Luminal Androgen Receptor Subtype Research Articles

Luminal androgen receptor subtype and tumor-infiltrating lymphocytes groups based on triple-negative breast cancer molecular subclassification.

In our previous study, we developed a triple-negative breast cancer (TNBC) subtype classification that correlated with the TNBC molecular subclassification. In this study, we aimed to evaluate the predictor variables of this subtype classification on the whole slide and to validate the model's performance by using an external test set. We explored the characteristics of this subtype classification and investigated genomic alterations, including genomic scar signature scores. First, TNBC was classified into the luminal androgen receptor (LAR) and non-luminal androgen receptor (non-LAR) subtypes based on the AR Allred score (≥ 6 and < 6, respectively). Then, the non-LAR subtype was further classified into the lymphocyte-predominant (LP), lymphocyte-intermediate (LI), and lymphocyte-depleted (LD) groups based on stromal tumor-infiltrating lymphocytes (TILs) (< 20%, > 20% but < 60%, and ≥ 60%, respectively). This classification showed fair agreement with the molecular classification in the test set. The LAR subtype was characterized by a high rate of PIK3CA mutation, CD274 (encodes PD-L1) and PDCD1LG2 (encodes PD-L2) deletion, and a low homologous recombination deficiency (HRD) score. The non-LAR LD TIL group was characterized by a high frequency of NOTCH2 and MYC amplification and a high HRD score.

Immunohistochemical Profile of Triple-Negative Breast Cancers: SOX10 and AR Dual Negative Tumors Have Worse Outcomes

Triple-negative breast cancer (TNBC) refers to an estrogen receptor–negative, progesterone receptor–negative, and HER2-negative breast cancer. Although accepted as a clinically valid category, TNBCs are heterogeneous at the histologic, immunohistochemical, and molecular levels. Gene expression profiling studies have molecularly classified TNBCs into multiple groups, but the prognostic significance is unclear except for a relatively good prognosis for the luminal androgen receptor subtype. Immunohistochemistry (IHC) has been used as a surrogate for basal and luminal subtypes within TNBC, but prognostication of TNBC using IHC is not routinely performed. We aimed to study immunophenotypic correlations in a well-annotated cohort of consecutive TNBCs, excluding postneoadjuvant chemotherapy cases. Tissue microarrays were constructed from a total of 245 TNBC cases. IHC stains were performed and consisted of luminal (AR and INPP4B), basal (SOX10, nestin, CK5, and EGFR), and diagnostic (GCDFP15, mammaglobin, GATA3, and TRPS1) markers. Survival analysis was performed to assess the significance of clinical-pathologic variables including age, histology, grade, lymphovascular invasion, Nottingham prognostic index category, American Joint Committee on Cancer (AJCC) stage, stromal tumor-infiltrating lymphocytes at 10% increment, CD8+ T-cell count, Ki-67 index, PD-L1 status, and chemotherapy along with the results of IHC markers. Apocrine tumors show prominent reactivity for luminal markers and GCDFP15, whereas no special-type carcinomas are often positive for basal markers. TRPS1 is a sensitive marker of breast carcinoma but shows low or no expression in apocrine tumors. High AJCC stage, lack of chemotherapy, and dual SOX10/AR negativity are associated with worse outcomes on both univariable and multivariable analyses. Lymphovascular invasion and higher Nottingham prognostic index category were associated with worse outcomes on univariable but not multivariable analysis. The staining for IHC markers varies based on tumor histology, which may be considered in determining breast origin. Notably, we report that SOX10/AR dual negative status in TNBC is associated with a worse prognosis along with AJCC stage and chemotherapy status.

Safety and efficacy of anlotinib combined with taxane and lobaplatin in neoadjuvant treatment of clinical stage II/III triple-negative breast cancer in China (the neoALTAL trial): a single-arm, phase 2 trial

Anlotinib is a new type of tyrosine kinase inhibitor that targets vascular endothelial growth factor receptors 1/2/3, platelet-derived growth factor receptors α/β, and fibroblast growth factor receptors 1-4 and c-Kit, with a broad spectrum of inhibitory effects on tumor angiogenesis and growth. It has been proven effective in HER2-negative metastatic breast cancer, but its efficacy in early-stage triple-negative breast cancer (TNBC) is unknown. This phase 2 study aims to evaluate the efficacy and safety of adding anlotinib to neoadjuvant chemotherapy in patients with TNBC. Patients with clinical stage II/III TNBC were treated with 5 cycles of anlotinib (12mg, d1-14, q3w) plus 6 cycles of taxanes (docetaxel 75 mg/m2 ,d1, q3w or nab-paclitaxel 125 mg/m2, d1 and d8, q3w) and lobaplatin (30 mg/m2, d1, q3w), followed by surgery. The primary endpoint was pathological complete response (pCR; ypT0/is ypN0) and the secondary endpoints include breast pCR (bpCR), axillary pCR (apCR), residual cancer burden (RCB), objective response rate (ORR), survival, and safety. Exploratory endpoints were efficacy biomarkers based on Fudan University Shanghai Cancer Center Immunohistochemical (FUSCC IHC) classification for TNBC and next-generation sequencing (NGS) of DNA from tumor tissue and blood samples of patients with 425-gene panel. This trial is registered with www.chictr.org.cn (ChiCTR2100043027). From Jan 2021 to Aug 2022, 48patients were assessed and 45 were enrolled. All patients received at least one dose of study treatment and underwent surgery. The median age was 48.5 years (SD: 8.7), 71% were nodal involved, and 20% had stage III. In the intention-to-treat population, 26 out of 45patients achieved pCR (57.8%; 90% CI, 44.5%-70.3%), and 39 achieved residual cancer burden class 0-I (86.7%; 95% CI, 73.2%-94.9%). The bpCR and apCR rate were 64.4% (29/45) and 71.9% (23/32), respectively. No recurrence or metastasis occurred during the short-term follow-up. Based on the FUSCC IHC-based subtypes, the pCR rates were 68.8% (11/16) for immunomodulatory subtype, 58.3% (7/12) for basal-like immune-suppressed subtype and 33.3% (4/12) for luminal androgen receptor subtype, respectively. NGS revealed that the pCR were 77% (10/13) and 50% (14/28) in MYC-amplified and wild-type patients, respectively, and 78% (7/9) and 53% (17/32) in gBRCA1/2-mutated and wild-type patients, respectively. The median follow-up time of the study was 14.9 months (95% CI: 13.5-16.3 months). There was no disease progression or death during neoadjuvant therapy. No deaths occurred during postoperative follow-up. In the safety population (N=45), Grade 3 or 4 treatment emergent adverse events occurred in 29patients (64%), and the most common events were neutropenia (38%), leukopenia (27%), thrombocytopenia (25%), anemia (13%), and hypertension (13%), respectively. The addition of anlotinib to neoadjuvant chemotherapy showed manageable toxicity and encouraging antitumor activity for patients with clinical stage II/III TNBC. Chongqing Talents Project, Chongqing Key Project of Technology Innovation and Application Development and Chongqing Outstanding Youth Natural Science Foundation.

Abstract 7592: Combined inhibition of CDK4/6 and AKT is highly active against the luminal androgen receptor (LAR) subtype of triple negative breast cancer (TNBC)

Abstract The LAR subtype of TNBC is enriched for targetable biomarkers such as androgen receptor (AR) expression, PIK3CA mutations, and intact Rb. The purpose of this study was to investigate the most effective combination of CDK4/6, AR, and PI3K-AKT inhibitors in preclinical models of LAR TNBC. The MDAMB453 and MFM223 (AR positive/Rb intact/PIK3CAmutant) LAR TNBC cells were treated with each inhibitor alone or in combination. Drug sensitivity was assessed using colony formation, cell viability, and live-cell analysis. The Loewe additivity equation was used to measure the additive drug effects. Immunoblot analysis was used to evaluate cell cycle and PI3K-AKT signaling and ARE luciferase assay was used to assess AR transcriptional activity. MDAMB453 and MFM223 cells were sensitive to the single agents palbociclib, alpelisib, and capivasertib (IC50, ~500 nM), which inhibited CDK4/6, PI3Kα, and AKT, respectively. Enzalutamide, an AR antagonist, exerted no growth inhibitory activity (IC50, 15-25 μM). Treatment with palbociclib, alpelisib, or capivasertib did not alter the AR protein levels or transcriptional activity. The combination of palbociclib+capivasertib synergistically inhibited the proliferation of MDAMB453 and MFM223 cells (synergistic scores 7.34, p=5.81-11, and 4.78, p=0.012, respectively) better than palbociclib+alpelisib. Enzalutamide did not enhance either combination. Palbociclib+capivasertib inhibited PI3KCA-mutant and Rb-intact LAR TNBC PDX growth more potently than palbociclib+alpelisib (p=0.046). Treatment of LAR TNBC cells with palbociclib suppressed Rb phosphorylation and resulted in adaptive activation of P-AKTS473/T308 and the AKT substrates GSK3β, PRAS40, and FoxO3a after 24 h. Capivasertib inhibited the phosphorylation of AKT and AKT substrates, following CDK4/6 blockade with palbociclib, more potently than alpelisib. PI3Kβ inhibitors (TGX221, GSK2636771) did not block AKT substrate upregulation, suggesting PI3Kβ does not mediate adaptive responses. Rictor knockdown failed to reduce AKT activation following palbociclib treatment, suggesting an mTORC2-independent mechanism. Human Phospho-kinase Array of MDA-MB-453 cells treated with palbociclib showed time dependent upregulation of GSK3βS9, STAT3Y727 and PDFGRβY751. PDGFRβ activation after palbociclib treatment was confirmed in MFM223 cells. PDGFRβ siRNAs in MDAMB453 cells blocked P-AKTS473 upregulation after palbociclib treatment. Treatment with palbociclib and the PDGFRβ small-molecule antagonist CP673451 arrested LAR TNBC growth similar to palbociclib+capivasertib, suggesting an adaptive response involving PDGFRβ signaling. In conclusion, this study supports the clinical testing of the palbociclib and capivasertib combination for LAR TNBC patients and reveals adaptive responses after palbociclib treatment through PDGFRβ signaling. Citation Format: Rosario Chica-Parrado, Gun Min Kim, Yasuaki Uemoto, Dan Ye, Fabiana Napolitano, Chang-Ching Lin, Emmanuel Bikorimana, Kyung-min Lee, Saurabh Mendiratta, Ariella B. Hanker, Carlos L. Arteaga. Combined inhibition of CDK4/6 and AKT is highly active against the luminal androgen receptor (LAR) subtype of triple negative breast cancer (TNBC) [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 7592.

Abstract 5363: New targeted therapy on SOCS1-related immune-response in triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is heterogenous, which includes basal-like, immunomodulatory, mesenchymal, mesenchymal stem cell and luminal androgen receptor subtypes. In addition to chemotherapy, PARP inhibitors and immune checkpoint inhibitors are effective for TNBC with BRCA-mutated and PD-L1-positive cases. However, overall survival of TNBC remains unfavorable. To explore new targeted therapy in TNBC, we reported previously that SOCS1 (suppressor of cytokine signaling 1), IL-13 and several genes were predicted as interactive targets of miRNA in TNBC from the microarray expression analysis (Agilent Technologies, Inc.) of small RNA extracted from 11 breast cancer specimens (AACR2020, #1709). Thus, we investigated SOCS1-related immune-response under co-culture of TNBC and monocyte cell lines with or without paclitaxel exposure. Materials and Methods: MDA-MB-231, MDA-MB-468, RAW264.7 cell lines were used with co-culture system (Falcon® Cell Culture Inserts, Corning, NY, USA). SOCS1-expression vector and siSOCS1 were transfected into TNBC cell lines with polyethylenimine (PEI Max; Polysciences, Inc., Warrington, PA). RAW264.7 was activated with lipopolysaccaride (5ug/ml) and IFNγ (10ng/ml) for 2 days before co-culture. Relative cell viability of TNBC cell lines with vehicle control (DMSO) or paclitaxel exposure was measured with WST-8 (Cell Counting Kit-8; Dojindo, Japan) using TC20 Automated cell counter (Bio-Rad Laboratories, Inc., Japan) after 2 days’ co-culture of TNBC and RAW264.7 cells under several conditions of SOCS1 overexpression and/or RAW264.7 activation. Results: First, paclitaxel inhibited cell growth of MDA-MB-231 and MDA-MB-468 in a dose-dependent manner (at 1nM~100nM). Second, at paclitaxel exposure of 10 nM and 50 nM, relative cell viability of MDA-MB-468 decreased with co-culture of activated RAW264.7. The tendency was enhanced with SOCS1 overexpression in breast cancer cell lines. Similar results were observed in MDA-MB-231 cells. Discussions: SOCS1 is well known as a negative regulator of JAK-STAT pathway. SOCS1 is also related to suppression of T cell activation and modulation of M1 macrophage. At AACR2020, we reported that SOCS1 gene amplification in cancer tissues after neoadjuvant chemotherapy was relatively lower in 6 cases with pathologically partial or complete response than in 11 cases with no pathological response. In vitro, paclitaxel-toxicity in TNBC cells was augmented by activated monocyte (M1 macrophage) and more sensitized with SOCS1 overexpression in TNBC cells. These results suggest that proinflammatory cytokines from M1 macrophage influence cell viability of TNBC. Conclusion: SOCS1 is a promising molecular target to modulate immune-response in TNBC. Citation Format: Shigeru Imoto, Tomohiro Chiba, Hirohito Seki, Yoshiharu Ishizaka, Ai Tsuchiya, Tomoko Kitaoka. New targeted therapy on SOCS1-related immune-response in triple-negative breast 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 5363.

Comprehensive Analysis Identifies Variability in PI3K Pathway Alterations in Triple-Negative Breast Cancer Subtypes.

The PI3K pathway is frequently altered in triple-negative breast cancer (TNBC). Limited cell line and human data suggest that TNBC tumors characterized as mesenchymal (M) and luminal androgen receptor (LAR) subtypes have increased incidence of alterations in the PI3K pathway. The impact of PI3K pathway alterations across TNBC subtypes is poorly understood. Pretreatment tumor was evaluated from operable TNBC patients enrolled on a clinical trial of neoadjuvant therapy (NAT; A Robust TNBC Evaluation fraMework to Improve Survival [ClinicalTrials.gov identifier: NCT02276443]). Tumors were characterized into seven TNBC subtypes per Pietenpol criteria (basal-like 1, basal-like 2, immunomodulatory, M, mesenchymal stem-like, LAR, and unstable). Using whole-exome sequencing, RNA sequencing, and immunohistochemistry for PTEN, alterations were identified in 32 genes known to activate the PI3K pathway. Alterations in each subtype were associated with pathologic response to NAT. In evaluated patients (N = 177), there was a significant difference in the incidence of PI3K pathway alterations across TNBC subtypes (P < .01). The highest incidence of alterations was seen in LAR (81%), BL2 (79%), and M (62%) subtypes. The odds ratio for pathologic complete response (pCR) in the presence of PIK3CA mutation, PTEN mutation, and/or PTEN loss was highest in the LAR subtype and lowest in the M subtype, but these findings did not reach statistical significance. Presence of PIK3CA mutation was associated with pCR in the LAR subtype (P = .02). PI3K pathway alteration can affect response to NAT in TNBC, and targeted agents may improve outcomes, particularly in patients with M and LAR TNBC.

Atezolizumab in Combination With Carboplatin and Survival Outcomes in Patients With Metastatic Triple-Negative Breast Cancer

Agents targeting programmed death ligand 1 (PD-L1) have demonstrated efficacy in triple-negative breast cancer (TNBC) when combined with chemotherapy and are now the standard of care in patients with PD-L1-positive metastatic disease. In contrast to microtubule-targeting agents, the effect of combining platinum compounds with programmed cell death 1 (PD-1)/PD-L1 immunotherapy has not been extensively determined. To evaluate the efficacy of atezolizumab with carboplatin in patients with metastatic TNBC. This phase 2 randomized clinical trial was conducted in 6 centers from August 2017 to June 2021. Patients with metastatic TNBC were randomized to receive carboplatin area under the curve (AUC) 6 alone or with atezolizumab, 1200 mg, every 3 weeks until disease progression or unacceptable toxic effects with a 3-year duration of follow-up. The primary end point was investigator-assessed progression-free survival (PFS). Secondary end points included overall response rate (ORR), clinical benefit rate (CBR), and overall survival (OS). Other objectives included correlation of response with tumor PD-L1 levels, tumor-infiltrating lymphocytes (TILs), tumor DNA- and RNA-sequenced biomarkers, TNBC subtyping, and multiplex analyses of immune markers. All 106 patients with metastatic TNBC who were enrolled were female with a mean (range) age of 55 (27-79) years, of which 12 (19%) identified as African American/Black, 1 (1%) as Asian, 73 (69%) as White, and 11 (10%) as unknown. Patients were randomized and received either carboplatin (n = 50) or carboplatin and atezolizumab (n = 56). The combination improved PFS (hazard ratio [HR], 0.66; 95% CI, 0.44-1.01; P = .05) from a median of 2.2 to 4.1 months, increased ORR from 8.0% (95% CI, 3.2%-18.8%) to 30.4% (95% CI, 19.9%-43.3%), increased CBR at 6 months from 18.0% (95% CI, 9.8%-30.1%) to 37.5% (95% CI, 26.0%-50.6%), and improved OS (HR, 0.60; 95% CI, 0.37-0.96; P = .03) from a median of 8.6 to 12.6 months. Subgroup analysis showed PD-L1-positive tumors did not benefit more from adding atezolizumab (HR, 0.62; 95% CI, 0.23-1.65; P = .35). Patients with high TILs (HR, 0.12; 95% CI, 0.30-0.50), high mutation burden (HR, 0.50; 95% CI, 0.23-1.06), and prior chemotherapy (HR, 0.59; 95% CI, 0.36-0.95) received greater benefit on the combination. Patients with obesity and patients with more than 125 mg/dL on-treatment blood glucose levels were associated with better PFS (HR, 0.35; 95% CI, 0.10-1.80) on the combination. TNBC subtypes benefited from adding atezolizumab, except the luminal androgen receptor subtype. In this randomized clinical trial, the addition of atezolizumab to carboplatin significantly improved survival of patients with metastatic TNBC regardless of PD-L1 status. Further, lower risk of disease progression was associated with increased TILs, higher mutation burden, obesity, and uncontrolled blood glucose levels. ClinicalTrials.gov Identifier: NCT03206203.

Molecular features and clinical implications of the heterogeneity in Chinese patients with HER2-low breast cancer

The molecular heterogeneity and distinct features of HER2-low breast cancers, particularly in the Chinese population, are not well understood, limiting its precise management in the era of antibody‒drug conjugates. To address this issue, we established a cohort of 434 Chinese patients with HER2-low breast cancer (433 female and one male) and integrated genomic, transcriptomic, proteomic, and metabolomic profiling data. In this cohort, HER2-low tumors are more distinguished from HER2-0 tumors in the hormone receptor–negative subgroup. Within HER2-low tumors, significant interpatient heterogeneity also exists in the hormone receptor–negative subgroup: basal-like tumors resemble HER2-0 disease, and non-basal-like HER2-low tumors mimic HER2-positive disease. These non-basal-like HER2-low tumors are enriched in the HER2-enriched subtype and the luminal androgen receptor subtype and feature PIK3CA mutation, FGFR4/PTK6/ERBB4 overexpression and lipid metabolism activation. Among hormone receptor–positive tumors, HER2-low tumors show less loss/deletion in 17q peaks than HER2-0 tumors. In this work, we reveal the heterogeneity of HER2-low breast cancers and emphasize the need for more precise stratification regarding hormone receptor status and molecular subtype.

Immunohistochemistry-based molecular subtyping of triple-negative breast cancer and its prognostic significance.

Background: Immunohistochemistry (IHC)-based protein markers representing molecular subtypes are of great value for routine use. This study aimed to evaluate the frequency distributions of the molecular subtypes of triple-negative breast cancer (TNBC) using IHC-based surrogate markers and examined their prognostic value. Methods: Patients with TNBC treated at a university hospital in Southern Thailand were included in this study. Expression levels of androgen receptor, CD8, Forkhead box transcription factor C1, and Doublecortin-like kinase 1 were detected in tumor tissue to classify them into luminal androgen receptor (LAR), immunomodulatory (IM), basal-like immunosuppressed (BLIS), mesenchymal-like (MES), and unclassifiable (UC) subtypes. The association between variables and disease-free survival (DFS) and overall survival (OS) was analyzed using Cox proportional hazards regression. Results: Among the 195 cases of TNBC, the frequency distribution of the IHC-based subtype was as follows: BLIS, 52.8%; LAR, 19.0%; IM, 17.4%; MES, 0.5%; and un-classifiable, 10.3%. BLIS subtype was significantly found in younger ages (mean: 49.6years) than other subtypes (mean: 51-57.7years). LAR and BLIS subtypes were significantly associated with poorer OS compared to the IM subtype in univariate analysis, however, only BLIS was significant in multivariate analysis (HR: 3.29, 95% CI: 1.01-10.72). IHC-based subtype was not found to be associated with DFS. Conclusion: This study revealed the differences in the proportion frequency of IHC-based TNBC subtypes in Thai patients compared to other populations. IHC-based molecular subtyping may be beneficial for prognosis. However further refinement of the molecular classification of TNBC is needed for better clinical relevance.

Abstract 5483: Combined inhibition of CDK4/6 and AKT is highly active against the luminal androgen receptor (LAR) subtype of triple negative breast cancer (TNBC)

Abstract The LAR subtype of TNBC is enriched for targetable biomarkers, including androgen receptor (AR) expression, PIK3CA mutations, and intact Rb. The purpose of this study was to investigate the most effective combinations of inhibitors of CDK4/6 (palbociclib), AR (enzalutamide), and PI3K-AKT (alpelisib/capivasertib) against preclinical models of LAR TNBC. MDA-MB-453 and MFM-223 (both AR positive/Rb-intact/PIK3CA-mutant) LAR TNBC cells were treated with each inhibitor alone or in different combinations. Drug sensitivity was measured as growth in 2D, colony formation, and CellTiterGlo viability. Synergistic drug effects were expressed as the combination index (CI) calculated by CompuSyn methods. Activation of cell cycle and PI3K-AKT signaling molecules in response to different inhibitors or siRNAs was measured by immunoblot analysis. An androgen response element (ARE) luciferase reporter assay was used to evaluate AR transcriptional activity. MDA-MB-453 and MFM-223 cells were sensitive to single-agent palbociclib, alpelisib, or capivasertib (IC50 ~500 nM) but not enzalutamide (IC50 15-25 µM). Palbociclib combined with either the PI3Kαi alpelisib or the AKTi capivasertib synergistically inhibited growth of both cell lines (CI values, 0.07-0.86). AR transcriptional reporter activity was not altered by any of these treatments. Treatment with palbociclib monotherapy (24 h) suppressed p-Rb and increased phosphorylation of AKTS473 and its substrates FOXO3A, GSK3β, and PRAS40, suggesting PI3K/AKT signaling mediates an adaptive response to CDK4/6 blockade. In MDA-MB-453 cells, palbociclib-induced phosphorylation of AKT substrates was suppressed by treatment with capivasertib but not with alpelisib alone or with the PI3Kβ/δ inhibitor AZD8186, suggesting that the compensatory activation of AKT was due to a mechanism independent of the PI3K isozymes. We next used RICTOR siRNAs to block mTORC2-mediated phosphorylation AKTS473 after palbociclib treatment. Gene silencing of RICTOR reduced levels of the mTORC2 substrate p-SGK1S422 but did not block phosphorylation of AKTS473 and its substrates in palbociclib-treated cells, suggesting that this adaptative response was mTORC2-independent. Mean CI values showed that the combination of palbociclib/capivasertib was clearly more synergistic than palbociclib/alpelisib in both cells lines (mean CI, 0.29 vs. 0.78). Currently, we are comparing both combinations in mice bearing established MDA-MB-453 xenografts. Further investigation of the mechanisms of adaptive activation of AKT upon blockade of CDK4/6 in TNBC cells are in progress. In sum, addition of an AKT inhibitor, but not PI3K inhibitors, to palbociclib suppressed the rebound activation of AKT following treatment with the CDK4/6i, supporting a testable therapeutic strategy in LAR TNBC with intact Rb. Citation Format: Maria del Rosario Chica-Parrado, Gun Min Kin, Chang-Ching Lin, Kyung-min Lee, Fabiana Napolitano, Dan Ye, Emmanuel Bikorimana, Saurabh Mendirata, Ariella Hanker, Carlos L. Arteaga. Combined inhibition of CDK4/6 and AKT is highly active against the luminal androgen receptor (LAR) subtype of triple negative breast cancer (TNBC). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5483.

Abstract P6-01-20: Luminal androgen receptor subtype and M2 macrophage signatures strongly associate with low pathological complete response rates and poor outcomes in patients with triple negative breast cancer receiving neoadjuvant chemotherapy

Abstract Background: Triple negative breast cancers (TNBC) are a heterogeneous group of cancers and it is difficult to predict which patients will respond to neoadjuvant chemotherapies (NACT). Achieving pathologic complete response (pCR) to NACT is prognostically favorable, whereas lack of pCR is associated with high rates of recurrence and death from TNBC. Currently, there is no universally accepted biomarker to predict TNBC response to NACT. Methods: We analyzed 25 in-house TNBC biopsies that were treated with neoadjuvant adriamycin (A), cyclophosphamide (C) and paclitaxel (T) and 31 residual TNBC after NACT-ACT using RNA-seq data from macro-dissected tumor tissues from formalin fixed paraffin embedded (FFPE) blocks. Raw reads were mapped to the Human reference genome GRCH38 using the kallisto aligner v0.46.1. Immune infiltrate fractions were estimated using the Cibersort algorithm derived from the LM22 gene-signature matrix of 22 hematopoietic cell types. TNBCtype-4 classification of samples was determined calculating the enrichment of gene-sets for: Luminal Androgen Receptor (LAR), Basal-like 1 and 2 (BL1, BL2), Mesenchymal(M). Overall immune-infiltrate analysis and cancer-intrinsic subtyping were conducted independently on each transcriptional profile. Results were validated by running our novel analyzing protocol in independent cohorts including 182 TNBC cases treated with NACT-ACT from a published Vanderbilt cohort and 179 TNBC cases from the TCGA database. Results: Twenty one (68%) of the 31 residual TNBC after neoadjuvant ACT were luminal androgen receptor (LAR) subtype and significantly enriched in M2 macrophage signature. The LAR subtype and monocyte or M2 macrophage signaturesstrongly associated with lack of pCR in the 25 TNBC biopsy cases and 182 Vanderbilt TNBC cases treated with NACT-ACT. Survival analysis of 179 TNBC cases from the TCGA database showed a significant association of LAR subtype and M2 macrophage signature with worse survival. Conclusions: We developed a novel RNA-seq analyzing protocol that combines tumor subtype and immune profile. The LAR subtype and M2 macrophage signatures strongly associated with lack of pCR and worse survival in TNBC patients when treated with NACT-ACT. Both tumor subtype and immune profile should be considered in biomarker development and further studied in specimens from patients treated with modern chemoimmunotherapy regimens. Citation Format: Jane Meisel, Eugene Douglass, Kevin Kalinsky, Lyra M. Griffiths, Zaibo Li, Xiaoxian Li. Luminal androgen receptor subtype and M2 macrophage signatures strongly associate with low pathological complete response rates and poor outcomes in patients with triple negative breast cancer receiving neoadjuvant chemotherapy [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-01-20.

Abstract P4-09-04: Correlation between histology and molecular subtypes in triple negative breast cancer

Abstract Correlation between histology and molecular subtypes in triple negative breast cancer Authors: Tabata Alves Domingos, MD; 1* Roberto Bonfim Pimenta Peixoto, MD; 1* Ashka Patel, BS1,2; Krishan Taneja, PhD; 1 Wendy Y. Chen, MD, MPH; 4,5,6 Elizabeth A. Mittendorf, MD, PhD; 5,6,7 Alexa Zimbalist, MS; 3 Elizabeth M. Cespedes Feliciano, ScD SM; 3 Deborah A. Dillon, MD 1,2 *equal contribution Author Affiliations 1. Department of Pathology, Brigham and Women’s Hospital, Boston, MA 02115 2. Breast Oncology, Dana-Farber Brigham Cancer Center, Boston, MA 02215 3. Division of Research, Kaiser Permanente Northern California, Oakland, CA 94612 4. Channing Division of Network Medicine, Brigham and Women’s Hospital, Boston, MA 02115 5. Department of Medical Oncology Dana Farber Cancer Institute, Boston, MA 02215 6. Harvard Medical School, Boston, MA 02215 7. Division of Breast Surgery, Brigham and Women’s Hospital, Boston, MA 02215 Background Recently defined molecular subtypes of triple negative breast cancer (TNBC) show distinct clinical outcomes and suggest new therapeutic targets but have not been integrated into current pathologic classification systems. Here, we describe the histopathologic features of TNBC according to four molecular subtypes: basal-like immune activated (BLIA), basal-like immune suppressed (BLIS), luminal androgen receptor (LAR) and mesenchymal (MES), classified using the NanoString BC360 gene expression assay. Methods Stage II and III invasive breast cancers were identified in the Kaiser Permanente (KP) clinical pathology archives (2005-2015) and triple negative status was determined from the KP Northern California Cancer Registry data on immunohistochemistry. Selected slides were reviewed by two pathologists who recorded key histopathologic features [histologic subtype, presence of apocrine, metaplastic or micropapillary features, nuclear grade, mitotic score, and Tumor Infiltrating Lymphocytes (TILs)] and marked the best tumor areas for molecular analysis. TILs were evaluated according to the guidelines of the International TILs Working Group. Cases were macrodissected and evaluated using the NanoString BC360 gene expression assay. Histologic features were then summarized according to molecular subtype. Results Of 72 TNBCs, 60 were classified as Basal-like (83.3%), 7 as HER2-enriched (9.7%) and 5 as Luminal A (6.9%). 41 cases were classified as BLIA (56.9%), 14 as BLIS (19.4%), 13 as LAR (18.0%) and 4 as MES (5.5%). Both BLIA and BLIS tumors showed uniformly high nuclear grade and high mitotic score but differed significantly in TILs (BLIA average 32% vs BLIS average 9%; p value&amp;lt; 0.001, t-test for mean difference in TILs). The majority of LAR cases (69%) showed apocrine differentiation, not present in any other molecular subtype (p value&amp;lt; 0.001, chi-square test for presence of apocrine differentiation). LAR cases showed high nuclear grade but a lower average mitotic score (average score of 2) compared with the basal-like subtypes. TILs in LAR tumors were intermediate (17%) between BLIA and BLIS tumors. Of the 4 MES cases, all showed high nuclear grade. TILs in the MES cases were also intermediate (14%) between BLIA and BLIS tumors. Other histologic features, including lobular subtype, metaplastic and micropapillary features were not associated with specific triple negative molecular subtypes. Conclusion TILs are high in the BLIA molecular subtype (average 32%), low in the BLIS subtype (average 9%) and intermediate in LAR (average 17%) and MES (average 14%) subtypes. Apocrine features, if present in a TNBC, are a strong predictor of LAR molecular subtype. The inclusion of TILs and apocrine features (both easily derived from H&amp;E slides) in routine pathology reporting could improve the classification of TNBC and aid in the identification of patients more likely to respond to specific therapies for the BLIA, BLIS and LAR subtypes, especially in resource-limited settings. Citation Format: Tabata Alves Domingos, Roberto Bonfim Pimenta Peixoto, Ashka Patel, Krishan Taneja, Wendy Y. Chen, Elizabeth A. Mittendorf, Alexa Zimbalist, Elizabeth M. Cespedes Feliciano, Deborah A. Dillon. Correlation between histology and molecular subtypes in triple negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-09-04.

Abstract P4-08-01: Targeting CDK7 enhances the antitumor efficacy of enzalutamide in androgen receptor-positive triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer. Among TNBC subtypes, the luminal androgen receptor (LAR) subtype expresses high levels of androgen receptor (AR), tends to be less proliferative, and generally responds poorly to neoadjuvant therapy. Previous studies have shown that AR inhibition suppressed proliferation of AR+ or LAR subtype TNBC cells and tumor growth in xenograft models. Thus, AR is a promising therapeutic target for this TNBC subtype. Here, we identified kinase targets for enhancing the antitumor efficacy of the AR inhibitor enzalutamide in preclinical models and investigated the underlying molecular mechanisms. Methods: We performed a nonbiased high-throughput kinome siRNA screening (targeting 709 genes) to identify a synergistic partner for enhancing the antitumor efficacy of the AR inhibitor enzalutamide in AR+ LAR TNBC. The growth inhibitory effects of enzalutamide alone or combined with kinase inhibitors were determined using the sulforhodamine B staining assay and clonogenic assay. The effect of treatments on the expression of target proteins of interest was examined by Western blot analysis. Results: Enzalutamide was not effective as a single agent to inhibit the proliferation of AR+ TNBC cells (IC50 &amp;gt;15 µM in MDA-MB-453, CAL-51, CAL-148, MFM223, HCC2185, SUM149, SUM159, and SUM185 cells). Nonbiased high-throughput kinome siRNA screening identified PI3K/AKT/mTOR, cell cycle, and JNK pathways as potential canonical targets for combination with enzalutamide to enhance its antitumor efficacy in AR+ LAR TNBC. Among these pathways, inhibition of cell cycle progression using the CDK7 inhibitor UD-017 showed the most synergistic anti-proliferation effect with enzalutamide in AR+ LAR MDA-MB-453 (50.61% reduction in proliferation compared with enzalutamide alone, P &amp;lt; 0.001; and 48.98% reduction in proliferation compared with UD-017 alone, P &amp;lt; 0.001) and SUM185 (40.41% reduction in proliferation compared with enzalutamide alone, P &amp;lt; 0.05; and 42.76% reduction in proliferation compared with UD-017 alone, P &amp;lt; 0.05) TNBC cells. Furthermore, CDK7 knockdown using siRNA significantly enhanced the sensitivity of MDA-MB-453 (60.98%, P &amp;lt; 0.01) and SUM185 (30.99%, P &amp;lt; 0.01) cells to enzalutamide, and AR knockdown significantly enhanced the sensitivity of MDA-MB-453 (32.64%, P &amp;lt; 0.01) and SUM185 (43.62%, P &amp;lt; 0.01) cells to UD-017, in both cases with a sensitivity similar to that of enzalutamide plus UD-017. This result suggests that the synergy of enzalutamide and UD-017 results from specific targeting of AR and CDK7. Downstream target analysis revealed that the combination of enzalutamide and UD-017 dramatically reduced the expression of c-MYC. c-MYC knockdown using siRNA dramatically suppressed colony formation in both MDA-MB-453 and SUM185 cells at a degree similar to that of enzalutamide plus UD-017, whereas c-MYC overexpression reversed the synergistic effect of the combination treatment. This result suggests that UD-017 synergizes with enzalutamide through inhibition of c-MYC–mediated tumorigenesis. Conclusion: Our results suggest that enzalutamide synergizes with UD-017 by inhibiting c-MYC–mediated oncogenic activity. These in vitro data warrant future in vivo studies of the antitumor synergy of enzalutamide plus UD-017 in AR+ LAR TNBC models. Citation Format: Xuemei Xie, Marwa Manai, Jon A. Fuson, Troy Pearson, Dileep R. Rampa, Debu Tripathy, Jangsoon Lee, Naoto T. Ueno. Targeting CDK7 enhances the antitumor efficacy of enzalutamide in androgen receptor-positive triple-negative breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-01.

Abstract PD9-02: MHC class I and PD-L1 expression in triple-negative breast cancer subtypes: impact on T-cell infiltration and clinical outcome

Abstract Background: Triple-negative breast cancer (TNBC) is a heterogeneous group of cancer with dismal prognosis. In an effort to discover therapeutic targets, TNBC has been further stratified into molecular subtypes. Immune checkpoint inhibitors targeting programmed cell death protein 1 (PD-1) and its ligand (PD-L1) have been increasingly utilized for the treatment of TNBC. Difficulty remains, however, in appropriate patient selection for treatment, as many PD-L1-positive cancers fail to show durable responses to PD-1/PD-L1 inhibition. Major histocompatibility complex (MHC) class I molecules play a crucial role in the presentation of tumor antigenic peptides to cytotoxic T cells. Loss of MHC class I expression in tumor cells represents a possible mechanism of immunotherapeutic resistance in PD-L1-positive cancers. However, little is known about the clinical impact and value of MHC class I expression in TNBC subtypes. Thus, this study examined MHC class I expression in TNBC subtypes with attention to PD-L1 expression and T cell infiltration. Materials and methods: MHC class I and PD-L1 expression were assessed by immunohistochemistry in 256 TNBC samples using tissue microarray. Immunohistochemistry for the TNBC molecular subtype-surrogate markers [cytokeratin 5/6 (CK5/6), CK14, epidermal growth factor receptor (EGFR), and androgen receptor (AR)], CD3, and CD8 was also performed. TNBC subtypes were classified into three subtypes: basal-like (BL), luminal AR (LAR), and unclassifiable type (UN). Results: All immunohistochemical markers were interpretable in 240 cases. TNBCs were classified into BL (65.8%), LAR (11.3%), and UN (22.9%) subtypes. Loss of MHC class I expression was found in 62 of 240 (25.8%) cases and was observed in 23.4% of BL, 40.7% of LAR, and 25.9% of UN subtype. PD-L1 expression in tumor-associated immune cells (≥1%) was seen in 69.2% (166/240). Among 166 PD-L1-positive TNBC cases, loss of MHC class I expression was seen in 16.4% of BL, 31.3% of LAR, and 20.0% of UN subtype. Loss of MHC class I expression was associated with low stromal TILs density and low CD3+ and CD8+ T-cell infiltration in BL subtype. CD3+ and CD8+ T-cell infiltration in TNBC subtype had a positive correlation with PD-L1 expression. In PD-L1 positive BL subtype, MHC class I lost expression showed a lower infiltration with CD3+ and CD8+ T-cells than MHC class I intact expression. In BL subtype, PD-L1 expression was associated with better disease-free survival and loss of MHC class I expression was associated with poor overall survival. However, MHC class I and PD-L1 expressions were not independent prognostic factors for disease-free or overall survival. Conclusions: Loss of MHC class I expression was found in TNBC, including PD-L1 positive cases. In PD-L1 positive BL subtype, loss of MHC class I expression was associated with low CD3 and CD8+ T-cell infiltration. Our results suggest that the evaluation of PD-L1 and MHC class I expression together is very important for the selection of potential responders to anti-PD-1/PD-L1 therapy for the TNBCs, especially the BL subtype. Citation Format: ji shin lee, nah ihm kim, min ho park. MHC class I and PD-L1 expression in triple-negative breast cancer subtypes: impact on T-cell infiltration and clinical outcome [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD9-02.

AKR1C2 Promotes Metastasis and Regulates the Molecular Features of Luminal Androgen Receptor Subtype in Triple Negative Breast Cancer Cells.

Patients with triple-negative breast cancer (TNBC) have an increased risk of distant metastasis compared to those with other subtypes. In this study, we aimed to identify the genes associated with distant metastasis in TNBC and their underlying mechanisms. We established patient-derived xenograft (PDX) models using surgically resected breast cancer tissues from 31 patients with TNBC. Among these, 15 patients subsequently developed distant metastases. Candidate metastasis-associated genes were identified using RNA sequencing. In vitro wound healing, proliferation, migration, and invasion assays and in vivo tumor xenograft and metastasis assays were performed to determine the functional importance of aldo-keto reductase family 1 member C2 (AKR1C2). Additionally, we used the METABRIC dataset to investigate the potential role of AKR1C2 in regulating TNBC subtypes and their downstream signaling activities. RNA sequencing of primary and PDX tumors showed that genes involved in steroid hormone biosynthesis, including AKR1C2, were significantly upregulated in patients who subsequently developed metastasis. In vitro and in vivo assays showed that silencing of AKR1C2 resulted in reduced cell proliferation, migration, invasion, tumor growth, and incidence of lung metastasis. AKR1C2 was upregulated in the luminal androgen receptor (LAR) subtype of TNBC in the METABRIC dataset, and AKR1C2 silencing resulted in the downregulation of LAR classifier genes in TNBC cell lines. The androgen receptor (AR) gene was a downstream mediator of AKR1C2-associated phenotypes in TNBC cells. AKR1C2 expression was associated with gene expression pathways that regulate AR expression, including JAK-STAT signaling or interleukin 6 (IL-6). The levels of phospho-signal transducer and activator of transcription and IL-6, along with secreted IL-6, were significantly downregulated in AKR1C2-silenced TNBC cells. Our data indicate that AKR1C2 is an important regulator of cancer growth and metastasis in TNBC and may be a critical determinant of LAR subtype features.

Prognostic Capability of TNBC 3-Gene Score among Triple-Negative Breast Cancer Subtypes.

Simple SummaryIn this study we evaluated the prognostic capability of the 3-gene score in the molecular subtypes of triple negative breast cancer and found that the score was able to predict the risk of distant recurrence in the immunomodulatory and mesenchymal stem-like subtypes. Additionally, a low 3-gene score was related to a high level of tumor-infiltrating lymphocytes. Our findings suggest that the prognostic capability of the 3-gene score is associated to tumor-infiltrating components.Background: Triple-negative breast cancer (TNBC) is a complex and molecularly heterogeneous entity, with the poorest outcome compared with other breast cancer subtypes. Previously, we developed a TNBC 3-gene score with a significant prognostic capability. This study aims to test the 3-gene score in the different TNBC subtypes. Methods: Data from 204 TNBC patients treated with neoadjuvant chemotherapy were retrieved from public datasets and pooled (GSE25066, GSE58812, and GSE16446). After removing batch effects, cases were classified into Lehman’s TNBC subtypes and then the TNBC 3-gene score was used to evaluate the risk of distant recurrence in each subgroup. In addition, the association with tumor-infiltrating lymphocyte (TILs) levels was evaluated in a retrospective group of 72 TNBC cases. Results: The TNBC 3-gene score was able to discriminate patients with different risks within the pooled cohort (HR = 2.41 for high vs. low risk; 95%CI: 1.50–3.86). The score showed predictive capability in the immunomodulatory subtype (HR = 4.16; 95%CI: 1.63–10.60) and in the mesenchymal stem-like subtype (HR = 18.76; 95%CI: 1.68–208.97). In the basal-like 1, basal-like-2, and mesenchymal subtypes, the observed differential risk patterns showed no statistical significance. The score had poor predictive capability in the luminal androgen receptor subtype (p = 0.765). In addition, a low TNBC 3-gene score was related to a high level of TIL infiltration (p < 0.001). Conclusions: The TNBC 3-gene score is able to predict the risk of distant recurrence in TNBC patients, specifically in the immunomodulatory and mesenchymal stem-like subtype. Despite a small sample size in each subgroup, an improved prognostic capability was seen in TNBC subtypes with tumor-infiltrating components.

Luminal androgen receptor (LAR) subtype of triple-negative breast cancer: molecular, morphological, and clinical features.

According to the classification presented by Lehmann BD (2016), triple-negative breast cancer (TNBC) is a heterogeneous group of malignant tumors with four specific subtypes: basal-like (subtype 1 and subtype 2), mesenchymal, and luminal androgen receptor (LAR) subtypes. The basal-like subtypes of carcinomas predominate in this group, accounting for up to 80% of all cases. Despite the significantly lower proportions of mesenchymal and LAR variants in the group of breast carcinomas with a TNBC profile, such tumors are characterized by aggressive biological behavior. To this end, the LAR subtype is of particular interest, since the literature on such tumors presents different and even contradictory data concerning the disease course and prognosis. This review is devoted to the analysis of the relevant literature, reflecting the main results of studies on the molecular properties and clinical features of the disease course of LAR-type TNBC carcinomas.

Integrative analysis of LncRNA-mRNA signature reveals a functional LincRNA in triple-negative breast cancer

PurposeTriple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer. It is still unclear that the mechanisms by which long non-coding RNA (lncRNA) regulates tumorigenesis of TNBC. In this study, we explored the function and regulation of lncRNA in TNBC.MethodsThe differentially expressed and overlapped lncRNAs were obtained from two microarray datasets of breast cancer. The cancer genome atlas (TCGA) data was applied to validate the roles of top differentially expressed lncRNAs. The potential relationship among lncRNAs, miRNAs, and mRNAs and the effects of them on the TNBC tumorigenesis were further explored through multiple bioinformatic methods.ResultsLong intergenic non-protein coding RNA 1351 (LINC01351) was first discovered to play an oncogenic role in TNBC. The highly expressed LINC01351 was significantly related to aggressive subtypes, advanced stages and metastasis of breast cancer. The overexpressed LINC01351 was associated with adverse prognosis of patients with TNBC. LINC01351 was found to negatively regulate ELK4 which was involved in the transcriptional regulation in cancer. The high expression of ELK4 showed favorable prognosis of patients with basal-like 1 subtype and luminal androgen receptor subtype of TNBC.ConclusionThe dysregulation of LINC01351 played an important role in triple-negative breast cancer. LINC01351 could be a poor prognostic marker and a potential target for patients with TNBC.

Abstract 2542: Unraveling heterogeneity of tumor microenvironment of TNBC patients by meta-analysis of 6 breast cancer scRNAseq studies

Abstract Breast cancer can be classified into several types. Among them, triple-negative breast cancer (TNBC) is breast cancer that does not express estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Since targeted therapy for breast cancer relies on the three receptors, treatment outcomes have been worst in TNBCs. However, clinical benefit of immune-checkpoint inhibitors (ICIs) with chemotherapy over chemotherapy alone was demonstrated in the KEYNOTE-355 and IMPASSION-130 trials in terms of overall survival, opening new avenue for patients with metastatic PD-L1+ TNBC. After several studies with ICIs, researchers found that the tumor microenvironment affects the response rate of immunotherapies. Therefore, to unravel the heterogeneity of tumor microenvironment of TNBC patients, we collected 28 TNBC samples from 6 public single cell RNA sequencing breast cancer studies. Results: From 124,301 cells populating tumors and tumor-microenvironment (TMEs), we first identified epithelial cells separately. Using epithelial cells alone, we identified the Baylor-proposed TNBC molecular subtype of each patient. This approach with epithelial cells revealed that 3 basal-like immune-activated (BLIA), 11 basal-like immune-suppressed (BLIS), 5 luminal- androgen receptor (LAR), and 9 unclassified subtypes. By comparing cell number and cell-cell interactions, the heterogeneity of TME-consisting cell populations between the TNBC subtypes was analyzed. Analysis of tumor-infiltrating lymphocytes revealed their difference in activation, expansion, and exhaustion programs across patients. Among the subtypes, the LAR subtype had less amount of exhausted CD8+ T cells and regulatory T cells. This finding was consistent with cell-cell interaction analysis. In the case of the LAR subtype, the interaction between regulatory T cells and CD8 T cells was less active than other subtypes. Also, the interaction between cytotoxic cells (T cells and NK cells) and regulatory T cells was less active in the LAR subtype. Additionally, tumor cells in the LAR subtype seem to inhibit cytotoxic cells to a lesser extent. When we repeated our analyses using whole cells including epithelial and immune-stromal cells, the molecular subtypes of each subject were changed (7 of 19, 36.8%). 4 of 11 BLIS were changed to BLIA, 1 of 11 BLIS were changed to mesenchymal (MES), and 2 of 5 LAR were changed to MES. Characteristics of immune cells in the epithelial-based LAR subtype were conserved in the whole cells-based MES. Conclusions:This extensive meta-analysis of public single cell RNA sequencing analysis enhances our knowledge about the heterogeneity and dynamics of the tumor microenvironment. These results offer insights about potential diagnostic and therapeutic targets for TNBC depending on their subtypes. Citation Format: Kyungsoo Kim, Sung Gwe Ahn, Soong June Bae, Chihhao Chu, Jung Hwan Ji, Jee Hung Kim, Joon Jeong. Unraveling heterogeneity of tumor microenvironment of TNBC patients by meta-analysis of 6 breast cancer scRNAseq studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2542.

Abstract 967: γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple negative breast cancer (TNBC) MBA-MB-231 and MDA-MB-453 cells is associated with a reduction in epithelial-to-mesenchymal transition (EMT)

Abstract Triple-negative breast cancers (TNBC) are a subset of breast cancer that is highly aggressive and has a poor prognosis. The TNBC subtype has no effective molecular targeted therapies. Gene expression studies have identified a subset of TNBC that is enriched with androgen receptors (AR) and androgen receptor signaling. AR levels are most abundant in the luminal AR (LAR) molecular subtype of TNBC, but other non-LAR molecular TNBC subtypes also display high levels of AR expression and activity. Interference with androgen signaling in TNBC with AR-inhibiting drugs have shown a reduction in epithelial-to-mesenchymal transition (EMT), which is a process by which epithelial cells lose their cell polarity and cell-cell adhesion and gain migratory and invasive properties to become mesenchymal-like stem cells. Approximately one-third of TNBC expressed AR, and evaluation of AR-positive TNBC primary tumors shows nuclear localization of AR, an indication of transcriptionally active receptors. Previous studies have shown that AR inhibition or AR knockdown significantly reduces migration and invasion and EMT in different TNBC cell lines. γ-Tocotrienol is a member of the vitamin E family of compounds that displays potent anticancer effects and have little or no effect on normal cell viability. Studies show that treatment with 0-7 µM γ-tocotrienol reduced AR levels, proliferation, migration and invasion in a dose-responsive manner in TNBC MDA-MB-231 and MDA MB-453 cell lines. Results also show that treatment with 5 µM (MDA-MB-231) and 7 µM (MDA-MB-453) γ-tocotrienol induced a reversal in EMT cell biomarkers, as well as reversal in EMT morphological and behavioral characteristics in these TNBC cell lines. Western blot analysis show that similar treatment with γ-tocotrienol significantly decreased DHT-induced N-cadherin (mesenchymal cell biomarker) and increased expression in cytokeratin 18 and E-cadherin (epithelial cell biomarkers) in these cells. AR signaling is known to play an important role in stimulating DHT-induced EMT by stimulating the STAT3/Snail signaling pathway in MDA-MB231. However, results in the present study shows that γ-tocotrienol treatment significantly inhibited activation of STAT3 and Snail proteins. Additional immunocytochemistry experiments showed that γ-tocotrienol treatment significantly inhibited DHT-induced cytoskeleton changes in TNBC MDA-MB-231 and MDA MB-453 cell lines. In conclusion, these results demonstrated that γ-tocotrienol treatment inhibits AR expression and DHT-dependent EMT and cytoskeleton changes in TNBC cells. These findings suggest that AR may be a potential therapeutic target for treating both LAR and non-LAR TNBC subtypes. This study was supported in part by funding from the Louisiana Cancer Foundation. Citation Format: Nayef Aldabaan, Tasmin A. Sultana, Paul W. Sylvester. γ-Tocotrienol inhibition of androgen receptor (AR) expression and activation in triple negative breast cancer (TNBC) MBA-MB-231 and MDA-MB-453 cells is associated with a reduction in epithelial-to-mesenchymal transition (EMT) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 967.