Concentration-independent MRI of pH with a dendrimer-based pH-responsive nanoprobe

The measurement of extracellular pH (pHe ) has significant clinical value for pathological diagnoses and for monitoring the effects of pH-altering therapies. One of the major problems of measuring pHe with a relaxation-based MRI contrast agent is that the longitudinal relaxivity depends on both pH and the concentration of the agent, requiring the use of a second pH-unresponsive agent to measure the concentration. Here we tested the feasibility of measuring pH with a relaxation-based dendritic MRI contrast agent in a concentration-independent manner at clinically relevant field strengths. The transverse and longitudinal relaxation times in solutions of the contrast agent (GdDOTA-4AmP)44 -G5, a G5-PAMAM dendrimer-based MRI contrast agent in water, were measured at 3 T and 7 T magnetic field strengths as a function of pH. At 3 T, longitudinal relaxivity (r1 ) increased from 7.91 to 9.65 mM(-1) s(-1) (on a per Gd(3+) basis) on changing pH from 8.84 to 6.35. At 7 T, r1 relaxivity showed pH response, albeit at lower mean values; transverse relaxivity (r2 ) remained independent of pH and magnetic field strengths. The longitudinal relaxivity of (GdDOTA-4AmP)44 -G5 exhibited a strong and reversible pH dependence. The ratio of relaxation rates R2 /R1 also showed a linear relationship in a pH-responsive manner, and this pH response was independent of the absolute concentration of (GdDOTA-4AmP)44 -G5 agent. Importantly, the nanoprobe (GdDOTA-4AmP)44 -G5 shows pH response in the range commonly found in the microenvironment of solid tumors.

Endothelial progenitor cells (EPCs) as gene carrier system for rat model of human glioma

Background

Due to their unique property to migrate to pathological lesions, stem cells are used as a delivery vehicle for therapeutic genes to tumors, especially for glioma. It is critically important to track the movement, localization, engraftment efficiency and functional capability or expression of transgenes of selected cell populations following transplantation. The purposes of this study were to investigate whether 1) intravenously administered, genetically transformed cord blood derived EPCs can carry human sodium iodide symporter (hNIS) to the sites of tumors in rat orthotopic model of human glioma and express transgene products, and 2) whether accumulation of these administered EPCs can be tracked by different in vivo imaging modalities.

Methods and Results

Collected EPCs were cultured and transduced to carry hNIS. Cellular viability, differential capacity and Tc-99m uptake were determined. Five to ten million EPCs were intravenously administered and Tc-99-SPECT images were acquired on day 8, to determine the accumulation of EPCs and expression of transgenes (increase activity of Tc-99m) in the tumors. Immunohistochemistry was performed to determine endothelial cell markers and hNIS positive cells in the tumors. Transduced EPCs were also magnetically labeled and accumulation of cells was confirmed by MRI and histochemistry. SPECT analysis showed increased activity of Tc-99m in the tumors that received transduced EPCs, indicative of the expression of transgene (hNIS). Activity of Tc-99m in the tumors was also dependent on the number of administered transduced EPCs. MRI showed the accumulation of magnetically labeled EPCs. Immunohistochemical analysis showed iron and hNIS positive and, human CD31 and vWF positive cells in the tumors.

Conclusion

EPC was able to carry and express hNIS in glioma following IV administration. SPECT detected migration of EPCs and expression of the hNIS gene. EPCs can be used as gene carrier/delivery system for glioma therapy as well as imaging probes.

Interaction of aliphatic cap group in inhibition of histone deacetylases by cyclic tetrapeptides

Inhibitors of histone deacetylases (HDACs) are a promising class of anticancer agents that effect gene regulation. To know the interaction of aliphatic cap groups with HDACs, cyclic tetrapeptide and bicyclic peptide disulfide hybrids were synthesized without aromatic ring in their macrocyclic framework. Benzene ring of l-Phe in chlamydocin was replaced with several aliphatic amino acids and also a fused bicyclic tetrapeptide was synthesized by ring closing metathesis using Grubb's first generation catalyst. The inhibitory activities of the cyclic peptides against histone deacetylase enzymes were evaluated, which demonstrated most of them are interesting candidates as anticancer agents.

Chlamydocin analogs bearing carbonyl group as possible ligand toward zinc atom in histone deacetylases

A series of chlamydocin analogs with various carbonyl functionalities were designed and synthesized as histone deacetylase (HDAC) inhibitors. Chlamydocin is a cyclic tetrapeptide containing an epoxyketone surrogate in the side chain which makes it irreversible inhibitor of HDACs, whereas apicidins are a class of cyclic tetrapeptides that contain an ethylketone moiety as zinc ligand. We replaced the epoxyketone moiety of chlamydocin with several ketones and aldehyde to synthesize potent reversible and selective HDAC inhibitors. The inhibitory activity of the cyclic tetrapeptides against histone deacetylase enzymes were evaluated and the result showed most of them are potent inhibitors. Some of them have remarkable selectivity among the HDACs.