Sensitivity Of Triple-negative Breast Cancer Research Articles

Ferroptosis: the emerging player in remodeling triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is a highly heterogeneous breast tumor type that is highly malignant, invasive, and highly recurrent. Ferroptosis is a unique mode of programmed cell death (PCD) at the morphological, physiological, and molecular levels, mainly characterized by cell death induced by iron-dependent accumulation of lipid peroxides, which plays a substantial role in a variety of diseases, including tumors and inflammatory diseases. TNBC cells have been reported to display a peculiar equilibrium metabolic profile of iron and glutathione, which may increase the sensitivity of TNBC to ferroptosis. TNBC possesses a higher sensitivity to ferroptosis than other breast cancer types. Ferroptosis also occurred between immune cells and tumor cells, suggesting that regulating ferroptosis may remodel TNBC by modulating the immune response. Many ferroptosis-related genes or molecules have characteristic expression patterns and are expected to be diagnostic targets for TNBC. Besides, therapeutic strategies based on ferroptosis, including the isolation and extraction of natural drugs and the use of ferroptosis inducers, are urgent for TNBC personalized treatment. Thus, this review will explore the contribution of ferroptosis in TNBC progression, diagnosis, and treatment, to provide novel perspectives and therapeutic strategies for TNBC management.

Self-assembled nanocomposites of carboxymethyl β-dextran/protamine sulfate for enhanced chemotherapeutic drug sensitivity of triple-negative breast cancer by autophagy inhibition via a ternary collaborative strategy

Drug resistance in cancer chemotherapy is a major confounding factor affecting the effectiveness of chemotherapeutic agents, thereby leading to poor clinical outcomes. Most chemotherapeutic drugs can induce protective autophagy and increase the resistance of tumors to chemotherapeutic drugs and reduce effective drug delivery to tumor cells. In this study, a tri-drug nanocomposite (NP) delivery system was devised using carboxymethyl β-dextran (CMD) and protamine sulfate (PS), two natural materials with good bio-compatibility. They were designed to carry the chemotherapeutic drug docetaxel (DTX), the autophagy inhibitor chloroquine (CQ), and Atg5 siRNA to cancer cells. The CQ + DTX + Atg5 siRNA NPs was driven by electrostatic interaction and self-assembly methods. The breast cancer cell line MDA-MB-231 was used for both cell culture and establishing mouse xenograft model. Our findings demonstrated that CQ and Atg5 siRNA encapsulated in NPs could enhance the sensitivity of tumor cells to DTX. The NPs exhibited remarkable considerable therapeutic effects for treating triple-negative breast cancer (TNBC) and good biosafety. Therefore, we established a novel multifunctional nanoplatform based on CMD and PS that enhances chemotherapeutic drug sensitivity through an autophagy inhibition strategy, providing new opportunities to overcome conventional drug resistance and enhance therapeutic efficiency against TNBC.

RNF126-Mediated MRE11 Ubiquitination Activates the DNA Damage Response and Confers Resistance of Triple-Negative Breast Cancer to Radiotherapy.

Triple-negative breast cancer (TNBC) has higher molecular heterogeneity and metastatic potential and the poorest prognosis. Because of limited therapeutics against TNBC, irradiation (IR) therapy is still a common treatment option for patients with lymph nodes or brain metastasis. Thus, it is urgent to develop strategies to enhance the sensitivity of TNBC tumors to low-dose IR. Here, the authors report that E3 ubiquitin ligase Ring finger protein 126 (RNF126) is important for IR-induced ATR-CHK1 pathway activation to enhance DNA damage repair (DDR). Mechanistically, RNF126 physically associates with the MRE11-RAD50-NBS1 (MRN) complex and ubiquitinates MRE11 at K339 and K480 to increase its DNA exonuclease activity, subsequent RPA binding, and ATR phosphorylation, promoting sustained DDR in a homologous recombination repair-prone manner. Accordingly, depletion of RNF126 leads to increased genomic instability and radiation sensitivity in both TNBC cells and mice. Furthermore, it is found that RNF126 expression is induced by IR activating the HER2-AKT-NF-κB pathway and targeting RNF126 expression with dihydroartemisinin significantly improves the sensitivity of TNBC tumors in the brain to IR treatment in vivo. Together, these results reveal that RNF126-mediated MRE11 ubiquitination is a critical regulator of the DDR, which provides a promising target for improving the sensitivity of TNBC to radiotherapy.

Mechanisms and Strategies to Overcome PD-1/PD-L1 Blockade Resistance in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is characterized by a high rate of systemic metastasis, insensitivity to conventional treatment and susceptibility to drug resistance, resulting in a poor patient prognosis. The immune checkpoint inhibitors (ICIs) represented by antibodies of programmed death receptor 1 (PD-1) and programmed death receptor ligand 1 (PD-L1) have provided new therapeutic options for TNBC. However, the efficacy of PD-1/PD-L1 blockade monotherapy is suboptimal immune response, which may be caused by reduced antigen presentation, immunosuppressive tumor microenvironment, interplay with other immune checkpoints and aberrant activation of oncological signaling in tumor cells. Therefore, to improve the sensitivity of TNBC to ICIs, suitable patients are selected based on reliable predictive markers and treated with a combination of ICIs with other therapies such as chemotherapy, radiotherapy, targeted therapy, oncologic virus and neoantigen-based therapies. This review discusses the current mechanisms underlying the resistance of TNBC to PD-1/PD-L1 inhibitors, the potential biomarkers for predicting the efficacy of anti-PD-1/PD-L1 immunotherapy and recent advances in the combination therapies to increase response rates, the depth of remission and the durability of the benefit of TNBC to ICIs.

CLDN1 Sensitizes Triple-Negative Breast Cancer Cells to Chemotherapy.

Simple SummaryTriple-negative breast cancer (TNBC) treatment represents a major challenge in oncology. TNBC evolves into chemotherapy resistance for 60 to 70% of the patients. About 77% of the TNBC displays a lack of claudin-1 (CLDN1), a major tight junction component. We demonstrated that CLDN1 increased the sensitivity of TNBC cell lines to the main chemotherapeutic agents commonly used for breast cancer treatment. Our data support the idea that CLDN1 may be a good predictive chemotherapy response marker to help therapeutic management of TNBC patients. In longer terms, this study could allow new treatment protocols creation aimed to induce CLDN1 expression in TNBCs to increase their sensitivity to chemotherapy. Triple-negative breast cancer (TNBC) is an aggressive subtype that constitutes 15–20% of breast cancer cases worldwide. Current therapies often evolve into chemoresistance and lead to treatment failure. About 77% of the TNBC lacks claudin-1 (CLDN1) expression, a major tight junction component, and this absence is correlated with poorer prognostic. Little is known about CLDN1 role on the chemosensitivity of breast cancer. Our clinical data analysis reveals that CLDN1 low expression is correlated to a poor prognostic in TNBC patients. Next, the sensitivity of various TNBC “claudin-1-high” or “claudin-1-low” cells to three compounds belonging to the main class of chemotherapeutic agents commonly used for the treatment of TNBC patients: 5-fluorouracil (5-FU), paclitaxel (PTX) and doxorubicin (DOX). Using RNA interference and stable overexpressing models, we demonstrated that CLDN1 expression increased the sensitivity of TNBC cell lines to these chemotherapeutic agents. Taken together, our data established the important role of CLDN1 in TNBC cells chemosensitivity and supported the hypothesis that CLDN1 could be a chemotherapy response predictive marker for TNBC patients. This study could allow new treatment protocols creation aimed to induce CLDN1 expression in TNBCs to increase their sensitivity to chemotherapy.

Leveraging diverse cell-death patterns to predict the prognosis and drug sensitivity of triple-negative breast cancer patients after surgery

BackgroundPostoperative progression and chemotherapy resistance is the major cause of treatment failure in patients with triple-negative breast cancer (TNBC). Currently, there is a lack of an ideal predictive model for the progression and drug sensitivity of postoperative TNBC patients. Diverse programmed cell death (PCD) patterns play an important role in tumor progression, which has the potential to be a prognostic and drug sensitivity indicator for TNBC after surgery. Materials and methodsTwelve PCD patterns (apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, entotic cell death, netotic cell death, parthanatos, lysosome-dependent cell death, autophagy-dependent cell death, alkaliptosis, and oxeiptosis) were analyzed for model construction. Bulk transcriptome, single-cell transcriptome, genomics, and clinical information were collected from TCGA-BRCA, METABRIC, GSE58812, GSE21653, GSE176078, GSE75688, and KM-plotter cohorts to validate the model. ResultsThe machine learning algorithm established a cell death index (CDI) with a 12-gene signature. Validated in five independent datasets, TNBC patients with high CDI had a worse prognosis after surgery. Two molecular subtypes of TNBC with distinct vital biological processes were identified by an unsupervised clustering model. A nomogram with high predictive performance was constructed by incorporating CDI with clinical features. Furthermore, CDI was associated with immune checkpoint genes and key tumor microenvironment components by integrated analysis of bulk and single-cell transcriptome. TNBC patients with high CDI are resistant to standard adjuvant chemotherapy regimens (docetaxel, oxaliplatin, etc.); however, they might be sensitive to palbociclib (an FDA-approved drug for luminal breast cancer). ConclusionGenerally, we established a novel CDI model by comprehensively analyzing diverse cell death patterns, which can accurately predict clinical prognosis and drug sensitivity of TNBC after surgery. A user-friendly website was created to facilitate the application of this prediction model (https://tnbc.shinyapps.io/CDI_Model/).

Hypoxia induces docetaxel resistance in triple-negative breast cancer via the HIF-1α/miR-494/Survivin signaling pathway

Cytotoxic chemotherapy is the major strategy to prevent and reduce triple-negative breast cancer (TNBC) progression and metastasis. Hypoxia increases chemoresistance and is associated with a poor prognosis for patients with cancer. Based on accumulating evidence, microRNAs (miRNAs) play an important role in acquired drug resistance. However, the role of miRNAs in hypoxia-induced TNBC drug resistance remains to be clarified. Here, we found that hypoxia induced TNBC docetaxel resistance by decreasing the miR-494 level. Modulating miR-494 expression altered the sensitivity of TNBC cells to DTX under hypoxic conditions. Furthermore, we identified Survivin as a direct miR-494 target. Hypoxia upregulated survivin expression. In a clinical study, the HIF-1α/miR-494/Survivin signaling pathway was also active in primary human TNBC, and miR-494 expression negatively correlated with HIF-1α and survivin expression. Finally, in a xenograft model, both miR-494 overexpression and the HIF-1α inhibitor PX-478 increased the sensitivity of TNBC to DTX by suppressing the HIF-1α/miR-494/Survivin signaling pathway in vivo. In conclusion, treatments targeting the HIF-1α/miR-494/Survivin signaling pathway potentially reverse hypoxia-induced drug resistance in TNBC.

MiR-1290 modulates the radioresistance of triple-negative breast cancer by targeting NLRP3-mediated pyroptosis.

To explore the roles and underlying mechanisms of miR-1290 in determining the sensitivity of triple-negative breast cancer (TNBC) to radiation therapy. ELISA was performed to detect the levels of IL-18 and IL-1β in radiosensitive cells and serum samples. The level of miR-1290 in radiosensitive cells and tissues was assessed by qRT-PCR assay. A luciferase reporter assay was performed to confirm NLRP3 as the target of miR-1290. Functionally, the roles of miR-1290 in TNBC radioresistance were analyzed by transfection of either miR-1290 mimic or miR-1290 inhibitor. Moreover, the involvement of the miR-1290/NLRP3 axis in TNBC radioresistance was analyzed by experiments with a miR-1290 mimic and NLRP3 overexpression. MTT and colony formation assays were used to detect radiation-induced cell viability and proliferation. qRT-PCR and western blot assays were used to detect pyroptosis markers (NLRP3, ACS and caspase-1). The results showed that radioresistance in TNBC cells was associated with a reduction in pyroptosis. miR-1290 expression was increased in radioresistant cells, and it had higher expression levels in the radioresistant tumor tissues of TNBC patients compared to the radiosensitive samples. The miR-1290 mimic suppressed radiation-induced pyroptosis and reduced the radiosensitivity of TNBC cells. Moreover, we found that NLRP3 was a potential target of miR-1290. Overexpression of NLRP3 partly reversed the effects of miR-1290 on pyroptosis and radioresistance. The mouse models showed that miR-1290 suppressed tumor size, tumor weight and pyroptosis. miR-1290/NLRP3-mediated pyroptosis may play an important role in determining radioresistance in TNBC and serve as a novel therapeutic option.

Active nanomaterials containing YAPTAZ reshape tumor immune microenvironment and enhance sensitivity of triple-negative breast cancer to immunotherapy

The present study designed a new type of active nanomaterials containing Yes-associated protein and transcriptional coactivator with PDZ-binding motif (YAPTAZ) to investigate its role in tumor immune microenvironment and treatment sensitivity in triple-negative breast cancer (TNBC). Three groups were established in this study, namely; blank control group (saline), YAPTAZ group and YAPTAZ-loaded active nanomaterial group. For in vitro assays, the functional role of active nanomaterials containing YAPTAZ in MDA-MB-231 cell proliferation, apoptosis, migration and invasion was analyzed by MTT assay, flow cytometry, scratch test and Transwell assay, respectively. For in vivo assays, tumor xenotransplantation experiment was performed to observe the effect of active nanomaterials containing YAPTAZ on treatment of TNBC. Administration of active nanomaterials containing YAPTAZ decreased proliferation, invasion and migration of TNBC cells, and promoted apoptosis, thereby enhancing the sensitivity of TNBC cells to treatments. The active nanomaterials were characterized by large surface area, high dispersion, specific adhesion function, tumor affinity and adhesion, when prolonging drug’s circulation time. The findings from our study highlight the potential for targeted active nanomaterials containing YAPTAZ for TNBC treatment, providing a new interventional therapy for TNBC.

Paclitaxel Resistance Modulated by the Interaction between TRPS1 and AF178030.2 in Triple-Negative Breast Cancer.

Paclitaxel is a chemotherapeutic agent that acts as an inhibitor of cellular mitosis and has been widely used in the treatment of triple-negative breast cancer (TNBC). However, paclitaxel resistance is one of the major reasons that contribute to the high failure rates of chemotherapy and the relapse of TNBC. Accumulating studies have demonstrated that long noncoding RNA (lncRNA) plays a role in the paclitaxel resistance and positively correlated with progression and metastasis of breast cancers. In the present study, microarray expression profile analysis of lncRNA was performed between paclitaxel-resistant TNBC cell line MDA-MB-231 and their parental cells. After verification with quantitative PCR, we identified that AF178030.2, an orphan lncRNA, was significantly upregulated in paclitaxel-resistant TNBC cells. Overexpression of AF178030.2 greatly attenuated the sensitivity of TNBC to paclitaxel, whereas knockdown of AF178030.2 enhanced the sensitivity of TNBC cells to paclitaxel. Furthermore, bioinformatic analysis and RNA binding protein immunoprecipitation assay reveal that AF178030.2 can directly bind with trichorhinophalangeal syndrome-1 (TRPS1), an oncogene in breast cancer, and downregulate its expression in paclitaxel-resistant TNBC cells. TRPS1 overexpression effectively increased the sensitivity of paclitaxel-resistant TNBC cells to paclitaxel. Taking together, high AF178030.2 expression contributed to paclitaxel resistance in TNBC through TRPS1 and poor clinical outcomes, which may provide a new treatment strategy for paclitaxel-resistant TNBC patients.

ERβ in Triple-Negative Breast Cancer: Emerging Concepts and Therapeutic Possibilities

Despite the improvements in diagnostic and therapeutic approaches, breast cancer still remains one of the world’s leading causes of death among women. Particularly, triple negative breast cancer (TNBC) is characterized by aggressiveness, metastatic spreading, drug resistance and a very high percentage of death in patients. Nowadays, identification of new targets in TNBC appears very compelling. TNBC are considered negative for the estrogen receptor alpha (ERα) expression. Nevertheless, they often express ERβ and its variants. As such, this TNBC subtype still responds to estrogens. While the ERβ1 variant seems to act as a tumor-suppressor, the two variants ERβ2 and 5 exhibit pro-oncogenic activities in TNBC. Thus, ERβ1 activation might be used to limit the growth and spreading as well as to increase the drug sensitivity of TNBC. In contrast, the pro-oncogenic properties of ERβ2 and ERβ5 suggest the possible development and clinical use of specific antagonists in TNBC treatment. Furthermore, the role of ERβ might be regarded in the context of the androgen receptor (AR) expression, which represents another key marker in TNBC. The relationship between AR and ERβ as well as the ability to modulate the receptor-mediated effects through agonists/antagonists represent a challenge to develop more appropriate therapies in clinical management of TNBC patients. In this review, we will discuss the most recent data in the field. Therapeutic implications of these findings are also presented in the light of the discovery of specific ERβ modulators.

263P Predicting bevacizumab efficacy in mTNBC

Triple-negative breast cancer (TNBC) has a very high rate of recurrence and till now there is no standard of care. Because of the sensitivity of TNBC to platinum compounds and the synergistic effect between bevacizumab and paclitaxel according to many studies, our aim was to combine all these agents to evaluate the efficacy of bevacizumab in combination with carboplatin and paclitaxel as first-line treatment in metastatic TNBC (mTNBC) and to predict whom can benefit from this combination.

CHFR-mediated degradation of RNF126 confers sensitivity to PARP inhibitors in triple-negative breast cancer cells

Ring-finger protein 126 (RNF126), an E3 ubiquitin ligase, plays crucial roles in various biological processes, including cell proliferation, DNA damage repair, and intracellular vesicle trafficking. Whether RNF126 is modulated by posttranslational modifications is poorly understood. Here, we show that PARP1 interacts with and poly(ADP)ribosylates RNF126, which then recruits the PAR-binding E3 ubiquitin ligase CHFR to promote ubiquitination and degradation of RNF126. Moreover, RNF126 is required for the activation of ATR-Chk1 signaling induced by either irradiation (IR) or a PARP inhibitor (PARPi), and depletion of RNF126 increases the sensitivity of triple-negative breast cancer (TNBC) cells to PARPi treatment. Our findings suggest that PARPi-mediated upregulation of RNF126 protein stability contributes to TNBC cell resistance to PARPi. Therefore, targeting the E3 ubiquitin ligase RNF126 may be a novel treatment for overcoming the resistance of TNBC cells to PARPi in clinical trials.

MiR-27-3p Enhances the Sensitivity of Triple-Negative Breast Cancer Cells to the Antitumor Agent Olaparib by Targeting PSEN-1, the Catalytic Subunit of Γ-Secretase.

Olaparib has been used in the treatment of triple-negative breast cancer (TNBC) with BRCA mutations. In the present study, we demonstrated the effect of miR-27-3p on the γ-secretase pathway by regulating the sensitivity of TNBC cells to olaparib. miR-27-3p, a microRNA with the potential to target PSEN-1, the catalytic subunit of γ-secretase mediating the second step of the cleavage of the Notch protein, was identified by the online tool miRDB and found to inhibit the expression of PSEN-1 by directly targeting the 3’-untranslated region (3’-UTR) of PSEN-1. The overexpression of miR-27-3p inhibited the activation of the Notch pathway via the inhibition of the cleavage of the Notch protein, mediated by γ-secretase, and, in turn, enhanced the sensitivity of TNBC cells to the antitumor agent olaparib. Transfection with PSEN-1 containing mutated targeting sites for miR-27-3p or the expression vector of the Notch protein intracellular domain (NICD) almost completely blocked the effect of miR-27-3p on the Notch pathway or the sensitivity of TNBC cells to olaparib, respectively. Therefore, our results suggest that the miR-27-3p/γ-secretase axis participates in the regulation of TNBC and that the overexpression of miR-27-3p represents a potential approach to enhancing the sensitivity of TNBC to olaparib.

Combined Photothermal and Ionizing Radiation Sensitization of Triple-Negative Breast Cancer Using Triangular Silver Nanoparticles.

BackgroundIonizing radiation (IR) is commonly used in triple-negative breast cancer (TNBC) treatment regimens. However, off-target toxicity affecting normal tissue and grueling treatment regimens remain major limitations. Hyperthermia is one of the greatest IR sensitizers, but only if heat is administered simultaneously or immediately prior to ionizing radiation. Difficulty in co-localizing ionizing radiation (IR) in rapid succession with hyperthermia, and confining treatment to the tumor have hindered widespread clinical adoption of combined thermoradiation treatment. Metal nanoparticle-based approaches to IR sensitization and photothermal heat generation may aid in overcoming these issues and improve treatment specificity.MethodsWe assessed the potential to selectively treat MDA-MB-231 TNBC cells without affecting non-malignant MCF-10A breast cells using a multimodal approach based upon combined photothermal therapy, IR sensitization, and specific cytotoxicity using triangular silver nanoparticles (TAgNPs) with peak absorbance in the near-infrared light (NIR) spectrum.ResultsWe found that TAgNP-mediated photothermal therapy and radiosensitization offer a high degree of specificity for treatment of TNBC without affecting non-malignant mammary epithelial cells.DiscussionIf given at a high enough dose, IR, heat, or TAgNPs alone could be sufficient for tumor treatment. However, when the dose of one or all of these modalities increases, off-target effects also increase. The challenge lies in identifying the minimal doses of each individual treatment such that when combined they provide maximum selectivity for treatment of TNBC cells with minimum off-target effects on non-malignant breast cells. Our results provide proof of concept that this combination is highly selective for TNBC cells while sparing non-malignant mammary epithelial cells. This treatment would be particularly important for patients undergoing breast conservation therapy and for treatment of invasive tumor margins near the periphery where each individual treatment might be at a sub-therapeutic level.

Molecular subtyping and functional validation of TTK, TPX2, UBE2C, and LRP8 in sensitivity of TNBC to paclitaxel

Triple-negative breast cancer (TNBC) patients exhibit variable responses to chemotherapy, suggesting an underlying molecular heterogeneity. In the current study, we analyzed publicly available transcriptome data from 360 TNBC and 88 normal breast tissues, which revealed activation of nucleosome and cell cycle as the hallmarks of TNBC. Mechanistic network analysis identified activation of FOXM1 and ERBB2, and suppression of TP53 and NURP1 networks in TNBC. Employing Iterative Clustering and Guide-gene Selection (ICGS), Uniform Manifold Approximation and Projection (UMAP), and dimensionality reduction analyses, we classified TNBC into seven molecular subtypes, each exhibiting a unique molecular signature, including immune infiltration (CD19, CD8, and macrophages) and mesenchymal signature, which correlated with variable disease outcomes in a larger cohort (1,070) of BC. Mechanistically, depletion of TTK, TPX2, UBE2C, CDCA7, MELK, NFE2L3, DDX39A, and LRP8 led to substantial inhibition of colony formation of TNBC models, which was further enhanced in the presence of paclitaxel. Our data provide novel insights into the molecular heterogeneity of TNBC and identified TTK, TPX2, UBE2C, and LRP8 as main drivers of TNBC tumorigenesis.

Predictive biomarkers for sacituzumab govitecan efficacy in Trop-2-expressing triple-negative breast cancer.

Sacituzumab govitecan (SG) is an antibody-drug conjugate composed of a humanized anti-Trop-2 IgG antibody conjugated via a hydrolysable linker to SN-38, the topoisomerase I-inhibitory active component of irinotecan. We investigated whether Trop-2-expression and homologous recombination repair (HRR) of SN-38-mediated double-strand DNA (dsDNA) breaks play a role in the sensitivity of triple-negative breast cancer (TNBC) to SG. Activation of HRR pathways, as evidenced by Rad51 expression, was assessed in SG-sensitive cell lines with low and moderate Trop-2-expression (SK-MES-1 squamous cell lung carcinoma and HCC1806 TNBC, respectively), compared to a low Trop-2-expressing, less SG-sensitive TNBC cell line (MDA-MB-231). Further, two Trop-2-transfectants of MDA-MB-231, C13 and C39 (4- and 25-fold higher Trop-2, respectively), were treated in mice with SG to determine whether increasing Trop-2 expression improves SG efficacy. SG mediated >2-fold increase in Rad51 in MDA-MB-231 but had no effect in SK-MES-1 or HCC1806, resulting in lower levels of dsDNA breaks in MDA-MB-231. SG and saline produced similar effects in parental MDA-MB-231 tumor-bearing mice (median survival time (MST) = 21d and 19.5d, respectively). However, in mice bearing higher Trop-2-expressing C13 and C39 tumors after Trop-2 transfection, SG provided a significant survival benefit, even compared to irinotecan (MST = 97d vs. 35d for C13, and 81d vs. 28d for C39, respectively; P < 0.0007). These results suggest that SG could provide better clinical benefit than irinotecan in patients with HRR-proficient tumors expressing high levels of Trop-2, as well as to patients with HRR-deficient tumors expressing low/moderate levels of Trop-2.

Abstract 5981: CAP70 suppresses the development of triple-negative breast cancer by inhibiting EGFR pathway activation

Abstract Background: Among all major subtypes of breast cancer, triple-negative breast cancer (TNBC) carries the worst prognosis for the patients. The poor clinical outcome of TNBC is further exacerbated by the lack of effective targeted therapies. Therefore, the identification of functional molecular targets for TNBC therapy is urgently needed. The goal of this study was to determine the role of CFTR-associated protein of 70 kDa (CAP70, also called PDZK1) in the development of TNBC and assess its value as a target for TNBC therapy. Methods: Bioinformatics analysis and immunohistochemistry were performed to determine the expression of CAP70 in TNBC. The functions of CAP70 were demonstrated in a series of in vitro and in vivo experiments. GST Pull-down, mass spectrometry, co-immunoprecipitation, bioinformatics analysis, pharmacologic treatment, and western blotting were performed to elucidate the potential mechanisms of CAP70 activities. Results: CAP70 was specifically downregulated in TNBC tissues and was related to tumor stage, lymph node metastasis, and patient survival. Functional assays showed that CAP70 suppressed TNBC carcinogenesis, progression, and metastasis by inhibiting EGFR signaling. Moreover, inhibition of EGFR signaling by CAP70 enhanced the sensitivity of TNBC to EGFR inhibitor erlotinib. Conclusions: CAP70 suppresses TNBC development and enhances its sensitivity to erlotinib by inhibiting EGFR signaling. CAP70 is a significant prognostic factor of TNBC and a potential molecular therapeutic target for the treatment of this subtype of breast cancer. Citation Format: Junfang Zheng, Yuanzhen Ma, Yijun Qi. CAP70 suppresses the development of triple-negative breast cancer by inhibiting EGFR pathway activation [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5981.

HEXIM1 controls P-TEFb processing and regulates drug sensitivity in triple-negative breast cancer.

The positive transcription elongation factor b (P-TEFb), composed of CDK9 and cyclin T, stimulates transcriptional elongation by RNA polymerase (Pol) II and regulates cell growth and differentiation. Recently, we demonstrated that P-TEFb also controls the expression of EMT regulators to promote breast cancer progression. In the nucleus, more than half of P-TEFb are sequestered in the inactive-state 7SK snRNP complex. Here, we show that the assembly of the 7SK snRNP is preceded by an intermediate complex between HEXIM1 and P-TEFb that allows transfer of the kinase active P-TEFb from Hsp90 to 7SK snRNP for its suppression. Down-regulation of HEXIM1 locks P-TEFb in the Hsp90 complex, keeping it in the active state to enhance breast cancer progression, but also rendering the cells highly sensitive to Hsp90 inhibition. Because HEXIM1 is often down-regulated in human triple-negative breast cancer (TNBC), these cells are particularly sensitive to Hsp90 inhibition. Our study provides a mechanistic explanation for the increased sensitivity of TNBC to Hsp90 inhibition.

Abstract P3-06-14: Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim

Abstract Background/Rationale: While some patients with triple negative breast cancer (TNBC) achieve long-term remission with standard-of-care chemotherapy, many have cancers that are chemotherapy resistant, putting them at risk for metastatic recurrence. There is also a lack of targeted therapies for TNBC, highlighting the need for novel therapeutic strategies for this subtype. PRKCQ, a member of the novel protein kinase C family, is preferentially expressed in TNBC compared to other breast cancer subtypes and we previously reported that PRKCQ expression is sufficient to promote oncogenic activities (growth-factor independent growth, anoikis resistance and migration). In addition, PRKCQ suppression inhibits growth of TNBC tumor xenografts. We sought to determine if PRKCQ expression modulation impacts sensitivity of triple negative breast cancer cells to standard of care chemotherapy and whether PRKCQ inhibition could be a strategy to enhance chemosensitivity of drug-resistant TNBC. Methods: We determined the effects of modulating PRKCQ expression, using PRKCQ cDNA or shRNA vectors, on sensitivity of TNBC cells to the apoptotic effects of standard-of-care chemotherapy, including those cancers that are relatively chemotherapy resistant at baseline. We also determined the mechanisms by which PRKCQ regulates sensitivity to chemotherapy. Results: Increased PRKCQ expression in non-transformed MCF-10A breast epithelial cells promotes resistance to the apoptosis-inducing effects of Doxorubicin or Paclitaxel treatment. These effects are dependent on PRKCQ kinase activity as a catalytically inactive PRKCQ failed to promote resistance. Downregulation of PRKCQ or inhibition of its kinase activity enhanced sensitivity of TNBC cells to chemotherapy. PRKCQ impacts chemotherapy sensitivity of TNBC by regulating epithelial-mesenchymal transition (EMT) and expression of Bim, a pro-apoptotic Bcl2 family protein. Conclusions. PRKCQ promotes resistance of TNBC to standard of care chemotherapies by promoting EMT and suppressing pro-apoptotic Bim. Inhibiting PRKCQ expression or activity sensitizes TNBC cells to chemotherapy and could be an effective strategy to overcome chemotherapy resistance of a subset of triple negative breast cancers, thereby improving patient outcomes. Citation Format: Hanna Yoko Irie, Jessica H. Byerly, Elisa R. Port. Inhibition of PRKCQ enhances chemosensitivity of triple negative breast cancer by regulating EMT and Bim [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-06-14.