Lucas, Peter C.

Abstract Invasive lobular breast carcinoma (ILC) is the most common special histological subtype of breast cancer, which accounts for 10-15% of all cases. To study the phenotype characteristics, metastatic growth kinetic and immune microenvironment of ILC, we developed an orthotopically transplantable cell line model from the spontaneous mammary fat pad tumor of CDH1-PTEN dual knockout C57BL/6 mouse with Cre-loxP system, designated CPT6. CPT6 recapitulates single-file growth pattern of human ILC, with pleomorphic features and a high mitotic index. RNA sequencing together with whole exome sequencing reveals a luminal A subtype with targetable driver mutations such as Kras G12C. As a novel orthotopically transplantable ILC model in immune competent mice, CPT6 shows robust in vivo growth and metastatic rate, and has moderate immunogenicity which appears to be T-cell independent. We also profiled the immune microenvironment of CPT6, revealing a myeloid-rich environment with dominant M2-macrophage population, which is concordant with human ILC. In summary, this model recapitulates human ILC phenotype and represents a valuable preclinical platform for evaluating immunotherapy and other therapeutic strategies for invasive lobular breast carcinoma.

Abstract Treatment resistance and metastases occur in 10–20% of patients with invasive lobular carcinoma (ILC), the most common special histological subtype of breast cancer. ILC metastasizes to the ovary more frequently than no special type (NST) tumors, also known as invasive ductal carcinoma (IDC). To characterize the genomic landscape of breast cancer ovarian metastases, we analyzed 15,613 local breast cancers, 22,010 non-ovarian metastases, and 246 ovarian metastases sequenced using FoundationOne®CDx or FoundationOne® assays. Ovarian metastases had enriched CDH1 , PIK3CA , and TBX3 mutations and depleted TP53 and MYC alterations relative to local breast cancers, with additional depletion of ESR1 mutations compared to non-ovarian metastases. CDH1 mutations were less frequent in ovarian metastases (47%) than local ILC (81.3%), with reduced 16q loss (64% vs 84%), indicating that ovarian metastases also arise from non-ILC tumors. We extended these findings to a UPMC cohort of 27 ovarian metastases (13 ILC, 8 IDC, 6 mixed ductal-lobular carcinoma) with patient-matched primary tumors in most cases. In both cohorts, patients with ovarian metastases were significantly younger than those with other metastatic sites. In the UPMC cohort, the most frequent mutations were in PIK3CA , CDH1 , KMT2C , FOXA1 , and RUNX1 . Transcriptomic analysis identified upregulated G protein-coupled receptor (GPCR) pathways, including metabotropic glutamate receptor signaling. Functional studies showed that calcium-sensing receptor (CaSR), a GPCR overexpressed in ovarian metastases, drives MEK/ERK-dependent migration and F-actin reorganization in ILC cell lines, enhanced by estrogen and blocked by calcilytic, MEK, or anti- estrogen treatment. Our findings inform future therapeutic targeting of ovarian metastasis.

Abstract Background: Antigen receptor stimulation induces assembly of the CARMA1-BCL10-MALT1 (CBM) signaling complex, which leads to activation of downstream transcriptional regulators including NF-κB and subsequent lymphocyte activation. Gain-of-function mutations in B-cell receptor subunits, CARMA1, or BCL10 which lead to constitutive activation of MALT1 underly the pathogenesis of multiple lymphoid malignancies, including activated B-cell–type diffuse large B-cell lymphoma (ABC-DLBCL). During previous efforts to identify regulators of MALT1 activity in lymphocytes, we discovered that G-protein-coupled receptor kinase 2 (GRK2) binds to MALT1, inhibits MALT1 scaffolding and proteolytic activities, and functions as a tumor suppressor in MALT1-dependent lymphomas. Notably, GRK2 mRNA expression is markedly lower in a subset of DLBCL tumors in comparison to normal B cells and lower GRK2 is associated with decreased patient survival in ABC-DLBCL. In light of these findings, we investigated the molecular mechanisms regulating GRK2 expression and then characterized the roles of specific GRK2-targeting miRNAs in ABC-DLBCL. Methods and Results: After finding that global impairment of miRNA processing through DICER1 depletion leads to increased GRK2 protein, we conducted bioinformatic analyses of patient tumor samples and microRNA Data Integration Portal screening to identify candidate microRNAs that target GRK2 in ABC-DLBCL. Direct targeting of GRK2 by candidate miRNAs was then confirmed by GRK2 3’UTR reporter assay. We tested for expression of three candidate microRNAs in ABC-DLBCL cells and observed elevated expression in both OCI-LY3 and TMD8 cells, which exhibited reduced GRK2 mRNA expression compared with primary B cells. Inhibition of candidate miRNAs in ABC-DLBCL cells, using anti-miRNA Locked Nucleic Acids (LNA) inhibitors, led to enhanced GRK2 expression, reduced MALT1 activity and decreased cell proliferation. Conversely, stable overexpression of candidate microRNAs led to reduced GRK2 expression, enhanced MALT1 activity and increased cell proliferation. In vivo, treatment of mice with inhibitors of candidate microRNAs abrogates the growth of ABC-DLBCL xenograft tumors. Conclusion: We have identified three miRNAs that negatively regulate GRK2 expression in ABC-DLBCL. By targeting GRK2 for downregulation, these miRNAs promote MALT1 oncoprotein scaffold and protease activities. Furthermore, inhibitors of these miRNAs enhance GRK2 expression and thereby suppress MALT1 activity and MALT1-dependent tumor cell proliferation in vitro and inhibit MALT1-dependent tumor growth in vivo. MicroRNA inhibitors that enhance GRK2 expression could represent a new approach for restraining MALT1-dependent lymphoma. Citation Format: Jing Cheng, Mei Smyers, Matt Trotta, Neil M. Carleton, Lisa M. Maurer, Uma R. Chandran, Min Xia, Ari M. Melnick, Peter C. Lucas, Linda M. McAllister-Lucas. Inhibitors of GRK2-targeting-microRNAs: New therapeutic strategies for MALT1-dependent lymphomas [abstract]. In: Proceedings of the Fifth AACR International Meeting on Advances in Malignant Lymphoma: From Discovery to Clinical Impact; 2026 Jun 24-27; Philadelphia, PA. Philadelphia (PA): AACR; Blood Cancer Discov 2026;7(3_Suppl):Abstract nr A033.

Abstract Background: Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer and remains difficult to treat due to the absence of targeted therapies. While recent advances in immunotherapy, particularly with immune checkpoint inhibitors (ICIs), have transformed the treatment landscape for many cancers, response rates to ICIs remain low for TNBC, largely due to tumor-intrinsic immune evasion mechanisms. Objective: We identify and characterize a novel immune evasion pathway in TNBC driven by deregulation of cancer cell-intrinsic protease-activated receptor 1 (PAR1), a thrombin receptor frequently upregulated in aggressive tumors. Methods and Results: Through integrative bioinformatic analyses, genetic perturbations, xenograft models (immunodeficient and immunocompetent), flow cytometry-based tumor immune profiling, and RNA-seq, we demonstrate that PAR1 activation enhances immune evasion in TNBC. Mechanistically, we show that the paracaspase MALT1 acts as a critical downstream effector of PAR1 signaling and promotes immune escape by driving PD-L1 expression in TNBC cells. Functional assays reveal that genetic depletion of MALT1 or PD-L1 increases TNBC cell susceptibility to T cell-mediated cytotoxicity in vitro and significantly suppresses tumor growth in vivo. Notably, through knock-in and rescue experiments using a catalytically inactive MALT1 mutant, we reveal that MALT1’s scaffolding - rather than protease - function is essential for PD-L1 regulation. Immune cell depletion assays further identify CD4+ T cells, CD8+ T cells, and natural killer (NK) cells as key mediators of the anti-tumor immune response suppressed by the PAR1-MALT1 axis. These findings are supported by human TNBC specimen analyses, where MALT1 expression inversely correlates with T cell activation and positively associates with PD-L1 in PAR1-high, but not PAR1-low, tumors. Conclusion: Our study reveals immune evasion as a novel mechanism of PAR1-driven breast cancer pathogenesis, mediated by a PAR1/MALT1/PD-L1 signaling cascade. These findings bridge a critical gap by positioning MALT1 at the interface between tumor-intrinsic signaling and the immune microenvironment - two areas of CARMA-BCL10-MALT1 (CBM) complex research that have largely evolved in parallel over the years. Importantly, targeting MALT1 may enhance immunotherapy efficacy in TNBC. Given the availability of MALT1 inhibitors in clinical development, our work supports combining MALT1 inhibition with ICIs or other immune-oncology agents as a promising strategy to overcome immune resistance in TNBC. Citation Format: Dong Hu, Prasanna Ekambaram, Zheqi Li, Linda Klei, Maria L. Beecher, Yi Liu, Zongyou Cai, John Little, Jeffrey A. Meridew, Jia-Ying Lee, E. Aubrey Thompson, Tullia C. Bruno, Lidija Covic, Seung-Oe Lim, Anushka Dongre, Heide L. Ford, Mien-Chie Hung, Adrian V. Lee, Steffi Oesterreich, Linda McAllister-Lucas, Peter C. Lucas. A cancer cell-intrinsic PAR1/MALT1/PD-L1 signaling pathway drives immune evasion in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 7392.

Abstract Introduction/Objectives: The CARMA1-BCL10-MALT1 (CBM) signalosome plays crucial role in mediating antigen receptor-induced activation of NF-κB transcription factor and subsequent lymphocyte activation. The effector protein of the signalosome, MALT1, functions both as a scaffold to recruit downstream NF-κB signaling machinery, and as a protease to cleave and inactivate multiple substrates including negative regulators of NF-κB. Constitutive MALT1 activation, which can occur as a result of gain-of-function mutations of the B cell receptor, CARMA1, BCL10 or chromosomal translocation involving the MALT1 gene, underlies the pathogenesis of multiple lymphoid malignancies including activated B-cell type-diffuse large B-cell lymphoma (ABC-DLBCL) and MALT lymphoma. We previously identified G-protein-coupled receptor kinase 2 (GRK2) as a tumor suppressor in MALT1-dependent lymphomas which binds MALT1 and inhibits MALT1 scaffolding and proteolytic activities. Accordingly, GRK2 mRNA levels are markedly lower in a subset of DLBCL tumors compared to normal B cells and lower GRK2 level in ABC-DLBCL is associated with reduced patient survival. In current study, we sought to investigate the mechanism of how GRK2 levels are regulated in ABC-DLBCL. Methods/Results: Using DICER1 depleted cells, we showed that globally impaired miRNA processing leads to increased GRK2 protein levels. We then conducted bioinformatic analyses of patient tumor samples and performed screening via microRNA Data Integration Portal to identify microRNAs that target GRK2 in ABC-DLBCL. Further GRK2 3’UTR reporter assay confirmed direct targeting of GRK2 by candidate miRNAs. ABC-DLBCL cell lines, OCI-LY3 and TMD8, which demonstrate reduced GRK2 mRNA expression compared to primary B cells, show elevated expression of candidate GRK2-targeting microRNAs. Stable overexpression of miR-125a, 125b, or 148b in OCI-LY3 or TMD8 cells led to reduced GRK2 expression, enhanced MALT1 activity and increased cell proliferation. Conversely, in vitro inhibition of candidate miRNAs using anti-miRNA Locked Nucleic Acids (LNA) inhibitors led to enhanced GRK2 expression, reduced MALT1 activity and decreased cell proliferation. Importantly, treatment of mice with inhibitors of miR-125b and miR-148b abrogates the growth of ABC-DLBCL xenograft tumors in vivo. Conclusion: We have identified miRNAs that negatively regulate GRK2 expression in ABC-DLBCL. These GRK2-targeting miRNAs serve a pro-tumorigenic role by promoting MALT1 oncoprotein’s scaffold and protease activity. Furthermore, inhibitors of these miRNAs can enhance GRK2 expression and thereby suppress MALT1 activity and MALT1-dependent tumor cell proliferation, both in vitro and in vivo. These studies suggest that microRNA inhibitors which enhance GRK2 expression could represent a novel approach for restraining MALT1-dependent lymphomagenesis. Citation Format: Jing Cheng, Mei Smyers, Matt Trotta, Neil M. Carleton, Lisa M. Maurer, Uma R. Chandran, Min Xia, Ari M. Melnick, Peter C. Lucas, Linda M. McAllister-Lucas. MicroRNAs targeting tumor suppressor GRK2: Novel potential therapeutic strategies for restraining MALT1-dependent DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2061.

Abstract Background: Spatial cellular ecosystems in the tumor microenvironment (TME) form dynamic signaling hubs that critically influence cancer disease progression and response to therapy, including response to immune checkpoint inhibitors (ICIs). However, tumor sampling bias and the impracticality of acquiring serial tumor biopsies have made it challenging to profile the TME clinically. To address this challenge, we developed Liquid EcoTyper, a multi-analyte AI framework to quantify TME spatial cellular ecosystems—termed spatial ecotypes (SEs)—noninvasively from cell-free DNA (cfDNA) methylation data. Methods: In previous work, we discovered nine spatial ecotypes, including SEs associated with ICI response (e.g., SE7 with benefit, SE4 with resistance), and quantified them from 1,249 bulk tumor RNA-seq profiles of melanoma, non-small cell lung cancer (NSCLC), and bladder cancer (BC) patients (Cancer Res (2025) 85 (8_Supplement_1): 153). Here we trained Liquid EcoTyper, an interpretable deep learning model, to transfer SE profiling to cell-free DNA using CpG methylation profiles. Performance was quantified using simulated and real data, including methylation profiles (EM-seq) of plasma cfDNA paired with tumor biopsy-derived SE levels determined by EM-seq (n=20 pairs) or 10x Visium (n=15 pairs). Clinical outcome prediction was evaluated using pretreatment plasma from patients treated with ICI alone (n=78 melanoma pts), chemotherapy and ICI (n=25 NSCLC pts), and enfortumab vedotin and ICI (n=10 localized muscle-invasive BC (MIBC) pts). Tumor mutational burden (TMB), tumor PD-L1, or circulating tumor DNA (ctDNA) were profiled as a comparator where possible. Results: We observed striking concordance between plasma-derived SE levels and tumor biopsy-confirmed SE levels from the same patients, demonstrating that liquid biopsy analysis of cfDNA methylomes can recapitulate TME spatial biology. Underscoring specificity, no reliable SE signal was detectable from peripheral blood mononuclear cells. In pre-ICI plasma, liquid SE levels were significantly associated with ICI-based response (SE7) versus resistance (SE4) in patients with melanoma, NSCLC, and MIBC, with a mean cross-cancer area under the curve (AUC) of 0.87 for SE7 (range 0.8-0.97) and 0.81 for SE4 (range 0.76-0.85)—far surpassing TMB, tumor PD-L1, and ctDNA in evaluable patients, both in binary analyses of response and multivariable models of survival. Our results also showed potential to predict pathologic complete response in the neoadjuvant setting. Conclusion: Liquid EcoTyper is a scalable noninvasive AI-based framework for spatiotemporal assessment of the TME. By enabling TME-informed risk stratification without surgical biopsies, Liquid EcoTyper has potential to enable more precise and actionable decision making in patients with solid tumors. Citation Format: Erin L. Brown, Wubing Zhang, Abul Usmani, Noah Earland, Ayesha Hashmi, Chibuzor Olelewe, Anushka Viswanathan, Pradeep S. Chauhan, Minji Kang, Chloé B. Steen, Hyun Soo Jeon, Susanna Avagyan, Irfan Alahi, Nicholas P. Semenkovich, Matteo Bergsagel, Janella C. Schwab, Chloe M. Sachs, Faridi Qaium, Peter K. Harris, Antonella Bacchiocchi, Qingyuan Cai, Andrew J. Gentles, Rondell P. Graham, Peter C. Lucas, Ryan C. Fields, Jacob J. Orme, Aaron S. Mansfield, Mario Sznol, Ruth Halaban, David Y. Chen, Aaron M. Newman, Aadel A. Chaudhuri. Liquid biopsy profiling of the tumor microenvironment to determine response to immunotherapy regimens across solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 94.

Invasive lobular breast carcinoma (ILC), the most common special histological subtype of breast cancer, is characterized by nearly universal expression of estrogen receptor alpha (ER) and unique sites of metastases, neither of which is fully recapitulated by genetically engineered mouse models. Using reporter-labeled ILC mouse xenografts, herein we used mammary fat pad, tail vein and intracardiac orthotopic growth to analyze spontaneous and experimental metastasis and gene expression. We observed ER-positive primary tumors with single-file histology and collagen deposition, and spontaneous metastasis from the mammary fat pad to bones, ovaries, and brain including the leptomeninges, thereby closely mirroring the growth and metastatic spread of human ILC. Brain metastases showed strong ER staining, confirmed by sequencing analyses which identified estrogen signaling as top activated pathway, and the lesions exhibited robust response to endocrine therapy. In summary, we report endocrine responsive mammary fat pad, tail vein and intracardiac xenografts that faithfully demonstrate unique ILC features and can serve as invaluable pre-clinical translational platforms for validating candidate ILC genetic drivers and testing novel therapeutics.

Abstract Background: Treatment for patients with triple-negative breast cancer (TNBC) relies on non-specific chemotherapy, underscoring the need for precision-based approaches. Our lab discovered that MALT1, the effector protein of the CARMA3-BCL10-MALT1 (CBM) signaling complex, is activated downstream of several oncogenic G protein-coupled receptors (GPCRs) implicated in breast cancer, including the thrombin (PAR1), angiotensin II (AGTR1), and lysophosphatidic acid (LPAR) receptors. When activated, MALT1 functions as a protease to cleave select protein substrates. Based on our finding that CBM activity in TNBC cells promotes tumor growth in immunocompetent but not in immunodeficient mouse models, we hypothesized that MALT1 protease activity induces a pro-tumor secretome that creates an immune-suppressed tumor immune microenvironment (TIME). Methods/Results: We confirmed by western that MALT1 protease is active in multiple human and mouse TNBC cell lines. Next, to identify MALT1-dependent secreted factors, we performed transcriptomic and proteomic analyses comparing TNBC cells treated with or without MALT1 protease inhibitors. We found that several secreted factors, including GM-CSF, CXCL1, and Pentraxin 3, were reduced by MALT1 protease inhibition. To assess the functional impact of the MALT1 protease-dependent secretome, we performed media transfer experiments comparing the effects of conditioned media (CM) from TNBC cells treated with or without MALT1 protease inhibitors. To account for species differences, experiments were performed evaluating human TNBC cell CM added to human PBMCs and mouse TNBC cell CM added to murine bone marrow cells. We found that the MALT1 protease-dependent secretome reduces the expression of iNOS in both human and murine macrophages. For use in validating our findings in human TNBC clinical specimens, we developed a “MALT1 protease active gene signature” using RNA-seq analysis. Conclusions/Future Directions: Our studies indicate that MALT1 protease activity in TNBC cells promotes expression of numerous immune-suppressive factors. In both human and mouse systems, blockade of MALT1 protease alters the tumor cell secretome and promotes an increase in expression of the anti-tumor M1-like marker iNOS in macrophages. Future studies will evaluate how this change in iNOS expression impacts functional properties of TNBC-associated macrophages. We will also assess the influence of the TNBC MALT1-dependent secretome on the TIME in vivo by comparing the effects of intratumoral injection of CM from MALT1 wild-type or MALT1 protease-deficient TNBC cells. Finally, we will utilize our MALT1 activity gene signature to evaluate TNBC clinical specimens for an association between MALT1 activity and tumor immune contexture, with an emphasis on tumor-associated macrophages. Our studies could nominate MALT1 protease as a potential therapeutic target for improving anti-tumor immunity in TNBC. Since multiple MALT1 protease inhibitors are in clinical trial, our findings could be rapidly translated to improve outcomes for patients with TNBC. Citation Format: John W. Little IV, Jeffrey A. Meridew, Dong Hu, Juliana Hofstätter Azambuja, Linda M. McAllister-Lucas, Peter C. Lucas. The GPCR-MALT1 protease signaling axis drives an immunosuppressive secretome in triple-negative breast cancer [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr B046.