From protein–protein interaction to therapy response: Molecular imaging of heat shock proteins

PET imaging of Hsp90 expression in pancreatic cancer using a new 64Cu-labeled dimeric Sansalvamide A decapeptide

Heat shock protein 90 (Hsp90) plays a vital role in the progress of malignant disease and elevated Hsp90 expression has been reported in pancreatic cancer. In this study, we radiolabeled a dimeric Sansalvamide A derivative (Di-San A1) with ⁶⁴Cu, and evaluated the feasibility of using ⁶⁴Cu-Di-San A1 for PET imaging of Hsp90 expression in a mouse model of pancreatic cancer. A macrocyclic chelator NOTA (1,4,7-triazacyclononane-1,4,7-trisacetic acid) was conjugated to Di-San A1. ⁶⁴Cu-Di-San A1 was successfully prepared in a radiochemical yield > 97% with a radiochemical purity > 98%. ⁶⁴Cu-Di-San A1 is stable in PBS and mouse serum with > 92% of parent probe intact after 4 h incubation. The cell binding and uptake revealed that ⁶⁴Cu-Di-San A1 binds to Hsp90-positive PL45 pancreatic cancer cells, and the binding can be effectively blocked by an Hsp90 inhibitor (17AAG). For microPET study, ⁶⁴Cu-Di-San A1 shows good in vivo performance in terms of tumor uptake in nude mice bearing PL45 tumors. The Hsp90-specific tumor activity accumulation of ⁶⁴Cu-Di-San A1 was further demonstrated by significant reduction of PL45 tumor uptake with a pre-injected blocking dose of 17AAG. The ex vivo PET imaging and biodistribution results were consistent with the quantitative analysis of PET imaging, demonstrating good tumor-to-muscle ratio (5.35 ± 0.46) of ⁶⁴Cu-Di-San A1 at 4 h post-injection in PL45 tumor mouse xenografts. ⁶⁴Cu-Di-San A1 allows PET imaging of Hsp90 expression in PL45 tumors, which may provide a non-invasive method to quantitatively characterize Hsp90 expression in pancreatic cancer.

The Effect of Tanespimycin (17-AAG) on Radioiodine Accumulation in Sodium-Iodide Symporter Expressing Cells

PURPOSE

The heat shock protein 90 inhibitor, tanespimycin, is an anticancer agent known to increase iodine accumulation in normal and cancerous thyroid cells. Iodine accumulation is regulated by membrane proteins such as sodium iodide symporter (NIS) and pendrin (PDS), and thus we attempted to characterize the effects of tanespimycin on those genes.

METHODS

Cells were incubated with tanespimycin in order to evaluate (125)I accumulation and efflux ability. Radioiodine uptake and efflux were measured by a gamma counter and normalized by protein amount. RT-PCR were performed to measure the level of gene expression.

RESULTS

After tanespimycin treatment, (125)I uptake was increased by ∼2.5-fold in FRTL-5, hNIS-ARO, and hNIS-MDA-MB-231 cells, but no changes were detected in the hNIS-HeLa cells. Tanespimycin significantly reduced the radioiodine efflux rate only in the FRTL-5 cells. In the FRTL-5 and hNIS-ARO cells, PDS mRNA levels were markedly reduced; the only other observed alteration in the levels of NIS mRNA after tanespimycin treatment was an observed increase in the hNIS-ARO cells.

CONCLUSIONS

These results indicate that cellular responses against tanespimycin treatment differed between the normal rat thyroid cells and human cancer cells, and the reduction in the (125)I efflux rate by tanespimycin in the normal rat thyroid cells might be attributable to reduced PDS gene expression.

Molecular imaging of cell-based cancer immunotherapy

Cell-based cancer immunotherapy represents a new and powerful weapon in the arsenal of anticancer treatments. Non-invasive monitoring of the disposition, migration and destination of therapeutic cells will facilitate the development of cell based therapy. The therapeutic cells can be modified intrinsically by a reporter gene or labeled extrinsically by introducing imaging probes into the cells or on the cell surface before transplant. Various advanced non-invasive molecular imaging techniques are playing important roles in optimizing cellular therapy by tracking cells and monitoring the therapeutic effects of transplanted cells in vivo. This review will summarize the application of multiple molecular imaging modalities in cell-based cancer immunotherapy.

Heat-shock proteins in cardiovascular disease

Heat-shock proteins (HSPs) belong to a group of highly conserved families of proteins expressed by all cells and organisms and their expression may be constitutive or inducible. They are generally considered as protective molecules against different types of stress and have numerous intracellular functions. Secretion or release of HSPs has also been described, and potential roles for extracellular HSPs reported. HSP expression is modulated by different stimuli involved in all steps of atherogenesis including oxidative stress, proteolytic aggression, or inflammation. Also, antibodies to HSPs may be used to monitor the response to different types of stress able to induce changes in HSP levels. In the present review, we will focus on the potential implication of HSPs in atherogenesis and discuss the limitations to the use of HSPs and anti-HSPs as biomarkers of atherothrombosis. HSPs could also be considered as potential therapeutic targets to reinforce vascular defenses and delay or avoid clinical complications associated with atherothrombosis.

Reversible, allosteric small-molecule inhibitors of regulator of G protein signaling proteins

Regulators of G protein signaling (RGS) proteins are potent negative modulators of G protein signaling and have been proposed as potential targets for small-molecule inhibitor development. We report a high-throughput time-resolved fluorescence resonance energy transfer screen to identify inhibitors of RGS4 and describe the first reversible small-molecule inhibitors of an RGS protein. Two closely related compounds, typified by CCG-63802 [((2E)-2-(1,3-benzothiazol-2-yl)-3-[9-methyl-2-(3-methylphenoxy)-4-oxo-4H-pyrido[1,2-a]pyrimidin-3-yl]prop-2-enenitrile)], inhibit the interaction between RGS4 and Galpha(o) with an IC(50) value in the low micromolar range. They show selectivity among RGS proteins with a potency order of RGS 4 > 19 = 16 > 8 >> 7. The compounds inhibit the GTPase accelerating protein activity of RGS4, and thermal stability studies demonstrate binding to the RGS but not to Galpha(o). On RGS4, they depend on an interaction with one or more cysteines in a pocket that has previously been identified as an allosteric site for RGS regulation by acidic phospholipids. Unlike previous small-molecule RGS inhibitors identified to date, these compounds retain substantial activity under reducing conditions and are fully reversible on the 10-min time scale. CCG-63802 and related analogs represent a useful step toward the development of chemical tools for the study of RGS physiology.