head and neck cancer, breast cancer, multiple myeloma, lymphoma, prostate cancer, melanoma and other cancers.[2][3]

Biomarkers are usually required to aid the selection of patients who will likely respond to a given targeted therapy.[4]

Co-targeted therapy involves the use of one or more therapeutics aimed at multiple targets, for example PI3K and MEK,[5] in an attempt to generate a synergistic response[6] and prevent the development of drug resistance.[7][8]

The definitive experiments that showed that targeted therapy would reverse the malignant phenotype of tumor cells involved treating Her2/neu transformed cells with monoclonal antibodies in vitro and in vivo by Mark Greene's laboratory and reported from 1985.[9]

Some have challenged the use of the term, stating that drugs usually associated with the term are insufficiently selective.[10] The phrase occasionally appears in scare quotes: "targeted therapy".[11] Targeted therapies may also be described as "chemotherapy" or "non-cytotoxic chemotherapy", as "chemotherapy" strictly means only "treatment by chemicals". But in typical medical and general usage "chemotherapy" is now mostly used specifically for "traditional" cytotoxic chemotherapy.

Types

The main categories of targeted therapy are currently small molecules and monoclonal antibodies.

Small molecules
Mechanism of imatinib

Many are tyrosine-kinase inhibitors.

Small molecule drug conjugates
  • Vintafolide is a small molecule drug conjugate consisting of a small molecule targeting the folate receptor. It is currently in clinical trials for platinum-resistant ovarian cancer (PROCEED trial) and a Phase 2b study(TARGET trial) in non-small-cell lung carcinoma (NSCLC).[22]

Serine/threonine kinase inhibitors (small molecules)

Monoclonal antibodies
Main article: Monoclonal antibody therapy

Several are in development and a few have been licensed by the FDA and the European Commission. Examples of licensed monoclonal antibodies include:

Many antibody-drug conjugates (ADCs) are being developed. See also ADEPT (antibody-directed enzyme prodrug therapy).

Progress and future

In the U.S., the National Cancer Institute's Molecular Targets Development Program (MTDP) aims to identify and evaluate molecular targets that may be candidates for drug development.

See also

References
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  4. Syn, Nicholas Li-Xun; Yong, Wei-Peng; Goh, Boon-Cher; Lee, Soo-Chin (2016-08-01). "Evolving landscape of tumor molecular profiling for personalized cancer therapy: a comprehensive review". Expert Opinion on Drug Metabolism & Toxicology. 12 (8): 911–922. doi:10.1080/17425255.2016.1196187. ISSN 1744-7607. PMID 27249175.
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