PSGL-1 attenuates early TCR signaling to suppress CD8+ T cell progenitor differentiation and elicit terminal CD8+ T cell exhaustion

PSGL-1 (P-selectin glycoprotein-1) is a T cell-intrinsic checkpoint regulator of exhaustion with an unknown mechanism of action. Here, we show that PSGL-1 acts upstream of PD-1 and requires co-ligation with the T cell receptor (TCR) to attenuate activation of mouse and human CD8⁺ T cells and drive terminal T cell exhaustion. PSGL-1 directly restrains TCR signaling via Zap70 and maintains expression of the Zap70 inhibitor Sts-1. PSGL-1 deficiency empowers CD8⁺ T cells to respond to low-affinity TCR ligands and inhibit growth of PD-1-blockade-resistant melanoma by enabling tumor-infiltrating T cells to sustain an elevated metabolic gene signature supportive of increased glycolysis and glucose uptake to promote effector function. This outcome is coupled to an increased abundance of CD8⁺ T cell stem cell-like progenitors that maintain effector functions. Additionally, pharmacologic blockade of PSGL-1 curtails T cell exhaustion, indicating that PSGL-1 represents an immunotherapeutic target for PD-1-blockade-resistant tumors.

Targeting the Dark Lipid Kinase PIP4K2C with a Potent and Selective Binder and Degrader

Phosphatidylinositol 5-phosphate 4-kinase, type II, gamma (PIP4K2C) remains a poorly understood lipid kinase with minimal enzymatic activity but potential scaffolding roles in immune modulation and autophagy-dependent catabolism. Achieving potent and selective agents for PIP4K2C while sparing other lipid and non-lipid kinases has been challenging. Here, we report the discovery of the highly potent PIP4K2C binder TMX-4102, which shows exclusive binding selectivity for PIP4K2C. Furthermore, we elaborated the PIP4K2C binder into TMX-4153, a bivalent degrader capable of rapidly and selectively degrading endogenous PIP4K2C. Collectively, our work demonstrates that PIP4K2C is a tractable and degradable target, and that TMX-4102 and TMX-4153 are useful leads to further interrogate the biological roles and therapeutic potential of PIP4K2C.

Shining light on reprogramming Tregs for cancer therapy

In this issue of Cell Chemical Biology, Bonazzi et al. demonstrate that pharmacologically degrading the transcription factor Helios (IKZF2) results in destabilization of regulatory T cells, which normally restrain anti-tumor immunity. These results highlight how molecular glue degraders can selectively target previously undruggable proteins with potential applications in the clinic.

Development of potent and selective degraders of PI5P4Kγ

Phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks), a family of three members in mammals (α, β and γ), have emerged as potential therapeutic targets due to their role in regulating many important cellular signaling pathways. In comparison to the PI5P4Kα and PI5P4Kβ, which usually have similar expression profiles across cancer cells, PI5P4Kγ exhibits distinct expression patterns, and pathological functions for PI5P4Kγ have been proposed in the context of cancer and neurodegenerative diseases. PI5P4Kγ has very low kinase activity and has been proposed to inhibit the PI4P5Ks through scaffolding function, providing a rationale for developing a selective PI5P4Kγ degrader. Here, we report the development and characterization of JWZ-1-80, a first-in-class PI5P4Kγ degrader. JWZ-1-80 potently degrades PI5P4Kγ via the ubiquitin-proteasome system and exhibits proteome-wide selectivity and is therefore a useful tool compound for further dissecting the biological functions of PI5P4Kγ.

Acute pharmacological degradation of ERK5 does not inhibit cellular immune response or proliferation

Recent interest in the role that extracellular signal-regulated kinase 5 (ERK5) plays in various diseases, particularly cancer and inflammation, has grown. Phenotypes observed from genetic knockdown or deletion of ERK5 suggested that targeting ERK5 could have therapeutic potential in various disease settings, motivating the development ATP-competitive ERK5 inhibitors. However, these inhibitors were unable to recapitulate the effects of genetic loss of ERK5, suggesting that ERK5 may have key kinase-independent roles. To investigate potential non-catalytic functions of ERK5, we report the development of INY-06-061, a potent and selective heterobifunctional degrader of ERK5. In contrast to results reported through genetic knockdown of ERK5, INY-06-061-induced ERK5 degradation did not induce anti-proliferative effects in multiple cancer cell lines or suppress inflammatory responses in primary endothelial cells. Thus, we developed and characterized a chemical tool useful for validating phenotypes reported to be associated with genetic ERK5 ablation and for guiding future ERK5-directed drug discovery efforts.

Redirecting the Neo-Substrate Specificity of Cereblon-Targeting PROTACs to Helios

Immunomodulatory imide drugs (IMiDs), such as thalidomide and its analogues, are some of the most commonly utilized E3 ligase ligands for the development of proteolysis targeting chimeras (PROTACs). While the canonical neo-substrates of IMiDs (i.e., Ikaros and Aiolos) are often considered to be unwanted targets of PROTACs, maintaining the degradation of these neo-substrates also provides the opportunity to synergistically degrade multiple proteins with a single compound. Here, we report the development of ALV-07-082-03, a CDK4/CDK6/Helios triple degrader that consists of palbociclib, an FDA-approved CDK4/6 inhibitor, conjugated to DKY709, a novel IMiD-based Helios degrader. Pharmacological codegradation of CDK4/6 and Helios resulted in potent suppression of downstream signaling and proliferation in cancer cells, as well as enhanced derepression of IL-2 secretion. Thus, not only do we demonstrate the possibility of rationally redirecting the neo-substrate specificity of PROTACs by incorporating alternative molecular glue molecules as E3 ligase ligands but our findings also suggest that cotargeting CDK4/6 and Helios may have synergistic effects.

Inhibition of CDK4/6 Promotes CD8 T-cell Memory Formation

CDK4/6 inhibitors are approved to treat breast cancer and are in trials for other malignancies. We examined CDK4/6 inhibition in mouse and human CD8+ T cells during early stages of activation. Mice receiving tumor-specific CD8+ T cells treated with CDK4/6 inhibitors displayed increased T-cell persistence and immunologic memory. CDK4/6 inhibition upregulated MXD4, a negative regulator of MYC, in both mouse and human CD8+ T cells. Silencing of Mxd4 or Myc in mouse CD8+ T cells demonstrated the importance of this axis for memory formation. We used single-cell transcriptional profiling and T-cell receptor clonotype tracking to evaluate recently activated human CD8+ T cells in patients with breast cancer before and during treatment with either palbociclib or abemaciclib. CDK4/6 inhibitor therapy in humans increases the frequency of CD8+ memory precursors and downregulates their expression of MYC target genes, suggesting that CDK4/6 inhibitors in patients with cancer may augment long-term protective immunity. SIGNIFICANCE: CDK4/6 inhibition skews newly activated CD8+ T cells toward a memory phenotype in mice and humans with breast cancer. CDK4/6 inhibitors may have broad utility outside breast cancer, particularly in the neoadjuvant setting to augment CD8+ T-cell priming to tumor antigens prior to dosing with checkpoint blockade.This article is highlighted in the In This Issue feature, p. 2355.

Acute pharmacological degradation of Helios destabilizes regulatory T cells

The zinc-finger transcription factor Helios is critical for maintaining the identity, anergic phenotype and suppressive activity of regulatory T (T_reg) cells. While it is an attractive target to enhance the efficacy of currently approved immunotherapies, no existing approaches can directly modulate Helios activity or abundance. Here, we report the structure-guided development of small molecules that recruit the E3 ubiquitin ligase substrate receptor cereblon to Helios, thereby promoting its degradation. Pharmacological Helios degradation destabilized the anergic phenotype and reduced the suppressive activity of T_reg cells, establishing a route towards Helios-targeting therapeutics. More generally, this study provides a framework for the development of small-molecule degraders for previously unligandable targets by reprogramming E3 ligase substrate specificity.

Selective Degradation of GSPT1 by Cereblon Modulators Identified via a Focused Combinatorial Library

Cereblon (CRBN) is an E3 ligase adapter protein that can be reprogrammed by imide-class compounds such as thalidomide, lenalidomide, and pomalidomide to induce the degradation of neo-substrate proteins. In order to identify additional small molecule CRBN modulators, we implemented a focused combinatorial library approach where we fused an imide-based CRBN-binding pharmacophore to a heterocyclic scaffold, which could be further elaborated. We screened the library for CRBN-dependent antiproliferative activity in the multiple myeloma cell line MM1.S and identified five hit compounds. Quantitative chemical proteomics of hit compounds revealed that they induced selective degradation of GSPT1, a translation termination factor that is currently being explored as a therapeutic target for the treatment of acute myeloid leukemia. Molecular docking studies with CRBN and GSPT1 followed by analogue synthesis identified a possible hydrogen bond interaction with the central pyrimidine ring as a molecular determinant of hit compounds' selectivity. This study demonstrates that a focused combinatorial library design, phenotypic screening, and chemical proteomics can provide a suitable workflow to efficiently identify novel CRBN modulators.

CDK7 Inhibition Potentiates Genome Instability Triggering Anti-tumor Immunity in Small Cell Lung Cancer

Cyclin-dependent kinase 7 (CDK7) is a central regulator of the cell cycle and gene transcription. However, little is known about its impact on genomic instability and cancer immunity. Using a selective CDK7 inhibitor, YKL-5-124, we demonstrated that CDK7 inhibition predominately disrupts cell-cycle progression and induces DNA replication stress and genome instability in small cell lung cancer (SCLC) while simultaneously triggering immune-response signaling. These tumor-intrinsic events provoke a robust immune surveillance program elicited by T cells, which is further enhanced by the addition of immune-checkpoint blockade. Combining YKL-5-124 with anti-PD-1 offers significant survival benefit in multiple highly aggressive murine models of SCLC, providing a rationale for new combination regimens consisting of CDK7 inhibitors and immunotherapies.

Development and Application of FASA, a Model for Quantifying Fatty Acid Metabolism Using Stable Isotope Labeling

It is well understood that fatty acids can be synthesized, imported, and modified to meet requisite demands in cells. However, following the movement of fatty acids through the multiplicity of these metabolic steps has remained difficult. To better address this problem, we developed Fatty Acid Source Analysis (FASA), a model that defines the contribution of synthesis, import, and elongation pathways to fatty acid homeostasis in saturated, monounsaturated, and polyunsaturated fatty acid pools. Application of FASA demonstrated that elongation can be a major contributor to cellular fatty acid content and showed that distinct pro-inflammatory stimuli (e.g., Toll-like receptors 2, 3, or 4) specifically reprogram homeostasis of fatty acids by differential utilization of synthetic and elongation pathways in macrophages. In sum, this modeling approach significantly advances our ability to interrogate cellular fatty acid metabolism and provides insight into how cells dynamically reshape their lipidomes in response to metabolic or inflammatory signals.

Argus et al. developed Fatty Acid Source Analysis (FASA), a model that quantifies cellular fatty acid synthesis, elongation, and import. FASA is used to demonstrate that elongation can be a major contributor to cellular fatty acid content and that different stimuli reprogram macrophage fatty acid elongation pathways in distinct ways.

Development of Dual and Selective Degraders of Cyclin-Dependent Kinases 4 and 6

Cyclin-dependent kinases 4 and 6 (CDK4/6) are key regulators of the cell cycle, and there are FDA-approved CDK4/6 inhibitors for treating patients with metastatic breast cancer. However, due to conservation of their ATP-binding sites, development of selective agents has remained elusive. Here, we report imide-based degrader molecules capable of degrading both CDK4/6, or selectively degrading either CDK4 or CDK6. We were also able to tune the activity of these molecules against Ikaros (IKZF1) and Aiolos (IKZF3), which are well-established targets of imide-based degraders. We found that in mantle cell lymphoma cell lines, combined IKZF1/3 degradation with dual CDK4/6 degradation produced enhanced anti-proliferative effects compared to CDK4/6 inhibition, CDK4/6 degradation, or IKZF1/3 degradation. In summary, we report here the first compounds capable of inducing selective degradation of CDK4 and CDK6 as tools to pharmacologically dissect their distinct biological functions.

Development of Highly Potent and Selective Steroidal Inhibitors and Degraders of CDK8

Cortistatin A is a natural product isolated from the marine sponge Corticium simplex and was found to be a potent and selective inhibitor of CDK8. Many synthetic groups have reported total syntheses of Cortistatin A; however, these syntheses require between 16 and 30 steps and report between 0.012-2% overall yields, which is not amenable to large-scale production. Owing to similarities between the complex core of Cortistatin A and the simple steroid core, we initiated a campaign to design simple, more easily prepared CDK8 inhibitors based on a steroid scaffold that would be more convenient for large-scale synthesis. Herein, we report the discovery and optimization of JH-VIII-49, a potent and selective inhibitor of CDK8 with a simple steroid core that has an eight-step synthesis with a 33% overall yield, making it suitable for large-scale preparation. Using this scaffold, we then developed a bivalent small molecule degrader, JH-XI-10-02, that can recruit the E3 ligase CRL4^Cereblon to promote the ubiquitination and proteosomal degradation of CDK8.

CDK4/6 Inhibition Augments Antitumor Immunity by Enhancing T-cell Activation

Immune checkpoint blockade, exemplified by antibodies targeting the PD-1 receptor, can induce durable tumor regressions in some patients. To enhance the efficacy of existing immunotherapies, we screened for small molecules capable of increasing the activity of T cells suppressed by PD-1. Here, we show that short-term exposure to small-molecule inhibitors of cyclin-dependent kinases 4 and 6 (CDK4/6) significantly enhances T-cell activation, contributing to antitumor effects in vivo, due in part to the derepression of NFAT family proteins and their target genes, critical regulators of T-cell function. Although CDK4/6 inhibitors decrease T-cell proliferation, they increase tumor infiltration and activation of effector T cells. Moreover, CDK4/6 inhibition augments the response to PD-1 blockade in a novel ex vivo organotypic tumor spheroid culture system and in multiple in vivo murine syngeneic models, thereby providing a rationale for combining CDK4/6 inhibitors and immunotherapies.Significance: Our results define previously unrecognized immunomodulatory functions of CDK4/6 and suggest that combining CDK4/6 inhibitors with immune checkpoint blockade may increase treatment efficacy in patients. Furthermore, our study highlights the critical importance of identifying complementary strategies to improve the efficacy of immunotherapy for patients with cancer. Cancer Discov; 8(2); 216-33. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Jenkins et al., p. 196This article is highlighted in the In This Issue feature, p. 127.

Ex Vivo Profiling of PD-1 Blockade Using Organotypic Tumor Spheroids

Ex vivo systems that incorporate features of the tumor microenvironment and model the dynamic response to immune checkpoint blockade (ICB) may facilitate efforts in precision immuno-oncology and the development of effective combination therapies. Here, we demonstrate the ability to interrogate ex vivo response to ICB using murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS). MDOTS/PDOTS isolated from mouse and human tumors retain autologous lymphoid and myeloid cell populations and respond to ICB in short-term three-dimensional microfluidic culture. Response and resistance to ICB was recapitulated using MDOTS derived from established immunocompetent mouse tumor models. MDOTS profiling demonstrated that TBK1/IKKε inhibition enhanced response to PD-1 blockade, which effectively predicted tumor response in vivo Systematic profiling of secreted cytokines in PDOTS captured key features associated with response and resistance to PD-1 blockade. Thus, MDOTS/PDOTS profiling represents a novel platform to evaluate ICB using established murine models as well as clinically relevant patient specimens.Significance: Resistance to PD-1 blockade remains a challenge for many patients, and biomarkers to guide treatment are lacking. Here, we demonstrate feasibility of ex vivo profiling of PD-1 blockade to interrogate the tumor immune microenvironment, develop therapeutic combinations, and facilitate precision immuno-oncology efforts. Cancer Discov; 8(2); 196-215. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Deng et al., p. 216This article is highlighted in the In This Issue feature, p. 127.

An optimized method for measuring fatty acids and cholesterol in stable isotope-labeled cells

Stable isotope labeling has become an important methodology for determining lipid metabolic parameters of normal and neoplastic cells. Conventional methods for fatty acid and cholesterol analysis have one or more issues that limit their utility for in vitro stable isotope-labeling studies. To address this, we developed a method optimized for measuring both fatty acids and cholesterol from small numbers of stable isotope-labeled cultured cells. We demonstrate quantitative derivatization and extraction of fatty acids from a wide range of lipid classes using this approach. Importantly, cholesterol is also recovered, albeit at a modestly lower yield, affording the opportunity to quantitate both cholesterol and fatty acids from the same sample. Although we find that background contamination can interfere with quantitation of certain fatty acids in low amounts of starting material, our data indicate that this optimized method can be used to accurately measure mass isotopomer distributions for cholesterol and many fatty acids isolated from small numbers of cultured cells. Application of this method will facilitate acquisition of lipid parameters required for quantifying flux and provide a better understanding of how lipid metabolism influences cellular function.

Maintenance therapy with decitabine in younger adults with acute myeloid leukemia in first remission: a phase 2 Cancer and Leukemia Group B Study (CALGB 10503)

In this prospective phase 2 clinical trial conducted by Cancer and Leukemia Group B (CALGB, now the Alliance), we studied decitabine as maintenance therapy for younger adults with acute myeloid leukemia (AML) who remained in first complete remission (CR1) following intensive induction and consolidation. Given that decitabine is clinically active in AML and with hypomethylating activity distinct from cytotoxic chemotherapy, we hypothesized that one year of maintenance therapy would improve disease-free survival (DFS) for AML patients <60 years who did not receive allogeneic stem cell transplantation (alloHCT) in CR1. After blood count recovery from final consolidation, patients received decitabine at 20mg/m² IV daily for 4–5 days, every 6 weeks for 8 cycles. One-hundred-thirty-four patients received decitabine, 85 (63%) had favorable risk AML. The median number of cycles received was 7 (range, 1–8), and the primary reason for discontinuation was relapse. DFS at 1-year and 3-years was 79% and 54%, respectively. These results are similar to the outcomes in the historical control comprised of similar patients treated on recent CALGB trials. Thus, maintenance with decitabine provided no benefit overall. Standard use of decitabine maintenance in younger AML patients in CR1 is not warranted. This trial was registered at www.clinicaltrials.gov as NCT00416598.

Limiting Cholesterol Biosynthetic Flux Spontaneously Engages Type I IFN Signaling

Cellular lipid requirements are achieved through a combination of biosynthesis and import programs. Using isotope tracer analysis, we show that type I interferon (IFN) signaling shifts the balance of these programs by decreasing synthesis and increasing import of cholesterol and long chain fatty acids. Genetically enforcing this metabolic shift in macrophages is sufficient to render mice resistant to viral challenge, demonstrating the importance of reprogramming the balance of these two metabolic pathways in vivo. Unexpectedly, mechanistic studies reveal that limiting flux through the cholesterol biosynthetic pathway spontaneously engages a type I IFN response in a STING-dependent manner. The upregulation of type I IFNs was traced to a decrease in the pool size of synthesized cholesterol and could be inhibited by replenishing cells with free cholesterol. Taken together, these studies delineate a metabolic-inflammatory circuit that links perturbations in cholesterol biosynthesis with activation of innate immunity.

Allosteric inhibition of the IRE1α RNase preserves cell viability and function during endoplasmic reticulum stress

Depending on endoplasmic reticulum (ER) stress levels, the ER transmembrane multidomain protein IRE1α promotes either adaptation or apoptosis. Unfolded ER proteins cause IRE1α lumenal domain homo-oligomerization, inducing trans autophosphorylation that further drives homo-oligomerization of its cytosolic kinase/endoribonuclease (RNase) domains to activate mRNA splicing of adaptive XBP1 transcription factor. However, under high/chronic ER stress, IRE1α surpasses an oligomerization threshold that expands RNase substrate repertoire to many ER-localized mRNAs, leading to apoptosis. To modulate these effects, we developed ATP-competitive IRE1α Kinase-Inhibiting RNase Attenuators-KIRAs-that allosterically inhibit IRE1α's RNase by breaking oligomers. One optimized KIRA, KIRA6, inhibits IRE1α in vivo and promotes cell survival under ER stress. Intravitreally, KIRA6 preserves photoreceptor functional viability in rat models of ER stress-induced retinal degeneration. Systemically, KIRA6 preserves pancreatic β cells, increases insulin, and reduces hyperglycemia in Akita diabetic mice. Thus, IRE1α powerfully controls cell fate but can itself be controlled with small molecules to reduce cell degeneration.

IRE1α cleaves select microRNAs during ER stress to derepress translation of proapoptotic Caspase-2

The endoplasmic reticulum (ER) is the primary organelle for folding and maturation of secretory and transmembrane proteins. Inability to meet protein-folding demand leads to "ER stress," and activates IRE1α, an ER transmembrane kinase-endoribonuclease (RNase). IRE1α promotes adaptation through splicing Xbp1 mRNA or apoptosis through incompletely understood mechanisms. Here, we found that sustained IRE1α RNase activation caused rapid decay of select microRNAs (miRs -17, -34a, -96, and -125b) that normally repress translation of Caspase-2 mRNA, and thus sharply elevates protein levels of this initiator protease of the mitochondrial apoptotic pathway. In cell-free systems, recombinant IRE1α endonucleolytically cleaved microRNA precursors at sites distinct from DICER. Thus, IRE1α regulates translation of a proapoptotic protein through terminating microRNA biogenesis, and noncoding RNAs are part of the ER stress response.

Molecular epidemiology and risk factors for colonization by vancomycin-resistant Enterococcus in patients with hematologic malignancies

OBJECTIVE

To study the molecular epidemiology of vancomycin-resistant Enterococcus (VRE) colonization and to identify modifiable risk factors among patients with hematologic malignancies.

SETTING

A hematology-oncology unit with high prevalence of VRE colonization.

PARTICIPANTS

Patients with hematologic malignancies and hematopoietic stem cell transplantation recipients admitted to the hospital.

METHODS

Patients underwent weekly surveillance by means of perianal swabs for VRE colonization and, if colonized, were placed in contact isolation. We studied the molecular epidemiology in fecal and blood isolates by pulsed-field gel electrophoresis over a 1-year period. We performed a retrospective case-control study over a 3-year period. Cases were defined as patients colonized by VRE, and controls were defined as patients negative for VRE colonization. Case patients and control patients were matched by admitting service and length of observation time.

RESULTS

Molecular genotyping demonstrated the primarily polyclonal nature of VRE isolates. Colonization occurred at a median of 14 days. Colonized patients were characterized by longer hospital admissions. Previous use of ceftazidime was associated with VRE colonization (P < .001), while use of intravenous vancomycin and antibiotics with anaerobic activity did not emerge as a risk factor. There was no association with neutropenia or presence of colonic mucosal disruption, and severity of illness was similar in both groups.

CONCLUSION

Molecular studies showed that in the majority of VRE-colonized patients the strains were unique, arguing that VRE acquisition was sporadic rather than resulting from a common source of transmission. Patient-specific factors, including prior antibiotic exposure, rather than breaches in infection control likely predict for risk of fecal VRE colonization.

Biologic features and treatment outcome of secondary acute lymphoblastic leukemia--a review of 101 cases

BACKGROUND

Secondary acute lymphoblastic leukemia (sALL) is a rare disease and its biologic features are not well characterized.

PATIENTS AND METHODS

We describe a cohort of seven patients and discuss 94 additional cases from the literature for whom biological parameters were described. Cases with incomplete data were excluded.

RESULTS

Hodgkin's disease (HD) was more common in the 18-59 age group while breast and prostate cancers were prevalent only in the >or=18-year-old patients. The time interval to develop sALL was similar among all age groups but was significantly longer for HD and neuroblastoma primary diagnoses and sALL with complex karyotype. T-cell immunophenotype was more common in the <18 age group. Complete remission was infrequent in the >or=60 age group. The overall survival was poor for all sALL regardless of age, primary diagnoses, cytogenetic subgroups, or immunophenotype. Allogeneic transplantation most probably represents the only chance of cure.

CONCLUSION

Better identification of prognostic factors to prevent the occurrence of sALL is indicated.

Reexamination of the cysteine residues in glucocerebrosidase

Glucocerebrosidase, the deficient enzyme in Gaucher disease, catalyzes the cleavage of the beta-glycosidic linkage of glucosylceramide. A previous study on the enzyme identified three disulfide bridges and a single sulfhydryl [Lee, Y., Kinoshita, H., Radke, G., Weiler, S., Barranger, J.A. and Tomich, J.M. (1995) Position of the sulfhydryl group and the disulfide bonds of human glucocerebrosidase. J. Protein Chem. 14(3), 127-137] but recent publication of the X-ray structure identifies only two disulfide bridges with three free sulfhydryls [Dvir, H., Harel, M., McCarthy, A.A., Toker, L., Silman, I., Futerman, A.H. and Sussman, J.L. (2003) X-ray structure of human acid-beta-glucosidase, the defective enzyme in Gaucher disease. EMBO. 4(7), 704-709]. Using chemical modifications, acid cleavage and enzymatic digestion methods, we report that three free sulfhydryls exist and that the remaining four cysteines form two disulfide bonds located within the first 25 amino-terminal residues, supporting the X-ray structure.

Acute myeloid leukemia with t(5;18)(q35;q21)

A case of acute myelocytic leukemia with a translocation (5;18)(q35;q21) is reported. Cytogenetic abnormalities of the long arm of chromosome 5 have long been known to affect hematopoiesis. Although translocations between 5q and other chromosomes have been associated with malignancy, this is the first reported case of a t(5;18) resulting in acute myeloid leukemia. Possible molecular mechanisms underlying the pathogenesis of the disease are discussed.

Subtilisin BPN' variants: increased hydrolytic activity on surface-bound substrates via decreased surface activity

Site-directed mutagenesis and random mutagenesis were used to produce variants of subtilisin BPN' (Bacillus amyloliquefaciens) protease with variable surface adsorption properties. Protease adsorption and peptide hydrolysis rate were measured for these variants using a model substrate consisting of a peptide covalently bound to a surface. While most variants adsorb at a level very similar to that of native BPN', several variants were identified which adsorb either more or less. For surface-bound substrates we report a linear dependence between the concentration of adsorbed protease enzyme and substrate hydrolysis, similar to the linear dependence between enzyme solution concentration and hydrolysis of soluble substrates. On the basis of this knowledge we hypothesized that variants designed to adsorb at a higher level on a surface-bound peptide substrate would hydrolyze that surface-bound substrate faster. Contrary to our original expectations, the variants that adsorb more on the covalently bound peptide surface hydrolyze this substrate slower. In addition, variants of BPN' which adsorb at a lower level than native BPN' hydrolyze the surface-bound substrate faster. Enzyme adsorption and the subsequent peptide hydrolysis are altered by substituting amino acids that modify the surface charge or hydrophobicity of the native enzyme. This effect is most dramatic when the changes were made at surface-exposed sites around the binding pocket/active site of the enzyme. One mechanism that is consistent with the data is based on the relationship between the level of adsorption and the enzyme's affinity for the surface. In this mechanism weakly adsorbed enzymes are postulated to move more rapidly from site to site on the surface, thereby increasing substrate hydrolysis.

Correlation of end-tidal CO2 measurements to arterial PaCO2 in nonintubated patients

STUDY OBJECTIVE

To determine the accuracy of end-tidal carbon dioxide levels as a measure of arterial carbon dioxide levels in nonintubated patients presenting to an emergency department for care.

DESIGN

A prospective, cross-sectional analysis.

SETTING

University hospital ED.

TYPE OF PARTICIPANT

Nonintubated adult patients presenting to the ED for care of a variety of problems.

INTERVENTIONS

Patients who had arterial blood gas samples taken as part of their ED evaluation were asked to breathe normally through an endotracheal tube adapter or a modified nasal cannula connected to a side port sampling capnometer while a sample for arterial blood gas was drawn from the radial artery.

MEASUREMENTS

End-tidal carbon dioxide levels (mm Hg) were recorded at the time of arterial blood gas sampling. The difference between end-tidal carbon dioxide and PaCO2 was tested with the paired t-test at a significance level of .05. The correlation of end-tidal carbon dioxide to PaCO2 was tested in all patients and in subgroups using simple linear regression.

RESULTS

Seventy-six patients were enrolled. In all patients, end-tidal carbon dioxide was 3.5 mm Hg lower than PaCO2 and correlated well with PaCO2 (r2 = .772). In patients with hypocapnia, there was no significant difference between end-tidal carbon dioxide and PaCO2 (P = .17), and the correlation of end-tidal carbon dioxide to PaCO2 was stronger (r2 = .838). In patients with a respiratory or metabolic acidosis, the difference between end-tidal carbon dioxide and PaCO2 was 6 mm Hg (P = .005), but end-tidal carbon dioxide correlated well to PaCO2 (r2 = .899).

CONCLUSION

Measurements of end-tidal carbon dioxide concentrations correlate well with PaCO2 values in nonintubated patients presenting with a variety of conditions to EDs. End-tidal carbon dioxide measurements may be sufficient measures of PaCO2 in selected patients and obviate the need for repeat arterial blood gas determination. Further study is warranted.

Cocaine-induced iritis

The case of a 31-year-old man who presented to the emergency department with iritis from intranasal cocaine use is described. This was the second episode of iritis in this patient after casual cocaine use. The differential diagnosis of iritis and a proposed pathophysiologic mechanism are discussed.