Radiolabelling of poly(histidine) derivatized biodegradable microspheres with the 188Re tricarbonyl complex [188Re(CO)3(H2O)3]+

OBJECTIVES: Many radiopharmaceuticals have been studied as radiation synovectomy agents. In this study, we developed a new potential agent for radiation synovectomy: poly(lactic acid)-histidine (PLA-his) microspheres radiolabelled with [188Re(CO)3(H2O)3]+. METHODS: The reaction conditions for the chelation of [188Re(CO)3(H2O)3]+ and the radiolabelling of PLA microspheres were optimized and the stabilities for both steps tested in vitro. RESULTS: The chelation efficiency of [188Re(CO)3(H2O)3]+ reached 93.12 +/- 1.82% with >95% radiochemical purity once the colloidal and free 188Re were removed by a small Sep-Pak column (Plus QMA). More than 90% of radioactivity stayed in the [188Re(CO)3(H2O)3]+ form over 5 h. The radiolabelling efficiency of PLA-his microspheres with [188Re(CO)3(H2O)3]+ was above 92%. After 3 days incubation at 37 degrees C in calf serum, more than 80% of the radioactivity was still bound to the microspheres. CONCLUSION: Such microspheres are potentially useful as a radiation synovectomy agent for the treatment of chronically inflamed arthritic joints. Furthermore, they might be valuable in cancer brachytherapy.     

Radiolabeling morpholinos with 90Y, 111In, 188Re and 99mTc

This laboratory is investigating morpholinos (MORF), a DNA analogue, for radiopharmaceutical applications. While we routinely radiolabel with (99m)Tc, we have now labeled MORFs with (111)In, (188)Re and (90)Y in anticipation of therapeutic studies. METHODS: A 25 mer MORF with a primary amine on the 3' equivalent end attached via a 10 member linker was conjugated with an isothiocyanate backbone derivative of DOTA (for labeling with (111)In and (90)Y) and with NHS-MAG(3) (for labeling with (188)Re and (99m)Tc). The in vitro stability of labeled MORFs were investigated and biodistribution was carried out in normal mice. RESULTS: As evident by size exclusion HPLC, ITLC and Sep-Pak analysis, all four radiolabeled MORFs were successfully radiolabeled. In each case, the labeled MORFs showed one sharp peak in HPLC that shifted completely to earlier retention times following addition of a polymer conjugated with the complementary MORF. In saline at room temperature and in 37 degrees C serum, the radioactivity profile of (111)In, (188)Re and (99m)Tc was unchanged over 48 h while over the same period, the (90)Y profile showed a pronounced lower molecular weight peak which did not shift and was shown to be most probably due to (90)Y-DOTA resulting from radiolysis. In addition, the recovery of (188)Re on HPLC decreased as samples aged probably due to oxidation to perrhenate which was retained by the HPLC column. The biodistributions at 1, 3 and 6 h in normal mice showed no important differences among all four labels with the exception that levels of radioactivity in stomach and thyroid were higher in the case of (188)Re due to in vivo oxidation of the radiolabel to perrhenate. CONCLUSIONS: When radiolabeled with DOTA, (90)Y-labeled MORF showed increased instabilities relative to that of (111)In and when radiolabeled with MAG(3), (188)Re showed in vitro and in vivo instabilities compared to (99m)Tc, but all labels were still largely intact after 48 h in saline or serum. Possibly because of the rapid clearance of MORFs, no important differences in biodistribution among (90)Y, (111)In and (99m)Tc labels were evident in normal mice. These strategies for labeling MORF with (90)Y and (188)Re therefore appear to be suitable for therapeutic applications although both show some evidence of instabilities.     

Synthesis of 99mTc-nimotuzumab with tricarbonyl ion: in vitro and in vivo studies

The Epidermal growth factor receptor (EGFR) family plays an important role in carcinogenesis. CIMAher? (Nimotuzumab), is a humanized monoclonal antibody, which recognizes EGFR with high affinity. The aim of this work was to perform the direct labeling of Nimotuzumab with [99mTc(CO)3(H2O)3]+ as precursor and to evaluate its labeling conditions, in vitro and in vivo stability and biodistrution in normal C57 BL/6J mice. 99mTc(CO3)-Nimotuzumab labeling yields were up to 90%. More than 90% of the complex remained intact after 24 h of incubation with L-Histidine (1/300 molar ratio). Biodistribution studies in normal mice were also performed. Inmunoreactivity was confirmed by cell binding assays with A431cells. These results encourage the evaluation of the potential role of 99mTc(CO)3-Nimotuzumab as a novel tumor-avid radiotracer for targeting in vivo EGFR expression.     

188Re-Herceptin-磁性纳米微粒的体外抗肿瘤作用

目的探讨^188Re—Herceptin-磁性纳米微粒在外置磁场下对HER-2／neu癌基因高表达的SKBR-3乳腺癌细胞的靶向结合性及抗癌作用。方法采用戊二醛交联法使人源性单克隆抗体Her—ceptin与磁性纳米微粒交联，用直接标记法制备^188Re—Herceptin及^188Re—Herceptin-磁性纳米微粒，用羰基铼标记法制备^188Re-磁性纳米微粒。肿瘤细胞体外抑制实验设4个组：^188Re—Herceptin-磁性纳米微粒组、^188Re—Herceptin组、^188Re-磁性纳米微粒组和^188ReO4^-组，各组均设3．7×10^4、18．5×10^4、37×10^4、55．5×10^4、74×10^4Bq／ml5个放射性剂量级别；另设生理盐水对照组。采用四甲基偶氮唑蓝（MTT）法测定各组的抑瘤效应，计算相对抑制率，采用半数抑制放射性浓度（IC50）对各组抑瘤作用进行比较和评价。结果^188Re—Herceptin-磁性纳米微粒和^188Re—Herceptin组对SKBR-3细胞均有较强杀伤作用，且呈剂量依赖性；而^188Re-磁性纳米微粒和^188Re04组的杀伤作用较弱0188Re—Herceptin-磁性纳米微粒组的IC50（53．1×10^4Bq／L）明显低于^188Re—Herceptin组（76．1×10^4Bq／L）；^188Re一磁性纳米微粒组和^188ReO4组的IC50分别为169×10^4和175×10^4Bq／L，明显高于前2组。结论^188Re—Herceptin-磁性纳米微粒和^188Re—Herceptin均可明显抑制体外培养的SKBR-3乳腺癌细胞增殖，且前者的抑制作用较后者强。     

A comparative study of 188Re(V)-meso-DMSA and 188Re(V)-rac-DMSA: preparation and in vivo evaluation in nude mice xenografted with a neuroendocrine tumor

Dimercaptosuccinic acid (DMSA) exists in meso and racemic (rac) forms. Unlike a meso isomer, rac-2,3-DMSA is very soluble in water, strongly acidic solutions and organic solvents. Despite these differences, rac-2,3-DMSA has not been studied as a radiopharmaceutical. In this study, ¹⁸⁸Re complexes with diastereomeric DMSA were prepared to compare the properties of ¹⁸⁸Re(V)-rac-DMSA with those of ¹⁸⁸Re(V)-meso-DMSA in in vitro and in vivo models.

Methods

rac-2,3-DMSA was synthesized and radiolabeled with ¹⁸⁸Re. The biodistribution and gamma camera imaging of ¹⁸⁸Re(V)-meso-DMSA and ¹⁸⁸Re(V)-rac-DMSA were performed in nude mice subcutaneously implanted with PC-12 cell lines.

Results and conclusions

Both ¹⁸⁸Re(V)-meso-DMSA and ¹⁸⁸Re(V)-rac-DMSA showed excellent radiochemical purity and stability at room temperature. Compared with ¹⁸⁸Re(V)-meso-DMSA, ¹⁸⁸Re(V)-rac-DMSA needed a higher concentration of rac-DMSA and metabisulfite for maximum yields. ¹⁸⁸Re(V)-meso-DMSA showed high labeling efficiency at pH 2, whereas ¹⁸⁸Re(V)-rac-DMSA showed maximum yields at pH 5. The tumor uptake of ¹⁸⁸Re(V)-rac-DMSA was 3.5 times higher than that of ¹⁸⁸Re(V)-meso-DMSA at 1 h (P<.01). Gamma camera images showed that ¹⁸⁸Re(V)-rac-DMSA was more selectively localized than ¹⁸⁸Re(V)-meso-DMSA at the tumor region in a xenograft model. These results demonstrate that ¹⁸⁸Re(V)-rac-DMSA may have better potential than ¹⁸⁸Re(V)-meso-DMSA as a therapeutic agent against neuroendocrine tumors.     

188 Re直接法标记生长抑素类似物RC-160及其体内分布研究

目的 探讨^188RE直接法标记生长抑素类似物RC－160的方法及观察其在小鼠体内的生物学分布。方法 酒石酸亚锡直接还原法进行RC－160的^188Re标记，标记完成后加入抗坏血酸以防标记产物的再氧化。硅胶纸层析测定放化纯，并行小鼠体内分布实验。结果 ^188Re－RC－160放化纯为96．2％，游离^188Re为0．8％，放射性胶体为3．0％。加抗坏血酸组在标记后24h放化纯为85％，对照组为50％。注射后0．5－1．0h血液中放射性下降了87．2％，肾脏无明显浓集，标记物24h内由消化系统排出体外。结论 ^188Re直接法标记RC－160放化纯高，方法简便，抗坏血酸的加入增加了标记物的稳定性。^188Re－RC－160在小鼠体现血液清除较快，经消化系统排除。     

In vivo examination of 188Re(I)-tricarbonyl-labeled trastuzumab to target HER2-overexpressing breast cancer

IntroductionTrastuzumab (Herceptin), a humanized IgG1 monoclonal antibody directed against the extracellular domain of the HER2 protein, acts as an immunotherapeutic agent for HER2-overexpressing human breast cancers. Radiolabeled trastuzumab with β- or α emitters can be used as radioimmunotherapeutic agent for the similar purpose but with additional radiation effect.MethodsIn this study, trastuzumab was labeled with ¹⁸⁸Re for radioimmunotherapy of HER2/neu-positive breast cancer. ¹⁸⁸Re(I)-tricarbonyl ion, [¹⁸⁸Re(OH₂)₃(CO)₃]⁺, was employed as a precursor for directly labeling the monoclonal antibody with ¹⁸⁸Re. The immunoreactivity of ¹⁸⁸Re(I)-trastuzumab was estimated by competition receptor-binding assay using HER2/neu-overexpressive BT-474 human breast cancer cells. The localization properties of ¹⁸⁸Re(I)-trastuzumab within both tumor and normal tissues of athymic mice bearing BT-474 human breast cancer xenografts (HER2/neu-overexpressive) and similar mice bearing MCF-7 human breast cancer xenografts (HER2/neu-low expressive) were investigated.ResultsWhen incubated with human serum albumin and histidine at 25°C, ¹⁸⁸Re(I)-trastuzumab was found to be stable within 24 h. The IC₅₀ of ¹⁸⁸Re(I)-trastuzumab was found to be 22.63±4.57 nM. ¹⁸⁸Re(I)-trastuzumab was shown to accumulate specifically in BT-474 tumor tissue in in vivo biodistribution studies. By microSPECT/CT, the image of ¹⁸⁸Re localized BT-474 tumor was clearly visualized within 24 h. In contrast, ¹⁸⁸Re(I)-trastuzumab uptake in HER2-low-expressing MCF-7 tumor was minimal, and the ¹⁸⁸Re image at the localization of the tumor was dim.ConclusionThese results reveal that ¹⁸⁸Re(I)-trastuzumab could be an appropriate radioimmunotherapeutic agent for the treatment of HER2/neu-overexpressing cancers.     

Preparation of cyclotron-produced 186Re and comparison with reactor-produced 186Re and generator-produced 188Re for the labeling of bombesin

The radioisotopes (186)Re and (188)Re have been extensively investigated for various forms of radiotherapy due to their useful and high-abundance beta particle emissions, low-abundance and imageable gamma-rays, and chemical resemblance to technetium. In addition, (188)Re is available in no-carrier-added (NCA) form from long lived W-188 generators, whereas (186)Re can be produced in large quantities from reactors, although not in NCA form. However, NCA (186)Re can be produced on a cyclotron by a (p,n) reaction on (186)W. The purpose of this study was to compare labeling of the peptide bombesin with these three forms of rhenium radioisotopes. Cyclotron-produced NCA (186)Re was separated radiochemically from enriched (186)W (96.9%) targets using high-purity methyl ethyl ketone (MEK). The resulting (186)Re-MEK was then loaded onto a small alumina column to separate the resulting NCA (186)Re from any remaining (186)W. The experimental levels of impurities associated with (186)Re at the end of the separation process were found to be 5.7 x 10(-6) Ci of (182)Re (0.57%, t(1/2) = 12.7 h) and 1.283 x 10(-5) Ci of (182m)Re (1.28%, t(1/2) = 2.67 days). The radionuclidic purity of the separated (186)Re was found to be 99.6%, whereas the chemical identity was determined by reversed phase high-performance liquid chromatography (RP-HPLC) to be perrhenate ((186)ReO(4)(-)). Generator-produced (188)ReO(4)(-) from a (188)W/(188)Re generator (Oak Ridge National Laboratory) and CA (186)ReO(4)(-) produced from a (185)Re(n,gamma)(186)Re reaction at the University of Missouri Research Reactor (MURR) were used for comparison with the NCA (186)Re in subsequent studies. N(3)S-5-Ava-BBN(7-14)NH(2) conjugates provide flexibility for designing (186,188)Re-labeled conjugates that retain high in vitro and in vivo specificity targeting of GRP receptor-expressing cells. This study showed that the N(3)S-5-Ava-BBN(7-14)NH(2) could be labeled with (186,188)Re following the preconjugation, postmetallation approach. The (186,188)Re(V)O-N(3)S-5-Ava-BBN(7-14)NH(2) complexes were found to form stable complexes following the reduction of perrhenate (Re(VII)O(4)(-)) with stannous chloride at room temperature, as verified by HPLC and stability studies. The radiolabeling yield was found to be >90%. The HPLC chromatograms of (186,188)Re-N(3)S-5-Ava-BBN(7-14)NH(2) complexes revealed two peaks for each conjugate, reflecting the presence of syn- and anti-isomers, which were resolvable by HPLC but re-isomerized on separation. The biodistribution studies showed that the compounds were excreted through the renal and hepatobiliary systems and demonstrated receptor-specific uptake with an average pancreas accumulation of 8.15% ID/g at 1 h postinjection. Administration of cold BBN effectively blocked pancreatic uptake and further reflects the high specificity this conjugate has for the GRP receptors. At low levels of radioactivity, radiolysis effects were not observed. Scale-up may or may not elicit this effect, particularly for the higher energy beta emitter (188)Re. The biodistribution studies demonstrated that the CA and NCA (186,188)Re conjugates behaved similarly, raising the question of whether NCA (186,188)Re is necessary for specific tumor receptor targeting.     

放射性榄香烯三羰基铼配合物在荷小细胞肺癌裸鼠体内的分布及其对肿瘤的生长抑制作用

Objective To observe the anti-tumor effect of elemene tricarbonyl rhenium-188 complex(ETRC)on small cell lung cancer(SCLC)bearing nude mice model,and also its biodistribution,tumor targeting features.Methods ETRC was synthesized from β-elemene,which is a active ingredient in Chinese herbal medicine.Twelve SCLC bearing nude mice were infused ETRC through tail vein.The radioactivity of tumor and diferent organs were measured in various time phase.And ％ID/g was calculated.All 20 mice models were divided into four groups randomly,concluding①Physiological saline infusion group;②Elemene infusiongroup;③~(188)Re infusion group;④ETRC infusion group.Twenty four days after infusion,the volume and weight of tumors were measured and analyzed.Results Six hours after infusion of ETRC,the highest radioactive upmke[(6.35±0.33)％ID/g]was found in tumor mass.Ratio of tumor/blood was 2.59,ratio of tumor/liver was 4.07 and ratio of tumor/spleen was 3.87.The volume and weight of tumor in four groups were:groups①:(2.945±0.567)cm~3,(5.438±1.232)g;groups②:(1.860±0.263)cm~3,(4.876±0.621)g;groups③:(1.861±0.896)cm~3,(4.691±1.595)g;groups④:(0.601±0.152)cm~3,(1.602±0.194)grespectively.There was significant difference between ETRC infusion group and each of other groups.Conclusion ETRC can effectively depress the growth of tumor and it is a promising agent for the treatment of SCLC.     

放射性榄香烯三羰基铼配合物在荷小细胞肺癌裸鼠体内的分布及其对肿瘤的生长抑制作用

目的 观察放射性榄香烯三羰基铼(ETRC)对荷小细胞肺癌裸鼠模型的肿瘤生长抑制作用,并分析其在裸鼠体内的分布、靶向性。方法 以中草药有效成分β-榄香烯为起始原料,人工合成ETRC;制备荷H128小细胞肺癌BALB/c裸鼠模型,12只荷瘤裸鼠尾静脉注射ETRC,分别在不同时间测量肿瘤组织及各器官的放射性,计算每克组织百分注射剂量率(%ID/g)。将20只荷瘤裸鼠随机分为4组:①对照组;②榄香烯治疗组;③188Re治疗组;④ETRC治疗组。尾静脉注射相应试剂后24d比较肿瘤的体积和质量。结果 给药后6h肿瘤组织的放射性最强,为(6.35±0.33)%ID/g,此时肿瘤/血液放射性比值为2.59,肿瘤/肝放射性比值为4.07,肿瘤/脾放射性比值为3.87.给药后24d,肿瘤体积和质量分别为①组:(2.945±0.567)cm3,(5.438±1.232)g;②组:(1.860±0.263)cm3,(4.876±0.621)g;③组:(1.861±0.896)cm3,(4.691±1.595)g;④组:(0.601±0.152)cm3,(1.602±0.194)g。ETRC治疗组显着好于其他各组。结论 ETRC能有效抑制裸鼠小细胞肺癌的生长,对小细胞肺癌治疗有潜在的应用前景。     

The stability and distribution of Tc-HIDA in vivo and in vitro

Tc-HIDA is a promising new agent for imaging the biliary system. In this study radiochromatography on paper or Sephadex G25 gel has been used to measure the proportions of TcHIDA, 'hydrolysed Tc' and pertechnetate in solutions from a commercial kit (CIS TCK 15) and in body fluids from patients and rats receiving this radiopharmaceutical. The tissue distribution in male and female rats has shown the radiopharmaceutical to be rapidly removed from the blood by the liver and then excreted via the intestines. There appears to be a sex difference in the uptake in the kidneys and in the urinary excretion in both rats and patients.     

The stability and distribution of Tc-HIDA in vivo and in vitro

Tc-HIDA is a promising new agent for imaging the biliary system. In this study radiochromatography on paper or Sephadex G25 gel has been used to measure the proportions of TcHIDA, hydrolysed Tc and pertechnetate in solutions from a comercial kit (CIS TCK 15) and in body fluids from patients and rat receiving this radiopharmaceutical. The tissue distribution in male and female rats has shown the radiopharmaceutical to be rapidly removed from the blood by the liver and then excreted via the intestines. There appears to be a sex difference in the uptake in the kidneys and in the urinary excretion in both rats and patients.     

Applied radioactivity in radiation synovectomy with [188Re]rhenium sulfide suspension

BACKGROUND: Early experience demonstrated absorbed dose in radiation synovectomy is about 100 Gy. For reaching this dose, the applied radioactivity should be calculated. METHOD: Twenty-nine synovitic models of rabbit were treated by intra-articular injection of [(188)Re]rhenium sulfide and histological changes of synovium and cartilage were examined. The applied radioactivity was calculated by method of absorbed dose factor. In clinical, eleven haemophilic patients with haemarthrosis were performed radiation synovectomy with treated [(188)Re]rhenium sulfide. The synovial thickness was evaluated by MR and its value was used to calculate the applied radioactivity. After radiation synovectomy, all patients were followed up by synovial thickness, regional inflammation, and clinical course including bleeding frequency. RESULTS: In rabbit models, the synovitic membrane can be eliminated by calculated radioactivity as planed without damaging the joint cartilage. In patients study, all patients exhibited significant reductions in synovial thickness and inflammation after radiation synovectomy with the planed radioactivities of [(188)Re]rhenium sulfide. Post-procedure bleeding frequency reduction in excellent and good reached to 63.6% by 18 months. In the cases of joint bleeding, the need for antihaemophilic factor treatment decreased immensely. Most of the recurrent episodes of bleeding were mild, subsiding with local means. CONCLUSION: The applied radioactivity in radiation synovectomy could be calculated according to thickness of inflamed synovium. Further study including comparison therapeutic results from calculated individual activities with results from fixed activities and long-term follow-up is warranted.     

Labeling and biodistribution of different particle materials for radioembolization therapy with 188Re.

Radioembolization of tumors after selective catheterization has been proven to be an effective therapy in nuclear medicine. The goal of the study was to evaluate the (188)Re labeling and in vitro and in vivo stability of several representative non-degradable polymeric microspheres and biodegradable particles. The biodistribution after i.v. injection in Wistar rats revealed excellent in vivo stability with low uptake in the non-target tissues over 48 h for some polymeric particles and especially for biodegradable human serum albumin microspheres.     

Storage conditions for 188Re-perrhenate solutions and their impact on the use of the 188Re-perrhenate in the preparation of 188Re labelled compounds

Rhenium-188 has a half life of 17 h and can be stored and/or transported prior to preparation of the labelled compounds. However, the radiolysis within the aqueous solutions can result in changes in the suitability of the perrhenate solution for use in the preparation of the labelled compound. This paper reports a study of the production of the major radiolysis product, hydrogen peroxide, its effect on the formation of one radiopharmaceutical together with the results of various attempts to limit or eliminate these effects.     

Proton spectroscopy provides accurate pathology on biopsy and in vivo

In the last 25 years, MR spectroscopy (MRS) has moved from being a basic research tool into routine clinical use. The spectroscopy method reports on those chemicals that are mobile on the MR time scale. Many of these chemicals reflect specific pathological processes but are complicated by the fact that many chemicals change at one time. There are currently two clinical applications for spectroscopy. The first is in the pathology laboratory, where it can be an adjunct to, and in some cases replacement, for difficult pathologies like Barrett's esophagus and follicular adenoma of the thyroid. The spectroscopy method on a breast biopsy can also report on prognostic indicators, including the potential for spread, from information present in the primary tumor alone. The second application for spectroscopy is in vivo to provide a preoperative diagnosis and this is now achievable for several organs including the prostate. The development of spectroscopy for clinical purposes has relied heavily on the serially-sectioned histopathology to confirm the high accuracy of the method. The combination of in vivo MRI, in vivo MRS, and ex vivo MRS on biopsy samples offers a modality of very high accuracy for preoperative diagnosis and provision of prognostic information for human cancers.     

99mTc(V)DMSA quantitatively predicts 188Re(V)DMSA distribution in patients with prostate cancer metastatic to bone

Rhenium-188 dimercaptosuccinic acid complex [188Re(V)DMSA], a potential therapeutic analogue of the tumour imaging agent 99mTc(V)DMSA, is selectively taken up in bone metastases in patients with prostate cancer. It would be helpful in planning palliative radionuclide therapy if 99mTc(V)DMSA could be used to predict tumour and kidney retention of 188Re(V)DMSA. The aim of this study was to determine the correlation between tumour-to-normal tissue ratios and kidney-to-soft tissue ratios of 99mTc(V)DMSA and 188Re(V)DMSA. This would determine whether a scan with 99mTc(V) DMSA could be used to identify patients for whom 188Re(V)DMSA treatment would be contra-indicated, and enable prediction of relative kidney and tumour radiation absorbed dose in 188Re(V)DMSA treatment. Ten patients with prostate carcinoma were recruited following observation of disseminated bone metastases on a recent 99mTc-hydroxydiphosphonate bone scan. Whole-body planar scans were obtained at ca. 4 h and 24 h after hydration and injection of 600 MBq 99mTc(V)DMSA, and a week later, at similar times after hydration and injection of 370 MBq 188Re(V)DMSA. A triple-energy window (TEW) scatter correction was applied to the 188Re scans. Counts per pixel were determined in regions of interest drawn over metastatic sites, kidneys and normal soft tissue. Tumour-to-soft tissue ratios were significantly lower (by a factor of approximately 0.8 after the TEW was applied) on 188Re scans than on 99mTc scans, but the two were highly linearly correlated both in all individual patients and in tumours pooled from all patients together both at 4 h and at 24 h. Kidney-to-soft tissue ratios were similarly correlated and were lower for 188Re than for 99mTc by a similar factor. Both tumour- and kidney-to-soft tissue ratios increased between 4 and 24 h but the latter increased more. In conclusion, only minor differences were seen between 99mTc and 188Re scans, and kidney-to-background ratios on 188Re scans were not higher than on 99mTc scans. These differences are insufficient to infer that they are due to a real difference in biodistribution, and they may be due only to different physical imaging characteristics. Thus 99mTc(V)DMSA scans are predictive of 188Re(V)DMSA biodistribution and could be used to estimate tumour and renal dosimetry and assess suitability of patients for 188Re(V)DMSA treatment.     

99mTc(V)DMSA quantitatively predicts 188Re(V)DMSA distribution in patients with prostate cancer metastatic to bone

Rhenium-188 dimercaptosuccinic acid complex [¹⁸⁸Re(V)DMSA], a potential therapeutic analogue of the tumour imaging agent ^99mTc(V)DMSA, is selectively taken up in bone metastases in patients with prostate cancer. It would be helpful in planning palliative radionuclide therapy if ^99mTc(V)DMSA could be used to predict tumour and kidney retention of ¹⁸⁸Re(V)DMSA. The aim of this study was to determine the correlation between tumour-to-normal tissue ratios and kidney-to-soft tissue ratios of ^99mTc(V)DMSA and ¹⁸⁸Re(V)DMSA. This would determine whether a scan with ^99mTc(V)DMSA could be used to identify patients for whom ¹⁸⁸Re(V)DMSA treatment would be contra-indicated, and enable prediction of relative kidney and tumour radiation absorbed dose in ¹⁸⁸Re(V)DMSA treatment. Ten patients with prostate carcinoma were recruited following observation of disseminated bone metastases on a recent ^99mTc-hydroxydiphosphonate bone scan. Whole-body planar scans were obtained at ca. 4 h and 24 h after hydration and injection of 600 MBq ^99mTc(V)DMSA, and a week later, at similar times after hydration and injection of 370 MBq ¹⁸⁸Re(V)DMSA. A triple-energy window (TEW) scatter correction was applied to the ¹⁸⁸Re scans. Counts per pixel were determined in regions of interest drawn over metastatic sites, kidneys and normal soft tissue. Tumour-to-soft tissue ratios were significantly lower (by a factor of approximately 0.8 after the TEW was applied) on ¹⁸⁸Re scans than on ^99mTc scans, but the two were highly linearly correlated both in all individual patients and in tumours pooled from all patients together both at 4 h and at 24 h. Kidney-to-soft tissue ratios were similarly correlated and were lower for ¹⁸⁸Re than for ^99mTc by a similar factor. Both tumour- and kidney-to-soft tissue ratios increased between 4 and 24 h but the latter increased more. In conclusion, only minor differences were seen between ^99mTc and ¹⁸⁸Re scans, and kidney-to-background ratios on ¹⁸⁸Re scans were not higher than on ^99mTc scans. These differences are insufficient to infer that they are due to a real difference in biodistribution, and they may be due only to different physical imaging characteristics. Thus ^99mTc(V)DMSA scans are predictive of ¹⁸⁸Re(V)DMSA biodistribution and could be used to estimate tumour and renal dosimetry and assess suitability of patients for ¹⁸⁸Re(V)DMSA treatment.     

99Tcm-MAG3: in vitro stability and in vivo behaviour at different times after preparation

A kit for preparing technetium-99m mercaptoacetyltriglycine (99Tcm-MAG3), a new radiopharmaceutical for gamma camera renography, is available commercially. A drawback to the use of this kit is the recommended 1h expiry for 99Tcm-MAG3. This short expiry is a consequence of the possible growth of an impurity which undergoes hepatobiliary excretion and might interfere with renal imaging. Radiochemical purity of 99Tcm-MAG3 was measured by high performance liquid chromatography at 0, 1 and 6 h after preparation and was found to be consistently greater than 95. 99Tcm-MAG3 was shown to contain five impurities, one of which increased from 0.5% to 1% over 6 h. Dilution of 99Tcm-MAG3 eliminated this effect. A two-part clinical study was undertaken. For Part I, 99Tcm-MAG3 was prepared at 400 MBq/4 ml. For Part II, 99Tcm-MAG3 was prepared at 1 GBq/4 ml then subdivided and diluted to give single doses of 175 MBq/2.5 ml. In both parts, 10 patients were injected within 1 h after preparation and 10 were injected 5-6 h after preparation. From gamma camera images of the abdomen acquired 30 min after injection, the % injected 99Tcm in gall bladder and liver were calculated. In both parts, the % injected 99Tcm in gall-bladders and livers of the 1 h group were compared with those in the 5-6 h group and not found significantly different (p greater than 0.05). In conclusion, 99Tcm-MAG3 prepared according to the methods described, can be used up to 6 h after preparation.