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Cell-based therapies are currently being developed for applications in both regenerative medicine and in oncology. Preclinical, translational, and clinical research on cell-based therapies will benefit tremendously from novel imaging approaches that enable the effective monitoring of the delivery, survival, migration, biodistribution, and integration of transplanted cells. Magnetic resonance imaging (MRI) offers several advantages over other imaging modalities for elucidating the fate of transplanted cells both preclinically and clinically. These advantages include the ability to image transplanted cells longitudinally at high spatial resolution without exposure to ionizing radiation, and the possibility to co-register anatomical structures with molecular processes and functional changes. However, since cellular MRI is still in its infancy, it currently faces a number of challenges, which provide avenues for future research and development. In this review, we describe the basic principle of cell-tracking with MRI; explain the different approaches currently used to monitor cell-based therapies; describe currently available MRI contrast generation mechanisms and strategies for monitoring transplanted cells; discuss some of the challenges in tracking transplanted cells; and suggest future research directions. [ABSTRACT FROM AUTHOR]

Magnetic resonance (MR) imaging is advantageous because it concurrently provides anatomic, functional, and molecular information. MR molecular imaging can combine the high spatial resolution of this established clinical modality with molecular profiling in vivo. However, as a result of the intrinsically low sensitivity of MR imaging, high local concentrations of biological targets are required to generate discernable MR contrast. We hypothesize that the prostate-specific membrane antigen (PSMA), an attractive target for imaging and therapy of prostate cancer, could serve as a suitable biomarker for MR-based molecular imaging. We have synthesized three new high-affinity, low-molecular-weight GdIII-based PSMA-targeted contrast agents containing one to three GdIII chelates per molecule. We evaluated the relaxometric properties of these agents in solution, in prostate cancer cells, and in an in vivo experimental model to demonstrate the feasibility of PSMA-based MR molecular imaging. [ABSTRACT FROM AUTHOR]

Magnetic resonance (MR) imaging is advantageous because it concurrently provides anatomic, functional, and molecular information. MR molecular imaging can combine the high spatial resolution of this established clinical modality with molecular profiling in vivo. However, as a result of the intrinsically low sensitivity of MR imaging, high local concentrations of biological targets are required to generate discernable MR contrast. We hypothesize that the prostate-specific membrane antigen (PSMA), an attractive target for imaging and therapy of prostate cancer, could serve as a suitable biomarker for MR-based molecular imaging. We have synthesized three new high-affinity, low-molecular-weight GdIII-based PSMA-targeted contrast agents containing one to three GdIII chelates per molecule. We evaluated the relaxometric properties of these agents in solution, in prostate cancer cells, and in an in vivo experimental model to demonstrate the feasibility of PSMA-based MR molecular imaging. [ABSTRACT FROM AUTHOR]

Mitochondrial-targeting photosensitizers have been associated with effective photodynamic responses. However, most photosensitizers absorb light between 400 and 700 nm, where light penetration through tissues is limited. Two-photon excitation is a rational approach to improve light penetration through tissues. In this report, the two-photon photophysical properties of a porphyrin-rhodamine B conjugate (TPP-Rh), previously demonstrated to target the mitochondria, were evaluated. The properties studied included: two-photon absorption (TPA) cross sections ( σ2); resonance energy transfer (RET) kinetics and dynamics; and singlet oxygen generation. The conjugation of Rh B to TPP-OH approximately doubled the σ2 of TPP-Rh at 800 nm (40 ± 4 GM) compared with the parent porphyrin, TPP-OH (16 ± 4 GM). Furthermore, the rate of DPBF oxidation by singlet oxygen generated from TPP-Rh was twice as fast compared with that from TPP-OH (73 % versus 33% in 10 min) following two-photon excitation at 800 nm. In addition, a significantly stronger luminescence signal was detected from TPP-Rh, than from TPP-OH at 1270 nm, following two-photon excitation. This study indicates that conjugating photosensitizers to Rh B could provide greater TPA at the near-infrared range in addition to preferential mitochondrial accumulation for improved photodynamic responses. [ABSTRACT FROM AUTHOR]

Abstract: Mitochondria are attractive targets in photodynamic therapy. Two conjugates: TPP–Rh (a porphyrin–rhodamine B conjugate) and TPP–AO (a porphyrin–acridine orange conjugate), each possessing a single delocalized lipophilic cation, were designed and synthesized as photosensitizers. Their ability to target the mitochondria for photodynamic therapy was evaluated. The conjugates were synthesized by conjugating a monohydroxy porphyrin (TPP-OH) to rhodamine B (Rh B) and acridine orange base (AO), respectively, via a saturated hydrocarbon linker. To evaluate the efficiency of the conjugates as photosensitizers, their photophysical properties and in vitro photodynamic activities were studied in comparison to those of TPP-OH. Although fluorescence energy transfer (FRET) was observed in the conjugates, they were capable of generating singlet oxygen at rates comparable to TPP-OH. Biologically, exciting results were observed with TPP–Rh, which showed a much higher phototoxicity [IC50, 3.95μM: irradiation of 400–850nm light (3mWcm−2) for 1h] than either TPP-OH or Rh B (both, IC50, >20μM) without significant dark toxicity at 20μM. This improved photodynamic activity might be due to a greater cellular uptake and preferential localization in mitochondria. The cellular uptake of TPP–Rh was 8 and 14 times greater than TPP-OH and Rh B, respectively. In addition, fluorescence imaging studies suggest that TPP–Rh localized more in mitochondria than TPP-OH. On the other hand, TPP–AO showed some dark toxicity at 10μM and stained both mitochondria and nucleus. Our study suggests that conjugation of photosensitizers to Rh might provide two benefits, higher cellular uptake and mitochondrial localization, which are two important subjects in photodynamic therapy. [Copyright &y& Elsevier]

Abstract: Thiaporphyrins 2–8 were prepared as analogues of 5,20-diphenyl-10,15-bis[4-(carboxymethyleneoxy)-phenyl]-21,23- dithiaporphyrin (1) to examine the effect of structural modifications: substituent changes in meso aryl groups of dithiaporphyrins with one water-solubilizing group (2–5), dihydroxylation of a pyrrole double bond and reduction to dihydroxychlorins (6 and 7), and the removal of two meso aryl groups to give unsubstituted meso positions (8). The impact of these structural modifications was measured in both physicochemical (UV spectra, generation of singlet oxygen, lipophilicity, and aggregate formation) and biological properties (dark toxicity and phototoxicity, cellular uptake, and subcellular localization). Mono-functionalized porphyrins had much higher lipophilicity than di-functionalized porphyrin 1 and, consequently, formed more aggregates in aqueous media. The formation of aggregates might lower the efficiency of lipophilic porphyrins as photosensitizers. Interestingly, dihydroxylation of a core pyrrole group in the dithiaporphyrin core did not affect either the absorption spectrum or the efficiency for generating singlet oxygen. The phototoxicity of dihydroxydithiachlorins mainly depended on their intracellular uptake. The potent phototoxicity of 6, IC50 =0.18μM, was attributed to the extraordinarily high uptake. The intracellular uptake of 6 was about 7.6 times higher than 1. In contrast, thiaporphyrin 8 with only two meso aryl groups was less effective as a photosensitizer, perhaps due to poorer uptake and a lower quantum yield for the generation of singlet oxygen. [Copyright &y& Elsevier]

Stem cell therapies are currently being investigated for the repair of brain injuries. Although exogenous stem cell labelling with superparamagnetic iron oxide nanoparticles (SPIONs) prior to transplantation provides a means to noninvasively monitor stem cell transplantation by magnetic resonance imaging (MRI), monitoring cell death is still a challenge. Here, we investigate the feasibility of using an MRI dual-contrast technique to detect cell delivery, cell migration and cell death after stem cell transplantation. Human mesenchymal stem cells were dual labelled with SPIONs and gadolinium-based chelates (GdDTPA). The viability, proliferation rate, and differentiation potential of the labelled cells were then evaluated. The feasibility of this MRI technique to distinguish between live and dead cells was next evaluated using MRI phantoms, and in vivo using both immune-competent and immune-deficient mice, following the induction of brain injury in the mice. All results were validated with bioluminescence imaging. In live cells, a negative (T2/T2*) MRI contrast predominates, and is used to track cell delivery and cell migration. Upon cell death, a diffused positive (T1) MRI contrast is generated in the vicinity of the dead cells, and serves as an imaging marker for cell death. Ultimately, this technique could be used to manage stem cell therapies. [ABSTRACT FROM AUTHOR]

This paper reports the damaging effects of magnetic iron-oxide nanoparticles (MNP) on magnetically labeled cancer cells when subjected to oscillating gradients in a strong external magnetic field. Human breast cancer MDA-MB-231 cells were labeled with MNP, placed in the high magnetic field, and subjected to oscillating gradients generated by an imaging gradient system of a 9.4T preclinical MRI system. Changes in cell morphology and a decrease in cell viability were detected in cells treated with oscillating gradients. The cytotoxicity was determined qualitatively and quantitatively by microscopic imaging and cell viability assays. An approximately 26.6% reduction in cell viability was detected in magnetically labeled cells subjected to the combined effect of a static magnetic field and oscillating gradients. No reduction in cell viability was observed in unlabeled cells subjected to gradients, or in MNP-labeled cells in the static magnetic field. As no increase in local temperature was observed, the cell damage was not a result of hyperthermia. Currently, we consider the coherent motion of internalized and aggregated nanoparticles that produce mechanical moments as a potential mechanism of cell destruction. The formation and dynamics of the intracellular aggregates of nanoparticles were visualized by optical and transmission electron microscopy (TEM). The images revealed a rapid formation of elongated MNP aggregates in the cells, which were aligned with the external magnetic field. This strategy provides a new way to eradicate a specific population of MNP-labeled cells, potentially with magnetic resonance imaging guidance using standard MRI equipment, with minimal side effects for the host. [ABSTRACT FROM AUTHOR]