Chang Sok Oh

Noninvasive Assessment of Tumor Hypoxia with 99mTc Labeled Metronidazole

AbstractPurpose. The assessment of tumor hypoxia by imaging modality prior to radiation therapy would provide a rational means of selecting patients for treatment with radiosensitizers or bioreductive drugs. This study aimed to develop a 99mTc-labeled metronidazole (MN) using ethylene-dicysteine (EC) as a chelator and evaluate its potential use to image tumor hypoxia.nMethods. EC was conjugated to amino analogue of MN using Sulfo-N-hydroxysuccinimide and l-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCl as coupling agents, the yield was 55%. Tissue distribution of 99mTc-EC-MN was determined in breast tumor-bearing rats at 0.5, 2, and 4 hrs. Planar imaging and whole-body autoradiograms were performed. The data was compared to that using 99mTc-EC (control), [l8F]fluoromisonidazole (FMISO) and [131I] iodomisonidazole (IMISO).nResults. In vivo biodistribution of 99mTc-EC-MN in breast tumor-bearing rats showed increased tumor-to-blood and tumor-to-muscle ratios as a function of time. Conversely, tumor-to-blood values showed time-dependent decrease with 99mTc-EC in the same time period. Planar images and autoradiograms confirmed that the tumors could be visualized clearly with 99mTc-EC-MN from 0.5 to 4 hrs. There was no significant difference of tumor-to-blood count ratios between 99mTc-EC-MN and [131I]IMISO at 2 and 4 hrs postinjection. From 0.5 to 4 hrs, both 99mTc-EC-MN and [131I]IMISO have higher tumor-to-muscle ratios compared to [18]FMISO.nConclusions. It is feasible to use 99mTc-EC-MN to image tumor hypoxia.

Assessment of epidermal growth factor receptor with 99mTc-ethylenedicysteine-C225 monoclonal antibody.

Epidermal growth factor receptor (EGFR) plays an important role in cell division and cancer progression, as well as angiogenesis and metastasis. Since many tumor cells exhibit the EGFR on their surface, functional imaging of EGFR provides not only a non-invasive, reproducible, quantifiable alternative to biopsies, but it also greatly complements pharmacokinetic studies by correlating clinical responses with biological effects. Moreover, molecular endpoints of anti-EGFR therapy could be assessed effectively. C225 is a chimeric monoclonal antibody that targets the human extracellular EGFR and inhibits the growth of EGFR-expressing tumor cells. Also, it has been demonstrated that C225, in combination with chemotherapeutic drugs or radiotherapy, is effective in eradicating well-established tumors in nude mice. We have developed 99mTc-labeled C225 using ethylenedicysteine (EC) as a chelator. This study aimed at measuring uptake of 99mTc–EC–C225 in EGFR+ tumor-bearing animal models and preliminary feasibility of imaging patients with head and neck carcinomas. In vitro Western blot analysis and cytotoxicity assays were used to examine the integrity of EC–C225. Tissue distribution studies of 99mTc–EC–C225 were evaluated in tumor-bearing rodents at 0.5–4u2009h. In vivo biodistribution of 99mTc–EC–C225 in tumor-bearing rodents showed increased tumor-to-tissue ratios as a function of time. In vitro and biodistribution studies demonstrated the possibility of using 99mTc–EC–C225 to assess EGFR expression. SPECT images confirmed that the tumors could be visualized with 99mTc–EC–C225 from 0.5 to 4u2009h in tumor bearing rodents. We conclude that 99mTc–EC–C225 may be useful to assess tumor EGFR expression. This may be useful in the future for selecting patients for treatment with C225.

Synthesis of [99mTc]ethylenedicysteine-colchicine for evaluation of antiangiogenic effect.

Angiogenesis is in part responsible for tumor growth and the development of metastasis. Radiolabeled angiongenesis inhibitors would be useful to assess tumor microvasculature density. Colchicine (COL), a potent antiangiogenic agent, is known to inhibit microtubule polymerization and cell arrest at metaphase. This study aimed to develop 99mTc-labeled COL (EC-COL) using ethylenedicysteine (EC) as a chelator to assess tumor microvascular density. EC was conjugated to trimethylcolchicinic acid using N-hydroxysuccinimide and 1-ethyl-3-dimethylaminopropyl carbodiimide as coupling agents with a yield of 50-60%. In vivo stability was analyzed in rabbit serum at 0.5-4 h. Tissue distribution and planar imaging studies of [99mTc]EC-COL were evaluated in breast tumor-bearing rats at 0.5, 2 and 4 h. The data was compared to that using [99mTc]EC (control). The radiochemical yield of [99mTc]EC-COL was greater than 95%. [99mTc]EC-COL was stable in rabbit serum. In vivo biodistribution of [99mTc]EC-COL in breast tumor-bearing rats showed increased tumor-to-blood (0.52+/-0.12 to 0.72+/-0.07) and tumor-to-muscle (3.47+/-0.40 to 7.97+/-0.93) ratios as a function of time. Conversely, tumor-to-blood values showed a time-dependent decrease with [99mTc]EC over the same time period. Planar images confirmed that the tumors could be visualized clearly with [99mTc]EC-COL from 0.5 to 4 h. [99mTc]EC-COL may be useful to assess antiangiogenic and therapeutic effects during chemotherapy.

Assessment of cyclooxygense-2 expression with 99mTc-labeled celebrex

Cyclooxygenase-2 (COX-2) plays an important role in angiogenesis and cancer progression. Since many tumor cells exhibit COX-2 expression, functional imaging of COX-2 expression using celebrex (CBX, a COX-2 inhibitor) may provide not only a non-invasive, reproducible, quantifiable alternative to biopsies, but it also greatly complements pharmacokinetic studies by correlating clinical responses with biological effects. Moreover, molecular endpoints of anti-COX-2 therapy could also be assessed effectively. This study aimed at measuring uptake of 99mTc-EC–CBX in COX-2 expression in tumor-bearing animal models. In vitro Western blot analysis and cellular uptake assays were used to examine the feasibility of using 99mTc-EC–CBX to measure COX-2 activity. Tissue distribution studies of 99mTc-EC–CBX were evaluated in tumor-bearing rodents at 0.5–4u2009h. Dosimetric absorption was then estimated. Planar scintigraphy was performed in mice, rats and rabbits bearing tumors. In vitro cellular uptake indicated that cells with higher COX-2 expression (A549 and 13762) had higher uptake of 99mTc-EC–CBX than lower COX-2 expression (H226). In vivo biodistribution of 99mTc-EC–CBX in tumor-bearing rodents showed increased tumor:tissue ratios as a function of time. In vitro and biodistribution studies demonstrated the possibility of using 99mTc-EC–CBX to assess COX-2 expression. Planar images confirmed that the tumors could be visualized with 99mTc-EC–CBX from 0.5 to 4u2009h in tumor-bearing animal models. We conclude that 99mTc-EC–CBX may be useful to assess tumor COX-2 expression. This may be useful in the future for selecting patients for treatment with anti-COX-2 agents.

99mTc-EC-Guanine: Synthesis, Biodistribution, and Tumor Imaging in Animals

PurposeDNA markers are useful in assessing cell proliferation. The purpose of this study was to synthesize 99mTc-ethylenedicysteine-guanine (EC-Guan) for evaluation of cell proliferation.MethodsTumor cells were incubated with 99mTc-EC-Guan for cell cycle analysis. Prostate tumor cells that were overexpressing the HSV thymidine kinase gene, or various tumor cells were incubated with 99mTc-EC-Guan at 0.5–2xa0h. Thymidine incorporation assays were performed in lung cancer cells incubated with EC-Guan at 0.1–1xa0mg/well. Tissue distribution, autoradiography, and planar scintigraphy of 99mTc-EC-Guan and 99mTc-EC (control) were determined in tumor-bearing rodents at 0.5–4xa0h.ResultsCell culture assays indicated that EC-Guan was incorporated in DNA, and there was no significant uptake difference between HSVTK overexpressed and normal groups. Biodistribution and scintigraphic imaging studies of 99mTc-EC-Guan showed increased tumor/tissue count density ratios as a function of time.ConclusionsOur results indicate that 99mTc-EC-Guan may be useful as a tumor proliferation imaging agent.

Targeted functional imaging of estrogen receptors with 99mTc-GAP-EDL

PurposeTo evaluate the feasibility of using 99mTc-glutamate peptide-estradiol in functional imaging of estrogen receptor-positive [ER(+)] diseases.Methods3-Aminoethyl estradiol (EDL) was conjugated to glutamate peptide (GAP) to yield GAP-EDL. Cellular uptake studies of 99mTc-GAP-EDL were conducted in ER(+) cell lines (MCF-7, 13762 and T47D). To demonstrate whether GAP-EDL increases MAP kinase activation, Western blot analysis of GAP-EDL was performed in 13762 cells. Biodistribution was conducted in nine rats with 13762 breast tumors at 0.5–4xa0h. Each rat was administered 99mTc-GAP-EDL. Two animal models (rats and rabbits) were created to ascertain whether tumor uptake of 99mTc-GAP-EDL was via an ER-mediated process. In the tumor model, breast tumor-bearing rats were pretreated with diethylstilbestrol (DES) 1xa0h prior to receiving 99mTc-GAP-EDL. In the endometriosis model, part of the rabbit uterine tissue was dissected and grafted to the peritoneal wall. The rabbit was administered with 99mTc-GAP-EDL.ResultsThere was a 10–40% reduction in uptake of 99mTc-GAP-EDL in cells treated with DES or tamoxifen compared with untreated cells. Western blot analysis showed an ERK1/2 phosphorylation process with GAP-EDL. Biodistribution studies showed that tumor uptake and tumor-to-muscle count density ratio in 99mTc-GAP-EDL groups were significantly higher than those in 99mTc-GAP groups at 4xa0h. Among 99mTc-GAP-EDL groups, region of interest analysis of images showed that tumor-to muscle ratios were decreased in blocking groups. In the endometriosis model, the grafted uterine tissue could be visualized by 99mTc-GAP-EDL.ConclusionCellular or tumor uptake of 99mTc-GAP-EDL occurs via an ER-mediated process. 99mTc-GAP-EDL is a useful agent for imaging functional ER(+) disease.