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Summary:Cerebral metabolic rate for oxygen (CMRO 2 ) and cerebral oxygen extraction fraction (OEF) are some of the most fundamental parameters to characterize the pathophysiologic status of cerebral tissue. Although O-15-labeled gases inhalation method is performed in clinical studies, application of the inhalation method on small animals requires too many intensive procedures. On this basis, the development of a new method to measure CMRO 2 and OEF in small animals is of interest. This study was aimed at developing a method to assess CMRO 2 and OEF using intravenously injectable oxygen (injectable 15

C-11- and I-123-labeled long chain fatty acid derivatives have been reported as useful radiopharmaceuticals for the estimation of myocardial fatty acid metabolism. We have reported that Tc-99m-labeled N-[[[(2-mercaptoethyl)amino]carbonyl]methyl]-N-(2-mercaptoethyl)-6-aminohexanoic acid ([99mTc]MAMA-HA), a medium chain fatty acid derivative, is metabolized by β-oxidation in the liver and that the MAMA ligand is useful for attaching to the omega-position of fatty acid derivatives as a chelating group for Tc-99m. On the basis of these findings, we focused on developing a Tc-99m-labeled long chain fatty acid derivative that reflected fatty acid metabolism in the myocardium. In this study, we synthesized a dodecanoic acid derivative, MAMA-DA, and a hexadecanoic acid derivative, MAMA-HDA, and performed radiolabeling and biodistribution studies. [99mTc]MAMA-DA and [99mTc]MAMA-HDA were prepared using a ligand-exchange reaction. Biodistribution studies were carried out in normal mice and rats. Then, a high initial uptake of Tc-99m was observed, followed by a rapid clearance from the heart. The maximum heart/blood ratio was 3.6 at 2 min postinjection of [99mTc]MAMA-HDA. These kinetics were similar to those with postinjection of p-[125I]iodophenylpentadecanoic acid. Metabolite analysis showed [99mTc]MAMA-HDA was metabolized by β-oxidation in the body. In conclusion, [99mTc]MAMA-HDA is a promising compound as a long chain fatty acid analogue for estimating β-oxidation of fatty acid in the heart.

Mitochondrial membrane potential (Δψm) alteration is an important target for cancer diagnosis. In this study, we designed a series of near-infrared fluorescent cationic cyanine dyes with varying alkyl chain lengths (IC7-1 derivatives) to provide diverse lipophilicities and serum albumin-binding rates, and we evaluated the usefulness of these derivatives for in vivo Δψm imaging. IC7-1 derivatives with side chains from methyl to hexyl (IC7-1-Me to IC7-1-He) were synthesized, and their optical properties were measured. Cellular uptake and intracellular distribution were investigated with depolarized HeLa cells from carbonyl cyanine m-chlorophenylhydrazone (CCCP) treatment using a spectrofluorometer and a fluorescence microscope. Serum albumin-binding rates were evaluated using albumin-binding inhibitors. In vivo optical imaging was performed with HeLa cell xenograft mice following intravenous administration of IC7-1 derivatives with or without warfarin and CCCP as in vivo blocking agents. IC7-1 derivatives showing maximum excitation and emission wavelengths at 823 nm and ∼845 nm, respectively, were synthesized. IC7-1-Me to -Bu showed fluorescence in mitochondria that decreased with CCCP treatment in a concentration-dependent manner, which showed that IC7-1-Me to -Bu successfully indicated Δψm. Tumors were clearly visualized after IC7-1-Bu administration. Treatment with warfarin or CCCP significantly decreased IC7-1-Bu fluorescence in the tumor region. In summary, IC7-1-Bu exhibited fluorescence localized to mitochondria dependent on Δψm, which enabled clear in vivo tumor imaging via serum albumin as a drug carrier for effective tumor targeting. Our data suggest that IC7-1-Bu is a promising NIR probe for in vivo imaging of the altered Δψm of tumor cells.

Membrane type-1 matrix metalloproteinase (MT1-MMP) expressed on the tumor cell surface activates pro-MMP-2 and pro-MMP-13 to exacerbate the malignancy, suggesting its suitability as a target molecule for diagnosis by in vivo molecular imaging. Thus, we prepared radiolabeled anti-MT1-MMP monoclonal antibody (mAb) as a novel radiolabeled probe for detecting MT1-MMP in vivo and evaluated its usefulness in breast tumor-bearing rodents. Tc-anti-MT1-MMP mAb was prepared using HYNIC as a bifunctional chelating agent and immunoreactivity was evaluated by flow cytometry. MT1-MMP expression in breast carcinoma cells (rat: Walker-256 and MRMT-1, mouse: FM3A) was measured by Western blotting. In vivo biodistribution was examined for 48 h using tumor-implanted rodents followed by estimation of radiation absorbed by a standard quantitation platform Organ Level Internal Dose Assessment (OLINDA).

Photoacoustic (PA) imaging has emerged as a noninvasive diagnostic method which detects ultrasonic waves thermoelastically induced by optical absorbers irradiated with laser. For tumor diagnosis, PA contrast agent has been proposed to enhance the PA effect for detecting tumors sensitively. Here, we prepared a human serum albumin (HSA) conjugated with indocyanine green (ICG) as a PA contrast agent allowing enhanced permeability and retention effect for sensitive tumor imaging. The feasibility of PA imaging with HSA-ICG to detect allografted tumors was evaluated in tumor-bearing mice. In vivo fluorescence imaging and radiolabeled biodistribution study showed that the biodistribution dramatically changed as the number of ICG bound to HSA increased, and the maximum accumulation of ICG was achieved when around three ICG molecules were loaded on an HSA. In vivo PA imaging demonstrated a tumor-selective and dose-dependent increase of PA signal intensity in mice injected with HSA-ICG (R2 = 0.88, 387% increase for HSA-ICG, 104 nmol ICG). In conclusion, HSA-ICG clearly visualized the allografted tumors with high tumor-to-background ratios having high quantitative and spatial resolution for the sensitive PA imaging of tumors. HSA-ICG could be useful as a favorable contrast agent for PA tumor imaging for the management of cancer.

We developed an intramuscular granuloma rat model that showed a high FDG uptake comparable to that of the tumor. The effect of prednisolone pretreatment on FDG uptake was greater in the granuloma than in the tumor. These results suggest that BCG-induced granuloma may be a valuable model and may provide a biological basis for FDG studies.

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