Cetuximab

Cetuximab is an epidermal growth factor receptor (EGFR) inhibitor used for the treatment of metastatic colorectal cancer, metastatic non-small cell lung cancer and head and neck cancer. Cetuximab is a chimeric (mouse/human) monoclonal antibody given by intravenous infusion that is distributed under the trade name Erbitux in the U.S. and Canada by the drug company Bristol-Myers Squibb and outside the U.S. and Canada by the drug company Merck KGaA. In Japan, Merck KGaA, Bristol-Myers Squibb and Eli Lilly have a co-distribution.

In July 2009, the FDA approved cetuximab (Erbitux) for treatment of colon cancer with wild-type KRAS, since it had little or no effect in colorectal tumors harboring a KRAS mutation (this also applied to the EGFR antibody panitumumab) This was the first genetic test to guide treatment of cancer. In July 2012, the FDA approved a real time PCR companion diagnostic test for KRAS, the therascreen KRAS test.

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Medical uses

A diagnostic immunohistochemistry assay (EGFR pharmDx) can be used to detect EGFR expression in the tumor material. Approximately 75% of patients with metastatic colorectal cancer have an EGFR-expressing tumor and are therefore considered eligible for treatment with cetuximab or panitumumab, according to FDA guidelines. Unfortunately, there is evidence that immunohistochemical EGFR receptor testing does not predict response to either cetuximab or panitumumab, so that this has been called a "misleading biomarker" that has nevertheless caused insurers and even health systems to deny payment for EGFR antibody treatment for patients who lack a positive tumor EGFR histochemical test.

Head and neck cancer

Cetuximab was approved by the FDA in March 2006 for use in combination with radiation therapy for treating squamous cell carcinoma of the head and neck (SCCHN) or as a single agent in patients who have had prior platinum-based therapy.

Side effects

One of the more serious side effects of cetuximab therapy is the incidence of acne-like rash. This rash rarely leads to dose reductions or termination of therapy. It is generally reversible.

Further severe infusion reactions include but are not limited to: fevers, chills, rigors, urticaria, itchiness, rash, hypotension, nausea, vomiting, headache, shortness of breath, wheezing, angioedema, dizziness, anaphylaxis, and cardiac arrest. Therefore, pretreatment with diphenhydramine 30-60 min. before administration is standard of care. Other common side effects include photosensitivity, hypomagnesemia due to magnesium wasting, and less commonly pulmonary and cardiac toxicity.

Alpha-gal allergy

Certain geographic regions have a high rate of anaphylactic reactions to cetuximab upon the first exposure to the medication. This is unusual because exposure to the allergen must occur before the development of an allergy. Fewer than 1% of people in the northeast United States reacted, while greater than 20% in the southeast did. The alpha-gal allergy is believed to result from tick bites. Lone star ticks are native to the regions of the US where reactions occurred and were found to be the vector. Cetuximab is produced in the mouse myeloma cell line SP2/0 and thus contains the alpha-gal oligosaccharide, as do all mammals other than primates.

Mechanism of action

Cetuximab is a chimeric (mouse/human) monoclonal antibody which binds to and inhibits EGFR.

KRAS Testing

The KRAS gene encodes a small G protein on the EGFR pathway. Cetuximab and other EGFR inhibitors only work on tumors in which KRAS is not mutated.

KRAS mutational analysis is commercially available from a number of laboratories.

In July 2009, the US Food and Drug Administration (FDA) updated the labels of two anti-EGFR monoclonal antibody drugs (panitumumab (Vectibix) and cetuximab (Erbitux)) indicated for treatment of metastatic colorectal cancer to include information about KRAS mutations.

Studies have indicated that detection of KRAS gene mutations helps physicians identify patients that are unlikely to respond to treatment with targeted EGFR inhibitors, including cetuximab and panitumumab. Accordingly, genetic testing to confirm the absence of KRAS mutations (and so the presence of the KRAS wild-type gene), is now clinically routine before the start of treatment with EGFR inhibitors. mCRC patients with wild-type KRAS tumors have been shown to benefit from a response rate of over 60% and a decreased risk for progression of over 40% when treated with Erbitux as 1st-line therapy. Around 65% of mCRC patients have the KRAS wild-type gene.

History

Michael Sela, Ester Hurwitz and co-workers published observations on EGFR inhibition in 1988. Yeda Research, on behalf of the Weizmann Institute of Science in Israel, challenged the Aventis-owned patent, licensed by Imclone, for the use of anti-epidermal growth factor receptor antibodies in combination with chemotherapy, to slow the growth of certain tumors which was filed in 1989 by Rhone-Poulenc-Rorer. The court ruled that Yeda is sole owner of the patent in the U.S., while Yeda and Sanofi-Aventis co-own the patent's foreign counterparts.

Society and culture

Manufacture

  • Eli Lilly and Company is responsible for the manufacture and supply of Erbitux in bulk-form active pharmaceutical ingredient (API) for clinical and commercial use in the U.S. and Canada, and Bristol-Myers Squibb purchases the API for commercial use from Eli Lilly.
  • Merck KGaA manufactures Erbitux for supply in its territory (outside the U.S. and Canada) as well as for Japan.

Distribution

  • Erbitux is marketed in the U.S. and Canada by Bristol-Myers Squibb. Eli Lilly has the option to co-promote Erbitux in the U.S. and Canada. Eli Lilly receives royalties from Bristol-Myers Squibb.
  • Outside the U.S. and Canada, Erbitux is commercialized by Merck KGaA. Eli Lilly receives royalties from Merck KGaA.
  • A separate agreement grants co-exclusive rights among Merck, Bristol-Myers Squibb and Eli Lilly in Japan and expires in 2032.

Sales

Cetuximab is given by intravenous therapy and costs up to $30,000 for eight weeks of treatment per patient.

Merck KGaA had 887 million euros ($1.15 billion) in Erbitux sales in 2012, from head and neck as well as bowel cancer, while Bristol-Myers Squibb generated $702 million in sales from the drug.

Erbitux was the eighth best-selling cancer drug of 2013, with sales of $1.87 billion.

Biosimilars

Erbitux had 2013 worldwide sales of US$1.9 billion making it a lucrative target for biosimilars developers. Additionally the patent protection for Erbitux in Europe expired in June 2014, and in the U.S. and in Japan the protection will expire in 2016. However biosimilars of Erbitux are not expected until 2018.

As of 2014 biosimilars of cetuximab were in development by several companies.

Insider trading

Cetuximab failed to get FDA approval in 2001, which caused the stock price of the developer ImClone to drop dramatically. Prior to the announcement, several executives sold stock, and the SEC launched an investigation into insider trading. This resulted in a widely publicized criminal case, which resulted in prison terms for media celebrity Martha Stewart, ImClone chief executive officer Samuel D. Waksal and Stewart's broker at Merrill Lynch, Peter Bacanovic.

Research

The efficacy of cetuximab was explored in a clinical trial of advanced gastric cancer published in 2013; cetuximab showed no survival benefit.

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