Biology subjects

Link, G.

Publications and source records attributed to Link, G..

5 recordsLinked to original sources

bioRxiv2026

Preclinical evaluation of ixazomib for high-risk pediatric brain tumors

Background: Many of the highest risk pediatric brain cancers continue to experience poor clinical outcomes despite intensification of current multimodal therapy. Proteasome inhibition has shown preclinical promise across a range of cancer models including diffuse midline glioma (DMG), medulloblastoma, and atypical teratoid / rhabdoid tumors (ATRT), though clinically viable agents have been limited. Recent studies in adults with glioblastoma suggest that ixazomib, a second-generation proteasome inhibitor, might achieve therapeutic concentrations in the CNS, presenting the opportunity that a CNS penetrant proteasome inhibitor might be similarly leveraged for benefit in childhood brain cancers. Methods: Ixazomib was tested against cell lines and orthotopic xenograft models of DMG, Myc-amplified medulloblastoma (Myc-MB), and ATRT. RNA sequencing and LC-MS based proteomics were utilized to define functional consequences of ixazomib treatment in these models. Proteasome activity readouts were used to assess ixazomib activity across brain regions and extracranial solid organs. Results: Ixazomib demonstrates consistent cytotoxic effect across high-risk brain tumor models at low nanomolar concentrations. Ixazomib treatment activates proteostatic stress response and apoptosis. Treatment with ixazomib does not demonstrate survival benefit in orthotopic models, however, and pharmacodynamic testing suggests insufficient inhibition of proteasome activity within the CNS compared to extracranial tissues. Conclusions: While many pediatric brain tumor models demonstrate susceptibility to proteasome inhibition, ixazomib may lack sufficient blood-brain barrier penetration to be a translationally viable means of exploiting this vulnerability.

cancer biology↗

bioRxiv2026

An Open-Source, Excitation-Resolved UV-NIR Imaging Platform for Bioluminescence, Luminescence-Decay, and Chemical Discrimination Measurements

Multispectral imaging is a cornerstone of chemical imaging, with bioluminescence, fluorescence, and phosphorescence imaging underpin much of preclinical and analytical chemical measurements. However, conventional implementations are typically proprietary, costly, and resolve spectral content from the reflectance of a broadband source, without control over the excitation spectrum. This architecture cannot isolate excitation-dependent photophysical processes. Spectral discrimination through sequentially resolved narrowband excitation, detected on a single broadband-sensitive camera, instead enables excitation-dependent fluorescence, phosphorescence, and reflectance measurements not available to such broadband approaches. We describe AURORA-MSI, an open-source multispectral platform that inverts this arrangement with fourteen narrowband LEDs spanning 367-940 nm, a 120-element annular illumination ring with eight independently addressable azimuthal sectors, and a thermoelectrically cooled monochrome CMOS camera. Radiometric calibration, spatial uniformity mapping, and camera noise characterization establish the quantitative measurement foundation. In bioluminescence imaging, AURORA-MSI localized sources in a calibrated tissue-mimicking mouse phantom comparably to a commercial Revvity IVIS Spectrum, detected luciferase-expressing HSJD-GBM1-001 glioblastoma cells across a dilution series, with reduced replicate consistency at the lowest densities, and mapped substrate-free fungal-pathway emission in an intact bioluminescent Petunia hybrida, none requiring photon-counting instrumentation. Time-resolved phosphorescence decay imaging of six inorganic phosphors over 33 minutes found tri-exponential models adequate at early times, while distributed-lifetime models were preferred at extended timescales. Multispectral image-texture features extracted across all fourteen excitation bands discriminated ten pharmaceutical and household powders spanning distinct chemical compositions and, in two cases, distinct formulations of the same compound. Generality beyond these regimes was established through dual-excitation fluorescence fingerprinting of fifteen mineral specimens and wavelength-selective plant-tissue imaging exploiting UV and NIR penetration-depth differences. Excitation-side spectral encoding enables photophysical measurements that detection-side systems with uncontrolled broadband illumination cannot isolate, and the cooled-camera architecture supports weak-signal modalities without photon-counting instrumentation.

biophysics↗

bioRxiv2025

Effects of Combination Therapy of a CDK4/6 and MEK Inhibitor in Diffuse Midline Glioma Preclinical Models

BackgroundDiffuse midline glioma (DMG) is an incurable brain cancer without a single FDA-approved drug that prolongs survival. CDK4/6 inhibitors have been evaluated in children with DMG with limited efficacy. Since MAPK pathway activation is upstream of cell proliferation, we hypothesized that MEK inhibitors may increase the anti-tumor effects of CDK4/6 inhibitors. Here, we evaluated the efficacy of the CDK4/6 inhibitor ribociclib and the MEK inhibitor trametinib in human and murine DMG models to investigate combinational effects. MethodsWe conducted in vitro and in vivo assays using DMG cell lines from human patient-derived xenografts (PDX) and murine genetically engineered models (GEM). In vitro, we assessed synergy across human DMG lines. In vivo, we evaluated therapeutic effects with histological examinations, survival analysis, pharmacokinetic measurements, and RNA-sequencing analysis. ResultsIn vitro, ribociclib and trametinib had variable synergistic effects against human DMG cell lines. In vivo, a five-day treatment with combination therapy in the GEM DMG model significantly decreased cell proliferation and increased apoptosis compared with the vehicle, with trametinib having mostly cytotoxic effects and ribociclib having primarily cytostatic effects. In addition, a 21-day treatment with combination therapy significantly prolonged mice survival compared with the vehicle in the GEM DMG model (median survival: 112 days vs. 71.5 days, log rank test p=0.0195). In an orthotopic PDX model, combination therapy did not prolong mice survival compared with vehicle, ribociclib, and trametinib. LC/MS analysis showed adequate drug delivery across the blood-brain-barrier (BBB) into tumor tissue in both GEM and PDX models. Transcriptomic analysis in the GEM model suggests that combination therapy inhibited the MAPK pathway and inflammation. ConclusionsCombination therapy with ribociclib and trametinib significantly prolonged survival in the GEM model but not in the PDX model, highlighting the importance of testing novel therapies in diverse models. Key PointsO_LICombination therapy had cytotoxic and cytostatic effects in vivo in the GEM model. C_LIO_LICombination therapy had variable synergy in vitro in human DIPG models. C_LIO_LICombination therapy significantly prolonged mice survival compared with the vehicle in the GEM model. C_LIO_LICombination therapy did not prolong survival in the PDX model. C_LIO_LITranscriptional analysis suggests that the combination modulated inflammation in the GEM model. C_LIO_LIThis work highlights the importance of testing novel therapies in diverse models. C_LI Importance of the StudyDMG is an incurable brain cancer without a single FDA-approved drug that prolongs survival. CDK4/6 inhibitors have been evaluated in children with DMG with limited efficacy. As MAPK pathway activation is known to be upstream of cell proliferation, we hypothesize that combination therapy will have additive effects relative to monotherapy. In this study, we evaluated the efficacy of the CDK4/6 inhibitor ribociclib and the MEK inhibitor trametinib in GEM and PDX DMG models. In vitro, the inhibitor combination demonstrated variable synergy in DMG human cell-lines, but in vivo, it had limited efficacy in a PDX orthotopic model. In the GEM model, the combination prolonged survival compared with the vehicle and with single agents. PK studies showed similar drug levels in tumor tissue between the GEM and PDX models. Transcriptomic analysis in the GEM suggests that the drug combination significantly inhibited inflammation. These results highlight the importance of testing therapies in diverse models and suggest that this combination may be an effective therapy in patients with DMG.

cancer biology↗

bioRxiv2024

PRMT5 maintains tumor stem cells to promote pediatric high-grade glioma tumorigenesis

BackgroundPediatric high-grade gliomas (PHGG) are aggressive, undifferentiated CNS tumors with poor outcomes, for which no standard-of-care drug therapy currently exists. Through a screen for epigenetic regulators, we identified PRMT5 as essential for PHGG growth. We hypothesized that, similar to its effect in normal cells, PRMT5 promotes self-renewal of stem-like PHGG tumor initiating cells (TICs) essential for tumor growth. Methods. We conducted in vitro assays, including limiting dilution studies of self-renewal, to determine the phenotypic effects of PRMT5 KD. We performed ChIP-Seq to identify PRMT5-mediated epigenetic changes and gene set enrichment analysis to identify pathways that PRMT5 regulates. Using an orthotopic xenograft model of PHGG, we tracked survival and histological characteristics resulting from PRMT5 KD or administration of a PRMT5 inhibitor {+/-} radiation therapy (RT). ResultsIn vitro, PRMT5 KD slowed cell cycle progression, tumor growth and self-renewal. PRMT5 KD reduced H3K4me3 occupancy at genes associated with self-renewal, tumor formation and growth. In vivo, PRMT5 KD increased survival and reduced tumor aggressiveness; however, pharmacological inhibition of PRMT5 with or without RT did not improve survival. ConclusionPRMT5 KD epigenetically reduced TIC self-renewal, leading to increased survival in preclinical models. Pharmacological inhibition of PRMT5 enzymatic activity may have failed in vivo due to insufficient reduction of PRMT5 activity by chemical inhibition, or this failure may suggest that non-enzymatic activities of PRMT5 are more relevant. ImplicationsOur findings show the importance of PRMT5 to maintain and promote the growth of stemlike cells that initiate and drive tumorigenesis in pediatric high grade glioma.

cancer biology↗

bioRxiv2022

PKD autoinhibition in trans regulates activation loop autophosphorylation in cis

Phosphorylation is a ubiquitous mechanism by which signals are transduced in cells. Protein kinases, enzymes that catalyze the phospho-transfer reaction are, themselves, often regulated by phosphorylation. Paradoxically, however, a substantial fraction of the more than 500 human protein kinases are capable of catalyzing their own activation loop phosphorylation. Commonly, these kinases perform this autophosphorylation reaction in trans, whereby transient dimerization leads to the mutual phosphorylation of the activation loop of the opposing protomer. In this study, we demonstrate that Protein Kinase D (PKD) is regulated by the inverse mechanism of dimerization-mediated trans-autoinhibition, followed by activation loop autophosphorylation in cis. We show that PKD forms a stable face-to-face homodimer that is incapable of either auto- or substrate phosphorylation. Dissociation of this trans-autoinhibited dimer results in activation loop autophosphorylation, which occurs exclusively in cis. Phosphorylation serves to increase PKD activity and prevent trans-autoinhibition, thereby switching PKD on. Our findings not only reveal the mechanism of PKD regulation, but have profound implications for the regulation of many other eukaryotic kinases.

biochemistry↗