Development of an in vitro model for assessing the in vivo stability of lanthanide chelates

An in vitro model was developed to evaluate the in vivo stability of lanthanide polyaminocarboxylate complexes. The ligand-to-metal ratios for the chelates EDTA, CDTA, DTPA, MA-DTPA (monoamide-DTPA) and DOTA with the lanthanides lanthanum, samarium, and lutetium were optimized to achieve > or = 98% complexation yield for the resultant radiolanthanide complexes. The exchange of the radiolanthanides from their EDTA, CDTA, DTPA, MA-DTPA and DOTA complexes with Ca(2+) was determined by in vitro adsorption and in vitro column studies using hydroxyapatite (HA), an in vitro bone model. In vitro serum stability of these radiolanthanide complexes was used as an additional indicator of in vivo stability, although the mechanism of instability in serum will be different than with bone. The in vitro studies were consistent with the expected findings that the smallest lanthanide (Lu) formed the most stable complexes. In vivo studies were done to validate the in vitro model. Biodistribution studies in normal CF-1 mice showed that in vivo stability of the complex (i.e., the more lanthanide remaining in complex form) could be assessed by a combination of the urinary, bone and liver uptake. For example, biodistribution studies demonstrate that high urinary excretion correlated with complex stability, while high liver plus bone uptake correlated with complex instability. The urinary excretion of the EDTA complexes decreased from (177)Lu to (140)La indicating a loss in stability in the direction of (140)La, consistent with the in vitro studies. The more stable a lanthanide complex is, the lower its exchange with HA in vitro will be, and the lower its combined bone plus liver uptake and higher its urinary excretion will be in vivo. This investigation indicates that the in vivo stability can be determined by a screening method that measures the degree of exchange from the lanthanide chelate with hydroxyapatite (HA) and its serum stability.

Current and potential therapeutic uses of lanthanide radioisotopes

In the last 25 years, diagnostic nuclear medicine has come to depend on the versatile chemistry of a single radioisotope, technetium-99m (Tc-99m). Different chelating molecules can be used to guide Tc-99m through various physiological pathways in the body to gain information about disease states. No single radioisotope similarly dominates therapeutic applications. In the field of radioisotope therapy, much discussion and debate have focused on what radioisotope might be "ideal" for treatment of malignant tumors. The ideal may not be a single radioisotope, but rather the class of very closely related radiolanthanides and lanthanide-like radioisotopes. These radioisotopes possess strikingly similar chemistries and thus all may be conjugated to biomolecules using a single chelate, the DOTA moiety (and its chemical analogs). They also provide a wide range of physical characteristics, such as half-lives and beta energies, that can be chosen to match the biological properties of the conjugated biomolecule and the malignant tumor. Thus, the radiolanthanide-DOTA bioconjugate model provides a set of physically diverse, but chemically very similar, therapeutic radiopharmaceutical agents, the individual members of which can be tailored to treat specific types of cancers.

Labeling and in vivo evaluation of novel copper(II) dioxotetraazamacrocyclic complexes

64Cu shows promise as both a positron emission tomography imaging and radiotherapeutic radionuclide due to its half-life (T(1/2) = 12. 7 h), decay characteristics (beta(+) [19%]; beta(-) [40%]), and the capability to produce it on a large-scale with high specific activity on a biomedical cyclotron. Macrocyclic chelators are generally used as bifunctional chelators to attach Cu(II) to antibodies and peptides due to their relatively high in vitro stability. To investigate neutral Cu(II) complexes, we performed labeling experiments with six tetraazamacrocyclic ligands with different chelate ring sizes. 1,4,8,11-Tetraazacyclotetradecane-3, 9-dione (1), 1,4,8,11-tetraazacyclotetradecane-5,7-dione (2), 1,4,7, 10-tetraazacyclotridecane-11,13-dione (3), 1,4,7, 10-tetraazacyclotridecane-2,9-dione (4), 1,4,7, 10-tetraazacyclododecane-2,9-dione (5), and 1,4,7, 10-tetraazacyclotridecane-3,8-dione (6) were radiolabeled with (64)Cu. Only (64)Cu-labeled 1 readily formed a complex in high purity, and therefore was evaluated in vivo. The rapid blood, liver, and kidney clearance of (64)Cu-labeled 1 suggest that ligand 1 may be useful as a macrocyclic structure to design new bifunctional chelators for copper radionuclides in diagnostic or radiotherapeutic studies and is a potential alternative to currently used macrocyclic bifunctional chelators.

High purity production and potential applications of copper-60 and copper-61

Previously we described the high yield production of 64Cu using a target system designed specifically for low energy, biomedical cyclotrons. In this study, the use of this target system for the production of 60Cu and 61Cu is described and the utility of these isotopes in the labeling of biomolecules for tumor and hypoxia imaging is demonstrated. 60Cu and 61Cu were produced by the 60Ni(p,n)60Cu, 61Ni(p,n)61Cu, and 60Ni(d,n)61Cu nuclear reactions. The nickel target (>99% enriched or natural nickel) was plated onto a gold disk as described previously (54-225 microm thickness) and irradiated (14.7 MeV proton beam and 8.1 MeV deuteron beam). The copper isotopes were separated from the nickel via ion exchange chromatography and the radioisotopic purity was assessed by gamma spectroscopy. Yields of up to 865 mCi of 60Cu have been achieved using enriched 60Ni. 61Cu has been produced with a maximum yield of 144 mCi using enriched 61Ni and 72 mCi using enriched 60Ni. Specific activities (using enriched material) ranged from 80 to 300 mCi/microg Cu for 60Cu and from 20 to 81 mCi/microg Cu for 61Cu. Bombardments of natural Ni targets were performed using both protons and deuterons. Yields and radioisotopic impurities were determined and compared with that for enriched materials. 60Cu was used to radiolabel diacetyl-bis(N4-methylthiosemicarbazone), ATSM. 60Cu-ATSM was injected into rats that had an occluded left anterior descending coronary artery. Uptake of 60Cu-ATSM in the hypoxic region of the heart was visualized clearly using autoradiography. In addition, 60Cu-ATSM was injected into dogs and excellent images of the heart and heart walls were obtained using positron emission tomography (PET). 61Cu was labeled to 1,4,8,11-tetraazacyclotetradecane-N,N',N",N"'-tetraacetic acid-octreotide (TETA-octreotide) and the PET images of tumor-bearing rats were obtained up to 2 h postinjection. After decay of the 61Cu, the same rat was injected with 64Cu-TETA-octreotide and the images were compared. The tumor images obtained using 61Cu were found to be superior to those using 64Cu as predicted based on the larger abundance of positrons emitted by 61Cu vs. 64Cu.

Evaluation of gallium-68 tris(2-mercaptobenzyl)amine: a complex with brain and myocardial uptake

Previous research into development of a gallium-radiolabeled agent that crosses the blood-brain barrier has met with limited success. In this study, we focused our attention on a Ga(III) complex of a 4-coordinate amine trithiolate tripod ligand, tris(2-mercaptobenzyl) amine (S3N). The Ga(III) S3N complex is small, neutral, and lipophilic, meeting the requirements for a potential brain imaging agent. The Ga-68 complex was easily formed with a radiochemical purity of >95%. In vitro stability of the Ga-S3N complex, determined in rat serum incubated at 37 degrees C, was greater than 95% intact at 2 h by silica gel and reversed-phase radio-thin layer chromatography. Biodistribution studies conducted in female Sprague-Dawley rats showed the complex cleared rapidly from the blood with initial high liver uptake followed by rapid washout. Significant uptake was observed in the brain, with brain:blood ratios increasing from 0.11 at 2 min postinjection to 3.8 at 60 min postinjection. Uptake was also observed in the heart going from a heart:blood ratio of 2.3 at 2 min postinjection to 11 at 60 min postinjection. Molecular mechanics were used to determine the coordination number, and demonstrated that the Ga(III) complex prefers to be 4-coordinate. Imaging studies with 68Ga-S3N in a Nemestrina macaque showed significant brain uptake, similar to other lipophilic agents. The extraction of 68Ga-S3N into the brains of both rodents and primates, higher than any 68Ga agent reported in the literature, suggests that this compound may have potential as a brain imaging agent for positron emission tomography.

Comparative studies of Cu-64-ATSM and C-11-acetate in an acute myocardial infarction model: ex vivo imaging of hypoxia in rats

Copper labeled diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) is a promising agent for the imaging of hypoxic tissues. In the present study 64Cu(t1/2 = 12.8 h) labeled Cu-ATSM was used in combination with 11C (t1/2 = 20.3 min) labeled acetate as a regional perfusion marker to visualize hypoxic rat heart tissue in an acute left anterior descending (LAD) coronary artery occluded rat model using an ex vivo tissue slice imaging technique. 64Cu-ATSM was injected intravenously c.a. 10 min after occlusion and rats were sacrificed by cervical dislocation 10 min after injection. Carbon-11-acetate was injected 1 min before sacrifice to obtain a measure of blood flow. The heart was dissected, frozen, and cut into 1-mm thick slices with a gauged slicer, and 11C images were obtained with an electronic autoradiography instrument. After decay of 11C, 64Cu images were obtained in the same manner. In ischemic regions, where there was low 11C accumulation, 64Cu showed high accumulation when compared with normal regions. In rats with a large occlusion, the center of the ischemia did not show any accumulation of either 11C or 64Cu, indicating no blood supply. Cu-ATSM appears to be useful for the detection of hypoxia with contrast being observed at short times (10 min) postinjection.

Pulmonary blastoma: case report of a patient with a 7-year remission and review of chemotherapy experience in the world literature

BACKGROUND

Pulmonary blastoma is a rare malignant neoplasm for which there currently are no treatment guidelines.

METHODS

A patient with locally advanced pulmonary blastoma is described. The treatment modality is discussed and the world literature is reviewed with respect to the use of chemotherapy.

RESULTS

A 54-year-old man had a 7-year disease free survival despite subtotal resection. He was treated with adjuvant radiotherapy and combination chemotherapy. Three cycles of cisplatin and etoposide were administered. The world literature was reviewed with regard to the use of adjuvant chemotherapy in the treatment of pulmonary blastoma.

CONCLUSIONS

Surgery, adjuvant radiotherapy, and combination chemotherapy with cisplatin and etoposide should be considered in the treatment of patients with this rare pulmonary neoplasm.

Efficient production of high specific activity 64Cu using a biomedical cyclotron

Copper-64 (T 1/2 = 12.7 h) is an intermediate-lived positron-emitting radionuclide that is a useful radiotracer for positron emission tomography (PET) as well as a promising radiotherapy agent for the treatment for cancer. Currently, copper-64 suitable for biomedical studies is produced in the fast neutron flux trap (irradiation of zinc with fast neutrons) at the Missouri University Research Reactor. Access to the fast neutron flux trap is only possible on a weekly basis, making the availability of this tracer very limited. In order to significantly increase the availability of this intermediate-lived radiotracer, we have investigated and developed a method for the efficient production of high specific activity Cu-64 using a small biomedical cyclotron. It has been suggested that it may be possible to produce Cu-64 on a small biomedical cyclotron utilizing the 64Ni(p,n)64Cu nuclear reaction. We have irradiated both natural nickel and enriched (95% and 98%) Ni-64 plated on gold disks. Nickel has been electroplated successfully at thicknesses of approximately 20-300 mm and bombarded with proton currents of 15-45 microA. A special water-cooled target had been designed to facilitate the irradiations on a biomedical cyclotron up to 60 microA. We have shown that it is possible to separate Cu-64 from Ni-64 and other reaction byproducts rapidly and efficiently by using ion exchange chromatography. Production runs using 19-55 mg of 95% enriched Ni-64 have yielded 150-600 mCi of Cu-64 (2.3-5.0 mCi/microAh) with specific activities of 94-310 mci/microgram Cu. The cyclotron produced Cu-64 had been used to radiolabel PTSM [pyruvaldehyde bis-(N4-methylthiosemicarbazone), used to quantify myocardial, cerebral, renal, and tumor blood flow], MAb 1A3 [monoclonal antibody MAb to colon cancer], and octreotide. A recycling technique for the costly Ni-64 target material has been developed. This technique allows the nickel eluted off the column to be recovered and reused in the electroplating of new targets with an overall efficiency of greater than 90%.

Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies

BACKGROUND & AIMS

The miss rate of colonoscopy for neoplasms is poorly understood. The aim of this study was to determine the miss rate of colonoscopy by same day back-to-back colonoscopy.

METHODS

Two consecutive same day colonoscopies were performed in 183 patients. The patients were randomized to undergo the second colonoscopy by the same or a different endoscopist and in the same or different position.

RESULTS

The overall miss rate for adenomas was 24%, 27% for adenomas < or = 5 mm, 13% for adenomas 6-9 mm, and 6% for adenomas > or = 1 cm. Patients with two or more adenomas at the first examination were more likely than patients with no or one adenoma detected at the first examination to have one or more adenomas at the second examination (odds ratio, 3.3; 95% confidence interval, 1.69-6.46). Right colon adenomas were missed more often (27%) than left colon adenomas (21%), but the difference was not significant. There was evidence of variation in sensitivity between endoscopists, but significant miss rates for small adenomas were found among essentially all endoscopists.

CONCLUSIONS

Using current colonoscopic technology, there are significant miss rates for adenomas < 1 cm even with meticulous colonoscopy. Miss rates are low for adenomas > or = 1 cm. The results suggest the need for improvements in colonoscopic technology.

Does routine intravenous glucagon administration facilitate colonoscopy? A randomized trial

BACKGROUND

Previous studies on the routine use of glucagon in colonoscopy have produced conflicting results.

METHODS

Two separate studies were performed. In one study (Study 1), 80 consecutive patients were randomized after cecal intubation to receive 1 mg glucagon (n = 41) or placebo (n = 39), intravenously, in double-blind fashion. In a second study (Study 2) 90 sedated patients undergoing colonoscopy were randomized to receive 1 mg glucagon (n = 46) or placebo (n = 44), intravenously, just before colonoscope insertion. In each study, colonoscope insertion and withdrawal time, therapeutic intervention time, the presence and severity of colonic spasm, colonoscopy yield, and side effects were recorded.

RESULTS

Mean withdrawal time in Study 1 was similar in those receiving glucagon (6.85 min) and in those receiving placebo (6.92 min). Mean insertion time in Study 2 (5.07 min) was identical between groups. Spasm scores and colonoscopy yield did not differ between glucagon and placebo in either study. There was a trend toward more side effects (nausea and vomiting) with glucagon in Study 1. Glucagon did not facilitate insertion or withdrawal in the subset of patients with diverticulosis.

CONCLUSIONS

Routine use of intravenous glucagon in a dosage of 1 mg does not facilitate colonoscopy by experienced examiners.