Dedicated high-resolution small animal imaging systems have recently emerged as important new tools for cancer research. These new imaging systems permit researchers to noninvasively screen animals for mutations or pathologies and to monitor disease progression and response to therapy. One imaging modality, X-ray microcomputed tomography (microCT) shows promise as a cost-effective means for detecting and characterizing soft-tissue structures, skeletal abnormalities, and tumors in live animals. MicroCT systems provide high-resolution images (typically 50 microns or less), rapid data acquisition (typically 5 to 30 minutes), excellent sensitivity to skeletal tissue and good sensitivity to soft tissue, particularly when contrast-enhancing media are employed. The development of microCT technology for small animal imaging is reviewed, and key considerations for designing small animal microCT imaging protocols are summarized. Recent studies on mouse prostate, lung and bone tumor models are overviewed.

Abstract. The ot6//34 complex is a member of the integrin family of adhesion receptors. It is found on a variety of epithelial cell types, but is most strongly expressed on stratified squamous epithelia. Fluorescent antibody staining of human epidermis suggests that the /~4 subunit is strongly localized to the basal region showing a similar distribution to that of the 230-kD bullous pemphigoid antigen. The or6 subunit is also strongly localized to the basal region but in addition is present over the entire surfaces of basal cells and some cells in the immediate suprabasal region. By contrast staining for ~31, o~2, and o~3 subunits was very weak basally, but strong on all other surfaces of basal epidermal cells. These results suggest that different integrin complexes play differing roles in cell-cell and cell-matrix adhesion in the epidermis.Immunoelectron microscopy showed that the a6/~4 complex at the basal epidermal surface is strongly localized to hemidesmosomes. This result provides the first well-characterized monoclonal antibody markers for hemidesmosomes and suggests that the ot6//34 complex plays a major role in epidermal cell-basement membrane adhesion. We suggest that the cytoplasmic domains of these transmembrane glycoproteins may contribute to the structure of hemidesmosomal plaques. Immunoultrastructural localization of the BP antigen suggests that it may be involved in bridging between hemidesmosomal plaques and keratin intermediate filaments of the cytoskeleton.

Distearoyl-N-(3-carboxypropionoyl poly(ethylene glycol) succinyl)phosphatidylethanolamine (DSPE-PEG-COOH) was newly synthesized and used to prepare novel immunoliposomes carrying monoclonal antibodies at the distal ends of the PEG chains (Type C). Liposomes were prepared from egg phosphatidylcholine (ePC) and cholesterol (CH) (2;1, m/m) containing 6 mol% of DSPE-PEG-COOH, and a monoclonal IgG antibody, 34A, which is highly specific to pulmonary endothelial cells, was conjugated to the carboxyl groups of DSPE-PEG-COOH to give various amounts of antibody molecules per liposome. Other immunoliposomes with PEG coating (Type B) or without PEG coating (an earlier type of immunoliposome, Type A) were prepared for comparison. The average molecular weight of PEG in Type B or C immunoliposomes was 2000. Type B and Type C liposomes without antibodies showed prolonged circulation time and reduced reticulo-endothelial system (RES) uptake owing to the presence of PEG. These three different types of 34A-immunoliposomes with 30-35 antibody molecules per vesicle were injected into mice to test the immunotargetability to the lung. The efficiency of lung binding of 34A-Type B was one-half of that of 34A-Type A, though a large amount of 34A-Type B remained in the blood circulation for a long time, suggesting that the steric hindrance of PEG chains reduced not only the immunospecific antibody-antigen binding, but also the RES uptake. The degree of lung binding of 34A-Type C was about 1.3-fold higher than that of 34A-Type A, indicating that recognition by the antibodies attached to the PEG terminal was not sterically hindered and that the free PEG (i.e., that not carrying antibody) was effective in increasing the blood concentration of immunoliposomes by enabling them to evade RES uptake. The latter phenomenon was confirmed by using nonspecific antibody-Type C immunoliposomes (14-Type C), which showed a high blood level for a long time. Our approach provides a simple means of conjugating antibodies directly to the distal end of PEG which is already bound to the liposome membrane, and should contribute to the development of superior targetable drug delivery vehicles for use in diagnostics and therapy.

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Heparan sulfate proteoglycans (HSPGs) are ubiquitous components of pathologic amyloid deposits in the organs of patients with disorders such as Alzheimer's disease or systemic light chain (AL) or reactive (AA) amyloidosis. Molecular imaging methods for early detection are limited and generally unavailable outside the United Kingdom. Therefore, there is an urgent need to develop novel, specific amyloidophilic radiotracers for imaging to assist in diagnosis, prognostication, and monitoring response to therapy. Amyloid-associated HSPG can be differentiated from HSPG found in surrounding healthy cells and tissues by the preferential binding of certain HS-reactive single chain variable fragments and therefore, represents a biomarker that can be targeted specifically with appropriate reagents. Using a murine model of AA amyloidosis, we have examined the in vivo amyloid reactivity of seven heparin-binding peptides by using single photon emission and X-ray computed tomographic imaging, microautoradiography, and tissue biodistribution measurements. All of the peptides bound amyloid deposits within 1 h post-injection, but the extent of the reactivity differed widely, which was evidenced by image quality and grain density in autoradiographs. One radiolabeled peptide bound specifically to murine AA amyloid in the liver, spleen, kidney, adrenal, heart, and pancreas with such avidity that it was observed in single photon emission tomography images as late as 24 h post-injection. In addition, a biotinylated form of this peptide was shown histochemically to bind human AA, ALκ, ALλ, transthyretin amyloidosis (ATTR), and Aβ amyloid deposits in tissue sections. These basic heparin-binding peptides recognize murine and human amyloid deposits in both in vivo and ex vivo tissues and therefore, have potential as radiotracers for the noninvasive molecular imaging of amyloid deposits in situ.