123I-ITdU-mediated nanoirradiation of DNA efficiently induces cell kill in HL60 leukemia cells and in doxorubicin-, beta-, or gamma-radiation-resistant cell lines.
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Resistance to radiotherapy or chemotherapy is a common cause of treatment failure in high-risk leukemias. We evaluated whether selective nanoirradiation of DNA with Auger electrons emitted by 5-(123)I-iodo-4'-thio-2'-deoxyuridine ((123)I-ITdU) can induce cell kill and break resistance to doxorubicin, beta-, and gamma-irradiation in leukemia cells. METHODS: 4'-thio-2'-deoxyuridine was radiolabeled with (123/131)I and purified by high-performance liquid chromatography. Cellular uptake, metabolic stability, DNA incorporation of (123)I-ITdU, and the effect of the thymidylate synthase (TS) inhibitor 5-fluoro-2'-deoxyuridine (FdUrd) were determined in HL60 leukemia cells. DNA damage was assessed with the comet assay and quantified by the olive tail moment. Apoptosis induction and irradiation-induced apoptosis inhibition by benzoylcarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD.fmk) were analyzed in leukemia cells using flow cytometry analysis. RESULTS: The radiochemical purity of ITdU was 95%. Specific activities were 900 GBq/micromol for (123)I-ITdU and 200 GBq/micromol for (131)I-ITdU. An in vitro cell metabolism study of (123)I-ITdU with wild-type HL60 cells demonstrated an uptake of 1.5% of the initial activity/10(6) cells of (123)I-ITdU. Ninety percent of absorbed activity from (123)I-ITdU in HL60 cells was specifically incorporated into DNA. (123)I-ITdU caused extensive DNA damage (olive tail moment > 12) and induced more than 90% apoptosis in wild-type HL60 cells. The broad-spectrum inhibitor of caspases zVAD-fmk reduced (123)I-ITdU-induced apoptosis from more than 90% to less than 10%, demonstrating that caspases were central for (123)I-ITdU-induced cell death. Inhibition of TS with FdUrd increased DNA uptake of (123)I-ITdU 18-fold and the efficiency of cell kill about 20-fold. In addition, (123)I-ITdU induced comparable apoptotic cell death (>90%) in sensitive parental leukemia cells and in leukemia cells resistant to beta-irradiation, gamma-irradiation, or doxorubicin at activities of 1.2, 4.1, 12.4, and 41.3 MBq/mL after 72 h. This finding indicates that (123)I-ITdU breaks resistance to beta-irradiation, gamma-irradiation, and doxorubicin in leukemia cells. CONCLUSION: (123)I-ITdU-mediated nanoirradiation of DNA efficiently induced apoptosis in sensitive and resistant leukemia cells against doxorubicin, beta-irradiation, and gamma-irradiation and may provide a novel treatment strategy for overcoming resistance to conventional radiotherapy or chemotherapy in leukemia. Cellular uptake and cell kill are highly amplified by inhibiting TS with FdUrd. (+info)
A new tool for molecular imaging: the microvolumetric beta blood counter.
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Radiotracer kinetic modeling in small animals with PET allows absolute quantification of physiologic and biochemical processes in vivo. It requires blood and tissue tracer concentrations as a function of time. Manual sampling, the reference method for blood tracer concentration measurements, requires fairly large amounts of blood besides being technically difficult and time-consuming. An automated microvolumetric beta blood counter (microBC) was designed to circumvent these limitations by measuring the blood activity in real time with PET scanning. METHODS: The microBC uses direct beta-particle detection to reduce its footprint and is entirely remote controlled for sampling protocol selection and real-time monitoring of measured parameters. Sensitivity has been determined for the most popular PET radioisotopes ((18)F, (13)N, (11)C, (64)Cu). Dispersion within the sampling catheter has been modeled to enable automatic correction. Blood curves obtained with the microBC were compared with manual samples and PET-derived data. The microBC was used to estimate the myocardial blood flow (MBF) of mice injected with (13)N-ammonia and to compare the myocardial metabolic rate of glucose (MMRG) of rats injected with (18)F-FDG for arterial and venous cannulation sites. RESULTS: The sensitivity limit ranges from 3 to 104 Bq/microL, depending on the isotope and the catheter used, and was found to be adequate for most small-animal studies. Automatic dispersion correction appears to be a good approximation of dispersion-free reference curves. Blood curves sampled with the microBC are well correlated with curves obtained from manual samples and PET images. With correction for dispersion, the MBF of anesthetized mice at rest was found to be 4.84 +/- 0.5 mL/g/min, which is comparable to values found in the literature for rats. MMRG values derived from the venous blood tracer concentration are underestimated by 60% as compared with those derived from arterial blood. CONCLUSION: The microBC is a compact automated counter allowing real-time measurement of blood radioactivity for pharmacokinetic studies in animals as small as mice. Reliable and reproducible, the device makes it possible to increase the throughput of pharmacokinetic studies with reduced blood sample handling and staff exposure, contributing to speed up new drug development and evaluation. (+info)
RBE of HTO to 60Co gamma-rays for cell killing of a radioresistant E. coli harboring plasmid.
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Radioresistant E. coli TGl harboring pUC 18 plasmid which was Ampicillin-resistant was exposed to 60Co gamma-rays or 3H beta-rays in saline to determine whether the relative biological effectiveness of 3H beta-rays is higher than one. After exposure to 60Co gamma-rays at a dose rate of 0.465 Gy/min, the D0 by colony formation was 145 Gy in the presence of Ampicillin in or absence from the agar medium; whereas, the D0 was calculated as 118 Gy with and without Ampicillin after exposure to 3H beta-rays at a dose rate of 0.431 Gy/min. The relative biological effectiveness established for 3H beta-rays to 60Co gamma-rays was 1.23. The reason for the higher effectiveness of 3H beta-rays as compared to the reference 60Co gamma-rays is discussed in terms of nascent 0 production. (+info)
Effect of low-dose electron radiation on rat skin wound healing.
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The aim of this study was to assess the effect of low-dose electron irradiation on morphological features of the wound healing process in rat skin. Surgical wounds were inflicted with a 2.3 x 1.4 cm template on 84 male rats that were assigned to 4 groups: IG1, immediately irradiated; IG2, irradiated 3 days after inflicting the wound; CG1 and CG2, control groups. Rats in IG1 and IG2 groups had their wounds exposed to 1 Gy of 6 MeV electron beam radiation, immediately after surgery and on the third postoperative day, respectively. Qualitative and histophotometric evaluations of tissue repair structures were carried out. Data were analyzed by ANOVA and Tukey's test (alpha = 0.05) and regression analysis. The repair process was delayed since the first sacrifice time in both irradiated groups, but in IG1, wound healing was closer to that of CG1; whereas in IG2, the delay was more pronounced. Based on the histological findings, it is possible to conclude that a low-dose of electron radiation delayed tissue repair in rat skin. The delay was longer in the skin irradiated 3 days after the beginning of tissue repair. However, the low-energy electron irradiation did not prevent wound healing. (+info)
Radiation carcinogenesis in mouse skin and its threshold-like response.
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Experiments on the dose-response of tumor development induced by repeated local beta irradiation of the back of mice are summarized. Results indicated a 100% tumor incidence on irradiation at 2.5-11.8 Gy per exposure (dose-saturation effect) and the threshold-like dose response at lower doses. The mechanism underlying these phenomena is discussed on the basis of the tissue-misrepair model, that is misrepair caused by repeated stimulation of cell growth after repeated tissue injury. (+info)
Estimation of the beta+ dose to the embryo resulting from 18F-FDG administration during early pregnancy.
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