Rhein-based necrosis-avid MRI contrast agents for early evaluation of tumor response to microwave ablation therapy.

PURPOSE: Early evaluation of tumor response to thermal ablation therapy can help identify untreated tumor cells and then perform repeated treatment as soon as possible. The purpose of this work was to explore the potential of rhein-based necrosis-avid contrast agents (NACAs) for early evaluation of tumor response to microwave ablation (MWA). METHODS: 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay was performed to test the cytotoxicity of rhein-based NACAs against HepG2 cells. Rat models of liver MWA were used for investigating the effectiveness of rhein-based NACAs in imaging the MWA lesion, the optimal time period for post-MWA MRI examination, and the metabolic behaviors of 68 Ga-labeled rhein-based NACAs. Rat models of orthotopic liver W256 tumor MWA were used for investigating the time window of rhein-based NACAs for imaging the MWA lesion, the effectiveness of these NACAs in distinguishing the residual tumor and the MWA lesion, and their feasibility in early evaluating the tumor response to MWA. RESULTS: Gadolinium 2,2',2''-(10-(2-((4-(4,5-Dihydroxy-9,10-dioxo-9,10-dihydroanthracene-2-carboxamido)butyl)amino)-2-oxoethyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (GdL2 ) showed low cytotoxicity and high quality in imaging the MWA region. The optimal time period for post-MWA MRI examination using GdL2 was 2 to 24 h after the treatment. During 2.5 to 3.5 h postinjection, GdL2 can better visualize the MWA lesion in comparison with gadolinium 2-[4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododec-1-yl]acetic acid (Gd-DOTA), and the residual tumor would not be enhanced. The tumor response to MWA as evaluated by using GdL2 -enhanced MRI was consistent with histological examination. CONCLUSION: GdL2 appears to be a promising NACA for the tumor response assessment after thermal ablation therapies.

Everolimus halts hepatic cystogenesis in a rodent model of polycystic-liver-disease.

AIM: To develop a MRI-based method for accurate determination of liver volume (LV) and to explore the effect of long-term everolimus (EVR) treatment on LV in PCK rats with hepatomegaly. METHODS: Thirty-one female PCK rats (model for polycystic-liver-disease: PCLD) were randomized into 3 groups and treatment was started at 16 wk, at the moment of extensive hepatomegaly (comparable to what is done in the human disease). Animals received: controls (n = 14), lanreotide (LAN: 3 mg/kg per 2 wk) (n = 10) or everolimus (EVR: 1 mg/kg per day) (n = 7). LV was measured at week 16, 24, 28. At week 28, all rats were sacrificed and liver tissue was harvested. Fibrosis was evaluated using quantitative image analysis. In addition, gene (quantitative RT-PCR) and protein expression (by Western blot) of the PI3K/AkT/mTOR signaling pathway was investigated. RESULTS: LV determination by MRI correlated excellent with the ex vivo measurements (r = 0.99, P < 0.001). The relative changes in LV at the end of treatment were: (controls) +31.8%; (LAN) +5.1% and (EVR) +8.8%, indicating a significantly halt of LV progression compared with controls (respectively, P = 0.01 and P = 0.04). Furthermore, EVR significantly reduced the amount of liver fibrosis (P = 0.004) thus might also prevent the development of portal hypertension. There was no difference in phosphorylation of Akt (Threonine 308) between LAN-treated PCK rats control PCK rats, whereas S6 was significantly more phosphorylated in the LAN group. Phosphorylation of Akt was not different between controls and EVR treated rats, however, for S6 there was significantly less phosphorylation in the EVR treated rats. Thus, both drugs interact with the PI3K/AkT/mTOR signaling cascade but acting at different molecular levels. CONCLUSION: Everolimus halts cyst growth comparable to lanreotide and reduces the development of fibrosis. mTOR-inhibition should be further explored in PCLD patients especially those that need immunosuppression.

An Imaging and Histological Study on Intrahepatic Microvascular Passage of Contrast Materials in Rat Liver.

Background. Lipiodol has been applied for decades in transarterial chemoembolization to treat liver malignancies, but its intrahepatic pathway through arterioportal shunt (APS) in the liver has not been histologically revealed. This rodent experiment was conducted to provide evidence for the pathway of Lipiodol delivered through the hepatic artery (HA) but found in the portal vein (PV) and to elucidate the observed unidirectional APS. Methods. Thirty rats were divided into 5 groups receiving systemic or local arterial infusion of red-stained iodized oil (RIO) or its hydrosoluble substitute barium sulfate suspension (BSS), or infusion of BSS via the PV, monitored by real-time digital radiography. Histomorphology of serial frozen and paraffin sections was performed and quantified. Results. After HA infusion, RIO and BSS appeared extensively in PV lumens with peribiliary vascular plexus (PVP) identified as the responsible anastomotic channel. After PV infusion, BSS appeared predominantly in the PV and surrounding sinusoids and to a much lesser extent in the PVP and HA (P < 0.001). Fluid mechanics well explains the one-way-valve phenomenon of APS. Conclusions. Intravascularly injected rat livers provide histomorphologic evidences: (1) the PVP exists in between the HA and PV, which is responsible to the APS of Lipiodol; and (2) the intrahepatic vascular inflow appears HA-PVP-PV unidirectional without a physical one-way valve, which can be postulated by the fluid mechanics.

Excretion and toxicity evaluation of 131I-Sennoside A as a necrosis-avid agent.

1. Sennoside A (SA) is a newly identified necrosis-avid agent that shows capability for imaging diagnosis and tumor necrosis targeted radiotherapy. As a water-soluble compound, 131I-Sennoside A (131I-SA) might be excreted predominately through the kidneys with the possibility of nephrotoxicity. 2. To further verify excretion pathway and examine nephrotoxicity of 131I-SA, excretion and nephrotoxicity were appraised. The pharmacokinetics, hepatotoxicity and hematotoxicity of 131I-SA were also evaluated to accelerate its possible clinical translation. All these studies were conducted in mice with ethanol-induced muscular necrosis following a single intravenous administration of 131I-SA at 18.5 MBq/kg or 370 MBq/kg. 3. Excretion data revealed that 131I-SA was predominately (73.5% of the injected dose (% ID)) excreted via the kidneys with 69.5% ID detected in urine within 72 h post injection. Biodistribution study indicated that 131I-SA exhibited initial high distribution in the kidneys but subsequently a fast renal clearance, which was further confirmed by the results of autoradiography and single-photon emission computed tomography-computed tomography (SPECT-CT) imaging. The maximum necrotic to normal muscle ratio reached to 7.9-fold at 48 h post injection, which further verified the necrosis avidity of 131I-SA. Pharmacokinetic parameters showed that 131I-SA had fast blood clearance with an elimination half-life of 6.7 h. Various functional indexes were no significant difference (p > 0.05) between before administration and 1 d, 8 d, 16 d after administration. Histopathology showed no signs of tissue damage. 4. These data suggest 131I-SA is a safe and promising necrosis-avid agent applicable in imaging diagnosis and tumor necrosis targeted radiotherapy.

Effects of Glycosylation on Biodistribution and Imaging Quality of Necrotic Myocardium of Iodine-131-Labeled Sennidins.

PURPOSE: Sennidins are necrosis-avid agents for noninvasive assessment of myocardial viability which is important for patients with myocardial infarction (MI). However, high accumulation of radioactivity in the liver interferes with the assessment of myocardial viability. In this study, we compared sennidins with sennosides to investigate the effects of glycosylation on biodistribution and imaging quality of sennidins. PROCEDURES: Sennidin A (SA), sennidin B (SB), sennoside A (SSA), and sennoside B (SSB) were labeled with I-131. In vitro binding to necrotic cells and hepatic cells and in vivo biodistribution in rats with muscular necrosis were evaluated by gamma counting, autoradiography, and histopathology. Single photon emission computed tomography/computed tomography (SPECT/CT) images were acquired in rats with acute MI. RESULTS: The uptake of [131I]SA, [131I]SSA, [131I]SB, and [131I]SSB in necrotic cells was significantly higher than that in viable cells (p < 0.05). Hepatic cells uptake of [131I]SSA and [131I]SSB were 7-fold and 10-fold lower than that of corresponding [131I]SA and [131I]SB, respectively. The biodistribution data showed that the radioactivities in the liver and feces were significantly lower with [131I]sennosides than those with [131I]sennidins (p < 0.01). Autoradiography showed preferential accumulation of these four radiotracers in necrotic areas of muscle, confirmed by histopathology. SPECT/CT imaging studies showed better image quality with [131I]SSB than with [131I]SB due to less liver interference. CONCLUSIONS: Glycosylation significantly decreased the liver uptake and improved the quality of cardiac imaging. [131I]SSB may serve as a promising necrosis-avid agent for noninvasive assessment of myocardial viability.

Biodistribution and radiation dosimetry of radioiodinated hypericin as a cancer therapeutic.

Iodine-131­labeled monoiodohypericin (131I­Hyp) is a necrosis avid compound used as a complementary anticancer agent. Herein, the biodistribution in rats with re-perfused partial liver infarction (RPLI) was used to estimate its human internal radiation dosimetry. Iodine-123­labeled monoiodohypericin (123I-Hyp) as a safer surrogate for 131I-Hyp was prepared with iodogen as oxidant. Determination of radiochemical yield and purification was performed by high performance liquid chromatography (HPLC). To control aggregation, the formulation was macroscopically and microscopically examined. Biodistribution of 123I-Hyp was studied in RPLI rats (n=18) at 4, 24 and 48 h post-injection. Tissue gamma counting (TGC), autoradiography and histology were performed. Dosimetry of 131I-Hyp in hepatic necrosis and in normal human organs was estimated using biodistribution data of 123I-Hyp, the Organ Level Internal Dose Assessment/Exponential Modeling (OLINDA/EXM®), a sphere model and male and female phantoms. A radiochemical yield of 95% was achieved in labeling of 123I-Hyp with a radiochemical purity of 99% after HPLC purification. In the Hyp added formulation, no macroscopic but minimal microscopic aggregation was observed. By TGC, selective accumulation in hepatic infarction and low uptake in viable liver of 123I­Hyp/Hyp were detected, as confirmed by autoradiography and histology. Significantly higher doses of 131I-Hyp were delivered to necrotic (276­93,600 mGy/MBq) than to viable (4.2 mGy/MBq) liver (P<0.05). In normal organs, 123I­Hyp was eliminated within 24 h except for relatively high levels in the lungs and thyroid. Hepatobiliary elimination was a major pathway of 123I-Hyp causing high activity in the intestines. For both genders, dosimetry showed the longest residence time of 131I-Hyp in the remainder, followed by the lungs, intestines and thyroid. The highest absorbed radiation dose was seen in necrotic tissues and the shortest residence times and lowest absorbed radiation dose were found in the brain. 131I-Hyp selectively delivers higher radiation dose to necrosis compared with the rest of the body. Among normal organs, thyroids, lungs and intestines receive considerable radiation dose, which deserves cautious attention in developing this anticancer approach.

Continuing pursuit for ideal systemic anticancer radiotherapeutics.

Cancer is one of the major causes of death for non-transmissible chronic diseases worldwide. Conventional treatments including surgery, chemotherapy and external beam radiotherapy are generally far from curative. Complementary therapies are attempted for achieving more successful treatment response. Systemic targeted radiotherapy (STR) is a radiotherapeutic modality based on systemic administration of radioactive agents for selectively delivering high doses of energy to destroy cancer cells. For this purpose, diverse tumour-target specific agents including monoclonal antibodies (MoAb), MoAb fragments and peptides have been tested and some of them have already got FDA approval for clinical use. However, MoAbs and their tailored analogues have shown non-homogeneous tumour distribution, limited diffusion, insufficient intratumoral accumulation and retention, unwanted uptake in normal tissues and scarcity of identified cancer antigens for generating new MoAbs. Similarly, peptides have also exhibited retention in normal organs, lacks of favourable membrane permeability or drug cell internalization and short-term residence in cancer cells. Recently, a new category of target-specific agent with strong affinity for necrosis has emerged as an excellent option for developing targeted radiotherapeutic agents to be used after necrosis-inducing treatments (NITs). The combination of their high, specific and long-term accumulation and retention at necrotic sites with the crossfire effect of ionizing particle-emitters allows irradiating adjacent residual viable tumour cells during a prolonged period of time. It may considerably enhance the therapeutic response and open a new horizon for improved cancer treatability or curability.

Non-invasive detection and quantification of acute myocardial infarction in rabbits using mono-[123I]iodohypericin microSPECT.

AIMS: Mono-[(123)I]iodohypericin ([(123)I]MIH) has been reported to have high avidity for necrosis. In the present study, by using rabbit models of acute myocardial infarction, we explored the suitability of [(123)I]MIH micro single photon emission computed tomography (microSPECT) for non-invasive visualization of myocardial infarcts in comparison with [(13)N]ammonia micro positron emission tomography (microPET) imaging, postmortem histomorphometry, and [(123)I]MIH autoradiography. METHODS AND RESULTS: Fourteen rabbits were divided into four groups. The left circumflex coronary artery was permanently occluded in group A (n = 3), reperfused by releasing the ligature after 15 min in group B (n = 3) or 90 min in group C (n = 6), or not occluded in group D (n = 2). Animals received [(13)N]ammonia microPET perfusion imaging 18 h after infarct induction followed by microSPECT imaging at 2-3.5, 9-11, and 22-24 h post injection (p.i.) of [(123)I]MIH. The cardiac images were assembled into polar maps for assessment of tracer uptake. Animals were sacrificed and the excised heart was sliced for autoradiography, triphenyl tetrazolium chloride, and haematoxylin-eosin staining. Using [(123)I]MIH microSPECT, infarcts were well delineated at 9 h p.i. Mean microSPECT infarct size was 38.8 and 32.7% of left ventricular area for groups A and C, respectively, whereas group B showed low uptake of [(123)I]MIH. Highest mean infarct/viable tissue activity ratio of 61/1 was obtained by autoradiography in group C animals at 24 h p.i. CONCLUSION: The study indicates the suitability of [(123)I]MIH for in vivo visualization of myocardial infarcts.