Faculty Bibliography

Trabecular bone structure is known to play a crucial role in the overall strength, and thus fracture risk, of such areas of the skeleton as the vertebrae, spine, femur, tibiae, or radius. Several MR methods devoted to probing this structure depend upon the susceptibility difference between the solid bone matrix and the intervening fluid/marrow/fat, usually in the context of a linewidth (1/T(2)') measurement or mapping technique. A recently demonstrated new approach to this system involves using internal gradients to encode diffusion weighting, and extracting structural information (e.g., surface-to-volume ratio) from the resulting signal decay. This contrast method has been demonstrated in bulk measurements on cleaned, water-saturated bovine trabecular bone samples. In the present work, microscopic imaging (0.156 mm in-plane resolution) is performed in order to spatially resolve this contrast on the trabecular level, and confirm its interpretation for the bulk measurements. It is found that the local rate of decay due to diffusion in the internal field (DDIF) is maximal close to the trabecular surfaces. The overall decay rate in a lower resolution scan probes the abundance of these surfaces, and provides contrast beyond that found in conventional proton density weighted or T(1)-weighted imaging. Furthermore, a microscopic calculation of internal field distributions shows a qualitative distinction between the structural sensitivities of DDIF and T(2)'. DDIF contrast is highly localized around trabecular walls than is the internal field itself, making it a less sensitive but more specific measure of such important properties as trabecular number

Cancer/testis (CT) antigens are the protein products of germ line-associated genes that are activated in a wide variety of tumors and can elicit autologous cellular and humoral immune responses. CT antigens can be divided between those that are encoded on the X chromosome (CT-X antigens) and those that are not (non-X CT antigens). Among the CT-X antigens, the melanoma antigen gene (MAGE) family, defined by a shared MAGE homology domain (MHD), is the largest. CT-X genes are frequently expressed in a coordinate manner in cancer cells, and their expression appears to be modulated by epigenetic mechanisms. The expression of CT-X genes is associated with advanced disease and poor outcome in different tumor types. We used the yeast two-hybrid system to identify putative MHD-interacting proteins. The MHD of MAGE-C1 (CT7) was used as bait to screen a human testis cDNA library. This study identified NY-ESO-1 (CT6) as a MAGE-C1 binding partner. Immunoprecipitation and immunofluorescence staining confirmed MAGE-C1 interaction with NY-ESO-1, and cytoplasmic co-localization of both proteins in melanoma cells. Co-expression of these two genes was found to occur in cancer cell lines from different origins, as well as in primary tumors (multiple myeloma and non-small cell lung cancer samples). This is the first report of direct interaction between two CT antigens and may be pertinent in the light of the frequently coordinated expression of these proteins

Cell cycle deregulation is central to the initiation and fatality of multiple myeloma, the second most common hematopoietic cancer, although impaired apoptosis plays a critical role in the accumulation of myeloma cells in the bone marrow. The mechanism for intermittent, unrestrained proliferation of myeloma cells is unknown, but mutually exclusive activation of cyclin-dependent kinase 4 (Cdk4)-cyclin D1 or Cdk6-cyclin D2 precedes proliferation of bone marrow myeloma cells in vivo. Here, we show that by specific inhibition of Cdk4/6, the orally active small-molecule PD 0332991 potently induces G(1) arrest in primary bone marrow myeloma cells ex vivo and prevents tumor growth in disseminated human myeloma xenografts. PD 0332991 inhibits Cdk4/6 proportional to the cycling status of the cells independent of cellular transformation and acts in concert with the physiologic Cdk4/6 inhibitor p18(INK4c). Inhibition of Cdk4/6 by PD 0332991 is not accompanied by induction of apoptosis. However, when used in combination with a second agent, such as dexamethasone, PD 0332991 markedly enhances the killing of myeloma cells by dexamethasone. PD 0332991, therefore, represents the first promising and specific inhibitor for therapeutic targeting of Cdk4/6 in multiple myeloma and possibly other B-cell cancers

NAD(+)-linked 15-hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes the oxidation of 15(S)-hydroxyl group of prostaglandins and lipoxins resulting in the formation of 15-keto metabolites which exhibit greatly reduced biological activities. Therefore, this enzyme has been considered the key enzyme responsible for the inactivation of prostaglandins and lipoxins. Both the cDNA and the genomic DNA of the 15-PGDH gene have been cloned. Structural characterization, transcriptional regulation and biological functions of this enzyme have been investigated. Molecular modeling corroborated with site-directed mutagenesis has identified key residues and domains involved in coenzyme and substrate binding. Catalytic mechanism has been proposed. Studies on the regulation of enzyme expression and activity by physiological and pharmacological agents have begun to uncover its significant roles in cancer, inflammation and reproduction. Apparently, 15-PGDH works with cyclooxygenase-2 to control the cellular levels of prostaglandins. Their reciprocal regulation within the same cells appears to determine the fate of the cells. Because of its ability to inactivate both prostaglandins and lipoxins of two opposite biological activities, the roles of 15-PGDH in cancer and inflammation are particularly intriguing and challenging. Future investigations in these areas are warranted.

Multiple myeloma, the second most common hematopoietic cancer, ultimately becomes refractory to treatment when self-renewing multiple myeloma cells begin unrestrained proliferation by unknown mechanisms. Here, we show that one, but not more than one, of the three early G(1) D cyclins is elevated in each case of multiple myeloma. Cyclin D1 or D3 expression does not vary in the clinical course, but that alone is insufficient to promote cell cycle progression unless cyclin-dependent kinase 4 (cdk4) is also elevated, in the absence of cdk6, to phosphorylate the retinoblastoma protein (Rb). By contrast, cyclin D2 and cdk6 are coordinately increased, thereby overriding the inhibition by cdk inhibitors p18(INK4c) and p27(Kip1) and phosphorylating Rb in conjunction with the existing cdk4. Thus, cyclin D1 pairs exclusively with cdk4 and cdk6 pairs only with cyclin D2, although cyclin D2 can also pair with cdk4 in multiple myeloma cells. The basis for this novel and specific cdk/D cyclin pairing lies in differential transcriptional activation. In addition, cyclin D1- or cyclin D3-expressing multiple myeloma cells are uniformly distributed in the bone marrow, whereas cdk6-specific phosphorylation of Rb occurs in discrete foci of bone marrow multiple myeloma cells before proliferation early in the clinical course and is then heightened with proliferation and disease progression. Mutually exclusive cdk4/cyclin D1 and cdk6/cyclin D2 pairing, therefore, is likely to be a critical determinant for cell cycle reentry and progression and may play a pivotal role in the expansion of self-renewing multiple myeloma cells

Multiple myeloma is a malignancy of plasma cells. Vaccine immunotherapy is among the novel therapeutic strategies under investigation for this disease. To identify myeloma-associated antigens as potential targets for vaccine immunotherapy, we surveyed a comprehensive panel of bone marrow specimens from patients with monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma for expression of cancer-testis (CT) antigens. Immunohistochemistry (IHC) demonstrated that 82% of stage-III myeloma specimens expressed the CT antigen CT7 (also known as melanoma antigen C1 [MAGE-C1]) and 70% expressed MAGE-A3/6. Messenger RNA for CT7 and MAGE-A family members was detected in 87% and 100% of stage-III samples, respectively. CT7 protein expression increased with advanced stage of disease. Higher levels of CT7 and MAGE-A3/6 proteins also correlated with elevated plasma-cell proliferation. These results show that CT7 and MAGE-A3/6 are promising myeloma-associated antigens for application in vaccine immunotherapy. Furthermore, the common expression and correlation with proliferation suggest a possible pathogenic role for these proteins in myeloma