NAC regulates metabolism and cell fate in intestinal stem cells.

Intestinal stem cells (ISCs) face the challenge of integrating metabolic demands with unique regenerative functions. Studies have shown an intricate interplay between metabolism and stem cell capacity; however, it is still not understood how this process is regulated. Combining ribosome profiling and CRISPR screening in intestinal organoids, we identify the nascent polypeptide-associated complex (NAC) as a key mediator of this process.

Senolysis by ABT-263 is associated with inherent apoptotic dependence of cancer cells derived from the non-senescent state.

Cellular senescence is a stress response that cells can employ to resist cell death. Senescent cells rely on anti-apoptotic signaling for their survival, which can be targeted by senolytic agents, like the BCL-XL, BCL-2, BCL-W inhibitor ABT-263. However, the response to ABT-263 of senescent cancer cells ranges from highly sensitive to refractory.

Gemcitabine therapeutically disrupts essential SIRT1-mediated p53 repression in atypical teratoid/rhabdoid tumors.

Atypical teratoid/rhabdoid tumors (ATRTs) are highly malignant embryonal tumors of the central nervous system with a dismal prognosis. Using a newly developed and validated patient-derived ATRT culture and xenograft model, alongside a panel of primary ATRT models, we found that ATRTs are selectively sensitive to the nucleoside analog gemcitabine. Gene expression and protein analyses indicate that gemcitabine treatment causes the degradation of sirtuin 1 (SIRT1), resulting in cell death through activation of nuclear factor κB (NF-κB) and p53.

ATP-binding cassette transporter inhibitor potency and substrate drug affinity are critical determinants of successful drug delivery enhancement to the brain.

Background: Pharmacotherapy for brain diseases is severely compromised by the blood-brain barrier (BBB). ABCB1 and ABCG2 are drug transporters that restrict drug entry into the brain and their inhibition can be used as a strategy to boost drug delivery and pharmacotherapy for brain diseases.

Methods: We employed elacridar and tariquidar in mice to explore the conditions for effective inhibition at the BBB.

The impact of ATP-binding cassette transporters in the diseased brain: Context matters.

ATP-binding cassette (ABC) transporters facilitate the movement of diverse molecules across cellular membranes, including those within the CNS. While most extensively studied in microvascular endothelial cells forming the blood-brain barrier (BBB), other CNS cell types also express these transporters. Importantly, disruptions in the CNS microenvironment during disease can alter transporter expression and function.

Acquired and intrinsic resistance to vemurafenib in BRAF -driven melanoma brain metastases.

BRAF -mutated melanoma brain metastases (MBMs) are responsive to BRAF inhibitors, but responses are generally less durable than those of extracranial metastases. We tested the hypothesis that the drug efflux transporters P-glycoprotein (P-gp; ABCB1) and breast cancer resistance protein (BCRP; ABCG2) expressed at the blood-brain barrier (BBB) offer MBMs protection from therapy. We intracranially implanted A375 melanoma cells in wild-type (WT) and Abcb1a/b;Abcg2 mice, characterized the tumor BBB, analyzed drug levels in plasma and brain lesions after oral vemurafenib administration, and determined the efficacy against brain metastases and subcutaneous lesions.

BCRP drives intrinsic chemoresistance in chemotherapy-naïve breast cancer brain metastasis.

Although initially successful, treatments with chemotherapy often fail because of the recurrence of chemoresistant metastases. Since these tumors develop after treatment, resistance is generally thought to occur in response to chemotherapy. However, alternative mechanisms of intrinsic chemoresistance in the chemotherapy-naïve setting may exist but remain poorly understood.

Protocol for live-cell imaging during Tumor Treating Fields treatment with Inovitro Live.

Tumor Treating Fields (TTFields) are an FDA-approved anticancer treatment using alternating electric fields. Here, we present a protocol to perform live-cell imaging (LCI) of cells during TTFields treatment with the Inovitro Live system. The setup we describe dissipates TTFields-related heat production and can be used in conjunction with any LCI-compatible microscope setup.

Tryptophan depletion results in tryptophan-to-phenylalanine substitutants.

Activated T cells secrete interferon-γ, which triggers intracellular tryptophan shortage by upregulating the indoleamine 2,3-dioxygenase 1 (IDO1) enzyme. Here we show that despite tryptophan depletion, in-frame protein synthesis continues across tryptophan codons. We identified tryptophan-to-phenylalanine codon reassignment (W>F) as the major event facilitating this process, and pinpointed tryptophanyl-tRNA synthetase (WARS1) as its source.

ATP-binding cassette transporters restrict drug delivery and efficacy against brain tumors even when blood-brain barrier integrity is lost.

The impact of a compromised blood-brain barrier (BBB) on the drug treatment of intracranial tumors remains controversial. We characterize the BBB integrity in several intracranial tumor models using magnetic resonance imaging, distribution and efficacy of docetaxel in brain tumors grafted in Abcb1-proficient and Abcb1-deficient mice. Leakiness of the tumor vasculature varies from extensive to absent.

Combined Therapy of AXL and HDAC Inhibition Reverses Mesenchymal Transition in Diffuse Intrinsic Pontine Glioma.

Purpose: Diffuse intrinsic pontine glioma (DIPG) is an incurable type of pediatric brain cancer, which in the majority of cases is driven by mutations in genes encoding histone 3 (H3K27M). We here determined the preclinical therapeutic potential of combined AXL and HDAC inhibition in these tumors to reverse their mesenchymal, therapy-resistant, phenotype.

Experimental Design: We used public databases and patient-derived DIPG cells to identify putative drivers of the mesenchymal transition in these tumors.

MEK/MELK inhibition and blood-brain barrier deficiencies in atypical teratoid/rhabdoid tumors.

Background: Atypical teratoid/rhabdoid tumors (AT/RT) are rare, but highly aggressive. These entities are of embryonal origin occurring in the central nervous system (CNS) of young children. Molecularly these tumors are driven by a single hallmark mutation, resulting in inactivation of SMARCB1 or SMARCA4.

ABCB1 Attenuates the Brain Penetration of the PARP Inhibitor AZD2461.

Poly (ADP-ribose) polymerase (PARP) inhibitors are a relatively new class of anticancer agents that have attracted attention for treatment of glioblastoma because of their ability to potentiate temozolomide chemotherapy. Previous studies have demonstrated that sufficient brain penetration is a prerequisite for efficacy of PARP inhibitors in glioma mouse models. Unfortunately, however, most of the PARP inhibitors developed to date have a limited brain penetration due to the presence of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) at the blood-brain barrier.

An Experimenter's Guide to Glioblastoma Invasion Pathways.

Glioblastoma is a highly aggressive brain tumor that is characterized by its unparalleled invasiveness. Invasive glioblastoma cells not only escape surgery and focal therapies but also are more resistant to current radio- and chemo-therapeutic approaches. Thus, any curative therapy for this deadly disease likely should include treatment strategies that interfere with glioblastoma invasiveness.

MELK Inhibition in Diffuse Intrinsic Pontine Glioma.

Diffuse intrinsic pontine glioma (DIPG) is a highly aggressive pediatric brain tumor, for which no effective therapeutic options currently exist. We here determined the potential of inhibition of the maternal embryonic leucine zipper kinase (MELK) for the treatment of DIPG. We evaluated the antitumor efficacy of the small-molecule MELK inhibitor OTSSP167 in patient-derived DIPG cultures, and identified the mechanism of action of MELK inhibition in DIPG by RNA sequencing of treated cells.

Buparlisib is a brain penetrable pan-PI3K inhibitor.

Characterization of the genomic landscapes of intracranial tumours has revealed a clear role for the PI3K-AKT-mTOR pathway in tumorigenesis and tumour maintenance of these malignancies, making phosphatidylinositol 3-kinase (PI3K) inhibition a promising therapeutic strategy for these tumours. Buparlisib is a novel pan-PI3K inhibitor that is currently in clinical development for various cancers, including primary and secondary brain tumours. Importantly however, earlier studies have revealed that sufficient brain penetration is a prerequisite for antitumor efficacy against intracranial tumours.

Improved Brain Penetration and Antitumor Efficacy of Temozolomide by Inhibition of ABCB1 and ABCG2.

The anticancer drug temozolomide is the only drug with proven activity against high-grade gliomas and has therefore become a part of the standard treatment of these tumors. P-glycoprotein (P-gp; ABCB1) and breast cancer resistance protein (BCRP; ABCG2) are transport proteins, which are present at the blood-brain barrier and limit the brain uptake of substrate drugs. We have studied the effect of P-gp and BCRP on the pharmacokinetics and pharmacodynamics of temozolomide, making use of a comprehensive set of in vitro transport experiments and in vivo pharmacokinetic and antitumor efficacy experiments using wild-type, Abcg2, Abcb1a/b, and Abcb1a/b;Abcg2 mice.

ATP-binding cassette transporters limit the brain penetration of Wee1 inhibitors.

Introduction Wee1 is an important kinase involved in the G2 cell cycle checkpoint and frequently upregulated in intracranial neoplasms such as glioblastoma (GBM) and diffuse intrinsic pontine glioma (DIPG). Two small molecules are available that target Wee1, AZD1775 and PD0166285, and clinical trials with AZD1775 have already been started. Since GBM and DIPG are highly invasive brain tumors, they are at least to some extent protected by the blood-brain barrier (BBB) and its ATP-binding cassette (ABC) efflux transporters.

Recycling drug screen repurposes hydroxyurea as a sensitizer of glioblastomas to temozolomide targeting de novo DNA synthesis, irrespective of molecular subtype.

Background: Glioblastoma (GBM) is the most common and most aggressive primary malignant brain tumor. Standard-of-care treatment involves maximal surgical resection of the tumor followed by radiation and chemotherapy (temozolomide [TMZ]). The 5-year survival rate of patients with GBM is <10%, a colossal failure that has been partially attributed to intrinsic and/or acquired resistance to TMZ through O6-methylguanine DNA methyltransferase (MGMT) promoter methylation status in the tumor.

The impact of P-glycoprotein and breast cancer resistance protein on the brain pharmacokinetics and pharmacodynamics of a panel of MEK inhibitors.

Mitogen/extracellular signal-regulated kinase (MEK) inhibitors have been tested in clinical trials for treatment of intracranial neoplasms, including glioblastoma (GBM), but efficacy of these drugs has not yet been demonstrated. The blood-brain barrier (BBB) is a major impediment to adequate delivery of drugs into the brain and may thereby also limit the successful implementation of MEK inhibitors against intracranial malignancies. The BBB is equipped with a range of ATP-dependent efflux transport proteins, of which P-gp (ABCB1) and BCRP (ABCG2) are the two most dominant for drug efflux from the brain.

Identification of a Druggable Pathway Controlling Glioblastoma Invasiveness.

Diffuse and uncontrollable brain invasion is a hallmark of glioblastoma (GBM), but its mechanism is understood poorly. We developed a 3D ex vivo organotypic model to study GBM invasion. We demonstrate that invading GBM cells upregulate a network of extracellular matrix (ECM) components, including multiple collagens, whose expression correlates strongly with grade and clinical outcome.