Triple-negative breast cancer brain metastasis: an update on druggable targets, current clinical trials, and future treatment options

Biological profile of breast cancer brain metastasis

Breast cancer is one of the leading causes of death worldwide. The aggressive behaviour of breast tumor results from their metastasis. Notably, the brain tissue is one of the common regions of metastasis, thereby reducing the overall survival of patients. Moreover, the metastatic tumors demonstrate poor response or resistance to therapies. In addition, breast cancer brain metastasis provides the poor prognosis of patients. Therefore, it is of importance to understand the mechanisms in breast cancer brain metastasis. Both cell lines and animal models have been developed for the evaluation of breast cancer brain metastasis. Moreover, different tumor microenvironment components and other factors such as lymphocytes and astrocytes can affect brain metastasis. The breast cancer cells can disrupt the blood-brain barrier (BBB) during their metastasis into brain, developing blood-tumor barrier to enhance carcinogenesis. The breast cancer brain metastasis can be increased by the dysregulation of chemokines, STAT3, Wnt, Notch and PI3K/Akt. On the other hand, the effective therapeutics have been developed for the brain metastasis such as introduction of nanoparticles. Moreover, the disruption of BBB by ultrasound can increase the entrance of bioactive compounds to the brain tissue. In order to improve specificity and selectivity, the nanoparticles for the delivery of therapeutics and crossing over BBB have been developed to suppress breast cancer brain metastasis.

Temozolomide-loaded bacterial magnetosomes improve targeted therapy for brain tumors

Novel active-targeting nano-therapeutic, Temozolomide-loaded magnetosomes conjugate has been developed to address the challenges of high metastatic rates and recurrence of tumors due to tumor circulating cells. Temozolomide-loaded magnetosomes as drug conjugate were characterized through a scanning electron microscope, Zeta-sizer, and UV-visible spectroscopy. The anti-tumor activity was studied in vitro (Cell viability, Cell proliferation, and flow cytometry) and in vivo (Xenograft tumor model). The particle size of temozolomide-coated magnetosomes is larger than that of uncoated magnetosomes. The zeta potential decreased to -11.2 from -21.6 mV for Temozolomide- magnetosomes conjugates. The drug-coated magnetosomes can sustain drug release, reducing the frequency of administration and enhancing their therapeutic effect. The study found that Temozolomide-loaded magnetosomes conjugate showed enhanced tumor cytotoxicity and apoptosis than free Temozolomide or magnetosomes. In vivo, the treatment of mice with Temozolomide-loaded magnetosomes inhibited tumor growth to 405.25 mm3 and reduced tumor weight (0.60 g), with fewer juvenile cells and increased necrotic area. These results suggest Bacterial magnetosomes as an appropriate choice for cancer therapy since they may be superior drug carriers with increased therapeutic efficacy and no undesirable side effects to the brain.

Prognostic factors of brain metastasis and subsequent survival in breast cancer patients: An 11-year, single-center, retrospective study

Female breast cancer is among the most prevalent cancers globally, often metastasizing to the brain. Despite advancements in treatment, brain metastasis incidence is rising, with a poor prognosis. Moreover, limited data exist on how breast cancer subtypes and patient characteristics impact survival. This study aimed to investigate prognostic factors affecting breast cancer patients with brain metastasis. We retrospectively reviewed 131 breast cancer patients with brain metastasis diagnosed at a single institution between 2010 and 2020. Demographic, clinical, pathological, and radiographic variables were analyzed. The median interval between breast cancer diagnosis and brain metastasis was 27 months. Patients diagnosed with a higher stage of breast cancer (median survival: stage 1: 97.2 months, stage 2: 44.4 months, stage 3: 38.1 months, stage 4: 13.0 months, P < .001) and those with ER-negative tumors (median survival: negative 25.3 months, positive 37.5 months, P = .034) had a shorter time between initial diagnosis and brain metastasis. Median survival after brain metastasis was 8.0 months. Multivariate analysis showed that triple-negative breast cancer was correlated to a high risk of death after brain metastasis (hazard ratio = 2.320, P < .001). Higher histological grade, low-performance status, extensive brain metastases, and leptomeningeal seeding was associated with shorter survival. Systemic chemotherapy after brain metastasis was the only treatment that improved survival (hazard ratio = 0.332, P < .001). The study suggests potential benefits of aggressive treatment, especially in nontriple-negative breast cancer subtypes, limited brain metastases, and good overall health. Further research with larger patient populations is needed.

miRNA signatures affecting the survival outcome in distant metastasis of triple-negative breast cancer

Triple-negative breast cancer (TNBC) constitutes for 10-15% of all breast cancer cases. Tumor heterogeneity, high invasiveness, distant metastasis, lack of estrogen receptors, progesterone receptors, and human epidermal growth factor receptor 2 expression contribute to TNBC associated with poor overall survival outcomes amongst diseased individuals. The disparity in clinico-pathological and metastatic patterns to distant sites has substantially enhanced the incidences of tumor recurrence. Survival outcomes amongst metastatic TNBC patients are worse in comparison to non-metastatic TNBC counterparts. MicroRNAs (miRNAs) have emerged as significant drivers to function either as oncogene or tumor suppressors by exerting modulating effects on the expression of target genes in the TNBC tumor microenvironment. The pleiotropic nature of miRNAs expands their preclinical and clinical utility in combating both metastatic and non-metastatic TNBC cases and thereby improves their survival outcomes. The present review article aims to highlight the varying survival outcomes in metastatic and non-metastatic TNBC cases. The present review article emphasizes the therapeutic and prognostic potential of miRNAs in TNBC to improve survival outcomes by retarding distant metastasis to lung, bone, brain, and lymph nodes.

Shikonin blocks CAF-induced TNBC metastasis by suppressing mitochondrial biogenesis through GSK-3β/NEDD4-1 mediated phosphorylation-dependent degradation of PGC-1α

BACKGROUND

Triple-negative breast cancer (TNBC) is characterized by its high metastatic potential, which results in poor patient survival. Cancer-associated fibroblasts (CAFs) are crucial in facilitating TNBC metastasis via induction of mitochondrial biogenesis. However, how to inhibit CAF-conferred mitochondrial biogenesis is still needed to explore.

METHODS

We investigated metastasis using wound healing and cell invasion assays, 3D-culture, anoikis detection, and NOD/SCID mice. Mitochondrial biogenesis was detected by MitoTracker green FM staining, quantification of mitochondrial DNA levels, and blue-native polyacrylamide gel electrophoresis. The expression, transcription, and phosphorylation of peroxisome-proliferator activated receptor coactivator 1α (PGC-1α) were detected by western blotting, chromatin immunoprecipitation, dual-luciferase reporter assay, quantitative polymerase chain reaction, immunoprecipitation, and liquid chromatography-tandem mass spectrometry. The prognostic role of PGC-1α in TNBC was evaluated using the Kaplan-Meier plotter database and clinical breast cancer tissue samples.

RESULTS

We demonstrated that PGC-1α indicated lymph node metastasis, tumor thrombus formation, and poor survival in TNBC patients, and it was induced by CAFs, which functioned as an inducer of mitochondrial biogenesis and metastasis in TNBC. Shikonin impeded the CAF-induced PGC-1α expression, nuclear localization, and interaction with estrogen-related receptor alpha (ERRα), thereby inhibiting PGC-1α/ERRα-targeted mitochondrial genes. Mechanistically, the downregulation of PGC-1α was mediated by synthase kinase 3β-induced phosphorylation of PGC-1α at Thr295, which associated with neural precursor cell expressed developmentally downregulated 4e1 recognition and subsequent degradation by ubiquitin proteolysis. Mutation of PGC-1α at Thr295 negated the suppressive effects of shikonin on CAF-stimulated TNBC mitochondrial biogenesis and metastasis in vitro and in vivo.

CONCLUSIONS

Our findings indicate that PGC-1α is a viable target for blocking TNBC metastasis by disrupting mitochondrial biogenesis, and that shikonin merits potential for treatment of TNBC metastasis as an inhibitor of mitochondrial biogenesis through targeting PGC-1α.

Unlocking Overexpressed Membrane Proteins to Guide Breast Cancer Precision Medicine

Breast cancer (BC) is a prevalent form of cancer affecting women worldwide. However, the effectiveness of current BC drugs is limited by issues such as systemic toxicity, drug resistance, and severe side effects. Consequently, there is an urgent need for new therapeutic targets and improved tumor tracking methods. This study aims to address these challenges by proposing a strategy for identifying membrane proteins in tumors that can be targeted for specific BC therapy and diagnosis. The strategy involves the analyses of gene expressions in breast tumor and non-tumor tissues and other healthy tissues by using comprehensive bioinformatics analysis from The Cancer Genome Atlas (TCGA), UALCAN, TNM Plot, and LinkedOmics. By employing this strategy, we identified four transcripts (LRRC15, EFNA3, TSPAN13, and CA12) that encoded membrane proteins with an increased expression in BC tissue compared to healthy tissue. These four transcripts also demonstrated high accuracy, specificity, and accuracy in identifying tumor samples, as confirmed by the ROC curve. Additionally, tissue microarray (TMA) analysis revealed increased expressions of the four proteins in tumor tissues across all molecular subtypes compared to the adjacent breast tissue. Moreover, the analysis of human interactome data demonstrated the important roles of these proteins in various cancer-related pathways. Taken together, these findings suggest that LRRC15, EFNA3, TSPAN13, and CA12 can serve as potential biomarkers for improving cancer diagnosis screening and as suitable targets for therapy with reduced side effects and enhanced efficacy.

Using anti-PD-L1 antibody conjugated gold nanoshelled poly (Lactic-co-glycolic acid) nanocapsules loaded with doxorubicin: A theranostic agent for ultrasound imaging and photothermal/chemo combination therapy of triple negative breast cancer

Triple negative breast cancer (TNBC) has the worst prognosis of all breast cancers, and it is difficult to progress through traditional chemotherapy. Therefore, the treatment of TNBC urgently requires agents with effective diagnostic and therapeutic capabilities. In this study, we obtained programmed death-ligand 1 (PD-L1) antibody conjugated gold nanoshelled poly(lactic-co-glycolic acid) (PLGA) nanocapsules (NCs) encapsulating doxorubicin (DOX) (DOX@PLGA@Au-PD-L1 NCs). PLGA NCs encapsulating DOX were prepared by a modified single-emulsion oil-in-water (O/W) solvent evaporation method, and gold nanoshells were formed on the surface by gold seed growth method, which were coupled with PD-L1 antibodies by carbodiimide method. The fabricated DOX@PLGA@Au-PD-L1 NCs exhibited promising contrast enhancement in vitro ultrasound imaging. Furthermore, DOX encapsulated in NCs displayed good pH-responsive and photo-triggered drug release properties. After irradiating 200 μg/mL NCs solution with a laser for 10 min, the solution temperature increased by nearly 23°C, indicating that the NCs had good photothermal conversion ability. The targeting experiments confirmed that the NCs had specific target binding ability to TNBC cells overexpressing PD-L1 molecules. Cell experiments exhibited that the agent significantly reduced the survival rate of TNBC cells through photochemotherapy combination therapy. As a multifunctional diagnostic agent, DOX@PLGA@Au-PD-L1 NCs could be used for ultrasound targeted contrast imaging and photochemotherapy combination therapy of TNBC cells, providing a promising idea for early diagnosis and treatment of TNBC.

A new treatment for breast cancer using a combination of two drugs: AZD9496 and palbociclib

In this study, we examined a mathematical model of breast cancer (BC) treatment that combines an oral oestrogen receptor inhibitor, AZD9496 with Palbociclib, a selective inhibitor of cyclin- dependent kinases CDK4 and CDK6. Treatment is described by analytical functions that enable us to control the dosage and time interval of the treatment, thus personalising the treatment for each patient. Initially, we investigated the effect of each treatment separately, and finally, we investigated the combination of both treatments. By applying numerical simulations, we confirmed that the combination of AZD9496 with palbociclib was the optimal treatment for BC. The dosage of AZD9496 increased and decreased throughout the treatment period, while the intervals were constant between treatments. Palbociclib changed almost cyclically, whereas the time intervals remained constant. To investigate the mathematical model, we applied the singularly perturbed homotopy analysis method, which is a numerical algorithm. The significant advantage of this method is that the mathematical model does not have to contain a small parameter (as is standard in perturbation theory). However, it is possible to artificially introduce a small parameter into the system of equations, making it possible to study the model using asymptotic methods.

ProNGF promotes brain metastasis through TrkA/EphA2 induced Src activation in triple negative breast cancer cells

BACKGROUND

Triple-Negative Breast Cancer is particularly aggressive, and its metastasis to the brain has a significant psychological impact on patients' quality of life, in addition to reducing survival. The development of brain metastases is particularly harmful in triple-negative breast cancer (TNBC). To date, the mechanisms that induce brain metastasis in TNBC are poorly understood.

METHODS

Using a human blood-brain barrier (BBB) in vitro model, an in vitro 3D organotypic extracellular matrix, an ex vivo mouse brain slices co-culture and in an in vivo xenograft experiment, key step of brain metastasis were recapitulated to study TNBC behaviors.

RESULTS

In this study, we demonstrated for the first time the involvement of the precursor of Nerve Growth Factor (proNGF) in the development of brain metastasis. More importantly, our results showed that proNGF acts through TrkA independent of its phosphorylation to induce brain metastasis in TNBC. In addition, we found that proNGF induces BBB transmigration through the TrkA/EphA2 signaling complex. More importantly, our results showed that combinatorial inhibition of TrkA and EphA2 decreased TBNC brain metastasis in a preclinical model.

CONCLUSIONS

These disruptive findings provide new insights into the mechanisms underlying brain metastasis with proNGF as a driver of brain metastasis of TNBC and identify TrkA/EphA2 complex as a potential therapeutic target.

Unravelling the Glioblastoma Tumour Microenvironment: Can Aptamer Targeted Delivery Become Successful in Treating Brain Cancers?

The key challenges to treating glioblastoma multiforme (GBM) are the heterogeneous and complex nature of the GBM tumour microenvironment (TME) and difficulty of drug delivery across the blood-brain barrier (BBB). The TME is composed of various neuronal and immune cells, as well as non-cellular components, including metabolic products, cellular interactions, and chemical compositions, all of which play a critical role in GBM development and therapeutic resistance. In this review, we aim to unravel the complexity of the GBM TME, evaluate current therapeutics targeting this microenvironment, and lastly identify potential targets and therapeutic delivery vehicles for the treatment of GBM. Specifically, we explore the potential of aptamer-targeted delivery as a successful approach to treating brain cancers. Aptamers have emerged as promising therapeutic drug delivery vehicles with the potential to cross the BBB and deliver payloads to GBM and brain metastases. By targeting specific ligands within the TME, aptamers could potentially improve treatment outcomes and overcome the challenges associated with larger therapies such as antibodies.

Therapeutic Role of Tamoxifen for Triple-Negative Breast Cancer: Leveraging the Interaction Between ERβ and Mutant p53

The absence of effective therapeutic targets and aggressive nature of triple-negative breast cancer (TNBC) renders this disease subset difficult to treat. Although estrogen receptor beta (ERβ) is expressed in TNBC, studies on its functional role have yielded inconsistent results. However, recently, our preclinical studies, along with other observations, have shown the potential therapeutic utility of ERβ in the context of mutant p53 expression. The current case study examines the efficacy of the selective estrogen receptor modulator tamoxifen in p53-mutant TNBC with brain metastases. Significant increase in ERβ protein expression and anti-proliferative interaction between mutant p53 and ERβ were observed after cessation of tamoxifen therapy, with significant regression of brain metastases. This case study provides supporting evidence for the use of tamoxifen in p53-mutant, ERβ+TNBC, especially in the setting of brain metastasis.

Sacituzumab govitecan and radiotherapy in metastatic, triple-negative, and BRCA-mutant breast cancer patient with active brain metastases: A case report

Background

Triple-negative breast cancer (TNBC) is an aggressive cancer subtype, owing to its high metastatic potential: Patients who develop brain metastases (BMs) have a poor prognosis due to the lack of effective systemic treatments. Surgery and radiation therapy are valid options, while pharmacotherapy still relies on systemic chemotherapy, which has limited efficacy. Among the new treatment strategies available, the antibody-drug conjugate (ADC) sacituzumab govitecan has shown an encouraging activity in metastatic TNBC, even in the presence of BMs.

Case presentation

A 59-year-old woman was diagnosed with early TNBC and underwent surgery and subsequent adjuvant chemotherapy. A germline pathogenic variant in BReast CAncer gene 2 (BRCA2) was revealed after genetic testing. After 11 months from the completion of adjuvant treatment, she had pulmonary and hilar nodal relapse and began first-line chemotherapy with carboplatin and paclitaxel. However, after only 3 months from starting the treatment, she experienced relevant disease progression, due to the appearance of numerous and symptomatic BMs. Sacituzumab govitecan (10 mg/kg) was started as second-line treatment as part of the Expanded Access Program (EAP). She reported symptomatic relief after the first cycle and received whole-brain radiotherapy (WBRT) concomitantly to sacituzumab govitecan treatment. The subsequent CT scan showed an extracranial partial response and a near-to-complete intracranial response; no grade 3 adverse events were reported, even if sacituzumab govitecan was reduced to 7.5 mg/kg due to persistent G2 asthenia. After 10 months from starting sacituzumab govitecan, a systemic disease progression was documented, while intracranial response was maintained.

Conclusions

This case report supports the potential efficacy and safety of sacituzumab govitecan in the treatment of early recurrent and BRCA-mutant TNBC. Despite the presence of active BMs, our patient had a progression-free survival (PFS) of 10 months in the second-line setting and sacituzumab govitecan was safe when administered together with radiation therapy. Further real-world data are warranted to confirm sacituzumab govitecan efficacy in this patient population.

Natural Blockers of PD-1/PD-L1 Interaction for the Immunotherapy of Triple-Negative Breast Cancer-Brain Metastasis

The limited treatment options for triple-negative breast cancer with brain metastasis (TNBC-BM) have left the door of further drug development for these patients wide open. Although immunotherapy via monoclonal antibodies has shown some promising results in several cancers including TNBC, it cannot be considered the most effective treatment for brain metastasis. This is due to the protective role of the blood-brain barrier (BBB) which limits the entrance of most drugs, especially the bulky ones such as antibodies, to the brain. For a drug to traverse the BBB via passive diffusion, various physicochemical properties should be considered. Since natural medicine has been a key inspiration for the development of the majority of current medicines, in this paper, we review several naturally-derived molecules which have the potential for immunotherapy via blocking the interaction of programmed cell death protein-1 (PD-1) and its ligand, PD-L1. The mechanism of action, physicochemical properties and pharmacokinetics of these molecules and their theoretical potential to be used for the treatment of TNBC-BM are discussed.

Mitochondrial Protein Cox7b Is a Metabolic Sensor Driving Brain-Specific Metastasis of Human Breast Cancer Cells

Distant metastases are detrimental for cancer patients, but the increasingly early detection of tumors offers a chance for metastasis prevention. Importantly, cancers do not metastasize randomly: depending on the type of cancer, metastatic progenitor cells have a predilection for well-defined organs. This has been theorized by Stephen Paget, who proposed the “seed-and-soil hypothesis”, according to which metastatic colonization occurs only when the needs of a given metastatic progenitor cell (the seed) match with the resources provided by a given organ (the soil). Here, we propose to explore the seed-and-soil hypothesis in the context of cancer metabolism, thus hypothesizing that metastatic progenitor cells must be capable of detecting the availability of metabolic resources in order to home in a secondary organ. If true, it would imply the existence of metabolic sensors. Using human triple-negative MDA-MB-231 breast cancer cells and two independent brain-seeking variants as models, we report that cyclooxygenase 7b (Cox7b), a structural component of Complex IV of the mitochondrial electron transport chain, belongs to a probably larger family of proteins responsible for breast cancer brain tropism in mice. For metastasis prevention therapy, this proof-of-principle study opens a quest for the identification of therapeutically targetable metabolic sensors that drive cancer organotropism.

New Achievements for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) constitutes a heterogeneous group of malignancies that are often aggressive and associated with a poor prognosis. The development of new TNBC treatment strategies has become an urgent clinical need. Diagnosis and subtyping of TNBC are essential to establish alternative treatments and targeted therapies for every TNBC patient. Chemotherapy, particularly with anthracycline and taxanes, remains the backbone for medical management for both early and metastatic TNBC. More recently, immune checkpoint inhibitors and targeted therapy have revolutionized cancer treatment. Included in the different strategies studied for TNBC treatment is drug repurposing. Despite the numerous medications available, numerous studies in medicinal chemistry are still aimed at the synthesis of new compounds in order to find new antiproliferative agents capable of treating TNBC. Additionally, some supplemental micronutrients, nutraceuticals and functional foods can potentially reduce the risk of developing cancer or can retard the rate of growth and metastases of established malignant diseases. Finally, nanotechnology in medicine, termed nanomedicines, introduces nanoparticles of variable chemistry and architecture for cancer treatment. This review highlights the most recent studies in search of new therapies for the treatment of TNBC, along with nutraceuticals and repositioning of drugs.