Epidermal Growth Factor Receptor Family Research Articles

Targeting HER3 to overcome EGFR TKI resistance in NSCLC.

Receptor tyrosine kinases (RTKs) play a crucial role in cellular signaling and oncogenic progression. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) have become the standard treatment for advanced non-small cell lung cancer (NSCLC) patients with EGFR-sensitizing mutations, but resistance frequently emerges between 10 to 14 months. A significant factor in this resistance is the role of human EGFR 3 (HER3), an EGFR family member. Despite its significance, effective targeting of HER3 is still developing. This review aims to bridge this gap by deeply examining HER3's pivotal contribution to EGFR TKI resistance and spotlighting emerging HER3-centered therapeutic avenues, including monoclonal antibodies (mAbs), TKIs, and antibody-drug conjugates (ADCs). Preliminary results indicate combining HER3-specific treatments with EGFR TKIs enhances antitumor effects, leading to an increased objective response rate (ORR) and prolonged overall survival (OS) in resistant cases. Embracing HER3-targeting therapies represents a transformative approach against EGFR TKI resistance and emphasizes the importance of further research to optimize patient stratification and understand resistance mechanisms.

Investigating the activity of Quinazoline derivatives against T790 mutant EGFR receptors employing computer-aided drug design

The uncontrolled growth of cancer cells is caused by their innate tendency to multiply without limits. In addition to colonizing adjacent tissues, they are capable of forming aggregates in isolated anatomical sites, thereby significantly increasing their invasiveness. Over time, malignant tumors that progressively destroy essential tissues and organs are ultimately lethal. It is well known that growth factor-driven signaling influence malignancy. The transmembrane receptor tyrosine kinases of growth factors influence the survival, differentiation, and proliferation of cells. To expedite cell division, neurotransmitters and proteins resembling epidermal growth factor (EGF) stimulate EGF receptor (EGFR) family members including HER2-4 and EGFR. The development and growth of numerous varieties of human cancer cells, as well as the morphogenesis of numerous animal species (nematodes to humans), are influenced by this signaling module, which is remarkably conserved. The EGFR family, consisting of over thirty ligands and four receptors, forms a complex and advanced human signal transduction network. The T790M mutation in the EGFR kinase enhances treatment resistance by increasing the affinity for ATP. This work used a molecular design tool to evaluate quinazoline derivatives with the highest IC50 values against EGFR and analyze the molecular interactions in the binding site. The goal was to uncover novel compounds with promising potential.

A phase I dose-escalation study of pulsatile afatinib in patients with recurrent or progressive brain cancer.

Afatinib (BIBW2992; Gilotrif®) is a selective and irreversible inhibitor of the epidermal growth factor receptor (ErbB; EGFR) family. It inhibits EGFR, HER2, and HER4 phosphorylation, resulting in tumor growth inhibition and regression. This phase I dose-escalation trial of pulsatile afatinib examined the safety, drug penetration into the central nervous system, preliminary antitumor activity, and recommended phase II dose in patients with progressive or recurrent brain cancers. Afatinib was taken orally once every 4 days or once every 7 days depending on dose cohort, until disease progression or unacceptable toxicity. A total of 24 patients received the investigational agent and were evaluable for safety analyses, and 21 patients were evaluable for efficacy. Dosing was administered at 80mg every 4 days, 120mg every 4 days, 180mg every 4 days, or 280mg every 7 days. A recommended phase II dose of pulsatile afatinib was established at 280mg every 7 days as there were no dose-limiting toxicities in any of the dosing cohorts and all toxicities were deemed manageable. The most common drug-related toxicities were diarrhea, rash, nausea, vomiting, fatigue, stomatitis, pruritus, and limb edema. Out of the 21 patients evaluable for efficacy, 2 patients (9.5%) exhibited partial response based on Response Assessment in Neuro-Oncology criteria and disease stabilization was seen in 3 patients (14.3%). Afatinib taken orally was safe and well-tolerated up to 280mg every 7 days in brain cancer patients.

Expert Consensus on the Diagnosis and Treatment of NRG1/2 Gene Fusion Solid Tumors.

The fusion genes NRG1 and NRG2 , members of the epidermal growth factor (EGF) receptor family, have emerged as key drivers in cancer. Upon fusion, NRG1 retains its EGF-like active domain, binds to the ERBB ligand family, and triggers intracellular signaling cascades, promoting uncontrolled cell proliferation. The incidence of NRG1 gene fusion varies across cancer types, with lung cancer being the most prevalent at 0.19 to 0.27%. CD74 and SLC3A2 are the most frequently observed fusion partners. RNA-based next-generation sequencing is the primary method for detecting NRG1 and NRG2 gene fusions, whereas pERBB3 immunohistochemistry can serve as a rapid prescreening tool for identifying NRG1 -positive patients. Currently, there are no approved targeted drugs for NRG1 and NRG2 . Common treatment approaches involve pan-ERBB inhibitors, small molecule inhibitors targeting ERBB2 or ERBB3, and monoclonal antibodies. Given the current landscape of NRG1 and NRG2 in solid tumors, a consensus among diagnostic and treatment experts is proposed, and clinical trials hold promise for benefiting more patients with NRG1 and NRG2 gene fusion solid tumors.

Targeted Inhibitors of EGFR: Structure, Biology, Biomarkers, and Clinical Applications.

Members of the EGFR family of tyrosine kinase receptors are major regulators of cellular proliferation, differentiation, and survival. In humans, abnormal activation of EGFR is associated with the development and progression of many cancer types, which makes it an attractive target for molecular-guided therapy. Two classes of EGFR-targeted cancer therapeutics include monoclonal antibodies (mAbs), which bind to the extracellular domain of EGFR, and tyrosine kinase inhibitors (TKIs), which mostly target the intracellular part of EGFR and inhibit its activity in molecular signaling. While EGFR-specific mAbs and three generations of TKIs have demonstrated clinical efficacy in various settings, molecular evolution of tumors leads to apparent and sometimes inevitable resistance to current therapeutics, which highlights the need for deeper research in this field. Here, we tried to provide a comprehensive and systematic overview of the rationale, molecular mechanisms, and clinical significance of the current EGFR-targeting drugs, highlighting potential candidate molecules in development. We summarized the underlying mechanisms of resistance and available personalized predictive approaches that may lead to improved efficacy of EGFR-targeted therapies. We also discuss recent developments and the use of specific therapeutic strategies, such as multi-targeting agents and combination therapies, for overcoming cancer resistance to EGFR-specific drugs.

Abstract C150: Targeted inhibition of homologous recombination and nonhomologous end joining in diffuse intrinsic pontine gliomas to prevent tumor recurrence

Abstract Therapeutic resistance remains a major obstacle to successful clinical management of Diffuse Intrinsic Pontine Glioma (DIPG), a high-grade pediatric tumor of the brain stem. In nearly all patients, available therapies fail to prevent progression. Innovative combinatorial therapies that penetrate the blood-brain barrier and lead to long-term control of tumor growth are desperately needed. We identified mechanisms of resistance to radiotherapy, the standard of care for DIPG. Based on these findings, we rationally designed a brain-penetrant small molecule, MTX-241F, that is a highly selective inhibitor of EGFR and PI3 kinase family members, including the DNA repair protein DNA-PK. Preliminary studies demonstrate that micromolar levels of this inhibitor can be achieved in murine brain tissue and that MTX-241F exhibits promising single-agent efficacy and radiosensitizing activity in patient-derived DIPG neurospheres. Its physiochemical properties include high exposure in the brain, indicating excellent brain penetrance. Since radiotherapy results in double-strand breaks that are repaired by homologous recombination (HR) and non-homologous DNA end joining (NHEJ), we have tested the combination of MTX-241F with an inhibitor of ATM to achieve blockade of HR and NHEJ, respectively, with or without radiotherapy. When HR blockers were combined with MTX-241F and radiotherapy, synthetic lethality was observed, providing impetus to explore this combination in clinically relevant models of DIPG. Our data provide proof-of-concept evidence to support advanced development of MTX-241F for the treatment of DIPG. Future studies will be designed to inform rapid clinical translation to ultimately impact patients diagnosed with this devastating disease. Citation Format: Ivana Barravecchia, Monika Sharma, Robert Teis, Jeanette Cruz, Rachel Mumby, Elizabeth Ziemke, Carlos Espinoza, Brian Magnuson, Mats Ljungman, Carl Koschmann, Christopher Whitehead, Judith Sebolt-Leopold, Stefanie Galban. Targeted inhibition of homologous recombination and nonhomologous end joining in diffuse intrinsic pontine gliomas to prevent tumor recurrence [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C150.

Progress in the Design of Molecular Targeted Drugs for Gastric Cancer

Gastric cancer is one of the most common cancers in China, and its pathogenesis is related to many molecular signaling pathways and related factors. The more critical molecular pathways include MET pathway, PI3K / AKT pathway, and MAPK pathway. In addition, the EGFR family and factors related to tumor angiogenesis are also important factors, which are closely related to tumor cell proliferation, apoptosis, and metastasis. The results of the study will provide new ideas and methods for the treatment of gastric cancer and lay the groundwork for the development of new gastric cancer drugs. On this basis, a variety of molecular targeted drugs have entered the clinical trial stage, among which, trastuzumab and apatinib have shown good efficacy. This paper summarizes the molecular pathogenesis of gastric cancer, and summarizes the mechanism of action, combination chemotherapy and research progress of trastuzumab and apatinib, so as to provide reference for future research on targeted therapy for gastric cancer.

DDDR-05. TARGETED INHIBITION OF DNA REPAIR AND SURVIVAL SIGNALING IN DIFFUSE INTRINSIC PONTINE GLIOMAS

Abstract Therapeutic resistance remains a major obstacle to successful clinical management of Diffuse Intrinsic Pontine Glioma (DIPG), a high-grade pediatric tumor of the brain stem. In nearly all patients, available therapies fail to prevent progression. Innovative combinatorial therapies that penetrate the blood-brain barrier and lead to long-term control of tumor growth are desperately needed. We identified mechanisms of resistance to radiotherapy, the standard of care for DIPG. Based on these findings, we rationally designed a brain-penetrant small molecule, MTX-241F, that is a highly selective inhibitor of EGFR and PI3 kinase family members, including the DNA repair protein DNA-PK. Preliminary studies demonstrate that micromolar levels of this inhibitor can be achieved in murine brain tissue and that MTX-241F exhibits promising single-agent efficacy and radiosensitizing activity in patient-derived DIPG neurospheres. Its physiochemical properties include high exposure in the brain, indicating excellent brain penetrance. Since radiotherapy results in double-strand breaks that are repaired by homologous recombination (HR) and non-homologous DNA end joining (NHEJ), we have tested the combination of MTX-241F with an inhibitor of ATM to achieve blockade of HR and NHEJ, respectively, with or without radiotherapy. When HR blockers were combined with MTX-241F and radiotherapy, synthetic lethality was observed, providing impetus to explore this combination in clinically relevant models of DIPG. Our data provide proof-of-concept evidence to support advanced development of MTX-241F for the treatment of DIPG. Future studies will be designed to inform rapid clinical translation to ultimately impact patients diagnosed with this devastating disease.

Functional analysis of a putative HER2-associated expressed enhancer, Her2-Enhancer1, in breast cancer cells

HER-2/neu (HER2) is a member of the epidermal growth factor receptors family, encoding a protein with tyrosine kinase activity. Following the gene amplification or increased HER2 transcription, carcinogenesis has been observed in some cancers. Genetic and epigenetic changes occurring in enhancer sequences can deeply affect the expression and transcriptional regulation of downstream genes, which can cause some physiological and pathological changes, including tumor progression. A therapeutic approach that directly targets the genomic sequence alterations is of high importance, with low side effects on healthy cells. Here, we employed the CRISPR/Cas9 method to genetically knockout an expressed putative enhancer (GH17J039694; we coined it as Her2-Enhancer1) located within the HER2 gene, 17q12: 39,694,339–39,697,219 (UCSC-hg38). We then investigated the potential regulatory effect of Her2-Enhancer1 on HER2 and HER2-interacting genes. To evaluate the cis and trans effects of Her2-Enhancer1, genetic manipulation of this region was performed in HER2-positive and -negative breast cancer cells. Our bioinformatics and real-time PCR data revealed that this putative enhancer region is indeed expressed, and acts as an expressed enhancer. Further functional analysis on edited and unedited cells revealed a significant alteration in the expression of HER2 variants, as well as some other target genes of HER2. Moreover, the apoptosis rate was considerably elevated within the edited cells. As we expected, Western blot analysis confirmed a reduction in protein levels of HER2, GRB7, the gene interacting with HER2, and P-AKT in the PI3K/AKT pathway. Altogether, our findings revealed an enhancer regulatory role for Her2-Enhancer1 on HER2 and HER2-interacting genes; and that this region has a potential for targeted therapy of HER2-positive cancers.

A variant in the 5′UTR of ERBB4 is associated with lifespan in Golden Retrievers

Genome-wide association studies (GWAS) in long-lived human populations have led to identification of variants associated with Alzheimer’s disease and cardiovascular disease, the latter being the most common cause of mortality in people worldwide. In contrast, naturally occurring cancer represents the leading cause of death in pet dogs, and specific breeds like the Golden Retriever (GR) carry up to a 65% cancer-related death rate. We hypothesized that GWAS of long-lived GRs might lead to the identification of genetic variants capable of modifying longevity within this cancer-predisposed breed. A GWAS was performed comparing GR dogs ≥ 14 years to dogs dying prior to age 12 which revealed a significant association to ERBB4, the only member of the epidermal growth factor receptor family capable of serving as both a tumor suppressor gene and an oncogene. No coding variants were identified, however, distinct haplotypes in the 5′UTR were associated with reduced lifespan in two separate populations of GR dogs. When all GR dogs were analyzed together (n = 304), the presence of haplotype 3 was associated with shorter survival (11.8 years vs. 12.8 years, p = 0.024). GRs homozygous for haplotype 3 had the shortest survival, and GRs homozygous for haplotype 1 had the longest survival (11.6 years vs. 13.5 years, p = 0.0008). Sub-analyses revealed that the difference in lifespan for GRs carrying at least 1 copy of haplotype 3 was specific to female dogs (p = 0.009), whereas survival remained significantly different in both male and female GRs homozygous for haplotype 1 or haplotype 3 (p = 0.026 and p = 0.009, respectively). Taken together, these findings implicate a potential role for ERBB4 in GR longevity and provide evidence that within-breed canine lifespan studies could serve as a mechanism to identify favorable or disease-modifying variants important to the axis of aging and cancer.

The Signaling of Neuregulin-Epidermal Growth Factor Receptors and Its Impact on the Nervous System

The activation of members of the Epidermal Growth Factor Receptor (EGFR) family (including ErbB) triggers pathways that have significant effects on cellular processes and have profound consequences both in physiological and pathological conditions. Within the nervous system, the neuregulin (NRG)/ErbB3 signaling plays a crucial role in promoting the formation and maturation of excitatory synapses. Noteworthy is ErbB3, which is actively involved in the process of cerebellar lamination and myelination. All members of the ErbB-family, in particular ErbB3, have been observed within the nuclei of various cell types, including both full-length receptors and alternative variants. One of these variants was detected in Schwann cells and in glioblastoma primary cells where it showed a neuregulin-dependent expression. It binds to promoters’ chromatin associated with genes, like ezrin, involved in the formation of Ranvier’s node. Its nucleolar localization suggests that it may play a role in ribosome biogenesis and in cell proliferation. The regulation of ErbB3 expression is a complex and dynamic process that can be influenced by different factors, including miRNAs. This mechanism appears to play a significant role in glioblastoma and is often associated with a poor prognosis. Altogether, the targeting of ErbB3 has emerged as an active area of research in glioblastoma treatment. These findings highlight the underappreciated role of ErbB3 as a significant receptor that can potentially play a pivotal role in diverse pathologies, implying the existence of a shared and intricate mechanism that warrants further investigation.

The Clinical and Molecular Profile of Lung Cancer Patients Harboring the TP53 R337H Germline Variant in a Brazilian Cancer Center: The Possible Mechanism of Carcinogenesis.

In southern and southeastern Brazil, the TP53 founder variant c.1010G>A (R337H) has been previously documented with a prevalence of 0.3% within the general population and linked to a heightened incidence of lung adenocarcinomas (LUADs). In the present investigation, we cover clinical and molecular characterizations of lung cancer patients from the Brazilian Li-Fraumeni Syndrome Study (BLISS) database. Among the 175 diagnosed malignant neoplasms, 28 (16%) were classified as LUADs, predominantly occurring in females (68%), aged above 50 years, and never-smokers (78.6%). Significantly, LUADs manifested as the initial clinical presentation of Li-Fraumeni Syndrome in 78.6% of cases. Molecular profiling was available for 20 patients, with 14 (70%) revealing EGFR family alterations. In total, 23 alterations in cancer driver genes were identified, comprising 7 actionable mutations and 4 linked to resistance against systemic treatments. In conclusion, the carriers of TP53 R337H demonstrate a predisposition to LUAD development. Furthermore, our results indicate that environmental pollution potentially impacts the carcinogenesis of lung tumors in the carriers of TP53 R337H.

Targeting DNA Repair and Survival Signaling in Diffuse Intrinsic Pontine Gliomas to Prevent Tumor Recurrence.

Therapeutic resistance remains a major obstacle to successful clinical management of diffuse intrinsic pontine glioma (DIPG), a high-grade pediatric tumor of the brain stem. In nearly all patients, available therapies fail to prevent progression. Innovative combinatorial therapies that penetrate the blood-brain barrier and lead to long-term control of tumor growth are desperately needed. We identified mechanisms of resistance to radiotherapy, the standard of care for DIPG. On the basis of these findings, we rationally designed a brain-penetrant small molecule, MTX-241F, that is a highly selective inhibitor of EGFR and PI3 kinase family members, including the DNA repair protein DNA-PK. Preliminary studies demonstrated that micromolar levels of this inhibitor can be achieved in murine brain tissue and that MTX-241F exhibits promising single-agent efficacy and radiosensitizing activity in patient-derived DIPG neurospheres. Its physiochemical properties include high exposure in the brain, indicating excellent brain penetrance. Because radiotherapy results in double-strand breaks that are repaired by homologous recombination (HR) and non-homologous DNA end joining (NHEJ), we have tested the combination of MTX-241F with an inhibitor of Ataxia Telangiectasia Mutated to achieve blockade of HR and NHEJ, respectively, with or without radiotherapy. When HR blockers were combined with MTX-241F and radiotherapy, synthetic lethality was observed, providing impetus to explore this combination in clinically relevant models of DIPG. Our data provide proof-of-concept evidence to support advanced development of MTX-241F for the treatment of DIPG. Future studies will be designed to inform rapid clinical translation to ultimately impact patients diagnosed with this devastating disease.

Androgen receptor transcriptional activity is required for heregulin-1β–mediated nuclear localization of the HER3/ErbB3 receptor tyrosine kinase

Prostate cancer is initially regulated by the androgen receptor (AR), a ligand-activated, transcription factor, and is in a hormone-dependent state (hormone-sensitive prostate cancer (HSPC)), but eventually becomes androgen-refractory (castration-resistant prostate cancer (CRPC)) because of mechanisms that bypass the AR, including by activation of ErbB3, a member of the epidermal growth factor receptor family. ErbB3 is synthesized in the cytoplasm and transported to the plasma membrane for ligand binding and dimerization, where it regulates downstream signaling, but nuclear forms are reported. Here, we demonstrate in prostatectomy samples that ErbB3 nuclear localization is observed in malignant, but not benign prostate, and that cytoplasmic (but not nuclear) ErbB3 correlated positively with AR expression but negatively with AR transcriptional activity. In support of the latter, androgen depletion upregulated cytoplasmic, but not nuclear ErbB3, while invivo studies showed that castration suppressed ErbB3 nuclear localization in HSPC, but not CRPC tumors. Invitro treatment with the ErbB3 ligand heregulin-1β (HRG) induced ErbB3 nuclear localization, which was androgen-regulated in HSPC but not in CRPC. In turn, HRG upregulated AR transcriptional activity in CRPC but not in HSPC cells. Positive correlation between ErbB3 and AR expression was demonstrated in AR-null PC-3cells where stable transfection of AR restored HRG-induced ErbB3 nuclear transport, while AR knockdown in LNCaP reduced cytoplasmic ErbB3. Mutations of ErbB3's kinase domain did not affect its localization but was responsible for cell viability in CRPC cells. Taken together, we conclude that AR expression regulated ErbB3 expression, its transcriptional activity suppressed ErbB3 nuclear translocation, and HRG binding to ErbB3 promoted it.

Ruscogenin ameliorates dasatinib-induced intestinal barrier dysfunction via ErbB4/YAP and ROCK/MLC pathways.

Dasatinib is effective in the treatment of chronic and acute myeloid leukemia, which could cause the side effect of gastrointestinal bleeding by overdose or longtime use. Ruscogenin (RUS) from the traditional Chinese medicine Ophiopogon japonicas could protect endothelial microvascular barrier function. In this study, the therapeutic effect and underlying mechanisms of RUS were investigated on intestinal barrier dysfunction induced by dasatinib. Male C57BL/6J mice were given three doses of dasatinib (70, 140, 210mg/kg, ig) and RUS (3, 10, 30μg/kg, ip) to explore the effect of dasatinib on intestinal barrier and the intervention of RUS. It was proved that dasatinib could reduce intestinal blood flow, inhibit phosphorylation of EGFR family member v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 4 (ErbB4)/YES-associated protein (YAP) and activation of Rho-associated coiled coil-containing protein kinase (ROCK)/phosphorylation of (myosin light chain) MLC. RUS could significantly increase intestinal blood flow, improve intestinal injury, reduce Evans blue leakage and serum content of FITC-dextran 4kDa, and increase the expression of connexin (ZO-1, Occludin and VE-cadherin). Meanwhile, the in vitro effect of RUS (0.01, 0.1, 1μM) on the dysfunction of the endothelial barrier was observed in dasatinib (150nM)-pretreated HUVECs. The results showed that RUS suppressed dasatinib-induced the leakage of Evans blue, and degradation of F-actin and connexin. Furthermore, RUS could significantly increase the phosphorylation of ErbB4 at Tyr1284 site and YAP at Ser397 site, and inhibit ROCK expression and phosphorylation of MLC at Ser19 site in vivo and in vitro. In conclusion, the present research proved that RUS could suppress the side effects of dasatinib-induced intestinal barrier dysfunction by regulating ErbB4/YAP and ROCK/MLC pathways.

AMT-562, a Novel HER3-targeting Antibody-Drug Conjugate, Demonstrates a Potential to Broaden Therapeutic Opportunities for HER3-expressing Tumors.

HER3 is a unique member of the EGFR family of tyrosine kinases, which is broadly expressed in several cancers, including breast, lung, pancreatic, colorectal, gastric, prostate, and bladder cancers and is often associated with poor patient outcomes and therapeutic resistance. U3-1402/Patritumab-GGFG-DXd is the first successful HER3-targeting antibody-drug conjugate (ADC) with clinical efficacy in non-small cell lung cancer. However, over 60% of patients are nonresponsive to U3-1402 due to low target expression levels and responses tend to be in patients with higher target expression levels. U3-1402 is also ineffective in more challenging tumor types such as colorectal cancer. AMT-562 was generated by a novel anti-HER3 antibody Ab562 and a modified self-immolative PABC spacer (T800) to conjugate exatecan. Exatecan showed higher cytotoxic potency than its derivative DXd. Ab562 was selected because of its moderate affinity for minimizing potential toxicity and improving tumor penetration purposes. Both alone or in combination therapies, AMT-562 showed potent and durable antitumor response in low HER3 expression xenograft and heterogeneous patient-derived xenograft/organoid models, including digestive system and lung tumors representing of unmet needs. Combination therapies pairing AMT-562 with therapeutic antibodies, inhibitors of CHEK1, KRAS, and tyrosine kinase inhibitor showed higher synergistic efficacy than Patritumab-GGFG-DXd. Pharmacokinetic and safety profiles of AMT-562 were favorable and the highest dose lacking severe toxicity was 30 mg/kg in cynomolgus monkeys. AMT-562 has potential to be a superior HER3-targeting ADC with a higher therapeutic window that can overcome resistance to generate higher percentage and more durable responses in U3-1402-insensitive tumors.

Abstract B021: Examining the role of HER2 signaling in promoting prostate cancer proliferation in an androgen receptor-low environment

Abstract Background: Intense neoadjuvant androgen deprivation therapy (inADT) reduces prostate cancer recurrence in approximately 40% of patients with intermediate/high risk prostate cancer. Using samples from our recent phase 2 study (NCT02430480) from patients undergoing 6 months of inADT prior to radical prostatectomy, we sought to examine molecular features present at baseline that correlate with pathologic response following surgery. Methods: Tumors from 37 patients with locally advanced prostate cancer were subjected to immunohistochemistry (IHC) and laser capture microdissection to obtain 143 histologically distinct foci. RNA was isolated from each focus and used to generate RNA-seq libraries. Differentially-expressed genes were determined per-unit of residual tumor volume using linear mixed-effect models. Histologic features and staining intensities were obtained from IHC of posttreatment specimens. Ingenuity Pathway Analysis (IPA) identified upstream regulators at baseline that interacted with pathologic outcome. Cancer cell lines were treated with a panel of EGFR family inhibitors and androgen receptor (AR) axis inhibitors. Protein and RNA expression were measured to identify the impact of dual inhibition. Results: In pre-treatment targeted biopsies from men with locally advanced prostate cancer, we observed that tumor samples that exhibited worse response to inADT had lower AR activity at baseline, presumably due to a decreased dependency on AR, potentially related to increased dependency on alternative growth pathways. These incomplete/nonresponding tumors displayed a significant increase in expression of EFGR family signaling (EGFR, HER2, and HER3) using IPA, which have previously been shown to serve as bypass mechanisms to AR signaling to drive downstream PI3K activity. HER2 was the most abundantly expressed protein by IHC in posttreatment tumors. Given the multitude of receptor tyrosine kinases (RTKs) regulated by EGFR family signaling and RTK inhibitors targeting this activity, we examined the impact of combining RTK inhibitors with ADT to overcome resistance to ADT. Afatinib, lapatinib, and neratinib showed the greatest anti-tumor efficacy in vitro. Treatment with these agents rapidly and dynamically increased AR expression and activity. We observed synergistic effects on cell viability and proliferation by treating cell lines with combination therapy of antiandrogen therapy and these inhibitors. Conclusions: Our data suggest that elevated HER2 activity defines an AR-low subtype of prostate cancer that is resistant to inADT. Disrupting the HER2-mediated bypass of AR blockade re-sensitized resistant PC cells to AR-targeted therapy. These effects were observed in an untreated setting and represent a divergent path in tumorigenesis where prostate tumors develop with intrinsically lower AR activity. These findings will be validated using genetic abrogation of HER2 in additional clinical samples, organoids, and patient-derived xenograft models, and represent new opportunities for combination therapy in newly-diagnosed high-risk disease. Citation Format: Scott Wilkinson, Anson Ku, Isaiah King, Anna Baj, Daniel Low, Huihui Ye, Stephanie A. Harmon, Nicholas T. Terrigino, John R. Bright, Rayann Atway, Shana Y. Trostel, Rosina T. Lis, Baris Turkbey, William L. Dahut, Fatima Karzai, Adam G. Sowalsky. Examining the role of HER2 signaling in promoting prostate cancer proliferation in an androgen receptor-low environment [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B021.

Abstract A007: Modulation of HER2 as a mechanism for AR expression

Abstract Background: Intense neoadjuvant androgen deprivation therapy (inADT) is an emerging treatment paradigm for localized high-risk prostate cancer, but in certain patients a subset of tumors will recur after surgery. In tumors with endogenously low androgen receptor (AR) activity, expression of the EGFR family protein HER2 was enriched. We sought to investigate the role of HER2 in driving the proliferation of prostate cancer under androgen-depleted environments. We hypothesized that overexpression of HER2 would decrease AR activity, while its knockdown would conversely increase AR expression beyond baseline levels. Methods: The AR-expressing 22Rv1 and LNCaP prostate cancer cell lines were cultured and plated for transfection. HER2 overexpression was achieved using an exogenous HER2 (ERBB2) plasmid, while HER2 knockdown was performed using siRNA, alongside controls for both groups. Cell lysates were collected at 24-, 48-, and 72-hour time points. Western blotting was performed to examine HER2, AR, PSA, and actin expression. Results: Western blot analysis confirmed successful overexpression and knockdown of HER2, using an exogenous HER2 plasmid and siRNA, respectively. In 22Rv1 and LNCaP cells overexpressing HER2, AR (and AR-V7 in 22Rv1 cells) levels were decreased compared to the control cells. Conversely, 22Rv1 and LNCaP cells with knockdown of HER2 exhibited elevated AR expression. Biological replicates to confirm these findings are in progress. Additional studies will also examine the impact of HER2 signaling and activity on downstream pro-proliferative pathways. Conclusions: Manipulation of HER2 expression highlights a potential role of EGFR family proteins as a mechanism for prostate cancer growth in androgen-deprived environments. Future studies will validate this finding at the RNA level using qPCR and probe downstream targets of HER2 using western blotting. These preliminary findings have implications for the treatment of advanced tumors for which inADT is not a viable option. Targeting HER2 and its downstream signaling pathways represent an intriguing mechanism to overcome resistance to androgen deprivation therapy in newly-diagnosed, treatment-naïve patients. Citation Format: Daniel K.Y. Low, Scott Wilkinson, Isaiah M. King, Shana Y. Trostel, Adam G. Sowalsky. Modulation of HER2 as a mechanism for AR expression [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A007.

Exploration of HER2 (ERBB2) immunohistochemistry in non-small cell lung cancer: correlation with ERBB2 mutational status: experimental research.

ERBB2 (HER2) is a gene in humans that encodes the ERBB2 protein, a member of the epidermal growth factor receptor family. Non-small cell lung carcinomas do not commonly harbour ERBB2 mutations, with clinical trials conducted to assess for targeted response and progression-free survival. We retrieved cases of lung adenocarcinoma with next-generation sequencing proven ERBB2 point mutations (n=8) or amplifications (n=11) and assessed the concordance of commercially available ERBB2 (HER2) immunohistochemical antibodies with the next-generation sequencing result. At present, no commercially available ERBB2 clone can accurately detect ERBB2 mutations consistently in non-small cell lung carcinoma specimens, but amplifications can be detected with reasonable diagnostic accuracy.

Molecular and clinical correlates of HER3 expression highlights its potential role as a therapeutic target in melanoma

Overexpression of the epidermal growth factor receptor family member HER3 (erbB3) has been implicated in several types of cancer and recently drugs targeting HER3 have shown promising clinical activity. In melanoma, HER3 overexpression has been linked to both metastasis formation and resistance to drug therapy in cell culture models. Here, we sought to characterise the expression of HER3 in 187 melanoma biopsies (149 cutaneous, 38 mucosal) using immunohistochemistry, as well as to analyse the association between HER3 expression and molecular, clinical and pathological variables. A subset of the cutaneous melanoma specimens was taken prior to treatment with immune checkpoint blockade therapy (pre-ICB) (n=79). HER3 expression (≥1+) was observed in 136 of 187 samples (∼73%). HER3 expression was found to be markedly lower in the mucosal melanomas, with 17 of the 38 tumours (∼45%) demonstrating no HER3 expression. In cutaneous melanomas, there was a negative association between HER3 expression and mutational load, a positive association with NRAS mutational status, and a trend of negative association with PD-L1 expression. In the pre-ICB cohort, an association was found between high HER3 expression (≥2+) and overall survival after anti-PD-1-based immunotherapy. Overall, our results indicate that HER3 is a promising therapeutic avenue in cutaneous melanoma worthy of further clinical evaluation.