Targeting MUC1-C Research Articles

MUC1-C Dependence for the Progression of Pancreatic Neuroendocrine Tumors Identifies a Druggable Target for the Treatment of This Rare Cancer.

Patients with pancreatic neuroendocrine tumors (pNETs) have limited access to effective targeted agents and invariably succumb to progressive disease. MUC1-C is a druggable oncogenic protein linked to driving pan-cancers. There is no known involvement of MUC1-C in pNET progression. The present work was performed to determine if MUC1-C represents a potential target for advancing pNET treatment. We demonstrate that the MUC1 gene is upregulated in primary pNETs that progress with metastatic disease. In pNET cells, MUC1-C drives E2F- and MYC-signaling pathways necessary for survival. Targeting MUC1-C genetically and pharmacologically also inhibits self-renewal capacity and tumorigenicity. Studies of primary pNET tissues further demonstrate that MUC1-C expression is associated with (i) an advanced NET grade and pathological stage, (ii) metastatic disease, and (iii) decreased disease-free survival. These findings demonstrate that MUC1-C is necessary for pNET progression and is a novel target for treating these rare cancers with anti-MUC1-C agents under clinical development.

Abstract CT070: Solid tumor patients require higher cyclophosphamide (cy) dose than multiple myeloma (MM) patients to achieve adequate lymphodepletion (LD) necessary to enable allogeneic CAR-T expansion

Abstract Introduction: Poseida is developing innovative allogeneic T stem cell memory rich CAR-T both for hematologic malignancies (HM) and solid tumors (ST) including P-BCMA-ALLO1 which targets BCMA for MM, and P-MUC1C-ALLO1 targeting MUC1-C for epithelial-derived ST. Optimal LD for allogeneic cell therapies remains to be established. Most research has focused on HM, where patients (pts) have likely undergone HSCT and are, therefore, LD experienced in contrast to ST pts. Consequently, ST pts may require higher doses of LD chemotherapy to achieve LD depth comparable to HM pts. This study sought to compare LD with higher doses of cy across our early phase 1 trials (NCT04960579/NCT05239143) which are enrolling ST and MM pts, respectively. Methods: P-BCMA-ALLO1 and P-MUC1C-ALLO1 are 3+3 phase 1 dose escalation studies enrolling heavily pre-treated pts. LD arm S used cy 300 mg/m2 + fludarabine (flu) 30 mg/m2 × 3 days, followed by CAR-T. Alternative arms tested higher cy doses: P1 (500 mg/m2) and P2 (1,000 mg/m2), both with flu. We assessed LD depth and cellular kinetics (CK) by measuring WBC, serum IL-15, and CAR-T transcripts (qPCR). Results: By Jan 4, 2024, 42 pts received P-BCMA-ALLO1 (22 in S, 13 in P1, 7 in P2), and 30 pts received P-MUC1C-ALLO1 (19 in S, 9 in P1, 2 in P2). ST pts presented with higher baseline WBC compared to MM pts with median counts of 5.7×103 vs. 4.4×103/µL. LD was less pronounced in ST pts with a median WBC nadir of 1.1×103/µL for both S and P1. In MM pts median WBC nadir was 0.6×103 for S vs. 0.2×103 for P1. For P-BCMA-ALLO1, CK at 2×106 cells/kg dose showed a mean Cmax of 130,811 copies (cp)/µg in P2 and 6,191 in P1 compared to 170 in S. Median WBC nadir was significantly (p=0.0002) lower for P2 (0.1×103/µL) compared to S (0.6×103), with corresponding AUC0-13d values of 3.5×103/µL for P2 vs. 10×103 for S (p=0.0013). Peak serum IL-15 in P2 was 66.1 pg/mL, significantly higher than 29.7 in S (p=0.0110). In P1, there was a trend towards improved LD with median WBC nadir for P1 of 0.3×103/µL and AUC0-13d of 6.4×103/µL.P1 LD for P-MUC1C-ALLO1 did not improve CK, with WBC nadir and AUC 0-13d values comparable to S. P-MUC1C-ALLO1 CK at 2×106 cells/kg showed a mean Cmax of 692 cp/µg DNA in S, 23 in P1, and 4,200 in P2. P-MUC1C-ALLO1 pts receiving P2 achieved the deepest LD (WBC nadir: 0.1×103/µL). Peak IL-15 in ST pts was increased and delayed to day 8 in P2, compared to day 0 - 1 in S or P1. Conclusion: Increasing cy dose to 500 or 1,000 mg/m2 improves CK for P-BCMA-ALLO1 pts due to enhanced LD depth. For P-MUC1C-ALLO1 pts, increasing cy to 500 does not improve LD depth or CK compared to 300. This difference suggests the need for higher LD doses in ST pts than MM pts to achieve optimal CK. This differential need for LD chemo for these two studies is unlikely due to cellular characteristics because of similar manufacturing technology with the only difference being the binder. Citation Format: Sabrina Haag, Jeff D. Eskew, Katherine McArthur, Joanne McCaigue, Sepideh Vaziri, Samuel DePrimo, Christopher E. Martin, Catherine Gregovics, Ann Murphy, Hamid Namini, Ellen Christie, Marcela Marinez-Prieto, Rajesh Belani, Stacey Cranert, Julia Coronella, Devon Shedlock. Solid tumor patients require higher cyclophosphamide (cy) dose than multiple myeloma (MM) patients to achieve adequate lymphodepletion (LD) necessary to enable allogeneic CAR-T expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT070.

Abstract 3279: MUC1 is necessary for the inflammatory memory response to osimertinib resistance in NSCLC cells

Abstract Emergence of resistance is an invariable outcome in cancer progression that may involve memory of cancer cells to treatment. The oncogenic MUC1-C protein confers pleotropic resistance of cancer cells to diverse cytotoxic and targeted agents by unclear mechanisms. We demonstrate that MUC1-C regulates the interferon (IFN) type I/II pathways in H1975 non-small cell lung cancer (NSCLC) cells selected for osimertinib resistance (H1975-OR). Targeting MUC1-C in H1975-OR cells suppressed STAT1 and inflammatory IFN signaling in association with reversing the osimertinib-resistant phenotype. Studies of H1975-OR cells selected for growth in the absence of osimertinib demonstrate that revertant H1975-RT cells retain MUC1-C-dependent memory necessary for recalling osimertinib resistance. Mechanistically, osimertinib treatment of H1975-RT cells activates the MUC1 gene at a (i) promoter-like signature (PLS) by MUC1-C and STAT1, and (ii) proximal enhancer-like signature (pELS) by PBAF and JUN/AP-1. Targeting MUC1-C in osimertinib-treated H1975-RT and MGH170 NSCLC MET-amplified cells isolated from a patient refractory to osimertinib treatment suppressed induction of STAT1 and downstream IFN-stimulated genes (ISGs) encoding MX1, OAS1 and ISG15. Targeting MUC1-C, STAT1, PBRM1/PBAF and JUN/AP-1 further confirmed their dependencies for reemergence of osimertinib resistance in H1975-RT and MGH170 cells. In support of these results, high MUC1-C protein expression analyzed by IHC is associated with shorter progression free survival for patients treated with osimertinib. These findings and the demonstration that MUC1-C is upregulated in NSCLC cells from patients refractory to osimertinib indicate that MUC1-C drives osimertinib resistance in NSCLC cells by promoting an inflammatory memory response. Citation Format: Naoki Haratake, Atrayee Bhattacharya, Ayako Nakashoji, Hiroki Ozawa, Mototsugu Shimokawa, Donald Kufe. MUC1 is necessary for the inflammatory memory response to osimertinib resistance in NSCLC cells [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 3279.

MUC1-C is a target of salinomycin in inducing ferroptosis of cancer stem cells

The oncogenic MUC1-C transmembrane protein is a critical effector of the cancer stem cell (CSC) state. Addiction to MUC1-C for self-renewal in the progression of human cancers has emphasized the need for development of anti-MUC1-C agents. However, there are presently no approved small molecules for targeting MUC1-C-dependent CSCs. In screening for small molecules, we identified salinomycin (SAL), an inducer of ferroptosis, as a potent inhibitor of MUC1-C signaling. We demonstrate that SAL suppresses MUC1-C expression by disrupting a NF-κB/MUC1-C auto-inductive circuit that is necessary for ferroptosis resistance. Our results show that SAL-induced MUC1-C suppression downregulates a MUC1-C→MYC pathway that activates genes encoding (i) glutathione-disulfide reductase (GSR), and (ii) the LDL receptor related protein 8 (LRP8), which inhibit ferroptosis by generating GSH and regulating selenium levels, respectively. GSR and LRP8 contribute to the function of glutathione peroxidase 4 (GPX4), an essential negative regulator of ferroptotic cell death. We demonstrate that targeting MUC1-C genetically or with the GO-203 peptide inhibitor suppresses GPX4 expression and GPX activity in association with the induction of ferroptosis. Studies of CSCs enriched by serial passage as tumorspheres further demonstrate that the effects of SAL are mediated by downregulation of MUC1-C and thereby overcoming resistance to ferroptosis. As confirmation of these results, rescue of MUC1-C downregulation with the MUC1-C cytoplasmic domain (i) reversed the suppression of GSR, LRP8 and GPX4 expression, and (ii) attenuated the induction of ferroptosis. These findings identify SAL as a unique small molecule inhibitor of MUC1-C signaling and demonstrate that MUC1-C is an important effector of resistance to ferroptosis.

MUC1-C is necessary for SHP2 activation and BRAF inhibitor resistance in BRAF(V600E) mutant colorectal cancer

Colorectal cancers (CRCs) harboring the BRAF(V600E) mutation are associated with aggressive disease and resistance to BRAF inhibitors by feedback activation of the receptor tyrosine kinase (RTK)→RAS→MAPK pathway. The oncogenic MUC1-C protein promotes progression of colitis to CRC; whereas there is no known involvement of MUC1-C in BRAF(V600E) CRCs. The present work demonstrates that MUC1 expression is significantly upregulated in BRAF(V600E) vs wild-type CRCs. We show that BRAF(V600E) CRC cells are dependent on MUC1-C for proliferation and BRAF inhibitor (BRAFi) resistance. Mechanistically, MUC1-C integrates induction of MYC in driving cell cycle progression with activation of the SHP2 phosphotyrosine phosphatase, which enhances RTK-mediated RAS→ERK signaling. We demonstrate that targeting MUC1-C genetically and pharmacologically suppresses (i) activation of MYC, (ii) induction of the NOTCH1 stemness factor, and (iii) the capacity for self-renewal. We also show that MUC1-C associates with SHP2 and is required for SHP2 activation in driving BRAFi-induced feedback of ERK signaling. In this way, targeting MUC1-C in BRAFi-resistant BRAF(V600E) CRC tumors inhibits growth and sensitizes to BRAF inhibition. These findings demonstrate that MUC1-C is a target for the treatment of BRAF(V600E) CRCs and for reversing their resistance to BRAF inhibitors by suppressing the feedback MAPK pathway.

MUC1-C is a master regulator of MICA/B NKG2D ligand and exosome secretion in human cancer cells

BackgroundThe MUC1-C protein evolved in mammals to protect barrier tissues from loss of homeostasis; however, MUC1-C promotes oncogenesis in association with chronic inflammation. Aberrant expression of MUC1-C in cancers has...

Targeting MUC1-C Suppresses Chronic Activation of Cytosolic Nucleotide Receptors and STING in Triple-Negative Breast Cancer.

Simple SummaryTriple-negative breast cancers (TNBCs) are recalcitrant tumors with limited therapeutic options. Cytotoxic agents, including platinum-based drugs, are a standard of care for advanced TNBCs. Olaparib is also used for the treatment of germline BRCA mutant TNBC tumors in the adjuvant and recurrent disease settings. Notably, however, the effectiveness of these genotoxic agents is often limited by intrinsic and adaptive DNA damage resistance. We demonstrate in TNBC cells that the oncogenic MUC1-C protein chronically activates the type I interferon (IFN) pathway, drives the cGAS/STING axis and induces expression of the DNA damage resistance gene signature (IRDS). Targeting MUC1-C inhibits activation of this pathway in the response to carboplatin and olaparib and sensitizes TNBC cells to these agents. These findings indicate that MUC1-C is a target, which is druggable, for overcoming the obstacle of DNA damage resistance in the treatment of TNBCs.The MUC1-C apical transmembrane protein is activated in the acute response of epithelial cells to inflammation. However, chronic MUC1-C activation promotes cancer progression, emphasizing the importance of MUC1-C as a target for treatment. We report here that MUC1-C is necessary for intrinsic expression of the RIG-I, MDA5 and cGAS cytosolic nucleotide pattern recognition receptors (PRRs) and the cGAS-stimulator of IFN genes (STING) in triple-negative breast cancer (TNBC) cells. Consistent with inducing the PRR/STING axis, MUC1-C drives chronic IFN-β production and activation of the type I interferon (IFN) pathway. MUC1-C thereby induces the IFN-related DNA damage resistance gene signature (IRDS), which includes ISG15, in linking chronic inflammation with DNA damage resistance. Targeting MUC1-C in TNBC cells treated with carboplatin or the PARP inhibitor olaparib further demonstrated that MUC1-C is necessary for expression of PRRs, STING and ISG15 and for intrinsic DNA damage resistance. Of translational relevance, MUC1 significantly associates with upregulation of STING and ISG15 in TNBC tumors and is a target for treatment with CAR T cells, antibody–drug conjugates (ADCs) and direct inhibitors that are under preclinical and clinical development.

Targeting MUC1-C reverses the cisplatin resistance of esophageal squamous cell carcinoma in vitro and in vivo.

BackgroundThe efficacy of chemotherapeutic treatment of esophageal squamous cell carcinoma (ESCC) is limited by drug resistance during. This severely compromises the long-term survival rate of patients. Therefore, reversing chemotherapy resistance in ESCC may improve the therapeutic outcome. Here, we investigated the molecular mechanism of MUC1-C, the C-terminal transmembrane subunit of MUC1 (a transmembrane heterodimer protein), and its role in the reversal of cisplatin sensitivity in ESCC cells.MethodsWe assessed the efficacy of GO-203, a cell-penetrating peptide, as a chemotherapeutic target of MUC1-C using cell proliferation, colony-forming, and transwell assays. Apoptosis was analyzed in GO-203-treated cells by flow cytometry. Tumor xenograft assay was performed in nude mice to corroborate our in vitro findings.ResultsGO-203 treatment inhibited cell proliferation and restrained the migration and invasion of cisplatin-resistant ESCC. Moreover, targeting MUC1 resulted in enhanced apoptosis in GO-203-treated cells. These in vitro pro-apoptotic and anti-proliferative effects of GO-203 in combination with cisplatin were validated by in vivo models. Significantly smaller tumor volumes were observed in ESCCs-xenografted nude mice treated with GO-203 in combination with cisplatin compared with mice treated with monotherapy or their control counterparts. We found that blocking MUC1-C with GO-203 significantly reversed the cisplatin resistance in ESCC via modulating Akt and ERK pathways.ConclusionsOur findings suggest that GO-203 may hold potential as an ancillary therapeutic molecule and a chemosensitizer to improve the outcomes of cisplatin-based chemotherapy especially in patients with cisplatin-resistant ESCC.

MUC1-C IS A DRUGGABLE TARGET FOR TREATMENT OF COLITIS AND PROGRESSION OF COLITIS-ASSOCIATED COLORECTAL CANCER

Abstract The MUC1-C oncoprotein evolved in mammals to protect epithelial cells, such as those lining the gastrointestinal tract, from loss of homeostasis. In this way, MUC1-C activates pathways that contribute to inflammation, proliferation and remodeling associated with the wound healing response. MUC1-C is upregulated in human tissues from inflamed ulcerative colitis (UC) mucosa as compared to that from normal and uninflamed UC mucosa. MUC1-C is also upregulated in a mouse MUC1+/-/IL-10-/- model of colitis, consistent with its involvement in the inflammatory response. MUC1-C forms a direct complex with NF-κB p65 and promotes the activation of NF-κB target genes, including MUC1 itself in an auto- inductive circuit. MUC1-C thereby drives proinflammatory NF-κB pathway genes in human inflamed UC tissues and in the genetically engineered mouse model (GEMM) of colitis. Mechanistically, MUC1-C induces the TGF-b-activated kinase 1 (TAK1), which is an essential effector of proinflammatory NF-κB signaling. Of further significance, MUC1-C drives the TAK1→NF-κB p65 pathway in human colon cancer cell lines, and MUC1 and TAK1 are upregulated in human colon cancers. These seminal findings supported the notion that MUC1-C contributes to colitis and progression to colon cancer. To extend these studies, MUC1-C was targeted with an inhibitor that blocks its homodimerization and function. Remarkably, treatment of the MUC1+/-/IL-10-/- GEMM with the GO-203 inhibitor was associated with decreases in the severity of colitis and progression of colitis to dysplasia and carcinomas. Intestinal stem cells (ISCs) that express Lgr5 are of importance in the inflammatory response to colitis and in progression to colitis-associated colorectal cancer (CACC). Targeting MUC1-C with GO-203 in mouse models of colitis suppressed Lgr5 expression, as well as induction of MYC and other core pluripotency factors. By extension to human colon cancer cells, we found that MUC1- C drives MYC with activation of LGR5 and stemness. MUC1-C also induces cancer stem cell (CSC) markers (BMI1, ALDH1, FOXA1, LIN28B) and the OCT4, SOX2, and NANOG pluripotency factors. Consistent with driving the CSC state, targeting MUC1-C suppressed the capacity of CRC cells to promote wound healing, invasion, self-renewal, and tumorigenicity. Analysis of human tissues further demonstrated that MUC1 expression associates with activation of inflammatory pathways, development of colitis, and aggressiveness of CRCs. These results collectively indicate that MUC1-C is of importance for integrating stemness and pluripotency in colitis and CRC. Of clinical relevance, the findings further indicate that MUC1-C represents a previously unrecognized target that is potentially druggable with orally administered GO-203 now being tested in the GEMMs for treating progression of colitis and CRC.

MUC1-C integrates activation of the IFN-γ pathway with suppression of the tumor immune microenvironment in triple-negative breast cancer

BackgroundImmune checkpoint inhibitors (ICIs) have had a profound impact on the treatment of many tumors; however, their effectiveness against triple-negative breast cancers (TNBCs) has been limited. One factor limiting responsiveness...

MUC1-C regulates lineage plasticity driving progression to neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is an aggressive malignancy with no effective targeted therapies. The oncogenic MUC1-C protein is overexpressed in castration-resistant prostate cancer (CRPC) and NEPC, but its specific role is unknown. Here, we demonstrate that upregulation of MUC1-C in androgen-dependent PC cells suppresses androgen receptor (AR) axis signaling and induces the neural BRN2 transcription factor. MUC1-C activates a MYC→BRN2 pathway in association with induction of MYCN, EZH2 and NE differentiation markers (ASCL1, AURKA and SYP) linked to NEPC progression. Moreover, MUC1-C suppresses the p53 pathway, induces the Yamanaka pluripotency factors (OCT4, SOX2, KLF4 and MYC) and drives stemness. Targeting MUC1-C decreases PC self-renewal capacity and tumorigenicity, suggesting a potential therapeutic approach for CRPC and NEPC. In PC tissues, MUC1 expression associates with suppression of AR signaling and increases in BRN2 expression and NEPC score. These results highlight MUC1-C as a master effector of lineage plasticity driving progression to NEPC.

MUC1-C Activates the NuRD Complex to Drive Dedifferentiation of Triple-Negative Breast Cancer Cells.

The NuRD chromatin remodeling and deacetylation complex, which includes MTA1, MBD3, CHD4, and HDAC1 among other components, is of importance for development and cancer progression. The oncogenic mucin 1 (MUC1) C-terminal subunit (MUC1-C) protein activates EZH2 and BMI1 in the epigenetic reprogramming of triple-negative breast cancer (TNBC). However, there is no known link between MUC1-C and chromatin remodeling complexes. Here, we showed that MUC1-C binds directly to the MYC HLH-LZ domain and identified a previously unrecognized MUC1-C→MYC pathway that regulates the NuRD complex. MUC1-C/MYC complexes selectively activated the MTA1 and MBD3 genes and posttranscriptionally induced CHD4 expression in basal- but not luminal-type BC cells. In turn, MUC1-C formed complexes with these NuRD components on the ESR1 promoter. Downregulating MUC1-C decreased MTA1/MBD3/CHD4/HDAC1 occupancy and increased H3K27 acetylation on the ESR1 promoter, with induction of ESR1 expression and downstream estrogen response pathways. Targeting MUC1-C and these NuRD components also induced expression of FOXA1, GATA3, and other markers associated with the luminal phenotype. These findings support a model in which MUC1-C activates the NuRD complex to drive dedifferentiation and reprogramming of TNBC cells. SIGNIFICANCE: MUC1-C directly interacts with MYC to activate the NuRD complex, mediating regulation of the estrogen receptor in triple-negative breast cancer cells.

Targeting MUC1-C Inhibits TWIST1 Signaling in Triple-Negative Breast Cancer

The oncogenic MUC1-C protein and the TWIST1 epithelial-mesenchymal transition transcription factor (EMT-TF) are aberrantly expressed in triple-negative breast cancer (TNBC) cells. However, there is no known association between MUC1-C and TWIST1 in TNBC or other cancer cells. Here, we show that MUC1-C activates STAT3, and that MUC1-C and pSTAT3 drive induction of the TWIST1 gene. In turn, MUC1-C binds directly to TWIST1, and MUC1-C/TWIST1 complexes activate MUC1-C expression in an autoinductive circuit. The functional significance of the MUC1-C/TWIST1 circuit is supported by the demonstration that this pathway is sufficient for driving (i) the EMT-TFs, ZEB1 and SNAIL, (ii) multiple genes in the EMT program as determined by RNA-seq, and (iii) the capacity for cell invasion. We also demonstrate that the MUC1-C/TWIST1 circuit drives (i) expression of the stem cell markers SOX2, BMI1, ALDH1, and CD44, (ii) self-renewal capacity, and (iii) tumorigenicity. In concert with these results, we show that MUC1-C and TWIST1 also drive EMT and stemness in association with acquired paclitaxel (PTX) resistance. Of potential therapeutic importance, targeting MUC1-C and thereby TWIST1 reverses the PTX refractory phenotype as evidenced by synergistic activity with PTX against drug-resistant cells. These findings uncover a master role for MUC1-C in driving the induction of TWIST1, EMT, stemness, and drug resistance, and support MUC1-C as a highly attractive target for inhibiting TNBC plasticity and progression.

MUC1-C represses the RASSF1A tumor suppressor in human carcinoma cells

RASSF1A encodes a tumor suppressor that inhibits the RAS→RAF→MEK→ERK pathway and is one of the most frequently inactivated genes in human cancers. MUC1-C is an oncogenic effector of the cancer cell epigenome that is overexpressed in diverse carcinomas. We show here that MUC1-C represses RASSF1A expression in KRAS wild-type and mutant cancer cells. Mechanistically, MUC1-C occupies the RASSF1A promoter in a complex with the ZEB1 transcriptional repressor. In turn, MUC1-C/ZEB1 complexes recruit DNA methyltransferase 3b (DNMT3b) to the CpG island in the RASSF1A promoter. Targeting MUC1-C, ZEB1, and DNMT3b thereby decreases methylation of the CpG island and derepresses RASSF1A transcription. We also show that targeting MUC1-C regulates KRAS signaling, as evidenced by RNA-seq analysis, and decreases MEK/ERK activation, which is of importance for RAS-mediated tumorigenicity. These findings define a previously unrecognized role for MUC1-C in suppression of RASSF1A and support targeting MUC1-C as an approach for inhibiting MEK→ERK signaling.

MUC1-C Integrates Chromatin Remodeling and PARP1 Activity in the DNA Damage Response of Triple-Negative Breast Cancer Cells.

The oncogenic MUC1-C protein is overexpressed in triple-negative breast cancer (TNBC) cells and contributes to their epigenetic reprogramming and chemoresistance. Here we show that targeting MUC1-C genetically or pharmacologically with the GO-203 inhibitor, which blocks MUC1-C nuclear localization, induced DNA double-strand breaks and potentiated cisplatin (CDDP)-induced DNA damage and death. MUC1-C regulated nuclear localization of the polycomb group proteins BMI1 and EZH2, which formed complexes with PARP1 during the DNA damage response. Targeting MUC1-C downregulated BMI1-induced H2A ubiquitylation, EZH2-driven H3K27 trimethylation, and activation of PARP1. As a result, treatment with GO-203 synergistically sensitized both mutant and wild-type BRCA1 TNBC cells to the PARP inhibitor olaparib. These findings uncover a role for MUC1-C in the regulation of PARP1 and identify a therapeutic strategy for enhancing the effectiveness of PARP inhibitors against TNBC. SIGNIFICANCE: These findings demonstrate that targeting MUC1-C disrupts epigenetics of the PARP1 complex, inhibits PARP1 activity, and is synergistic with olaparib in TNBC cells.

Inhibition of MUC1-C regulates metabolism by AKT pathway in esophageal squamous cell carcinoma.

Esophageal squamous cell carcinoma (ESCC) is one of the most common digestive tumors worldwide. The Mucin 1 (MUC1) heterodimeric protein has been confirmed that is overexpressed in ESCC and induced adverse outcomes. However, the detailed mechanism(s) remained challenging. So, we investigated the relationship between MUC1‐C and metabolism in ESCC cells. In the results, TP53‐induced glycolysis and apoptosis regulator (TIGAR) was overexpressed and correlative with MUC1‐C positively in ESCC tissue. Targeting MUC1‐C inhibits AKT–mTORC–S6K1 signaling and blocks TIGAR translation. We found that the inhibitory effect of GO‐203 on TIGAR was mediated by inhibition of AKT–mTOR–S6K1 pathway. The findings also demonstrated that the suppressive effect of GO‐203 on TIGAR is related to the decrease of glutathione level, the increase of reactive oxygen species and the loss of mitochondrial transmembrane membrane potential. In xenograft tissues, GO‐203 inhibited the growth of ESCC cells and lead to the low expression of transmembrane C‐terminal subunit (MUC1‐C) and TIGAR. This evidence supports the contention that MUC1‐C is significant for metabolism in ESCC and indicated that MUC1‐C is a potential target for the treatment of ESCC.

Targeting MUC1-C suppresses BCL2A1 in triple-negative breast cancer

B-cell lymphoma 2-related protein A1 (BCL2A1) is a member of the BCL-2 family of anti-apoptotic proteins that confers resistance to treatment with anti-cancer drugs; however, there are presently no agents that target BCL2A1. The MUC1-C oncoprotein is aberrantly expressed in triple-negative breast cancer (TNBC) cells, induces the epithelial–mesenchymal transition (EMT) and promotes anti-cancer drug resistance. The present study demonstrates that targeting MUC1-C genetically and pharmacologically in TNBC cells results in the downregulation of BCL2A1 expression. The results show that MUC1-C activates the BCL2A1 gene by an NF-κB p65-mediated mechanism, linking this pathway with the induction of EMT. The MCL-1 anti-apoptotic protein is also of importance for the survival of TNBC cells and is an attractive target for drug development. We found that inhibiting MCL-1 with the highly specific MS1 peptide results in the activation of the MUC1-C→NF-κB→BCL2A1 pathway. In addition, selection of TNBC cells for resistance to ABT-737, which inhibits BCL-2, BCL-xL and BCL-W but not MCL-1 or BCL2A1, is associated with the upregulation of MUC1-C and BCL2A1 expression. Targeting MUC1-C in ABT-737-resistant TNBC cells suppresses BCL2A1 and induces death, which is of potential therapeutic importance. These findings indicate that MUC1-C is a target for the treatment of TNBCs unresponsive to agents that inhibit anti-apoptotic members of the BCL-2 family.

MUC1-C Induces PD-L1 and Immune Evasion in Triple-Negative Breast Cancer.

The immune checkpoint ligand PD-L1 and the transmembrane mucin MUC1 are upregulated in triple-negative breast cancer (TNBC), where they contribute to its aggressive pathogenesis. Here, we report that genetic or pharmacological targeting of the oncogenic MUC1 subunit MUC1-C is sufficient to suppress PD-L1 expression in TNBC cells. Mechanistic investigations showed that MUC1-C acted to elevate PD-L1 transcription by recruitment of MYC and NF-κB p65 to the PD-L1 promoter. In an immunocompetent model of TNBC in which Eo771/MUC1-C cells were engrafted into MUC1 transgenic mice, we showed that targeting MUC1-C associated with PD-L1 suppression, increases in tumor-infiltrating CD8+ T cells and tumor cell killing. MUC1 expression in TNBCs also correlated inversely with CD8, CD69, and GZMB, and downregulation of these markers associated with decreased survival. Taken together, our findings show how MUC1 contributes to immune escape in TNBC, and they offer a rationale to target MUC1-C as a novel immunotherapeutic approach for TNBC treatment.Significance: These findings show how upregulation of the transmembrane mucin MUC1 contributes to immune escape in an aggressive form of breast cancer, with potential implications for a novel immunotherapeutic approach. Cancer Res; 78(1); 205-15. ©2017 AACR.

Targeting MUC1-C suppresses polycomb repressive complex 1 in multiple myeloma

The polycomb repressive complex 1 (PRC1) includes the BMI1, RING1 and RING2 proteins. BMI1 is required for survival of multiple myeloma (MM) cells. The MUC1-C oncoprotein is aberrantly expressed by MM cells, activates MYC and is also necessary for MM cell survival. The present studies show that targeting MUC1-C with (i) stable and inducible silencing and CRISPR/Cas9 editing and (ii) the pharmacologic inhibitor GO-203, which blocks MUC1-C function, downregulates BMI1, RING1 and RING2 expression. The results demonstrate that MUC1-C drives BMI1 transcription by a MYC-dependent mechanism. MUC1-C thus promotes MYC occupancy on the BMI1 promoter and thereby activates BMI1 expression. We also show that the MUC1-C→MYC pathway induces RING2 expression. Moreover, in contrast to BMI1 and RING2, we found that MUC1-C drives RING1 by an NF-κB p65-dependent mechanism. Targeting MUC1-C and thereby the suppression of these key PRC1 proteins was associated with downregulation of the PRC1 E3 ligase activity as evidenced by decreases in ubiquitylation of histone H2A. Targeting MUC1-C also resulted in activation of the PRC1-repressed tumor suppressor genes, PTEN, CDNK2A and BIM. These findings identify a heretofore unrecognized role for MUC1-C in the epigenetic regulation of MM cells.

MUC1-C activates EZH2 expression and function in human cancer cells

The EZH2 histone methyltransferase is a member of the polycomb repressive complex 2 (PRC2) that is highly expressed in diverse human cancers and is associated with a poor prognosis. MUC1-C is an oncoprotein that is similarly overexpressed in carcinomas and has been linked to epigenetic regulation. A role for MUC1-C in regulating EZH2 and histone methylation is not known. Here, we demonstrate that targeting MUC1-C in diverse human carcinoma cells downregulates EZH2 and other PRC2 components. MUC1-C activates (i) the EZH2 promoter through induction of the pRB→E2F pathway, and (ii) an NF-κB p65 driven enhancer in exon 1. We also show that MUC1-C binds directly to the EZH2 CXC region adjacent to the catalytic SET domain and associates with EZH2 on the CDH1 and BRCA1 promoters. In concert with these results, targeting MUC1-C downregulates EZH2 function as evidenced by (i) global and promoter-specific decreases in H3K27 trimethylation (H3K27me3), and (ii) activation of tumor suppressor genes, including BRCA1. These findings highlight a previously unreported role for MUC1-C in activating EZH2 expression and function in cancer cells.