Phillip H. Kuo

Evaluations of extracellular pH within in vivo tumors using acidoCEST MRI.

A practical, noninvasive method is needed to measure the extracellular pH (pHe) within in vivo tumors to longitudinally monitor tumor acidosis. We have optimized a biomedical imaging method, termed acidoCEST MRI, to provide noninvasive assessments of tumor pHe in preclinical models of mammary carcinoma.

Gadolinium-Containing MRI Contrast Agents: Important Variations on a Theme for NSF

Millions of doses of gadolinium-based contrast agents (GBCAs) are administered annually to improve the clinical utility of magnetic resonance imaging. All the approved agents incorporate one atom of the rare earth metal gadolinium into a chelate to improve the safety of the ordinarily toxic free gadolinium. The undeniable epidemiologic link between GBCAs and nephrogenic systemic fibrosis (NSF) has prompted renewed investigation into the different chemical properties of the GBCAs despite their clinical interchangeability. Gadolinium-based contrast agents can be divided into different categories: linear versus macrocyclic structure, ionic versus nonionic, and non-protein-binding versus protein-binding agents. The GBCAs differ significantly with respect to transmetallation and kinetic and thermodynamic stability and therefore their propensity to release free gadolinium, which is hypothesized to induce NSF. That gadodiamide, with its susceptibility to transmetallation and relatively low thermodynamic and kinetic stability, is associated with the most cases of NSF supports this hypothesis. On the other hand, the greater stability of a macrocyclic agent hypothetically would confer a greater safety margin with regard to NSF. Because few published data on an experimental model of NSF exist, continuing vigilance is necessary to report new cases of NSF, especially with regard to the agents with small market share.

Stability and functionality of cysteine-less FOF1 ATP synthase from Escherichia coli

All 21 native cysteines in the Escherichia coli FOF1 ATP synthase were replaced by alanines. In isolated E. coli membranes, ATP‐dependent proton pumping, turnover of ATP hydrolysis and steady‐state transition state thermodynamic parameters of the cysteine‐less enzyme were similar to wild‐type. The cysteine‐less enzyme was solubilized in n‐octyl β‐d‐glucopyranoside, purified by affinity chromatography, and reconstituted into pre‐formed liposomes made from E. coli lipids. The properties of the reconstituted, purified enzyme were not significantly different from the membranous enzyme. These data demonstrate that cysteine‐less FOF1 is biochemically stable and has functionality similar to wild‐type.

Gadolinium-containing magnetic resonance image contrast agent promotes fibrocyte differentiation

Gadolinium‐containing magnetic resonance imaging (MRI) contrast agents such as Omniscan are associated with nephrogenic systemic fibrosis (NSF). To determine if Omniscan can affect the differentiation of monocytes into fibroblast‐like cells called fibrocytes that are found in the fibrotic lesions of NSF, peripheral blood mononuclear cells (PBMCs) from NSF patients, hemodialysis patients without NSF, and healthy, renally sufficient controls were exposed to Omniscan in a standardized in vitro fibrocyte differentiation protocol. When added to PBMCs, the gadolinium‐containing MRI contrast agent Omniscan generally had little effect on fibrocyte differentiation. However, 10−8 to 10−3 mg/mL Omniscan reduced the ability of the fibrocyte differentiation inhibitor serum amyloid P (SAP) to decrease fibrocyte differentiation in PBMCs from 15 of 17 healthy controls and one of three NSF patients. Omniscan reduced the ability of SAP to decrease fibrocyte differentiation from purified monocytes, indicating that the Omniscan effect does not require the presence of other cells (such as T cells) in the PBMCs. Omniscan also reduced the ability of a different fibrocyte differentiation inhibitor, interleukin‐12, to decrease fibrocyte differentiation. These data suggest that Omniscan interferes with the regulatory action of signals that inhibit the differentiation of monocytes to fibrocytes. J. Magn. Reson. Imaging 2009;30:1284–1288.

Molecular mechanisms of rotational catalysis in the F0F1 ATP synthase

Rotation of the F(0)F(1) ATP synthase gamma subunit drives each of the three catalytic sites through their reaction pathways. The enzyme completes three cycles and synthesizes or hydrolyzes three ATP for each 360 degrees rotation of the gamma subunit. Mutagenesis studies have yielded considerable information on the roles of interactions between the rotor gamma subunit and the catalytic beta subunits. Amino acid substitutions, such as replacement of the conserved gammaMet-23 by Lys, cause altered interactions between gamma and beta subunits that have dramatic effects on the transition state of the steady state ATP synthesis and hydrolysis reactions. The mutations also perturb transmission of specific conformational information between subunits which is important for efficient conversion of energy between rotation and catalysis, and render the coupling between catalysis and transport inefficient. Amino acid replacements in the transport domain also affect the steady state catalytic transition state indicating that rotation is involved in coupling to transport.

Nephrogenic Systemic Fibrosis

There seems to be an association between exposure to intravenous gadolinium-based contrast agents (GBCAs) and nephrogenic systemic fibrosis (NSF), a debilitating and sometimes fatal disease. This article addresses the relationship between GBCAs and NSF and answers some common questions. The policy deployed at Yale-New Haven Hospital for prevention of NSF and screening for patients at risk is delineated and discussed along with recommendations by the Food and Drug Administration.

FDG-PET/CT for the evaluation of response to therapy of cutaneous T-cell lymphoma to vorinostat (suberoylanilide hydroxamic acid, SAHA) in a phase II trial.

IntroductionHarnessing the power of molecular imaging in particular positron emission tomography (PET) to assess response to therapy in early clinical trials has the potential to yield crucial data on efficacy and streamline drug development. Vorinostat (also known as SAHA, suberoylanilide hydroxamic acid) is a histone deacetylase (HDAC) inhibitor which alters gene transcription to inhibit proliferation and promote apoptosis.MethodsIn a phase II trial of vorinostat for cutaneous T cell lymphoma (CTCL), 2-deoxy-2-[F-18]fluoro-d-glucose (FDG)-PET/computed tomography (CT) was performed on patients with both cutaneous and nodal disease. FDG-PET/CT fuses the power of metabolic imaging from FDG-PET with the anatomic detail of CT. Scans were conducted on subjects pre-therapy and during therapy.ResultsChanges in the values of FDG uptake and measurements of nodal dimensions and thickness of cutaneous lesions were tabulated. FDG-PET/CT provided an objective measure of the response (or lack thereof) of both cutaneous and nodal disease to therapy with vorinostat. The results of this study are encouraging for the potential utility of FDG-PET/CT in future trials with HDAC inhibitors for other diseases and for CTCL with other therapies.ConclusionFurther study will be required to determine the prognostic value of the initial PET/CT scan and response on follow-up scans.

Clinical Translation of Tumor Acidosis Measurements with AcidoCEST MRI

PurposeWe optimized acido-chemical exchange saturation transfer (acidoCEST) magnetic resonance imaging (MRI), a method that measures extracellular pH (pHe), and translated this method to the radiology clinic to evaluate tumor acidosis.ProceduresA CEST-FISP MRI protocol was used to image a flank SKOV3 tumor model. Bloch fitting modified to include the direct estimation of pH was developed to generate parametric maps of tumor pHe in the SKOV3 tumor model, a patient with high-grade invasive ductal carcinoma, and a patient with metastatic ovarian cancer. The acidoCEST MRI results of the patient with metastatic ovarian cancer were compared with DCE MRI and histopathology.ResultsThe pHe maps of a flank model showed pHe measurements between 6.4 and 7.4, which matched with the expected tumor pHe range from past acidoCEST MRI studies in flank tumors. In the patient with metastatic ovarian cancer, the average pHe value of three adjacent tumors was 6.58, and the most reliable pHe measurements were obtained from the right posterior tumor, which favorably compared with DCE MRI and histopathological results. The average pHe of the kidney showed an average pHe of 6.73 units. The patient with high-grade invasive ductal carcinoma failed to accumulate sufficient agent to generate pHe measurements.ConclusionsOptimized acidoCEST MRI generated pHe measurements in a flank tumor model and could be translated to the clinic to assess a patient with metastatic ovarian cancer.

Male primary breast cancer found on FDG-PET/CT.

We report a case of male primary breast cancer found incidentally on whole body FDG-PET/CT scanning with mammographic and histologic correlation. The relative lack of glandular activity in the male breast potentially increases the sensitivity of FDG-PET/CT for detection of male breast cancer. As in this case, even mild uptake in a male breast lesion should be regarded with suspicion. Although the incidental detection of breast masses on whole body FDG-PET/CT requires great vigilance, the modality provides both anatomic and physiologic data to help characterize primary breast cancer.

18F sodium fluoride PET/CT detects osseous metastases from breast cancer missed on FDG PET/CT with marrow rebound.

Intense FDG uptake by bone marrow following recent chemotherapy limits evaluation for osseous metastases. The impact of marrow rebound on accuracy of (18)F-fluoride PET/CT is unclear. A 73-year-old woman with breast cancer presented for restaging FDG PET/CT, which showed intense activity throughout almost the entire axial skeleton and no osseous metastases. An (18)F-fluoride PET/CT performed 7 days later identified multiple osseous metastases in the spine, ribs, and pelvis. This case demonstrates that (18)F-fluoride PET/CT should be considered for the evaluation of osseous metastases in patients with rebound marrow uptake on FDG PET/CT.