Cetuximab is a chimeric monoclonal IgG1 antibody that is specifically directed against the epidermal growth factor receptor (EGFR).
EGFR signalling pathways are involved in the control of cell survival, cell cycle progression, angiogenesis, cell migration and cellular invasion/metastasis.
Cetuximab binds to the EGFR with an affinity that is approximately 5-to 10-fold higher than that of endogenous ligands. Cetuximab blocks binding of endogenous EGFR ligands resulting in inhibition of the function of the receptor. It further induces the internalisation of EGFR, which can lead to down-regulation of EGFR. Cetuximab also targets cytotoxic immune effector cells towards EGFR- expressing tumour cells (antibody dependent cell-mediated cytotoxicity, ADCC).
Cetuximab does not bind to other receptors belonging to the HER family.
The protein product of the proto-oncogene RAS (rat sarcoma) is a central down-stream signal- transducer of EGFR. In tumours, activation of RAS by EGFR contributes to EGFR-mediated increased proliferation, survival and the production of pro-angiogenic factors.
RAS is one of the most frequently activated family of oncogenes in human cancers. Mutations of RAS genes at certain hot-spots on exons 2, 3 and 4 result in constitutive activation of RAS proteins independently of EGFR signalling.
In both in vitro and in vivo assays, cetuximab inhibits the proliferation and induces apoptosis of human tumour cells that express EGFR. In vitro cetuximab inhibits the production of angiogenic factors by tumour cells and blocks endothelial cell migration. In vivo cetuximab inhibits expression of angiogenic factors by tumour cells and causes a reduction in tumour neo-vascularisation and metastasis.
The development of human anti-chimeric antibodies (HACA) is a class effect of monoclonal chimeric antibodies. Current data on the development of HACAs is limited. Overall, measurable HACA titres were noted in 3.4% of the patients studied, with incidences ranging from 0% to 9.6% in the target indication studies. No conclusive data on the neutralising effect of HACAs on cetuximab is available to date. The appearance of HACA did not correlate with the occurrence of hypersensitivity reactions or any other undesirable effect to cetuximab.
A diagnostic assay (EGFR pharmDx) was used for immunohistochemical detection of EGFR expression in tumour material. A tumour was considered to be EGFR-expressing, if one stained cell could be identified. Approximately 75% of the patients with metastatic colorectal cancer screened for clinical studies had an EGFR-expressing tumour and were therefore considered eligible for cetuximab treatment. The efficacy and safety of cetuximab have not been documented in patients with tumours where EGFR was not detected.
Study data demonstrate that patients with metastatic colorectal cancer and activating RAS mutations are highly unlikely to benefit from treatment with cetuximab or a combination of cetuximab and chemotherapy and as add-on to FOLFOX4 a significant negative effect on progression-free survival time (PFS) was shown.
Cetuximab as a single agent or in combination with chemotherapy was investigated in 5 randomised controlled clinical studies and several supportive studies. The 5 randomised studies investigated a total of 3734 patients with metastatic colorectal cancer, in whom EGFR expression was detectable and who had an ECOG performance status of ≤2. The majority of patients included had an ECOG performance status of ≤1.
The KRAS exon 2 status was recognised as predictive factor for the treatment with cetuximab in 4 of the randomised controlled studies (EMR 62 202-013, EMR 62 202-047, CA225006, and CA225025). KRAS mutational status was available for 2072 patients. Further post-hoc analyses were performed for studies EMR 62 202-013 and EMR 62 202-047, where also mutations on RAS genes (NRAS and KRAS) other than KRAS exon 2 have been determined. Only in study EMR 62 202-007, a post-hoc analysis was not possible.
In addition, cetuximab was investigated in combination with chemotherapy in an investigator-initiated randomised controlled phase-III study (COIN, COntinuous chemotherapy plus cetuximab or INtermittent chemotherapy). In this study EGFR expression was not an inclusion criterion. Tumour samples from approximately 81% of patients were analysed retrospectively for KRAS expression.
FIRE-3, an investigator-sponsored clinical phase-III study, compared the treatment of FOLFIRI in combination with either cetuximab or bevacizumab in the first-line treatment of patients with KRAS exon 2 wild-type mCRC. Further post-hoc analyses on mutations on RAS genes other than KRAS exon 2 have been evaluated.
Immunohistochemical detection of EGFR expression was not performed since more than 90% of patients with squamous cell cancer of the head and neck have tumours that express EGFR.
Cetuximab pharmacokinetics were studied when cetuximab was administered as monotherapy or in combination with concomitant chemotherapy or radiation therapy in clinical studies. Intravenous infusions of cetuximab exhibited dose-dependent pharmacokinetics at weekly doses ranging from 5 to 500 mg/m² body surface area.
When cetuximab was administered at an initial dose of 400 mg/m² body surface area, the mean volume of distribution was approximately equivalent to the vascular space (2.9 L/m² with a range of 1.5 to 6.2 L/m²). The mean Cmax (± standard deviation) was 185±55 microgram per mL. The mean clearance was 0.022 L/h per m² body surface area. Cetuximab has a long elimination half-life with values ranging from 70 to 100 hours at the target dose.
Cetuximab serum concentrations reached stable levels after three weeks of cetuximab monotherapy. Mean peak cetuximab concentrations were 155.8 microgram per mL in week 3 and 151.6 microgram per mL in week 8, whereas the corresponding mean trough concentrations were 41.3 and 55.4 microgram per mL, respectively. In a study of cetuximab administered in combination with irinotecan, the mean cetuximab trough levels were 50.0 microgram per mL in week 12 and 49.4 microgram per mL in week 36.
Several pathways have been described that may contribute to the metabolism of antibodies. All of these pathways involve the biodegradation of the antibody to smaller molecules, i.e. small peptides or amino acids.
An integrated analysis across all clinical studies showed that the pharmacokinetic characteristics of cetuximab are not influenced by race, age, gender, renal or hepatic status.
Only patients with adequate renal and hepatic function have been investigated to date (serum creatinine ≤ 1.5fold, transaminases ≤5fold and bilirubin ≤1.5fold the upper limit of normal).
In a phase-I study in paediatric patients (1-18 years) with refractory solid tumours, cetuximab was administered in combination with irinotecan. The pharmacokinetic results were comparable to those in adults.
Dose-dependent skin alterations, starting at dose levels equivalent to those used in humans, were the major findings observed in toxicity studies with Cynomolgus monkeys (a chronic repeat-dose toxicity study and an embryo-foetal development study).
An embryo-foetal toxicity study in Cynomolgus monkeys revealed no signs of teratogenicity. However, dependent on the dose, an increased incidence of abortion was observed.
Non-clinical data on genotoxicity and local tolerance including accidental administration by routes other than the intended infusion revealed no special hazard for humans.
No formal animal studies have been performed to establish the carcinogenic potential of cetuximab or to determine its effects on male and female fertility.
Toxicity studies with co-administration of cetuximab and chemotherapeutic agents have not been performed.
No non-clinical data on the effect of cetuximab on wound healing are available to date. However, in preclinical wound healing models EGFR selective tyrosine kinase inhibitors were shown to retard wound healing.
© All content on this website, including data entry, data processing, decision support tools, "RxReasoner" logo and graphics, is the intellectual property of RxReasoner and is protected by copyright laws. Unauthorized reproduction or distribution of any part of this content without explicit written permission from RxReasoner is strictly prohibited. Any third-party content used on this site is acknowledged and utilized under fair use principles.
