Immunological techniques

Cancer Metabolism and Tumor Heterogeneity: Imaging Perspectives Using MR Imaging and Spectroscopy

Cancer cells reprogram their metabolism to maintain viability via genetic mutations and epigenetic alterations, expressing overall dynamic heterogeneity. The complex relaxation mechanisms of nuclear spins provide unique and convertible tissue contrasts, making magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) pertinent imaging tools in both clinics and research. In this review, we summarized MR methods that visualize tumor characteristics and its metabolic phenotypes on an anatomical, microvascular, microstructural, microenvironmental, and metabolomics scale. The review will progress from the utilities of basic spin-relaxation contrasts in cancer imaging to more advanced imaging methods that measure tumor-distinctive parameters such as perfusion, water diffusion, magnetic susceptibility, oxygenation, acidosis, redox state, and cell death. Analytical methods to assess tumor heterogeneity are also reviewed in brief. Although the clinical utility of tumor heterogeneity from imaging is debatable, the quantification of tumor heterogeneity using functional and metabolic MR images with development of robust analytical methods and improved MR methods may offer more critical roles of tumor heterogeneity data in clinics. MRI/MRS can also provide insightful information on pharmacometabolomics, biomarker discovery, disease diagnosis and prognosis, and treatment response. With these future directions in mind, we anticipate the widespread utilization of these MR-based techniques in studying in vivo cancer biology to better address significant clinical needs.

Cancer heterogeneity is not compatible with one unique cancer cell metabolic map

The Warburg effect and its accompanying metabolic features (anaplerosis, cataplerosis) are presented in textbooks and reviews as a hallmark (general characteristic): the metabolic map of cancer. On the other hand, research articles on specific tumors since a few years emphasize various biological features of different cancers, different cells in a cancer and the dynamic heterogeneity of these cells. We have analysed the research literature of the subject and show the generality of a dynamic, evolving biological and metabolic, spatial and temporal heterogeneity of individual cancers. We conclude that there is no one metabolic map of cancer but several and describe the two extremes of a panel from the hypoxic to the normoxic state. The implications for the significance of general 'omic' studies, and on therapeutic conclusions drawn from them and for the diagnostic use of fractional biopsies is discussed.

The HIV-1 pathogenicity factor Nef interferes with maturation of stimulatory T-lymphocyte contacts by modulation of N-Wasp activity

The Nef protein is a key determinant of human immunodeficiency virus (HIV) pathogenicity that, among other activities, sensitizes T-lymphocytes for optimal virus production. The initial events by which Nef modulates the T-cell receptor (TCR) cascade are poorly understood. TCR engagement triggers actin rearrangements that control receptor clustering for signal initiation and dynamic organization of signaling protein complexes to form an immunological synapse. Here we report that Nef potently interferes with cell spreading and formation of actin-rich circumferential rings in T-lymphocytes upon surface-supported TCR stimulation. These effects were conserved among Nef proteins from different lentiviruses and occurred in HIV-1-infected primary human T-lymphocytes. This novel Nef activity critically depended on its Src homology 3 domain binding motif and required efficient association with Pak2 activity. Notably, whereas overall signaling microcluster formation immediately following TCR engagement occurred normally in Nef-expressing cells, the viral protein inhibited the concomitant activation of the actin organizer N-Wasp. During the subsequent maturation phase of the stimulatory contact, Nef interfered with the translocation of N-Wasp to the cell periphery, the overall induction of tyrosine phosphorylation, and the selective recruitment of phosphorylated LAT to stimulatory contacts. Consistent with such a critical role of N-Wasp in this process, Nef also blocked morphological changes induced by the known N-Wasp regulators Rac1 and Cdc42. Together, our results demonstrate that Nef alters both the amount and composition of signaling microclusters. We propose modulation of actin dynamics as an important mechanism for Nef-induced alterations of TCR signaling.

Dynamic imaging of cellular interactions with extracellular matrix

Adhesive and proteolytic interactions of cells with components of the extracellular matrix (ECM) are fundamental to morphogenesis, tissue assembly and remodeling, and cell migration as well as signal acquisition from tissue-bound factors. The visualization from fixed samples provides snapshot-like, static information on the cellular and molecular dynamics of adhesion receptor and protease functions toward ECM, such as interstitial fibrillar tissues and basement membranes. Recent technological developments additionally support the dynamic imaging of ECM scaffolds and the interaction behavior of cells contained therein. These include differential interference contrast, confocal reflection microscopy, optical coherence tomography, and multiphoton microscopy and second-harmonic generation imaging. Most of these approaches are combined with fluorescence imaging using derivates of GFP and/or other fluorescent dyes. Dynamic 3D imaging has revealed an unexpected degree of dynamics and turnover of cell adhesion and migration as well as basic mechanisms that lead to proteolytic remodeling of connective tissue by stromal cells and invading tumor cells.