A phase 1 study of ABT-806 in subjects with advanced solid tumors

EGFR, the Lazarus target for precision oncology in glioblastoma

The Lazarus effect is a rare condition that happens when someone seemingly dead shows signs of life. The epidermal growth factor receptor (EGFR) represents a target in the fatal neoplasm glioblastoma (GBM) that through a series of negative clinical trials has prompted a vocal subset of the neuro-oncology community to declare this target dead. However, an argument can be made that the core tenets of precision oncology were overlooked in the initial clinical enthusiasm over EGFR as a therapeutic target in GBM. Namely, the wrong drugs were tested on the wrong patients at the wrong time. Furthermore, new insights into the biology of EGFR in GBM vis-à-vis other EGFR-driven neoplasms, such as non-small cell lung cancer, and development of novel GBM-specific EGFR therapeutics resurrects this target for future studies. Here, we will examine the distinct EGFR biology in GBM, how it exacerbates the challenge of treating a CNS neoplasm, how these unique challenges have influenced past and present EGFR-targeted therapeutic design and clinical trials, and what adjustments are needed to therapeutically exploit EGFR in this devastating disease.

Depatuxizumab mafodotin in EGFR-amplified newly diagnosed glioblastoma: A phase III randomized clinical trial

BACKGROUND

Approximately 50% of newly diagnosed glioblastomas (GBMs) harbor epidermal growth factor receptor gene amplification (EGFR-amp). Preclinical and early-phase clinical data suggested efficacy of depatuxizumab mafodotin (depatux-m), an antibody-drug conjugate comprised of a monoclonal antibody that binds activated EGFR (overexpressed wild-type and EGFRvIII-mutant) linked to a microtubule-inhibitor toxin in EGFR-amp GBMs.

METHODS

In this phase III trial, adults with centrally confirmed, EGFR-amp newly diagnosed GBM were randomized 1:1 to radiotherapy, temozolomide, and depatux-m/placebo. Corneal epitheliopathy was treated with a combination of protocol-specified prophylactic and supportive measures. There was 85% power to detect a hazard ratio (HR) ≤0.75 for overall survival (OS) at a 2.5% 1-sided significance level (ie traditional two-sided p ≤ 0.05) by log-rank testing.

RESULTS

There were 639 randomized patients (median age 60, range 22-84; 62% men). Prespecified interim analysis found no improvement in OS for depatux-m over placebo (median 18.9 vs. 18.7 months, HR 1.02, 95% CI 0.82-1.26, 1-sided p = 0.63). Progression-free survival was longer for depatux-m than placebo (median 8.0 vs. 6.3 months; HR 0.84, 95% confidence interval [CI] 0.70-1.01, p = 0.029), particularly among those with EGFRvIII-mutant (median 8.3 vs. 5.9 months, HR 0.72, 95% CI 0.56-0.93, 1-sided p = 0.002) or MGMT unmethylated (HR 0.77, 95% CI 0.61-0.97; 1-sided p = 0.012) tumors but without an OS improvement. Corneal epitheliopathy occurred in 94% of depatux-m-treated patients (61% grade 3-4), causing 12% to discontinue.

CONCLUSIONS

Interim analysis demonstrated no OS benefit for depatux-m in treating EGFR-amp newly diagnosed GBM. No new important safety risks were identified.

Antibody Drug Conjugates in Glioblastoma - Is There a Future for Them?

Glioblastoma (GBM) is an aggressive and fatal malignancy that despite decades of trials has limited therapeutic options. Antibody drug conjugates (ADCs) are composed of a monoclonal antibody which specifically recognizes a cellular surface antigen linked to a cytotoxic payload. ADCs have demonstrated superior efficacy and/or reduced toxicity in a range of haematological and solid tumors resulting in nine ADCs receiving regulatory approval. ADCs have also been explored in patients with brain tumours but with limited success to date. While earlier generations ADCs in glioma patients have had limited success and high toxicity, newer and improved ADCs characterised by low immunogenicity and more effective payloads have shown promise in a range of tumour types. These newer ADCs have also been tested in glioma patients, however, with mixed results. Factors affecting the effectiveness of ADCs to target the CNS include the blood brain barrier which acts as a physical and biochemical barrier, the pro-cancerogenic and immunosuppressive tumor microenvironment and tumour characteristics like tumour volume and antigen expression. In this paper we review the data regarding the ongoing the development of ADCs in glioma patients as well as potential strategies to overcome these barriers to maximise their therapeutic potential.

Receptor tyrosine kinases as druggable targets in glioblastoma: Do signaling pathways matter?

Glioblastoma (GBM) is the most malignant primary brain tumor without effective therapies. Since bevacizumab was FDA approved for targeting vascular endothelial growth factor receptor 2 (VEGFR2) in adult patients with recurrent GBM, targeted therapy against receptor tyrosine kinases (RTKs) has become a new avenue for GBM therapeutics. In addition to VEGFR, the epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), hepatocyte growth factor receptor (HGFR/MET), and fibroblast growth factor receptor (FGFR) are major RTK targets. However, results from clinical Phase II/III trials indicate that most RTK-targeting therapeutics including tyrosine kinase inhibitors (TKIs) and neutralizing antibodies lack clinical efficacy, either alone or in combination. The major challenge is to uncover the genetic RTK alterations driving GBM initiation and progression, as well as to elucidate the mechanisms toward therapeutic resistance. In this review, we will discuss the genetic alterations in these 5 commonly targeted RTKs, the clinical trial outcomes of the associated RTK-targeting therapeutics, and the potential mechanisms toward the resistance. We anticipate that future design of new clinical trials with combination strategies, based on the genetic alterations within an individual patient’s tumor and mechanisms contributing to therapeutic resistance after treatment, will achieve durable remissions and improve outcomes in GBM patients.

High-Affinity Chimeric Antigen Receptor With Cross-Reactive scFv to Clinically Relevant EGFR Oncogenic Isoforms

Tumor heterogeneity is a key reason for therapeutic failure and tumor recurrence in glioblastoma (GBM). Our chimeric antigen receptor (CAR) T cell (2173 CAR T cells) clinical trial (NCT02209376) against epidermal growth factor receptor (EGFR) variant III (EGFRvIII) demonstrated successful trafficking of T cells across the blood–brain barrier into GBM active tumor sites. However, CAR T cell infiltration was associated only with a selective loss of EGFRvIII+ tumor, demonstrating little to no effect on EGFRvIII^- tumor cells. Post-CAR T-treated tumor specimens showed continued presence of EGFR amplification and oncogenic EGFR extracellular domain (ECD) missense mutations, despite loss of EGFRvIII. To address tumor escape, we generated an EGFR-specific CAR by fusing monoclonal antibody (mAb) 806 to a 4-1BB co-stimulatory domain. The resulting construct was compared to 2173 CAR T cells in GBM, using in vitro and in vivo models. 806 CAR T cells specifically lysed tumor cells and secreted cytokines in response to amplified EGFR, EGFRvIII, and EGFR-ECD mutations in U87MG cells, GBM neurosphere-derived cell lines, and patient-derived GBM organoids. 806 CAR T cells did not lyse fetal brain astrocytes or primary keratinocytes to a significant degree. They also exhibited superior antitumor activity in vivo when compared to 2173 CAR T cells. The broad specificity of 806 CAR T cells to EGFR alterations gives us the potential to target multiple clones within a tumor and reduce opportunities for tumor escape via antigen loss.

Specificity, Safety, Efficacy of EGFRvIII-Retargeted Oncolytic HSV for Xenotransplanted Human Glioblastoma

Glioblastoma is a lethal primary brain tumor lacking effective therapy. The secluded onset site, combined with the infiltrative properties of this tumor, require novel targeted therapies. In this scenario, the use of oncolytic viruses retargeted to glioblastoma cells and able to spread across the tumor cells represent an intriguing treatment strategy. Here, we tested the specificity, safety and efficacy of R-613, the first oncolytic HSV fully retargeted to EGFRvIII, a variant of the epidermal growth factor receptor carrying a mutation typically found in glioblastoma. An early treatment with R-613 on orthotopically transplanted EGFRvIII-expressing human glioblastoma significantly increased the median survival time of mice. In this setting, the growth of human glioblastoma xenotransplants was monitored by a secreted luciferase reporter and showed that R-613 is able to substantially delay the development of the tumor masses. When administered as late treatment to a well-established glioblastomas, R-613 appeared to be less effective. Notably the uninfected tumor cells derived from the explanted tumor masses were still susceptible to R-613 infection ex vivo, thus suggesting that multiple treatments could enhance R-613 therapeutic efficacy, making R-613 a promising oncolytic HSV candidate for glioblastoma treatment.

A Phase 1 and Biodistribution Study of ABT-806i, an 111In-Radiolabeled Conjugate of the Tumor-Specific Anti-EGFR Antibody ABT-806

ABT-806 is a tumor-specific antibody targeting the epidermal growth factor receptor (EGFR). This study assessed safety, biodistribution, and pharmacokinetics of ¹¹¹In-radiolabeled ABT-806 (ABT-806i) and effects of repeated doses of ABT-806 on receptor occupancy. Methods: Eligible patients had advanced tumors likely to express EGFR/EGFRvIII; adequate performance status and organ function; and measurable disease by RECIST 1.1. In cohort 1, 6 patients received a bolus administration of ABT-806i and underwent SPECT followed by whole-body planar scans. In cohort 2, 12 patients were imaged similarly as in 1 initially; thereafter, they received 3 doses of unlabeled ABT-806, before another dose of ABT-806i with associated SPECT and whole-body planar scans. At the end of both cohorts, patients who had stable or responding disease were able to enroll into an extension study (M12-326) in which they received unlabeled ABT-806 every 2 wk until disease progression, withdrawal of consent, or intolerable toxicity. Results: No toxicity related to ABT-806i infusion was observed. ABT-806i showed minimal uptake in normal tissues and cleared gradually from blood with a half-life of 6.0 ± 1.5 d. The mean effective dose of ABT-806i was 0.137 mSv/MBq for males and 0.183 mSv/MBq for females. ABT-806i tumor uptake varied and did not correlate with archived tumor EGFR expression. No change in ABT-806i uptake was observed after interval ABT-806 treatment, indicating stable EGFR expression in tumor. The patient with highest tumor uptake of ABT-806i had advanced head and neck cancer and experienced a partial response. Conclusion: ABT-806i allows for real-time imaging of EGFR conformational expression in tumors, has an acceptable radiation dosimetry, and provides important additional information about antigen expression compared with standard approaches using archival tissue. Its role to assist in patient selection for EGFR-based therapeutics and investigate treatment resistance should be further investigated.

Synergistic therapeutic benefit by combining the antibody drug conjugate, depatux-m with temozolomide in pre-clinical models of glioblastoma with overexpression of EGFR

PURPOSE

Depatux-m is an antibody drug conjugate (ADC) that targets and inhibits growth of cancer cells overexpressing the epidermal growth factor receptor (EGFR) or the 2-7 deletion mutant (EGFRvIII) in tumor models in vitro and in vivo. Treatment of patients suffering from relapsed/refractory glioblastoma (GBM) with a combination of depatux-m and temozolomide (TMZ) tended to increase overall survival. As a first step to understand the nature of the interaction between the two drugs, we investigated whether the interaction was synergistic, additive or antagonistic.

METHODS

The efficacy of ADCs, antibodies, TMZ and radiation was tested in xenograft models of GBM, U-87MG and U-87MG EGFRvIII. Both models express EGFR. U-87MG EGFRvIII was transduced to express EGFRvIII. Changes in tumor volume, biomarkers of cell death and apoptosis after treatment were used to measure efficacy of the various treatments. Synergism of depatux-m and TMZ was verified in three-dimensional cultures of U-87MG and U-87MG EGFRvIII by the method of Chou and Talalay.

RESULTS

Combined with TMZ and radiotherapy (RT), depatux-m inhibited xenograft growth of U-87MG and U-87MG EGFRvIII more than either treatment with depatux-m or TMZ + RT. Durability of the response to depatux-m + TMZ + RT or depatux-m + TMZ was more pronounced in U-87MG EGFRvIII than in U-87MG. Efficacy of depatux-m + TMZ was synergistic in U-87MG EGFRvIII and additive in U-87MG.

CONCLUSION

Adding depatux-m enhances the efficacy of standard of care therapy in preclinical models of GBM. Durability of response to depatux-m + TMZ in vivo and synergy of the drug-drug interaction correlates with the amount of antigen expressed by the tumor cells.

Personalized Antibodies for Gastroesophageal Adenocarcinoma (PANGEA): A Phase II Study Evaluating an Individualized Treatment Strategy for Metastatic Disease

The one-year and median overall survival (mOS) rates of advanced gastroesophageal adenocarcinomas (GEA) are ∼50% and <12 months, respectively. Baseline spatial and temporal molecular heterogeneity of targetable alterations may be a cause of failure of targeted/immunooncologic therapies. This heterogeneity, coupled with infrequent incidence of some biomarkers, has resulted in stalled therapeutic progress. We hypothesized that a personalized treatment strategy, applied at first diagnosis then serially over up to three treatment lines using monoclonal antibodies combined with optimally sequenced chemotherapy, could contend with these hurdles. This was tested using a novel clinical expansion-platform type II design with a survival primary endpoint. Of 68 patients by intention-to-treat, the one-year survival rate was 66% and mOS was 15.7 months, meeting the primary efficacy endpoint (one-sided P = 0.0024). First-line response rate (74%), disease control rate (99%), and median progression-free survival (8.2 months) were superior to historical controls. The PANGEA strategy led to improved outcomes warranting a larger randomized study. SIGNIFICANCE: This study highlights excellent outcomes achieved by individually optimizing chemotherapy, biomarker profiling, and matching of targeted therapies at baseline and over time for GEA. Testing a predefined treatment strategy resulted in improved outcomes versus historical controls. Therapeutic resistance observed in correlative analyses suggests that dual targeted inhibition may be beneficial.This article is highlighted in the In This Issue feature, p. 211.

Targeting and Efficacy of Novel mAb806-Antibody-Drug Conjugates in Malignant Mesothelioma

Epidermal growth factor receptor (EGFR) is highly overexpressed in malignant mesothelioma (MM). MAb806 is a novel anti-EGFR antibody that selectively targets a tumor-selective epitope. MAb806-derived antibody drug conjugates (ADCs), ABT-414, ABBV-221 and ABBV-322, may represent a novel therapeutic strategy in MM. EGFR and mAb806 epitope expressions in mesothelioma cell lines were evaluated using an array of binding assays, and the in vitro cell effects of ABT-414 and ABBV-322 were determined. In vivo therapy studies were conducted in mesothelioma xenograft and patient-derived xenograft (PDX) tumor models. We also performed biodistribution and imaging studies to allow the quantitative targeting of MM by mAb806 using a 89Zr-labeled immunoconjugate-ch806. A high EGFR expression was present in all mesothelioma cell lines evaluated and mAb806 binding present in all cell lines, except NCIH-2452. ABT-414 and ABBV-322 resulted in significant tumor growth inhibition in MM models with high EGFR and mAb806 epitope expressions. In contrast, in an EGFR-expressing PDX model that was negative for the mAb806 epitope, no growth inhibition was observed. We demonstrated the specific targeting of the mAb806 epitope expressing MM tumors using 89Zr-based PET imaging. Our data suggest that targeting EGFR in MM using specific ADCs is a valid therapeutic strategy and supports further investigation of the mAb806 epitope expression as a predictive biomarker.

The Latest Battles Between EGFR Monoclonal Antibodies and Resistant Tumor Cells

Epidermal growth factor receptor (EGFR) is a tyrosine kinase receptor involved in homeostatic regulation of normal cells and carcinogenesis of epithelial malignancies. With rapid development of the precision medicine era, a series of new therapies targeting EGFR are underway. Four EGFR monoclonal antibody drugs (cetuximab, panitumumab, nimotuzumab, and necitumumab) are already on the market, and a dozen other EGFR monoclonal antibodies are in clinical trials. Here, we comprehensively review the newly identified biological properties and anti-tumor mechanisms of EGFR monoclonal antibodies. We summarize recently completed and ongoing clinical trials of the classic and new EGFR monoclonal antibodies. More importantly, according to our new standard, we re-classify the complex evolving tumor cell resistance mechanisms, including those involving exosomes, non-coding RNA and the tumor microenvironment, against EGFR monoclonal antibodies. Finally, we analyzed the limitations of EGFR monoclonal antibody therapy, and discussed the current strategies overcoming EGFR related drug resistance. This review will help us better understand the latest battles between EGFR monoclonal antibodies and resistant tumor cells, and the future directions to develop anti-tumor EGFR monoclonal antibodies with durable effects.

Alkaloids of fascaplysin are promising chemotherapeutic agents for the treatment of glioblastoma: Review

Glioblastoma is one of the most aggressive human brain tumors. Even following all the modern protocols of complex treatment, the median patient survival typically does not exceed 15 months. This review analyzes the main reasons for glioblastoma resistance to therapy, as well as attempts at categorizing the main approaches to increasing chemotherapy efficiency. Special emphasis is placed on the specific group of compounds, known as marine alkaloids and their synthetic derivatives exerting a general antitumor effect on glioblastoma cells. The unique mechanisms of marine alkaloid influence on the tumor cells prompt considering them as a promising basis for creating new chemotherapeutic agents for glioblastoma treatment.

Safety and efficacy of depatuxizumab mafodotin + temozolomide in patients with EGFR-amplified, recurrent glioblastoma: results from an international phase I multicenter trial

Background

Patients with glioblastoma (GBM) have a dismal prognosis. Nearly all will relapse with no clear standard of care for recurrent disease (rGBM). Approximately 50% of patients have tumors harboring epidermal growth factor receptor (EGFR) amplification. The antibody-drug conjugate depatuxizumab mafodotin (depatux-m) binds cells with EGFR amplification, is internalized, and releases a microtubule toxin, killing the cell. Here we report efficacy, safety and pharmacokinetics (PK) of depatux-m + temozolomide (TMZ) in patients with EGFR-amplified rGBM.

Methods

M12-356 (NCT01800695) was an open-label study encompassing patients with newly diagnosed or rGBM across 3 treatment arms. Results are reported for adults with EGFR-amplified, measurable rGBM who received depatux-m (0.5-1.5 mg/kg) on days 1 and 15, and TMZ (150-200 mg/m2) on days 1-5 in a 28-day cycle. Patients were bevacizumab and nitrosourea naïve.

Results

There were 60 patients, median age 56 years (range, 20-79). Fifty-nine patients previously received TMZ. Common adverse events (AEs) were blurred vision (63%), fatigue (38%), and photophobia (35%). Grades 3/4 AEs were split between ocular and non-ocular AEs, occurring in 22% of patients each. Systemic PK exposure of depatux-m was dose proportional. The objective response rate was 14.3%, the 6-month progression-free survival rate was 25.2%, and the 6-month overall survival rate was 69.1%.

Conclusions

Depatux-m + TMZ displayed an AE profile similar to what was described previously. Antitumor activity in this TMZ-refractory population was encouraging. Continued study of depatux-m in patients with EGFR-amplified, newly diagnosed, or recurrent GBM is ongoing in 2 global, randomized trials (NCT02573324, NCT02343406).

RN765C, a low affinity EGFR antibody drug conjugate with potent anti-tumor activity in preclinical solid tumor models

Epidermal growth factor receptor (EGFR) is a clinically validated target and often overexpressed in some solid tumors. Both EGFR tyrosine kinase inhibitors and ligand-blocking antibodies have been approved for treatment of NSCLC, head and neck cancers and colorectal cancers. However, clinical response is limited and often accompanied by significant toxicities due to normal tissue expression. To improve the effectiveness of targeting EGFR while minimizing the toxicities on normal tissues, we developed a low-affinity anti-EGFR antibody drug conjugate (ADC), RN765C. Potent in vitro cytotoxicity of RN765C, with nanomolar to subnanomolar EC50, was observed on a panel of cancer cell lines expressing moderate to high level of EGFR. In contrast, RN765C was less effective in killing normal human keratinocytes, presumably due to its lower receptor expression. Mechanistically, RN765C has multiple modes of action: inducing payload mediated mitotic arrest and cell death, blocking EGFR pathway signal and mediating antibody dependent cell cytotoxicity. In preclinical studies, a single dose of RN765C at 1.5-3 mg/kg was generally sufficient to induce tumor regression in multiple cell line and patient-derived xenograft models, including those that are resistant to EGFR-directed tyrosine kinase inhibitors. Our data support further investigation of RN765C in the clinic to treat EGFR expressing solid tumors.

Targeted Therapies for Targeted Populations: Anti-EGFR Treatment for EGFR-Amplified Gastroesophageal Adenocarcinoma

Previous anti-EGFR trials in unselected patients with gastroesophageal adenocarcinoma (GEA) were resoundingly negative. We identified EGFR amplification in 5% (19/363) of patients at the University of Chicago, including 6% (8/140) who were prospectively screened with intention-to-treat using anti-EGFR therapy. Seven patients received ≥1 dose of treatment: three first-line FOLFOX plus ABT-806, one second-line FOLFIRI plus cetuximab, and three third/fourth-line cetuximab alone. Treatment achieved objective response in 58% (4/7) and disease control in 100% (7/7) with a median progression-free survival of 10 months. Pretreatment and posttreatment tumor next-generation sequencing (NGS), serial plasma circulating tumor DNA (ctDNA) NGS, and tumor IHC/FISH for EGFR revealed preexisting and/or acquired genomic events, including EGFR-negative clones, PTEN deletion, KRAS amplification/mutation, NRAS, MYC, and HER2 amplification, and GNAS mutations serving as mechanisms of resistance. Two evaluable patients demonstrated interval increase of CD3+ infiltrate, including one who demonstrated increased NKp46+, and PD-L1 IHC expression from baseline, suggesting an immune therapeutic mechanism of action. EGFR amplification predicted benefit from anti-EGFR therapy, albeit until various resistance mechanisms emerged.Significance: This paper highlights the role of EGFR inhibitors in EGFR-amplified GEA-despite negative results in prior unselected phase III trials. Using serial ctDNA and tissue NGS, we identified mechanisms of primary and acquired resistance in all patients, as well as potential contribution of antibody-dependent cell-mediated cytotoxicity to their clinical benefit. Cancer Discov; 8(6); 696-713. ©2018 AACR.See related commentary by Strickler, p. 679This article is highlighted in the In This Issue feature, p. 663.

Efficacy and safety results of depatuxizumab mafodotin (ABT-414) in patients with advanced solid tumors likely to overexpress epidermal growth factor receptor

BACKGROUND

Epidermal growth factor receptor (EGFR) alterations are associated with multiple cancers. Current EGFR-directed therapies have led to increased efficacy but are associated with specific side effects. The antibody-drug conjugate depatuxizumab mafodotin (depatux-m) targets EGFR with a monoclonal antibody linked to a cytotoxin, and is highly tumor-specific.

METHODS

This phase 1/2 study evaluated the safety, pharmacokinetics, and efficacy of depatux-m in patients who had advanced solid tumors with known wild-type EGFR overexpression, amplification, or mutated EGFR variant III. A 3 + 3 dose escalation was used, and 2 dosing schedules were evaluated. Depatux-m also was manufactured under an alternate process to reduce the drug load and improve the safety profile, and it was tested at the maximum tolerated dose (MTD). In another cohort, prolonged infusion time of depatux-m was evaluated; and a cohort with confirmed EGFR amplification also was evaluated at the MTD.

RESULTS

Fifty-six patients were treated. The MTD and the recommended phase 2 dose for depatux-m was 3.0 mg/kg. Common adverse events (AEs) were blurred vision (48%) and fatigue (41%). A majority of patients (66%) experienced 1 or more ocular AEs. Grade 3 or 4 AEs were observed in 43% of patients. One patient with EGFR-amplified, triple-negative breast cancer had a partial response. Stable disease was observed in 23% of patients. Pharmacokinetics revealed that depatux-m exposures were approximately dose-proportional.

CONCLUSIONS

Depatux-m resulted in infrequent nonocular AEs but increased ocular AEs. Patient follow-up confirmed that ocular AEs were reversible. Lowering the drug-antibody ratio did not decrease the number of ocular AEs. A partial response in 1 patient with EGFR-amplified disease provides the opportunity to study depatux-m in diseases with a high incidence of EGFR amplification. Cancer 2018;124:2174-83. © 2018 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Epidermal growth factor receptor and EGFRvIII in glioblastoma: signaling pathways and targeted therapies

Amplification of epidermal growth factor receptor (EGFR) and its active mutant EGFRvIII occurs frequently in glioblastoma (GBM). While EGFR and EGFRvIII play critical roles in pathogenesis, targeted therapy with EGFR-tyrosine kinase inhibitors (TKIs) or antibodies has only shown limited efficacy in patients. Here we discuss signaling pathways mediated by EGFR/EGFRvIII, current therapeutics, and novel strategies to target EGFR/EGFRvIII-amplified GBM.

Toward the use of precision medicine for the treatment of head and neck squamous cell carcinoma

Precision medicine is a new strategy that aims at preventing and treating human diseases by focusing on individual variations in people's genes, environment and lifestyle. Precision medicine has been used for cancer diagnosis and treatment and shows evident clinical efficacy. Rapid developments in molecular biology, genetics and sequencing technologies, as well as computational technology, has enabled the establishment of "big data", such as the Human Genome Project, which provides a basis for precision medicine. Head and neck squamous cell carcinoma (HNSCC) is an aggressive cancer with a high incidence rate and low survival rate. Current therapies are often aggressive and carry considerable side effects. Much research now indicates that precision medicine can be used for HNSCC and may achieve improved results. From this perspective, we present an overview of the current status, potential strategies, and challenges of precision medicine in HNSCC. We focus on targeted therapy based on cell the surface signaling receptors epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF) and human epidermal growth factor receptor-2 (HER2), and on the PI3K/AKT/mTOR, JAK/STAT3 and RAS/RAF/MEK/ERK cellular signaling pathways. Gene therapy for the treatment of HNSCC is also discussed.

Highly Specific and Effective Targeting of EGFRvIII-Positive Tumors with TandAb Antibodies

To harness the cytotoxic capacity of immune cells for the treatment of solid tumors, we developed tetravalent, bispecific tandem diabody (TandAb) antibodies that recognize EGFRvIII, the deletion variant III of the epidermal growth factor receptor (EGFR), and CD3 on T-cells, thereby directing immune cells to eliminate EGFRvIII-positive tumor cells. Using phage display, we identified scFv antibodies selectively binding to EGFRvIII. These highly EGFRvIII-specific, fully human scFv were substantially improved by affinity maturation, achieving K_Ds in the picomolar range, and were used to construct a set of bispecific EGFRvIII-targeting TandAbs with a broad range of binding and cytotoxic properties. These antibodies exhibited an exquisite specificity for a distinguished epitope in the N-terminal portion of EGFRvIII, as shown on recombinant antigen in Western Blot, SPR, and ELISA, as well as on antigen-expressing cells in FACS assays, and did not bind to the wild-type EGFR. High-affinity EGFRvIII/CD3 TandAbs were most potent in killing assays, displaying cytotoxicity toward EGFRvIII-expressing CHO, F98 glioma, or human DK-MG cells with EC₅₀ values in the range of 1-10 pM in vitro. They also demonstrated dose-dependent growth control in vivo in an EGFRvIII-positive subcutaneous xenograft tumor model. Together with the tumor-exclusive expression of EGFRvIII, the EGFRvIII/CD3 TandAbs' high specificity and strictly target-dependent activation with no off-target activity provide an opportunity to target tumor cells and spare normal tissues, thereby reducing the side effects associated with other anti-EGFR therapies. In summary, EGFRvIII/CD3 TandAbs are highly attractive therapeutic antibody candidates for selective immunotherapy of EGFRvIII-positive tumors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Epidermal Growth Factor Receptor Cell Proliferation Signaling Pathways

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

Antibody-Drug Conjugates (ADCs) for Personalized Treatment of Solid Tumors: A Review

Attaching a cytotoxic "payload" to an antibody to form an antibody-drug conjugate (ADC) provides a mechanism for selective delivery of the cytotoxic agent to cancer cells via the specific binding of the antibody to cancer-selective cell surface molecules. The first ADC to receive marketing authorization was gemtuzumab ozogamicin, which comprises an anti-CD33 antibody conjugated to a highly potent DNA-targeting antibiotic, calicheamicin, approved in 2000 for treating acute myeloid leukemia. It was withdrawn from the US market in 2010 following an unsuccessful confirmatory trial. The development of two classes of highly potent microtubule-disrupting agents, maytansinoids and auristatins, as payloads for ADCs resulted in approval of brentuximab vedotin in 2011 for treating Hodgkin lymphoma and anaplastic large cell lymphoma, and approval of ado-trastuzumab emtansine in 2013 for treating HER2-positive breast cancer. Their success stimulated much research into the ADC approach, with >60 ADCs currently in clinical evaluation, mostly targeting solid tumors. Five ADCs have advanced into pivotal clinical trials for treating various solid tumors-platinum-resistant ovarian cancer, mesothelioma, triple-negative breast cancer, glioblastoma, and small cell lung cancer. The level of target expression is a key parameter in predicting the likelihood of patient benefit for all these ADCs, as well as for the approved compound, ado-trastuzumab emtansine. The development of a patient selection strategy linked to target expression on the tumor is thus critically important for identifying the population appropriate for receiving treatment.

Effects of antibody, drug and linker on the preclinical and clinical toxicities of antibody-drug conjugates

Antibody-drug conjugates (ADCs) represent a new class of cancer therapeutics. Their design involves a tumor-specific antibody, a linker and a cytotoxic payload. They were designed to allow specific targeting of highly potent cytotoxic agents to tumor cells whilst sparing normal cells. Frequent toxicities that may be driven by any of the components of an ADC have been reported. There are currently more than 50 ADCs in active clinical development, and a further ∼20 that have been discontinued. For this review, the reported toxicities of ADCs were analysed, and the mechanisms for their effects are explored in detail. Methods to reduce toxicities, including dosing strategies and drug design, are discussed. The toxicities reported for active and discontinued drugs are important to drive the rational design and improve the therapeutic index of ADCs of the future.

ABT-414, an Antibody-Drug Conjugate Targeting a Tumor-Selective EGFR Epitope

Targeting tumor-overexpressed EGFR with an antibody-drug conjugate (ADC) is an attractive therapeutic strategy; however, normal tissue expression represents a significant toxicity risk. The anti-EGFR antibody ABT-806 targets a unique tumor-specific epitope and exhibits minimal reactivity to EGFR in normal tissue, suggesting its suitability for the development of an ADC. We describe the binding properties and preclinical activity of ABT-414, an ABT-806 monomethyl auristatin F conjugate. In vitro, ABT-414 selectively kills tumor cells overexpressing wild-type or mutant forms of EGFR. ABT-414 inhibits the growth of xenograft tumors with high EGFR expression and causes complete regressions and cures in the most sensitive models. Tumor growth inhibition is also observed in tumor models with EGFR mutations, including activating mutations and those with the exon 2-7 deletion [EGFR variant III (EGFRvIII)], commonly found in glioblastoma multiforme. ABT-414 exhibits potent cytotoxicity against glioblastoma multiforme patient-derived xenograft models expressing either wild-type EGFR or EGFRvIII, with sustained regressions and cures observed at clinically relevant doses. ABT-414 also combines with standard-of-care treatment of radiation and temozolomide, providing significant therapeutic benefit in a glioblastoma multiforme xenograft model. On the basis of these results, ABT-414 has advanced to phase I/II clinical trials, and objective responses have been observed in patients with both amplified wild-type and EGFRvIII-expressing tumors. Mol Cancer Ther; 15(4); 661-9. ©2016 AACR.