Abstract 1043: Advances in cystine-dense peptide (CDP) screening and therapeutic applications

Cystine-dense peptides (CDPs) are a class of drug-like miniproteins that marry many of the advantages of biologics (high affinity and specificity) and small molecule therapeutics (high tissue permeability and low immunogenicity). The beneficial properties of CDPs, and miniproteins in general, have driven interest in therapeutic applications. However, CDP diversity is vast from every clade of life, and properly interrogating “CDP space” requires specialized screening and modeling tools.

With this in mind, we have created an optimized mammalian surface display platform to screen for CDPs of clinical interest using libraries of structurally-diverse native scaffolds optimized for stability. These native CDPs can be structurally modeled, which we did in determining the structures of over 4200 native CDPs. This modeling permits further selection in silico as well as targeted mutagenesis for favorable target-binding capabilities. Hits from these screens are routinely matured to sub-nM affinity. These CDPs can play numerous roles in a drug design pipeline, from an independent drug candidate to a delivery agent for tissue-targeting to a module in a polyspecific biologic. Recent novel CDP candidates have shown promise in immune-oncology space as part of a bispecific T-cell engager targeting PD-L1, where a single 2-week treatment was capable of eliminating subcutaneous PC3 prostate cancer xenograft tumors in 27/30 mice.

Besides bispecifics, future directions for the platform include exploring targeted protein degradation. Additionally, we are expanding upon our previous work on CDPs to explore CNS or tumor delivery of therapeutic cargo. The versatility of CDPs and novel screening tools to rapidly identify and mature candidates of interest can facilitate rapid advancement of CDP therapeutics to address difficult targets in oncology.

Citation Format: Zachary R. Crook, Emily J. Girard, Gregory P. Sevilla, Mi-Youn Brusniak, Peter B. Rupert, Della J. Friend, Mesfin M. Gewe, Midori Clarke, Ida Lin, Raymond Ruff, Doan Phi, Ashok Bandaranayake, Colin E. Correnti, Andrew J. Mhyre, Natalie W. Nairn, Roland K. Strong, James M. Olson. Advances in cystine-dense peptide (CDP) screening and therapeutic applications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1043.

POS1099 QUALITY OF LIFE, WORK IMPAIRMENT, AND DAILY ACTIVITY IMPAIRMENT OF PATIENTS WITH PSORIASIS VERSUS PSORIATIC ARTHRITIS: A REAL-WORLD SURVEY IN US AND EUROPE

Background

Psoriasis (PsO) and psoriatic arthritis (PsA) and are chronic immune-mediated diseases characterised by joint inflammation and skin lesions which negatively impact patients’ health-related quality of life (HRQoL). Several previous comparative studies have focused on PsA patients with or without skin involvement. Better understanding of the impact of both PsO and PsA on HRQoL and work / activity impairment will improve understanding of the incremental burden of PsA compared to PsO, and may lead to more personalised treatment options.

Objectives

To compare HRQoL, work impairment, and daily activity impairment of patients with a PsO diagnosis (dx) only, PsO dx with musculoskeletal (MSK) symptoms (sx), PsA dx with active skin sx, and PsA dx without active skin sx.

Methods

Data were drawn from the Adelphi PsO & PsA Disease Specific Programmes™ (DSP), real-world point-in-time surveys of rheumatologists, dermatologists and their consulting patients in the United States and Europe (France, Germany, Italy, Spain and UK); conducted in 2018/19. Patients were grouped according to their symptoms and confirmed diagnoses, comprising four groups:

1. Patients with PsO dx only,

2. Patients with PsO dx and with MSK sx,

3. Patients with PsA dx and with active skin sx,

4. Patients with PsA dx with no active skin sx,

Multivariate linear regression analyses with marginal mean predictions examined differences in patient-reported outcome measures (PROMs) between the four groups. Measures included HRQoL (EuroQol 5-Dimension 5-Level [EQ-5D Utility] and EuroQoL Visual Analogue Scale [EQ-VAS]), work impairment, and daily activity impairment (Work Productivity and Activity Impairment Questionnaire [WPAI]). Analyses controlled for demographics (age, sex, BMI), comorbidities present in >10% of patients and current treatment class (biologics, csDMARDs, steroids & other).

Results

4491 patients were included: Group 1 (n=1833), Group 2 (n=91), Group 3 (n=2451), and Group 4 (n=116). 54% of patients were male, 89% of patients were white, with a mean age of 46.6 years. Demographics were consistent across all patient groups.

The model-predicted EQ-5D-Utility was lower in Groups 2, 3 and 4, compared with Group 1 (p=0.003, p<0.001 and p=0.004 respectively). Similarly, predicted EQ-VAS was lower in Group 3 compared with Group 1 (p=0.006), Table 1.

Table 1.

Predictions of PROMs for PsO-PsA patient groups

PRO toolGroup [n]*Predicted PRO valuePopulation norm (MCID)Regression model p-value (vs. reference group)EQ-5D Utility score (n=1839)1 (ref) [743]0.9220.88 (0.07)2 [32]0.8160.0033 [1023]0.810<0.0014 [41]0.8500.004EQ-VAS (n=1882)1 (ref) [763]78.7878.2 (n/a)2 [36]70.560.0573 [1040]73.890.0064 [43]75.230.248WPAI % overall work impairment (n=1015)1 (ref) [422]15.36n/a (15.0)2 [14]17.860.5603 [558]22.16<0.0014 [21]26.090.014WPAI % work time missed (n=1028)1 (ref) [424]0.91n/a (n/a)2 [14]3.570.4863 [569]4.460.0024 [21]10.430.003WPAI % impairment while working (n=1153)1 (ref) [486]14.90n/a (20.0)2 [18]13.890.8463 [626]19.63<0.0014 [23]17.390.435WPAI % activity impairment (n=1818)1 (ref) [732]18.02n/a (20.0)2 [32]26.250.1223 [1012]26.14<0.0014 [42]25.240.044

*n values provided for reference, but margins are predictions as a result of the model and not for the specific number of patients in each subgroup.

(1) patients with PsO dx only

(2) Patients with PsO dx and MSK sx

(3) Patients with PsA dx and with active skin sx

(4) Patients with PsA dx with no active skin sx

Overall work impairment increased in Groups 3 and 4, compared with Group 1 (p<0.001 and p=0.014 respectively). Furthermore, Groups 3 and 4 missed more work compared with Group 1 (p=0.002 and p=0.003 respectively). Group 3 patients exhibited an increase in presenteeism and activity impairment compared with Group 1 (p<0.001), Table 1.

Conclusion

Patients experiencing PsA dx or MSK sx experienced an additional disease burden compared to patients with PsO sx alone, as measured by worse HRQoL and work impairment.

Disclosure of Interests

Joseph F. Merola Consultant of: Merck Research Laboratories, Abbvie, Dermavant, Eli Lilly and Company, Novartis, Janssen, UCB, Samumed, Celgene, Sanofi Regeneron, GSK, Almirall, Sun Pharma, Biogen, Pfizer, Incyte, Aclaris, and Leo Pharma, Lars Erik Kristensen Speakers bureau: Pfizer, AbbVie, Amgen, UCB, Gilead, Biogen, BMS, MSD, Novartis, Eli Lilly, and Janssen Pharmaceuticals, Consultant of: Pfizer, AbbVie, Amgen, UCB, Gilead, Biogen, BMS, MSD, Novartis, Eli Lilly, and Janssen Pharmaceuticals, Grant/research support from: Novo, UCB, Eli Lilly; Novartis and Abbvie, Feifei Yang Employee of: Employee of Janssen Pharmaceuticals, Steve Peterson Employee of: Employee of Janssen Pharmaceuticals, Rachel Teneralli Employee of: Employee of Janssen Pharmaceuticals, Nicola Massey Employee of: Adelphi Real World, Soumya D. Chakravarty Employee of: Employee of Janssen Pharmaceuticals, Megan Hughes Employee of: Adelphi Real World, May Shawi Employee of: Employee of Janssen Pharmaceuticals, Sarah Weatherby Employee of: Adelphi Real World, Christine Contre Employee of: Employee of Janssen Pharmaceuticals, Iris Lin Employee of: Employee of Janssen Pharmaceuticals, Fareen Hassan Employee of: Employee of Janssen Pharmaceuticals, M Elaine Husni Consultant of: Abbvie, Amgen, Eli Lilly, Novartis, Janssen, UCB, Pfizer, Regeneron, and BMS

Ex silico engineering of cystine-dense peptides yielding a potent bispecific T cell engager

Cystine-dense peptides (CDPs) are a miniprotein class that can drug difficult targets with high affinity and low immunogenicity. Tools for their design, however, are not as developed as those for small-molecule and antibody drugs. CDPs have diverse taxonomic origins, but structural characterization is lacking. Here, we adapted Iterative Threading ASSEmbly Refinement (I-TASSER) and Rosetta protein modeling software for structural prediction of 4298 CDP scaffolds and performed in silico prescreening for CDP binders to targets of interest. Mammalian display screening of a library of docking-enriched, methionine and tyrosine scanned (DEMYS) CDPs against PD-L1 yielded binders from four distinct CDP scaffolds. One was affinity-matured, and cocrystallography yielded a high-affinity (K_D = 202 pM) PD-L1-binding CDP that competes with PD-1 for PD-L1 binding. Its subsequent incorporation into a CD3-binding bispecific T cell engager produced a molecule with pM-range in vitro T cell killing potency and which substantially extends survival in two different xenograft tumor-bearing mouse models. Both in vitro and in vivo, the CDP-incorporating bispecific molecule outperformed a comparator antibody-based molecule. This CDP modeling and DEMYS technique can accelerate CDP therapeutic development.

Immunotherapeutic Targeting of Mesothelin Positive Pediatric AML Using Bispecific T Cell Engaging Antibodies

Simple Summary

Immunotherapy development in pediatric AML has been slow due to the paucity of validated AML-specific targets. We recently identified mesothelin (MSLN) as a therapeutic target in pediatric AML. Mice receiving T cell engaging bispecific antibodies (BsAbs) targeting MSLN and CD3 achieved complete remission and durable responses in two MSLN-positive patient-derived xenograft (PDX) models. This is a first report showing MSLN-targeting BsAbs are a viable immunotherapy for MSLN-positive pediatric AML.

Abstract

Advances in the treatment of pediatric AML have been modest over the past four decades. Despite maximally intensive therapy, approximately 40% of patients will relapse. Novel targeted therapies are needed to improve outcomes. We identified mesothelin (MSLN), a well-validated target overexpressed in some adult malignancies, to be highly expressed on the leukemic cell surface in a subset of pediatric AML patients. The lack of expression on normal bone marrow cells makes MSLN a viable target for immunotherapies such as T-cell engaging bispecific antibodies (BsAbs) that combine two distinct antibody-variable regions into a single molecule targeting a cancer-specific antigen and the T-cell co-receptor CD3. Using antibody single-chain variable region (scFv) sequences derived from amatuximab-recognizing MSLN, and from either blinatumomab or AMG330 targeting CD3, we engineered and expressed two MSLN/CD3-targeting BsAbs: MSLN^AMA-CD3^L2K and MSLN^AMA-CD3^AMG, respectively. Both BsAbs promoted T-cell activation and reduced leukemic burden in MV4;11:MSLN xenografted mice, but not in those transplanted with MSLN-negative parental MV4;11 cells. MSLN^AMA-CD3^AMG induced complete remission in NTPL-146 and DF-5 patient-derived xenograft models. These data validate the in vivo efficacy and specificity of MSLN-targeting BsAbs. Because prior MSLN-directed therapies appeared safe in humans, MSLN-targeting BsAbs could be ideal immunotherapies for MSLN-positive pediatric AML patients.

Dysplasia Should Not Be Ignored in Lichenoid Mucositis

Oral lichen planus is categorized as a potentially malignant condition by the World Health Organization; however, some argue that only lichen planus with dysplasia have malignant potential. Many pathologists call lichen planus with dysplasia "dysplasia with lichenoid mucositis (LM)" or "LM with dysplasia." Previous research has shown that certain high-risk patterns of loss of heterozygosity (LOH) in dysplastic lesions are associated with significantly increased cancer risk. However, LM without dysplasia lacks such molecular patterns, supporting the hypothesis that LM, by itself, is not potentially malignant and that only those with dysplasia have malignant potential. To further investigate the premalignant nature of LM with dysplasia, this study compared the rate of malignant progression of dysplasia with LM with that of dysplasia without LM. Patients from a population-based prospective cohort study with >10 y of follow-up were analyzed. Study eligibility included a histological diagnosis of a primary low-grade dysplasia with or without LM. A total of 446 lesions in 446 patients met the selection criteria; 373 (84%) were classified as dysplasia without LM, while 73 (16%) were classified as dysplasia with LM. Demographic and habit information, clinical information, and outcome (progression) were compared between the 2 groups. Forty-nine of 373 cases of dysplasia (13%) progressed compared to 8% (6/73) of dysplasia with LM. However, the difference was not statistically different ( P = 0.24). The 3- and 5-y rate of progression did not differ between the groups (6.7% and 12.5% for dysplasia without LM and 2.9% and 6.6% for those with LM; P = 0.36). Progression was associated with nonsmoking, location at a high-risk site, and diagnosis of moderate dysplasia regardless of whether LM was present or not. Dysplasia with or without LM had similar cancer risk, and dysplasia should not be discounted in the presence of LM.

RNA Primer Extension Hinders DNA Synthesis by Escherichia coli Mutagenic DNA Polymerase IV

In Escherichia coli the highly conserved DNA damage regulated dinB gene encodes DNA Polymerase IV (DinB), an error prone specialized DNA polymerase with a central role in stress-induced mutagenesis. Since DinB is the DNA polymerase with the highest intracellular concentrations upon induction of the SOS response, further regulation must exist to maintain genomic stability. Remarkably, we find that DinB DNA synthesis is inherently poor when using an RNA primer compared to a DNA primer, while high fidelity DNA polymerases are known to have no primer preference. Moreover, we show that the poor DNA synthesis from an RNA primer is conserved in DNA polymerase Kappa, the human DinB homolog. The activity of DinB is modulated by interactions with several other proteins, one of which is the equally evolutionarily conserved recombinase RecA. This interaction is known to positively affect DinB's fidelity on damaged templates. We find that upon interaction with RecA, DinB shows a significant reduction in DNA synthesis when using an RNA primer. Furthermore, with DinB or DinB:RecA a robust pause, sequence and lesion independent, occurs only when RNA is used as a primer. The robust pause is likely to result in abortive DNA synthesis when RNA is the primer. These data suggest a novel mechanism to prevent DinB synthesis when it is not needed despite its high concentrations, thus protecting genome stability.

Anti-resorptive agents reduce the size of resorption cavities: a three-dimensional dynamic bone histomorphometry study

Alterations in resorption cavities and bone remodeling events during anti-resorptive treatment are believed to contribute to reductions in fracture risk. Here, we examine changes in the size of individual remodeling events associated with treatment with a selective estrogen receptor modulator (raloxifene) or a bisphosphonate (risedronate). Adult female rats (6months of age) were submitted to ovariectomy (n=17) or sham surgery (SHAM, n=5). One month after surgery, the ovariectomized animals were separated into three groups: untreated (OVX, n=5), raloxifene treated (OVX+Ral, n=6) and risedronate treated (OVX+Ris, n=6). At 10months of age, the lumbar vertebrae were submitted to three-dimensional dynamic bone histomorphometry to examine the size (depth, breadth and volume) of individual resorption cavities and formation events. Maximum resorption cavity depth did not differ between the SHAM (23.66±1.87μm, mean±SD) and OVX (22.88±3.69μm) groups but was smaller in the OVX+Ral (14.96±2.30μm) and OVX+Ris (14.94±2.70μm) groups (p<0.01). Anti-resorptive treatment was associated with reductions in the surface area of resorption cavities and the volume occupied by each resorption cavity (p<0.01 each). The surface area and volume of individual formation events (double-labeled events) in the OVX+Ris group were reduced as compared to other groups (p<0.02). Raloxifene treated animals showed similar amounts of bone remodeling (ES/BS and dLS/BS) compared to sham-operated controls but smaller cavity size (depth, breadth and volume). The current study shows that anti-resorptive agents influence the size of resorption cavities and individual remodeling events and that the effect of anti-resorptives on individual remodeling events may not always be directly related to the degree of suppression of bone remodeling.

Observation of multifractal intermittent dust-acoustic-wave turbulence

Intermittent dust acoustic wave turbulence self-excited by downward ion flow in dissipative dusty plasma is experimentally observed and investigated. The power spectra of the temporal dust density fluctuation show distinct bumps in the low-frequency regime and power-law scaling in the high-frequency regime. The structure-function analysis demonstrates the multifractal dynamics of the wave turbulence. Decreasing dissipation by decreasing neutral pressure leads to a more turbulent state with a less distinct low-frequency bump in the power spectrum, more stretched non-Gaussian tails in the histogram of the wave-height increment at a small time interval τ, and a higher degree of multifractality. The loss of long time memory with increasing τ for a more turbulent state causes a change from the distribution with stretched non-Gaussian tails to Gaussian with increasing τ.

An active site aromatic triad in Escherichia coli DNA Pol IV coordinates cell survival and mutagenesis in different DNA damaging agents

DinB (DNA Pol IV) is a translesion (TLS) DNA polymerase, which inserts a nucleotide opposite an otherwise replication-stalling N(2)-dG lesion in vitro, and confers resistance to nitrofurazone (NFZ), a compound that forms these lesions in vivo. DinB is also known to be part of the cellular response to alkylation DNA damage. Yet it is not known if DinB active site residues, in addition to aminoacids involved in DNA synthesis, are critical in alkylation lesion bypass. It is also unclear which active site aminoacids, if any, might modulate DinB's bypass fidelity of distinct lesions. Here we report that along with the classical catalytic residues, an active site "aromatic triad", namely residues F12, F13, and Y79, is critical for cell survival in the presence of the alkylating agent methyl methanesulfonate (MMS). Strains expressing dinB alleles with single point mutations in the aromatic triad survive poorly in MMS. Remarkably, these strains show fewer MMS- than NFZ-induced mutants, suggesting that the aromatic triad, in addition to its role in TLS, modulates DinB's accuracy in bypassing distinct lesions. The high bypass fidelity of prevalent alkylation lesions is evident even when the DinB active site performs error-prone NFZ-induced lesion bypass. The analyses carried out with the active site aromatic triad suggest that the DinB active site residues are poised to proficiently bypass distinctive DNA lesions, yet they are also malleable so that the accuracy of the bypass is lesion-dependent.

Analysis of parathyroid hormone (PTH)/secretin receptor chimeras differentiates the role of functional domains in the pth/ pth-related peptide (PTHrP) receptor on hormone binding and receptor activation

The type 1 parathyroid hormore receptor (PTH1r) belongs to the class II family of G protein-coupled receptors. To delineate the sites in the PTH1r's N-terminal region, and the carboxy-core domain (transmembrane segments + extracellular loops) involved in PTH binding, we have evaluated the functional properties of 27 PTH1-secretin chimeras receptors stably expressed in HEK-293 cells. The wild type and chimeric receptors were analyzed for cell surface expression, binding for PTH and secretin, and functional responsiveness (cAMP induction) toward secretin and PTH. The expression levels of the chimeric receptors were comparable to that of the PTH1r (60-100%). The N-terminal region of PTH1r was divided into three segments that were replaced either singly or in various combinations with the homologous region of the secretin receptor (SECr). Substitution of the carboxy-terminal half (residues 105-186) of the N-terminal region of PTH1r for a SECr homologous segment did not reduced affinity for PTH but abolished signaling in response to PTH. This data indicate that receptor activation is dissociable from high affinity hormone binding in the PTH1r, and that the N-terminal region might play a critical role in the activation process. Further segment replacements in the N-termini focus on residues 105-186 and particularly residues 146-186 of PTH1r as providing critical segments for receptor activation. The data obtained suggest the existence of two distinct PTH binding sites in the PTH1r's N-terminal region: one site in the amino-terminal half (residues 1-62) (site 1) that participates in high-affinity PTH binding; and a second site of lower affinity constituted by amino acid residues scattered throughout the carboxy-terminal half (residues 105-186) (site 2). In the absence of PTH binding to site 1, higher concentrations of hormone are required to promote receptor activation. In addition, elimination of the interaction of PTH with site 2 results in a loss of signal transduction without loss of high-affinity PTH binding. Divers substitutions of the extracellular loops of the PTH1r highlight the differential role of the first- and third extracellular loop in the process of PTH1r activation after hormone binding. A chimera containing the entire extracellular domains of the PTH1r and the transmembrane + cytoplasmic domains of SECr had very low PTH binding affinity and did not signal in response to PTH. Further substitution of helix 5 of PTH1r in this chimera increased affinity for PTH that is close to the PTH affinity for the wild-type PTH1r but surprisingly, did not mediate signaling response. Additional substitutions of PTH1r's helices in various combinations emphasize the fundamental role of helix 3 and helix 6 on the activation process of the PTH1r. Overall, our studies demonstrated that several PTH1r domains contribute differentially to PTH binding affinity and signal transduction mechanism and highlight the role of the N-terminal domain and helix 3 and helix 6 on receptor activation.

Varicella-zoster virus retains major histocompatibility complex class I proteins in the Golgi compartment of infected cells

We sought to examine the effects of varicella-zoster virus (VZV) infection on the expression of major histocompatibility complex class I (MHC I) molecules by human fibroblasts and T lymphocytes. By flow cytometry, VZV infection reduced the cell surface expression of MHC I molecules on fibroblasts significantly, yet the expression of transferrin receptor was not affected. Importantly, when human fetal thymus/liver implants in SCID-hu mice were inoculated with VZV, cell surface MHC I expression was downregulated specifically on VZV-infected human CD3+ T lymphocytes, a prominent target that sustains VZV viremia. The stage in the MHC I assembly process that was disrupted by VZV in fibroblasts was examined in pulse-chase and immunoprecipitation experiments in the presence of endoglycosidase H. MHC I complexes continued to be assembled in VZV-infected cells and were not retained in the endoplasmic reticulum. In contrast, immunofluorescence and confocal microscopy showed that VZV infection resulted in an accumulation of MHC I molecules which colocalized to the Golgi compartment. Inhibition of late viral gene expression by treatment of infected fibroblasts with phosphonoacetic acid did not influence the modulation of MHC I expression, nor did transfection of cells with plasmids expressing immediate early viral proteins. However, cells transfected with a plasmid carrying the early gene ORF66 did result in a significant downregulation of MHC I expression, suggesting that this gene encodes a protein with an immunomodulatory function. Thus, VZV downregulates MHC I expression by impairing the transport of MHC I molecules from the Golgi compartment to the cell surface; this effect may enable the virus to evade CD8+ T-cell immune recognition during VZV pathogenesis, including the critical phase of T-lymphocyte-associated viremia.

Packings and defects of strongly coupled two-dimensional Coulomb clusters: numerical simulation

The packings and defects of the strongly coupled two-dimensional Coulomb clusters with particle number N from a few to a few hundred with different forms of mutual repulsion and central confining potentials at zero temperature are investigated using molecular-dynamics simulation through many annealing cycles. The circular symmetry of the confining potential and the interplay with the mutual repulsion lead to the strong competition between the outer circular shells and the inner triangular lattice. Generic packing behaviors, such as the concentric shells with the classical periodic packing sequence at small N, and the triangular latticelike inner core surrounded by a few outer circular shells at large N are observed. The effects of changing the interaction and confining potentials on the detailed packing sequence, the radial variation of packing density, and the positions of the shell-triangular core interface are investigated with a detailed study of the cluster structures along with the formation and distribution of topological defects.

Interleukin (IL)-10, IL-12, and interferon-gamma production in primary and memory immune responses to varicella-zoster virus

Varicella immunization provided the opportunity to examine the kinetics of interleukin (IL)-10, IL-12 and interferon (IFN)-gamma production elicited during primary in vivo sensitization with proteins of varicella-zoster virus (VZV), a common human herpesvirus. VZV-specific IFN-gamma release and T cell proliferation were elicited by immunization and persisted through 15 months of follow-up. The induction of VZV-specific T cells and IgG antibodies was accompanied by transient increases in IL-10 and IL-12 production. T cell proliferation to VZV was significantly lower in adults at 15 months than in vaccinated children or naturally immune subjects and correlated with lower IFN-gamma responses in individual vaccinees. After primary immunity was induced, continued IL-12 production was not necessary to maintain the predominant Th1-type response elicited by VZV. Cytokine profiles observed during primary in vivo sensitization to VZV suggest that parallel increases in IFN-gamma and IL-10 may be important in the induction of immunity to some viral pathogens.

Removal of a broken Synthes proximal spiral blade

Use of cephalomedullary nails is an option for treatment of subtrochanteric femur fractures. However, the magnitude of bending forces in this area of the femur often can lead to implant failure before union. We report on a case of hardware failure of a specific device (Synthes spiral blade) and a method for removal.

Distal soft tissue release using direct and indirect approaches: an anatomic study

Two surgical approaches for distal soft tissue release in the correction of hallux valgus, one using a dorsal first web space incision and the other a longitudinal medial capsulotomy incision (used also for medial eminence resection), were studied to compare and delineate the structures actually incised. Anatomic dissections were performed on six fresh-frozen amputation specimens using each of the approaches. The adequacy of release of the adductor hallucis, transverse and oblique heads, first metatarsophalangeal lateral capsule, and suspensory ligament was reviewed. Any inadvertent damage to the first metatarsal head cartilage, second metatarsophalangeal capsule, and lateral head of the flexor hallucis brevis tendon was also noted. Distal soft tissue release is thought to be an important part of hallux valgus surgery. Based on our anatomic dissections, the actual extent of the release may be inconsistent and unpredictable, and may have implications for the predictability of results after hallux valgus surgery.

Metabolism of cottonseed microsomal N-acylphosphatidylethanolamine

N-acylphosphatidylethanolamine (NAPE) was recently shown to be synthesized in vitro in cottonseed microsomes by the direct N-acylation of phosphatidylethanolamine (PE) with unesterfied fatty acids (K.D. Chapman and T. S. Moore, 1993, Plant Physiol. 102, 761-769). Here we examine the relationship of the synthesis and turnover of NAPE in cottonseed microsomes to the O-acylation of other membrane phospholipids. PE was N-acylated in a time-dependent manner with [1-14C]palmitic acid independent of exogenously supplied ATP. O-Acylation of PE and phosphatidylcholine (PC) with [1-14C]palmitic acid proceeded only in the presence of ATP. Further radiolabeling experiments with [1-14C]palmitoylCoA and phosphatidyl(N-[1-14C]-palmitoyl)ethanolamine indicated that O-acylation of phospholipids occurred via an acylCoA intermediate and not via an NAPE intermediate. [1-14C]palmitic acid was released from PC[1-14C-dipalmitoyl] in cottonseed microsomes in a Ca(2+)-dependent manner and this [14C]-FFA was incorporated into [14C]NAPE in a linear fashion. Cottonseed NAPE was selectively hydrolyzed to N-acylethanolamine (NAE) and N-acyl lysophosphatidylethanolamine (NAlysoPE) by Ca(2+)-independent, membrane-bound phospholipase D and A activities, respectively. NAlysoPE was not hydrolyzed to NAE, indicating that the phospholipase D that was active toward NAPE did not recognize NAlysoPE; instead NAlysoPE was converted to NAPE in the presence of Ca2+. Collectively, our results indicate that NAPE synthesis and the O-acylation of other phospholipids occur by two separate pathways and that microsomal NAPE is selectively turned over by membrane-bound phospholipase activities. A pathway for the metabolism of cottonseed NAPE is outlined.

Investigation of the regiospecificity and stereospecificity of proton transfer in the yeast inorganic pyrophosphatase catalyzed reaction

The regiospecificity and stereospecificity of proton transfer in the yeast inorganic pyrophosphatase (PPase) catalyzed hydrolysis of P1,P2-bidentate Mg(H2O)4(PPi)2- were probed with exchange-inert metal complexes of imidodiphosphate (PNP) and thiopyrophosphate (PPS). PPase was unable to catalyze the hydrolysis of Mg(H2O)4PNP and P1,P2-bidentate Co(NH3)4PNP under conditions that resulted in rapid hydrolysis of the corresponding metal-PPi complexes. PPase was found to catalyze the hydrolysis of Mg(H2O)4PPS at 17% the rate of Mg(H2O)4PPi hydrolysis. The Km of Mg(H2O)4PPS was determined to be 300 microM, which is a value 10-fold greater than that observed for Mg(H2O)4PPi. P1,P2-Bidentate Cr(H2O)4PPS and Co(NH3)4PPS (prepared from PPS) were both found to be substrates for PPase. The enzyme specifically catalyzed the hydrolysis of the Rp enantiomers of these complexes and not the Sp enantiomers. These results are accommodated by a reaction mechanism involving enzyme-mediated proton transfer to the pro-R oxygen atom of the incipient phosphoryl leaving group of the bound P1,P2-bidentate Mg(H2O)4PPi2- complex.