MIB Guides: Measuring the Immunoreactivity of Radioimmunoconjugates

Immunoglobulins, both full-length antibodies and smaller antibody fragments, have long been regarded as effective platforms for diagnostic and therapeutic radiopharmaceuticals. The construction of radiolabeled immunoglobulins (i.e., radioimmunoconjugates) requires the manipulation of the biomolecule through the attachment of a radiohalogen or the bioconjugation of a chelator that is subsequently used to coordinate a radiometal. Both synthetic approaches have historically relied upon the stochastic modification of amino acids within the immunoglobulin, a process which poses a risk to the structural and functional integrity of the biomolecule itself. Not surprisingly, radioimmunoconjugates with impaired antigen binding capacity will inevitably exhibit suboptimal in vivo performance. As a result, the biological characterization of any newly synthesized radioimmunoconjugate must include an assessment of whether it has retained its ability to bind its antigen. Herein, we provide straightforward and concise protocols for three assays that can be used to determine the immunoreactivity of a radioimmunoconjugate: (1) a cell-based linear extrapolation assay; (2) a cell-based antigen saturation assay; and (3) a resin- or bead-based assay. In addition, we will provide a critical analysis of the relative merits of each assay, an examination of the inherent limitations of immunoreactivity assays in general, and a discussion of other approaches that may be used to interrogate the biological behavior of radioimmunoconjugates.

Deconvolving microbial and environmental controls on marine sedimentary pyrite sulfur isotope ratios

Reconstructions of past environmental conditions and biological activity are often based on bulk stable isotope proxies, which are inherently open to multiple interpretations. This is particularly true of the sulfur isotopic composition of sedimentary pyrite (δ34Spyr), which is used to reconstruct ocean-atmosphere oxidation state and track the evolution of several microbial metabolic pathways. We present a microanalytical approach to deconvolving the multiple signals that influence δ34Spyr, yielding both the unambiguous determination of microbial isotopic fractionation (εmic) and new information about depositional conditions. We applied this approach to recent glacial-interglacial sediments, which feature over 70‰ variations in bulk δ34Spyr across these environmental transitions. Despite profound environmental change, εmic remained essentially invariant throughout this interval and the observed range in δ34Spyr was instead driven by climate-induced variations in sedimentation.

Pretargeting with Cucurbituril-Adamantane Host-Guest Pair in Xenograft Models

The goal of reducing the total-body radiation dose of macromolecule-based nuclear medicine with a 2-step pretargeting strategy has been achieved with several pretargeting methodologies in preclinical and clinical settings. However, the lack of modularity, biocompatibility, and in vivo stability in existing pretargeting agents obstructs their respective platforms' wide clinical use. We hypothesized that host-guest chemistry would provide an optimal pretargeting methodology. A cucurbit[7]uril host and an adamantane guest molecule form a high-affinity host-guest complex (association constant, ∼1014 M-1), and in this work, we explored the use of this noncovalent interaction as the basis for antibody-based pretargeted PET. Along with the straightforward modularity of these agents, cucurbit[7]uril and adamantane are recognized to have high in vivo stability and suitability for human use, which is why we proposed this methodology as the ideal approach for pretargeted nuclear medicine. Methods: Three 64Cu-labeled adamantane guest radioligands were developed, and their in vitro stability, lipophilicity, and in vivo blood half-lives were compared. The adamantane radioligands were analyzed for pretargeting using a cucurbit[7]uril-modified carcinoembryonic antigen-targeting full-length antibody, hT84.66-M5A, as the macromolecule pretargeting agent with 2 different dosing schedules. These molecules were evaluated for pretargeting in human pancreatic cancer BxPC3 and MIAPaCa-2 mouse xenografts using PET and in vivo biodistribution studies. The dosimetry of the cucurbit[7]uril-adamantane (CB7-Adma) pretargeting approach in men was calculated and compared with that of the directly 89Zr-labeled hT84.66-M5A. Results: The adamantane radioligands possessed high in vitro stability up to 24 h (>90%). Pretargeted PET with CB7-Adma methodology resulted in specific tumor uptake (P < 0.05) with low background signal. The in vivo formed CB7-Adma complex was demonstrated to be stable, with high tumor uptake up to 24 h after radioligand injection (12.0 ± 0.9 percentage injected dose/g). The total-body radiation dose of the pretargeting strategy was only 3.3% that of the directly 89Zr-labeled hT84.66-M5A. Conclusion: The CB7-Adma strategy is highly suitable for pretargeted PET. The exceptional stability of the pretargeting agents and the specific and high tumor uptake of the pretargeted adamantane radioligands provide great potential for the platform.

Investigation of Copper-64-Based Host-Guest Chemistry Pretargeted Positron Emission Tomography

Pretargeting is a technique that uses macromolecules as targeting agents for nuclear imaging and therapy with the goal of reducing the radiation toxicity to healthy tissues often associated with directly radiolabeled macromolecules. In pretargeting, a macromolecule is radiolabeled in vivo at the target site using a radiolabeled small molecule (radioligand) that interacts with the macromolecule with high specificity. We report an investigation of host-guest chemistry-driven pretargeting using copper-64 radiolabeled ferrocene (Fc; guest) compounds and a cucurbit[7]uril (CB7; host) molecule functionalized carcinoembryonic antigen targeting hT84.66-M5A monoclonal antibody (CB7-M5A). Two novel ferrocene-based radioligands ([⁶⁴Cu]Cu-NOTA-PEG₃-Fc and [⁶⁴Cu]Cu-NOTA-PEG₇-Fc) were prepared, and their in vitro stability, pharmacokinetic in vivo profile in healthy mice, and pretargeting performance in a subcutaneous BxPC3 human pancreatic cancer cell xenograft mouse model were compared. The antibody dosing was optimized using a zirconium-89 radiolabeled M5A antibody ([⁸⁹Zr]Zr-DFO-M5A) in a BxPC3 xenograft model, and the dosimetry of [⁸⁹Zr]Zr-DFO-M5A and the pretargeting approach were compared. Finally, the effects of varying lag times up to 9 days between CB7-M5A and radioligand injection were investigated. In vivo pretargeting studies with both ferrocene radioligands resulted in specific tumor uptake (p = 0.0006 and p = 0.003) and also showed that the host-guest-based pretargeting approach excels with extended lag times up to 9 days with good tumor localization, suggesting that host-guest pretargeting may be suitable for use without clearing agents which have complicated clinical application of this technique. To our knowledge, the reported lag time of 9 days is the longest investigated lag time in any reported pretargeting studies.

Cucurbituril-Ferrocene: Host-Guest Based Pretargeted Positron Emission Tomography in a Xenograft Model

Pretargeted positron emission tomography is a macromolecule-driven nuclear medicine technique that involves targeting a preadministered antigen target-bound macromolecule with a radioligand in vivo, aiming to minimize the overall radiation dose. This study investigates the use of antibody based host-guest chemistry methodology for pretargeted positron emission tomography. We hypothesize that the novel pretargeting approach reported here overcomes the challenges the current pretargeting platforms have with the in vivo stability and modularity of the pretargeting components. A cucurbit[7]uril host molecule modified, anti-carcinoembryonic antigen antibody (M5A; CB7-M5A) and a 68Ga-radiolabeled ferrocene guest radioligand ([68Ga]Ga-NOTA-PEG3-NMe2-Fc) were studied as potential host-guest chemistry pretargeting agents for positron emission tomography in BxPC3 xenografted nude mice. The viability of the platform was studied via in vivo biodistribution and positron emission tomography. Tumor uptake of [68Ga]Ga-NOTA-PEG3-NMe2-Fc was significantly higher in mice which received CB7-M5A prior to the radioligand injection (pretargeted) (3.3 ± 0.7%ID/g) compared to mice which only received the radioligand (nonpretargeted) (0.2 ± 0.1%ID/g).

Current Landscape in Clinical Pretargeted Radioimmunoimaging and Therapy

The principle of pretargeted radioimmunoimaging and therapy has been investigated over the past 30 y in preclinical and clinical settings with the aim of reducing the radiation burden of healthy tissue for antibody-based nuclear medicine techniques. In the past few decades, 4 pretargeting methodologies have been proposed, and 2 of them-the bispecific antibody-hapten and the streptavidin-biotin platforms-have been evaluated in humans in phase 1 and 2 studies. With this review article, we aim to survey clinical pretargeting studies in order to understand the challenges that these platforms have faced in human studies and to provide an overview of how the clinical approval of the pretargeting system has proceeded in the past several decades. Additionally, we will discuss the successes of the pretargeting human studies and compare and highlight the pretargeting approaches and conditions that will advance clinical translation of the pretargeting platform in the future.

ImmunoPET Predicts Response to Met-targeted Radioligand Therapy in Models of Pancreatic Cancer Resistant to Met Kinase Inhibitors

Background: Pancreatic ductal adenocarcinoma (PDAC) has limited standard of care therapeutic options. While initially received with enthusiasm, results from targeted therapy with small molecule tyrosine kinases inhibitors (TKIs) have been mixed, in part due to poor patient selection and compensatory changes in signaling networks upon blockade of one or more kinase of tumors. Here, we demonstrate that in PDACs otherwise resistant to rational kinase inhibition, Met-directed immuno-positron emission tomography (immunoPET) can identify targets for cell-signaling independent targeted radioligand therapy (RLT). In this study, we use Met-directed immunoPET and RLT in models of human pancreatic cancer that are resistant to Met- and MEK-selective TKIs, despite over-expression of Met and KRAS-pathway activation. Methods: We assessed cell membrane Met levels in human patient samples and pancreatic ductal adenocarcinoma (PDAC) cell lines (BxPC3, Capan2, Suit2, and MIA PaCa-2) using immunofluorescence, flow cytometry and cell-surface biotinylation assays. To determine whether Met expression levels correlate with sensitivity to Met inhibition by tyrosine kinase inhibitors (TKIs), we performed cell viability studies. A Met-directed imaging agent was engineered by labeling Met-specific onartuzumab with zirconium-89 (Zr-89) and its in vivo performance was evaluated in subcutaneous and orthotopic PDAC xenograft models. To assess whether the immunoPET agent would predict for targeted RLT response, onartuzumab was then labeled with lutetium (Lu-177) as the therapeutic radionuclide to generate our [¹⁷⁷Lu]Lu-DTPA-onartuzumab RLT agent. [¹⁷⁷Lu]Lu-DTPA-onartuzumab was administered at 9.25MBq (250μCi)/20μg in three fractions separated by three days in mice subcutaneously engrafted with BxPC3 (high cell-membrane Met) or MIA PaCa-2 (low cell-membrane Met). Primary endpoints were tumor response and overall survival. Results: Flow cytometry and cell-surface biotinylation studies showed that cell-membrane Met was significantly more abundant in BxPC3, Capan2, and Suit2 when compared with MIA PaCa-2 pancreatic tumor cells. Crizotinib and cabozantinib, TKIs with known activity against Met and other kinases, decreased PDAC cell line viability in vitro. The TKI with the lowest IC₅₀ for Met, capmatinib, had no activity in PDAC lines. No additive effect was detected on cell viability when Met-inhibition was combined with MEK1/2 inhibition. We observed selective tumor uptake of [⁸⁹Zr]Zr-DFO-onartuzumab in mice subcutaneously and orthotopically engrafted with PDAC lines containing high cell-surface levels of Met (BxPC3, Capan2, Suit2), but not in mice engrafted with low cell-surface levels of Met (MIA PaCa-2). Significant tumor growth delay and overall survival benefit were observed in both BxPC3 and MIA PaCa-2 engrafted animals treated with RLT when compared to controls, however, the benefit was more pronounced and more durable in the BxPC3 engrafted animals treated with [¹⁷⁷Lu]Lu-DTPA-onartuzumab RLT. Conclusions: Our findings demonstrate that while over-expression of Met is not predictive of Met-directed TKI response, immunoPET can detect Met over-expression in vivo and predicts for therapeutic response to Met-selective RLT. This phenomenon can be exploited for other Met-overexpressing tumor types specifically, and to any differentially overexpressed surface molecule more broadly.

Tumor-Specific Zr-89 Immuno-PET Imaging in a Human Bladder Cancer Model

Purpose

Tumor-specific molecular imaging is an important tool for assessing disease burden and treatment response. CA19.9 is an important tumor-specific marker in several malignancies, including urothelial carcinoma. [⁸⁹Zr]DFO-HuMab-5B1 (MVT-2163) is a CA19.9-specific antibody-based construct that has been validated in preclinical animal models of lung, colorectal, and pancreatic malignancies for positron emission tomography (PET) imaging and is currently in a phase I trial for pancreatic cancer (NCT02687230). Here, we examine whether [⁸⁹Zr]DFO-HuMab-5B1 may be useful in defining urothelial malignancies.

Procedures

Surface expression of CA19.9 was confirmed in the human bladder cancer line HT 1197. The radioimmunoconjugate [⁸⁹Zr]DFO-HuMab-5B1 was injected into mice bearing HT 1197 xenografts, and followed by PET imaging, ex vivo experiments including biodistribution, histology and autoradiography, and analysis of blood samples for shed antigen levels were performed.

Results

[⁸⁹Zr]DFO-HuMab-5B1 specifically accumulates in HT 1197 engrafted tumors when imaged with PET. Ex vivo biodistribution of organs and autoradiography of engrafted tumors confirm our construct’s specific tumor binding. The target antigen CA19.9 was not found to be shed in vitro or in vivo.

Conclusions

[⁸⁹Zr]DFO-HuMab-5B1 can be used to delineate urothelial carcinomas by PET imaging and may provide tumor-specific information prior to, during, and after systemic therapies.

Leveraging PET to image folate receptor α therapy of an antibody-drug conjugate

BACKGROUND

The folate receptor α (FRα)-targeting antibody-drug conjugate (ADC), IMGN853, shows great antitumor activity against FRα-expressing tumors in vivo, but patient selection and consequently therapy outcome are based on immunohistochemistry. The aim of this study is to develop an antibody-derived immuno-PET imaging agent strategy for targeting FRα in ovarian cancer as a predictor of treatment success.

METHODS

We developed [89Zr]Zr-DFO-M9346A, a humanized antibody-based radiotracer targeting tumor-associated FRα in the preclinical setting. [89Zr]Zr-DFO-M9346A's binding ability was tested in an in vitro uptake assay using cell lines with varying FRα expression levels. The diagnostic potential of [89Zr]Zr-M9346A was evaluated in KB and OV90 subcutaneous xenografts. Following intravenous injection of [89Zr]Zr-DFO-M9346A (~90 μCi, 50 μg), PET imaging and biodistribution studies were performed. We determined the blood half-life of [89Zr]Zr-DFO-M9346A and compared it to the therapeutic, radioiodinated ADC [131I]-IMGN853. Finally, in vivo studies using IMG853 as a therapeutic, paired with [89Zr]Zr-DFO-M9346A as a companion diagnostic were performed using OV90 xenografts.

RESULTS

DFO-M9346A was labeled with Zr-89 at 37 °C within 60 min and isolated in labeling yields of 85.7 ± 5.7%, radiochemical purities of 98.0 ± 0.7%, and specific activities of 3.08 ± 0.43 mCi/mg. We observed high specificity for binding FRα positive cells in vitro. For PET and biodistribution studies, [89Zr]Zr-M9346A displayed remarkable in vivo performance in terms of excellent tumor uptake for KB and OV xenografts (45.8 ± 29.0 %IA/g and 26.1 ± 7.2 %IA/g), with low non-target tissue uptake in other organs such as kidneys (4.5 ± 1.2 %IA/g and 4.3 ± 0.7 %IA/g). A direct comparison of the blood half life of [89Zr]Zr-M9346A and [131I]-IMGN853 corroborated the equivalency of the radiopharmaceutical and the ADC, paving the way for a companion PET imaging study.

CONCLUSIONS

We developed a new folate receptor-targeted 89Zr-labeled PET imaging agent with excellent pharmacokinetics in vivo. Good tumor uptake in subcutaneous KB and OV90 xenografts were obtained, and ADC therapy studies were performed with the precision predictor.

Abstract 5204: Preclinical development of MVT-1075 as radioimmunotherapy for pancreatic cancer and other CA19-9 positive malignancies

Rationale: The CA19-9 antigen is frequently overexpressed in pancreatic and other GI tumors. MVT-5873 (HuMab-5B1), a fully human monoclonal antibody currently in phase I study, targets the sialyl Lewis A (sLea) epitope on CA19-9, and is a promising platform for development of a targeted radioimmunotherapy (RIT). MVT-5873 was conjugated with the chelator CHX-A″-DTPA and radiolabeled with the beta-emitting isotopes Lutetium -177 (177Lu) or Yttrium-90 (90Y) to form the RIT agents MVT-1075 (177Lu- CHX-A″-DTPA-HuMAb-5B1) and MVT-1916 (90Y- CHX-A″-DTPA-HuMAb-5B1), respectively. The antitumor efficacy of each of the constructs was studied in nude mice bearing BxPC3 human pancreatic tumor xenografts, known to express CA19-9.

Methods: The initial dose-finding studies utilized doses of MVT-1075 of 75-450 μCi and MVT-1916 of 25-250 μCi, administered to groups of mice (n = 8) bearing subcutaneous (subQ) BxPC3 tumors (~ 150 mm3). Further studies focused on MVT-1075 and assessed antitumor effect in an orthotopic xenograft model, the effect of dose fractionation, and biodistribution in nontumor bearing (normal) and BxPC3 tumor-bearing mice.

Results: A single dose of MVT-1075 at 75, 150, 300, or 450 μCi significantly inhibited subQ BxPC3 tumor growth at all dose levels, with sustained suppression with higher doses. MVT-1916 produced similar results. MVT-1075 was selected based on the favorable half-life of 177Lu (6.7 d) and its utility for clinical biodistribution assessments. In an orthotopic BxPC3 tumor model, treatment with a single dose of MVT-1075 at 300 μCi significantly inhibited tumor growth, with Day 20 tumor volume approximately 50% that of the initial starting volume. A third BxPC3 xenograft study evaluated fractionated dosing schedules, (150 μCi x 1, 75 μCi x 2, 50 μCi x3), with both single-dose and fractionated schedules effectively inhibiting subQ BxPC3 tumor growth. Biodistribution studies in normal mice showed an expected gradually decreasing activity in blood, heart, and lungs, with low uptake in normal pancreas. In subQ BxPC3 tumor-bearing mice, tumor uptake was rapid, reaching 69% ID/g by 24 h and 86% ID/g by 120 h. Otherwise, the biodistribution pattern paralleled that of normal mice, with relative %ID/g values within about ± 25% of normal mice across all time points comparing blood, heart, lungs, kidneys, and pancreas, with slightly higher uptake in liver and slightly lower uptake in spleen.

Conclusions: MVT-1075 demonstrates promising antitumor activity in a human pancreatic cancer xenograft model, with efficacy shown in both single dose and fractionated schedules. Biodistribution shows rapid and substantial tumor uptake, with much lower uptake in normal organs. These findings support the phase I clinical trial of MVT-1075 in patients with CA19-9 positive pancreatic cancers planned to begin in early 2017.

Citation Format: Jacob L. Houghton, Ryan Lanning, Dayla Abdel-atti, Toni Jun, Christine M. Kearns, Michael Schlosser, Wolfgang Scholz, Jason S. Lewis, Paul W. Maffuid. Preclinical development of MVT-1075 as radioimmunotherapy for pancreatic cancer and other CA19-9 positive malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5204. doi:10.1158/1538-7445.AM2017-5204

Abstract B44: Optimization and IND enabling investigations of MVT-2163 (89Zr-DFO-5B1) leading to First-in-Human readiness

Rationale: MVT-2163 (89Zr-DFO-5B1) — an anti-CA19.9 human monoclonal antibody formed via conjugation of the chelator desferoxamine (DFO) and radiolabeling with zirconium-89 (89Zr) — was recently reported to have excellent ability to delineate CA19-9 positive malignancies via PET imaging, including pancreatic cancer.(1) Additionally, preclinical studies have shown the antibody has antitumor properties alone(2) and, more recently, in combination with frontline chemotherapies such as nab-Paclitaxel and gemcitabine. Herein, we report the preclinical optimization and characterization of MVT-2163 that led to the recent approval of an IND application for first-in-human trials in patients with metastatic pancreatic cancer.

Methods: The conditions for appending the chelator DFO to MVT-5873 (5B1) were optimized by screening various combinations of reaction pH, stoichiometric ratios of chelate to antibody, buffer type, and incubation times. The optimized conjugation strategy was used to prepare clinical grade DFO-5B1 that was subsequently radiolabeled with 89Zr to yield MVT-2163 for use in human subjects. The biodistribution was determined in healthy female, athymic nude mice at 1, 24, 48, 72, and 120h via gamma counting of resected tissues and comparison to standards. The normal-organ radiation doses were estimated for the 70-kg Standard Adult anatomic model using the time-dependent organ activity concentrations and total-body activities, and the Standard Adult mean organ dose and effective dose were calculated using OLINDA. The stability of MVT-2163 in formulation buffer and in human serum at 37°C was assessed (24, 48, 96, 120, and 168h) via thin layer chromatography and size exclusion chromatography. Additionally, the remaining immunoreactive fraction was determined at the same time points using an in vitro cellular binding assay with BxPC3 cells.

Results: We found that the optimal conjugation strategy was to buffer exchange MVT-5873 into 100mM sodium bicarbonate buffer (pH9) prior to letting the DFO react at 32.5°C for 90m. Unincorporated DFO was removed by buffer exchanging the reaction mixture into 1M ammonium acetate (pH7) buffer. The final MVT-7686 (DFO-5B1) product was stored in long term storage at -80°C. Biodistribution of the MVT-2163 indicated tissue retentions that were within expected norms for a 89Zr-labeled antibody. The highest uptake at 120h in terms of percent injected dose per gram of tissue (%ID/g) was found in the bone, which is common for osteophilic radiometals such as 89Zr. Dosimetry calculations based on the biodistribution results predicted a total absorbed dose of 8.1 rem when accounting for the proposed accompanying low-dose CT scan. The absorbed doses to all organs were within acceptable limits at the proposed human study dose (5 mCi), and the absorbed dose in red marrow — which is often the dose-limiting factor — was within ranges predicted and observed with other 89Zr-radiolabeled antibodies in humans.

The radiochemical purity data indicate that the tracer remains intact in formulation buffer up to 120 hours. Cell binding assays performed with multiple lots of the same material showed that the immunoreactivity remains above 75% when stored up to 120h at room temperature, indicating exemplary stability. The stability and immunoreactivity were slightly lower when incubated in human serum at 37°C. However, the data shows that the immunoreactivity is maintained in human serum for more than up to 168h.

Conclusions: The stability studies in both formulation buffer and human serum indicate that MVT-2163 maintains sufficient radiochemical purity and immunoreactivity. The results of the reported studies support the proposed specifications and the excellent performance has resulted in MVT-2163 being accepted for first in human trials at MSKCC, which are set to begin in Q2 2016.

1. Viola-Villegas NT, et al. J Nucl Med. 2013;54(11):1876-82.

2. Sawada R, et al. Clin Cancer Res. 2011;17(5):1024-32.

Citation Format: Jacob L. Houghton, Serge K. Lyashchenko, Ritsuko Sawada, Pat Zanzonico, Scott Rudge, Wolfgang W. Scholz, Paul Maffuid, Jason S. Lewis.{Authors}. Optimization and IND enabling investigations of MVT-2163 (89Zr-DFO-5B1) leading to First-in-Human readiness. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B44.

Establishment of the In Vivo Efficacy of Pretargeted Radioimmunotherapy Utilizing Inverse Electron Demand Diels-Alder Click Chemistry

The pretargeting system based on the inverse electron demand Diels-Alder reaction (IEDDA) between trans-cyclooctene (TCO) and tetrazine (Tz) combines the favorable pharmacokinetic properties of radiolabeled small molecules with the affinity and specificity of antibodies. This strategy has proven to be an efficient method for the molecularly targeted delivery of pharmaceuticals, including isotopes for radiological imaging. Despite encouraging results from in vivo PET imaging studies, this promising system has yet to be thoroughly evaluated for pretargeted radioimmunotherapy (PRIT). Toward that end, we synthesized two novel ¹⁷⁷Lu-labeled tetrazine-bearing radioligands. Next, we compared the usefulness of our ligands for PRIT when paired with TCO-modified 5B1-a human, anti-CA19.9 mAb-in preclinical murine models of pancreatic cancer. The exemplary ligand, ¹⁷⁷Lu-DOTA-PEG₇-Tz, showed rapid (4.6 ± 0.8% ID/g at 4 hours) and persistent (16.8 ± 3.9% ID/g at 120 hours) uptake in tumors while concurrently clearing from blood and nontarget tissues. Single-dose therapy studies using 5B1-TCO and varying amounts of ¹⁷⁷Lu-DOTA-PEG₇-Tz (400, 800, and 1,200 μCi) showed that our system elicits a dose-dependent therapeutic response in mice bearing human xenografts. Furthermore, dosimetry calculations suggest that our approach is amenable to clinical applications with its excellent dosimetric profile in organs of clearance (i.e., liver and kidneys) as well as in dose-limiting tissues, such as red marrow. This study established that a pretargeted methodology utilizing the IEDDA reaction can rapidly and specifically deliver a radiotherapeutic payload to tumor tissue, thus illustrating its excellent potential for clinical translation. Mol Cancer Ther; 16(1); 124-33. ©2016 AACR.

Congestive heart failure with normal ejection fraction

Clinicians must remain undaunted when history, physical examination, and chest radiography suggest congestive heart failure but left ventricular systolic function is normal. Many of these patients have diastolic dysfunction, and standard therapy for left ventricular systolic dysfunction is often ineffectual or detrimental. Noninvasive testing is subject to many pitfalls but may confirm a clinical suspicion and provide indications to treat or to proceed with invasive testing. In the absence of clinical signs and symptoms of congestive failure, however, abnormal diastolic indexes should not be interpreted as diagnostic of diastolic dysfunction and are not an indication to treat.

Thiosulfate oxidation by Thiomicrospira thermophila: metabolic flexibility in response to ambient geochemistry

Previous studies of the stoichiometry of thiosulfate oxidation by colorless sulfur bacteria have failed to demonstrate mass balance of sulfur, indicating that unidentified oxidized products must be present. Here the reaction stoichiometry and kinetics under variable pH conditions during the growth of Thiomicrospira thermophila strain EPR85, isolated from diffuse hydrothermal fluids at the East Pacific Rise, is presented. At pH 8.0, thiosulfate was stoichiometrically converted to sulfate. At lower pH, the products of thiosulfate oxidation were extracellular elemental sulfur and sulfate. We were able to replicate previous experiments and identify the missing sulfur as tetrathionate, consistent with previous reports of the activity of thiosulfate dehydrogenase. Tetrathionate was formed under slightly acidic conditions. Genomic DNA from T. thermophila strain EPR85 contains genes homologous to those in the Sox pathway (soxAXYZBCDL), as well as rhodanese and thiosulfate dehydrogenase. No other sulfur oxidizing bacteria containing sox(CD)2 genes have been reported to produce extracellular elemental sulfur. If the apparent modified Sox pathway we observed in T. thermophila is present in marine Thiobacillus and Thiomicrospira species, production of extracellular elemental sulfur may be biogeochemically important in marine sulfur cycling.

(18)F-Based Pretargeted PET Imaging Based on Bioorthogonal Diels-Alder Click Chemistry

A first-of-its-kind (18)F pretargeted PET imaging approach based on the bioorthogonal inverse electron demand Diels-Alder (IEDDA) reaction between tetrazine (Tz) and trans-cyclooctene (TCO) is presented. As proof-of-principle, a TCO-bearing immunoconjugate of the anti-CA19.9 antibody 5B1 and an Al[(18)F]NOTA-labeled tetrazine radioligand were harnessed for the visualization of CA19.9-expressing BxPC3 pancreatic cancer xenografts. Biodistribution and (18)F-PET imaging data clearly demonstrate that this methodology effectively delineates tumor mass with activity concentrations up to 6.4 %ID/g at 4 h after injection of the radioligand.

Pretargeted Immuno-PET of Pancreatic Cancer: Overcoming Circulating Antigen and Internalized Antibody to Reduce Radiation Doses

5B1 is a fully human, monoclonal antibody that has shown promise for the PET imaging of cancers expressing carbohydrate antigen 19.9 (CA19.9)--a carbohydrate prevalent in cells with aberrant glycosylation and an established effector of metastasis. The long physiologic half-life of the antibody and interference from circulating CA19.9 may increase the time required to generate quality images as well as the risk of radiation exposure to healthy tissues during repeated PET imaging. Pretargeting methodologies are an effective approach to expeditiously acquire PET images, but in this case, the pretargeting approach is complicated by the internalization of 5B1 by CA19.9-expressing cells. We sought to adapt and optimize a pretargeting strategy that exploits the bioorthogonal reaction between transcyclooctene (TCO) and tetrazine (Tz) to overcome these complications.

METHODS

5B1 was modified with TCO, and a novel NOTA-PEG7-Tz radioligand was synthesized with the goal of improving on a previously reported analog. BxPC3 and Capan-2 cells were evaluated for their ability to internalize anti-CA19.9 antibodies using a fluorometric assay, and xenografts of the same lines were used for in vivo studies. The pretargeting approach was optimized, and the 2 radioligands were compared using biodistribution and PET imaging in murine models of pancreatic cancer.

RESULTS

BxPC3 and Capan-2 cells were shown to rapidly internalize anti-CA19.9 monoclonal antibodies, including 5B1. (64)Cu-NOTA-PEG7-Tz showed improved in vivo pharmacokinetics relative to (64)Cu-NOTA-Tz using 5B1-TCO as the targeting vector. PET imaging and biodistribution studies showed that injecting the radioligand 72 h after the administration of 5B1-TCO resulted in the best uptake (8.2 ± 1.7 percentage injected dose per gram at 20 h after injection) and tumor-to-background activity concentration ratios. Dosimetry calculations revealed that the pretargeting system produced a greater than 25-fold reduction in total body radiation exposure relative to (89)Zr-desferrioxamine-5B1. PET/CT imaging in an orthotopic Capan-2 xenograft model--which secretes large amounts of CA19.9 and more rapidly internalizes anti-CA19.9 antibodies--showed that this approach is viable even in the difficult circumstances presented by a circulating antigen and internalized targeting vector.

CONCLUSION

The 5B1-TCO and (64)Cu-NOTA-PEG7-Tz system evaluated in these studies can delineate CA19.9-positive xenografts in murine models of pancreatic cancer despite the challenges posed by the combination of circulating antigen and internalization of the 5B1-TCO.

Underscoring the influence of inorganic chemistry on nuclear imaging with radiometals

Over the past several decades, radionuclides have matured from largely esoteric and experimental technologies to indispensible components of medical diagnostics. Driving this transition, in part, have been mutually necessary advances in biomedical engineering, nuclear medicine, and cancer biology. Somewhat unsung has been the seminal role of inorganic chemistry in fostering the development of new radiotracers. In this regard, the purpose of this Forum Article is to more visibly highlight the significant contributions of inorganic chemistry to nuclear imaging by detailing the development of five metal-based imaging agents: (64)Cu-ATSM, (68)Ga-DOTATOC, (89)Zr-transferrin, (99m)Tc-sestamibi, and (99m)Tc-colloids. In a concluding section, several unmet needs both in and out of the laboratory will be discussed to stimulate conversation between inorganic chemists and the imaging community.

Chemical and structural insights into the regioversatility of the aminoglycoside acetyltransferase Eis

A recently discovered cause of tuberculosis resistance to a drug of last resort, the aminoglycoside kanamycin, results from modification of this drug by the enhanced intracellular survival (Eis) protein. Eis is a structurally and functionally unique acetyltransferase with an unusual capability of acetylating aminoglycosides at multiple positions. The extent of this regioversatility and its defining protein features are unclear. Herein, we determined the positions and order of acetylation of five aminoglycosides by NMR spectroscopy. This analysis revealed unprecedented acetylation of the 3''-amine of kanamycin, amikacin, and tobramycin, and the γ-amine of the 4-amino-2-hydroxybutyryl group of amikacin. A crystal structure of Eis in complex with coenzyme A and tobramycin revealed how tobramycin can be accommodated in the Eis active site in two binding modes, consistent with its diacetylation. These studies, describing chemical and structural details of acetylation, will guide future efforts towards designing aminoglycosides and Eis inhibitors to overcome resistance in tuberculosis.

Unexpected N-acetylation of capreomycin by mycobacterial Eis enzymes

OBJECTIVES

The enhanced intracellular survival (Eis) protein from Mycobacterium tuberculosis (Eis_Mtb), a regio-versatile N-acetyltransferase active towards many aminoglycosides (AGs), confers resistance to kanamycin A in some cases of extensively drug-resistant tuberculosis (XDR-TB). We assessed the activity of Eis_Mtb and of its homologue from Mycobacterium smegmatis (Eis_Msm) against a panel of anti-tuberculosis (TB) drugs and lysine-containing compounds.

METHODS AND RESULTS

Both enzymes acetylated capreomycin and some lysine-containing compounds, but not other non-AG non-lysine-containing drugs tested. Modelling studies predicted the site of modification on capreomycin to be one of the two primary amines in its β-lysine side chain. Using Eis_Mtb, we established via nuclear magnetic resonance (NMR) spectroscopy that acetylation of capreomycin occurs on the ε-amine of the β-lysine side chain. Using Msm, we also demonstrated for the first time to our knowledge that acetylation of capreomycin results in deactivation of the drug.

CONCLUSIONS

Eis is a unique acetyltransferase capable of inactivating the anti-TB drug capreomycin, AGs and other lysine-containing compounds.

AMP-activated protein kinase and ATP-citrate lyase are two distinct molecular targets for ETC-1002, a novel small molecule regulator of lipid and carbohydrate metabolism

ETC-1002 (8-hydroxy-2,2,14,14-tetramethylpentadecanedioic acid) is a novel investigational drug being developed for the treatment of dyslipidemia and other cardio-metabolic risk factors. The hypolipidemic, anti-atherosclerotic, anti-obesity, and glucose-lowering properties of ETC-1002, characterized in preclinical disease models, are believed to be due to dual inhibition of sterol and fatty acid synthesis and enhanced mitochondrial long-chain fatty acid β-oxidation. However, the molecular mechanism(s) mediating these activities remained undefined. Studies described here show that ETC-1002 free acid activates AMP-activated protein kinase in a Ca(2+)/calmodulin-dependent kinase β-independent and liver kinase β 1-dependent manner, without detectable changes in adenylate energy charge. Furthermore, ETC-1002 is shown to rapidly form a CoA thioester in liver, which directly inhibits ATP-citrate lyase. These distinct molecular mechanisms are complementary in their beneficial effects on lipid and carbohydrate metabolism in vitro and in vivo. Consistent with these mechanisms, ETC-1002 treatment reduced circulating proatherogenic lipoproteins, hepatic lipids, and body weight in a hamster model of hyperlipidemia, and it reduced body weight and improved glycemic control in a mouse model of diet-induced obesity. ETC-1002 offers promise as a novel therapeutic approach to improve multiple risk factors associated with metabolic syndrome and benefit patients with cardiovascular disease.

Biochemical and structural analysis of aminoglycoside acetyltransferase Eis from Anabaena variabilis

The Mycobacterium tuberculosis enhanced intracellular survival (Eis_Mtb) protein is a clinically important aminoglycoside (AG) multi-acetylating enzyme. Eis homologues are found in a variety of mycobacterial and non-mycobacterial species. Variation of the residues lining the AG-binding pocket and positions of the loops bearing these residues in the Eis homologues dictates the substrate specificity and, thus, Eis homologues are Nature-made tools for elucidating principles of AG recognition by Eis. Here, we demonstrate that the Eis from Anabaena variabilis (Eis_Ava), the first non-mycobacterial Eis homologue reported, is a multi-acetylating AG-acetyltransferase. Eis_Ava, Eis from Mycobacterium tuberculosis (Eis_Mtb), and Eis from Mycobacterium smegmatis (Eis_Msm) have different structures of their AG-binding pockets. We perform comparative analysis of these differences and investigate how they dictate the substrate and cosubstrate recognition and acetylation of AGs by Eis.

The structural basis for substrate versatility of chloramphenicol acetyltransferase CATI

Novel antibiotics are needed to overcome the challenge of continually evolving bacterial resistance. This has led to a renewed interest in mechanistic studies of once popular antibiotics like chloramphenicol (CAM). Chloramphenicol acetyltransferases (CATs) are enzymes that covalently modify CAM, rendering it inactive against its target, the ribosome, and thereby causing resistance to CAM. Of the three major types of CAT (CAT(I-III)), the CAM-specific CAT(III) has been studied extensively. Much less is known about another clinically important type, CAT(I). In addition to inactivating CAM and unlike CAT(III), CAT(I) confers resistance to a structurally distinct antibiotic, fusidic acid. The origin of the broader substrate specificity of CAT(I) has not been fully elucidated. To understand the substrate binding features of CAT(I), its crystal structures in the unbound (apo) and CAM-bound forms were determined. The analysis of these and previously determined CAT(I)-FA and CAT(III)-CAM structures revealed interactions responsible for CAT(I) binding to its substrates and clarified the broader substrate preference of CAT(I) compared to that of CAT(III).

Dissecting the cosubstrate structure requirements of the Staphylococcus aureus aminoglycoside resistance enzyme ANT(4')

Aminoglycosides are important antibiotics used against a wide range of pathogens. As a mechanism of defense, bacteria have evolved enzymes able to inactivate these drugs by regio-selectively adding a variety of functionalities (acetyl, phospho, and nucelotidyl groups) to their scaffolds. The aminoglycoside nucleotidyltransferase ANT(4') is one of the most prevalent and unique modifying-enzymes. Here, by TLC, HRMS, and colorimetric assays, we demonstrate that the resistance enzyme ANT(4') from Staphylococcus aureus is highly substrate and cosubstrate promiscuous. We show that deoxy-ribonucleotide triphosphates (dNTPs) are better cosubstrates than NTPs. We demonstrate that the position of the triphosphate group (5' and not 3') on the ribose/deoxyribose ring is important for recognition by ANT(4'), and that NTPs with larger substituents at the 3'-position of the ribose ring are not cosubstrates for ANT(4'). We confirm that for all aminoglycosides tested, the respective nucleotidylated products are completely inactive. These results provide valuable insights into the development of strategies to combat the ever-growing bacterial resistance problem.

An experimental and theoretical approach to determining linkages between geochemical variability and microbial biodiversity in seafloor hydrothermal chimneys

New experimental results of fluid-mineral reactions at hydrothermal conditions relevant to life demonstrate that key redox reactions involving iron, sulfur, and hydrogen remain at disequilibrium at 100 °C, even in a heterogeneous system and thus are energetically favorable for microbial metabolism. Predictions from geochemical models utilizing the experimental results and specific to two contrasting case studies from the East Pacific Rise were statistically characterized and correlated to the energetics of redox reactions available for intra-chimney microbial populations. In general, predictions of available energy for autotrophic metabolism are largely similar between the mature and the nascent chimneys, although important differences still exist. Metabolic processes predicted by energetics exhibit the same trends observed in the field data for the mature chimney, but overestimate the diversity observed in the nascent chimney. Several combinations of redox reaction pairs are predicted to support mixed consortia, while some combinations appear to favor more versatile microbes capable of utilizing several reactions under rapidly changing environmental conditions within chimney walls. In addition, conditions favorable to elemental sulfur reduction and methanogenesis exhibit a negative control on the diversity of microbial populations within these chimney walls, whereas H₂S oxidation, elemental sulfur oxidation and the knallgas reaction are positively correlated with both abundance and diversity of micro-organisms. Coupling field observations of both microbial diversity and geochemical heterogeneity with lab-based experimental and theoretical modeling can facilitate translation of the observed genetic diversity into physiological diversity, thus enhancing understanding of linked phenomena of microbially induced biogeochemical transformations in complex heterogeneous systems.

The future of aminoglycosides: the end or renaissance?

Although aminoglycosides have been used as antibacterials for decades, their use has been hindered by their inherent toxicity and the resistance that has emerged to these compounds. It seems that such issues have relegated a formerly front-line class of antimicrobials to the proverbial back shelf. However, recent advances have demonstrated that novel aminoglycosides have a potential to overcome resistance as well as to be used to treat HIV-1 and even human genetic disorders, with abrogated toxicity. It is not the end for aminoglycosides, but rather, the challenges faced by researchers have led to ingenuity and a change in how we view this class of compounds, a renaissance.

Exploring the substrate promiscuity of drug-modifying enzymes for the chemoenzymatic generation of N-acylated aminoglycosides

Aminoglycosides are broad-spectrum antibiotics commonly used for the treatment of serious bacterial infections. Decades of clinical use have led to the widespread emergence of bacterial resistance to this family of drugs limiting their efficacy in the clinic. Here, we report the development of a methodology that utilizes aminoglycoside acetyltransferases (AACs) and unnatural acyl coenzyme A analogues for the chemoenzymatic generation of N-acylated aminoglycoside analogues. Generation of N-acylated aminoglycosides is followed by a simple qualitative test to assess their potency as potential antibacterials. The studied AACs (AAC(6')-APH(2'') and AAC(3)-IV) show diverse substrate promiscuity towards a variety of aminoglycosides as well as acyl coenzyme A derivatives. The enzymes were also used for the sequential generation of homo- and hetero-di-N-acylated aminoglycosides. Following the clinical success of the N-acylated amikacin and arbekacin, our chemoenzymatic approach offers access to regioselectively N-acylated aminoglycosides in quantities that allow testing of the antibacterial potential of the synthetic analogues making it possible to decide which molecules will be worth synthesizing on a larger scale.

Continuous enrichment culturing of thermophiles under sulfate and nitrate-reducing conditions and at deep-sea hydrostatic pressures

A continuous culture bioreactor was developed to enrich for nitrate and sulfate reducing thermophiles under in situ deep-sea pressures. The ultimate objective of this experimental design was to be able to study microbial activities at chemical and physical conditions relevant to seafloor hydrothermal vents. Sulfide, sulfate and oxide minerals from sampled seafloor vent-chimney structures [East Pacific Rise (9 degrees 46'N)] served as source mineral and microbial inoculum for enrichment culturing using nitrate and sulfate-enriched media at 70 and 90 degrees C and 250 bars. Changes in microbial diversity during the continuous reaction flow were monitored using denaturing gradient gel electrophoresis (DGGE) of PCR amplified 16S rRNA gene fragments. Time series changes in fluid chemistry were also monitored throughout the experiment to assess the feedback between mineral-fluid reaction and metabolic processes. Data indicate a shift from the dominance of epsilon Proteobacteria in the initial inoculum to the several Aquificales-like phylotypes in nitrate-reducing enrichment media and Thermodesulfobacteriales in the sulfate-reducing enrichment media. Methanogens were detected in the original sulfide sample and grew in selected sulfate-enriched experiments. Microbial interactions with anhydrite and pyrrhotite in the chimney material resulted in measurable changes in fluid chemistry despite a fluid residence time only 75 min in the reactor. Changes in temperature rather than source material resulted in greater differences in microbial enrichments and mediated geochemical reactions.

Cholesterol lowering with pravastatin improves resistance artery endothelial function: report of six subjects with normal coronary arteriograms

STUDY OBJECTIVES

Improvement in coronary artery endothelial function has been demonstrated after cholesterol lowering in hypercholesterolemic patients with significant atherosclerosis. However, to our knowledge, no previous study has shown improvement in resistance artery function in subjects with normal coronary arteries after cholesterol lowering. The purpose of our study was to investigate the effect of cholesterol lowering with pravastatin on coronary resistance artery endothelial function in the setting of angiographically normal coronary arteries.

METHODS

Invasive testing of coronary endothelial and vasomotor function was performed at baseline and after 6 months of pravastatin treatment in six patients with normal coronary arteriograms.

RESULTS

After 6 months of pravastatin treatment, low-density lipoprotein cholesterol level dropped from 157+/-11 to 117+/-8 mg/dL (p = 0.02) and percent increase in coronary blood flow after acetylcholine improved from 97+/-13% to 160+/-16% (p = 0.01). There was a trend (p = 0.17) toward enhanced epicardial dilation in response to acetylcholine after pravastatin treatment when compared with the baseline study.

CONCLUSIONS

Our study demonstrates significant improvement in coronary resistance artery endothelial function after 6 months of cholesterol lowering with pravastatin in six subjects presenting with chest pain who were found to have normal coronary arteriograms. A trend toward improved epicardial vasomotion was also observed.

Basal and reserve renal artery blood flow: effect of endothelium-dependent and -independent vasoactive agonists and radiographic contrast medium in two patients

This manuscript describes the results of invasive testing of renal artery and arteriolar reactivity in two patients using a panel of endothelium-dependent and -independent agents including radiographic contrast medium. We found that the renal artery and microcirculation dilate in response to graded acetylcholine infusions and to bolus nitroglycerin infusion; the renal microcirculation dilates in response to papaverine but constricts after adenosine and after radiographic contrast medium. Future indications for this testing are briefly discussed.

Spontaneous multivessel coronary artery dissection: repeated presentation in a healthy postmenopausal woman

Spontaneous coronary artery dissection is a rare cause of acute myocardial infarction which is infrequently diagnosed antemortem. Most previously reported cases were found in women of whom a significant proportion presented during pregnancy or the postpartum period. We describe the first antemortem case of spontaneous coronary artery dissection, unrelated to pregnancy or the postpartum state, which ultimately resulted in diffuse involvement of both the left and right coronary arteries over a period of 4 months. Pathophysiology and case management of this disorder are discussed.

Left ventricular free wall rupture during coronary intervention after acute myocardial infarction: report of two cases exhibiting fatal pseudocomplications

Two cases of left ventricular free wall rupture occurring in temporal relation to interventional coronary procedures are presented as autopsy-verified pseudocomplications. The possible impact of pseudocomplications on operator-specific registry data and credentialing is briefly discussed.

Heterogeneous vasomotor responses of coronary conduit and resistance vessels in hypertension

OBJECTIVES

The purpose of our study was to investigate the relation between conductance and resistance coronary vasomotor responsiveness in hypertensive patients without atherosclerosis.

BACKGROUND

Although similar in morphology, conduit and resistance coronary vessels differ importantly in size, function and local environment and appear to be differentially affected in certain disease processes, such as atherosclerosis and hypertension. However, little is known about the effect of hypertension on contiguous coronary conduit and resistance vessels in humans.

METHODS

Changes in coronary blood flow (a measure of resistance vessel reactivity) and coronary artery diameter (a measure of conduit vessel reactivity) were investigated in response to graded infusion of the endothelium-dependent agonist acetylcholine (ACh) in 98 patients with normal coronary arteries.

RESULTS

In 31 normotensive, euglycemic patients, conduit and resistance coronary artery responses to intracoronary infusion of ACh were significantly correlated (r = 0.73, p = 1 x 10[-6]), although eight patients (26%) had constriction of conduit but dilation of resistance arteries at peak effect. In 28 hypertensive patients without left ventricular hypertrophy (LVH), conduit and resistance artery responses to ACh remained significantly correlated (r = 0.5, p = 0.006), although 12 patients (43%) had discordant findings. Finally, in 39 hypertensive patients with LVH, conduit and resistance artery responses to ACh displayed the lowest correlation (r = 0.38, p = 0.02), with 22 patients (56%) demonstrating conduit artery constriction and resistance artery dilation.

CONCLUSIONS

Despite angiographically normal coronary arteries, heterogeneous vasomotor responses (dilation and constriction) were demonstrated in contiguous conduit and resistance arteries in normotensive and hypertensive patients referred for cardiac catheterization because of chest pain. In addition to more severe endothelial dysfunction among conduit and resistance arteries, a greater frequency of discordant conduit and resistance artery responses and resistance vessel constriction was found with increasing severity of hypertension. Our study suggests differing mechanisms of endothelium responsiveness to ACh among conduit and resistance coronary arteries.

Coronary vasomotor reactivity among normotensive African and white American subjects with chest pain

BACKGROUND AND OBJECTIVES

Excess cardiovascular morbidity and mortality among African (black) Americans is the subject of intensive investigation but the etiology remains speculative. One hypothesis proposes that inherent, or intrinsic, differences in coronary vascular reactivity and endothelial function predispose African Americans to enhanced vasoconstriction and/or depressed vasodilation, resulting in excess ischemia. The objective of this study was to establish whether coronary vasoreactivity differs among normotensive, nondiabetic African and white Americans with normal arteries referred for coronary arteriography because of chest pain.

PATIENTS AND METHODS

Eleven African American (8 female, 3 male) and 28 white American (9 female, 19 male) normotensive, euglycemic patients with normal coronary arteries were prospectively recruited for invasive testing of coronary artery and microvascular relaxation using the endothelium-dependent and -independent agents, acetylcholine and adenosine; a Doppler tipped intracoronary guidewire; and quantitative coronary angiography.

RESULTS

The study cohort consisted of 17 women (44%) and 22 men (56%) with a mean age of 46 +/- 10 yrs. Of 8 African American women, 6 were premenopausal and 2 were postmenopausal on estrogen replacement therapy. Of 9 white American women, 2 were premenopausal, 1 was 46-year old with a previous history of hysterectomy without ovariectomy, 2 were postmenopausal on estrogen replacement therapy, 2 were perimenopausal and 44- and 54-year old, and 2 were postmenopausal without estrogen replacement therapy. In response to maximal infusion of acetylcholine, epicardial coronary arteries and resistance vessels dilated similarly in black and white subjects. Dose-response curves revealed no significant racial differences during submaximal graded infusion of acetylcholine. In response to peak effect of adenosine, there were no racial differences in dilation of the microcirculation.

CONCLUSIONS

In the absence of hypertension, diabetes mellitus, and angiographic evidence of coronary artery disease, African American women demonstrate no evidence of intrinsic predisposition to enhanced coronary conduit vasoconstriction or depressed microcirculatory dilation in response to the endothelium-dependent and -independent vasodilator agonists-acetylcholine and adenosine-when compared with responses of similar white men and women. Because of low enrollment of black males, definitive conclusions cannot be drawn regarding this group.

Effect of African-American race and hypertensive left ventricular hypertrophy on coronary vascular reactivity and endothelial function

Excess cardiovascular morbidity and mortality among African (black) Americans remains an important yet unexplained public health problem. One possible explanation proposes that intrinsic or acquired abnormalities in coronary vascular reactivity and endothelial function result in excess ischemia among black Americans. To examine this hypothesis, we subjected 80 individuals with normal coronary arteries to invasive testing of coronary artery and microvascular relaxation using intracoronary infusions of acetylcholine and adenosine, a Doppler tipped intracoronary guide wire, and quantitative coronary angiography. We measured the percent increase in coronary blood flow and epicardial diameter after graded infusion of intracoronary acetylcholine and in coronary blood flow after intracoronary adenosine in 31 normotensive subjects (10 black, 21 white) and 49 hypertensive subjects with left ventricular hypertrophy (25 black, 24 white). Categorical and multivariate analyses revealed that in response to intracoronary adenosine and acetylcholine, the depression in endothelium-independent and -dependent microvascular relaxation during peak agonist effect was largely related to the presence of chronic hypertension and left ventricular hypertrophy. Normotensive subjects demonstrated no intrinsic racial differences in conduit and resistance vessel vasoreactivity. In response to maximal infusion of acetylcholine, epicardial coronary arteries constricted similarly in black and white subjects with hypertensive left ventricular hypertrophy and dilated similarly in normotensive black and white subjects. Thus, our study shows that in a cohort of black and white subjects referred for coronary arteriography because of chest pain, African American race is not associated with excess intrinsic or acquired depression in coronary vascular relaxation during the peak effect of the endothelium-dependent and -independent agonists acetylcholine and adenosine, after adjustment for the presence of left ventricular hypertrophy.

Coronary vasomotor function in a normotensive, nondiabetic referral population with normal coronary arteriograms

In a referral normal cardiac population, endothelium-independent coronary relaxation is nearly always normal, but endothelium-dependent relaxation may be depressed in a significant proportion of patients. Further study of the natural history of referral subjects with endothelial dysfunction is necessary to assess the potential cardiovascular risk of this finding in a presumed low-risk population.

Unstable angina. Pharmaceutical versus invasive therapy

Because unstable angina is often a precursor of myocardial infarction or death, patients with chest pain that persists for more than 20 minutes and is refractory to sublingual nitroglycerin should be hospitalized in an intensive care unit and given appropriate pharmacologic therapy. If symptoms persist despite adequate management with drugs, coronary arteriography should be performed and consideration given to an invasive procedure, such as angioplasty or coronary artery bypass grafting, for high-risk conditions. If necessary, the invasive procedure should be delayed until the patient's condition has stabilized.

Hypertensive heart disease. How does blood pressure affect left ventricular mass?

Currently, echocardiography is the most accepted tool for diagnosing the left ventricular hypertrophy that characterizes hypertensive heart disease; electrocardiography is not adequately sensitive. The symptoms and signs of coronary artery disease (CAD) and of hypertensive heart disease are similar and include angina, myocardial infarction, systolic and diastolic heart failure, atrial fibrillation, ventricular ectopy, and sudden death. Thallium stress testing is useful for excluding significant CAD; a positive test requires cardiac catheterization to eliminate large-vessel disease as the cause of myocardial ischemia. Regression of left ventricular hypertrophy is a treatment goal.

Racial differences in myocardial ischemia and coronary flow reserve in hypertension

OBJECTIVES

Using invasive measurements of endothelium-independent coronary flow reserve and stress thallium testing with or without dipyridamole, this study investigated racial differences in ischemia and coronary reserve in hypertensive left ventricular hypertrophy.

BACKGROUND

African Americans compared with Caucasian Americans appear to have a higher case fatality from coronary heart disease but lesser amounts of atherosclerotic coronary artery disease. This paradox may be explainable by intrinsic or acquired racial differences in coronary arteriolar autoregulation and vasoreactivity.

METHODS

The study enrolled 91 African and 81 Caucasian Americans referred for cardiac catheterization because of suspected myocardial ischemia but found to have no significant coronary stenosis. Patients were stratified by degree of left ventricular hypertrophy for comparison purposes after calculation of indexed left ventricular mass by means of echocardiographic M-mode measurements. Coronary flow reserve measurements were made using the intracoronary Doppler catheter and hyperemic doses of intravenous dipyridamole in 100 patients and intracoronary papaverine and adenosine in 72 patients. Seventy-seven percent of patients underwent adequate stress thallium testing with or without dipyridamole.

RESULTS

In African Americans, mean (+/- SD) coronary flow reserve decreased from 4.4 +/- 2.3 for 38 without mass hypertrophy to 3.2 +/- 1.3 for 53 with hypertrophy (p = 0.005) to 2.7 +/- 1.1 for 12 with severe hypertrophy (p = 0.02). Thallium testing was abnormal in 31% of those without mass hypertrophy and 59% of those with hypertrophy. In Caucasian Americans, coronary flow reserve decreased from 4.1 +/- 2 for 58 without hypertrophy to 3.6 +/- 1.5 for 23 with hypertrophy (p = NS) to 3 +/- 1.5 for 6 with severe hypertrophy (p = NS). Thallium testing was abnormal in 36% without mass hypertrophy and in 39% with hypertrophy.

CONCLUSIONS

This study establishes that development of left ventricular hypertrophy in hypertension carries greater physiologic morbidity for African compared with Caucasian Americans, typified by marked reduction in endothelium-independent coronary flow reserve and increased frequency of abnormal thallium tests.

Correction of left ventricular ischemia in blacks with hypertensive heart disease

Among hypertensive patients, blacks are more likely than whites to have ischemia by electrocardiographic and 201Tl-myocardial stress imaging, possibly due to racial differences in the regulation of coronary blood flow or velocity. This investigation was undertaken to determine whether intensive antihypertensive therapy with two or more drugs can correct or reduce ischemia in black hypertensive patients. Thallium myocardial stress imaging and electrocardiographic and echocardiographic studies were performed on 13 black patients with essential hypertension and ischemic heart disease due to hypertensive heart disease (without significant obstructive epicardial coronary artery disease). The studies were made at baseline and after 4 to 48 months of intensive treatment, with a calcium antagonist and an angiotensin converting enzyme (ACE) inhibitor as the main components of the antihypertensive drug regimen. The majority of the patients with abolition or reversal of myocardial ischemia documented by 201Tl-myocardial imaging also had a significant reduction in left ventricular mass (LVM). However, some patients either did not have LV hypertrophy at baseline or had changes in LVM beyond the precision of the echocardiographic M-mode mass calculations. The finding indicated that factors other than reduction of LVM were involved in the reversal of the ischemia. The most likely factor was a change in the regulation of coronary blood flow. Reduction in LVM and reversal of myocardial ischemia determined either by electrocardiography or by thallium myocardial imaging studies may be considered indicators of the effectiveness of treatment.

Long-term severe pulmonary hypertension associated with right atrial myxoma

An 18-year-old black woman presented with marginally compensated right heart failure, severe pulmonary hypertension, tricuspid incompetence, and right atrial myxoma. Catheterization suggested a substantial reactive component to her P-HTN, especially to nifedipine. Initial management consisted of excision of two right atrial myxomas and tricuspid annuloplasty, and postdischarge management with nifedipine, 30 mg four times daily. Emergency pulmonary thromboendarterectomy was required two weeks later for acute cor pulmonale. It is suggested that concomitant procedures are mandatory in this setting because of the otherwise accelerated adverse pathophysiology of obliterative pulmonary vascular obstructive disease.

Postpartum myocardial infarction treated by balloon coronary angioplasty

Acute myocardial infarction in pregnancy is a rare event that carries substantial morbidity and mortality. New technologies have been developed in cardiology to open obstructed vessels during the acute evolution of coronary thrombosis. We present a case of acute postpartum myocardial infarction in a woman with class F/R diabetes. She underwent successful balloon angioplasty but developed chest pain suspicious of angina pectoris 6 weeks after the procedure. A thallium scan demonstrated fixed defects in the inferoposterior and posterolateral segments and minimal apical redistribution. This represents the second case of angioplasty performed in pregnancy and the first for an acute myocardial infarction.

Pharmacotherapy of unstable angina

All patients with unstable angina should be admitted to a coronary or an intensive care unit. There should be an attempt to classify the patient according to the proposed Braunwald nomenclature. If the patient has a secondary cause for unstable angina (e.g., tachyarrhythmia, heart failure, fever, thyrotoxicosis, severe hypertension, hypoxia, unusual emotional stress, or anemia), this condition should be treated initially with therapy specific for that etiology. If the patient does not have a secondary etiology, therapy should be initiated with nitrates, preferably intravenous nitroglycerin. Heparin should be concomitantly administered. If the patient cannot receive heparin, aspirin should be initiated. All patients should receive beta-blockers. If the patient cannot take a beta-blocker, a calcium antagonist (probably diltiazem) should be initiated. However, if the patient is refractory to beta-blockers, the dihydropyridine nifedipine should be added. Failure to all pharmacologic interventions necessitates a progressive invasive approach dictated by the potential surgical risk of the patient. Long-term aspirin and beta-blockers should be strongly considered.

Case report: acute presentation of pseudo myocardial infarction secondary to metastatic cancer

Electrocardiographic ST segment changes that mimic myocardial infarction (MI) may occur secondary to metastatic carcinoma. Presented here is a case in which symptomatology suggestive of acute MI occurred with impressive new anterior ST segment elevation in a patient with a history of laryngeal carcinoma. Clinical options in this setting are discussed, including use of thrombolytic agents and acute catheterization.

A negative thallium (+/- dipyridamole) stress test excludes significant obstructive epicardial coronary artery disease in hypertensive patients

The operating characteristics of thallium stress testing for detection of significant epicardial coronary artery disease (CAD) in hypertensive subjects with chest pain or electrocardiographic (ECG) ischemia have not been previously defined. This becomes important because of the high prevalence of both hypertensive heart disease and CAD. Ninety-two hypertensives with a history of typical or atypical chest pain or ECG myocardial ischemia underwent coronary arteriography, 2D-guided echocardiography, and thallium-201 stress testing, combined with intravenous dipyridamole if the rate-pressure product was less than 20,000. Patients with myocardial infarction, prior revascularization procedure, valvular heart disease, and chronic ethanol abuse were excluded. The mean age was 54.8 +/- 9.9 years with 55% blacks and 46% women. Eighteen patients (19.6%) had significant (greater than or equal to 50% luminal diameter narrowing) epicardial CAD at catheterization, of whom 17 had positive thallium scans. Overall, there were 17 true positives, 47 true negatives, 27 false positives, and one false negative resulting in 94.4 +/- 5.4% sensitivity (95% confidence limits [95% CL] 71 to 100%), 63.5 +/- 5.6% specificity (95% CL 51 to 74%), 38.6 +/- 7.3% positive predictive value (95% CL 25 to 54%), 97.9 +/- 2.1% negative predictive value (95% CL 88 to 100%), and 69.6 +/- 4.8% overall accuracy (95% CL 59 to 79%). For hypertensive patients with chest pain or ECG myocardial ischemia, the high sensitivity and negative predictive value and low false negative rate support the role of thallium stress testing +/- dipyridamole as an exclusion test for significant CAD.