Synovial Lipomatosis With Extra-articular Extension in the Arthritic Wrist: An Unexpected Diagnosis.

ABSTRACT: Synovial lipomatosis is a rare condition characterized by adipocyte proliferation within joint synovial tissue. It most commonly affects the knee and is typically intra-articular. Only 5 published case reports describe extra-articular synovial lipomatosis of the wrist. We present a case of a sexagenarian patient seen for his wrist arthropathy. His x-ray revealed pan-wrist arthritis and inflammatory soft tissue swelling. The patient was slated for a wrist fusion and Darrach procedure. Following the dorsal skin incision in the operating room, an unusual adipose mass was identified infiltrating all extensor compartments: midcarpal, radiocarpal, and distal radioulnar joints. The mass was excised and sent to pathology prior to proceeding with the slated surgery. Synovial lipomatosis was diagnosed postoperatively based on histopathology. Six weeks postoperatively, the wrist fusion had healed clinically and radiographically, and his pain had improved. There was no evidence of recurrence. Synovial lipomatosis is a rare entity that may imitate multiple other pathologies. It is possible that synovial lipomatosis may represent a secondary occurrence following degenerative articular disease or trauma in older patients. This is the first case report to date describing synovial lipomatosis of the wrist with extra-articular extension in the setting of pan-carpal wrist arthritis.

Predicting Structural Motifs of Glycosaminoglycans using Cryogenic Infrared Spectroscopy and Random Forest.

In recent years, glycosaminoglycans (GAGs) have emerged into the focus of biochemical and biomedical research due to their importance in a variety of physiological processes. These molecules show great diversity, which makes their analysis highly challenging. A promising tool for identifying the structural motifs and conformation of shorter GAG chains is cryogenic gas-phase infrared (IR) spectroscopy. In this work, the cryogenic gas-phase IR spectra of mass-selected heparan sulfate (HS) di-, tetra-, and hexasaccharide ions were recorded to extract vibrational features that are characteristic to structural motifs. The data were augmented with chondroitin sulfate (CS) disaccharide spectra to assemble a training library for random forest (RF) classifiers. These were used to discriminate between GAG classes (CS or HS) and different sulfate positions (2-O-, 4-O-, 6-O-, and N-sulfation). With optimized data preprocessing and RF modeling, a prediction accuracy of >97% was achieved for HS tetra- and hexasaccharides based on a training set of only 21 spectra. These results exemplify the importance of combining gas-phase cryogenic IR ion spectroscopy with machine learning to improve the future analytical workflow for GAG sequencing and that of other biomolecules, such as metabolites.

State-of-the-art glycosaminoglycan characterization.

Glycosaminoglycans (GAGs) are heterogeneous acidic polysaccharides involved in a range of biological functions. They have a significant influence on the regulation of cellular processes and the development of various diseases and infections. To fully understand the functional roles that GAGs play in mammalian systems, including disease processes, it is essential to understand their structural features. Despite having a linear structure and a repetitive disaccharide backbone, their structural analysis is challenging and requires elaborate preparative and analytical techniques. In particular, the extent to which GAGs are sulfated, as well as variation in sulfate position across the entire oligosaccharide or on individual monosaccharides, represents a major obstacle. Here, we summarize the current state-of-the-art methodologies used for GAG sample preparation and analysis, discussing in detail liquid chromatograpy and mass spectrometry-based approaches, including advanced ion activation methods, ion mobility separations and infrared action spectroscopy of mass-selected species.

Evidence-Based Assessment of Genes in Dilated Cardiomyopathy.

BACKGROUND: Each of the cardiomyopathies, classically categorized as hypertrophic cardiomyopathy, dilated cardiomyopathy (DCM), and arrhythmogenic right ventricular cardiomyopathy, has a signature genetic theme. Hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy are largely understood as genetic diseases of sarcomere or desmosome proteins, respectively. In contrast, >250 genes spanning >10 gene ontologies have been implicated in DCM, representing a complex and diverse genetic architecture. To clarify this, a systematic curation of evidence to establish the relationship of genes with DCM was conducted. METHODS: An international panel with clinical and scientific expertise in DCM genetics evaluated evidence supporting monogenic relationships of genes with idiopathic DCM. The panel used the Clinical Genome Resource semiquantitative gene-disease clinical validity classification framework with modifications for DCM genetics to classify genes into categories on the basis of the strength of currently available evidence. Representation of DCM genes on clinically available genetic testing panels was evaluated. RESULTS: Fifty-one genes with human genetic evidence were curated. Twelve genes (23%) from 8 gene ontologies were classified as having definitive (BAG3, DES, FLNC, LMNA, MYH7, PLN, RBM20, SCN5A, TNNC1, TNNT2, TTN) or strong (DSP) evidence. Seven genes (14%; ACTC1, ACTN2, JPH2, NEXN, TNNI3, TPM1, VCL) including 2 additional ontologies were classified as moderate evidence; these genes are likely to emerge as strong or definitive with additional evidence. Of these 19 genes, 6 were similarly classified for hypertrophic cardiomyopathy and 3 for arrhythmogenic right ventricular cardiomyopathy. Of the remaining 32 genes (63%), 25 (49%) had limited evidence, 4 (8%) were disputed, 2 (4%) had no disease relationship, and 1 (2%) was supported by animal model data only. Of the 16 evaluated clinical genetic testing panels, most definitive genes were included, but panels also included numerous genes with minimal human evidence. CONCLUSIONS: In the curation of 51 genes, 19 had high evidence (12 definitive/strong, 7 moderate). It is notable that these 19 genes explain only a minority of cases, leaving the remainder of DCM genetic architecture incompletely addressed. Clinical genetic testing panels include most high-evidence genes; however, genes lacking robust evidence are also commonly included. We recommend that high-evidence DCM genes be used for clinical practice and that caution be exercised in the interpretation of variants in variable-evidence DCM genes.

The interaction of chondroitin sulfate with a lipid monolayer observed by using nonlinear vibrational spectroscopy.

The first vibrational sum-frequency generation (VSFG) spectra of chondroitin sulfate (CS) interacting with dipalmitoyl phosphatidylcholine (DPPC) at air-liquid interface are reported here, collected at a laser repetition rate of 100 kHz. By studying the VSFG spectra in the regions of 1050-1450 cm-1, 2750-3180 cm-1, and 3200-3825 cm-1, it was concluded that in the presence of Ca2+ ions, the head groups together with the head-group-bound water molecules in the DPPC monolayer are strongly influenced by the interaction with CS, while the organization of the phospholipid tails remains mostly unchanged. The interactions were observed at a CS concentration below 200 nM, which exemplifies the potential of VSFG in studying biomolecular interactions at low physiological concentrations. The VSFG spectra recorded in the O-H stretching region at chiral polarization combination imply that CS molecules are organized into ordered macromolecular superstructures with a chiral secondary structure.

Chondroitin Sulfate Disaccharides in the Gas Phase: Differentiation and Conformational Constraints.

Glycosaminoglycans (GAGs) are a family of complex carbohydrates vital to all mammalian organisms and involved in numerous biological processes. Chondroitin and dermatan sulfate, an important class of GAGs, are linear macromolecules consisting of disaccharide building blocks of N-acetylgalactosamine and two different uronic acids. The varying degree and the site of sulfation render their characterization challenging. Here, we combine mass spectrometry with cryogenic infrared spectroscopy in the wavenumber range from 1000 to 1800 cm-1. Fingerprint spectra were recorded for a comprehensive set of disaccharides bearing all known motifs of sulfation. In addition, state-of-the-art quantum chemical calculations were performed to aid the understanding of the differences in the experimental fingerprint spectra. The results show that the degree and position of charged sulfate groups define the size of the conformational landscape in the gas phase. The detailed understanding of cryogenic infrared spectroscopy for acidic and often highly sulfated glycans may pave the way to utilize the technique in fragment-based sequencing approaches.

Cryogenic Infrared Spectroscopy Reveals Structural Modularity in the Vibrational Fingerprints of Heparan Sulfate Diastereomers.

Heparan sulfate and heparin are highly acidic polysaccharides with a linear sequence, consisting of alternating glucosamine and hexuronic acid building blocks. The identity of hexuronic acid units shows a variability along their sequence, as d-glucuronic acid and its C5 epimer, l-iduronic acid, can both occur. The resulting backbone diversity represents a major challenge for an unambiguous structural assignment by mass spectrometry-based techniques. Here, we employ cryogenic infrared spectroscopy on mass-selected ions to overcome this challenge and distinguish isomeric heparan sulfate tetrasaccharides that differ only in the configuration of their hexuronic acid building blocks. High-resolution infrared spectra of a systematic set of synthetic heparan sulfate stereoisomers were recorded in the fingerprint region from 1000 to 1800 cm-1. The experiments reveal a characteristic combination of spectral features for each of the four diastereomers studied and imply structural modularity in the vibrational fingerprints. Strong spectrum-structure correlations were found and rationalized by state-of-the-art quantum chemical calculations. The findings demonstrate the potential of cryogenic infrared spectroscopy to extend the mass spectrometry-based toolkit for the sequencing of heparan sulfate and structurally related biomolecules.

The importance of genetics and genetic counselors in the evaluation of patients with bicuspid aortic valve and aortopathy.

PURPOSE OF REVIEW: Bicuspid aortic valve (BAV) is a common congenital heart defect, with an estimated frequency of 1-2% in the general population. BAV may occur as an isolated finding or as a feature of certain syndromes. This article discusses potential genetic causes of BAV, includes a list of current known and candidate genes associated with BAV, provides a hypothetical case demonstrating the importance of genetic testing and cascade screening, and highlights the value of genetic counselors specializing in cardiovascular genetics. RECENT FINDINGS: Individuals with BAV are at significantly increased risk of progressive aortic valve disease and aortic root aneurysms. There is high heritability associated with BAV, and several specific genes have recently been associated with BAV. There is wide phenotypic variability among BAV malformations, including which cusps are involved and the degree of aortic root involvement. Genotype-phenotype correlations exist that impact treatment recommendations. Genetic testing can reduce morbidity and mortality by guiding management strategies and identifying asymptomatic relatives before significant complications occur. SUMMARY: Identifying cases of BAV with an identifiable genetic cause can significantly impact patients and family members. The list of associated genes is constantly growing. Genetic counselors have an important role in the evaluation of families at risk of BAV.

MicroRNA Profiling Reveals Marker of Motor Neuron Disease in ALS Models.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder marked by the loss of motor neurons (MNs) in the brain and spinal cord, leading to fatally debilitating weakness. Because this disease predominantly affects MNs, we aimed to characterize the distinct expression profile of that cell type to elucidate underlying disease mechanisms and to identify novel targets that inform on MN health during ALS disease time course. microRNAs (miRNAs) are short, noncoding RNAs that can shape the expression profile of a cell and thus often exhibit cell-type-enriched expression. To determine MN-enriched miRNA expression, we used Cre recombinase-dependent miRNA tagging and affinity purification in mice. By defining the in vivo miRNA expression of MNs, all neurons, astrocytes, and microglia, we then focused on MN-enriched miRNAs via a comparative analysis and found that they may functionally distinguish MNs postnatally from other spinal neurons. Characterizing the levels of the MN-enriched miRNAs in CSF harvested from ALS models of MN disease demonstrated that one miRNA (miR-218) tracked with MN loss and was responsive to an ALS therapy in rodent models. Therefore, we have used cellular expression profiling tools to define the distinct miRNA expression of MNs, which is likely to enrich future studies of MN disease. This approach enabled the development of a novel, drug-responsive marker of MN disease in ALS rodents.SIGNIFICANCE STATEMENT Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease in which motor neurons (MNs) in the brain and spinal cord are selectively lost. To develop tools to aid in our understanding of the distinct expression profiles of MNs and, ultimately, to monitor MN disease progression, we identified small regulatory microRNAs (miRNAs) that were highly enriched or exclusive in MNs. The signal for one of these MN-enriched miRNAs is detectable in spinal tap biofluid from an ALS rat model, where its levels change as disease progresses, suggesting that it may be a clinically useful marker of disease status. Furthermore, rats treated with ALS therapy have restored expression of this MN RNA marker, making it an MN-specific and drug-responsive marker for ALS rodents.

Optimization of mRNA untranslated regions for improved expression of therapeutic mRNA.

mRNA based therapies hold great promise for the treatment of genetic diseases. However, this therapeutic approach suffers from multiple challenges including the short half-life of exogenously administered mRNA and subsequent protein production. Modulation of untranslated regions (UTR) represents one approach to enhance both mRNA stability and translation efficiency. The current studies describe and validate screening methods using a diverse set of 5'UTR and 3'UTR combinations for improved expression of the Arginase 1 (ARG1) protein, a potential therapeutic mRNA target. Data revealed a number of critical aspects which need to be considered when developing a screening approach for engineering mRNA improvements. First, plasmid-based screening methods do not correlate with protein expression driven by exogenously expressed mRNA. Second, improved ARG1 protein production was driven by increased translation and not improved mRNA stability. Finally, the 5' UTR appears to be the key driver in protein expression for exogenously delivered mRNA. From the testing of the combinatorial library, the 5'UTR for complement factor 3 (C3) and cytochrome p4502E1 (CYP2E1) showed the largest and most consistent increase in protein expression relative to a reference UTR. Collectively, these data provide important information for the development and optimization of therapeutic mRNAs.

Direct and Absolute Quantification of over 1800 Yeast Proteins via Selected Reaction Monitoring.

Defining intracellular protein concentration is critical in molecular systems biology. Although strategies for determining relative protein changes are available, defining robust absolute values in copies per cell has proven significantly more challenging. Here we present a reference data set quantifying over 1800Saccharomyces cerevisiaeproteins by direct means using protein-specific stable-isotope labeled internal standards and selected reaction monitoring (SRM) mass spectrometry, far exceeding any previous study. This was achieved by careful design of over 100 QconCAT recombinant proteins as standards, defining 1167 proteins in terms of copies per cell and upper limits on a further 668, with robust CVs routinely less than 20%. The selected reaction monitoring-derived proteome is compared with existing quantitative data sets, highlighting the disparities between methodologies. Coupled with a quantification of the transcriptome by RNA-seq taken from the same cells, these data support revised estimates of several fundamental molecular parameters: a total protein count of ∼100 million molecules-per-cell, a median of ∼1000 proteins-per-transcript, and a linear model of protein translation explaining 70% of the variance in translation rate. This work contributes a "gold-standard" reference yeast proteome (including 532 values based on high quality, dual peptide quantification) that can be widely used in systems models and for other comparative studies.

Versatile Separation and Analysis of Heparan Sulfate Oligosaccharides Using Graphitized Carbon Liquid Chromatography and Electrospray Mass Spectrometry.

Heparin and heparan sulfate (HS) by nature contain multiple isomeric structures, which are fundamental for the regulation of biological processes. Here we report the use of a porous graphitized carbon (PGC) LC-MS method with effective separation and sensitivity to separate mixtures of digested HS oligosaccharides. Application of this method allowed the separation of oligosaccharide mixtures with various degree of polymerization (dp) ranging from dp4 to dp8, two dp4 isomers that were baseline resolved, four dp6 isomers, and the observation of a dp3 oligosaccharide. PGC LC-MS of complex mixtures demonstrated that compounds eluted from the column in decreasing order of hydrophilicity, with the more highly sulfated structures eluting first. Our data indicate that sulfation levels, chain length, and conformation all effect elution order. We found that PGC's resolving capabilities for the dp4 and dp6 isomeric structures makes this methodology particularly useful for the sequencing of HS saccharides, because the lack of contaminating isomeric structures provides unambiguous structural assignments from the MS/MS data. Collectively this work demonstrates that PGC column-based methods are powerful tools for enhanced separation and analysis of heterogeneous mixtures of HS saccharide species.

Label-Free Discovery Array Platform for the Characterization of Glycan Binding Proteins and Glycoproteins.

The identification of carbohydrate-protein interactions is central to our understanding of the roles of cell-surface carbohydrates (the glycocalyx), fundamental for cell-recognition events. Therefore, there is a need for fast high-throughput biochemical tools to capture the complexity of these biological interactions. Here, we describe a rapid method for qualitative label-free detection of carbohydrate-protein interactions on arrays of simple synthetic glycans, more complex natural glycosaminoglycans (GAG), and lectins/carbohydrate binding proteins using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. The platform can unequivocally identify proteins that are captured from either purified or complex sample mixtures, including biofluids. Identification of proteins bound to the functionalized array is achieved by analyzing either the intact protein mass or, after on-chip proteolytic digestion, the peptide mass fingerprint and/or tandem mass spectrometry of selected peptides, which can yield highly diagnostic sequence information. The platform described here should be a valuable addition to the limited analytical toolbox that is currently available for glycomics.

Enrichment of Two Isomeric Heparin Oligosaccharides Exhibiting Different Affinities toward Monocyte Chemoattractant Protein-1.

Chemokine-GAG interactions are crucial to facilitate chemokine immobilization, resulting in the formation of chemokine gradients that guide cell migration. Here we demonstrate chromatographic isolation and purification of two heparin hexasaccharide isomers that interact with the oligomeric chemokine Monocyte Chemoattractant Protein-1 (MCP-1)/CCL2 with different binding affinities. The sequences of these two hexasaccharides were deduced from unique MS/MS product ions and HPLC compositional analysis. Ion mobility mass spectrometry (IM-MS) showed that the two isolated oligosaccharides have different conformations and both displayed preferential binding for one of the two distinct conformations known for MCP-1 dimers. A significant shift in arrival time distribution of close to 70 Å2 was observed, indicating a more compact protein:hexasaccharide conformation. Clear differences in the MS spectra between bound and unbound protein allowed calculation of Kd values from the resulting data. The structural difference between the two hexasaccharides was defined as the differential location of a single sulfate at either C-6 of glucosamine or C-2 of uronic acid in the reducing disaccharide, resulting in a 200-fold difference in binding affinity for MCP-1. These data indicate sequence specificity for high affinity binding, supporting the view that sulfate position, and not simply the number of sulfates, is important for heparan sulfate protein binding.

Heparin Isomeric Oligosaccharide Separation Using Volatile Salt Strong Anion Exchange Chromatography.

The complexity of heparin and heparan sulfate saccharides makes their purification, including many isomeric structures, very challenging and is a bottleneck for structure-activity studies. High-resolution separations have been achieved by strong anion exchange (SAX) chromatography on Propac PA1 and cetyltrimethylammonium (CTA)-C18 silica columns; however, these entail subsequent desalting methodologies and consequent sample losses and are incompatible with orthogonal chromatography methodologies and, in particular, mass spectrometry. Here, we present the CTA-SAX purification of heparin oligosaccharides using volatile salt (VS) buffer. In VSCTA-SAX, the use of ammonium bicarbonate buffer for elution improves resolution through both weaker dissociation and conformational coordination of the ammonium across the sulfate groups. Using ion mobility mass spectrometry, we demonstrate that isomeric structures have different structural conformations, which makes chromatographic separation achievable. Resolution of such structures is improved compared to standard SAX methods, and in addition, VSCTA-SAX provides an orthogonal method to isolate saccharides with higher purity. Because ammonium bicarbonate is used, the samples can be evaporated rather than desalted, preventing substantial sample loss and allowing more effective subsequent analysis by electrospray mass spectrometry. We conclude that VSCTA-SAX is a powerful new tool that helps address the difficult challenge of heparin/heparan sulfate saccharide separation and will enhance structure-activity studies.

Composition, sequencing and ion mobility mass spectrometry of heparan sulfate-like octasaccharide isomers differing in glucuronic and iduronic acid content.

Here we report ion mobility mass spectrometry (IMMS) separation and tandem mass spectrometry (MS(2)) sequencing methods used to analyze and differentiate six synthetically produced heparin/heparan sulfate (HS)-like octasaccharide (dp8) isomeric structures. These structures are isomeric with regard to either glucuronic acid (GlcA) or iduronic acid (IdoA) residues at various positions. IMMS analysis showed that a fully GlcA structure exhibited a more compact conformation, whereas the fully IdoA structure was more extended. Interestingly, the change from IdoA to GlcA in specific locations resulted in strong conformational distortions. MS(2) of the six isomers showed very different spectra with unique sets of diagnostic product ions. Analysis of MS(2) product ion spectra suggests that the GlcA group correlated with the formation of a glycosidic product ion under lower energy conditions. This resulted in an earlier product ion formation and more intense product ions. Importantly, this knowledge enabled a complete sequencing of the positions of GlcA and IdoA in each of the four positions located in each unique dp8 structure.

5-HT neurons of the area postrema become c-Fos-activated after increases in plasma sodium levels and transmit interoceptive information to the nucleus accumbens.

Serotonergic (5-hydroxytryptamine, 5-HT) neurons of the area postrema (AP) represent one neuronal phenotype implicated in the regulation of salt appetite. Tryptophan hydroxylase (Tryp-OH, synthetic enzyme-producing 5-HT) immunoreactive neurons in the AP of rats become c-Fos-activated following conditions in which plasma sodium levels are elevated; these include intraperitoneal injections of hypertonic saline and sodium repletion. Non-Tryp-OH neurons also became c-Fos-activated. Sodium depletion, which induced an increase in plasma osmolality but caused no significant change in the plasma sodium concentration, had no effect on the c-Fos activity in the AP. Epithelial sodium channels are expressed in the Tryp-OH-immunoreactive AP neurons, possibly functioning in the detection of changes in plasma sodium levels. Since little is known about the neural circuitry of these neurons, we tested whether the AP contributes to a central pathway that innervates the reward center of the brain. Stereotaxic injections of pseudorabies virus were made in the nucleus accumbens (NAc), and after 4 days, this viral tracer produced retrograde transneuronal labeling in the Tryp-OH and non-Tryp-OH AP neurons. Both sets of neurons innervate the NAc via a multisynaptic pathway. Besides sensory information regarding plasma sodium levels, the AP→NAc pathway may also transmit other types of chemosensory information, such as those related to metabolic functions, food intake, and immune system to the subcortical structures of the reward system. Because these subcortical regions ultimately project to the medial prefrontal cortex, different types of chemical signals from visceral systems may influence affective functions.

Chemokine Oligomers and the Impact of Fondaparinux Binding.

Heparin, a widely used clinical anticoagulant, is generally well-tolerated; however, approximately 1% of patients develop heparin-induced thrombocytopenia (HIT), a serious side effect. While efforts to understand the role of chemokines in HIT development are ongoing, certain aspects remain less studied, such as the stabilization of chemokine oligomers by heparin. Here, we conducted a combined ion mobility-native mass spectrometry study to investigate the stability of chemokine oligomers and their complexes with fondaparinux, a synthetic heparin analog. Collision-induced dissociation and unfolding experiments provided clarity on the specificity and relevance of chemokine oligomers and their fondaparinux complexes with varying stoichiometries, as well as the stabilizing effects of fondaparinux binding.

Structure and function of Semaphorin-5A glycosaminoglycan interactions.

Integration of extracellular signals by neurons is pivotal for brain development, plasticity, and repair. Axon guidance relies on receptor-ligand interactions crosstalking with extracellular matrix components. Semaphorin-5A (Sema5A) is a bifunctional guidance cue exerting attractive and inhibitory effects on neuronal growth through the interaction with heparan sulfate (HS) and chondroitin sulfate (CS) glycosaminoglycans (GAGs), respectively. Sema5A harbors seven thrombospondin type-1 repeats (TSR1-7) important for GAG binding, however the underlying molecular basis and functions in vivo remain enigmatic. Here we dissect the structural basis for Sema5A:GAG specificity and demonstrate the functional significance of this interaction in vivo. Using x-ray crystallography, we reveal a dimeric fold variation for TSR4 that accommodates GAG interactions. TSR4 co-crystal structures identify binding residues validated by site-directed mutagenesis. In vitro and cell-based assays uncover specific GAG epitopes necessary for TSR association. We demonstrate that HS-GAG binding is preferred over CS-GAG and mediates Sema5A oligomerization. In vivo, Sema5A:GAG interactions are necessary for Sema5A function and regulate Plexin-A2 dependent dentate progenitor cell migration. Our study rationalizes Sema5A associated developmental and neurological disorders and provides mechanistic insights into how multifaceted guidance functions of a single transmembrane cue are regulated by proteoglycans.

The anticancer ruthenium complex KP1019 induces DNA damage, leading to cell cycle delay and cell death in Saccharomyces cerevisiae.

The anticancer ruthenium complex trans-[tetrachlorobis(1H-indazole)ruthenate(III)], otherwise known as KP1019, has previously been shown to inhibit proliferation of ovarian tumor cells, induce DNA damage and apoptosis in colon carcinoma cells, and reduce tumor size in animal models. Notably, no dose-limiting toxicity was observed in a Phase I clinical trial. Despite these successes, KP1019's precise mechanism of action remains poorly understood. To determine whether Saccharomyces cerevisiae might serve as an effective model for characterizing the cellular response to KP1019, we first confirmed that this drug is internalized by yeast and induces mutations, cell cycle delay, and cell death. We next examined KP1019 sensitivity of strains defective in DNA repair, ultimately showing that rad1Δ, rev3Δ, and rad52Δ yeast are hypersensitive to KP1019, suggesting that nucleotide excision repair (NER), translesion synthesis (TLS), and recombination each play a role in drug tolerance. These data are consistent with published work showing that KP1019 causes interstrand cross-links and bulky DNA adducts in mammalian cell lines. Published research also showed that mammalian cell lines resistant to other chemotherapeutic agents exhibit only modest resistance, and sometimes hypersensitivity, to KP1019. Here we report similar findings for S. cerevisiae. Whereas gain-of-function mutations in the transcription activator-encoding gene PDR1 are known to increase expression of drug pumps, causing resistance to structurally diverse toxins, we now demonstrate that KP1019 retains its potency against yeast carrying the hypermorphic alleles PDR1-11 or PDR1-3. Combined, these data suggest that S. cerevisiae could serve as an effective model system for identifying evolutionarily conserved modulators of KP1019 sensitivity.