ERβ Expression Research Articles

Sex-Specific Regulation of Local Gonadal Hormone Signaling During Pathological Cardiac Remodeling in Spontaneously Hypertensive Rats

Hypertensive heart disease is characterized by cardiac fibrosis in the left ventricle (LV). Angiotensin II (Ang II) promotes cardiac fibrosis through direct actions on cardiac fibroblasts. Gonadal hormones are known to impact cardiac fibrosis either through direct actions on fibroblasts or through modulation of Ang II receptors. We have previously shown that Ang II infusion alters collagen gene expression in a sex-specific manner. The present study seeks to further understand our observed sex difference by investigating the impact of Ang II on gonadal hormone regulation in the left ventricle (LV) and cardiac fibroblasts (CFs) following a fibrogenic stimulus. For whole LV analysis, male and female SHR (15-week-old) were infused with Ang II (400ng/kg/min, s.c.) or vehicle for 2 weeks via an osmotic mini pump (n=8-11 per group per sex). For CF-specific analysis, primary CFs were isolated from adult male and female SHR LV and cultured on CytoSoft cell culture plates (8 kPa stiffness) coated with Type I Collagen. CFs were brought to P1 for expansion and treated with TGFb1 (10ug/uL) or vehicle (PBS + 0.1% BSA) for 48 hours (n=7-8 per group per sex). Col1a1, AT1aR, estrogen receptors α and β (ER-α, ER-β), androgen receptor (AR), 5α-reductase (5α-R), and aromatase gene expression in the left ventricle was assessed via RT-qPCR and data analyzed by Two-Way ANOVA. Ang II infusion significantly increased ER-α gene expression in male, but not female LV (sex x Ang II interaction p=0.0303). ER-β gene expression was also significantly increased in the male LV (p=0.0066), but not females. AR gene expression remained unchanged in the Ang II-infused male LV but was significantly reduced in female LV when compared to control (sex x Ang II interaction p=0.0084). Ang II significantly increased 5α-R gene expression in male (p=0.0024), but not female LV. Aromatase gene expression tended to increase in both male and female Ang II-infused animals when compared to control. Ang II-induced changes in LV gonadal hormone gene expression did not significantly correlate with Col1a1 gene expression. In vitro stimulation of CFs with TGFb1 results in a significant reduction in ER-α (p<0.0001) and AR (p<0.0001) in both males and females. ER-β tended to decrease in males stimulated with TGFb1, but not females, relative to control. Taken together, the opposing findings between LV and CF may indicate cell-specific regulation of gonadal hormone receptors. It may be that upregulation of local estrogen signaling in the remodeling LV in males serves to offset the pathological effects of Ang II stimulation. Future studies will evaluate the consequences of changes in gonadal hormone receptor levels at the cellular and tissue level. NHLBI R01HL153112. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Tipping the balance — the move of aging females towards higher ERβ:ERα ratio and away from estrogen mediated vascular protection

Objective: The menopausal transition, marked by the cessation of endogenous estrogen production, is a hallmark of vascular aging in women, as the vascular function radically declines in the years hereafter (Parker et al. 2010). Primarily based on animal and in-vitro studies (Novella et al. 2012; Novensà et al. 2011; Park et al. 2017) it has been hypothesized that this is linked to menopause-dependent changes in the balance between the two dominant estrogen receptors, ERα and ERβ; as previous studies suggest that ERα favors NO-bioavailability whereas ERβ mediates increases in oxidative stress. However, it remains unresolved how aging actually influences changes in the balance between ERα and ERβ in skeletal muscle of females and how changes are related to downstream protein targets such as eNOS and NADPH oxidases. Study design: We measured skeletal muscle protein expression of estrogen receptors, androgen receptors, eNOS, SOD2, GPX1, gp91phox/-NOX2 and NOX4 in 82 females ranging from 20-70 yrs. of age. For age comparisons, data from the muscle biopsies were grouped by 5-year intervals. Statistical analyses were conducted by on one-way ANOVA and Pearson’s product moment correlations Results: The ERβ:ERα ratio was significantly higher in the 65+ yrs. compared to all other groups (p<0.01) and correlation analysis revealed that the ERβ/ERα ratio increased with aging (p=0.02, R2=0.07). The 65+ yrs. group presented a lower eNOS expression (p<0.05) than the 20-54 yrs. groups and correlation analysis showed a decrease in eNOS expression with aging (p=0.0002 R2=0.16). Gp91phox/-NOX2 expression correlated with ERβ and the expression of gp91phox/NOX2 (p=<0.0001 R2=0.4) was lower in the three middle groups, 45-59 yrs., compared with both the younger and older groups (p<0.05). ERα correlated with the antioxidants SOD2 and GPX1 (p=0.0001 R2=0.18 and p=<0.0001 R2=0.21, respectively). Conclusions: This study is the first to show that skeletal muscle expression of ERβ:ERα increases with age and that the expression of eNOS in skeletal muscle declines as a function of age in females. Our data also provides indirect support for that aging is associated with a shift from a more prominent ERα coupled antioxidant effect, through - SOD2/GPX1 related mechanisms, towards a more pro-oxidant environment through an ERβ mediated upregulation of Gp91phox/-NOX2. This shift, combined with the observation of an age induced decline in eNOS expression, could be mechanisms underlying reduced NO bioavailability in aging females. Further analyses are ongoing to throw light in these mechanisms and additional studies are warranted to fully elucidate the mechanistic pathways involved. Funding The study was funded by The Danish Ministry of Culture Fund for Research in Sports, The Independent Research Fund Denmark, Eva and Henry Frænkel Memorial Fund, and the Toyota Foundation. The study is part of The Copenhagen Women Study for which fi- nancial support was provided by the University of Copenhagen Excellence Programme for Interdisciplinary Research. The study was also supported by The Danish Ministry of Culture: Sports Research. Financial support is greatly appreciated from the Aarhus University Research Foundation (AUFF); the Hartmann Foundation; the A.P. Møller Foundation; the Toyota-Fonden, Denmark; and the Augustinus Foundation and Team Denmark. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Concordance between ER, PR, Ki67, and HER2-low expression in breast cancer by MammaTyper RT-qPCR and immunohistochemistry: implications for the practising pathologist.

There are limited data on the role of multigene tests and their correlation with immunohistochemistry (IHC), especially on core biopsy. MammaTyper is a quantitative conformite Europeeanne (CE) marked, National Institute for Health and Care excellence (NICE) approved, in in vitro diagnostic quantitative real-time polymerase chain reaction (RT-qPCR) test for assessment of mRNA expression of four biomarkers (ESR1, PGR, ERBB2, MKI67). We evaluated the concordance of MammaTyper with oestrogen receptor (ER), progesterone receptor(PR), HER2, and Ki67 by IHC on 133 core needle biopsies of breast cancer. HER2 was positive if IHC 3+ or 2+ and fluorescence in situ hybridization (FISH)-amplified. Global and hotspot Ki67 expression was analysed using a cutoff of ≥20% assessed manually and by digital image analysis. Agreements were expressed as overall percent agreement (OPA), positive percent agreement (PPA), negative percent agreement (NPA), and Cohen's kappa. RT-qPCR results of ESR1 were highly concordant with IHC with OPA of 94.7% using 1% cutoff and 91.7% when the low ER-positive category was included. The PPA and NPA between RT-qPCR and IHC for PR was 91.5% and 88.0%, respectively, when using the 1% cutoff. For ERBB2/HER2, the OPA was 95% and the PPA was 84.6%. 40 of 72 HER2 IHC score 0 tumours were classified as ERBB2 low. Best concordance between MKI67 by MammaTyper and Ki67 IHC was achieved using hotspot digital image analysis (OPA: 87.2%, PPA: 90.6%, NPA: 80%). RT-qPCR-based assessment of the mRNA expression of ESR1, PGR, ERBB2, and MKI67 showed high concordance with IHC, suggesting that the MammaTyper test on core needle biopsies represents a reliable, efficient, and reproducible alternative for breast cancer classification and refining HER2 low categorisation.

25-hydroxycholesterol promotes proliferation and metastasis of lung adenocarcinoma cells by regulating ERβ/TNFRSF17 axis.

Lung adenocarcinoma is the main type of lung cancer in women. Our previous findings have evidenced that 25-hydroxycholesterol (25-HC) promotes migration and invasion of lung adenocarcinoma cells (LAC), during which LXR as a 25-HC receptor plays an important role. Estrogen receptor beta (ERβ) is a receptor of 27-hydroxycholesterol that is structurally analogous to 25-HC, but its role in the functional actions of 25-HC remained largely unknown. In this study, we demonstrated that 25-HC treatment triggered ERβ expression in LAC. Knockdown of ERβ inhibited 25-HC-mediated proliferation, migration and invasion, and reduced 25-HC-induced LAC metastasis in vivo. Further investigation revealed that ERβ knockdown restrained the expression of TNFRSF17 (BCMA). In vivo experiments also confirmed that ERβ knockdown blocked 25-HC-induced TNFRSF17 expression. TNFRSF17 knockdown also restrained 25-HC-induced proliferation, migration and invasion. Bioinformatic analysis showed that the levels of ERβ and TNFRSF17 were elevated in lung adenocarcinoma, and were closely related to tumor stages and nodal metastasis status. These results suggested that 25-HC promoted the proliferation and metastasis of LAC by regulating ERβ/TNFRSF17 axis.

The Role of Estrogen and Estrogen Receptors in Head and Neck Tumors.

Head and neck squamous cell carcinoma (HNSCC) is the most common histological form of head and neck tumors (HNTs), which originate from the epithelium of the lips and oral cavity, pharynx, larynx, salivary glands, nasal cavity, and sinuses. The main risk factors include consumption of tobacco in all forms and alcohol, as well as infections with high-risk human papillomaviruses or the Epstein-Barr virus. Regardless of the etiological agent, the risk of developing different types of HNTs is from two to more than six times higher in males than in females. The reason for such disparities probably lies in a combination of both biological and psychosocial factors. Therefore, it is hypothesized that exposure to female sex hormones, primarily estrogen, provides women with protection against the formation and metastasis of HNTs. In this review, we synthesized available knowledge on the role of estrogen and estrogen receptors (ERs) in the development and progression of HNTs, with special emphasis on membrane ERs, which are much less studied. We can summarize that in addition to epidemiologic studies unequivocally pointing to the protective effect of estrogen in women, an increased expression of both nuclear ERs, ERα, and ERβ, and membrane ERs, ERα36, GPER1, and NaV1.2, was present in different types of HNSCC, for which anti-estrogens could be used as an effective therapeutic approach.

Mendelian randomization analysis identifies druggable genes and drugs repurposing for chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is a prevalent condition that significantly impacts public health. Unfortunately, there are few effective treatment options available. Mendelian randomization (MR) has been utilized to repurpose existing drugs and identify new therapeutic targets. The objective of this study is to identify novel therapeutic targets for COPD. Cis-expression quantitative trait loci (cis-eQTL) were extracted for 4,317 identified druggable genes from genomics and proteomics data of whole blood (eQTLGen) and lung tissue (GTEx Consortium). Genome-wide association studies (GWAS) data for doctor-diagnosed COPD, spirometry-defined COPD (Forced Expiratory Volume in one second [FEV1]/Forced Vital Capacity [FVC] <0.7), and FEV1 were obtained from the cohort of FinnGen, UK Biobank and SpiroMeta consortium. We employed Summary-data-based Mendelian Randomization (SMR), HEIDI test, and colocalization analysis to assess the causal effects of druggable gene expression on COPD and lung function. The reliability of these druggable genes was confirmed by eQTL two-sample MR and protein quantitative trait loci (pQTL) SMR, respectively. The potential effects of druggable genes were assessed through the phenome-wide association study (PheWAS). Information on drug repurposing for COPD was collected from multiple databases. A total of 31 potential druggable genes associated with doctor-diagnosed COPD, spirometry-defined COPD, and FEV1 were identified through SMR, HEIDI test, and colocalization analysis. Among them, 22 genes (e.g., MMP15, PSMA4, ERBB3, and LMCD1) were further confirmed by eQTL two-sample MR and protein SMR analyses. Gene-level PheWAS revealed that ERBB3 expression might reduce inflammation, while GP9 and MRC2 were associated with other traits. The drugs Montelukast (targeting the MMP15 gene) and MARIZOMIB (targeting the PSMA4 gene) may reduce the risk of spirometry-defined COPD. Additionally, an existing small molecule inhibitor of the APH1A gene has the potential to increase FEV1. Our findings identified 22 potential drug targets for COPD and lung function. Prioritizing clinical trials that target these identified druggable genes with existing drugs or novel medications will be beneficial for the development of COPD treatments.

Estrogen receptors alpha and beta expression in different canine cancer types with an emphasis on hematopoietic malignancies.

Estrogen receptors (ERs) are located in both healthy and neoplastic tissues. The type of estrogen receptor expressed varies depending on its location, tumor type, and species. Estrogen action is mediated by binding to ER and activating the transcriptional and signaling processes that result in the control of gene expression. There are two main types of estrogen receptors: ER alpha (ERα) and ER beta (ERβ). Both receptors are functionally different, they may act antagonistically and are distributed in different tissues but their structure is similar - as they are composed of 5 different domains: A/B, C, D, E, and F. The signaling pathway and hence regulation of the gene expression by ERs is a complex and multifactorial process that involves both genomic and nongenomic actions. In the human reproductive tract, both ERα and β are present, with predominant expression of ERβ, while there are no satisfactory data distinguishing the type of ERs expressed in the canine reproductive tract. In mammary gland neoplasia, a decreased or lacking ERα expression in humans is associated with a poorer prognosis. This is similar to dogs, where higher ERα expression intensity was noted in benign tumors than in carcinomas. In human hematopoietic malignancies, ERβ is a predominant receptor. Selective and non-selective ERβ agonists have an antiproliferative and pro-apoptotic effect on human lymphoma cell lines and may be effective in the therapy of ERβ positive lymphomas and leukemias. In canine lymphoma tissues, none or only marginal expression of ERs was detected over the decades. Considering available data, we conducted preliminary studies proving that, in contrast to humans, the dominant ER expressed in canine hematopoietic tumors is ERα.

Empagliflozin and liraglutide ameliorate HFpEF in mice via augmenting the Erbb4 signaling pathway.

Heart failure with preserved ejection fraction (HFpEF) is closely associated with metabolic derangement. Sodium glucose cotransporter-2 inhibitors (SGLT2i) and glucagon-like peptide-1 receptor agonists (GLP-1RA) exert anti-HFpEF effects, but the underlying mechanisms remain unclear. In this study, we explored the anti-HFpEF effects of empagliflozin and liraglutide and the underlying molecular mechanisms in a mouse model of HFpEF. This model was established by high-fat diet (HFD) feedingplus Nω-nitro-L-arginine methyl ester (L-NAME) treatment. The mice were treated with empagliflozin (20 mg·kg-1·d-1, i.g.) or liraglutide (0.3 mg·kg-1·d-1, i.p.) or their combination for 4 weeks. At the end of the experimental protocol, cardiac function was measured using ultrasound, then mice were euthanized and heart, liver, and kidney tissues were collected. Nuclei were isolated from frozen mouse ventricular tissue for single-nucleus RNA-sequencing (snRNA-seq). We showed that administration of empagliflozin or liraglutide alone or in combination significantly improved diastolic function, ameliorated cardiomyocyte hypertrophy and cardiac fibrosis, as well as exercise tolerance but no synergism was observed in the combination group. Furthermore, empagliflozin and/or liraglutide lowered body weight, improved glucose metabolism, lowered blood pressure, and improved liver and kidney function. After the withdrawal of empagliflozin or liraglutide for 1 week, these beneficial effects tended to diminish. The snRNA-seq analysis revealed a subcluster of myocytes, in which Erbb4 expression was down-regulated under HFpEF conditions, and restored by empagliflozin or liraglutide. Pseudo-time trajectory analysis and cell-to-cell communication studies confirmed that the Erbb4 pathway was a prominent pathway essential for both drug actions. In the HFpEF mouse model, both empagliflozin and liraglutide reversed Erbb4 down-regulation. In rat h9c2 cells, we showed that palmitic acid- or high glucose-induced changes in PKCα and/or ERK1/2 phosphorylation at least in part through Erbb4. Collectively, the single-cell atlas reveals the anti-HFpEF mechanism of empagliflozin and liraglutide, suggesting that Erbb4 pathway represents a new therapeutic target for HFpEF. Effects and mechanisms of action of empagliflozin and liraglutide in HFpEF mice. HFpEF was induced with a high-fat diet and L-NAME for 15 weeks, and treatment with empagliflozin and liraglutide improved the HFpEF phenotype. Single nucleus RNA sequencing (snRNA-seq) was used to reveal the underlying mechanism of action of empagliflozin and liraglutide.

Abstract LB450: Mechanisms of acquired resistance to AKT inhibitor capivasertib in AKT1 mutant patient derived breast cancer models

Abstract Capivasertib, a pan-AKT inhibitor, has recently been approved in combination with fulvestrant to treat ER+ HER2- breast cancer patients with one or more of PI3KCA/AKT1/PTEN alterations. However, as with many targeted therapies acquired drug resistance remains a challenge. In this study, we investigated the mechanisms of acquired capivasertib resistance in AKT1 mutant breast cancer models. We established two estrogen receptor positive (ER+) AKT1 E17K mutant breast cancer patient derived organoids (PDOs), that were sensitive to capivasertib in vitro. PDOs were chronically exposed to 1µM capivasertib. PDOs were sequenced (DNA &amp; RNA) at multiple timepoints of treatment (3 days, 4 and 9 weeks after development of resistance). Using CRISPR-Cas9 editing we also engineered CAMA1 (ER+) cells to express AKT1 E17K, and generated derived resistant AKT1 mutant and parental models in response to continuous capivasertib exposure. CAMA1 AKT1 mutant and parental resistant were screened with an siRNA Kinome library supplemented with genes from the PDO RNA-sequencing. Phosphoproteomics was performed on capivasertib resistant E17K models in the presence and absence of capivasertib. PDO models persisting after either 4 or 9 weeks of capivasertib treatment showed no acquisition of genetic driver events, or changes in AKT copy number. Resistant organoids at 9 weeks treatment showed increased expression of ERBB3 (HER3), EGFR3 and LPAR5 as well as increased expression of MAPK signalling components. In siRNA screens on CAMA1 derived resistant models, siRNA targeting ERBB2, CDK4, PLK4 and CHEK1, ESR1 and LPAR5 modulated sensitivity to capivasertib. Analysis of phosphoproteins in capivasertib resistant models revealed reactivation of mTORC1 signalling despite sustained AKT inhibition, with dramatic upregulation of PDK1 and mTORC2. Consistent with the siRNA screens, drug combinations identified fulvestrant as a synergistic agent with capivasertib in the resistant E17K models. Sensitivity to mTOR inhibition was maintained in capivasertib resistant models, with mTOR inhibition re-sensitizing cells to capivasertib. In these models, acquired resistance to capivasertib occurs through upregulation of ER signalling and rewiring of pathway signalling to bypass AKT inhibition and reactivate mTORC1. Targeting these mechanisms could prolong the use of capivasertib, with future work focusing on validating these mechanisms and re-sensitizing drug combinations in other AKT1 mutant models &amp; PDOs. Citation Format: Sarah Mearns, Alex Pearson, Li-Xuan Sim, Rosalind Cutts, Prithika Sritharan, Heena Shah, Aditi Gulati, Stuart Williamson, Simon Barry, Elza De-Bruin, Nicholas C. Turner. Mechanisms of acquired resistance to AKT inhibitor capivasertib in AKT1 mutant patient derived breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB450.

The Estrogenic Effect of Lysiphyllum strychnifolium (Craib) A. Schmitz Leaf Water Extract in MCF-7 Cells

Lysiphyllum strychnifolium (Craib) A. Schmitz (LS) has been widely used as traditional medicine in the northeast region of Thailand to stimulate the production of breast milk. There are no known studies on the estrogenic action of LS on the stimulation of breast milk production. Hence, the present study aimed to investigate the estrogenic effect of LS leaf water extract compared with quercetin, one of the compounds in LS, in human breast cancer cells (MCF-7). The effect of LS leaf water extract and quercetin on cell viability of MCF-7 cells was studied by MTT assay at a concentration range of 0 to 500 µg/mL. The expression of estrogen-dependent genes, the pS2, ERα, and ERβ was also examined by real-time RT-PCR, and the expression of ERα protein was detected by Western blotting. The quercetin content in the LS water extract was 285.67 ± 0.11 µg/g of dry extract. MCF-7 cells treated with LS leaf water extract (20 µg/mL) showed an upregulation of pS2 gene expression similar to that of the treatment with E2 (10−9 M) compared with that of the untreated control. The ERα gene expression was found to be upregulated by quercetin (0.16 µg/mL) and E2 (10−5 M) compared with the untreated control. In addition, quercetin (0.16 µg/mL) and LS extract (0.8, 4, and 20 µg/mL) decreased the phosphorylation of ERα at Ser167. LS extract (20 µg/mL) decreased ERα, but there was no significant effect on the ERα at Ser118 protein expression. This study provided scientific evidence for the potential estrogenic activities of LS leaf water extract. This indicates that ER-dependent pathways in MCF-7 cells served as mediators, facilitating the estrogenic properties of LS and its compounds to function effectively. Since LS induced pS2 gene transcription, it was confirmed that this could affect the transcription of estrogen-responsive genes, causing estrogenic effects. HIGHLIGHTSThis is the first study to demonstrate the estrogenic effect of Lysiphyllum strychnifolium leaf water extract. L. strychnifolium leaf water extract induced pS2 gene transcription, and it was confirmed that this could affect the transcription of estrogen-responsive genes which cause estrogenic effects. The results of this study support the mechanism and scientific evaluation on the use of L. strychnifolium for stimulation of breast milk in folk medicine. GRAPHICAL ABSTRACT

Regulatory role of miR-125a expression with respect to its target genes LIFR, ERBB2 and STAT3 in the pathogenesis of recurrent pregnancy losses.

Studies have investigated miR-125a for its predictable role in recurrent pregnancy loss (RPL) cases to regulate many biological events required for the maintenance of pregnancy by regulating its confirmed target genes LIFR, ERBB2 and STAT3. The present study included 40 cases of women with at least two RPLs in ≤20 weeks of gestation against 40 healthy multiparous women without a previous history of abortion. Expression analysis of ERBB2, LIFR, STAT3 and miR-125a was conducted by quantitative real-time PCR (qPCR). The expression of miR-125a was significantly lower in the plasma of RPL cases (P = 0.0001) and showed a significantly increased mean expression level in product of conception (2.56-fold, P < 0.0001). Among the target gene of miR-125a, ERBB2 and STAT3 gene expression level was significantly increased (2.58-fold, P = 0.04; 1.87-fold, P = 0.025), respectively in RPL cases while the LIFR gene revealed comparable expression (P = 0.64). Furthermore, expression analysis of ERBB2 gene with respect to its regulatory miR-125a cases depicted a significant association (P = 0.0005). Kaplan-Meier survival analysis revealed cases with low miR-125a expression had significantly shorter time to miscarriages, (log-rank P = 0.02). Also, decreased expression of miR-125a significantly conferred >2-fold increased risk for RPL (HR = 2.34: P < 0.05). The overall conclusion of the study was that altered miR-125a expression may cause deregulation in target genes LIFR, ERBB2 and STAT3 resulting in adverse consequence in the outcome of pregnancy.

Abstract 1139: Unravelling tumor heterogeneity in patients with HER2-low hormone receptor-positive breast cancer using spatial transcriptomics

Abstract Background: The current binary distinction between HER2-positive and HER2-negative breast cancer (BC) has recently been challenged by the emergence of the HER2-low entity. Antibody-drug conjugates targeting HER2 have shown efficacy in both HER2-positive and HER2-low BC, while some preliminary evidence showed efficacy also in patients with HER2-zero BC. Here, by combining spatial transcriptomics (ST) and morphological annotation, we aimed to investigate the inter- and intra-tumor heterogeneity of ERBB2 expression in relation to breast cancer IHC subtypes. Methods: We performed ST (Visium 10X Genomics) on frozen tumor samples from patients with hormone receptor positive (HR+) ductal BC with HER2 IHC staining and FISH. Hematoxylin/eosin slides were morphologically annotated integrating manual and machine learning-based approaches reaching single-cell resolution (QuPath software). The relative histomorphological categories composition of each spot across the ST slide was computed as percentage of pixels. Spots were defined as tumoral if the percentile of pixels in that spot surpassed the 80th percentile of all the tumor spots in the cohort. Results: Our cohort consisted of 56 HER2-zero (IHC 0), 30 HER2-low (IHC 1+) and 20 HER2-positive (IHC 2+/FISH positive or IHC 3+) samples. HER2-zero samples contained a significantly higher percentage of acellular stroma spots compared to HER2-low (pvalue=0.04), while no other morphological annotation showed a difference, including tumor spots. Only tumor spots were retained for downstream analysis. A difference in the ERBB2 gene expression was found at the spot level, with a higher expression in HER2-low samples compared to HER2-zero samples (median expression 0.4, 0.7 and 3.1 in HER2-zero, HER2-low and HER2-positive, respectively). Inter-sample heterogeneity was observed, with 27% of the HER2-zero samples having equal or higher mean ERBB2 expression that the mean ERBB2 expression of the HER2-low cohort. Variability within individual samples was observed, revealing two peaks in ERBB2 expression, one characterized by low levels and the other by medium-high levels. This pattern was frequently observed in samples classified as HER2-zero and HER2-low, indicating the existence of tumor spots with diverse ERBB2 expression. Conclusions: Our results revealed inter- and intra-tumor heterogeneity of ERBB2 expression in HER2-zero and HER2-low BC. The use of spatial transcriptomics can provide more details of the spatial distribution of ERBB2. Further validation is warranted. Citation Format: Danai Fimereli, Matteo Serra, Mattia Rediti, Frederic Lifrange, Nicola Occelli, Laetitia Collet, Delphine Vincent, Ghizlane Rouas, Ligia Craciun, Denis Larsimont, David Venet, Miikka Vikkula, Francois P. Duhoux, Françoise Rothé, Christos Sotiriou. Unravelling tumor heterogeneity in patients with HER2-low hormone receptor-positive breast cancer using spatial transcriptomics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1139.

Abstract 6264: Role of Nuclear ErbB3 localization in regulating ligand-dependent ErbB2-ErbB3 heterodimer activation and downstream targets in prostate cancer

Abstract Objective: Prostate cancer (PCa)-specific nuclear expression of ErbB3, a receptor tyrosine kinase of the epidermal growth factor receptor (EGFR) family, has long been recognized. While an 80kDa nuclear variant of ErbB3 has been identified, full-length 185 kDa ErbB3 also translocates to the nucleus in PCa in a bone microenvironment and androgen status-dependent manner. Here, we studied potential mechanisms by which nuclear ErbB3 may regulate PCa progression. Methods: ErbB3 localization was investigated in vitro (human prostate cancer cell lines, LNCaP, C4-2, 22Rv1) using amiloride or heregulin-1β (ErbB3-specific ligand). ErbB3 expression and subcellular localization were analyzed using immunofluorescent microscopy and subcellular fractionation followed by immunoblot. Physiological readouts included viability, migration and reporter gene assays. Results: Here we show that ErbB3 can occupy a nuclear/perinuclear location in prostate cancer cells. The hormone sensitive PCa line LNCaP expressed higher levels of nuclear ErbB3 compared to castration resistant lines C4-2 and 22Rv1. The diuretic amiloride was previously shown to inhibit ErbB3 internalization by macropinocytosis thus we investigated whether it could also modulate ErbB3 nuclear localization in PCa cells. In LNCaP cells, amiloride dose dependently prevented ErbB3 nuclear transport, whereas in C4-2 and 22Rv1, no such effect was observed. Further analysis revealed that amiloride promoted ErbB3 expression in the membrane, where ErbB3 underwent ligand-dependent phosphorylation, formed ErbB2/ErbB3 dimers, and in turn phosphorylated the downstream targets AKT and ERK1/2 (p42/p44MAPK). On the other hand, EGFR phosphorylation and dimerization were unaffected by amiloride. Our results suggest that ErbB3 is stored in the nuclear region in an inactive form, whereas upon stress induction, including androgen deprivation, ErbB3 is translocated to the plasma membrane, where it is activated by ligand binding, and causes downstream signaling. Conclusion: We previously showed that the EGFR/ErbB2 dual inhibitor lapatinib failed to affect PCa - we now show that this may be due to modulation of nuclear and cytoplasmic ErbB3 expression. Amiloride prevented translocation (and thus expression of) ErbB3 to the nucleus and retained this RTK in the membrane, resulting in the formation of active ErbB2/ErbB3 dimers. Lapatinib was then able to inhibit and inactivate its specific target, ErbB2, thereby inducing significant apoptosis. The above indicates a novel role for nuclear ErbB3 in PCa that can be regulated by the combination of amiloride and lapatinib. Citation Format: Maitreyee K. Jathal, Maria M. Mudryj, Paramita M. Ghosh. Role of Nuclear ErbB3 localization in regulating ligand-dependent ErbB2-ErbB3 heterodimer activation and downstream targets in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6264.

Abstract 4619: Prolonged inhibition of androgen receptor signaling induces expression of Nuclear ErbB3 which renders prostate cancer cells susceptible to targeted inhibitors

Abstract Objective: Nuclear expression of the receptor tyrosine kinase (RTK) ErbB3/HER3 increases in highly aggressive prostate cancer cells, but its nuclear transport mechanism is currently unknown. Prostate tumors rely on the androgen receptor (AR), whose activation transcriptionally controls ErbB3 expression, but its role in ErbB3 nuclear localization had not previously been reported. Here, we investigated the mechanism by which subcellular localization of ErbB3 was altered in prostate cancer. Methods: ErbB3 localization was investigated in the human prostate cancer tumor progression model LNCaP, C4, C4-2 and C4-2B. ErbB3 was stimulated with heregulin-1β (HRG). Nuclear translocation was tested with a nucleocytoplasmic transport inhibitor panel (chlorpromazine, filipin III, amiloride and Leptomycin B) LNCaP and C4 cells were continuously cultured with the AR activation inhibitor abiraterone acetate (AbiAc) or ethanol (VEH) or treated with the AR inhibitors enzalutamide, darolutamide and apalutamide. ErbB3 activity and subcellular localization were analyzed using confocal microscopy/subcellular fractionation/immunoblot. Cell viability was determined by MTT assay. Proliferation and apoptosis were determined by flow cytometry. Invasive potential was investigated by crystal violet staining of cell colonies. ErbB3 expression was reduced by siRNA technology. Results: The ratio of nuclear to cytoplasmic ErbB3 increased in untreated cells from LNCaP&amp;lt;C4-2&amp;lt;C4&amp;lt;C4-2B. In all four lines, nuclear localization of ErbB3 peaked at 30 minutes after HRG treatment, with a rapid return to the cytoplasm in LNCaP cells (at 1 hour), slower in C4 cells (at 4 hours), and continued accumulation in the nucleus in C4-2 and C4-2B 8 hours following HRG treatment. Treatment with the transport inhibitor panel showed that nuclear accumulation of ErbB3 was prevented by the clathrin-dependent endocytosis inhibitor Chlorpromazine (CPZ) but not by the others. In LN-VEH and C4-VEH cells, HRG induced nuclear translocation of ErbB3 but not in LN-AbiAc or C4-AbiAc cells. Accordingly, HRG increased ErbB3 phosphorylation at Y1328 and nuclear Akt phosphorylation at S473 in VEH but not AbiAc cells. C4 cells, which had high baseline nuclear ErbB3, were more sensitive to the AR inhibitors and showed decreased viability and invasive potential compared to LNCaP cells. Conclusions: These results indicate that (1) ErbB3 nuclear localization required clathrin-dependent endocytosis (2) ligand binding of ErbB3 as well as the presence of an active AR is necessary for ErbB3 nuclear localization and (3) the presence of nuclear ErbB3 increases sensitivity to AR inhibitors. Citation Format: Maitreyee K. Jathal, Maria M. Mudryj, Paramita M. Ghosh. Prolonged inhibition of androgen receptor signaling induces expression of Nuclear ErbB3 which renders prostate cancer cells susceptible to targeted inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4619.

Abstract 6392: Activity of HER2-and TROP2- antibody drug conjugates (ADCs) in small cell lung cancer (SCLC) models with SLFN11 as a predictive biomarker

Abstract Background: Small-cell lung cancer (SCLC) is a highly aggressive malignancy with its few treatment options devoid of biomarker selection, and a 5-year survival rate of less than 7%. Our group previously established four transcriptionally defined subtypes of SCLC, each with distinct cell surface targets (Gay et al, Cancer Cell 2021). Further, we identified SLFN11 (a putative DNA/RNA helicase) as a candidate biomarker of sensitivity to DNA-damaging agents, including topoisomerase inhibitors. Human epidermal growth factor receptor 2 (HER2/ERBB2) expression has been previously described in a subset of SCLCs and has been linked to poor prognosis. HER2 antibody-drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd) (where the payload is a topoisomerase I inhibitor) have received FDA approval for various solid tumors, highlighting their therapeutic potential. Similarly, TROP2 (TACSTD2) ADC sacituzumab govitecan has shown promising clinical efficacy in a SCLC (TROPiCS-03 basket trial). However, it is unclear what the predictive biomarkers are to these ADCs in SCLC. Methods: Expression of ERBB2 and TACSTD2 mRNA was analyzed using publicly available patient datasets. We also characterized surface expression of HER2 and TROP2 by flow cytometry in SCLC cell lines at baseline and after cisplatin/etoposide treatment. We then assessed the cytotoxicity of T-Dxd and sacituzumab govitecan in a panel of SCLC cell lines representative of each SCLC subtype, as well as SLFN11 status. Results: Analyses of HER2/ERBB2 and TROP2/TACSTD2 in SCLC cell lines and patient datasets showed a range of ERBB2 and TACSTD2 expression with enrichment in the non-neuroendocrine subtypes (SCLC-P and SCLC- I subtypes). We further validated HER2 and TROP2 surface levels by flow cytometry in a subset of SCLC cell lines. Intriguingly, we observed that surface expression of both HER2 and TROP2 increase after frontline chemotherapy cisplatin/etoposide treatment. As expected, T-Dxd and sacituzumab govitecan exhibit cytotoxicity in a subset of SCLC cell lines. We found a strong correlation between the in vitro cytotoxicity (IC50) of sacituzumab govitecan with SLFN11 (rho= 0.74, p=0.015). Importantly, SLFN11 is bimodally distributed in SCLC and we found ERBB2 and TACSTD2 to be enriched in the SLFN11-high group of SCLC patients. We also found ERBB2 and TACSTD2 to be correlated with each other (rho = 0.53, p &amp;lt;0.001). Conclusion: In this study, we demonstrate that HER2/ERBB2 and TROP2/TACSTD2 are enriched in a subset of SCLC. FDA-approved ADCs, T-DXd and sacituzumab govitecan each have preclinical activity in SCLC with SLFN11 as a predictive biomarker of payload cytotoxicity. We also found HER2 and TROP2 target levels increase after frontline chemotherapy (cisplatin/etoposide) in SCLC, which suggest their efficacy may be enhanced in relapsed SCLC where treatment options are extremely limited. Citation Format: Bingnan Zhang, Ali Ibrahim, C.Allison Stewart, Lixia Diao, Qi Wang, Li Shen, Yuann xi, Alejandra Serrano, Luisa M. Solis, Wei-Lien Wang, Kavya Ramkumar, Robert J. Cardnell, Runsheng Wang, Alberto Duarte, Jing Wang, Lauren A. Byers, Carl Gay. Activity of HER2-and TROP2- antibody drug conjugates (ADCs) in small cell lung cancer (SCLC) models with SLFN11 as a predictive biomarker [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6392.

Abstract 5168: Analysis of biomarker and outcomes data: 7-year update from COLUMBUS

Abstract Background: In the randomized, 2-part, phase 3 COLUMBUS study (NCT01909453), encorafenib (enco) + binimetinib (bini)—an approved regimen in the US, EU, and other countries—improved 7-year PFS and OS vs vemurafenib (vemu) in patients (pts) with BRAF V600E/K-mutant locally advanced unresectable or metastatic melanoma. We investigated genetic and transcriptional correlates of outcomes in an exploratory biomarker analysis of COLUMBUS Parts 1 and 2. Methods: In Part 1, 577 pts were randomized 1:1:1 to enco 450 mg QD + bini 45 mg BID, enco 300 mg QD, or vemu 960 mg BID; in Part 2, 344 pts were randomized 3:1 to enco 300 mg QD + bini 45 mg BID or enco 300 mg QD. Baseline tumor samples were analyzed using the ACE ImmunoID NeXT whole exome sequencing/whole transcriptome sequencing (WES/WTS) assays (Personalis). PFS and OS were analyzed (cutoff: Jan 13, 2023) by treatment arm and presence of specific genetic or transcriptomic alterations. Results: Among treated pts, 668 had WES or WTS data. K-means clustering identified 3 major transcriptional clusters: (1) microphthalmia-associated transcription factor (MITF)-low (invasive dedifferentiated tumor cell phenotype), (2) MITF-high (proliferative melanocytic phenotype), and (3) immune-high. Cluster assignments were significantly associated with biopsy site (P&amp;lt;0.001), with cluster 1 enriched in skin biopsies and cluster 3 in lymph node metastases; biopsy site-independent characteristics were also captured. Improved PFS with enco + bini vs vemu was most pronounced in cluster 3 (Table 1). ERBB2 expression and PI3KCA pathway mutation, previously found to be associated with reduced survival benefit with enco + bini vs vemu, were enriched in clusters 1 and 2 vs cluster 3. Conclusions: Enco + bini showed benefit across molecular subtypes in BRAF V600E/K-mutant melanoma. The contribution of bini was most pronounced in the immune-high cluster. Improved outcomes in this cluster support ongoing trials of combinations with immune checkpoint inhibitors, such as STARBOARD and PORTSIDE. Table 1. Hazard ratios of PFS and OS for enco + bini or enco vs vemu by cluster HR (95% CI) vs vemu PFS OS Enco + bini Enco Enco + bini Enco Overall n=255 vs 100 n=159 vs 100 n=255 vs 100 n=159 vs 100 0.47 (0.35, 0.63) 0.78 (0.57, 1.07) 0.66 (0.50, 0.86) 0.85 (0.63, 1.13) Clusters Cluster 1: MITF-low n=72 vs 34 n=44 vs 34 n=72 vs 34 n=44 vs 34 0.74 (0.44, 1.26) 0.92 (0.51, 1.66) 0.63 (0.40, 1.00) 0.57 (0.34, 0.96) Cluster 2: MITF-high n=120 vs 46 n=76 vs 46 n=120 vs 46 n=76 vs 46 0.48 (0.32, 0.74) 0.75 (0.48, 1.17) 0.66 (0.45, 0.97) 0.86 (0.56, 1.32) Cluster 3: Immune-high n=63 vs 20 n=39 vs 20 n=63 vs 20 n=39 vs 20 0.23 (0.12, 0.44) 0.64 (0.33, 1.21) 0.80 (0.40, 1.59) 1.55 (0.76, 3.15) Numbers are given as the number of pts included in the treatment arm vs the number of pts in the comparator arm (vemu-treated). Statistical significance (P&amp;lt;0.05) is shown by bold font. Bini, binimetinib; enco, encorafenib; MITF, microphthalmia-associated transcription factor; pts, patients; vemu, vemurafenib. Citation Format: Reinhard Dummer, Keith Flaherty, Shibing Deng, Tao Xie, Phineas Hamilton, Nuzhat Pathan, Caroline Robert, Ana Arance, Jan Willem de Groot, Claus Garbe, Helen J. Gogas, Ralf Gutzmer, Ivana Krajsová, Gabriella Liszkay, Carmen Loquai, Mario Mandala, Dirk Schadendorf, Naoya Yamazaki, Paolo A. Ascierto, Alessandra di Pietro, Craig B. Davis. Analysis of biomarker and outcomes data: 7-year update from COLUMBUS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5168.

Abstract 4708: Potency and selectivity of ERBB2-targeting antibody drug conjugates in vitro

Abstract Previously we have reported on the relevance of the joint ProLiFiler and Cancer DataMiner platforms when studying the antitumor efficacy of novel antibody-drug conjugates (ADCs), such as Sacituzumab govitecan. In this study, we use our platforms to investigate and compare the selectivity of two FDA-approved Trastuzumab-based ADCs targeting ERBB2: Kadcyla, the first-in-class ADC employing a microtubule inhibitor bound via a non-cleavable linker, and Enhertu, which combines a topoisomerase inhibitor with a protease-cleavable linker. We performed a cell proliferation and survival assay using the ProLiFilerTM (Reaction Biology) to characterize the in vitro antitumor effects of Enhertu, Kadcyla, and their individual cytotoxins, deruxtecan &amp; mertansine on 160 human cancer cell lines (CLs). The resulting data were uploaded to 4HF´s Cancer DataMiner platform for data analysis. First, we confirmed high potency and limited selectivity of mertansine, as it displayed an IC50 &amp;lt; 250 nM (mean: 27.3 nM) in 95% of cell lines (CLs). A COMPARE analysis confirmed that mertansine data correlated best with those of other microtubule inhibitors in our drug databases (e.g., MMAE, Spearman rho = 0.79, p=9.6E-27). Conversely, a paired analysis showed that CLs were less sensitive to Kadcyla than to mertansine except for CLs overexpressing ERBB2. The 160-CL panel included a total of nine CLs (six mammary, two gastric, one ovarian) with strong ERBB2 overexpression (Affymetrix data &amp;gt;10), mostly associated with ERBB2 gene amplification; seven of them were the most sensitive CLs to Kadcyla (IC50 &amp;lt; 6 nM). Focusing solely on breast cancer cell lines (breast cancer is the approved indication for Kadcyla), we observed a strong correlation between sensitivity to Kadcyla and ERBB2 expression (Spearman r = -0.78, p = 0.003). Interestingly, in line with published data, the ERBB2-overexpressing cell lines SNU-216 (stomach cancer) and JIM-T1 (breast cancer) were less sensitive to Kadcyla. In non-ERBB2-amplified CLs, Kadcyla sensitivity did not correlate with ERBB2 expression levels. Focusing on ERBB2-negative CLs such as hematological CLs, we unexpectedly observed consistent cell inhibition (mean IC50 =33 nM) with Kadcyla, suggesting that the ADC was cleaved, and the payload released into the medium. Overall, this study has demonstrated the relevance of our platforms to study and compare newly developed ADCs. Cytotoxic activities recorded for conjugates and free payloads, along with molecular data for the test cell lines, provides insight in the mode of action of conjugates and their target cell populations and hence can support the development of ADCs. Investigations are underway with Enhertu and its payload deruxtecan, and results will be compared with those obtained for Kadcyla and mertansine. Citation Format: Anne-Lise Peille, Kaja Holtorf, Pablo Anton Garcia, Nadine Obier, Daniel Feger, Thomas Metz, Sebastian Dempe, Heinz-Herbert Fiebig, Jan Ehlert, Vincent Vuaroqueaux. Potency and selectivity of ERBB2-targeting antibody drug conjugates in vitro [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4708.

Clinical, Epidemiologic, and Pathologic Significance of ERBB2-Low Expression in Breast Cancer

It is unclear whether breast cancer (BC) with low ERBB2 expression (ERBB2-low) is a distinct clinical, pathological, and epidemiological entity from BC classified as no ERBB2 expression (ERBB2-negative). To evaluate the clinical, pathological, and epidemiologic features of BC with ERBB2-low expression compared with ERBB2-negative BC in a large population study. This cohort study was conducted as part of the Pathways Study, a prospective, racially and ethnically diverse cohort study of women with BC enrolled between 2006 and 2013 in Kaiser Permanente Northern California (KPNC). The hematoxylin and eosin slides underwent centralized pathology review, including the percentage of tumor infiltrating lymphocytes (TILs). Breast biomarker results were extracted from pathology reports, and women were included if they had a documented ERBB2 value that was not classified ERBB2-positive. Data were analyzed from February 2023 through January 2024. Clinical and tumor characteristics associated with BC and ERBB2-low or ERBB2-negative status. ERBB2-low was defined as immunohistochemistry score of 1+ or 2+ (negative by in situ hybridization); ERBB2-negative was defined as immunohistochemistry score of 0+. Other data were collected by self-report or extraction from electronic health records, including BC risk factors, tumor characteristics, treatment modality, and survival outcomes, with recurrence-free survival (RFS) as the primary outcome and overall survival (OS) and BC-specific mortality (BCSM) as secondary outcomes. The clinical, pathological, and epidemiological variables were compared between ERBB2-low and ERBB2-negative BC. Of 2200 eligible patients (all female; with mean [SD] age, 60.4 [11.9] years), 1295 (57.2%) had tumors that were ERBB2-low. Hormone receptors were positive in 1956 patients (88.9%). The sample included 291 Asian patients (13.2%), 166 Black patients (7.5%), 253 Hispanic patients (11.5%), 1439 White patients (65.4%), and 51 patients (2.3%) who identified as other race or ethnicity (eg, American Indian or Alaska Native and Pacific Islander). Within the hormone receptor-negative group, patients whose tumors had ERBB2-low staining, compared with those with ERBB2-negative tumors, had better OS (hazard ratio [HR], 0.54; 95% CI, 0.33-0.91; P = .02), RFS (HR, 0.53; 95% CI, 0.30-0.95; P = .03), and BCSM (HR, 0.43; 95% CI, 0.22-0.84; P = .01). In multivariable survival analysis stratified by hormone receptor status and adjusted for key covariates, patients with ERBB2-low and hormone receptor-negative tumors had lower overall mortality (HR, 0.48; 95% CI, 0.27-0.83; P = .009), RFS (HR, 0.45; 95% CI, 0.24-0.86; P = .02), and BCSM (subdistribution HR, 0.21; 95% CI, 0.10-0.46; P < .001) compared with patients with ERBB2-negative and hormone receptor-negative tumors. Within the hormone receptor-negative subtype, patients with ERBB2-low and high TILs tumors had better survival across all 3 outcomes compared with patients with ERBB2-negative and low TILs tumors. Additionally, patients with ERBB2-low and low TILs tumors had better BCSM (subdistribution HR, 0.36; 95% CI, 0.14-0.92; P = .03). These findings suggest that there were clinical, pathological, and epidemiological differences between ERBB2-low and ERBB2-negative BC, raising the possibility that ERBB2-low might be a unique biologic entity.

Abstract 6939: Residual disease after HER2 inhibition is driven by a primary tumor subpopulation expressing an ERBB2-low associated transcriptional program

Abstract Background: In HER2+ breast cancer (BC), residual disease (RD) after neoadjuvant HER2 inhibition is associated with increased risk of recurrence. However, the genetic and non-genetic resistance mechanisms underlying RD remain incompletely characterized. Here we used single nuclei (sn) RNA and DNA sequencing to profile genetic and transcriptional changes in growing, residual, and recurrent tumors from an inducible mouse tumor model of HER2+ breast cancer. Methods: We used mammary tumors/tumor bed (n=2-3/time point) from female MMTV-rtTA; TetO-ERBB2 mice at 9 weeks DoxOn (HER2on), 7 days DoxOff (HER2off) and 12-21 weeks Doxoff (recurrent). Samples were snap frozen and single nuclei isolation was performed. snRNAseq was performed using 10 × 5’ v2 kits for library preparation and sequencing. snDNAseq was performed using a custom amplicon panel targeting the mouse genome and human ERBB2 locus via the MissionBio Tapestri platform. Results: For snRNAseq analysis, tumor cell clusters were identified by Epcam and ERBB2 gene expression. Tumor cells were further subclustered into 18 unique clusters that separated by ERBB2 expression. Seven subclusters of HER2on tumor cells were characterized by low ERRB2 expression: 1.38 vs 2.94 (median normalized log counts) in HER2on-ERBB2high cells. Top 5 differentially expressed genes (DEG) per condition (log2 fold change &amp;gt;1.5, adjusted p value &amp;lt; 0.05) were: HER2on: Erbb2, Csn3, Lcn2, Csn2, Wfdc18; HER2on-ERBB2high: Csn3, Igfbp5, Csn2, Lcn2, Trf; HER2on-ERBB2low: Lars2, Gm47283, Cmss1, Gm42418, Neat1; HER2off: Lars2, Hexb, Cmss1, Gphn, Gm42418; Recurrent: Capza2, Vim, Lgals1, Crabp1, S100a6. HER2on-ERBB2low cells were more closely related in transcriptional space to HER2off residual tumor cells than HER2on-ERBB2high tumor cells. Trajectory analysis suggested that HER2off RD evolved from HER2on-ERRB2low cells and formed the basis of recurrent disease. To determine clonal evolution over time, we used common top 10 DEGs between HER2on vs HER2off vs HER2low snRNAseq data and intersected that set with significantly enriched single nucleotide variants (SNVs) from our snDNAseq data. We identified 16 clones containing at least 1 SNV at &amp;gt;1% frequency across all samples. We observed clonal persistence, relative enrichment and extinguishment between HER2on, HER2off and recurrent samples but without clonal dominance. Conclusion: Time-series analysis of genetic and transcriptional evolution in a mouse model of HER2+ BC RD suggests that a tumor cell subpopulation characterized by an ERBB2low-associated transcriptional program drives RD after HER2 inhibition. Citation Format: Sheheryar K. Kabraji, Weihua Wang, Yali Zhang, Johann Bergholz, Tao Jiang, Vittal Kurisetty, Maia Homsi, Jianmin Wang, Jean Zhao. Residual disease after HER2 inhibition is driven by a primary tumor subpopulation expressing an ERBB2-low associated transcriptional program [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6939.

Abstract 6657: Oncolytic Vaccinia Virus Carrying OPCML Tumor Suppressor is active in Epithelial Ovarian Cancer

Abstract Objective: Epithelial Ovarian cancer (EOC) has the highest mortality rate among gynecologic malignancies, necessitating novel therapeutic approaches. Viral oncolytic immunotherapy with recombinant oncolytic vaccinia virus (OVV) offers promise for advanced-stage cancer treatment. OPCML is a GPI-anchored 3 Ig-domain tumor suppressor inactivated by somatic methylation in 87% of EOC. OVV with OPCML (OVV-OPCML) gene insertion may have potential as a therapeutic agent. This study explores the oncolytic, signaling-inhibitory, anti-angiogenic and synergistic immunotherapeutic properties of OVV-OPCML in EOC treatment, evaluating its therapeutic potential. Methods: To create OVV-OPCML, the virulent vaccinia virus Copenhagen strain F3L site was modified with OPCML cDNA, confirmed by qPCR and western blot. Oncolytic potential was assessed through in vitro and in vivo EOC cell infection with OVV-OPCML. Real-time cell analysis (RTCA) assessed cell proliferation. Xenograft tumor models in nude mice were used to evaluate in vivo oncolytic activity, while OVV-OPCML combined with anti-PD-1 treatment was tested using a syngeneic orthotopic EOC mouse model (ID8) in C57BL/6 immunocompetent mice. Serum IFN-γ and TNF-α were quantified via ELISA. Receptor Tyrosine Kinases, angiogenesis and phosphorylation together with immune markers were examined by western blotting and by multiplex immunohistochemistry (mIHC) analysis of tumor sections. Results: OVV-OPCML selectively infected OC cells, leading to viral replication and tumor cell death, while sparing normal ovarian cells in-vitro. OPCML protein expression increased post-infection. OVV-OPCML reduced ERBB2, EGFR, and FGFR1 expression in SKVO3 OV cells. Intratumoral or intraperitoneal (IP) OVV-OPCML administration in human ovarian cancer nude mouse models reduced tumor growth and improved survival. IP in-vivo OVV-OPCML in combination with anti-PD-1 treatment in vivo, in the IP ID8 syngeneic model demonstrated synergy with survival improvement. H&amp;E staining showed tumor cell damage without significant harm to normal tissues. Protein expression of ERBB2, EGFR, FGFR1, and their phosphorylated forms decreased. CD31, VEGFR2, p-VEGFR2 (Tyr1175), and p-VEGFR2 (Tyr1214) downregulation suggested tumor angiogenesis disruption. OVV-OPCML treatment elevated serum TNF-α and INF-γ levels and increased CD8+ T cells and PD-L1 expression in OVV-OPCML treated syngeneic tumors. Conclusions: OPCML gene enhances OVV selectivity against OC cells through direct oncolysis and OPCML protein production, inhibiting specific RTKs, suppressing angiogenesis, and activating antitumor immune responses synergistically with anti-PD-1. OVV-OPCML therapy shows promise as a targeted strategy for ovarian cancer treatment. Citation Format: Yong Tang, Yingzhao Liu, Mingjing Deng, Fei Huang, Jiahu Wang, Paul Blake, Hani Gabra, Qi Wang. Oncolytic Vaccinia Virus Carrying OPCML Tumor Suppressor is active in Epithelial Ovarian Cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6657.