Non-ionic Gd-based MRI contrast agents are optimal for encapsulation into phosphatidyldiglycerol-based thermosensitive liposomes.

Thermosensitive liposomes (TSL) with encapsulated magnetic resonance imaging (MRI) longitudinal relaxation time (T(1)) contrast agents (CAs) have been proposed for MRI assisted interventional thermotherapy in solid tumors. Here the feasibility of 6 clinically approved CAs (Gd-DTPA, Gd-BOPTA, Gd-DOTA, Gd-BT-DO3A, Gd-DTPA-BMA, and Gd-HP-DO3A) for formulation into TSL was investigated. CAs were passively encapsulated with 323 mOs kg(-1) into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1,2-distearoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol 50/20/30 (mol/mol) TSL (DPPG(2)-TSL) to obtain stable formulations. T(1) relaxivity (r(1)) and diffusive permeability to water (P(d)) across the membrane were determined. Shelf life at 4°C was investigated by determining lysolipid content up to 10 weeks after preparation. All preparations were monodispersed with comparable small vesicle sizes (~135 nm). Neither zeta potential nor phase transition temperature (T(m)) was affected by the CA. The formulations showed an increase in r(1) in the temperature range between 38 and 44°C. This correlated with the phase transition. Change in r(1) (Δr(1)=r(1)(45.3°C)-r(1)(37.6°C)) and r(1) (T

Size of thermosensitive liposomes influences content release.

Thermosensitive liposomes (TSL) in combination with regional hyperthermia represent a powerful tool for tumor specific drug delivery. The objective of this study was to investigate the influence of vesicle size on the biophysical properties of TSL. TSL were composed of DPPC/DSPC/1,2-dipalmitoyl-sn-glycero-3-phosphoglyceroglycerol (DPPG(2)) 50:20:30 (mol/mol) (DPPG(2)-TSL) and DPPC/P-Lyso-PC/DSPE-PEG2000 90:10:4 (mol/mol) (PEG/Lyso-TSL) with encapsulated fluorescent dye carboxyfluorescein, anticancer drug doxorubicin or magnetic resonance contrast agent gadodiamide. Extrusion was performed with polycarbonate filters of distinct pore size to obtain TSL with different diameters (50 to 200nm). Phase transition temperature (T(m)) of the bilayer forming phospholipids was not influenced by vesicle size in the tested range. However, vesicle size had a major impact on in vitro content release properties of TSL in the investigated temperature range between 30 and 45°C. Generally, vesicle size was inversely related to content release properties with increased content release rates for decreased vesicle sizes. Size dependency of content release properties varied between all tested formulations and DPPG(2)-TSL were generally less affected by size changes in the range of 100 to 150nm as compared to PEG/Lyso-TSL. Independent from gadodiamide release, vesicle size influenced the signal intensity of DPPG(2)-TSL also at temperatures below T(m) due to improved water exchange for smaller vesicles. Liposomes around 100nm in size are routinely used in vivo, hence a quality control for TSL preparations is required prior to use. Even small changes in size or a wider size distribution might affect stability and release properties and thus yield in decreased efficacy or unwanted side effects of drug loaded TSL during in vivo applications.

Comparison of radiological and pathohistological response to neoadjuvant chemotherapy combined with regional hyperthermia (RHT) and study of response dependence on the applied thermal parameters in patients with soft tissue sarcomas (STS).

PURPOSE: To compare the radiological criteria RECIST, WHO, and tumor volume for evaluation of tumor response in patients with soft tissue sarcomas (STS) showing either good or poor pathohistological response to neoadjuvant chemotherapy combined with regional hyperthermia, and to examine the dependence of the findings on the applied thermal dose. MATERIALS AND METHODS: 19 patients with pathohistological complete response (no vital tumor cells, group 1) and 27 with pathohistological no response (<25% necrosis, group 2) were selected from our previous clinical trials. The change in tumor size before and after therapy was determined. Intratumoral temperature (T(90)) and thermal dose (CEM 43 degrees C T(90)) were calculated for 13 patients. RESULTS: In the first group, 6 partial response (PR) and 13 stable disease (SD) according to RECIST, 7 PR and 12 SD according to WHO, 7 PR and 12 SD according to volumetric criteria were evaluated. In the second group, the results were 10 PR and 17 SD (RECIST), 9 PR and 18 SD (WHO), 8 PR and 19 SD (volume). The concordance of these criteria was 73.7% in group 1 and 74% in group 2. PR and SD were equally distributed in both groups (p > 0.421). Thermal parameters were not different between the groups (p > 0.327). CONCLUSIONS: SD or PR in radiological response assessment does not correlate with the pathohistological response after neoadjuvant thermochemotherapy. RECIST, WHO and volumetric criteria for response evaluation in STS are in substantial agreement. For irregularly shaped lesions, volumetric criteria seem to be more appropriate.

MR characterization of mild hyperthermia-induced gadodiamide release from thermosensitive liposomes in solid tumors.

OBJECTIVES: Thermal dose in tumor tissue is a key factor for regional hyperthermia (HT) combined with chemotherapy and for drug delivery using thermosensitive liposomes (TSL). It influences therapy outcome, affects the accumulation of liposomes, and triggers the content release from TSL in the target tissue. For the development and clinical application of TSL, noninvasive visualization is of critical importance. For this purpose, TSL loaded with MRI contrast agent (CA) have been developed. With increase in temperature, the CA is released from TSL at the phase transition temperature Tm resulting in a relaxation time change, which allows MRI monitoring. The purpose of this study was to examine the feasibility of an in vivo application and MR characterization of Gd-DTPA-BMA-loaded phosphatidylglyceroglycerol-TSL (Gd-TSL) at mild HT conditions in tumor tissue using a clinically relevant setting. MATERIAL AND METHODS: Gd-TSL were characterized in vitro with varying thermal doses between 37 degrees C and 45 degrees C and distinct solvents by MR at 0.5 T and 1.5 T. In vivo studies were performed in C57BL/6 mice bearing BFS-1 fibrosarcomas at 1.5 T. One tumor-bearing leg was immersed in a temperature-controlled water bath (T). Gd-TSL (Tm = 43.5 +/- 0.2 degrees C) were injected either intratumorally or intravenously at T = 37.3 +/- 0.1 degrees C or T = 42.5 +/- 0.3 degrees C. As a control, nonliposomal Gd-DTPA-BMA was injected intravenously at T = 43.1 +/- 0.3 degrees C. A second tumor on the contralateral limb, which remained unheated, served as a control. CA release was monitored by T1-weighted spin-echo. RESULTS: The in vitro characterization demonstrated at heated and unheated samples a strong increase in T1-relaxivity of Gd-TSL solutions from 0.4 mM-1 s-1 (37.5 degrees C) to 4.2 mM-1 s-1 (43.3 degrees C) at 0.5 T. Thermal dose and solvent affected the rate of relaxation time change significantly. A fast and complete release was observed in samples with serum, whereas Gd-TSL in glucose was only partially released within 1 hour. A dedicated experimental setup was developed for standardized in vivo investigation. Tumor signal intensity changes were detectable in all animals. After intratumoral injection of Gd-TSL, the signal increased heterogeneously (max., +52% +/- 25%) within 3 minutes after temperature increase and decreased strongly thereafter, whereas after i.v. injection, the signal increased homogeneously (+19% +/- 3%) within 2 minutes persisting thereafter. The unheated control tumors on the contralateral legs showed a 10% +/- 3% signal increase within 2 minutes. Injection at 37 degrees C showed a continuous signal increase in "heated" and unheated tumors of up to 8% to 10%. Nonliposomal CA injection demonstrated that tumors were well perfused during HT. CONCLUSION: HT-induced CA release from Gd-TSL was monitored and characterized by MRI after i.v. injection in tumor-bearing mice. Higher temperatures resulted in higher signal changes. Immediately after i.v. injection, heated tumor tissue was distinguishable from unheated tumor tissue. The Gd-TSL appears to be suitable for MR monitoring of HT tumor treatment in a clinical MRI setting independent of field strength.

In vitro characterization of phosphatidylglyceroglycerol-based thermosensitive liposomes with encapsulated 1H MR T1-shortening gadodiamide.

Thermosensitive liposomes (TSL) with encapsulated proton (1H) magnetic resonance (MR) contrast agents have been proposed for noninvasive online temperature monitoring during tumor treatment using chemotherapy combined with hyperthermia (HT). The technique exploits the fact that water exchange between the TSL interior and exterior is increased and/or the encapsulated 1H MR contrast agent is released near the gel-to-liquid crystalline phase transition temperature (Tm) of TSL and thus shortens the 1H MR relaxation time of tissue. In this work, newly developed, phosphatidylglyceroglycerol (DPPGOG)-based TSL with encapsulated 1H MR longitudinal relaxation time (T1)-shortening gadodiamide (Gd-DTPA-BMA) were characterized in vitro by measuring the temperature dependence of the T1 of these gadodiamide-containing DPPGOG-TSL samples between 30 and 50 degrees C. The measurements revealed that the T1 nonlinearly slightly decreased with increasing temperature from 30 to 37 degrees C, mainly due to increased water exchange between the gadodiamide-containing DPPGOG-TSL interior and exterior with the exception of negligible gadodiamide release. This implies that gadodiamide-containing DPPGOG-TSL were stable at temperatures < or =37 degrees C, which was also confirmed by an independent stability study. From 37 to 44 degrees C, the T1 nonlinearly markedly decreased with increasing temperature since encapsulated gadodiamide was rapidly released. Above 44 degrees C, gadodiamide was completely released and the T1 was directly proportional to temperature while heated from 44 to 50 degrees C and cooled from 50 to 30 degrees C, respectively. Additionally, gadodiamide release was theoretically quantified and this calculated concentration was consistent with the actually released amount directly obtained from the cooling course of empty DPPGOG-TSL with completely released gadodiamide.

Assessment of human pulmonary function using oxygen-enhanced T(1) imaging in patients with cystic fibrosis.

Indirect qualitative MRI of pulmonary function is feasible using the paramagnetic effects of oxygen physically dissolved in blood. In this study, a more quantitative oxygen-enhanced pulmonary function test based on the slope of a plot of R(1) vs. oxygen concentration-the oxygen transfer function (OTF)-was developed and tested in a pool of five healthy volunteers and five patients with cystic fibrosis (CF). The lung T(1) relaxation rate, R(1), under normoxic conditions (room air, 21% O(2)), and the response to various hyperoxic conditions (40%-100% O(2)) were studied. Lung T(1) in healthy volunteers showed a relatively homogeneous distribution while they breathed room air, and a homogeneous decrease under hyperoxic conditions. Lung T(1) in CF patients showed an inhomogeneous distribution while they breathed room air, and the observed lung T(1) decrease under hyperoxia depended on the actual state of the diseased lung tissue. In the selected group of CF patients, areas with reduced OTF also showed reduced perfusion, as confirmed by qualitative contrast-enhanced MR pulmonary perfusion imaging. The results demonstrate that this completely noninvasive oxygen-enhanced pulmonary function test has potential for clinical applications in the serial diagnosis of lung diseases such as CF. .

Quantitative perfusion mapping of the human lung using 1H spin labeling.

PURPOSE: To evaluate the feasibility and reproducibility of a noninvasive, rapid and quantitative pulmonary perfusion mapping method using a two-compartment tissue model in combination with a (1)H spin labeling technique. MATERIALS AND METHODS: Ten healthy volunteers and three patients with cystic fibrosis (CF) were examined on a 1.5-T whole-body scanner. Global and selective lung T(1) maps based on an inversion recovery Snapshot FLASH technique were acquired from each subject with breath-holds at end-expiration. For comparison, corresponding Gd-DTPA-enhanced (1)H MR perfusion images were also obtained from each CF patient. RESULTS: Quantitative perfusion maps were calculated from the global and selective T(1) maps. The measured perfusion rates of the upper right lung in volunteers ranged from 400 to 600 mL/100 g/minute. The method showed a high intra-study reproducibility and low relative errors. In CF-patients, perfusion defects detected using Gd-DTPA-enhanced MR imaging were also detected using the spin labeling method. The perfusion rates of diseased lung tissues were less than 200 mL/100 g/minute. CONCLUSION: Noninvasive, robust and quantitative (1)H MR mapping of pulmonary perfusion was successfully performed using a rapid lung T(1) mapping in combination with spin labeling within the imaging slice. The proposed method has the potential to provide both important qualitative functional information and quantitative pulmonary perfusion rates in various lung diseases at various stages without the need of contrast agents.

Magnetization transfer short inversion time inversion recovery enhanced 1H MRI of the human lung.

The unique characteristics of the human lung arising from low proton density and multiple air-tissue interfaces of the alveoli cause difficulty in 1H lung magnetic resonance imaging. In addition, the dominating signal from sources such as the thoracic muscle and subcutaneous fat hampers the visualization of the lung parenchyma. In this contribution, an efficient tissue suppression technique is presented which allows one to significantly enhance lung parenchyma visibility. A short inversion time inversion recovery (STIR) experiment combined with a magnetization transfer (MT) experiment was used for magnetization preparation in order to suppress the signal from muscle. A half-Fourier single-shot turbo spin-echo sequence was used as acquisition module. This approach was used to perform lung anatomical imaging in eight healthy human subjects and five patients with cystic fibrosis. The results obtained demonstrate that with MT-STIR approach high quality human lung images can be obtained and that this approach has the potential for the evaluation of lung pathologies.