Targeting RET alterations in non-small cell lung cancer.

Rearranged during transfection (RET) alterations, which lead to aberrant activation of the RET proto-oncogene, have been identified in various cancers. In non-small cell lung cancer (NSCLC), RET mutations often manifest as RET fusion genes and are observed in 1-2 % of patients with NSCLC. In recent years, selective RET inhibitors such as selpercatinib and pralsetinib, approved by the Food and Drug Administration (FDA) in 2020, have been part of the revolutionary changes in the treatment landscape for non-small cell lung cancer. While first-generation RET inhibitors have become part of the standard of care for RET-fusion positive NSCLC, a new challenge has emerged: acquired resistance to RET inhibitors. RET resistance is a complex phenomenon that can manifest as either on-target or off-target resistance. Numerous studies have been conducted to identify the mechanisms behind this resistance. This review provides an overview of the biology of RET in NSCLC, methods of RET testing, and a comprehensive analysis of the clinical outcomes associated with multikinase and selective RET inhibitors for NSCLC. Additionally, we will explore future perspectives for RET fusion-positive NSCLC, including ongoing trials and the challenges involved in overcoming resistance to RET inhibitors.

Trajectory of Healthcare Contact Days for Veterans With Advanced Gastrointestinal Malignancy.

How and where patients with advanced cancer facing limited survival spend their time is critical. Healthcare contact days (days with healthcare contact outside the home) offer a patient-centered and practical measure of how much of a person's life is consumed by healthcare. We retrospectively analyzed contact days among decedent veterans with stage IV gastrointestinal cancer at the Minneapolis Veterans Affairs Healthcare System from 2010 to 2021. Among 468 decedents, the median overall survival was 4 months. Patients spent 1 in 3 days with healthcare contact. Over the course of illness, the percentage of contact days followed a "U-shaped" pattern, with an initial post-diagnosis peak, a lower middle trough, and an eventual rise as patients neared the end-of-life. Contact days varied by clinical factors and by sociodemographics. These data have important implications for improving care delivery, such as through care coordination and communicating expected burdens to and supporting patients and care partners.

Luciferase Calibrants Enable Absolute Quantitation of Bioluminescence Power.

Bioluminescence emitted from a luciferase-catalyzed oxidation of luciferin has been broadly utilized to report on biological events, predominantly through relative changes in the light output. Recent advances in protein engineering and synthetic chemistry have yielded bioluminescent systems with markedly improved brightness and bioavailability. These developments have enabled not only the detection of biological events at far lower expression levels but also new opportunities utilizing bioluminescence to power photochemistry in cells. Regardless of the application, bioluminescence analyses have leaned heavily on the use of luminometers to measure the light output of a system. Current luminometers report the light output of a sample in relative units, limiting the ability to compare data between instruments and preventing the absolute power of a bioluminescent system from being quantified. Luminescent solution calibrants comprising luciferases and their cognate luciferins that have been characterized for absolute light output would enable calibration of any given luminometer for absolute photon counting. To this end, we have built a custom light detection apparatus and used it alongside wavelength-matched LED light sources emitting at 450 and 561 nm to characterize the absolute power of a series of NanoLuc and firefly luciferase solutions, respectively. This approach revealed that these two common luciferases produce 3.72 × 10-18 and 7.25 × 10-20 watts/molecule, respectively. Components of these luminescent solution calibrants are commercially available and produce stable bioluminescent signals over 2-5 min, enabling any luminometer to be calibrated for power measurements of bioluminescence emitted by these two luciferases in units of watts or photons per second.

Cyclin D1 extensively reprograms metabolism to support biosynthetic pathways in hepatocytes.

Cell proliferation requires metabolic reprogramming to accommodate biosynthesis of new cell components, and similar alterations occur in cancer cells. However, the mechanisms linking the cell cycle machinery to metabolism are not well defined. Cyclin D1, along with its main partner cyclin-dependent kinase 4 (Cdk4), is a pivotal cell cycle regulator and driver oncogene that is overexpressed in many cancers. Here, we examine hepatocyte proliferation to define novel effects of cyclin D1 on biosynthetic metabolism. Metabolomic studies reveal that cyclin D1 broadly promotes biosynthetic pathways including glycolysis, the pentose phosphate pathway, and the purine and pyrimidine nucleotide synthesis in hepatocytes. Proteomic analyses demonstrate that overexpressed cyclin D1 binds to numerous metabolic enzymes including those involved in glycolysis and pyrimidine synthesis. In the glycolysis pathway, cyclin D1 activates aldolase and GAPDH, and these proteins are phosphorylated by cyclin D1/Cdk4 in vitro. De novo pyrimidine synthesis is particularly dependent on cyclin D1. Cyclin D1/Cdk4 phosphorylates the initial enzyme of this pathway, carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase (CAD), and metabolomic analysis indicates that cyclin D1 depletion markedly reduces the activity of this enzyme. Pharmacologic inhibition of Cdk4 along with the downstream pyrimidine synthesis enzyme dihydroorotate dehydrogenase synergistically inhibits proliferation and survival of hepatocellular carcinoma cells. These studies demonstrate that cyclin D1 promotes a broad network of biosynthetic pathways in hepatocytes, and this model may provide insights into potential metabolic vulnerabilities in cancer cells.

Inhibition of Mitochondrial Antioxidant Defense and CDK4/6 in Mesothelioma.

Advanced mesothelioma is considered an incurable disease and new treatment strategies are needed. Previous studies have demonstrated that mitochondrial antioxidant defense proteins and the cell cycle may contribute to mesothelioma growth, and that the inhibition of these pathways may be effective against this cancer. We demonstrated that the antioxidant defense inhibitor auranofin and the cyclin-dependent kinase 4/6 inhibitor palbociclib could decrease mesothelioma cell proliferation alone or in combination. In addition, we determined the effects of these compounds on colony growth, cell cycle progression, and the expression of key antioxidant defense and cell cycle proteins. Auranofin and palbociclib were effective in decreasing cell growth and inhibiting the above-described activity across all assays. Further study of this drug combination will elucidate the contribution of these pathways to mesothelioma activity and may reveal a new treatment strategy.

Gross Hematuria and Lower Urinary Tract Symptoms Associated With Military Burn Pits Exposures in US Veterans Deployed to Iraq and Afghanistan.

OBJECTIVE: The aim of the study is to describe rates of hematuria and other lower urinary tract symptoms, including self-reported cancer rates, among veterans postburn pits emissions exposure during deployment to Iraq and Afghanistan. METHODS: US post-9/11 veterans with burn pits emissions exposure confirmed via DD214 forms in the Burn Pits360.org Registry were sent a modified survey. Data were deidentified and anonymously coded. RESULTS: Twenty-nine percent of the 155 respondents exposed to burn pits self-reported seeing blood in their urine. The average index score of our modified American Urological Association Symptom Index Survey was 12.25 (SD, 7.48). High rates of urinary frequency (84%) and urgency (76%) were self-reported. Bladder, kidney, or lung cancers were self-reported in 3.87%. CONCLUSIONS: US veterans exposed to burn pits are self-reporting hematuria and other lower urinary tract symptoms.

An optimized bioluminescent substrate for non-invasive imaging in the brain.

Bioluminescence imaging (BLI) allows non-invasive visualization of cells and biochemical events in vivo and thus has become an indispensable technique in biomedical research. However, BLI in the central nervous system remains challenging because luciferases show relatively poor performance in the brain with existing substrates. Here, we report the discovery of a NanoLuc substrate with improved brain performance, cephalofurimazine (CFz). CFz paired with Antares luciferase produces greater than 20-fold more signal from the brain than the standard combination of D-luciferin with firefly luciferase. At standard doses, Antares-CFz matches AkaLuc-AkaLumine/TokeOni in brightness, while occasional higher dosing of CFz can be performed to obtain threefold more signal. CFz should allow the growing number of NanoLuc-based indicators to be applied to the brain with high sensitivity. Using CFz, we achieve video-rate non-invasive imaging of Antares in brains of freely moving mice and demonstrate non-invasive calcium imaging of sensory-evoked activity in genetically defined neurons.

Protein kinase CK2 - diverse roles in cancer cell biology and therapeutic promise.

The association of protein kinase CK2 (formerly casein kinase II or 2) with cell growth and proliferation in cells was apparent at early stages of its investigation. A cancer-specific role for CK2 remained unclear until it was determined that CK2 was also a potent suppressor of cell death (apoptosis); the latter characteristic differentiated its function in normal versus malignant cells because dysregulation of both cell growth and cell death is a universal feature of cancer cells. Over time, it became evident that CK2 exerts its influence on a diverse range of cell functions in normal as well as in transformed cells. As such, CK2 and its substrates are localized in various compartments of the cell. The dysregulation of CK2 is documented in a wide range of malignancies; notably, by increased CK2 protein and activity levels with relatively moderate change in its RNA abundance. High levels of CK2 are associated with poor prognosis in multiple cancer types, and CK2 is a target for active research and testing for cancer therapy. Aspects of CK2 cellular roles and targeting in cancer are discussed in the present review, with focus on nuclear and mitochondrial functions and prostate, breast and head and neck malignancies.

Potent Activation of NAD+-Dependent Deacetylase Sirt7 by Nucleosome Binding.

Sirtuin-7 (Sirt7) is a nuclear NAD+-dependent deacetylase with a broad spectrum of biological functions. Sirt7 overexpression is linked to several pathological states and enhances anticancer drug resistance, making the enzyme a promising target for the development of novel therapeutics. Despite a plethora of reported in vivo functions, the biochemical characterization of recombinant Sirt7 remains inadequate for the development of novel drug candidates. Here, we conduct an extensive biochemical analysis of Sirt7 using newly developed binding and kinetic assays to reveal that the enzyme preferentially interacts with and is activated by nucleosomes. Sirt7 activation by nucleic acids alone is effective toward long-chain acylated hydrophobic substrates, while only nucleosome binding leads to 105-fold activation of the deacetylase activity. Using endogenous chromatin and recombinant acetylated nucleosomes, we reveal that Sirt7 is one of the most efficient deacetylases in the sirtuin family and that its catalytic activity is limited by the rate of dissociation from deacetylated nucleosomes.

Sirt6 regulates lifespan in Drosophila melanogaster.

Sirt6 is a multifunctional enzyme that regulates diverse cellular processes such as metabolism, DNA repair, and aging. Overexpressing Sirt6 extends lifespan in mice, but the underlying cellular mechanisms are unclear. Drosophila melanogaster are an excellent model to study genetic regulation of lifespan; however, despite extensive study in mammals, very little is known about Sirt6 function in flies. Here, we characterized the Drosophila ortholog of Sirt6, dSirt6, and examined its role in regulating longevity; dSirt6 is a nuclear and chromatin-associated protein with NAD+-dependent histone deacetylase activity. dSirt6 overexpression (OE) in flies produces robust lifespan extension in both sexes, while reducing dSirt6 levels shortens lifespan. dSirt6 OE flies have normal food consumption and fertility but increased resistance to oxidative stress and reduced protein synthesis rates. Transcriptomic analyses reveal that dSirt6 OE reduces expression of genes involved in ribosome biogenesis, including many dMyc target genes. dSirt6 OE partially rescues many effects of dMyc OE, including increased nuclear size, up-regulation of ribosome biogenesis genes, and lifespan shortening. Last, dMyc haploinsufficiency does not convey additional lifespan extension to dSirt6 OE flies, suggesting dSirt6 OE is upstream of dMyc in regulating lifespan. Our results provide insight into the mechanisms by which Sirt6 OE leads to longer lifespan.

DARPP-32 promotes ERBB3-mediated resistance to molecular targeted therapy in EGFR-mutated lung adenocarcinoma.

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI)-refractory lung adenocarcinoma (LUAD) progression is a major clinical problem. New approaches to predict and prevent acquired resistance to EGFR TKIs are urgently needed. Here, we show that dopamine and cyclic AMP-regulated phosphoprotein, Mr 32000 (DARPP-32) physically recruits ERBB3 (HER3) to EGFR to mediate switching from EGFR homodimers to EGFR:ERBB3 heterodimers to bypass EGFR TKI-mediated inhibition by potentiating ERBB3-dependent activation of oncogenic signaling. In paired LUAD patient-derived specimens before and after EGFR TKI-refractory disease progression, we reveal that DARPP-32 and kinase-activated EGFR and ERBB3 proteins are overexpressed upon acquired resistance. In mice, DARPP-32 ablation sensitizes gefitinib-resistant xenografts to EGFR TKIs, while DARPP-32 overexpression increases gefitinib-refractory LUAD progression in gefitinib-sensitive lung tumors. We introduce a DARPP-32-mediated, ERBB3-dependent mechanism the LUAD cells use to evade EGFR TKI-induced cell death, potentially paving the way for the development of therapies to better combat therapy-refractory LUAD progression.

CX-4945 and siRNA-Mediated Knockdown of CK2 Improves Cisplatin Response in HPV(+) and HPV(-) HNSCC Cell Lines.

Head and neck squamous cell carcinoma (HNSCC) can be categorized into human papillomavirus (HPV) positive or negative disease. Elevated protein kinase CK2 level and activity have been historically observed in HNSCC cells. Previous studies on CK2 in HNSCC did not generally include consideration of HPV(+) and HPV(-) status. Here, we investigated the response of HPV(+) and HPV(-) HNSCC cells to CK2 targeting using CX-4945 or siRNA downregulation combined with cisplatin treatment. HNSCC cell lines were examined for CK2 expression levels and activity and response to CX-4945, with and without cisplatin. CK2 levels and NFκB p65-related activity were high in HPV(+) HNSCC cells relative to HPV(-) HNSCC cells. Treatment with CX-4945 decreased viability and cisplatin IC50 in all cell lines. Targeting of CK2 increased tumor suppressor protein levels for p21 and PDCD4 in most instances. Further study is needed to understand the role of CK2 in HPV(+) and HPV(-) HNSCC and to determine how incorporation of the CK2-targeted inhibitor CX-4945 could improve cisplatin response in HNSCC.

Use of Comprehensive Geriatric Assessment in Oncology Patients to Guide Treatment Decisions and Predict Chemotherapy Toxicity.

PURPOSE: Our objective was to review the utility of pretreatment comprehensive geriatric assessment (CGA) and its impact on decision making regarding choice and intensity of oncologic therapeutic regimens for older, frail, or poor-functional-status patients, as well as using this prospective assessment to predict chemotherapy-related toxicities. Database searches were conducted in Medline, PubMed, and Ovid for clinical studies, review articles, and journal publications. Search terms included geriatric assessment, medical oncology, chemotherapy, frailty, toxicity, and functional status. Thirty-seven pertinent articles were retrieved and serve as the basis for this clinical review. OBSERVATIONS: CGA is an important tool for examining aspects of frailty and functional status that are not captured by traditional performance status measures. These findings may then be used in selection of appropriate therapeutic regimens for a given patient that are efficacious and tolerable. Such pretreatment assessments also have been used in predicting therapy-related toxicities. CONCLUSIONS: Frail and older patients are common in oncology practices and are at high risk for therapy-related toxicities because of comorbidities and physiologic changes, presenting a considerable clinical challenge. CGA establishes evidence-based strategies to better assess the functional status of such patients and is predictive for chemotherapy-related toxicities in this vulnerable group. Despite publications on these measures in the oncology literature, there is limited evidence-based research to demonstrate the utility of CGA by practicing oncology providers and how to implement it into practice.

Multivalent interactions drive nucleosome binding and efficient chromatin deacetylation by SIRT6.

The protein deacetylase SIRT6 maintains cellular homeostasis through multiple pathways that include the deacetylation of histone H3 and repression of transcription. Prior work suggests that SIRT6 is associated with chromatin and can substantially reduce global levels of H3 acetylation, but how SIRT6 is able to accomplish this feat is unknown. Here, we describe an exquisitely tight interaction between SIRT6 and nucleosome core particles, in which a 2:1 enzyme:nucleosome complex assembles via asymmetric binding with distinct affinities. While both SIRT6 molecules associate with the acidic patch on the nucleosome, we find that the intrinsically disordered SIRT6 C-terminus promotes binding at the higher affinity site through recognition of nucleosomal DNA. Together, multivalent interactions couple productive binding to efficient deacetylation of histones on endogenous chromatin. Unique among histone deacetylases, SIRT6 possesses the intrinsic capacity to tightly interact with nucleosomes for efficient activity.

Biological and catalytic functions of sirtuin 6 as targets for small-molecule modulators.

Sirtuin 6 (SIRT6) is a nuclear NAD+-dependent deacetylase of histone H3 that regulates genome stability and gene expression. However, nonhistone substrates and additional catalytic activities of SIRT6, including long-chain deacylation and mono-ADP-ribosylation of other proteins, have also been reported, but many of these noncanonical roles remain enigmatic. Genetic studies have revealed critical homeostatic cellular functions of SIRT6, underscoring the need to better understand which catalytic functions and molecular pathways are driving SIRT6-associated phenotypes. At the physiological level, SIRT6 activity promotes increased longevity by regulating metabolism and DNA repair. Recent work has identified natural products and synthetic small molecules capable of activating the inefficient in vitro deacetylase activity of SIRT6. Here, we discuss the cellular functions of SIRT6 with a focus on attributing its catalytic activity to its proposed biological functions. We cover the molecular architecture and catalytic mechanisms that distinguish SIRT6 from other NAD+-dependent deacylases. We propose that combining specific SIRT6 amino acid substitutions identified in enzymology studies and activity-selective compounds could help delineate SIRT6 functions in specific biological contexts and resolve the apparently conflicting roles of SIRT6 in processes such as tumor development. We further highlight the recent development of small-molecule modulators that provide additional biological insight into SIRT6 functions and offer therapeutic approaches to manage metabolic and age-associated diseases.

Cyclin-dependent kinase inhibition: an opportunity to target protein-protein interactions.

Cyclin-dependent kinases (CDKs) play an integral part in cellular activities. To date, most of the activities have been evaluated in the cell cycle and transcription. Several diseases are affected by abnormalities in CDKs, related-pathways, or proteins that regulate CDK activity. CDKs are primarily dependent on activation by binding other proteins, namely Cyclins. In addition, phosphorylation of key CDK residues also plays a major part in CDK activity. To date, the most successful drugs have been developed against CDK4 and CDK6 and are FDA approved for use in advanced breast cancer. However, this is likely only a small fraction of the potential for targeting CDKs as a strategy against cancer and other diseases. Based on the extensive protein-protein interactions made by CDKs with other proteins (Cyclins and others), there are numerous possibilities for targeting strategies against protein-protein interactions. Here we describe the predominant roles of CDKs in the cell, key interacting proteins, significant 3-dimensional structural characteristics, and summarize the work-to-date in inhibition of CDKs.

Cyclin-Dependent Kinase and Antioxidant Gene Expression in Cancers with Poor Therapeutic Response.

Pancreatic cancer, hepatocellular carcinoma (HCC), and mesothelioma are treatment-refractory cancers, and patients afflicted with these cancers generally have a very poor prognosis. The genomics of these tumors were analyzed as part of The Cancer Genome Atlas (TCGA) project. However, these analyses are an overview and may miss pathway interactions that could be exploited for therapeutic targeting. In this study, the TCGA Pan-Cancer datasets were queried via cBioPortal for correlations among mRNA expression of key genes in the cell cycle and mitochondrial (mt) antioxidant defense pathways. Here we describe these correlations. The results support further evaluation to develop combination treatment strategies that target these two critical pathways in pancreatic cancer, hepatocellular carcinoma, and mesothelioma.

Mechanism of activation for the sirtuin 6 protein deacylase.

The histone deacetylase sirtuin 6 (SIRT6) regulates numerous biological functions, including transcriptional repression, DNA repair, and telomere maintenance. Recombinant SIRT6 displays catalytic efficiencies 2 orders of magnitude greater for long-chain deacylation than deacetylation against peptide substrates; however, deacetylation can be enhanced by allosteric small-molecule activators. Here, we investigated the mechanisms of activated lysine deacetylation and enhanced long-chain acyl-group removal by SIRT6. Activity-based screening identified compounds that activated histone peptide deacetylation 18-48-fold. Chemical optimization based on structure-activity relationships yielded an activator with improved potency and selectivity for SIRT6. Using this novel activator, we conducted biochemical and kinetic analyses revealing that SIRT6 is activated via acceleration of a catalytic step occurring after substrate binding but before NAD+ cleavage. We identified a SIRT6 variant, R65A, that maintains basal deacetylase activity but cannot be activated and failed to enhance long-chain deacylation. Additional biochemical studies revealed that Arg-65 is critical for activation by facilitating a conformational step that initiates chemical catalysis. This work suggests that SIRT6 activation of deacetylation involves a similar mechanism to improved catalysis as that of long-chain deacylation. The identification of novel SIRT6 activators and the molecular insights into activation and catalysis presented here provide a foundational understanding for physiological SIRT6 activation and for rational design of activating molecules.

An inactivating mutation in the histone deacetylase SIRT6 causes human perinatal lethality.

It has been well established that histone and DNA modifications are critical to maintaining the equilibrium between pluripotency and differentiation during early embryogenesis. Mutations in key regulators of DNA methylation have shown that the balance between gene regulation and function is critical during neural development in early years of life. However, there have been no identified cases linking epigenetic regulators to aberrant human development and fetal demise. Here, we demonstrate that a homozygous inactivating mutation in the histone deacetylase SIRT6 results in severe congenital anomalies and perinatal lethality in four affected fetuses. In vitro, the amino acid change at Asp63 to a histidine results in virtually complete loss of H3K9 deacetylase and demyristoylase functions. Functionally, SIRT6 D63H mouse embryonic stem cells (mESCs) fail to repress pluripotent gene expression, direct targets of SIRT6, and exhibit an even more severe phenotype than Sirt6-deficient ESCs when differentiated into embryoid bodies (EBs). When terminally differentiated toward cardiomyocyte lineage, D63H mutant mESCs maintain expression of pluripotent genes and fail to form functional cardiomyocyte foci. Last, human induced pluripotent stem cells (iPSCs) derived from D63H homozygous fetuses fail to differentiate into EBs, functional cardiomyocytes, and neural progenitor cells due to a failure to repress pluripotent genes. Altogether, our study described a germline mutation in SIRT6 as a cause for fetal demise, defining SIRT6 as a key factor in human development and identifying the first mutation in a chromatin factor behind a human syndrome of perinatal lethality.