Abstract 1815: AVA6000, a novel Precision medicine, targeted to the tumor microenvironment via Fibroblast Activation Protein (FAP) mediated cleavage

AVA6000 is a therapeutic product based on proprietary pre|CISION™ technology which incorporates a substrate that is sensitive to cleavage by FAP. The pre|CISION™ substrate can be utilized in a drug conjugate linker or to generate chemotherapy prodrugs that are only activated in the tumor microenvironment. AVA6000 consists of a doxorubicin molecule covalently bonded to a dipeptide (pyridine-4-carbonyl)-D-Ala-L-Pro), which is designed to be susceptible to hydrolysis by Fibroblast Activation Protein α (FAP) but is resistant to hydrolysis by both closely related and wider mammalian peptidases. FAP, a post-prolyl endopeptidase, is overexpressed on the surface of activated fibroblastic cells which are abundant in the supporting stroma of over 90% of malignant epithelial cancers, as well as in bone and soft tissue sarcoma. While FAP is also present both in normal tissues and as a soluble enzyme in plasma, levels are significantly lower than those present in malignant epithelial cancers. Consequently, AVA6000 has the potential to deliver doxorubicin directly to the tumor microenvironment, while exposing the patient to a lesser degree of doxorubicin-associated toxicities. The primary mechanism of action of doxorubicin is thought to involve stabilisation of a topoisomerase-II-DNA cleavable complex through non-specific DNA-intercalation. The non-specific DNA-intercalation causes a number of downstream effects, which may ultimately result in apoptotic cell death. Although doxorubicin has been one of the most effective and widely used chemotherapeutic agents for the treatment of various solid malignancies for over 40 years, its clinical utility is limited by dose-limiting toxicities, including myelosuppression and cardiotoxicity. The unique FAP specificity of the N-(pyridine-4-carbonyl)-D-Ala-L-Pro leaving group conjugated to doxorubicin in AVA6000 is supported by the absence of cleavage of the fluorogenic analogue, 3114-AMC, in FAP gene-knockout mice (Fap-/-). In vitro cytotoxicity assessments involving human tumor cell lines showed that AVA6000 was between 80-fold to 4,000-fold less cytotoxic compared to doxorubicin. In several in vivo efficacy studies in tumours with high FAP levels, AVA6000 significantly decreased tumor volume and increased survival in a dose-dependent manner. In a PDX model of osteosarcoma, AVA6000 significantly decreased tumor volume while doxorubicin had no significant effect. The efficacy and tolerability profile of AVA6000 strongly support its clinical development, and a Phase I trial in patients with locally advanced or metastatic selected solid tumours in underway.

Citation Format: Fiona McLaughlin, Sarah E. Poplawski, David G. Sanford, Andrew Saunders, Jack H. Lai, Matthew Vincent, William W. Bachovchin, Neil Bell. AVA6000, a novel Precision medicine, targeted to the tumor microenvironment via Fibroblast Activation Protein (FAP) mediated cleavage [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 1815.

Abstract 3303: Pre-clinical characterization of the novel FAP targeting ligand PNT6555 for imaging and therapy of cancer

Background: Fibroblast Activation Protein-α (FAP) is a transmembrane glycoprotein highly expressed on activated fibroblasts. It is a constitutively active 170 kDa serine protease and a member of the dipeptide peptidase (DPP) family, sharing ~50% homology with DPPIV. FAP expression is only rarely expressed in normal adult tissues and is overexpressed in many epithelial cancers through upregulation on cancer-associated fibroblasts present in the stroma of various types of tumor. POINT BioPharma is developing PNT6555, which comprises a DOTA chelator linked to a FAP-targeting moiety, for imaging and therapeutic applications.

Methods: PNT6555 and its radiometal chelates were evaluated for potency, selectivity, biodistribution and efficacy using biochemical and cellular assays as well as imaging, biodistribution and efficacy studies in tumor bearing mice.

Results: PNT6555 and its gallium (natGa-PNT6555) and lutetium (natLu-PNT6555) chelates showed potent activity in FAP inhibition assays using human, mouse, and rat sources of FAP. PNT6555, natLu-PNT6555 and natGa-PNT6555 also showed significantly reduced potency when tested against PREP and DPPIV, two closely related homologous proteins. In vivo time-course biodistribution studies (by PET-imaging) with 68Ga-PNT6555 showed rapid clearance of 68Ga-PNT6555 from blood through the kidneys and urinary tract, with rising 68Ga-PNT6555 activity observed in the tumor through 60 minutes. At 60 minutes, the tumor was the only site of significant retained activity (>10 %ID/g). In vivo biodistribution studies (by SPECT imaging and direct organ assay) with 177Lu-PNT6555 showed rapid renal clearance into the bladder. After 24 hours, the tumor was the only tissue with significant activity retention. Direct organ assay showed little 177Lu-PNT6555 accumulation and retention in normal tissues with a high level of tumor retention observed out to 168h (>10 %ID/g). Therapeutic studies, using a single dose of 177Lu-PNT6555 or 225Ac-PNT6555, were completed in pre-clinical mouse models of cancer. In the HEK-mFAP model, significant dose responsive efficacy was observed in mice treated with either 177Lu-PNT6555 or 225Ac-PNT6555, with no apparent weight loss observed at all tested dose levels. Several mice experienced long-term survival >100 days at multiple of the tested dose levels.

Conclusions: PNT6555, and its radiometal chelates, are potent and specific inhibitors of FAP. 68Ga/177Lu-PNT6555 showed rapid and prolonged uptake into FAP expressing tumors with limited uptake or retention observed in normal tissues. 177Lu/225Ac-PNT6555 showed compelling efficacy in pre-clinical tumor models that expressed FAP. Clinical studies with imaging and therapeutic chelates of PNT6555 are warranted.

Citation Format: Robin M. Hallett, Sarah E. Poplawski, Mark H. Dornan, Shin Hye Ahn, Shuang Pan, Wu Wengen, Liu Yuxin, David G. Sanford, Valerie S. Hergott, Quang-De Nguyen, Anthony P. Belanger, Jack H. Lai, William Bachovchin, Joe A. McCann. Pre-clinical characterization of the novel FAP targeting ligand PNT6555 for imaging and therapy of cancer [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 3303.

DPP8 and DPP9 inhibition induces pro-caspase-1-dependent monocyte and macrophage pyroptosis

Val-boroPro (Talabostat, PT-100), a nonselective inhibitor of post-proline cleaving serine proteases, stimulates mammalian immune systems through an unknown mechanism of action. Despite this lack of mechanistic understanding, Val-boroPro has attracted substantial interest as a potential anticancer agent, reaching phase 3 trials in humans. Here we show that Val-boroPro stimulates the immune system by triggering a proinflammatory form of cell death in monocytes and macrophages known as pyroptosis. We demonstrate that the inhibition of two serine proteases, DPP8 and DPP9, activates the pro-protein form of caspase-1 independent of the inflammasome adaptor ASC. Activated pro-caspase-1 does not efficiently process itself or IL-1β but does cleave and activate gasdermin D to induce pyroptosis. Mice lacking caspase-1 do not show immune stimulation after treatment with Val-boroPro. Our data identify what is to our knowledge the first small molecule that induces pyroptosis and reveals a new checkpoint that controls the activation of the innate immune system.

A high-throughput, multiplexed assay for superfamily-wide profiling of enzyme activity

The selectivity of an enzyme inhibitor is a key determinant of its usefulness as a tool compound or its safety as a drug. Yet selectivity is never assessed comprehensively in the early stages of the drug discovery process, and only rarely in the later stages, because technical limitations prohibit doing otherwise. Here, we report EnPlex, an efficient, high-throughput method for simultaneously assessing inhibitor potency and specificity, and pilot its application to 96 serine hydrolases. EnPlex analysis of widely used serine hydrolase inhibitors revealed numerous previously unrecognized off-target interactions, some of which may help to explain previously confounding adverse effects. In addition, EnPlex screening of a hydrolase-directed library of boronic acid- and nitrile-containing compounds provided structure-activity relationships in both potency and selectivity dimensions from which lead candidates could be more effectively prioritized. Follow-up of a series of dipeptidyl peptidase 4 inhibitors showed that EnPlex indeed predicted efficacy and safety in animal models. These results demonstrate the feasibility and value of high-throughput, superfamily-wide selectivity profiling and suggest that such profiling can be incorporated into the earliest stages of drug discovery.

Identification of selective and potent inhibitors of fibroblast activation protein and prolyl oligopeptidase

Fibroblast activation protein (FAP) is a serine protease selectively expressed on reactive stromal fibroblasts of epithelial carcinomas. It is widely believed to play a role in tumor invasion and metastasis and therefore to represent a potential new drug target for cancer. Investigation into its biological function, however, has been hampered by the current unavailability of selective inhibitors. The challenge has been in identifying inhibitors that are selective for FAP over both the dipeptidyl peptidases (DPPs), with which it shares exopeptidase specificity, and prolyl oligopeptidase (PREP), with which it shares endopeptidase specificity. Here, we report the first potent FAP inhibitor with selectivity over both the DPPs and PREP, N-(pyridine-4-carbonyl)-d-Ala-boroPro (ARI-3099, 6). We also report a similarly potent and selective PREP inhibitor, N-(pyridine-3-carbonyl)-Val-boroPro (ARI-3531, 22). Both are boronic acid based inhibitors, demonstrating that high selectivity can be achieved using this electrophile. The inhibitors are stable, easy to synthesize, and should prove to be useful in helping to elucidate the biological functions of these two unique and interesting enzymes, as well as their potential as drug targets.

4-Substituted boro-proline dipeptides: synthesis, characterization, and dipeptidyl peptidase IV, 8, and 9 activities

The boroProline-based dipeptidyl boronic acids were among the first DPP-IV inhibitors identified, and remain the most potent known. We introduced various substitutions at the 4-position of the boroProline ring regioselectively and stereoselectively, and incorporated these aminoboronic acids into a series of 4-substituted boroPro-based dipeptides. Among these dipeptidyl boronic acids, Arg-(4S)-boroHyp (4q) was the most potent inhibitor of DPP-IV, DPP8 and DPP9, while (4S)-Hyp-(4R)-boroHyp (4o) exhibited the most selectivity for DPP-IV over DPP8 and DPP9.

Pro-soft Val-boroPro: a strategy for enhancing in vivo performance of boronic acid inhibitors of serine proteases

Val-boroPro, 1, is a potent, but relatively nonspecific inhibitor of the prolyl peptidases. It has antihyperglycemic activity from inhibition of DPPIV but also striking anticancer activity and a toxicity for which the mechanisms are unknown. 1 cyclizes at physiological pH, which attenuates its inhibitory potency >100-fold, which is a "soft drug" effect. Here we show that this phenomenon can be exploited to create prodrugs with unique properties and potential for selective in vivo targeting. Enzyme-mediated release delivers 1 to the target in the active form at physiological pH; cyclization attenuates systemic pharmacological effects from subsequent diffusion. This "pro-soft" design is demonstrated with a construct activated by and targeted to DPPIV, including in vivo results showing improved antihyperglycemic activity and reduced toxicity relative to 1. Pro-soft derivatives of 1 can help to illuminate the mechanisms underlying the three biological activities, or to help localize 1 at a tumor and thereby lead to improved anticancer agents with reduced toxicity. The design concept can also be applied to a variety of other boronic acid inhibitors.

Dipeptide boronic acid inhibitors of dipeptidyl peptidase IV: determinants of potency and in vivo efficacy and safety

Dipeptidyl peptidase IV (DPP-IV; E.C. 3.4.14.5), a serine protease that degrades the incretin hormones GLP-1 and GIP, is now a validated target for the treatment of type 2 diabetes. Dipeptide boronic acids, among the first, and still among the most potent DPP-IV inhibitors known, suffer from a concern over their safety. Here we evaluate the potency, in vivo efficacy, and safety of a selected set of these inhibitors. The adverse effects induced by boronic acid-based DPP-IV inhibitors are essentially limited to what has been observed previously for non-boronic acid inhibitors and attributed to cross-reactivity with DPP8/9. While consistent with the DPP8/9 hypothesis, they are also consistent with cross-reactivity with some other intracellular target. The results further show that the potency of simple dipeptide boronic acid-based inhibitors can be combined with selectivity against DPP8/9 in vivo to produce agents with a relatively wide therapeutic index (>500) in rodents.

Synthesis and Characterization of Constrained Peptidomimetic Dipeptidyl Peptidase IV Inhibitors: Amino-Lactam boroAlanines

We describe here the epimerization-free synthesis and characterization of a new class of conformationally constrained lactam aminoboronic acid inhibitors of dipeptidyl peptidase IV (DPP IV; E.C. 3.4.14.5). These compounds have the advantage that they cannot undergo the pH-dependent cyclization prevalent in most dipeptidyl boronic acids that attenuates their potency at physiological pH. For example, D-3-amino-1-[L-1-boronic-ethyl]-pyrrolidine-2-one (amino-D-lactam-L-boroAla), one of the best lactam inhibitors of DPP IV, is several orders of magnitude less potent than L-Ala-L-boroPro, as measured by Ki values (2.3 nM vs 30 pM, respectively). At physiological pH, however, it is actually more potent than L-Ala-L-boroPro, as measured by IC50 values (4.2 nM vs 1400 nM), owing to the absence of the potency-attenuating cyclization. In an interesting and at first sight surprising reversal of the relationship between stereochemistry and potency observed with the conformationally unrestrained Xaa-boroPro class of inhibitors, the L-L diastereomers of the lactams are orders of magnitude less effective than the D-L lactams. However, this interesting reversal and the unexpected potency of the D-L lactams as DPP IV inhibitors can be understood in structural terms, which is explained and discussed here.

T antigen origin-binding domain of simian virus 40: determinants of specific DNA binding

To better understand origin recognition and initiation of DNA replication, we have examined by NMR complexes formed between the origin-binding domain of SV40 T antigen (T-ag-obd), the initiator protein of the SV40 virus, and cognate and noncognate DNA oligomers. The results reveal two structural effects associated with "origin-specific" binding that are absent in nonspecific DNA binding. The first is the formation of a hydrogen bond (H-bond) involving His 203, a residue that genetic studies have previously identified as crucial to both specific and nonspecific DNA binding in full-length T antigen. In free T-ag-obd, the side chain of His 203 has a pK(a) value of approximately 5, titrating to the N(epsilon)(1)H tautomer at neutral pH (Sudmeier, J. L., et al. (1996) J. Magn. Reson., Ser. B 113, 236-247). In complexes with origin DNA, His 203 N(delta)(1) becomes protonated and remains nontitrating as the imidazolium cation at all pH values from 4 to 8. The H-bonded N(delta1)H resonates at 15.9 ppm, an unusually large N-H proton chemical shift, of a magnitude previously observed only in the catalytic triad of serine proteases at low pH. The formation of this H-bond requires the middle G/C base pair of the recognition pentanucleotide, GAGGC. The second structural effect is a selective distortion of the A/T base pair characterized by a large (0.6 ppm) upfield chemical-shift change of its Watson-Crick proton, while nearby H-bonded protons remain relatively unaffected. The results indicate that T antigen, like many other DNA-binding proteins, may employ "catalytic" or "transition-state-like" interactions in binding its cognate DNA (Jen-Jacobson, L. (1997) Biopolymers 44, 153-180), which may be the solution to the well-known paradox between the relatively modest DNA-binding specificity exhibited by initiator proteins and the high specificity of initiation.

Tautomerism, acid-base equilibria, and H-bonding of the six histidines in subtilisin BPN' by NMR

We have determined by (15)N, (1)H, and (13)C NMR, the chemical behavior of the six histidines in subtilisin BPN' and their PMSF and peptide boronic acid complexes in aqueous solution as a function of pH in the range of from 5 to 11, and have assigned every (15)N, (1)H, C(epsilon 1), and C(delta2) resonance of all His side chains in resting enzyme. Four of the six histidine residues (17, 39, 67, and 226) are neutrally charged and do not titrate. One histidine (238), located on the protein surface, titrates with pK(a) = 7.30 +/- 0.03 at 25 degrees C, having rapid proton exchange, but restricted mobility. The active site histidine (64) in mutant N155A titrates with a pK(a) value of 7.9 +/- 0.3 and sluggish proton exchange behavior, as shown by two-site exchange computer lineshape simulation. His 64 in resting enzyme contains an extremely high C(epsilon 1)-H proton chemical shift of 9.30 parts per million (ppm) owing to a conserved C(epsilon 1)-H(.)O=C H-bond from the active site imidazole to a backbone carbonyl group, which is found in all known serine proteases representing all four superfamilies. Only His 226, and His 64 at high pH, exist as the rare N(delta1)-H tautomer, exhibiting (13)C(delta1) chemical shifts approximately 9 ppm higher than those for N(epsilon 2)-H tautomers. His 64 in the PMSF complex, unlike that in the resting enzyme, is highly mobile in its low pH form, as shown by (15)N-(1)H NOE effects, and titrates with rapid proton exchange kinetics linked to a pK(a) value of 7.47 +/- 0.02.

Unusual 1H NMR chemical shifts support (His) C(epsilon) 1...O==C H-bond: proposal for reaction-driven ring flip mechanism in serine protease catalysis

13C-selective NMR, combined with inhibitor perturbation experiments, shows that the C(epsilon)(1)H proton of the catalytic histidine in resting alpha-lytic protease and subtilisin BPN' resonates, when protonated, at 9.22 ppm and 9.18 ppm, respectively, which is outside the normal range for such protons and approximately 0.6 to 0.8 ppm further downfield than previously reported. They also show that the previous alpha-lytic protease assignments [Markley, J. L., Neves, D. E., Westler, W. M., Ibanez, I. B., Porubcan, M. A. & Baillargeon, M. W. (1980) Front. Protein Chem. 10, 31-61] were to signals from inactive or denatured protein. Simulations of linewidth vs. pH demonstrate that the true signal is more difficult to detect than corresponding signals from inactive derivatives, owing to higher imidazole pK(a) values and larger chemical shift differences between protonated and neutral forms. A compilation and analysis of available NMR data indicates that the true C(epsilon)(1)H signals from other serine proteases are similarly displaced downfield, with past assignments to more upfield signals probably in error. The downfield displacement of these proton resonances is shown to be consistent with an H-bond involving the histidine C(epsilon)(1)H as donor, confirming the original hypothesis of Derewenda et al. [Derewenda, Z. S., Derewenda, U. & Kobos, P. M. (1994) J. Mol. Biol. 241, 83-93], which was based on an analysis of literature x-ray crystal structures of serine hydrolases. The invariability of this H-bond among enzymes containing Asp-His-Ser triads indicates functional importance. Here, we propose that it enables a reaction-driven imidazole ring flip mechanism, overcoming a major dilemma inherent in all previous mechanisms, namely how these enzymes catalyze both the formation and productive breakdown of tetrahedral intermediates.

Alternative aging

During perimenopause and menopause, women face a variety of health concerns. Women in midlife recognize their health risks and want to modify them. They also have an increased appreciation of wellness and desire to promote their own optimal health.

Solution structure of the origin DNA-binding domain of SV40 T-antigen

The structure of the domain from simian virus 40 (SV40) large T-antigen that binds to the SV40 origin of DNA replication (T-ag-OBD131-260) has been determined by nuclear magnetic resonance spectroscopy. The overall fold, consisting of a central five-stranded antiparallel beta-sheet flanked by two alpha-helices on one side and one alpha-helix and one 3(10)-helix on the other, is a new one. Previous mutational analyses have identified two elements, termed A (approximately 152-155) and B2 (203-207), as essential for origin-specific recognition. These elements form two closely juxtaposed loops that define a continuous surface on the protein. The addition of a duplex oligonucleotide containing the origin recognition pentanucleotide GAGGC induces chemical shift changes and slows amide proton exchange in resonances from this region, indicating that this surface directly contacts the DNA.

Eye injuries in athletics and recreation

Sports-related eye injuries represent a significant eye health hazard worldwide. In the USA, it is estimated that eye injuries from sports account for more than 100,000 physician visits per year at the cost of greater than $175 million. The sports responsible for the greatest number of injuries are baseball, ice hockey, and racquet sports. In the USA there are over 189 million participants in these sports with a disproportionate number (one-third) of injuries involving the pediatric population. The most common injuries are abrasions and contusions, followed by more serious injuries, including hyphema. Substantial reduction in the incidence of eye injuries through prevention has been demonstrated in the sport of hockey which can serve as a model for other sports. Specific criteria for protective eyewear must be developed. Polycarbonate plastic lenses and frames which are sturdy and impact resistant provide optimal protection. Lensless goggles, street wear and spectacle correction glasses do not provide adequate eye protection. The ophthalmologist's role in preventing sports-related eye injuries includes addressing particular sports participants needs, identifying one-eyed athletes, and informing patients of the need for protective eyewear.

Structure and function of the epidermal growth factor domain of P-selectin

P-selectin is a multidomain adhesion protein on the surface of activated platelets and endothelial cells that functions in the recruitment of leukocytes to the site of inflammation. The amino-terminal lectin and EGF domains constitute the ligand recognition unit. We have produced a synthetic 40-residue P-selectin EGF domain (P-sel:EGF) to examine the structure and function of this domain independent of P-selectin. The peptide was folded in vitro and exhibited the same disulfide bonding pattern as other EGF-like domains. P-sel:EGF did not inhibit P-selectin-mediated cellular adhesion assays, indicating that the lectin domain is also required. We undertook the study of the P-selectin EGF by 1H NMR to determine its structure independent of the lectin domain and to compare its structure to that of E-selectin determined crystallographically [Graves et al. (1994) Nature 367, 532]. Although the binding of P-selectin to its carbohydrate ligand is calcium dependent, and some EGF domains have calcium binding sites, addition of calcium had no effect on the NMR spectrum or on the pH-induced changes. Nearly complete resonance assignments were made from 2D 1H NMR spectra at pH 6.0. Two sections of antiparallel beta-sheet were identified on the basis of the pattern of long-range NOEs, 3JHN alpha coupling constants, and slowly exchanging amides. The solution structure of the peptide backbone was determined using distance geometry and simulated annealing calculations. The backbone RMSD to the geometric average for 19 final structures is 0.64 +/- 0.17 A. The resulting fold closely resembles that of other EGF-like peptides, including the E-selectin EGF domain (RMSD approximately 1.08 A). However, compared to the E-selectin EGF structure which also contains the lectin domain, some residues from 1-11 are less ordered, and novel contacts occur between the amino terminus and the core beta-sheet. Despite marked structural homology of the selectin polypeptide backbones, the selectin EGF surfaces show unique distributions of charged residues, a feature that likely correlates to the functional differences.

The effect of organizational type and hierarchical level on nurses' perceptions of hospital issues

Managers in four acute care hospitals in southeast Florida described the resource, management, outcome, and external issues confronting their organizations. Eight major issues and four contributing and resulting subissues associated with each were identified from the 746 separate issue statements the managers made. Nurses in the same four hospitals were asked to evaluate the impact of the eight issues on their organization and their work, as well as the extent to which the subissues had either contributed to or resulted from the main ones. Overall perceptual patterns are discussed, as well as the differential effects of both hospital type and level of employment on perceptions. It is suggested that differential perceptions among such a key component of the care delivery system as nurses will need to be better understood as hospitals seek to survive in a turbulent environment.

Human immunodeficiency virus 1 Tat binds to dipeptidyl aminopeptidase IV (CD26): a possible mechanism for Tat's immunosuppressive activity

The human immunodeficiency virus 1 (HIV-1) Tat protein suppresses antigen-induced, but not mitogen-induced, activation of human T cells when added to T-cell cultures [Viscidi, R. P., Mayur, K., Lederman, H. M. & Frankel, A. D. (1989) Science 246, 1606-1608]. This activity is potentially pertinent to the development of AIDS because lymphocytes from HIV-infected individuals exhibit a similar antigen-specific dysfunction. Here we report that Tat binds with high affinity to the T-cell activation molecule dipeptidyl aminopeptidase IV (DP IV), also known as CD26. This molecule occurs on the surface of CD4+ cells responsible for the recall antigen response and appears to play an essential role in this response. Tat binds to both the cell surface and soluble forms of DP IV at physiological salt concentrations without inhibiting the protease activity of DP IV against small chromogenic substrates used to assay activity, but Tat markedly inhibits the activity of DP IV at lower salt concentrations. The kinetics of inhibition indicate the affinity of Tat for DP IV varies from 20 pM to 11 nM, and the activity of the Tat-DP IV complex varies from 13% to 100%, as the NaCl concentration varies from 0 to 140 mM. Cytofluorometry experiments demonstrate that Tat competes with anti-Ta1, a monoclonal antibody (mAb) specific for DP IV, for binding to cell surface DP IV, thus indicating that Tat binds DP IV at or near the Ta1 epitope. Moreover, the anti-Ta1 mAb blocks the immunosuppressive activity of Tat. The high affinity of Tat for DP IV, previous evidence implicating DP IV in antigen-specific T-cell activation events, and the ability of anti-Ta1 mAb to block the immunosuppressive effect of Tat make DP IV a plausible receptor for Tat's immunosuppressive activity.

The targets and genes for antibodies to Z-DNA

Antibodies to Z-DNA serve as models for recognition of nucleic acid structure by proteins that use peptide loops rather than helix-loop-helix, zinc-finger or other recurrent motifs for DNA binding. Anti-Z-DNA antibodies have been elicited in rabbits, mice and goats by injection of brominated poly(dG-dC), a stable form of Z-DNA. Detailed studies of two mouse monoclonal antibodies to Z-DNA, Z22 and Z44, have been reported. Epitopes on Z-DNA have been mapped by both serological reactions and n.m.r. spectroscopy. Antibodies Z22 and Z44 recognize different sites on the Z-DNA. They are both encoded by members of the VH10 gene family, which also encodes known autoantibodies to DNA. Vectors for bacterial expression of single-chain Fv molecules have been used to determine the importance of specific H- and L-chain combinations and particular CDR3 sequences for Z-DNA binding. Changes in the H-chain CDR3 cause a decrease in the highly selective Z-DNA binding and an increase in autoantibody-like binding of B-DNA and single-stranded DNA.

Structural characterization of an N-acetyl-2-aminofluorene (AAF) modified DNA oligomer by NMR, energy minimization, and molecular dynamics

An N-acetyl-2-aminofluorene (AAF) modified deoxyoligonucleotide duplex, d(C1-C2-A3-C4-[AAF-G5]-C6-A7-C8-C9).d(G10-G11-T12-G13-C14-++ +G15-T16-G17-G18), was studied by one- and two-dimensional NMR spectroscopy. Eight of the nine complementary nucleotides form Watson-Crick base pairs, as shown by NOEs between the guanine imino proton and cytosine amino protons for G.C base pairs or by an NOE between the thymine imino proton and adenine H2 proton for A.T base pairs. The AAF-G5 and C14 bases show no evidence of complementary hydrogen bond formation to each other. The AAF-G5 base adopts a syn conformation, as indicated by NOEs between the G5 imino proton and the A3-H3' and A3-H2'/H2" protons and by NOEs between the fluorene-H1 proton of AAF and the G5-H1' or C6-H1' proton. The NOEs from the C4-H6 proton to C4 sugar protons are weak, and thus the glycosidic torsion angle in this nucleotide is not well defined by these NMR data. The remaining bases are in the anti conformation, as depicted by the relative magnitude of the H8/H6 to H2' NOEs when compared to the H8/H6 to H1' NOEs. The three base pairs on each end of the duplex exhibit NOEs characteristic of right-handed B-form DNA. Distance restraints obtained from NOESY data recorded at 32 degrees C using a 100-ms mixing time were used in conformational searches by molecular mechanics energy minimization studies. The final, unrestrained, minimum-energy conformation was then used as input for an unrestrained molecular dynamics simulation. Chemical exchange cross peaks are observed, and thus the AAF-9-mer exists in more than a single conformation on the NMR time scale. The NMR data, however, indicate the presence of a predominant conformation (> or = 70%). The structure of the predominant conformation of the AAF-9-mer shows stacking of the fluorene moiety on an adjacent base pair, exhibiting features of the base-displacement [Grunberger, D., Nelson, J. H., et al. (1970) Proc. Natl. Acad. Sci. U.S.A. 66, 488-494] and insertion-denaturation models [Fuchs, R.P.P., & Daune, M. (1971) FEBS Lett. 14, 206-208], while the distal ring of the fluorene moiety protrudes into the minor groove.

Structure of the propeptide of prothrombin containing the gamma-carboxylation recognition site determined by two-dimensional NMR spectroscopy

The propeptides of the vitamin K dependent blood clotting and regulatory proteins contain a gamma-carboxylation recognition site that directs precursor forms of these proteins for posttranslational gamma-carboxylation. Peptides corresponding to the propeptide of prothrombin were synthesized and examined by circular dichroism (CD) and nuclear magnetic resonance spectroscopy (NMR). CD spectra indicate that these peptides have little or no secondary structure in aqueous solutions but that the addition of trifluoroethanol induces or stabilizes a structure containing alpha-helical character. The maximum helical content occurs at 35-40% trifluoroethanol. This trifluoroethanol-stabilized structure was solved by two-dimensional NMR spectroscopy. The NMR results demonstrate that residues -13 to -3 form an amphipathic alpha-helix. NMR spectra indicate that a similar structure is present at 5 degrees C, in the absence of trifluoroethanol. Of the residues previously implicated in defining the gamma-carboxylation recognition site, four residues (-18, -17, -16, and -15) are adjacent to the helical region and one residue (-10) is located within the helix. The potential role of the amphipathic alpha-helix in the gamma-carboxylation recognition site is discussed.

Characterization of anti-Z-DNA antibody binding sites on Z-DNA by nuclear magnetic resonance spectroscopy

Two monoclonal anti-Z-DNA antibodies, Z22 and Z44, were shown to bind to the oligonucleotides, d(CG)2 and d(CG)3, and to interact with different parts of the helix. 1H nuclear magnetic resonance spectroscopy showed that Fab fragments stabilize an ordered structure in the tetranucleotide d(CG)2. Nuclear Overhauser effects measured in the presence of Z22 Fab indicate a syn conformation of guanine residues of d(CG)2. Intermolecular transfer of saturation between the Fabs and bound d(CG)3 was detected by a saturation of the protein spectrum and observation of changes in the DNA spectrum. Antibodies with deuterated aromatic amino acids were prepared to eliminate the protein aromatic resonances and thereby allow a more detailed analysis of the transfer to the DNA base protons. The greatest transfer with Z44 was to the dC-5 protons although all of the base protons interact with this antibody. Little, if any, transfer to the DNA base protons was observed with Z22. These results are consistent with a Z44 binding site on the convex surface of the Z-helix (analogous to the major groove of B-DNA) and a Z22 binding site on the sugar-phosphate backbone.

Immunochemical detection of multiple conformations within a 36 base pair oligonucleotide

A 36 base pair chimeric oligonucleotide containing a central core of DNA duplex flanked by RNA/DNA hybrid at each end was synthesized. These distinct regions of the oligonucleotide adopt different conformations which were detected with antibody probes. Enzyme linked immunosorbent assays (ELISA) and a gel electrophoresis retardation assay were used to demonstrate the binding of antibodies which recognize B-DNA, Z-DNA and RNA/DNA hybrid. The DNA duplex core of this oligonucleotide adopts the B-conformation in 0.14 M NaCl. In high salt solution (4 M NaCl) the DNA core adopts the Z-conformation. The RNA/DNA hybrid at the ends of the oligomer adopt a conformation which is distinct from both B-DNA and A-RNA.

N-acetoxy-2-acetylaminofluorene modification of a deoxyoligonucleotide duplex

The carcinogen N-acetoxy-2-acetylaminofluorene was reacted with d (CCACGCACC) to form a covalent adduct with attachment at the single guanine. The sample was purified, mixed 1:1 with d (GGTGCGTGG) and studied by thermal denaturation experiments. The Tm for the mixture was 35 +/- 3 degrees C, consistent with duplex formation. The method of continuous variation shows that the modified oligomer, d (CCACGAAFCACC), forms a 1:1 duplex with d (GGTGCGTGG). Circular dichroism spectra also indicate the formation of a duplex and suggest that the modified duplex has a left-handed conformation. Addition of the intercalating drug ethidium alters the CD spectrum of the modified duplex, resulting in a CD spectrum similar to that of ethidium bound to right-handed DNA.