Study on tumor affinity of technetium-99m-labeled radiopharmaceuticals. (1) 99mTc-pertechnetate, 99mTc-human serum albumin, and 99mTc-trasylol]

This paper describes biologic distributions, sequential images and macroautoradiograms of 99mTcO4 (pertechnetate), 99mTc-Sn-HSA (human serum albumin) and 99mTc-Sn-TSL (trasylol) in tumor-bearing mice as the first report on tumor affinity of 99mTc-labeled radiopharmaceutical. (1) Maximum tumor concentration (% administered dose/g of tissue weight) of 99mTcO4, 99mTc-HSA and 99mTc-TSL in Ehrlich's tumor-bearing mice resulted in 2.03+/-0.57 at 1 hr, 4.02+/-0.19 at 3 hr and 1.97+/-0.31 at 1 hr respectively. (2) However, tumor to blood concentration ratio of 99mTc-HSA was lowest among them. (3) The corrected tumor accumulation (% 100g dose/g of tissue wt.=% dose/% body weight) of 99mTc-TSL to Ehrlich's tumor in mouse was not different from that of Yoshida's sarcoma in rat, on the contrary to our expectation that the tumor concentration of 99mTc-TSL in them might be different due to differency of the tissue fibrinolytic activity between the respective tumors. (4) Sequential images of the implanted tumor in mouse was best positively delineated with 99mTc-HSA. (5) Macroautoradiograms of Ehrlich's tumor with 99mTcO4, 99mTc-HSA and 99mTc-TSL demonstrated the following findings: all of them were not only accumulated markedly into the tumor cells which were shown as basophilic tissue with H?matoxylin-Eosin staining but also accumulated around the tumor tissue and on the interstitial tissue which were stained as eosinophilic tissue with the above same staining.     

Tumor affinity of 99mTc-labeled radiopharmaceuticals, 99mTc-Sn-urokinase and 99mTc-Sn-mannitol

Biolgic distribution of 99mTc-labeled fibrinolytic agent, urokinase, and 99mTc-labeled mannitol, which was obtained as a side-product in the preparation of 99mTc(Sn)-urokinase, have been studied in Ehrlich's tumor-bearing mice to get a promising indicator for the positive delineation of malignant tumor. The preparation of 99mTc-labeled radiopharmaceuticals, 99mTc-UK and 99mTc-Man, was made by the reduction with stannous chloride and labeling efficiency was examined by Sephadex G-25M gel chromatography and by silica gel plate thin layer chromatography. Labeling yield of 99mTc-UK by Sephadex G25M in 0.9% NaCl eluant was 13% and that of 99mTc-Man by TLC in 85% methanol solvent was over 95%. A higher uptake to the implanted solid tumor tissue in mice was found in 99mTc-Man than in 99mTc-UK, of which the excellent tumor accumulation was expected from the positive delineation of malignant tumor with 131I-fibrinogen, 131I-fibrinogen antibody and 125I-plasmin. The poor result in 99mTc-UK, however, may be attributed to the poor fibrinolytic activity of Ehrlich's tumor. In biologic distribution of 99mTc-UK was found high concentration for liver kidney and stomach. In the other hand, a higher tumor tissue uptake, a fast blood disappearance and a low concentration for different organs were found in biologic distribution of 99mTc-Man. Therefore, 99mTc-Man may be assumed as a more preferable 99mTc-labeled tumor localizing radiopharmaceuticals, to which it would be needed as absolute biologic characteristics that 99mTc-labeled compounds possess a high tumor uptake as well as a fast blood disappearance with a low uptake for different organs. However, the possible delineation with 99mTc-labeled fibrinolytic agents, including urokinase and streptokinase, may be promised for malignant tumors in human-subject, which generally have a higher activity in fibrinogenesis than in fibrinolysis.     

Study of distribution of 203Hg-chlormerodrin, 203Hg-nitrate and 99mTc-DMSA in kidney by macroautoradiography (author's transl)]

Serial macroautoradiograms were obtained to determine the distribution of 203Hg-chlormerodrin, 203Hg-nigrate and 99mTc-DMSA in kidney. In the study, normal rats were used and these three radiopharmaceuticals were injected intravenously. Initial images of 203Hg-chlormerodrin showed the accumulation in the outer cortex, but no significant radioactivity in the medullary. On the other hand, delayed images revealed radioactivity shifting in concentration from the outer cortex to the inner cortex. Distribution pattern of 203Hg-nitrate was similar to that of 203Hg-chlormerodrin. In contrast to 203Hg-chlormerodrin and 203Hg-nitrate, 99mTc-DMSA was retained in the outer cortex without temporal changes in the distribution.     

Investigation of 99mTc labeled tumor seeking agents--usefulness of 99mTc-isoniazid

For the development of 99mTc labeled tumor seeking agents, 273 drugs and chemicals were evaluated. Agents labeled by SnCl2-HCl method were injected to rats bearing Yoshida sarcoma. Scintigrams of the rats 2 hours after injection and the excised tumor and organs placed on a plate were taken and evaluated their affinity to the tumor. Isoniazid (INH) was found to be the most useful agent as a result of this screening study. Intensive study on 99mTc-INH was subsequently performed. Another labeling method, FeSO4-H2SO4 method, was evaluated and shown to be superior in both absolute tumor uptake and tumor to muscle ratio. Uptake of 99mTc-INH to Yoshida sarcoma occurred early after injection and maintained its level until later time. On the other hand, radioactivity in the blood and muscle decreased rapidly; that is, tumor to blood and muscle ratio showed rapid increase. Other animal tumor models, mouse bearing Ehrlich tumor or Sarcoma 180, were also used to evaluate the usefulness of 99mTc-INH. The labeled agent showed good localization in these tumors too. In conclusion 99mTc-INH might be a good tumor seeking agent and further clinical trials would be warrant.     

Biodistribution of A14C-and99mTc-labeled N-substituted nitrosourea (CCNU) in an animal tumor model

One formulation of¹⁴C labeled and another of^99mTc labeled 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU) were administered i.v. to tumor (glioma) bearing rats. The radiopharmacokinetics of¹⁴C-CCNU were followed up to 24 hours post injection. On a per organ basis the blood, liver, small bowel, kidney cortex and muscle contained most of the activity. Optimum tumor to organ ratios occurred at 4–12 hours. The^99mTc-CCNU biodistribution was determined at 4 hours and compared to^99mTc-NaTcO₄. Tumor capsule to brain (29.5) and to muscle (10.59) ratios suggest^99mTc-CCNU to be a potential tumor seeking agent. Funded in part by USPHS Grant RR-05486-12.     

The interactions of99mTc phosphorus radiopharmaceuticals and human serum proteins

Dialysis and precipitation methods have been used to study the binding affinity of selected technetium-99m phosphorus radiopharmaceuticals to human serum proteins. The binding affinities of three different^99mTc bone imaging agents were found to be inversely related to their respective clearance rates from blood in vivo. The binding order showed^99mTcPPi>^99mTcHEDP>^99mTcMDP. The^99mTc phosphorus radiopharmaceuticals were bound primarily to alpha globulins. The results suggest that the binding of^99mTc phosphorus radiopharmaceuticals to human serum proteins in blood is largely determined by their affinities to the alpha globulins.     

Novel 99mTc labeled σ receptor ligand as a potential tumor imaging agent

A novel 99mTc labeled complex, [N-[2-((2-oxo-2-(4-(3-phenylpropyl)piperazin-1-yl)ethyl) (2-mercaptoethyl)amino)acetyl]-2-aminoethanethiolato]Technetium(V) oxide (PPPE-MAMA′-99mTcO) ([99mTc]-2) has been designed and prepared based on the integrated approach. The corresponding rhenium complex (PPPE-MAMA′-ReO)(Re-2) has been prepared and characterized. In vitro competition binding assays show moderate affinity of Re-2 towards σ1 and σ2 receptors with Ki values of 8.67 ± 0.07 and 5.71 ± 1.88 μmol, respectively. Planar images obtained at 0.5 h, 4 h, 20 h after I.v. Injection indicate the accumulation of [99mTc]-2 in MCF-7 human breast tumor bearing mice at 20 h. Furthermore, the accumulation of [99mTc]-2 has been inhibited at 20 h after co-injection of [99mTc]-2 plus haloperidol (1 mg/kg). Biodistribution studies of [99mTc]-2 display an in vivo tumor uptake of 0.14% ± 0.01% ID/g at 24 h post I.v. Injection with a tumor/muscle ratio of 6.02 ± 0.87. The above results suggest that [99mTc]-2, derived from a previously published lead compound, retains certain tumor uptake and affinity for σ receptors. [99mTc]-2 may be used as a basis for further structural modifications to develop tumor imaging agents with high affinity for σ receptors.     

Synthesis and biological evaluation of novel 99mTcN-labeled bisnitroimidazole complexes containing monoamine-monoamide dithiol as potential tumor hypoxia markers

Tumor hypoxia can decrease the efficacy of clinical therapy due to resistance toward radiation damage and chemotherapy, thus detection of tumor hypoxia by radiolabeled hypoxia markers is important for the control of tumor. Radiopharmaceuticals with two bioreductive groups, such as propylene amine oxime-bisnitroimidazole or monoamine-monoamide dithiol (MAMA) -bisnitroimidazole, have potential to improve hypoxia selectivity. In order to obtain radiopharmaceuticals with better features, we synthesized two novel [^99mTcN]²⁺ complexes with bisnitroimidazole moieties and MAMA ligand for targeting tumor hypoxia. Their physicochemical characters and biodistribution were also investigated. Both the [^99mTcN]²⁺ complexes show good stability and hydrophilicity. They show faster clearance from blood and soft tissues, better tumor retention and favorable tumor-to-tissue ratios compared with a control complex without nitroimidazole group. In addition, both of them show more favorable biodistribution patterns than the corresponding [^99mTcO]³⁺ complexes. These results indicate that the ^99mTcN-labeled MAMA-bisnitroimidazole complexes would have potential to image tumor hypoxia in vivo.     

Paper chromatographic and paper elettrophoretic study of the solution chemistry of Tc-99m-methylendiphosphonate and of Tc-99m-dimercaptosuccinate for improving the tumour-affinity of Tc-99m during scintigraphic imaging of cancer

In order to find the conditions under which Tc-99m-methylenediphosphonate (Tc-99m-MDP) and Tc-99m(V)-dimercaptosuccinate (Tc-99m(V)-DMSA) may become tumour-seeking agents, leaving healthy organs free from the radionuclide uptake, the solution chemistry of these radiopharmaceuticals was studied by paper chromatography and paper electrophoresis in distilled water, in physiological saline, in NAHCO3, and ascorbic acid solutions. Both radiopharmaceuticals are anionic in the radiopharmaceutical solution but get easily hydrolysed to form cationic Tc-99m species which concentrates in healthy bone and in some bone metastases. Tc-99m (V)-DMSA being more stable remains long in the blood pool giving undesirable presence of the radionuclide in lung, heart and kidneys, in addition to its reduced uptake in bone metastases and in some primaries. We are trying to eliminate these drawbacks of healthy organ uptake of Tc-99-m(V)-DMSA not only to get a clean scintigraphic image of the tumour with this radiopharmaceutical but to extend its formulation, thus obtained, to prepare radiopharmaceutical with Re-188, which is the higher homologue of Tc-99m, for systemic therapy of cancer. Essentially similar solution chemistry of both radiopharmaceuticals suggests that like Tc-99m-MDP, technetium-99m-dimercaptosuccinate is also a complex of tetravalent Tc-99m and not of pentavalent Tc-99m as so far supposed to be.     

Tc标记的叶酸肿瘤显像剂

叶酸受体在许多源于上皮组织的恶性肿瘤中高度表达,是目前肿瘤放射性显像研究的一个新的靶点。由于叶酸对于叶酸受体具有很高的亲和性,作为重要的特异性靶向介导分子,^99mTc标记叶酸肿瘤显像剂已成为当前放射性药物的研究热点之一。本文对不同类型的^99mTc标记的叶酸类放射性肿瘤显像剂的研究进展、应用情况和存在的问题进行了评述,探讨了^99mTc标记叶酸显像剂的一般设计方法,并对其未来发展方向进行了展望。     

Evaluation of fresh and old eluate of <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generators used for labeling of different pharmaceutical kits

Summary Sixty ⁹⁹Mo/^99mTc wet column generators, loaded with two different ⁹⁹Mo activities, were analyzed in order to assess the quality of their eluates. Each elution was used for labeling of different radiopharmaceuticals, in order to evaluate whether “risky” elutions, namely those performed just after generator delivery and at 72 hours or more from the last elution, could be conveniently employed when fresh available radioactivity is not enough for the planned labeling or when shipping problems arise, or delay in delivery of a new generator occurs. Radiochemical quality control of all radiopharmaceuticals labeled with these elutions was performed. The elutions differed mainly in ⁹⁹Tc ground state (^99gTc) and amounts of oxidizing impurities. Radiolabeling procedures, however, were not affected, suggesting that these “risky” elutions might be appropriately used, in “emergency” conditions, for labeling radiopharmaceuticals although their radiochemical purity control is recommended prior to patient administration.     

Comparative quality control of some bone-seeking99mTc radiopharmaceuticals by gel chromatography

The radiochemical purity of the three osteopatic ligands:^99mTc(Sn)-PyP,^99mTc(Sn)-DPD and^99mTc(Sn)-MDP has been determined by gel chromatography on Sephadex. The results of the analyses strongly depend on the composition of the eluent. The dilution effect of pure saline as eluent was observed in all the preparations examined. The most sensitive was found to be^99mTc(Sn)-PyP. The retention of^99mTc activity bound to the gel matrix (^99mTc-hydrolyte) was over 30%. The diphosphonates were found to be more stable (retention 10–15%). The retention is substantially lower, i.e. a high recovery of the labeled complexes is obtained when the eluent contains the ligand. The best results are obtained when the eluent contains the same concentrations of ligand and reductant as in the labeled complex. There was no significant difference in the behavior of the given radiopharmaceuticals prepared as a fresh solution and in the freeze-dried kit.     

Radiosynthesis and evaluation of novel [99mTc(I)]+ and [99mTc(I)(CO)3]+ complexes with a 4-nitroimidazole isocyanide for imaging tumor hypoxia

[^99mTc(I)]⁺ and [^99mTc(I)(CO)₃]⁺ complexes with isocyanide exhibit high stability, which makes them suitable platforms to develop novel ^99mTc radiopharmaceuticals. To develop novel ^99mTc radiotracers for imaging hypoxia, in this study, a novel L ligand (4-nitroimidazole isocyanide derivative) was synthesized and labelled using [^99mTc(I)]⁺ core and [^99mTc(I)(CO)₃]⁺ core to produce [^99mTc(L)₆]⁺ and [^99mTc(CO)₃(L)₃]⁺ with high yields. To verify the structure of the ^99mTc complexes, corresponding rhenium analogues were synthesized and characterized. Both of the ^99mTc complexes were stable and hydrophilic. in vitro cellular uptake results showed they could exhibit good hypoxic selectivity. The evaluation of biodistribution in mice bearing S180 tumors indicated both of them could accumulate in tumor. Between them, [^99mTc(L)₆]⁺ exhibited higher tumor uptake and tumor/non-target ratio than [^99mTc(CO)₃(L)₃]⁺. Further, single photon emission computed tomography (SPECT) imaging studies of [^99mTc(L)₆]⁺ indicated an obvious accumulation in tumor and the value of the region-of-interest (ROI) ratio of the uptake for the tumor site to the corresponding non-tumor region was 5.64 ± 0.52. The above results suggested [^99mTc(L)₆]⁺ would be a potential tracer for imaging tumor hypoxia.     

99mTc放射性药物中的配位化学

在99mTc间接标记放射性药物中双功能螯合剂起到重要的连接作用,其在很大程度上决定了放射性药物的理化性质。99mTc标记放射性药物中常用的双功能螯合剂大都含有N、S、P等杂原子,本文以与锝核配位杂原子的不同对双功能螯合剂进行分类,分别对NxS(4-x)型配体、“3＋1”混合配体、含膦配体以及以[99mTc(CO)3]+为配位中心的99mTc放射性药物逐一进行介绍。     

A novel electrochemical <Superscript>99</Superscript>Mo/<Superscript>99m</Superscript>Tc generator

A novel electrochemical process to avail clinical grade ^99mTc from (n,γ)⁹⁹Mo has been demonstrated. The electrochemical parameters were optimized to maximize the ^99mTc yield with minimal ⁹⁹Mo contamination. ⁹⁹Mo/^99mTc generators containing up to 29.6 GBq (800 mCi) ⁹⁹Mo were developed and their performance were extensively evaluated for 10 days without changing the operating conditions. Very high radioactive concentration of ^99mTcO₄ ⁻ of acceptable quality, commensurate with hospital radiopharmacy requirements could be availed from the system with >90% yield. The compatibility of the product for the formulation of ^99mTc labeled radiopharmaceuticals such as ^99mTc-DMSA and ^99mTc-EC was found to be satisfactory in terms of high labeling yields. The proposed route represents an important step for enhancing the scope of accessing clinical grade ^99mTc from low specific activity (n, γ)⁹⁹Mo.     

Clinical comparison of 99mTc-diethylenetriaminepentaacetic acid-human serum albumin (99mTc-HSA-D) and 99mTc-human serum albumin (99mTc-HSA) for cardiac blood pool imaging

99mTc-HSA-D has been developed as a new blood pool scanning agent. Clinical comparison of 99mTc-HSA-D and 99mTc-HSA was made in 16 cases. The activity concentration of 99mTc in blood was measured during 2 hours after the injection in five cases. 99mTc-HSA-D showed higher concentration compared to 99mTc-HSA with the passage of time. Quantitative analysis of contrast between left ventricle and septum was performed on end diastolic frames of gated images 10 minutes after the injection. There was no obvious difference between 99mTc-HSA-D and 99mTc-HSA. The subjective comparison of detectability of lesions between the two agents was performed on three directional gated images. 99mTc-HSA-D was superior to 99mTc-HSA, because the images of the latter deteriorated with the passage of time. On anterior view images 1 hour after the injection, left ventricle/lung and abdominal aorta/background count ratios were greater for 99mTc-HSA-D in many cases. There was no obvious difference in liver/background and kidney/background count ratios between the two agents. Urinary excretion of 99mTc was considerably lesser for 99mTc-HSA-D. The results indicated that 99mTc-HSA-D was superior to 99mTc-HSA for cardiac blood pool imaging.     

Preparation and biological evaluation of the new chlorin photosensitizer T3,4BCPC for detection and treatment of tumors

The new water-soluble photosensitizer 5,10,15,20-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]chlorin (T3,4BCPC) has been prepared, characterized and labeled with 99mTc radionuclide. The radiotracer was evaluated for tissue distribution in Wistar rats. Accumulation of administrated activities in the liver, kidney, bladder and large intestine at 4 h post-injection indicated that the labeled ligand was largely eliminated through the renal and partly through the hepatobiliary system. In vivo biodistribution studies of the labeled compound were carried out in rodent and murine tumor models in comparison with other tumor-seeking radiopharmaceuticals such as 99mTc(V)-dimercaptosuccinic acid (DMSA), 201thallous chloride (TlCl) and 99mTc-citrate using a gamma camera computer system. In N-nitrosomethylurea (NMU)-induced rat mammary tumors, the labeled ligand showed a five-fold tumor to muscle (T/M) ratio compared to 99mTc(V)-DMSA (3-fold) and 201TlCl (3-fold). In the case of C(3)H/J virus-induced spontaneous mammary tumors, the differences were not marked. However, in the transplanted rat C(6)-glioma, the T/M ratio of the labeled compound was appreciably higher (four-fold) than that noted with 99mTc(V)-DMSA (two-fold), 201TlCl (three-fold) and 99mTc-citrate (more than three-fold). These findings suggest that the radiolabeled T3,4BCPC may have potential for the detection of cancer. In order to ascertain the efficacy of the compound for photodynamic therapy applications, a preclinical PDT study was carried out in fibrosarcoma-bearing mice after injecting 5.0 mg/kg body weight of the T3,4BCPC. A laser dose of 20 mW for 60 s resulted in 80% destruction of tumors. These data suggest that this molecule could be useful for PDT of cancer. The labeled agent could also be useful in monitoring the progression/regression of tumors before, during, and after chemotherapy, radiation therapy or PDT.     

Stable and lipophilic technetium-99m dithiosemicarbazone complexes with 5-6-5 membered chelate ring structure

Modification of the chelate ring structure of technetium-99m (99mTc) dithiosemicarbazone (DTS) chelate was carried out in pursuit of a more stable and lipophilic compound. A new DTS chelating molecule, pentane-2,4-dione bis(N-methylthiosemicarbazone) (PETS), with a 5-6-5 membered chelate ring structure, was synthesized and labeled with 99mTc, PETS generated two 99mTc compounds as major products. Both had much higher stability and lipophilicity than a 5-5-5 membered 99mTc DTS compound, as well as great stability in plasma. Both 99mTc-PETS compounds were rapidly extracted by the brain and heart when injected into mice. Thus, the modified chelate ring structure afforded a preferable characteristics to DTS chelate as for the chelating site for technetium radiopharmaceuticals.     

Evaluation of 99mTc-ceftazidime as bacterial infection imaging agent

Although our understanding of microorganisms has advanced significantly and antimicrobial therapy has become increasingly available, infection remains a major cause of patient morbidity and mortality. The use of radiopharmaceuticals for diagnosis of infection is increasing due to their ability to distinguish between septic and aseptic inflammation. A wide range of radiopharmaceuticals have been proposed to visualize infection and inflammation scintigraphically. Ceftazidime a cephalosporin antibiotic used to treat bacterial infections was investigated to label with ^99mTc. Labeling was performed using sodium dithionite as reducing agent at 100 °C for 10 min and radiochemical analysis involved ITLC and HPLC methods. The stability of labeled antibiotic was checked in the presence of human serum at 37 °C up to 24 h. The maximum radiolabeling yield was 95.4 ± 2.0 % corresponding to a specific activity of 178 GBq/mmol. Bacterial binding assay was performed with S. aureus and the in vivo distribution was studied in mice. Images showed minimal accumulation in nontarget tissues, with an average target/nontarget ratio of % 1.4 ± 0.2.     

Synthesis and biological evaluation of pyrazolo[1,5-a]-pyrimidine-containing 99mTc Nitrido radiopharmaceuticals as imaging agents for tumors

The compound 5-((2-aminoethylamino)methyl)-7-(4-bromoanilino)-3-cyano-pyrazolo[1,5-a]pyrimidine (ABCPP) was synthesized and conjugated with N-mercapto-acetylglycine (MAG), N-mercaptoacetylphenylalanine (MAF) and N-mercaptoacetylvaline (MAA), respectively. These three compounds were labeled successfully with [99mTcN]2+ intermediate in high radiochemical purities. Biodistribution in tumor-bearing mice demonstrated that the three new complexes showed tumor accumulation, high tumor-to-muscle (T/M) ratios and fast clearance from blood and muscle. Among them, the 99mTcN-MAG-ABCPP showed the most favorable characteristics, with tumor/blood and tumor/ muscle ratios reaching 1.51 and 2.97 at 30 min post-injection, 1.84 and 2.49 at 60 min post-injection, suggesting it could be further studied as potential tumor imaging agent for single photon emission computed tomography (SPECT).