Development of ABX-EGF, a fully human anti-EGF receptor monoclonal antibody, for cancer therapy

Current challenges and clinical investigations of epidermal growth factor receptor (EGFR)- and ErbB family-targeted agents in the treatment of head and neck squamous cell carcinoma (HNSCC)

Overexpression of the epidermal growth factor receptor (EGFR) is a common characteristic of head and neck squamous cell carcinomas (HNSCC). Cetuximab is a chimeric anti-EGFR monoclonal antibody (mAb) with multiple approved indications in HNSCC, including with radiation therapy (RT) for locoregionally advanced disease, as monotherapy after platinum progression, and with platinum/5-fluorouracil for recurrent or metastatic disease. There remain, however, numerous unanswered questions regarding the optimal use of cetuximab in HNSCC, including patient selection, its mechanisms of action and resistance, the effect of human papillomavirus status on outcomes, its role when combined with induction chemotherapy or adjuvant radiation, and optimal management of skin toxicity and hypersensitivity reactions. In addition, a variety of other anti-EGFR agents (the multitargeted small molecule tyrosine kinase inhibitors [TKIs] lapatinib, dacomitinib, and afatinib and the anti-EGFR mAbs zalutumumab, nimotuzumab, and panitumumab) are currently under investigation in phase II and III clinical trials in different HNSCC therapeutic settings. The anti-EGFR TKI erlotinib is currently in phase III development for oral cancer prevention. Numerous other drugs are in earlier stages of development for HNSCC treatment, including novel anti-EGFR mAbs (MEHD7945A, necitumumab, and RO5083945), small-molecule TKIs (vandetanib, icotinib, and CUDC-101), EGFR antisense, various add-on therapies to radiation and chemotherapy (bevacizumab, interleukin-12, lenalidomide, alisertib, and VTX-2337), and drugs (temsirolimus, everolimus, OSI-906, dasatinib, and PX-866) intended to overcome resistance to anti-EGFR agents. Overall, a wealth of clinical trial data is expected in the coming years, with the potential to modify significantly the approach to anti-EGFR therapy for HNSCC.

Anti-cancer Therapies in High Grade Gliomas

High grade gliomas represent one of the most aggressive and treatment-resistant types of human cancer, with only 1–2 years median survival rate for patients with grade IV glioma. The treatment of glioblastoma is a considerable therapeutic challenge; combination therapy targeting multiple pathways is becoming a fast growing area of research. This review offers an up-to-date perspective of the literature about current molecular therapy targets in high grade glioma, that include angiogenic signals, tyrosine kinase receptors, nodal signaling proteins and cancer stem cells related approaches. Simultaneous identification of proteomic signatures could provide biomarker panels for diagnostic and personalized treatment of different subsets of glioblastoma. Personalized medicine is starting to gain importance in clinical care, already having recorded a series of successes in several types of cancer; nonetheless, in brain tumors it is still at an early stage.

Gene expression profiles can predict panitumumab monotherapy responsiveness in human tumor xenograft models

BACKGROUND

Epidermal growth factor receptor (EGFR)-targeted agents have demonstrated clinical benefit in patients with cancer. Identifying tissue-of-origin-independent predictive biomarkers is important to optimally treat patients. We sought to identify a gene array profile that could predict responsiveness to panitumumab, a fully human EGFR-binding antibody, using preclinical models of human cancer.

METHODS

Mice bearing 25 different xenograft models were treated twice weekly with panitumumab or immunoglobulin G2 control to determine their responsiveness to panitumumab. Samples from these xenografts and untreated xenografts were arrayed on the Affymetrix human U133A gene chip to identify gene sets predicting responsiveness to panitumumab using univariate and multivariate analyses. The predictive models were validated using the leave-one-group-out (LOO) method.

RESULTS

Of the 25 xenograft models tested, 12 were responsive and 13 were resistant to panitumumab. Unsupervised analysis demonstrated that the xenograft models clustered by tissue type rather than responsiveness to panitumumab. After normalizing for tissue effects, samples clustered by responsiveness using an unsupervised multidimensional scaling. A multivariate selection algorithm was used to select 13 genes that could stratify xenograft models based on responsiveness after adjustment for tissue effects. The method was validated using the LOO method on a training set of 22 models and confirmed independently on three new models. In contrast, a univariate gene selection method resulted in higher misclassification rates.

CONCLUSION

A model was constructed from microarray data that prospectively predict responsiveness to panitumumab in xenograft models. This approach may help identify patients, independent of disease origin, likely to benefit from panitumumab.

Promising new molecular targeted therapies in head and neck cancer

Despite advances in multimodality therapies for the treatment of squamous cell carcinoma of the head and neck (SCCHN), survival rates, functional outcomes and toxicities of therapy remain poor. The recognition of the prognostic value of human papillomavirus (HPV) status, and the advent of biologically targeted therapies with potential for decreased toxicities and increased selectivity, represent significant developments in our understanding of SCCHN. Targeted agents currently approved or under investigation for SCCHN include epidermal growth factor receptor (EGFR) monoclonal antibodies (cetuximab, panitumumab, zalutumumab, nimotuzumab), EGFR tyrosine kinase inhibitors (gefitinib, erlotinib, lapatinib, afatanib, dacomitinib), vascular endothelial growth factor receptor (VEGFR) inhibitors (bevacizumab, sorafenib, sunitinib, vandetanib) and various inhibitors of other pathways and targets, including phosphatidylinositol 3' kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR), MET and insulin-like growth factor receptor (IGF-1R). On-going clinical trials are evaluating these emerging agents and their combinations in the treatment of SCCHN.

From bench to bedside: lessons learned in translating preclinical studies in cancer drug development

The development of targeted agents in oncology has rapidly expanded over the past 2 decades and has led to clinically significant improvements in the treatment of numerous cancers. Unfortunately, not all success at the bench in preclinical experiments has translated to success at the bedside. As preclinical studies shift toward defining proof of mechanism, patient selection, and rational drug combinations, it is critical to understand the lessons learned from prior translational studies to gain an understanding of prior drug development successes and failures. By learning from prior drug development, future translational studies will provide more clinically relevant data, and the underlying hope is that the clinical success rate will improve and the treatment of patients with ineffective targeted therapy will be limited.

Markers of resistance to anti-EGFR therapy in colorectal cancer

Epidermal growth factor receptor (EGFR) is a therapeutic target in colorectal cancer (CRC). The benefit from EGFR inhibitors appears to be limited to a subset of patients with CRC. Mechanisms of resistance to EGFR inhibitors are being identified. KRAS codon 12 activating mutation is a predominate mechanism of resistance to EGFR inhibitors in around 40% of patients with advanced CRC. Other potential mechanisms of resistance include ligand expression, increased EGFR number, mutations of BRAF and activation of alternate signaling pathways.

Epidermal growth factor receptor targeting in cancer: a review of trends and strategies

The epidermal growth factor receptor (EGFR) is a cell-surface receptor belonging to ErbB family of tyrosine kinase and it plays a vital role in the regulation of cell proliferation, survival and differentiation. However; EGFR is aberrantly activated by various mechanisms like receptor overexpression, mutation, ligand-dependent receptor dimerization, ligand-independent activation and is associated with development of variety of tumors. Therefore, specific EGFR inhibition is one of the key targets for cancer therapy. Two major approaches have been developed and demonstrated benefits in clinical trials for targeting EGFR; monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs). EGFR inhibitors like, cetuximab, panitumumab, etc. (mAbs) and gefitinib, erlotinib, lapatinib, etc. (TKIs) are now commercially available for treatment of variety of cancers. Recently, many other agents like peptides, nanobodies, affibodies and antisense oligonucleotide have also shown better efficacy in targeting and inhibiting EGFR. Now a days, efforts are being focused to identify molecular markers that can predict patients more likely to respond to anti-EGFR therapy; to find out combinatorial approaches with EGFR inhibitors and to bring new therapeutic agents with clinical efficacy. In this review we have outlined the role of EGFR in cancer, different types of EGFR inhibitors, preclinical and clinical status of EGFR inhibitors as well as summarized the recent efforts made in the field of molecular EGFR targeting.

Functional dissection of the epidermal growth factor receptor epitopes targeted by panitumumab and cetuximab

Cetuximab and panitumumab, two antibodies targeting the extracellular domain of the epidermal growth factor receptor (EGFR), are of major clinical importance particularly in the treatment of metastatic colorectal cancer. As patients may acquire resistance-mediating mutations within the extracellular EGFR domain, functional dissection of the exact binding sites of EGFR targeting antibodies may help predict treatment responses. We therefore assessed the epitope recognition of panitumumab by screening phage-displayed random cyclic 7mer and linear 12mer peptide libraries on this antibody. Phage screenings revealed two strong, potentially epitope-mimicking consensus motifs targeted by panitumumab. A computational approach was used to map the sequences back to the potential epitope region on domain III of EGFR. The presumed epitope regions (386)WPEXRT(391) and a biochemically similar though discontinuous region P349-F352-D355 on a neighboring loop of domain III could be confirmed as part of the functionally relevant binding site of panitumumab by site-directed mutational analysis. To more accurately differentiate the panitumumab epitope from the previously characterized cetuximab epitope, binding studies were performed on a broad range of additional mutants. Taken together, this analysis revealed two large, partially overlapping functional epitopes consisting of 17 critical amino acid positions. Four of these positions were selectively targeted by cetuximab (I467, S468, Q408, and H409), whereas another four were selectively recognized by panitumumab (W386, E388, R390, and T391). In view of the clinical significance of extracellular domain mutations, our data may help guide treatment decisions in selected patients receiving EGFR-targeted therapies.

Zirconium-89 labeled panitumumab: a potential immuno-PET probe for HER1-expressing carcinomas

INTRODUCTION

Anti-HER1 monoclonal antibody (mAb), panitumumab (Vectibix) is a fully human mAb approved by the FDA for the treatment of epidermal growth factor receptor (EGFR, HER1)-expressing colorectal cancers. By combining the targeted specificity of panitumumab with the quantitative in vivo imaging capabilities of PET, we evaluated the potential of (89)Zr-DFO-panitumumab PET/CT imaging and performed non-invasive, in vivo imaging of HER1 expression and estimated human dosimetry.

METHODS

Panitumumab was radiolabeled with (89)Zr using a derivative of desferrioxamine (DFO-Bz-NCS) and with (111)In using CHX-A" DTPA as bifunctional chelators. Comparative biodistribution/dosimetry of both radiotracers was performed in non-tumor bearing athymic nude mice (n=2 females and n=2 males) over 1-week following i.v. injection of either using (89)Zr-DFO-panitumumab or (111)In-CHX-A"-DTPA-panitumumab. Micro-PET/CT imaging of female athymic nude mice bearing human breast cancer tumors (n=5 per tumor group) with variable HER1-expression very low (BT-474), moderate (MDA-MB-231), and very high (MDA-MB-468) was performed at over 1 week following i.v. injection of (89)Zr-DFO-panitumumab.

RESULTS

Radiochemical yield and purity of (89)Zr-Panitumumab was >70% and >98% respectively with specific activity 150 ± 10 MBq/mg of panitumumab in a ~4 hr synthesis time. Biodistribution of (111)In-CHX-A" DTPA -panitumumab and (89)Zr-DFO-panitumumab in athymic non-tumor bearing nude mice displayed similar percent injected dose per gram of tissue with prominent accumulation of both tracers in the lymph nodes, a known clearance mechanism of panitumumab. Also exhibited was prolonged blood pool with no evidence of targeted accumulation in any organ. Human radiation dose estimates showed similar biodistributions with estimated human effective doses of 0.578 and 0.183 mSv/MBq for (89)Zr-DFO-panitumumab and (111)In-CHX-A"-DTPA-panitumumab, respectively. Given the potential quantitative and image quality advantages of PET, imaging of tumor bearing mice was only performed using (89)Zr-DFO-panitumumab. Immuno-PET imaging of (89)Zr-DFO-panitumumab in mice bearing breast cancer xenograft tumors with variable HER1 expression showed high tumor uptake (SUV >7) in the MDA-MB-468 high HER1-expressing mice and a strong correlation between HER1-expression level and tumor uptake (R(2)= 0.857, P < .001).

CONCLUSIONS

(89)Zr-DFO-panitumumab can prepared with high radiochemical purity and specific activity. (89)Zr-DFO-panitumumab microPET/CT showed uptake corresponding to HER-1 expression. Due to poor clearance, initial dosimetry estimates suggest that only a low dose (89)Zr-DFO-panitumumab shows favorable human dosimetry; however due to high tumor uptake, the use of (89)Zr-DFO-panitumumab is expected to be clinically feasible.

Epidermal growth factor receptor as a therapeutic target in glioblastoma

Glioblastoma represents one of the most challenging problems in neurooncology. Among key elements driving its behavior is the transmembrane epidermal growth factor receptor family, with the first member epidermal growth factor receptor (EGFR) centered in most studies. Engagement of the extracellular domain with a ligand activates the intracellular tyrosine kinase (TK) domain of EGFR, leading to autophosphorylation and signal transduction that controls proliferation, gene transcription, and apoptosis. Oncogenic missense mutations, deletions, and insertions in the EGFR gene are preferentially located in the extracellular domain in glioblastoma and cause constitutive activation of the receptor. The mutant EGFR may also transactivate other cell surface molecules, such as additional members of the EGFR family and the platelet-derived growth factor receptor, which ignite signaling cascades that synergize with the EGFR-initiated cascade. Because of the cell surface location and increased expression of the receptor along with its important biological function, EGFR has triggered much effort for designing targeted therapy. These approaches include TK inhibition, monoclonal antibody, vaccine, and RNA-based downregulation of the receptor. Treatment success requires that the drug penetrates the blood-brain barrier and has low systemic toxicity but high selectivity for the tumor. While the blockade of EGFR-dependent processes resulted in experimental and clinical treatment success, cells capable of using alternative signaling ultimately escape this strategy. A combination of interventions targeting tumor-specific cell surface regulators along with convergent downstream signaling pathways will likely enhance efficacy. Studies on EGFR in glioblastoma have revealed much information about the complexity of gliomagenesis and also facilitated the development of strategies for targeting drivers of tumor growth and combination therapies with increasing complexity.

Acute cytotoxic effects of photoimmunotherapy assessed by 18F-FDG PET

We have recently developed a cancer-specific therapy, photoimmunotherapy, which uses an antibody-IR700 (phototoxic phthalocyanine dye) conjugate to bind to the cell membrane and near-infrared light to induce immediate and highly specific tumor killing in vivo. For monitoring the acute cytotoxic effects of photoimmunotherapy before the tumor begins to shrink, we used (18)F-FDG PET before and after this intervention in mice.

METHODS

Photoimmunotherapy was performed by binding panitumumab (anti-HER1)-IR700 to HER1-positive tumor cells (A431), followed by near-infrared light irradiation in vitro and in vivo. The uptake of (18)F-FDG in the tumor after photoimmunotherapy was evaluated in cellular uptake studies and PET imaging studies. Serial histologic analyses were conducted after photoimmunotherapy.

RESULTS

The in vitro cellular uptake of (18)F-FDG was reduced as the dose of light increased, and at high light dose (2 J/cm(2)) the uptake was reduced by more than 99% within 1 h after photoimmunotherapy. In vivo (18)F-FDG PET imaging showed that the accumulation of radioactivity in the treated tumors decreased 76% at 75 min after photoimmunotherapy and did not change for 24 h. In contrast, no significant changes were demonstrated in nontreated tumors. None of tumors changed size within 24 h after photoimmunotherapy, although diffuse necrosis was observed in photoimmunotherapy-treated tumors.

CONCLUSION

Immediate cytotoxic effects induced by photoimmunotherapy were clearly detected by decreased glucose uptake using (18)F-FDG PET even before changes in tumor size became evident. (18)F-FDG allows the clinical assessment of the therapeutic effects of photoimmunotherapy earlier than anatomic methods that rely on tumor size.

Mechanisms of resistance to EGFR targeted therapies

EGFR is a validated therapeutic target in many human cancers. EGFR targeted therapies are in widespread clinical use in patients with non-small cell lung cancer and other tumor types. Despite the clinical success of EGFR targeted therapy, resistance to treatment is a significant barrier to the optimized use of EGFR inhibitors to cure patients with lung and other cancers. Here, we review established and emerging mechanisms of resistance to EGFR targeted therapy and highlight strategies that could overcome treatment resistance and therefore enhance clinical outcomes.

Optimizing treatment of metastatic colorectal cancer patients with anti-EGFR antibodies: overcoming the mechanisms of cancer cell resistance

INTRODUCTION

A number of anti-EGFR monoclonal antibodies (mAbs) have been recently developed for the treatment of refractory metastatic colorectal cancer (mCRC). These mAbs, blocking ligand/receptor interactions, exert their biological activity via multiple mechanisms, including inhibition of cell cycle progression, potentiation of cell apoptosis, inhibition of angiogenesis, tumor cell invasion and metastasis and, potentially, induction of immunological effector mechanisms.

AREAS COVERED

Cetuximab is an anti-EGFR mAb currently used in mCRC treatment. Despite the evidence of efficacy of cetuximab in the treatment of mCRC patients, the observation of low response rates was the proof of concept of resistance to anti-EGFR mAbs treatment. An increasing number of molecular alterations have been more recently hypothesized to be involved in resistance to anti-EGFR mAbs in CRC: mutations in BRAF, NRAS and PIK3CA, loss of expression of PTEN and, now, activation of HER2 signaling through HER2 gene amplification and/or increased heregulin stimulation.

EXPERT OPINION

This review focuses on the development of new strategies such as combination with other agents blocking alternative escape pathways, cancer cell prioritization hyperactivating EGFR pathway, combination with immune system, development of nanotech devices to increase efficacy of antibody-based therapy and overcome the mechanisms of cancer cell resistance.

KRAS p.G13D mutations are associated with sensitivity to anti-EGFR antibody treatment in colorectal cancer cell lines

PURPOSE

Targeted therapies using the anti-EGFR antibodies panitumumab (Pmab) or cetuximab (Cmab) are currently restricted to patients with metastatic colorectal adenocarcinoma whose tumours do not show a mutation in KRAS. However, recent retrospective studies indicated that patients with tumours mutated in codon 13 of KRAS may benefit from treatment with Cmab in contrast to patients with tumours mutated in KRAS codon 12.

METHODS

To study the functional impact of the subtype of KRAS mutations on the efficiency of EGFR-targeted therapies, we correlated the KRAS mutation status of 15 colorectal carcinoma cell lines with the in vitro sensitivity of these cells to Cmab/Pmab. Mutations in the potential predictive biomarkers BRAF and PIK3CA as well as protein expression of EGFR and PTEN were also determined.

RESULTS

Four out of seven KRAS-mutated cell lines were characterised by the p.G13D mutation. Treatment of these cells using Cmab/Pmab induced a significant growth inhibition in contrast to cell lines showing a KRAS mutation at codon 12 or 61. Out of the eight KRAS wild-type cell lines, five were insensitive to Cmab/Pmab. These cell lines were characterised either by BRAF mutation or by absence of EGFR or PTEN protein expression.

CONCLUSIONS

Since KRAS p.G13D-mutated tumour cells may respond to EGFR-targeted therapy, we suggest including subtype analysis of KRAS mutations in prospective clinical trials. In KRAS wild-type tumour cells, BRAF mutations and loss of EGFR or PTEN expression may lead to resistance to EGFR-targeted therapy and should be considered as additional negative predictive biomarkers.

Recombinant IgE antibody engineering to target EGFR

Monoclonal antibodies have become a mainstay for the targeted treatment of cancer today. Some of the most successful targets of monoclonal antibodies are constituted by the epidermal growth factor receptor family spearheaded by the epidermal growth factor receptor (EGFR). Prompted by studies indicating that IgE compared to IgG may harness alternate effector functions to eradicate malignant cells, we addressed the establishment, engineering, and the potential tumoricidal effects of recombinant anti-EGFR IgE. Therefore, two different therapeutic EGFR-specific antibodies, 225 and 425, were chosen for re-cloning into different chimeric IgE and IgG formats and produced in human cells. Simultaneous antibody binding to the sEGFR demonstrated accessibility of both epitopes for recombinant IgE. Proliferation and cytotoxicity assays demonstrated signal blocking and effector mediating capability of IgE isotypes. Pronounced degranulation in the presence of sEGFR upon activation exclusively with two IgE antibodies verified the epitope proximity and provides evidence that tumor-targeting by anti-EGFR IgE is safe with regard to soluble target structures. Degranulation mediated by tumor cells expressing EGFR could be demonstrated for singular and combined IgE antibodies; however, use of two IgE specificities was not superior to use of one IgE alone. The data suggest that the surface distribution of EGFR is optimally suited to mount a robust effector cell trigger and corroborate the potential and specificity of the IgE/IgE receptor network to react to xenobiotic or pathogenic patterns for targeting malignancies.

Feasibility of eradication of breast cancer cells remaining in postlumpectomy cavity and draining lymph nodes following intracavitary injection of radioactive immunoliposomes

Most diagnosed early stage breast cancer cases are treated by lumpectomy and adjuvant radiation therapy, which significantly decreases the locoregional recurrence but causes inevitable toxicity to normal tissue. By using a technique of preparing liposomes carrying technetium-99m ((99m)Tc), rhenium-186 ((186)Re), or rhenium-188 ((188)Re) radionuclides, as well as chemotherapeutic agents, or their combination, for cancer therapy with real time image-monitoring of pharmacokinetics and prediction of therapy effect, this study investigated the potential of a novel targeted focal radiotherapy with low systemic toxicity using radioactive immunoliposomes to treat both the surgical cavity and draining lymph nodes in a rat breast cancer xenograft positive surgical margin model. Immunoliposomes modified with either panitumumab (anti-EGFR) or bevacizumab (anti-VEGF) were remote loaded with (99m)Tc diagnostic radionuclide, and injected into the surgical cavity of female nude rats with positive margins postlumpectomy. Locoregional retention and systemic distribution of (99m)Tc-immunoliposomes were investigated by nuclear imaging, stereofluorescent microscopic imaging, and gamma counting. Histopathological examination of excised draining lymph nodes was performed. The locoregional retention of (99m)Tc-immunoliposomes in each animal was influenced by the physiological characteristics of the surgical site of individual animals. Panitumumab- and bevacizumab-liposome groups had higher intracavitary retention compared with the control liposome groups. Draining lymph node uptake was influenced by both the intracavitary radioactivity retention level and metastasis status. The panitumumab-liposome group had higher accumulation on the residual tumor surface and in the metastatic lymph nodes. Radioactive liposomes that were cleared from the cavity were metabolized quickly and accumulated at low levels in vital organs. Therapeutic radionuclide-carrying specifically targeted panitumumab- and bevacizumab-liposomes have increased potential compared to non-antibody targeted liposomes for postlumpectomy focal therapy to eradicate remaining breast cancer cells inside the cavity and draining lymph nodes with low systemic toxicity.

Panitumumab: a summary of clinical development in colorectal cancer and future directions

Panitumumab is a fully human, monoclonal antibody targeting the EGF receptor with proven clinical activity in KRAS wild-type metastatic colorectal carcinoma. Treatment with panitumumab has been shown to significantly improve response rate and progression-free survival in this subgroup of patients, with a manageable toxicity profile. Panitumumab's first worldwide indication was as a single agent in chemorefractory patients. Recently, the EMA approved its use as part of a chemotherapy regimen in first- and second-line settings, following the encouraging results of large randomized Phase III trials. In order to identify patients with higher chances of benefiting from the treatment, additional molecular aberrations in the EGF receptor signaling pathway are being investigated as predictive biomarkers. In this article we review 10 years of drug development, focusing on the clinical evidence for panitumumab's indication in metastatic colorectal cancer and future strategies of investigation.

Tumor penetration and epidermal growth factor receptor saturation by panitumumab correlate with antitumor activity in a preclinical model of human cancer

Background

Successful treatment of solid tumors relies on the ability of drugs to penetrate into the tumor tissue.

Methods

We examined the correlation of panitumumab (an anti-epidermal growth factor [EGFR] antibody) tumor penetration and EGFR saturation, a potential obstacle in large molecule drug delivery, using pharmacokinetics, pharmacodynamics, and tumor growth rate in an A431 epidermoid carcinoma xenograft model of human cancer. To determine receptor saturation, receptor occupancy, and levels of proliferation markers, immunohistochemical and flow cytometric methods were used. Pharmacokinetic data and modeling were used to calculate growth characteristics of panitumumab-treated tumors.

Results

Treatment with panitumumab in vivo inhibited pEGFR, Ki67 and pMAPK levels vs control. Tumor penetration and receptor saturation were dose- and time-dependent, reaching 100% and 78%, respectively. Significant tumor inhibition and eradication (p < 0.05) were observed; plasma concentration associated with tumor eradication was estimated to be 0.2 μg/ml. The tumor inhibition model was able to describe the mean tumor growth and death rates.

Conclusions

These data demonstrate that the antitumor activity of panitumumab correlates with its ability to penetrate into tumor tissue, occupy and inhibit activation of EGFR, and inhibit markers of proliferation and MAPK signaling.

The epidermal growth factor receptor as a therapeutic target in epithelial ovarian cancer

A majority of patients with ovarian carcinoma who receive conventional treatment of surgical staging and platinum-based chemotherapy recur and ultimately succumb to their diseases. Novel therapies that target specific pathways involved in ovarian tumorigenesis are rapidly emerging. The epidermal growth factor receptor (EGFR) is overexpressed in 30-98% of epithelial ovarian carcinoma (EOC), and the signaling cascades activated are related with cell proliferation, migration and invasion, and angiogenesis, as well as resistance to cell apoptosis. Various trials are ongoing focusing on EGFR as an attractive target in treatment of EOC. Anti-EGFR monoclonal antibodies (MAbs), cetuximab and panitumumab, and tyrosine kinase inhibitors (TKIs), erlotinib and gefitinib, are the most advanced in clinical development. The available data suggests that MAbs and TKIs only show marginal activity when they are used alone, but combination with platinum-based chemotherapy can induce elevated overall response rate in recurrent EOC patients. Consequently, mechanisms for intrinsic and extrinsic resistance have been explored due to the poor clinical response to EGFR-targeted therapy. Careful consideration of these clinical studies and the possible mechanisms involved in resistance can provide evidence for improvements in subsequent research. Identification of responder profiles and development of rational regimen of combination therapy of EGFR-targeted therapy with other effective treatment modalities may eventually bring about substantial progress in the treatment of epithelial ovarian cancers.

Concordance of preclinical and clinical pharmacology and toxicology of therapeutic monoclonal antibodies and fusion proteins: cell surface targets

Monoclonal antibodies (mAbs) and fusion proteins directed towards cell surface targets make an important contribution to the treatment of disease. The purpose of this review was to correlate the clinical and preclinical data on the 15 currently approved mAbs and fusion proteins targeted to the cell surface. The principal sources used to gather data were: the peer reviewed Literature; European Medicines Agency 'Scientific Discussions'; and the US Food and Drug Administration 'Pharmacology/Toxicology Reviews' and package inserts (United States Prescribing Information). Data on the 15 approved biopharmaceuticals were included: abatacept; abciximab; alefacept; alemtuzumab; basiliximab; cetuximab; daclizumab; efalizumab; ipilimumab; muromonab; natalizumab; panitumumab; rituximab; tocilizumab; and trastuzumab. For statistical analysis of concordance, data from these 15 were combined with data on the approved mAbs and fusion proteins directed towards soluble targets. Good concordance with human pharmacodynamics was found for mice receiving surrogates or non-human primates (NHPs) receiving the human pharmaceutical. In contrast, there was poor concordance for human pharmacodynamics in genetically deficient mice and for human adverse effects in all three test systems. No evidence that NHPs have superior predictive value was found.

Recent advances in the application of antibodies as therapeutics

The application of antibodies as therapeutic agents in the treatment of cancer now represents a significant proportion of the oncology drug arena. Despite this success, the ability to engineer and exploit antibodies in many different formats is ensuring that new avenues for their therapeutic application are constantly being examined. This review examines a selection of novel antibody-based therapeutic strategies that are currently in late preclinical and clinical evaluation.

Treatment of recurrent metastatic head and neck cancer: focus on cetuximab

EGFR belongs to the ErbB family of receptor tyrosine kinases and is associated with worse prognosis in head and neck squamous cell carcinoma (HNSCC). Cetuximab is a monoclonal antibody to the extracellular domain of EGFR and inhibits its downstream actions via multiple mechanisms. Besides its proven efficacy in locally advanced and incurable HNSCC, cetuximab has the distinct advantage of having a relatively tolerable side effect profile and not potentiating radiation toxicity. Though therapies for advanced HNSCC are evolving, locoregional recurrence and/or distant metastases occur in a large percentage of patients. Though some patients can be salvaged with surgery or radiation therapy, the majority are incurable, and are treated palliatively with systemic therapy. In the setting of first line therapy for recurrent/metastatic HNSCC, the EXTREME trial provided level 1 evidence that cetuximab improves overall survival when combined with cisplatinum and 5 FU. Following progression on first line chemotherapy, several phase II trials suggest that cetuximab monotherapy is a reasonable choice in this setting. Future studies should concentrate on clinical and molecular markers that may allow more personalized approaches to treating HNSCC, and combining EGFR inhibitors with other agents in a synergistic approach.

Predicting the F(ab)-mediated effect of monoclonal antibodies in vivo by combining cell-level kinetic and pharmacokinetic modelling

Cell-level kinetic models for therapeutically relevant processes increasingly benefit the early stages of drug development. Later stages of the drug development processes, however, rely on pharmacokinetic compartment models while cell-level dynamics are typically neglected. We here present a systematic approach to integrate cell-level kinetic models and pharmacokinetic compartment models. Incorporating target dynamics into pharmacokinetic models is especially useful for the development of therapeutic antibodies because their effect and pharmacokinetics are inherently interdependent. The approach is illustrated by analysing the F(ab)-mediated inhibitory effect of therapeutic antibodies targeting the epidermal growth factor receptor. We build a multi-level model for anti-EGFR antibodies by combining a systems biology model with in vitro determined parameters and a pharmacokinetic model based on in vivo pharmacokinetic data. Using this model, we investigated in silico the impact of biochemical properties of anti-EGFR antibodies on their F(ab)-mediated inhibitory effect. The multi-level model suggests that the F(ab)-mediated inhibitory effect saturates with increasing drug-receptor affinity, thereby limiting the impact of increasing antibody affinity on improving the effect. This indicates that observed differences in the therapeutic effects of high affinity antibodies in the market and in clinical development may result mainly from Fc-mediated indirect mechanisms such as antibody-dependent cell cytotoxicity.

Long-term treatment of metastatic colorectal cancer with panitumumab

Colorectal cancer is one of the leading causes of cancer-related deaths worldwide. More than 30% patients present with metastases at diagnoses and will require systemic chemotherapy. In recent years many anti-EGFR targets have been developed. Among them, panitumumab, a fully human IgG2 monoclonal antibody has shown important benefits in the treatment of this disease.

Safety, efficacy and pharmacokinetics of neratinib (HKI-272) in Japanese patients with advanced solid tumors: a Phase 1 dose-escalation study

OBJECTIVE

Neratinib (HKI-272), a potent, irreversible, small-molecule, orally administered, pan-ErbB inhibitor that blocks signal transduction via inhibition of three epidermal growth factor receptors [ErbB1, ErbB2 (Her2) and ErbB4], is being developed for the treatment of solid tumors, including breast cancer. This Phase 1 dose-escalation study assessed the safety, tolerability, maximum-tolerated dose, antitumor activity and pharmacokinetics of neratinib in Japanese patients with advanced solid tumors.

METHODS

Patients received neratinib 80, 160, 240 or 320 mg orally; each patient enrolled in only one dose cohort. Patients received a single dose in week 1, followed by daily continuous doses. Blood samples collected were on days 1 and 21 for pharmacokinetic analyses.

RESULTS

Twenty-one patients were enrolled (3 breast cancer; 17 colorectal cancer; 1 gastric cancer). Neratinib-related adverse events (all grades) included diarrhea (20 patients), fatigue (14 patients), nausea and abdominal pain (9 patients each) and anorexia (8 patients). Grade ≥3 neratinib-related adverse events in two or more patients were diarrhea and anorexia (two patients each). Dose-limiting toxicities were diarrhea and anorexia (two patients, 320 mg dose). The maximum-tolerated dose and recommended dose was neratinib 240 mg once daily. Of 21 evaluable patients, 2 with breast cancer had partial response, 3 had stable disease ≥24 weeks, 7 had stable disease ≥16 weeks and 9 had progressive disease. Pharmacokinetic analyses indicated that neratinib exposures increased with dose.

CONCLUSIONS

The safety, efficacy and pharmacokinetic profiles of neratinib are consistent with those reported for non-Japanese patients and warrant further investigation of neratinib in Japanese patients with solid tumors.

Combining bacterial-immunotherapy with therapeutic antibodies: a novel therapeutic concept

Immunotherapeutic strategies become more and more important for cancer treatment. Therapeutic monoclonal antibodies (mAbs) like Panitumumab binding and blocking the EGF-receptor are in routine clinical use for the treatment of colorectal carcinoma (CRC). Also, bacterial therapy proved beneficial for experimental treatment of different tumor entities. The latter has been attributed to an activation of the immune system. Here, we describe a combination of both immunotherapeutic approaches in order to develop a novel targeted therapy for CRC. The therapeutic mAbs Trastuzumab and Panitumumab were conjugated to heat-inactivated bacteria expressing protein A or protein G. The potential of the conjugates was tested in comparison to the single components both in vitro and in vivo using a panel of patient-derived CRC cell lines. Antitumoral effects observed in vitro were strictly dependent on the presence of bacteria. Generally, effects could be enhanced by the addition of human lymphocytes. Detailed analysis of effector cells in autologous and allogeneic long-term stimulated lymphocyte cultures revealed the predominance of NK-cell-like cytolytic effectors. Reactivity was observed both against CRC target cells but also against the NK cell target K562. Similarly, in a subsequent in vivo study we observed substantial tumor growth delay accompanied by an increase in circulating NK cells. Contrary to this, the monotherapy with mAb alone caused only marginal effects and the treatment with bacteria was comparable to the mock-treated control. These data demonstrate successful targeting of CRC by bacteria/mAb conjugates. This novel concept may be interesting for future clinical approaches. Additionally, it illustrates the effectiveness of NK cells for cancer immunotherapy.

Targeting the EGFR signaling pathway in cancer therapy

INTRODUCTION

Cancer is a devastating disease; however, several therapeutic advances have recently been made, wherein EGFR and its family members have emerged as useful biomarkers and therapeutic targets. EGFR, a transmembrane glycoprotein is a member of the ERBB receptor tyrosine kinase superfamily. EGFR binds to its cognate ligand EGF, which further induces tyrosine phosphorylation and receptor dimerization with other family members leading to enhanced uncontrolled proliferation. Several anti-EGFR therapies such as monoclonal antibodies and tyrosine kinase inhibitors have been developed, which has enabled clinicians to identify and treat specific patient cohorts.

AREAS COVERED

This review covers the basic mechanism of EGFR activation and the role of EGFR signaling in cancer progression. Furthermore, current developments made toward targeting the EGFR signaling pathway for the treatment of epithelial cancers and a summary of the various anti-EGFR therapeutic agents that are currently in use are also presented in this review.

EXPERT OPINION

EGFR signaling is a part of a complex network that has been the target of effective cancer therapies. However, a further understanding of the system is required to develop an effective anticancer regimen. A combination therapy that comprises an anti-EGFR and a chemotherapeutic/chemopreventive agent will exhibit a multi-pronged approach that can be developed into a highly attractive and specific molecular oriented remedy.

KRAS mutant colorectal tumors: past and present

The treatment of metastatic colorectal cancer (mCRC) remains one of the largest hurdles in cancer therapeutics to date. The most advanced treatment option for mCRC patients are anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (mAbs) that bind to and inhibit the activity of EGFR. While the use of anti-EGFR mABs has had great impact in the treatment of mCRC, it has now been widely accepted that mCRC tumors with a mutation in the small GTPase KRAS do not respond to these therapies. KRAS mutations allow for EGFR independent activation of various oncogenic signaling cascades. In attempts to inhibit KRAS mutant tumor growth, BRAF, MEK and farsenyltransferase inhibitors have been used, however, their clinical efficacy is still accruing in the setting of CRC. Recent data suggests that various other inhibitors, including inhibitors of Src family kinases (SFK) and hepatocyte growth factor receptor (MET), may have potential preclinical and clinical success in KRAS mutant tumors. Additionally, it is becoming increasingly clear that different KRAS missense mutations may have varied biological responses to cetuximab, suggesting that cetuximab may still be a potential therapeutic option in some KRAS mutant tumors. In this review, we highlight the importance for both improved multimodality approaches for treating KRAS mutant mCRC tumors and stratification of KRAS mutations in response to different treatment regimes in order to optimize the best possible care for mCRC patients.

Progress of molecular targeted therapies for prostate cancers

Prostate cancer remains the most commonly diagnosed malignancy and the second leading cause of cancer-related deaths in men in the United States. The current standard of care consists of prostatectomy and radiation therapy, which may often be supplemented with hormonal therapies. Recurrence is common, and many develop metastatic prostate cancer for which chemotherapy is only moderately effective. It is clear that novel therapies are needed for the treatment of the malignant forms of prostate cancer that recur after initial therapies, such as hormone refractory (HRPC) or castration resistant prostate cancer (CRPC). With advances in understanding of the molecular mechanisms of cancer, we have witnessed unprecedented progress in developing new forms of targeted therapy. Several targeted therapeutic agents have been developed and clinically used for the treatment of solid tumors such as breast cancer, non-small cell lung cancer, and renal cancer. Some of these reagents modulate growth factors and/or their receptors, which are abundant in cancer cells. Other reagents target the downstream signal transduction, survival pathways, and angiogenesis pathways that are abnormally activated in transformed cells or metastatic tumors. We will review current developments in this field, focusing specifically on treatments that can be applied to prostate cancers. Finally we will describe aspects of the future direction of the field with respect to discovering biomarkers to aid in identifying responsive prostate cancer patients.

Targeting colorectal cancer with anti-epidermal growth factor receptor antibodies: focus on panitumumab

Panitumumab is a fully humanized monoclonal antibody with a high degree of affinity for the extracellular domain of the epidermal growth factor receptor. Phase II clinical evaluation of this drug, when administered as a single agent, in patients with metastatic colorectal cancer refractory to chemotherapy, demonstrated a modest objective radiographic response rate with acceptable toxicity; the most frequently observed side effect is rash. A randomized phase III study in subjects with chemotherapy-refractory metastatic colorectal cancer documented a progression-free survival advantage in subjects treated with panitumumab plus best supportive care versus best supportive care alone; a difference in survival was not observed, likely due to the high cross over rate. Primary tumor KRAS mutation analysis performed in this study indicated that the benefit was confined to those patients whose tumors did not contain a KRAS mutation. Further studies with panitumumab will be required to develop biomarkers of response and to determine if panitumumab has a role in combination with cytotoxic chemotherapy. This article summarizes the current state-of-the-science knowledge on panitumumab therapy in the treatment of advanced colorectal cancer.

Phase I pharmacokinetic and pharmacodynamic dose-escalation study of RG7160 (GA201), the first glycoengineered monoclonal antibody against the epidermal growth factor receptor, in patients with advanced solid tumors

PURPOSE

We conducted a phase I dose-escalation study to characterize the safety, efficacy, pharmacokinetic (PK), and pharmacodynamic properties of RG7160 (GA201), a humanized and glycoengineered immunoglobulin G(1) anti-epidermal growth factor receptor (EGFR) monoclonal antibody with enhanced antibody-dependent cell-mediated cytotoxicity.

PATIENTS AND METHODS

Seventy-five patients with advanced EGFR-positive solid tumors received RG7160 (50 to 1,400 mg) administered every week, every 2 weeks, or every 3 weeks. Dose escalation followed a three-plus-three trial design.

RESULTS

No maximum-tolerated dose was reached for any dosing schedule. Common adverse events (AEs) included rash (80% of patients), infusion-related reactions (77%), and hypomagnesemia (56%). Grades 3 and 4 AEs were rash (grade 3, 25%), infusion-related reaction (grade 3, 7%; grade 4, 1%), paronychia (grade 3, 3%), and hypomagnesemia (grade 3, 1%; grade 4, 1%). RG7160 exposure increased greater than proportionally over the 50- to 400-mg dose range (with greater than proportional decline in clearance) and approximately dose proportionally above 400 mg (where clearance plateaued). A marked reduction in circulating natural killer cells and increased infiltration of immune effector cells into skin rash were seen. Clinical efficacy included one complete response and two partial responses in patients with colorectal cancer (including one with KRAS mutation) and disease stabilization in 27 patients.

CONCLUSION

RG7160 had an acceptable safety profile with manageable AEs and demonstrated promising efficacy in this heavily pretreated patient cohort. On the basis of modeling of available PK parameters, the RG7160 dose selected for part two of this study is 1,400 mg on days 1 and 8 followed by 1,400 mg every 2 weeks.

Targeting colorectal cancer with human anti-EGFR monoclonocal antibodies: focus on panitumumab

The human anti-epidermal growth factor receptor (EGFR) monoclonal antibody, panitumumab, represents a significant advance in the treatment of colorectal cancer. The strategy to target this receptor is based on sound cancer biology demonstrating its essential role in colorectal carcinogenesis. Panitumumab, unlike its predecessor, cetuximab, is fully human and thus reduces the incidence of hypersensitivity reactions. But, in several clinical trials, unexpected toxicities have become more apparent, raising concerns of how readily panitumumab can succeed cetuximab. This paper reviews the development of this agent and the pivotal clinical trials that help our understanding of its optimal use in colorectal cancer treatment.

Molecular mechanisms of resistance to the EGFR monoclonal antibody cetuximab

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase belonging to the HER family of receptor tyrosine kinases. Receptor activation upon ligand binding leads to down stream activation of the PI3K/AKT, RAS/RAF/MEK/ERK and PLCγ/PKC pathways that influence cell proliferation, survival and the metastatic potential of tumor cells. Increased activation by gene amplification, protein overexpression or mutations of the EGFR has been identified as an etiological factor in a number of human epithelial cancers (e.g., NSCLC, CRC, glioblastoma and breast cancer). Therefore, targeting the EGFR has been intensely pursued as a cancer treatment strategy over the last two decades. To date, five EGFR inhibitors, including three small molecule tyrosine kinase inhibitors (TKIs) and two monoclonal antibodies have gained FDA approval for use in oncology. Both approaches to targeting the EGFR have shown clinical promise and the anti-EGFR antibody cetuximab is used to treat HNSCC and CRC. Despite clinical gains arising from use of cetuximab, both intrinsic resistance and the development of acquired resistance are now well recognized. In this review we focus on the biology of the EGFR, the role of EGFR in human cancer, the development of antibody-based anti-EGFR therapies and a summary of their clinical successes. Further, we provide an in depth discussion of described molecular mechanisms of resistance to cetuximab and potential strategies to circumvent this resistance.

EGFR-Targeting as a Biological Therapy: Understanding Nimotuzumab's Clinical Effects

Current clinical trials of epidermal growth factor receptor (EGFR)-targeted therapies are mostly guided by a classical approach coming from the cytotoxic paradigm. The predominant view is that the efficacy of EGFR antagonists correlates with skin rash toxicity and induction of objective clinical response. Clinical benefit from EGFR-targeted therapies is well documented; however, chronic use in advanced cancer patients has been limited due to cumulative and chemotherapy-enhanced toxicity. Here we analyze different pieces of data from mechanistic and clinical studies with the anti-EGFR monoclonal antibody Nimotuzumab, which provides several clues to understand how this antibody may induce a biological control of tumor growth while keeping a low toxicity profile. Based on these results and the current state of the art on EGFR-targeted therapies, we discuss the need to evaluate new therapeutic approaches using anti-EGFR agents, which would have the potential of transforming advanced cancer into a long-term controlled chronic disease.

Pharmacokinetic and pharmacodynamic perspectives on the clinical drug development of panitumumab

Panitumumab is a recombinant, fully human IgG2 monoclonal antibody directed against the epidermal growth factor receptor (EGFR). It is indicated for use as monotherapy in the treatment of patients with EGFR-expressing metastatic colorectal cancer after disease progression with standard chemotherapy. The currently indicated dose is 6 mg/kg given every 2 weeks. Panitumumab is mainly distributed into the vascular space and exhibits nonlinear pharmacokinetics that are consistent with target-mediated drug disposition, involving saturable binding to EGFR and subsequent internalization and degradation inside the cells. Panitumumab is also cleared in a linear fashion by the reticuloendothelial system, similarly to other endogenous immunoglobulins. After single-dose administration of panitumumab as a 1-hour intravenous infusion, the area under the serum concentration-time curve increases in a greater-than-dose-proportional manner as the dose increases from 0.75 to 5 mg/kg; however, at doses above 2 mg/kg, the exposure to panitumumab increases in a dose-proportional manner. Panitumumab pharmacokinetics are not meaningfully affected by the tumour type, EGFR membrane expression, tumour KRAS mutation, sex, age, race or renal or hepatic dysfunction. In addition, irinotecan-containing and paclitaxel/carboplatin-containing chemotherapeutic regimens do not appear to affect panitumumab pharmacokinetics. The results of population pharmacokinetic analyses have shown that bodyweight is the most influential covariate on panitumumab exposure, supporting the current use of bodyweight-adjusted doses (mg/kg). The relationship between the weekly dose of panitumumab and skin rash, an on-target pharmacodynamic effect of EGFR inhibition, reaches a plateau at 2.5 mg/kg, indicating that this is the optimal weekly dose. Two less-frequent dosing regimens (6 mg/kg given every 2 weeks and 9 mg/kg given every 3 weeks) achieve steady-state serum trough concentrations similar to those achieved by 2.5 mg/kg given every week, ensuring maximal EGFR coverage. Anti-panitumumab antibody production is uncommon and does not appear to have an impact on the pharmacokinetics of panitumumab.

New trends in epidermal growth factor receptor-directed monoclonal antibodies

The epidermal growth factor receptor (EGFR) has been the focus of much attention in the age of targeted cancer therapeutics. In addition to its role in signal transduction under physiological conditions, it has been of interest because it is highly expressed in many tumor types and influences growth and survival in malignant states. Advances in the understanding of the EGFR and in genetic engineering have led to the development of monoclonal antibodies targeting the extracellular domain of the membrane-bound receptor. Cetuximab and panitumumab are the two most advanced such compounds. Thus far, cetuximab has achieved regulatory approval in metastatic colorectal cancer, and locally advanced and metastatic squamous cell cancer of the head and neck; panitumumab has been approved for metastatic colorectal cancer. This review will focus on the EGFR signaling network, monoclonal antibodies against EGFR and the pertinent clinical trials in this field of oncology using such agents.

Targeting epidermal growth factor receptor in the treatment of non-small-cell lung cancer

IMPORTANCE OF THE FIELD

The management of non-small-cell lung cancer (NSCLC) has undergone a paradigm shift in the last decade, with the survival advantage demonstrated by the incorporation of anti-epidermal growth factor receptor (EGFR) agents to the standard treatment of advanced/metastatic NSCLC.

AREAS COVERED IN THIS REVIEW

We review the existing data regarding the distinct anti-EGFR agents in the NSCLC treatment and the potential role of the investigated biomarkers in the clinical outcome.

WHAT THE READER WILL GAIN

Tyrosine kinase inhibitors have been used in first-line, second-line and more settings with extremely good results in a subgroup of patients. Cetuximab remains the only anti-EGFR monoclonal antibody to show survival benefit when combined with a cytotoxic agent in the front-line setting. Anti-EGFR treatment is associated with a dramatic clinical benefit in a subgroup of patients, emphasizing the importance of customizing treatment. Several biomarkers have been investigated for their predictive or prognostic value. Validation of identification of biomarkers remains a focus of intense research that may ultimately guide therapeutic decision making, as none of these is considered ideal to discriminate responding from non-responding patients. However, the current evidence of the EGFR mutation analysis from a recent randomised trial suggests that EGFR mutation analysis is quite a good predictive marker for responsiveness to anti-EGFR TKIs. Moreover, the identification of surrogate markers to indicate optimal activity of the anti-EGFR agent is also needed. This review article provides data from large clinical trials using anti-EGFR agents and correlates these results with the tested biomarkers.

TAKE HOME MESSAGE

EGFR inhibition has shown very encouraging results and has improved the outcome of the NSCLC treatment. However, a plateau of significant clinical benefit seems to have been reached and we believe that the time to move away from the traditional treatment approach to more individualizing therapies has come.

[Biotechnological advances in monoclonal antibody therapy: the RANK ligand inhibitor antibody]

Biological drugs have been used since the middle of the last century in medicine. Nowadays we are witnesses of the intensive development and wider administration of these drugs in clinical practice. Around 250 biological drugs are available and more than 350 million patients have been treated since their marketed authorization. Among the biologics there are protein based macromolecules, which mass production can be performed with the help of biotechnology. This term referring to the use of living organisms for production of molecules, was introduced by the Hungarian engineer, Károly Ereky. The present review focuses on the research, production and development of monoclonal antibodies manufactured by biotechnology. Some steps of this development have changed our immunological knowledge and the outcome of several diseases. The development of antibodies was highly recognized by two Nobel prizes. Authors detail the structure and functions of immunoglobulins, and their development, including fully human monoclonal antibodies. The RANKL inhibitor denosumab, a fully human IgG2 monoclonal antibody belongs to this latter group and it is available for treatment of osteoporosis. Authors also summarize the basic process of bone metabolism and the benefits of RANK ligand inhibition.

Targeted therapies for solid tumors: current status and future perspectives

The therapeutic benefits of targeted clinical interventions with increased selectivity and fewer adverse effects hold great promise in the treatment of solid malignancies, both in monotherapy and in combination. Molecular targeted therapies offer increasingly customized solutions based on the targeting of multiple specific pathways essential for cancer development and metastasis, allowing the maintenance of quality of life while efficiently attacking the tumor. To date, several monoclonal antibodies (mAbs) and small-molecule inhibitors have been approved for the treatment of colorectal, breast, head and neck, non-small cell lung and renal cell cancer. A number of additional targeted therapies are currently being investigated in ongoing clinical trials in various tumor types such as lung, gastric, cervical, uterine melanoma, and brain tumors. This article describes current and newly developed targeted therapies in solid tumors, with a special focus on tyrosine kinase inhibitors. These include mAbs and small-molecule inhibitors that aim to specifically disrupt receptor signaling pathways, which are essential for proliferation, survival and migration of tumor cells.

Development of an ErbB-overexpressing A-431 optical reporting tumor xenograft model to assess targeted photodynamic therapy regimens

To better assess the efficacy of erbB-targeted therapies, it would help to have optical reporting human tumor xenograft models that abundantly express erbB receptors. A-431 cells have frequently been used in erbB1-targeting studies, but a well-characterized optical reporting version of the cell line has not been readily available. In this study, optical reporting A-431 clones were developed that express both a fluorescent protein reporter (green, GFP; or red, RFP) and a bioluminescent reporter, firefly luciferase. Reporter genes were transduced into cells using commercial lentiviral vectors, and clonal selection was carried out using a series of procedures. A number of clones were isolated for further characterization. A GFP/luciferase clone, A-431/D4, and an RFP/luciferase clone, A-431/G4, were obtained that exhibit erbB1 expression levels and tumor growth kinetics similar to the parental cells. To demonstrate the utility of the optical reporting clones, A-431/G4 tumors were grown subcutaneously in nude mice and treated with vascular-targeted photodynamic therapy (PDT), which targets the angiogenic consequences of erbB signaling. The A-431/G4 tumor model permitted highly sensitive longitudinal monitoring of PDT treatment response using optical imaging. A-431/D4 and A-431/G4 optical reporting tumor models should also prove useful for assessing therapies that directly target the erbB1 receptor.

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

Panitumumab is the first fully human monoclonal antibody to Epidermal Growth Factor Receptor (EGFR) to enter clinical trials for the treatment of solid tumors. The anti-tumor activity of panitumumab has been tested in vitro and in vivo, and inhibition of tumor growth has been observed in numerous cancer models, particularly lung, kidney and colorectal (CRC). Preclinical and clinical studies have established a role for panitumumab in metastatic colorectal cancer (mCRC) refractory to multiple chemotherapeutic regimens. Based on these encouraging findings, panitumumab was approved by the US Food and Drug Administration for the treatment of patients with epidermal growth factor receptor-expressing mCRC refractory to fluoropyrimidine-, oxaliplatin-, and/or irinotecan-containing chemotherapeutic regimens. The improvement in progression free survival (PFS) and response rate (RR) produced by panitumumab monotherapy was significantly greater in patients with non mutated (wild-type) K-RAS than in those with mutant K-RAS. Therefore implementing routine K-RAS screening and limiting the use of EGFR inhibitors to patients with wild-type K-RAS appears the better strategy for select only the patients who could benefit from the therapy with panitumumab and also may have the potential for cost savings. The purpose of this review was to evaluate the patient-related, disease-related and economic-related evidence for the use of panitumumab in the treatment of metastatic colorectal cancer in clinical practice.

Integration of anti-epidermal growth factor receptor therapies with cytotoxic chemotherapy

Treatment of colorectal cancer (CRC) with conventional anticancer treatments has clear benefits in both adjuvant and metastatic settings; however, there are undeniable limitations both in terms of efficacy and toxicity. Molecular targeted therapies have emerged as a new generation of molecules aiming to increase anticancer activity while minimizing side effects. A further desirable attribute is the capacity to be combined with chemotherapy or radiotherapy. Epidermal growth factor receptor inhibitors have emerged to impact outcomes of cancer patients and gain routine clinical use. Cetuximab and panitumumab are the 2 most advanced such compounds. Both have achieved regulatory approval for metastatic CRC. This topic review will focus on the molecular basis and the mechanisms of action of epidermal growth factor receptor inhibitors, the clinical trials in this field and future trends of such compounds in CRC.

Understanding resistance to EGFR inhibitors-impact on future treatment strategies

EGFR is a tyrosine kinase that participates in the regulation of cellular homeostasis. Following ligand binding, EGFR stimulates downstream cell signaling cascades that influence cell proliferation, apoptosis, migration, survival and complex processes, including angiogenesis and tumorigenesis. EGFR has been strongly implicated in the biology of human epithelial malignancies, with therapeutic applications in cancers of the colon, head and neck, lung, and pancreas. Accordingly, targeting EGFR has been intensely pursued, with the development of a series of promising molecular inhibitors for use in clinical oncology. As is common in cancer therapy, challenges with respect to treatment resistance emerge over time. This situation is certainly true of EGFR inhibitor therapies, where intrinsic and acquired resistance is now well recognized. In this Review, we provide a brief overview regarding the biology of EGFR, preclinical and clinical development of EGFR inhibitors, and molecular mechanisms that underlie the development of treatment resistance. A greater understanding of the mechanisms that lead to EGFR resistance may provide valuable insights to help design new strategies that will enhance the impact of this promising class of inhibitors for the treatment of cancer.