Panitumumab: the evidence for its use in the treatment of metastatic colorectal cancer

Development of therapeutic antibodies for the treatment of diseases

It has been more than three decades since the first monoclonal antibody was approved by the United States Food and Drug Administration (US FDA) in 1986, and during this time, antibody engineering has dramatically evolved. Current antibody drugs have increasingly fewer adverse effects due to their high specificity. As a result, therapeutic antibodies have become the predominant class of new drugs developed in recent years. Over the past five years, antibodies have become the best-selling drugs in the pharmaceutical market, and in 2018, eight of the top ten bestselling drugs worldwide were biologics. The global therapeutic monoclonal antibody market was valued at approximately US$115.2 billion in 2018 and is expected to generate revenue of $150 billion by the end of 2019 and $300 billion by 2025. Thus, the market for therapeutic antibody drugs has experienced explosive growth as new drugs have been approved for treating various human diseases, including many cancers, autoimmune, metabolic and infectious diseases. As of December 2019, 79 therapeutic mAbs have been approved by the US FDA, but there is still significant growth potential. This review summarizes the latest market trends and outlines the preeminent antibody engineering technologies used in the development of therapeutic antibody drugs, such as humanization of monoclonal antibodies, phage display, the human antibody mouse, single B cell antibody technology, and affinity maturation. Finally, future applications and perspectives are also discussed.

Investigational therapies targeting the ErbB (EGFR, HER2, HER3, HER4) family in GI cancers

INTRODUCTION

Gastrointestinal (GI) malignancies account for nearly one-fourth of all cancer-related deaths in the United States and approximately 30% of all cancer-related deaths worldwide. Use of combination cytotoxic therapy offers a modest improvement in survival, but the prognosis and long-term survival of most patients with GI cancer remains poor. In certain GI malignancies, therapies that target members of the HER family of receptors have positively impacted patient care.

AREAS COVERED

In this review, we discuss the significance of the HER family of receptors in esophagogastric, hepatobiliary, pancreatic, and colorectal cancers and explain the rationale supporting the use of monoclonal antibodies (mAbs) and small molecule tyrosine kinase inhibitors (TKIs) to inhibit HER activation and downstream events that contribute to tumor proliferation, migration, and survival.

EXPERT OPINION

Despite recent advances, the treatment of GI cancers remains challenging. Therapies targeting the HER family of receptors have been extensively studied in these malignancies with inconsistent results. The rationale behind varied tumor responses with these agents remains uncertain. We believe that additional studies are needed to identify biomarkers that could help identify a population of patients who would be more responsive to a given therapy.

Alterations in epidermal growth factor receptors 1 and 2 in esophageal squamous cell carcinomas

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) shows a 5-year survival rate below 10%, demonstrating the urgency in improving its treatment. Alterations in epidermal growth factor receptors are closely related to malignancy transformation in a number of tumors and recent successful targeted therapies have been directed to these molecules. Therefore, in this study, we analyzed the expression of EGFR and HER2 and evaluated EGFR mutation profile as well as the presence of mutations in hotspots of KRAS and BRAF in ESCC patients.

METHODS

We performed RT-qPCR, immunohistochemistry and Fluorescent in situ hybridization to determine EGFR and HER2 expression in ESCC patients, and direct sequencing and PCR-RFLP for mutations and polymorphism analysis.

RESULTS

Our results showed an increased EGFR mRNA expression in tumors compared to surrounding tissue (p <0.05), with 11% of the cases presenting at least a four-fold difference between tumor and paired adjacent mucosa. EGFR protein overexpression was present only in 4% of the cases. The median expression of HER2 mRNA was not different between tumors and adjacent mucosa. Still, 7% of the tumors presented at least a 25-fold higher expression of this gene when compared to its paired counterpart. Immunohistochemical analysis revealed that 21% of the tumors were positive for HER2 (scores 2+ and 3+), although only 3+ tumors presented amplification of this gene. Mutation analysis for EGFR (exons 18-21), KRAS (codons 12 and 13) and BRAF (V600E) showed no mutations in any of the hotspots of these genes in almost 100 patients analyzed. EGFR presented synonymous polymorphisms at codon 836 (C>T) in 2.1% of the patients, and at codon 787 (G>A) in 79.2% of the cases. This last polymorphism was also evaluated in 304 healthy controls, which presented a similar frequency (73.7%) in comparison with ESCC patients. The absence of mutations of EGFR, KRAS and BRAF as well as the overexpression of EGFR and HER2 in less than 10% of the patients suggest that this signaling pathway is altered in only a small proportion of patients with ESCC.

CONCLUSION

HER receptors target therapies may have the potential to be effective in only a minor fraction of patients with ESCC.

Hyperactivation of constitutively dimerized oncogenic EGF receptors by autocrine loops

The epidermal growth factor (EGF) receptor (EGFR) has a key role in normal embryonic development, adult tissue homeostasis and many pathological processes, in particular tumour formation. Aberrant EGFR activation occurs in many cancer types, and inhibition of this receptor is a promising anti-tumour strategy. Besides overexpression of the wild-type receptor, mutated oncogenic EGFR variants are often associated with malignant transformation. In human non-small-cell lung cancers, kinase mutants of the EGFR are rather common. Human glioblastoma often express the truncated EGFRvIII version as well as other dimerized and permanently activated mutants of the receptor, which are considered as tumour drivers. Similarly, the mutated and dimerized EGFR variant Xiphophorus melanoma receptor kinase (Xmrk) is causative for the development of malignant pigment cell tumours in medaka and Xiphophorus melanoma models. It is generally believed that oncogenic receptors that are active due to dimerizing mutations are ligand independent. Here, we show that different EGFR variants from fish and human efficiently induce autocrine loops by inducing EGFR ligands such as amphiregulin and HB-EGF. Importantly, the pre-dimerized oncogenic EGFR versions Xmrk from Xiphophorus and human EGFR(C600F), though already active in absence of ligands, respond to ligand stimulation with enhanced oncogenic signalling. In summary, our data show that autocrine or paracrine loops are still acting on pre-dimerized oncogenic EGFRs and contribute to their pro-tumorigenic signalling.

A comparison of in vitro methods for determining the membrane receptor expression in cell lines

INTRODUCTION

Determining the number of expressed receptors per cell (NRPC) in cell lines is an important prerequisite for many experimental procedures in biomedical research. This paper focuses on the comparison of a newly developed method of determining NRPC - the Kinetic extrapolation method (KEX) - with the standard saturation method. These two methods, both based on radiolabeled ligand-receptor binding, were compared with the data on receptor expression found using quantified western blotting.

METHODS

Four cell lines with different expressions of epidermal growth factor receptor (EGFR) were chosen for the experiment: A431, HaCaT, HCT116 and HepG2. Two radiolabeled monoclonal antibodies specific for EGFR were used as ligands: [(131)I]-cetuximab and [(131)I]-panitumumab. The classic manual technique based on the saturation of cell receptors was performed on cells seeded in 24-well plates. The KEX method uses the LigandTracer, a special instrument which detects ligand retention in real time from seeded cells onto a rotating Petri dish. The western blot analysis was performed according to the routinely used procedure.

RESULTS

A very close accordance between the manual saturation technique and the KEX method was found in all four cell lines used. The NRPC in the cell lines follows the same order using both ligands: A431>HaCaT>HCT116≈HepG2. Similarly, consistent data on EGFR expression in the studied cell lines were obtained using western blot analysis and the radiolabeled ligand binding assays.

CONCLUSIONS

The KEX method could be as similarly useful for determining receptor expression as is the classic saturation method and western blotting.

Panitumumab (vectibix)

Panitumumab (Vectibix), is a human monoclonal antibody EGFR antagonist indicated as a single agent for the treatment of metastatic colorectal carcinoma with disease progression on or following fluoropyrimidine, oxaliplatin, and irinotecan chemotherapy regimens. This article will present the mechanism of action as well as the clinical role for this monoclonal antibody.