Triple-negative Breast Cancer Mouse Research Articles

Abstract PO4-28-05: Prolactin drives labile iron transfer from macrophages to breast cancer cells through CD44

Abstract Cancer cells are “ferrophilic” and exhibit great dependence on iron. While iron metabolism is closely related to tumor development, the source of iron and the mechanisms cancer cells adopt to actively acquire iron is not well understood. In the present study, we discovered a novel function of the lactating hormone, prolactin, in the regulation of iron transport. In breast cancer cells using mouse triple negative breast cancer cell lines EO771 and Py230 for demonstration, prolactin stimulation increased intracellular labile iron pool. Analyses of gene expression involved in iron transport revealed dramatic induction of CD44, a surface receptor for iron bound hyaluronan. Other genes involved in iron uptake including transferrin receptor (TFRC), CD163 and divalent metal transporter 1 (DMT1) were not changed. The utilization of neutralizing antibodies against CD44 significantly blocked prolactin mediated labile iron pool accumulation in breast cancer cells. In contrast to what was found in breast cancer cells, prolactin had the opposite impact on immune macrophages. Prolactin treatment increased ferroportin (FPN I, iron exporter) but had no influence on all iron uptake transporters leading to net iron release by macrophages. To further determine if the iron released by macrophages can be a direct source of iron utilized by breast cancer cells, we conducted co-culture work of macrophages with pre-stained labile iron pool and breast cancer cells without any iron staining and found a gradual increase of fluorescent iron pool developed in breast cancer cells over time. In conclusion, our work presents a multidisciplinary regulation of iron transport among prolactin, macrophages, and cancer cells. The novel regulatory role of prolactin to drive iron flow can provide new information on fine-tuning immune responses in tumor microenvironment and potentially benefit the development of novel therapeutics. Citation Format: Reagan Farrell, Nicholas Pascuzzi, Yi-Ling Chen, Miguel Torres, Mary Kim, Lauren Gollahon, Kuan-Hui Chen. Prolactin drives labile iron transfer from macrophages to breast cancer cells through CD44 [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-28-05.

Abstract PO4-03-13: High B7-H3 expression with low PD-L1 expression identifies armored-cold tumors suggesting potential anti-B7-H3 therapy in triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) is generally regarded as the most aggressive subtype among breast cancer. B7 homolog 3 protein (B7-H3), also known as CD276, is an emerging immune checkpoint molecule, which plays a dual role in the immune system. Multiple anti-B7-H3 therapies has been raised, such as DS-7300, MGA271, MGD009, and B7-H3 chimeric antigen receptor T-cell immunotherapy (CAR-T). However, the expression of B7-H3 in TNBC and its value as a biomarker identifying therapeutic options has not been elucidated Methods: A total of 165 samples (83 non-TNBC and 82 TNBC) were included in this study, and 6 samples included paired para-tumor samples. In addition, 30 TNBC patients receiving standardized neoadjuvant chemotherapy (NAT) were recruited. After 8 cycles of NAT, the response to NAT was assessed by RECIST1.1 criterion before surgical operation. Moreover, multiple public cohorts of breast cancer and TNBC were obtained, including the TCGA dataset, the METABRIC dataset, the GSE176307 (durvalumab-based therapy) dataset, the PRJNA558949 (durvalumab-based therapy) dataset, the GSE194040 (paclitaxel-based therapy) dataset, and the GSE34138 (anthracycline-based therapy) dataset. Based on multiple in-house and public cohorts, we investigated the expression features of B7-H3 in breast cancer and checked the anti-tumor effect of the B7-H3 monoclonal antibody in mouse model. We also developed a novel classifier combined B7-H3 and PD-L1 expression in TNBC. Results: B7-H3 was highly expressed in tumor tissues in the in-house and the TCGA cohorts. B7-H3 expression did not differ significantly between non-TNBC and TNBC samples in the in-house and the TCGA cohorts, excepting for the METABIRC cohort. There was no notable difference in CD8+ cells infiltration between B7-H3 low and high expressed non-TNBC samples, but CD8+ cells was notably higher in the B7-H3 low expressed TNBC samples. The similar findings were also observed in the TCGA and the METABIRC cohorts. In addition, enrichment analysis of transcriptome data and analysis of in-house samples showed that B7-H3 was positively related to most collagens. Moreover, anti-B7-H3 therapy significantly inhibited tumor growth in mouse TNBC model, notably increased immune cells infiltration, and also reduced collagen deposition within the tumor. Given the notable value of PD-L1 in predicting immunotherapy responses, we also combined B7-H3 and PD-L1 expression to establish a novel subtyping strategy. TNBC patients with B7-H3highPDL1low feature exhibited the lowest anti-tumor immune infiltration and higher collagen deposition level. In the durvalumab-dependent cohort, paclitaxel-dependent cohort, anthracycline-dependent cohort, and our recruited NAT cohort, the B7-H3highPDL1low subgroup exhibited the lowest therapeutic response. Conclusions: Overall, this research provides a novel subtyping strategy based on the combination of B7-H3/PD-L1 expression that could potentially be applied to predict the therapeutic responses in TNBC, and suggests a potential biomarker-guided anti-B7-H3 therapy. Based on the classifier, we can select potential beneficiaries to deliver personalized medical services. Citation Format: Jie Mei, Yun Cai, Ziyi Fu, Yongmei Yin. High B7-H3 expression with low PD-L1 expression identifies armored-cold tumors suggesting potential anti-B7-H3 therapy in triple-negative breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-03-13.

Abstract PO3-24-02: Molecular characterization and therapeutic approach for VISTA+ triple-negative breast cancers

Abstract Introduction: Current FDA-approved immunotherapeutics for triple-negative breast cancer are only available for a subset of patients, highlighting the need to develop improved immune-targeting strategies. VISTA (V-domain Ig suppressor of T cell activation) is a single-pass transmembrane immune checkpoint receptor that is an emerging clinical target for cancer immunotherapy. It is expressed widely on lymphoid and myeloid cells in healthy individuals, is commonly expressed on cells of the tumor microenvironment and can be abnormally upregulated on tumor cells in a wide variety of tumors. Although VISTA confers quiescence to naïve T cells, molecular mechanisms responsible for this effect remain unclear. Also, the effects of VISTA expression on tumor cells remains poorly defined. Methods: Multi-omic profiling was performed in human breast cancer cells lines to determine immune regulatory genes controlled by growth factor stimulation. Human triple-negative breast cancer tumor specimens (N=248) were examined by immunohistochemistry for expression of VISTA, PDL1, PD1 and FoxP3. VISTA expression was engineered into human and mouse triple-negative breast cancer cell lines and growth metrics were characterized in vitro and in immunocompetent (syngeneic) and immunodeficient (xenograft) mouse tumor models. Membrane receptor trafficking and localization of EGFR was performed in human TNBC cells lines expressing VISTA and VISTA mutants. Proximity biotinylation identified protein partners that interacted with VISTA’s intracellular domain. Deletion mutagenesis was performed to identify motifs required for biochemical interactions between VISTA and clathrin adaptor proteins. Clathrin adapter localization was examined in WT and VISTA knock-out cell lines. Cytokine response, clathrin adaptor localization and tumor growth kinetics were measured in TNBC cell lines expressing VISTA or VISTA mutants. Results: A class of human triple-negative breast cancers were identified with high VISTA expression, low tumor infiltrating lymphocytes and low proliferative index (8-20% of all TNBCs). Tumor models demonstrated that enforced expression of VISTA in tumor cells caused growth suppression, even in the absence of an immune system. This effect was mapped to the cytoplasmic domain of VISTA, which lacks defined signaling domains. Through biochemical approaches, the clathrin-adaptor molecules NUMB and GULP1 were found in complex with a VISTA intracellular NPGF motif. This motif sequestered NUMB at early endosomes, resulting in diminished NUMB recycling for EGFR endocytosis, thereby causing growth suppression. VISTA impaired NUMB recycling by blocking Rab11 effector complex formation. VISTA NPGF mutations did not disrupt cytokine secretion in mixed lymphocyte assays. VISTA-targeted antibodies did not disrupt NUMB sequestration. VISTA+ tumors were selectively sensitive to VISTA-blocking antibodies. Conclusions: VISTA+ TNBC have distinct features including slower proliferative index and increased sensitivity to VISTA-blocking antibodies. This work identifies mechanisms by which VISTA enforces a quiescent cellular state by sequestering clathrin adapter proteins away from sites of endocytosis in cancer cells. This is the first description of intracellular molecular mechanisms controlled by VISTA’s intracellular tail. It may inform features of the VISTA-dependent immune checkpoint that could be exploited to improve anti-tumor immunity. Citation Format: Yan Zhao, Fatima Charles, Andrew Lipchik, Yan Peng, James Ford, Melinda Telli, Song Zhang, Allison Kurian, Michael Snyder, Joshua Gruber. Molecular characterization and therapeutic approach for VISTA+ triple-negative breast cancers [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-24-02.

Abstract PO1-26-06: The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model

Abstract Background: Metastatic triple-negative breast cancer (TNBC) is an aggressive sub-type of breast cancer that is challenging to treat. While the addition of immunotherapy (IT) with pembrolizumab (pembro) to chemotherapy prolongs overall survival in patients with programmed death-ligand 1 positive (PD-L1+) TNBC, few patients obtain long-term benefit. Radiotherapy (RT) can stimulate cellular damage, release of tumor antigens and promote the T cell anti-tumor response including at distant sites (abscopal response) when used with IT. The purpose of this study was to investigate the combination of RT with pembro and paclitaxel (pac) in a TNBC humanized mouse model. Methods: Human Immune System BRGS (BALB/c, Rag2-/-, IL2RγC-/-, NODSIRPa ) mice were engrafted with TNBC MDA-MB-231 cells in bilateral flanks. Treatments included: vehicle, pac 10 mg/kg intra-peritoneal (IP) weekly, pembro 15 mg/kg IP weekly, and RT 8 Gy x 3 fractions every other day the first week of treatment to one-sided tumors (contralateral tumors received no RT). Mice were treated and analyzed in the following groups: vehicle, pac + pembro, RT + pac, and RT + pac + pembro. Treatments began when tumors reached 100-300 mm3 and tumors were measured twice weekly. At the end of study, sera, lymph nodes (LNs), spleen, and tumor tissue were collected for immunohistochemistry, single cell suspensions, and flow cytometry analysis for immune cell populations. Results: All treatment arms resulted in a decrease in tumor volume when compared to vehicle with the greatest reduction in the RT + pac and RT + pac + pembro arms. Combination therapy with RT + paclitaxel (p=0.0002) and RT + pac + pembro (p=0.008) resulted in a statistically significant decrease in specific growth rate (SGR) when compared to vehicle. An abscopal effect was not observed in the non-RT tumors compared to RT-tumors in either group. RT + pembro was associated with an increase in hCD45 T cells in LNs and spleens but not in tumors. In mice that received RT, a decrease was noted in HLA-ABC class I and Intermediate Class II major histocompatibility complex (MHC). In addition, RT-tumors had reduced expression of PD-L1 and polio virus receptor (PVR) and increased expression of PD-1. The percentage of interferon gamma (IFNg+), tumor necrosis factor alpha (TNFa+) CD8+ T cells increased with radiation. This percentage was the highest in the triplet therapy with RT+ pembro + pac. Conclusion: Combination treatment with RT + immunochemotherapy resulted in a significant increase in anti-tumor activity when compared to immunochemotherapy alone, however, an abscopal effect was not observed in contralateral non-RT tumors. RT resulted in down-regulation of immune inhibitory receptors and tumor MHC. Citation Format: Anna Schreiber, Stacey Bagby, Stephen Smoots, Adrian Dominguez, Christine Fisher, Julie Lang, Todd Pitts, Jennifer Diamond. The effect of localized radiotherapy in combination with chemoimmunotherapy in a humanized triple-negative breast cancer mouse model [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-26-06.

Ganoderma lucidum spores-derived particulate β-glucan treatment improves antitumor response by regulating myeloid-derived suppressor cells in triple-negative breast cancer.

Granular β-1,3-glucan extracted from the wall of Ganoderma lucidum spores, named GPG, is a bioregulator. In this study, we investigated the structural, thermal, and other physical properties of GPG. We determined whether GPG ameliorated immunosuppression caused by Gemcitabine (GEM) chemotherapy. Triple-negative breast cancer mice with GPG combined with GEM treatment had reduced tumor burdens. In addition, GEM treatment alone altered the tumor microenvironment(TME), including a reduction in antitumor T cells and a rise in myeloid-derived suppressor cells (MDSC) and regulatory T cells (Tregs). However, combined GPG treatment reversed the tumor immunosuppressive microenvironment induced by GEM. GPG inhibited bone marrow (BM)-derived MDSC differentiation and reversed MDSC expansion induced by conditioned medium (CM) in GEM-treated E0771 cells through a Dectin-1 pathway. In addition, GPG downgraded PD-L1 and IDO1 expression on MDSC while boosting MHC-II, CD86, TNF-α, and IL-6 expression. In conclusion, this study demonstrated that GPG could alleviate the adverse effects induced by GEM chemotherapy by regulating TME.

Small animal PET imaging with the 68Ga-labeled pH (low) insertion peptide-like peptide YJL-4 in a triple-negative breast cancer mouse model

BackgroundThe aim of this study was to prepare a novel 68Ga-labeled pH (low) insertion peptide (pHLIP)-like peptide, YJL-4, and determine its value for the early diagnosis of triple-negative breast cancer (TNBC) via in vivo imaging of tumor-bearing nude mice. The novel peptide YJL-4 was designed using a template-assisted method and synthesized by solid-phase peptide synthesis. After modification with the chelator 1,4,7‑triazacyclononane-N,N′,N″-triacetic acid (NOTA), the peptide was labeled with 68Ga. Then, the biodistribution of 68Ga-YJL-4 in tumor-bearing nude mice was investigated, and the mice were imaged by small animal positron emission tomography (PET).ResultsThe radiochemical yield and radiochemical purity of 68Ga-YJL-4 were 89.5 ± 0.16% and 97.95 ± 0.06%, respectively. The biodistribution of 68Ga-YJL-4 in tumors (5.94 ± 1.27% ID/g, 6.72 ± 1.69% ID/g and 4.54 ± 0.58% ID/g at 1, 2 and 4 h after injection, respectively) was significantly greater than that of the control peptide in tumors at the corresponding time points (P < 0.01). Of the measured off-target organs, 68Ga-YJL-4 was highly distributed in the liver and blood. The small animal PET imaging results were consistent with the biodistribution results. The tumors were visualized by PET at 2 and 4 h after the injection of 68Ga-YJL-4. No tumors were observed in the control group.ConclusionsThe novel pHLIP family peptide YJL-4 can adopt an α-helical structure for easy insertion into the cell membrane in an acidic environment. 68Ga-YJL-4 was produced in high radiochemical yield with good stability and can target TNBC tissue. Moreover, the strong concentration of radioactive 68Ga-YJL-4 in the abdomen does not hinder the imaging of early TNBC.

IL1R2 blockade alleviates immunosuppression and potentiates anti-PD-1 efficacy in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited therapeutic options. Interleukin-1 receptor type 2 (IL1R2) promotes breast tumor-initiating cell (BTIC) self-renewal and tumor growth in TNBC, indicating that targeting it could improve patient treatment. Here, we observed that IL1R2 blockade strongly attenuated macrophage recruitment and the polarization of tumor-associated macrophages (TAMs) to inhibit BTIC self-renewal and CD8+ T cell exhaustion, which resulted in reduced tumor burden and prolonged survival in TNBC mouse models. IL1R2 activation by TAM-derived IL1β increased PD-L1 expression by interacting with the transcription factor yin yang 1 (YY1) and inducing YY1 ubiquitination and proteasomal degradation in both TAMs and TNBC cells. Loss of YY1 alleviated the transcriptional repression of c-Fos, which is a transcriptional activator of PD-L1. Combined treatment with an IL1R2-neutralizing antibody and anti-PD-1 led to enhanced anti-tumor efficacy and reduced TAMs, BTICs, and exhausted CD8+ T cells. These results suggest that IL1R2 blockade might be a strategy to potentiate immune checkpoint blockade efficacy in TNBC to improve patient outcomes.

Heat shock factor 1 inhibition enhances the effects of modulated electro hyperthermia in a triple negative breast cancer mouse model

Female breast cancer is the most diagnosed cancer worldwide. Triple negative breast cancer (TNBC) is the most aggressive type and there is no existing endocrine or targeted therapy. Modulated electro-hyperthermia (mEHT) is a non-invasive complementary cancer therapy using an electromagnetic field generated by amplitude modulated 13.56 MHz frequency that induces tumor cell destruction. However, we have demonstrated a strong induction of the heat shock response (HSR) by mEHT, which can result in thermotolerance. We hypothesized that inhibition of the heat shock factor 1 (HSF1) can synergize with mEHT and enhance tumor cell-killing. Thus, we either knocked down the HSF1 gene with a CRISPR/Cas9 lentiviral construct or inhibited HSF1 with a specific small molecule inhibitor: KRIBB11 in vivo. Wild type or HSF1-knockdown 4T1 TNBC cells were inoculated into the mammary gland’s fat pad of BALB/c mice. Four mEHT treatments were performed every second day and the tumor growth was followed by ultrasound and caliper. KRIBB11 was administrated intraperitoneally at 50 mg/kg daily for 8 days. HSF1 and Hsp70 expression were assessed. HSF1 knockdown sensitized transduced cancer cells to mEHT and reduced tumor growth. HSF1 mRNA expression was significantly reduced in the KO group when compared to the empty vector group, and consequently mEHT-induced Hsp70 mRNA upregulation diminished in the KO group. Immunohistochemistry (IHC) confirmed the inhibition of Hsp70 upregulation in mEHT HSF1-KO group. Demonstrating the translational potential of HSF1 inhibition, combined therapy of mEHT with KRIBB11 significantly reduced tumor mass compared to either monotherapy. Inhibition of Hsp70 upregulation by mEHT was also supported by qPCR and IHC. In conclusion, we suggest that mEHT-therapy combined with HSF1 inhibition can be a possible new strategy of TNBC treatment with great translational potential.

Insights into Mechanisms and Promising Triple Negative Breast Cancer Therapeutic Potential for a Water-Soluble Ruthenium Compound.

Triple negative breast cancer (TNBC) represents a subtype of breast cancer that does not express the three major prognostic receptors of human epidermal growth factor receptor 2 (HER2), progesterone (PR), and estrogen (ER). This limits treatment options and results in a high rate of mortality. We have reported previously on the efficacy of a water-soluble, cationic organometallic compound (Ru-IM) in a TNBC mouse xenograft model with impressive tumor reduction and targeted tumor drug accumulation. Ru-IM inhibits cancer hallmarks such as migration, angiogenesis, and invasion in TNBC cells by a mechanism that generates apoptotic cell death. Ru-IM displays little interaction with DNA and appears to act by a P53-independent pathway. We report here on the mitochondrial alterations caused by Ru-IM treatment and detail the inhibitory properties of Ru-IM in the PI3K/AKT/mTOR pathway in MDA-MB-231 cells. Lastly, we describe the results of an efficacy study of the TNBC xenografted mouse model with Ru-IM and Olaparib monotherapy and combinatory treatments. We find 59% tumor shrinkage with Ru-IM and 65% with the combination. Histopathological analysis confirmed no test-article-related toxicity. Immunohistochemical analysis indicated an inhibition of the angiogenic marker CD31 and increased levels of apoptotic cleaved caspase 3 marker, along with a slight inhibition of p-mTOR. Taken together, the effects of Ru-IM in vitro show similar trends and translation in vivo. Our investigation underscores the therapeutic potential of Ru-IM in addressing the challenges posed by TNBC as evidenced by its robust efficacy in inhibiting key cancer hallmarks, substantial tumor reduction, and minimal systemic toxicity.

Effects of Metformin on JNK Signaling Pathway and PD-L1 Expression in Triple Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer. Metformin has been shown to have the potential to inhibit the proliferation of malignant cells. This study aimed to investigate the regulatory effect of metformin on the expression of programmed death protein ligand 1(PD-L1) and mechanisms in TNBC. Mouse breast cancer cell line 4T1 was co-cultured with metformin, and the effect of metformin on cell proliferation was detected by MTT assay. The effect of metformin on the expression of JNK, RSK2 and CREB was detected by MAPK pathway protein chip. BALB/c mice were inoculated with 4T1 cells with knockdown/overexpression of C-Jun N-terminal kinase (JNK), and administered with metformin. The weight of tumor tissue was observed at the end of the experiment. The expression of PD-L1 in tumor cells was observed by immunofluorescence staining and the level of INF-γwas quantitatively determined by ELISA. Metformin inhibited the viability of 4T1 cells and increased the phosphorylation of JNK to reduce the phosphorylation of RSK2 and CREB. Metformin and JNK knockdown reduced the expression of PD-L1 in tumor cells, but there was no significant difference in the weight of tumor tissue. Metformin can reduce the level of INF-γ in tumor tissues, but JNK has no effect. Metformin can inhibit the expression of PD-L1 in triple-negative breast cancer mice and improve the tumor microenvironment, but does not reduce the size of the tumor.

Targeting CD73 with flavonoids inhibits cancer stem cells and increases lymphocyte infiltration in a triple-negative breast cancer mouse model.

Chemotherapy remains the mainstay treatment for triple-negative breast cancer (TNBC) due to the lack of specific targets. Given a modest response of immune checkpoint inhibitors in TNBC patients, improving immunotherapy is an urgent and crucial task in this field. CD73 has emerged as a novel immunotherapeutic target, given its elevated expression on tumor, stromal, and specific immune cells, and its established role in inhibiting anti-cancer immunity. CD73-generated adenosine suppresses immunity by attenuating tumor-infiltrating T- and NK-cell activation, while amplifying regulatory T cell activation. Chemotherapy often leads to increased CD73 expression and activity, further suppressing anti-tumor immunity. While debulking the tumor mass, chemotherapy also enriches heterogenous cancer stem cells (CSC), potentially leading to tumor relapse. Therefore, drugs targeting both CD73, and CSCs hold promise for enhancing chemotherapy efficacy, overcoming treatment resistance, and improving clinical outcomes. However, safe and effective inhibitors of CD73 have not been developed as of now. We used in silico docking to screen compounds that may be repurposed for inhibiting CD73. The efficacy of these compounds was investigated through flow cytometry, RT-qPCR, CD73 activity, cell viability, tumorsphere formation, and other in vitro functional assays. For assessment of clinical translatability, TNBC patient-derived xenograft organotypic cultures were utilized. We also employed the ovalbumin-expressing AT3 TNBC mouse model to evaluate tumor-specific lymphocyte responses. We identified quercetin and luteolin, currently used as over-the-counter supplements, to have high in silico complementarity with CD73. When quercetin and luteolin were combined with the chemotherapeutic paclitaxel in a triple-drug regimen, we found an effective downregulation in paclitaxel-enhanced CD73 and CSC-promoting pathways YAP and Wnt. We found that CD73 expression was required for the maintenance of CD44highCD24low CSCs, and co-targeting CD73, YAP, and Wnt effectively suppressed the growth of human TNBC cell lines and patient-derived xenograft organotypic cultures. Furthermore, triple-drug combination inhibited paclitaxel-enriched CSCs and simultaneously improved lymphocyte infiltration in syngeneic TNBC mouse tumors. Conclusively, our findings elucidate the significance of CSCs in impairing anti-tumor immunity. The high efficacy of our triple-drug regimen in clinically relevant platforms not only underscores the importance for further mechanistic investigations but also paves the way for potential development of new, safe, and cost-effective therapeutic strategies for TNBC.

Abstract 6661: Profiling response to oncolytic adenovirus and immune checkpoint inhibitors by mass cytometry in a triple negative breast cancer mouse model

Abstract Immune checkpoint inhibitors (ICIs) based immunotherapy has found success in treating breast cancers but for more immunosuppressive cancer types, especially most of triple negative breast cancers (TNBCs), response rates generally are low. Also, combination immunotherapy with oncolytic adenoviruses (OAVs) has been shown to induce a more immune inflamed phenotype in many pre-clinical studies. Here, by using a 40-antibody panel for mass cytometry, we profiled comprehensive changes of cell phenotypes in a TNBC mouse model both systemically and in the tumor microenvironment in response to the treatment of ICIs and/or a new systemically delivered, TGFβ signaling inhibiting OAV, mHAdLyp.sT. The samples in this study were collected on day 16 of tumor cell inoculation, while mHAdLyp.sT were applied by tail vein on day 7 and 9, and anti-PD-1 and anti-CTLA-4 antibodies were injected Intraperitoneally on day 8, 10, 12, 14. After sample processing and data acquisition on Helios system, a standard workflow was applied for data preprocessing including normalization, compensation, transformation, diagnostic analysis, marker ranking, cell population identification, visual representation, differential analysis, and statistical analysis. In blood samples, for T cell clusters, percentages of effector CD8+ T cells, naïve CD8+ T cells, and CD44lowCD62Llow CD8+ T cells among total cells were increased by mHAdLyp.sT, anti-PD-1, and anti-CTLA-4 combination when compared to the buffer group but none of these significant changes were observed in groups treated with mHAdLyp.sT or ICI antibodies alone. Combination treatment also increased percentages of clusters of CD272highCD44high DCs, CD44highCD62Llow B cells, and CD44high macrophages significantly. In spleen, combination treatment significantly increased several T cell clusters, including TCRβhighCD38highRORγthigh T cells, TCRβhigh CD4+ T cells, effector CD8+ T cells, TCRβhighCD44lowCD62Llow CD8+ T cells, and CD11bhigh CD8+ T cells when compared to the buffer group. Interestingly, while ICIs treatment increased several macrophage clusters, such as CD44highLy-6G/Chigh macrophages, CD11blow macrophages, and CD44highCD11bhigh macrophages, they are not significantly increased in the combination treatment group. In the tumor, we did not detect any significant changes by the combination treatment in the clusters we identified now although the average percentages of several clusters were either increased or decreased. We will refine these algorithm-generated clusters from tumors once we obtain our data from day 24 sample collection point for advanced analysis. In short, our current results suggested that the combination therapy is more potent in generating cytotoxic T cells and other anti-tumor immune cell populations systemically in the early stage of the treatment and tumor progression. Citation Format: Weidong Xu, Qiaoshan Lin, Yan Li, Beniamin Filimon, Soon Cheon Shin, Michael Olson, Mengjie Chen. Profiling response to oncolytic adenovirus and immune checkpoint inhibitors by mass cytometry in a triple negative breast cancer mouse model [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 6661.

Abstract 6800: The tumor progression mechanism of increasing CXCL16-CXCR6 pathway within the tumor microenvironment in TNBC

Abstract Background: Triple negative breast cancer (TNBC) is characterized rapid progression, higher relapse, and poor prognosis, so the establishment of an effective therapeutic target is required. CXCL16, a chemokine abundantly present in the TNBC tumor microenvironment (TME), is secreted by tumor-associated macrophages (TAM) and is known to promote tumor growth and metastasis. However, the exact mechanism through which CXCL16 facilitates tumor growth and metastasis remains unclear. This study aims to study the role of CXCL16 in the tumor progression and confirm the anti-tumor effects of CXCL16 neutralization in TNBC model. Method: MDA-MB-231 human TNBC cell lines were utilized for in vitro validation, and a syngeneic model involving 4T1 mouse TNBC cell lines and Balb/c mice was used for in vivo studies. Results: Stimulation of TNBC cells with recombinant human CXCL16 protein (rhCXCL16) activates the tumor growth signaling pathways, including pAKT and STAT3, as well as EMT markers. These results shows that CXCL16 can promote tumor growth and metastasis. Treatment with CXCL16 neutralizing antibodies inhibited the promotion of cancer growth and metastasis by rhCXCL16. Additionally, combination treatment of CXCL16 antibodies with PD-1 antibodies in the 4T1 syngeneic model increased the proportion of CD8+ T cells and CD80+ M1 like macrophages. These results shows that neutralization of CXCL16 can regulate polarization of macrophage and proportion of T cells. These regulation and changes of immune cells allow neutralization of CXCL16 control the TME to resist tumor cells, suggesting that optimal condition can be constructed to maximize the effectiveness of anti-cancer drugs. Conclusion: This study confirms that the CXCL16-CXCR6 pathway within the TME triggers tumor growth and metastasis, while neutralization of CXCL16 can inhibit tumor progression. This effect is attributed to the increase in CD8+ T cell and M1 macrophage proportions within the TME. In conclusion, these research findings propose the potential of CXCL16 as a novel biomarker and therapeutic target for TNBC. Citation Format: Yun sun Lee, Cham Han Lee, Seong Yun Ha, Sang Hyeob Lee, Jin Yi Yang, Young Sang Kim, Sung Moo Kim, Seong Keun Kim. The tumor progression mechanism of increasing CXCL16-CXCR6 pathway within the tumor microenvironment in 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 6800.

Abstract 7553: Dual inhibition of chromatin remodeling and DNA methylation as a novel treatment for triple negative breast cancer

Abstract Epigenetics plays a central role in the initiation, establishment, and progression of cancer. In this capacity, epigenetics regulates several abnormal nuclear processes in the cancer cell including DNA replication, DNA damage repair and most prominently transcription. Because of their reversibility, epigenetic modifications have been aggressively pursued pharmacologically to correct abnormal cancer biology in the hopes of reversing cancer phenotypes. To develop novel epigenetic based therapeutic strategies for triple negative breast cancer (TNBC) we combined the DNA methyltransferase inhibitor (DNMTi) guadecitabine (Gua) with a genetic CRISPR/Cas9 mediated knockout (KO) of the chromatin remolding protein Bromodomain PHD-finger Transcription Factor (BPTF). Using the E0771 and 4T1 mouse TNBC models we show that BPTF depleted tumor cells are more susceptible to the antitumor effects of Gua. These antitumor effects are not observed in culture, or in immune compromised NSG mice, suggesting that their effects on cancer cell growth are not cancer cell intrinsic. RNA-Seq, ATAC-Seq and MBD-Seq analysis from FACS purified cancer cells shows that the combination of BPTF inhibition and Gua alters immune regulatory cytokine expression (BMP4 and CSF3) in the cancer cell, and it is theorized that these changes alter the tumor microenvironment to become less immune suppressive and permissive to the antitumor effects of immune cells. This hypothesis is supported by Cytek phenotyping of tumor resident and peripheral immune cells from treated mice showing reduced levels of immune suppressive myeloid derived suppressor cells (MDSC). Inhibiting BPTF pharmacologically using the bromodomain inhibitor AU1 does not recapitulate the effects of the genetic inhibition suggesting that the benefits of BPTF depletion to sensitization to Gua are not captured by inhibition of its bromodomain. To model the effects of pharmacologic BPTF inhibition we created a BPTF mouse KO genetically modified mouse model (GEMM). We show using this GEMM that BPTF KO in the adult mouse (a tamoxifen inducible Cre) is not lethal and has beneficial effects to the control of E0771 tumors, possibly through depleting tumor resident naïve T cells, and that transplanting BPTF KO E0771 tumors into BPTF KO adult mice further improves tumor growth control. These benefits in tumor growth control are prevented with CD8 depletion. These results in total suggests that a combination therapy regimen including BPTF inhibition (a PROTAC degradation approach) with a DNMTi could provide clinical benefits to patients with TNBC through both tumor cell intrinsic and extrinsic mechanisms. Citation Format: Joseph W. Landry, Jubin Kang, Christiane Morecock, Harry Bear, Rebecca Martin. Dual inhibition of chromatin remodeling and DNA methylation as a novel treatment for 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 7553.

Abstract 5568: Understanding the role of immune exclusion in mammary tumor growth

Abstract Multiple solid tumor types, including triple-negative breast cancer (TNBC), respond poorly to immunotherapy due to low infiltration of CD8+ T cells into the tumor core. The extracellular matrix (ECM) and its components such as collagen have been found to contribute to immune cell exclusion. Discoidin domain receptor 1 (DDR1) is a collagen receptor known to be aberrantly expressed in TNBC among multiple solid tumor types. We have uncovered a previously unappreciated function of DDR1 in immune exclusion through shaping a collagen fiber-based tumor defense against anti-tumor immunity (Sun et al, Nature 599, 673-678 (2021)). Our study showed that deletion of DDR1 in mouse mammary carcinoma cell lines such as E0771 and M-Wnt (syngeneic with C57BL/6 strain background) promotes infiltration of CD8+ T cells and reduces tumor growth in an immunocompetent mouse model. Extending the published study to other immunocompetent mouse strain backgrounds, we observed that deletion of DDR1 in EMT6 cells, another immune excluded TNBC mouse model in the BALB/c strain, increased the infiltration of CD8+ T cells to the tumor core and reduced tumor growth. Data concerning the DDR1-dependent spatial architecture of the mammary tumor microenvironment will be presented. Identifying specific immune and stromal cell populations and proteins spatially modified in the presence or absence of DDR1 may aid in development of new stand-alone or combination anti-cancer treatments with anti DDR1 antibody. Citation Format: Payal Mitra, Jorge Azpurua, Huai-Chin Chiang, Rong Li. Understanding the role of immune exclusion in mammary tumor growth [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 5568.

Abstract 2458: Targeting the CXCR3 axis in HER2+ breast cancer to enhance anti-tumor immunity

Abstract Breast cancer (BC) is the most frequently diagnosed cancer in women worldwide with more than 2 million new cases in 2020. The efficacy of immunotherapies for BC is limited, with response rates of &amp;lt;10% for anti-PD-1/PDL1 monotherapy in pre-treated triple-negative breast cancer (TNBC) patients and even lower in subtypes that express human epidermal growth factor receptor 2 (HER2+) and/or hormone receptors. Hence, there is an urgent need to improve immune based strategies for BC. One possible approach to enhance response is the application of intratumoral (IT) immunotherapy utilizing IL-12; a potent pro-inflammatory cytokine that is critical in producing an anti-tumor response. However, systemic delivery of IL-12 has substantial toxicity and localized delivery of protein has insufficient residence time. To circumvent these issues, we have previously reported the efficacy of intratumorally injected plasmid IL-12 (pIL-12-EP) followed by electroporation in a TNBC mouse model and in clinical trials. Following pIL-12-EP, treated tumor expressed genes that were associated with increased CD8+ T cell infiltration, activation, trafficking, antigen presentation, and exhaustion. Single-cell RNA sequencing (scRNAseq) of tumor infiltrating immune cells from treated tumors revealed a striking enrichment of the CXCL9/10/11/CXCR3 family. This CXCR3 axis is upregulated in response to IFNγ production and has been studied extensively in melanoma and NSCLC patients as a potential predictive biomarker for responses to immune checkpoint inhibitors but has not been well characterized in BC. We hypothesized that this axis may be the critical component downstream of pIL-12-EP treatment that is responsible for anti-tumor responses and that targeting it will be effective in other molecular subtypes of BC beyond TNBC. We first evaluated the expression of CXCR3 by tumor infiltrating lymphocytes (TILs) in biopsies of human HER2+ BC. Using a single cell resolution spatial transcriptomic Xenium instrument we find not only expression of CXCR3 by TILs, but can also track the distance and gradients of the chemokine ligands CXCL9 and CXCL10 in this tumor microenvironment. Having confirmed the activity of this axis in human HER2+ BC, we used our well-established spontaneous HER2-driven mouse model to compare treatment of HER2+ tumors with pIL-12-EP or pCXCL9-EP intratumorally. We observed tumor growth inhibition in both treatment groups as compared to control treated tumors. Interestingly, the abscopal effect previously seen with pIL-12-EP was not evident for distant tumors in mice treated with pCXCL9-EP. These data suggest that IT CXCL9 therapies may benefit from combination with a systemic immune activator like a vaccine or immunogenic chemotherapy. Ongoing studies will continue to evaluate ways to better target this axis therapeutically and define clinically active combination therapies. Citation Format: Anchit Bhagat, Jesuchristopher Joseph, Joshua D. Ginzel, Christopher Rabiola, Amy C. Hobeika, Joshua C. Snyder, Herbert K. Lyerly, Erika J. Crosby. Targeting the CXCR3 axis in HER2+ breast cancer to enhance anti-tumor immunity [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 2458.

Abstract 3716: Enhancing anti-tumor responses in triple-negative breast cancer by combining SIRPα inhibition with immunogenic chemotherapy or antibody-drug conjugates

Abstract Background: Triple-negative breast cancer (TNBC) is a subtype of breast cancer defined by the absence of hormone receptors and HER2 receptor on tumor cells. Because of a lack of targetable receptors and poor response to PD1/PDL1 immunotherapy, TNBC has limited systemic treatment options. In previous work using a genomic screen (Shuptrine et al., 2017), we identified CD47 as one of the leading factors that contributes to TNBC immune evasion. The CD47-SIRPα axis is an innate immune checkpoint that primarily regulates myeloid cells. In the context of cancer, tumor cells upregulate CD47 to engage SIRPα inhibitory signaling to block phagocytosis. While CD47 or SIRPα blockade alone show limited antitumor effect, therapies that combine blockade of this axis with other treatment agents, such as tumor-antigen specific antibodies, show superior tumor inhibition. Thus, we hypothesize that the addition of SIRPα inhibition to existing TNBC treatments (chemotherapy and Trop2-antibody drug conjugates (ADC)) will improve their treatment efficacy. Methods: To ascertain the impact of SIRPα inhibition combined with chemotherapy and Trop2-ADC, we utilized and validated a novel SIRPα KO mouse, along with SIRPα mAbs, in our previously utilized models of Triple-Negative Breast Cancer (TNBC) (Crosby et al., 2018). Using both in vitro and in vivo tumor models, we tested the therapeutic impact of SIRPα inhibition/blockade combined with different immunogenic chemotherapies (doxorubicin/cyclophosphamide) and Sacituzumab govitecan (SG) in TNBC. Results: After validating the loss of SIRPα in KO mice, we found that E0771 TNBC cells had comparable growth rates in WT and SIRPα KO mice. Similarly, we did not observe different anti-tumor responses to Doxorubicin between WT and SIRPα-KO mice. However, we observed more profound suppression of E0771 tumors after cyclophosphamide treatment in SIRPα KO mice than in WT mice. To evaluate the efficacy of SG in inducing antibody-dependent cellular phagocytosis (ADCP), we co-cultured SIRPα KO and WT mouse macrophages with a syngeneic mouse TNBC model (MM3MG-Trop2-WT). We found that SG promotes ADCP in WT macrophages, and SIRPα loss further increased this ADCP, suggesting the potential importance of antibody-mediated phagocytosis as a mechanism of action for SG. In vivo, we implanted human TNBC cells (MDA-MB-468) in mice and treated them with SG with and without SIRPα antibody blockade. These studies demonstrated an anti-tumor effect from SG that was potentially enhanced by SIRPα blockade, suggesting the clinical potential of this combination in TNBC. Conclusion: Our study demonstrates that the addition of SIRPα inhibition to chemotherapy or SG may promote tumor phagocytosis and stimulate stronger antitumor immunity in TNBC. These results support further investigation of SIRPα-targeting combination therapies for TNBC. Citation Format: Xingru Ma, Li-Chung Tsao, Tao Wang, Cong-Xiao Liu, Melissa Gajda, Xiao Yang, Gangjun Lei, Junping Wei, Zachary Hartman. Enhancing anti-tumor responses in triple-negative breast cancer by combining SIRPα inhibition with immunogenic chemotherapy or antibody-drug conjugates [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 3716.

Abstract 3902: The Nanoprimer: A significant opportunity to boost the efficacy of cancer therapies

Abstract Nanomedicines are among the most promising novel delivery systems and are highly promising as therapeutic agents in oncology. However, their use is still limited by nanoparticle hepatic clearance which is responsible for low delivery to the target site. Moreover, the unintended liver distribution could cause harmful side effects. Curadigm’s innovative Nanoprimer technology aims to shift the balance of therapeutics bioavailability and toxicity. The platform is designed to decrease nanomedicines' liver trapping and increase their systemic bioavailability for optimal accumulation in target tissues. This technology can redefine the benefit/risk ratio of therapeutics, improving their clinical outcomes and treatment value. The Nanoprimer is an engineered, biocompatible liposome that transiently and specifically occupies the cells of the mononuclear phagocytic system responsible for sub-optimal therapeutics bioavailability. The Nanoprimer is administered just before the therapeutic, temporarily reducing drug clearance and elimination. Proofs-of-concept were realized by combining the Nanoprimer with different therapeutic agents such as irinotecan-loaded liposomes and nucleic acid-loaded lipid nanoparticles (LNP). One example is a study conducted in collaboration with the Langer Lab at MIT that shows that the Nanoprimer increases mRNA- and siRNA-based therapeutics efficiency by 32% and 49% respectively. Efficacy studies in a triple-negative breast cancer mouse model reveal that the Nanoprimer increases by 2-fold the anti-tumor efficacy of siRNA LNP therapy. Data demonstrate the safety of the Nanoprimer, along with its ability to maximize the inhibition of primary tumor growth and pulmonary metastasis by systemic siRNA LNP treatment. In a collaborative study with the NCL*, the Nanoprimer was shown to stimulate the immune response in a systemic vaccine model using ovalbumin-coated gold nanoparticles (GNP-OVA). Administration of the Nanoprimer before immunization of mice by intravenous injection of GNP-OVA, results in a dramatic increase in anti-OVA antibody levels with IgGs detected as early as 7 days. Furthermore, IgG and IgM antibodies remain elevated at day 28 showing a robust and sustainable immune response. Nanoprimer ability to enhance immune response shows its great potential in immunotherapy, especially for cancer vaccines. Altogether, these data demonstrate that the ubiquitous nature of the Nanoprimer mode of action allows its application to a broad spectrum of therapeutics, from nucleic acid-loaded LNP to immunotherapy. Efficacy studies conducted in mouse models highlight the potential for the Nanoprimer to empower nanotechnology for oncology treatments. *We acknowledge NCL, Frederick National Laboratory for Cancer Research sponsored by the NCI for the help with conducting these experiments. Citation Format: Julie Devallière, Laurence Poul, Maxime Bergère, Francis Mpambani, Audrey Darmon, Océane Jibault, Matthieu Germain. The Nanoprimer: A significant opportunity to boost the efficacy of cancer therapies [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 3902.

Assessment of the Efficacy of the Combination of RNAi of lncRNA DANCR with Chemotherapy to Treat Triple Negative Breast Cancer Using Magnetic Resonance Molecular Imaging.

Long noncoding RNA (lncRNA) differentiation antagonizing noncoding RNA (DANCR) is overexpressed in human triple-negative breast cancer (TNBC) and promotes cell migration and proliferation. TNBC is limited in treatment options relative to hormone-receptor-positive breast cancer and is commonly treated with chemotherapy, which is often compromised by acquired resistance. DANCR has been implicated in the development of chemoresistance across multiple cancer types. Here, we applied magnetic resonance molecular imaging (MRMI) with a targeted contrast agent, MT218, specific to extradomain-B fibronectin (EDB-FN), a marker for epithelial-to-mesenchymal transition, to assess the therapeutic efficacy of the combination of paclitaxel and ZD2-PEG-ECO/siDANCR nanoparticles (ZD2-siDANCR-ELNP) to treat TNBC. The treatment of orthotopic MDA-MB-231 TNBC in mice with paclitaxel significantly suppressed tumor growth but with a significant increase of EDB-FN in the tumor, as revealed by MRMI and immunohistochemistry. Combining ZD2-siDANCR-ELNP with paclitaxel further reduced tumor sizes, along with reduced EDB-FN expression. Interestingly, MT218-MRMI revealed a lower reduction of tumor signal enhancement with the combination treatment than that with the siDANCR treatment alone, which was supported by higher cell density in the tumors treated with the combination therapy, as shown by histochemical analysis. MT218-MRMI clearly revealed the changes of the tumor microenvironment in response to various therapies and is effective to noninvasively assess the response of TNBC tumors to the therapies. Regulating oncogenic lncRNA DANCR is an effective strategy for improving the outcomes of chemotherapy in TNBC.

EPAC inhibitor suppresses angiogenesis and tumor growth of triple-negative breast cancer

AimsExchange protein directly activated by cAMP 1 (EPAC1), a major isoform of guanine nucleotide exchange factors, is highly expressed in vascular endothelia cells and regulates angiogenesis in the retina. High intratumor microvascular densities (MVD) resulting from angiogenesis is responsible for breast cancer development. Downregulation of EPAC1 in tumor cell reduces triple-negative breast cancer (TNBC)-induced angiogenesis. However, whether Epac1 expressed in vascular endothelial cells contributes to angiogenesis and tumor development of TNBC remains elusive. Main methodsWe employed NY0123, a previously identified potent EPAC inhibitor, to explore the anti-angiogenic biological role of EPAC1 in vitro and in vivo through vascular endothelial cells, rat aortic ring, Matrigel plug, and chick embryo chorioallantoic membrane (CAM) and yolk sac membrane (YSM) assays, as well as the in vivo xenograft tumor models of TNBC in both chick embryo and mice. Key findingsInhibiting EPAC1 in vascular endothelial cells by NY0123 significantly suppresses angiogenesis and tumor growth of TNBC. In addition, NY0123 possesses a better inhibitory efficacy than ESI-09, a reported specific EPAC inhibitor tool compound. Importantly, inhibiting EPAC1 in vascular endothelia cells regulates the typical angiogenic signaling network, which is associated with not only vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor-2 (VEGFR2) signaling, but also PI3K/AKT, MEK/ERK and Notch pathway. ConclusionsOur findings support that EPAC1 may serve as an effective anti-angiogenic therapeutic target of TNBC, and EPAC inhibitor NY0123 has the therapeutic potential to be developed for the treatment of TNBC.