Targeted Therapies for Brain Metastases from Breast Cancer

The discovery of various driver pathways and targeted small molecule agents/antibodies have revolutionized the management of metastatic breast cancer. Currently, the major targets of clinical utility in breast cancer include the human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF) receptor, mechanistic target of rapamycin (mTOR) pathway, and the cyclin-dependent kinase 4/6 (CDK-4/6) pathway. Brain metastasis, however, remains a thorn in the flesh, leading to morbidity, neuro-cognitive decline, and interruptions in the management of systemic disease. Approximately 20%–30% of patients with metastatic breast cancer develop brain metastases. Surgery, whole brain radiation therapy, and stereotactic radiosurgery are the traditional treatment options for patients with brain metastases. The therapeutic paradigm is changing due to better understanding of the blood brain barrier and the advent of tyrosine kinase inhibitors and monoclonal antibodies. Several of these agents are in clinical practice and several others are in early stage clinical trials. In this article, we will review the common targetable pathways in the management of breast cancer patients with brain metastases, and the current state of the clinical development of drugs against these pathways.     

Behind Brain Metastases Formation: Cellular and Molecular Alterations and Blood–Brain Barrier Disruption

Breast cancer (BC) brain metastases is a life-threatening condition to which accounts the poor understanding of BC cells’ (BCCs) extravasation into the brain, precluding the development of preventive strategies. Thus, we aimed to unravel the players involved in the interaction between BCCs and blood–brain barrier (BBB) endothelial cells underlying BBB alterations and the transendothelial migration of malignant cells. We used brain microvascular endothelial cells (BMECs) as a BBB in vitro model, under conditions mimicking shear stress to improve in vivo-like BBB features. Mixed cultures were performed by the addition of fluorescently labelled BCCs to distinguish individual cell populations. BCC–BMEC interaction compromised BBB integrity, as revealed by junctional proteins (β-catenin and zonula occludens-1) disruption and caveolae (caveolin-1) increase, reflecting paracellular and transcellular hyperpermeability, respectively. Both BMECs and BCCs presented alterations in the expression pattern of connexin 43, suggesting the involvement of the gap junction protein. Myosin light chain kinase and phosphorylated myosin light chain were upregulated, revealing the involvement of the endothelial cytoskeleton in the extravasation process. β4-Integrin and focal adhesion kinase were colocalised in malignant cells, reflecting molecular interaction. Moreover, BCCs exhibited invadopodia, attesting migratory properties. Collectively, hub players involved in BC brain metastases formation were unveiled, disclosing possible therapeutic targets for metastases prevention.     

MicroRNAs and Extracellular Vesicles as Distinctive Biomarkers of Precocious and Advanced Stages of Breast Cancer Brain Metastases Development

Triple negative breast cancer presents higher mortality and poorer survival rates than other breast cancer (BC) types, due to the proneness to brain metastases formation, which are usually diagnosed at advanced stages. Therefore, the discovery of BC brain metastases (BCBM) biomarkers appears pivotal for a timely intervention. With this work, we aimed to disclose microRNAs (miRNAs) and extracellular vesicles (EVs) in the circulation as biomarkers of BCBM formation. Using a BCBM animal model, we analyzed EVs in plasma by nanoparticle tracking analysis and ascertained their blood-brain barrier (BBB) origin by flow cytometry. We further evaluated circulating miRNAs by RT-qPCR and their brain expression by in situ hybridization. In parallel, a cellular model of BCBM formation, combining triple negative BC cells and BBB endothelial cells, was used to differentiate the origin of biomarkers. Established metastases were associated with an increased content of circulating EVs, particularly of BBB origin. Interestingly, deregulated miRNAs in the circulation were observed prior to BCBM detection, and their brain origin was suggested by matching alterations in brain parenchyma. In vitro studies indicated that miR-194-5p and miR-205-5p are expressed and released by BC cells, endothelial cells and during their interaction. These results highlight miRNAs and EVs as biomarkers of BCBM in early and advanced stages, respectively.     

Blood–Brain Barrier in Brain Tumors: Biology and Clinical Relevance

The presence of barriers, such as the blood–brain barrier (BBB) and brain–tumor barrier (BTB), limits the penetration of antineoplastic drugs into the brain, resulting in poor response to treatments. Many techniques have been developed to overcome the presence of these barriers, including direct injections of substances by intranasal or intrathecal routes, chemical modification of drugs or constituents of BBB, inhibition of efflux pumps, physical disruption of BBB by radiofrequency electromagnetic radiation (EMP), laser-induced thermal therapy (LITT), focused ultrasounds (FUS) combined with microbubbles and convection enhanced delivery (CED). However, most of these strategies have been tested only in preclinical models or in phase 1–2 trials, and none of them have been approved for treatment of brain tumors yet. Concerning the treatment of brain metastases, many molecules have been developed in the last years with a better penetration across BBB (new generation tyrosine kinase inhibitors like osimertinib for non-small-cell lung carcinoma and neratinib/tucatinib for breast cancer), resulting in better progression-free survival and overall survival compared to older molecules. Promising studies concerning neural stem cells, CAR-T (chimeric antigen receptors) strategies and immunotherapy with checkpoint inhibitors are ongoing.     

Blood–Brain Barrier Transporters: Opportunities for Therapeutic Development in Ischemic Stroke

Globally, stroke is a leading cause of death and long-term disability. Over the past decades, several efforts have attempted to discover new drugs or repurpose existing therapeutics to promote post-stroke neurological recovery. Preclinical stroke studies have reported successes in identifying novel neuroprotective agents; however, none of these compounds have advanced beyond a phase III clinical trial. One reason for these failures is the lack of consideration of blood–brain barrier (BBB) transport mechanisms that can enable these drugs to achieve efficacious concentrations in ischemic brain tissue. Despite the knowledge that drugs with neuroprotective properties (i.e., statins, memantine, metformin) are substrates for endogenous BBB transporters, preclinical stroke research has not extensively studied the role of transporters in central nervous system (CNS) drug delivery. Here, we review current knowledge on specific BBB uptake transporters (i.e., organic anion transporting polypeptides (OATPs in humans; Oatps in rodents); organic cation transporters (OCTs in humans; Octs in rodents) that can be targeted for improved neuroprotective drug delivery. Additionally, we provide state-of-the-art perspectives on how transporter pharmacology can be integrated into preclinical stroke research. Specifically, we discuss the utility of in vivo stroke models to transporter studies and considerations (i.e., species selection, co-morbid conditions) that will optimize the translational success of stroke pharmacotherapeutic experiments.     

Recent Development in NKT-Based Immunotherapy of Glioblastoma: From Bench to Bedside

Glioblastoma multiforme (GBM) is an aggressive and dismal disease with a median overall survival of around 15 months and a 5-year survival rate of 7.2%. Owing to genetic mutations, drug resistance, disruption to the blood–brain barrier (BBB)/blood–brain tumor barrier (BBTB), and the complexity of the immunosuppressive environment, the therapeutic approaches to GBM represent still major challenges. Conventional therapies, including surgery, radiotherapy, and standard chemotherapy with temozolomide, have not resulted in satisfactory improvements in the overall survival of GBM patients. Among cancer immunotherapeutic approaches, we propose that adjuvant NKT immunotherapy with invariant NKT (iNKT) and cytokine-induced killer (CIK) cells may improve the clinical scenario of this devastating disease. Considering this, herein, we discuss the current strategies of NKT therapy for GBM based primarily on in vitro/in vivo experiments, clinical trials, and the combinatorial approaches with future therapeutic potential.     

Novel Emerging Molecular Targets in Non-Small Cell Lung Cancer

In the scenario of systemic treatment for advanced non-small cell lung cancer (NSCLC) patients, one of the most relevant breakthroughs is represented by targeted therapies. Throughout the last years, inhibitors of the epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), c-Ros oncogene 1 (ROS1), and V-raf murine sarcoma viral oncogene homolog B (BRAF) have been approved and are currently used in clinical practice. However, other promising molecular drivers are rapidly emerging as therapeutic targets. This review aims to cover the molecular alterations with a potential clinical impact in NSCLC, including amplifications or mutations of the mesenchymal–epithelial transition factor (MET), fusions of rearranged during transfection (RET), rearrangements of the neurotrophic tyrosine kinase (NTRK) genes, mutations of the Kirsten rat sarcoma viral oncogene (KRAS) and phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA), as well as amplifications or mutations of human epidermal growth factor receptor 2 (HER2). Additionally, we summarized the current status of targeted agents under investigation for such alterations. This revision of the current literature on emerging molecular targets is needed as the evolving knowledge on novel actionable oncogenic drivers and targeted agents is expected to increase the proportion of patients who will benefit from tailored therapeutic approaches.     

The Second-Generation PIM Kinase Inhibitor TP-3654 Resensitizes ABCG2-Overexpressing Multidrug-Resistant Cancer Cells to Cytotoxic Anticancer Drugs

Human ATP-binding cassette (ABC) subfamily G member 2 (ABCG2) mediates the transport of a wide variety of conventional cytotoxic anticancer drugs and molecular targeted agents. Consequently, the overexpression of ABCG2 in cancer cells is linked to the development of the multidrug resistance (MDR) phenotype. TP-3654 is an experimental second-generation inhibitor of PIM kinase that is currently under investigation in clinical trials to treat advanced solid tumors and myelofibrosis. In this study, we discovered that by attenuating the drug transport function of ABCG2, TP-3654 resensitizes ABCG2-overexpressing multidrug-resistant cancer cells to cytotoxic ABCG2 substrate drugs topotecan, SN-38 and mitoxantrone. Moreover, our results indicate that ABCG2 does not mediate resistance to TP-3654 and may not play a major role in the induction of resistance to TP-3654 in cancer patients. Taken together, our findings reveal that TP-3654 is a selective, potent modulator of ABCG2 drug efflux function that may offer an additional combination therapy option for the treatment of multidrug-resistant cancers.     

Thyroid Cancers: From Surgery to Current and Future Systemic Therapies through Their Molecular Identities

Differentiated thyroid cancers (DTC) are commonly and successfully treated with total thyroidectomy plus/minus radioiodine therapy (RAI). Medullary thyroid cancer (MTC) is only treated with surgery but only intrathyroidal tumors are cured. The worst prognosis is for anaplastic (ATC) and poorly differentiated thyroid cancer (PDTC). Whenever a local or metastatic advanced disease is present, other treatments are required, varying from local to systemic therapies. In the last decade, the efficacy of the targeted therapies and, in particular, tyrosine kinase inhibitors (TKIs) has been demonstrated. They can prolong the disease progression-free survival and represent the most important therapeutic option for the treatment of advanced and progressive thyroid cancer. Currently, lenvatinib and sorafenib are the approved drugs for the treatment of RAI-refractory DTC and PDTC while advanced MTC can be treated with either cabozantinib or vandetanib. Dabrafenib plus trametinib is the only approved treatment by FDA for BRAF^V600E mutated ATC. A new generation of TKIs, specifically for single altered oncogenes, is under evaluation in phase 2 and 3 clinical trials. The aim of this review was to provide an overview of the current and future treatments of thyroid cancer with regards to the advanced and progressive cases that require systemic therapies that are becoming more and more targeted on the molecular identity of the tumor.     

Brain Metastases Management in Oncogene-Addicted Non-Small Cell Lung Cancer in the Targeted Therapies Era

The therapeutic landscape in patients with advanced non-small-cell lung cancer harboring oncogenic biomarkers has radically changed with the development of targeted therapies. Although lung cancers are known to frequently metastasize to the brain, oncogene-driven non-small-cell lung cancer patients show a higher incidence of both brain metastases at baseline and a further risk of central nervous system progression/relapse. Recently, a new generation of targeted agents, highly active in the central nervous system, has improved the control of intracranial disease. The intracranial activity of these drugs poses a crucial issue in determining the optimal management sequence in oncogene-addicted non-small-cell lung cancer patients with brain metastases, with a potential change of paradigm from primary brain irradiation to central nervous system penetrating targeted inhibitors.     

Mesenchymal Stem/Stromal Cell Therapy in Blood–Brain Barrier Preservation Following Ischemia: Molecular Mechanisms and Prospects

Ischemic stroke is the leading cause of mortality and long-term disability worldwide. Disruption of the blood–brain barrier (BBB) is a prominent pathophysiological mechanism, responsible for a series of subsequent inflammatory cascades that exacerbate the damage to brain tissue. However, the benefit of recanalization is limited in most patients because of the narrow therapeutic time window. Recently, mesenchymal stem cells (MSCs) have been assessed as excellent candidates for cell-based therapy in cerebral ischemia, including neuroinflammatory alleviation, angiogenesis and neurogenesis promotion through their paracrine actions. In addition, accumulating evidence on how MSC therapy preserves BBB integrity after stroke may open up novel therapeutic targets for treating cerebrovascular diseases. In this review, we focus on the molecular mechanisms of MSC-based therapy in the ischemia-induced prevention of BBB compromise. Currently, therapeutic effects of MSCs for stroke are primarily based on the fundamental pathogenesis of BBB breakdown, such as attenuating leukocyte infiltration, matrix metalloproteinase (MMP) regulation, antioxidant, anti-inflammation, stabilizing morphology and crosstalk between cellular components of the BBB. We also discuss prospective studies to improve the effectiveness of MSC therapy through enhanced migration into defined brain regions of stem cells. Targeted therapy is a promising new direction and is being prioritized for extensive research.     

Nanoparticles for Targeted Brain Drug Delivery: What Do We Know?

The blood–brain barrier (BBB) is a barrier that separates the blood from the brain tissue and possesses unique characteristics that make the delivery of drugs to the brain a great challenge. To achieve this purpose, it is necessary to design strategies to allow BBB passage, in order to reach the brain and target the desired anatomic region. The use of nanomedicine has great potential to overcome this problem, since one can modify nanoparticles with strategic molecules that can interact with the BBB and induce uptake through the brain endothelial cells and consequently reach the brain tissue. This review addresses the potential of nanomedicines to treat neurological diseases by using nanoparticles specially developed to cross the BBB.     

Targeting AKT in ER-Positive HER2-Negative Metastatic Breast Cancer: From Molecular Promises to Real Life Pitfalls?

The AKT protein kinase plays a central role in several interconnected molecular pathways involved in growth, apoptosis, angiogenesis, and cell metabolism. It thereby represents a therapeutic target, especially in hormone receptor-positive (HR) breast cancers, where the PI3K/AKT signaling pathway is largely hyperactivated. Moreover, resistance to therapeutic classes, including endocrine therapy, is associated with the constitutive activation of the PI3K/AKT pathway. Improved knowledge on the molecular mechanisms underlying resistance to endocrine therapy has led to the diversification of the therapeutic arsenal, notably with the development of PI3K and mTOR inhibitors, which are currently approved for the treatment of advanced HR-positive breast cancer patients. AKT itself constitutes a novel pharmacological target for which AKT inhibitors have been developed and tested in clinical trials. However, despite its pivotal role in cell survival and anti-apoptotic mechanisms, as well as in endocrine therapy resistance, few drugs have been developed and are available for clinical practice. The scope of the present review is to focus on the pivotal role of AKT in metastatic breast cancer through the analysis of its molecular features and to discuss clinical implications and remaining challenges in the treatment of HR-positive metastatic breast cancer.     

Sensitization of MCF7 Cells with High Notch1 Activity by Cisplatin and Histone Deacetylase Inhibitors Applied Together

Histone deacetylase inhibitors (HDIs) are promising anti-cancer agents that inhibit proliferation of many types of cancer cells including breast carcinoma (BC) cells. In the present study, we investigated the influence of the Notch1 activity level on the pharmacological interaction between cisplatin (CDDP) and two HDIs, valproic acid (VPA) and suberoylanilide hydroxamic acid (SAHA, vorinostat), in luminal-like BC cells. The type of drug–drug interaction between CDDP and HDIs was determined by isobolographic analysis. MCF7 cells were genetically modified to express differential levels of Notch1 activity. The cytotoxic effect of SAHA or VPA was higher on cells with decreased Notch1 activity and lower for cells with increased Notch1 activity than native BC cells. The isobolographic analysis demonstrated that combinations of CDDP with SAHA or VPA at a fixed ratio of 1:1 exerted additive or additive with tendency toward synergism interactions. Therefore, treatment of CDDP with HDIs could be used to optimize a combined therapy based on CDDP against Notch1-altered luminal BC. In conclusion, the combined therapy of HDIs and CDDP may be a promising therapeutic tool in the treatment of luminal-type BC with altered Notch1 activity.     

DNA Nanobarrel-Based Drug Delivery for Paclitaxel and Doxorubicin

Co-delivery of anticancer drugs and target agents by endogenous materials is an inevitable approach towards targeted and synergistic therapy. Employing DNA base pair complementarities, DNA nanotechnology exploits a unique nanostructuring method and has demonstrated its capacity for nanoscale positioning and templated assembly. Moreover, the water solubility, biocompatibility, and modifiability render DNA structure suitable candidate for drug delivery applications. We here report single-stranded DNA tail conjugated antitumor drug paclitaxel (PTX), and the co-delivery of PTX, doxorubicin and targeting agent mucin 1 (MUC-1) aptamer on a DNA nanobarrel carrier. We investigated the effect of tail lengths on drug release efficiencies and dual drug codelivery-enabled cytotoxicity. Owing to the rapidly developing field of structural DNA nanotechnology, functional DNA-based drug delivery is promising to achieve clinical therapeutic applications.     

Patidegib in Dermatology: A Current Review

Background: Basal cell carcinoma is one of the most common types of non-melanoma skin cancers, which can be locally destructive despite low-rate metastasis. Surgery is the treatment of choice, but it lacks of efficacy on advanced cases. Hedgehog pathway inhibitors are a class of drugs providing a new therapeutic option for patients affected by advanced disease. Besides systemic therapy, such as vismodegib and sonidegib, also topical inhibitors have been developed. Patidegib is able to decrease tumor burden, reducing the adverse effects induced by systemic targeted therapies. Methods: We performed comprehensive research to summarize the use of patidegib in advanced and recurrent aggressive basal cell carcinomas. Only English language human studies were included in the search. Results: Seven trials reported the application of patidegib. Both topical and systemic patidegib demonstrated safety, tolerability, and efficacy in naïve patients with stage II and III basal cell carcinomas, while stage IV disease and not-naïve patients did not show any benefit. Conclusion: Unlike systemic Hedgehog pathway inhibitors, patidegib 2% gel is not associated with systemic adverse effects and allows a better patient management. Considering the multidisciplinary management of neoplasia, in the era of precision medicine, it is mandatory to confide in pharmacogenomics to obtain personalized combined or sequential therapies.     

Improving the Utility of a Dynorphin Peptide Analogue Using Mannosylated Glycoliposomes

Peptide therapeutics offer numerous advantages in the treatment of diseases and disorders of the central nervous system (CNS). However, they are not without limitations, especially in terms of their pharmacokinetics where their metabolic lability and low blood–brain barrier penetration hinder their application. Targeted nanoparticle delivery systems are being tapped for their ability to improve the delivery of therapeutics into the brain non-invasively. We have developed a family of mannosylated glycoliposome delivery systems for targeted drug delivery applications. Herein, we demonstrate via in vivo distribution studies the potential of these glycoliposomes to improve the utility of CNS active therapeutics using dynantin, a potent and selective dynorphin peptide analogue antagonist of the kappa opioid receptor (KOR). Glycoliposomal entrapment protected dynantin against known rapid metabolic degradation and ultimately improved brain levels of the peptide by approximately 3–3.5-fold. Moreover, we linked this improved brain delivery with improved KOR antagonist activity by way of an approximately 30–40% positive modulation of striatal dopamine levels 20 min after intranasal administration. Overall, the results clearly highlight the potential of our glycoliposomes as a targeted delivery system for therapeutic agents of the CNS.     

Molecular Mechanisms of Treatment Resistance in Glioblastoma

Glioblastoma is the most common malignant primary brain tumor in adults and is almost invariably fatal. Despite our growing understanding of the various mechanisms underlying treatment failure, the standard-of-care therapy has not changed over the last two decades, signifying a great unmet need. The challenges of treating glioblastoma are many and include inadequate drug or agent delivery across the blood–brain barrier, abundant intra- and intertumoral heterogeneity, redundant signaling pathways, and an immunosuppressive microenvironment. Here, we review the innate and adaptive molecular mechanisms underlying glioblastoma’s treatment resistance, emphasizing the intrinsic challenges therapeutic interventions must overcome—namely, the blood–brain barrier, tumoral heterogeneity, and microenvironment—and the mechanisms of resistance to conventional treatments, targeted therapy, and immunotherapy.