Biomedical subjects

Lawrence P Szajek

Publications and source records attributed to Lawrence P Szajek.

7 recordsLinked to original sources

PubMed2006

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.

Animals↗

PubMed2006

Noninvasive molecular imaging to detect transgene expression of lentiviral vector in nonhuman primates.

UNLABELLED: Noninvasive imaging of a reporter gene is a new and promising technique to quantify transgene expression after gene therapy. This study was performed to demonstrate visualization of lentiviral-marked cells by PET. METHODS: We transduced nonhuman primate CD34+ hematopoietic cells with a lentiviral vector expressing a PET reporter gene, the mutant viral herpes simplex virus type 1-thymidine kinase (HSV1-sr39tk) gene. 1-(2-Fluoro-2-deoxy-beta-D-arabinofuranosyl)-76Br-5-bromouracil (76Br-FBAU) was used as the substrate for the viral tk enzyme. Upon phosphorylation, 76Br-FBAU was retained by cells and imaged by PET. The long half-life of 76Br, 16.2 h, permitted us to perform extended pharmacokinetic and imaging studies. RESULTS: 76Br-FBAU was retained in vascular tissues of the animals with transplanted tk lentiviral vector-transduced CD34+ cells. Elimination of 76Br-FBAU was through renal and hepatic excretion. CONCLUSION: Noninvasive molecular imaging using PET will help us, in the future, to define the contribution and distribution of cells and their progeny to tissue repair and development.

Animals↗

PubMed2005

Evaluation of (76)Br-FBAU as a PET reporter probe for HSV1-tk gene expression imaging using mouse models of human glioma.

UNLABELLED: The utility of 5-(76)Br-bromo-2'-fluoro-2'-deoxyuridine ((76)Br-FBAU), a uracil analog, as a PET reporter probe for use with the herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene system for gene expression imaging was evaluated in vivo and in vitro using human and rat glioma cells. METHODS: Human glioma cell lines U87 and U251 were transduced with replication-defective adenovirus constitutively expressing HSV1-tk (Ad.TK) or a control expressing green fluorescent protein (Ad.GFP). These cells were incubated with (76)Br-FBAU for 20-120 min to determine the percentage of total dose uptake. In vitro uptake of equimolar concentrations (1.8 x 10(-8) mol/L) of (76)Br-FBAU and 2'-fluoro-2'-deoxy-5-iodouracil-beta-d-arabinofuranoside ((14)C-FIAU) was also determined in RG2-TK rat glioma cells stably expressing HSV1-tk and in control RG2 cells at 30-120 min. In vivo uptake of (76)Br-FBAU was determined in subcutaneous U87 tumor intratumorally transduced with Ad.TK by ex vivo biodistribution. Uptake in intracranial U87 tumors transduced with Ad.TK expressing HSV1-tk was measured by brain autoradiography. In vivo PET was performed on subcutaneous and intracranial U87 tumors transduced with Ad.TK and on subcutaneous and intracranial stably expressing RG2-TK tumors. RESULTS: U87 and U251 cells transduced with Ad.TK had significantly increased uptake of (76)Br-FBAU compared with cells transduced with Ad.GFP over 20-120 min. In stably expressing cells at 120 min, (14)C-FIAU uptake in RG2-TK tumor cells was 11.3 %ID (percentage injected dose) and in RG2 control cells was 1.7 %ID, and (76)Br-FBAU uptake in RG2-TK tumor cells was 14.2 %ID and in RG2 control cells was 1.5 %ID. Ex vivo biodistribution of subcutaneous U87 tumors transduced with Ad.TK accumulated (76)Br-FBAU significantly more than in the control Ad.GFP transduced tumor and normal tissue, with the lowest uptake in brain. Autoradiography showed localized uptake in intracranial U87 and U251 cells transduced with Ad.TK. PET image analyses of mice with RG2-TK tumors resulted in an increased tumor-to-background ratio of 13 and 26 from 2 to 6 h after injection, respectively, in intracranial tumors. CONCLUSION: (76)Br-FBAU accumulates in glioma cells constitutively expressing HSV1-tk by either adenoviral transduction or in stably expressing cell lines both in vitro and in vivo. (76)Br-FBAU shows promise as a PET reporter probe for use with the HSV1-tk in vivo gene expression imaging system.

Animals↗

PubMed2004

Semi-automated 86Y purification using a three-column system.

The separation of (86)Y from (86)Sr was optimized by a semi-automated purification system involving the passage of the target sample through three sequential columns. The target material was dissolved in 4 N HNO(3) and loaded onto a Sr-selective (Sr-Spec) column to retain the (86)Sr. The yttrium was eluted with 4 N HNO(3) onto the second Y-selective (RE-Spec) column with quantitative retention. The RE-Spec column was eluted with a stepwise decreasing concentration of HNO(3) to wash out potential metallic impurities to a waste container. The eluate was then pumped onto an Aminex A5 column with 0.1 N HCl and finally with 3 N HCl to collect the radioyttrium in 0.6-0.8 mL with a >80% recovery. This method enabled us to decontaminate Sr by 250,000 times and label 30 micro g of DOTA-Biotin with a >95% yield.

Biotin↗

PubMed2003

Autoradiographic visualization of corticotropin releasing hormone type 1 receptors with a nonpeptide ligand: synthesis of [(76)Br]MJL-1-109-2.

A high-affinity, nonpeptide radioligand for the CRHR1 was synthesized and showed distribution in rat brain consistent with CRHR1 using in vitro autoradiography. This is the first nonpeptide radiotracer combining high affinity and appropriate lipophilicity that penetrates the blood-brain barrier and hence has the potential to be used for PET imaging studies. In vivo visualization of changes in the CRH1 receptor or its occupancy would further the understanding of the pathophysiology of stress related diseases.

Animals↗

PubMed2003

Fluoro-, bromo-, and iodopaclitaxel derivatives: synthesis and biological evaluation.

Paclitaxel (Taxol) is a clinically important chemotherapeutic agent. We describe the synthesis of fluoro-, bromo-, and iodopaclitaxel and their [(18)F]fluoro-, [(76)Br]bromo-, and [(124)I]iodo- analogues. [(18)F]Fluoropaclitaxel shows high uptake and rapid clearance from tissues in rats. Preadministration of paclitaxel in normal rats significantly increases (p < 0.005) retention of [(18)F]fluoropaclitaxel and [(76)Br]bromopaclitaxel in blood (33.0%), heart (32.0%), lung (37.6%) kidney (142.4%); and blood (33.4%), lung (42.3%), kidney (62.4%), respectively. [(18)F]Fluoropaclitaxel uptake in the brain of mdr1a/1b(-/-) mice is increased 1400% (p < 1.3e-07) relative to wild-type controls. Preadministration of paclitaxel or XR9576, a modulator, had little effect on the biodistribution in these mdr1a/1b(-/-) mice. As a result, [(18)F]fluoropaclitaxel will be a useful radiopharmaceutical for the study of multidrug resistant tumors.

Animals↗

PubMed2002

Evaluation of [76Br]FBAU 3',5'-dibenzoate as a lipophilic prodrug for brain imaging.

[76Br]FBAU is a potential PET tracer for assessing proliferation. This study proposes that [76Br]FBAU 3',5'-dibenzoate has higher blood-brain-barrier permeability than [76Br]FBAU itself and thus might be better suited for applications in the brain. The brain uptake indexes of the two compounds measured after carotid injection (29.6 +/- 13.9 for [76Br]FBAU 3',5'-dibenzoate, versus 10.0 +/- 8.7 for [76Br]FBAU) support this claim. Biodistribution study also showed that the brain accumulation of activity was higher in rats injected with [76Br]FBAU 3',5'-dibenzoate than with [76Br]FBAU (0.119+/-0.023 DUR at 1 h, versus 0.061 +/- 0.006). [76Br]FBAU 3',5'-dibenzoate was relatively stable in rat plasma, gradually being hydrolyzed to [76Br]FBAU exponentially with a calculated half-life of 0.8 h. DNA incorporation of [76Br]FBAU was also confirmed. The results presented support the hypothesis that the 3',5'-dibenzoate can act as a prodrug for FBAU and deliver more radiolabeled nucleoside to the brain.

Animals↗