Instantaneous preparation of radiolabeled 5-iodo-2'-deoxyuridine

Organomercury Nucleic Acids: Past, Present and Future

Synthetic efforts towards nucleosides, nucleotides, oligonucleotides and nucleic acids covalently mercurated at one or more of their base moieties are summarized, followed by a discussion of the proposed, realized and abandoned applications of this unique class of compounds. Special emphasis is given to fields in which active research is ongoing, notably the use of HgII -mediated base pairing to improve the hybridization properties of oligonucleotide probes. Finally, this minireview attempts to anticipate potential future applications of organomercury nucleic acids.

Diesterified derivatives of 5-iodo-2'-deoxyuridine as cerebral tumor tracers

With the aim to develop beneficial tracers for cerebral tumors, we tested two novel 5-iodo-2'-deoxyuridine (IUdR) derivatives, diesterified at the deoxyribose residue. The substances were designed to enhance the uptake into brain tumor tissue and to prolong the availability in the organism. We synthesized carrier added 5-[125I]iodo-3',5'-di-O-acetyl-2'-deoxyuridine (Ac2[125I]IUdR), 5-[125I]iodo-3',5'-di-O-pivaloyl-2'-deoxyuridine (Piv2[125I]IUdR) and their respective precursor molecules for the first time. HPLC was used for purification and to determine the specific activities. The iodonucleoside tracer were tested for their stability against human thymidine phosphorylase. DNA integration of each tracer was determined in 2 glioma cell lines (Gl261, CRL2397) and in PC12 cells in vitro. In mice, we measured the relative biodistribution and the tracer uptake in grafted brain tumors. Ac2[125I]IUdR, Piv2[125I]IUdR and [125I]IUdR (control) were prepared with labeling yields of 31-47% and radiochemical purities of >99% (HPLC). Both diesterified iodonucleoside tracers showed a nearly 100% resistance against degradation by thymidine phosphorylase. Ac2[125I]IUdR and Piv2[125I]IUdR were specifically integrated into the DNA of all tested tumor cell lines but to a less extend than the control [125I]IUdR. In mice, 24 h after i.p. injection, brain radioactivity uptakes were in the following order Piv2[125I]IUdR>Ac2[125I]IUdR>[125I]IUdR. For Ac2[125I]IUdR we detected lower amounts of radioactivities in the thyroid and stomach, suggesting a higher stability toward deiodination. In mice bearing unilateral graft-induced brain tumors, the uptake ratios of tumor-bearing to healthy hemisphere were 51, 68 and 6 for [125I]IUdR, Ac2[125I]IUdR and Piv2[125I]IUdR, respectively. Esterifications of both deoxyribosyl hydroxyl groups of the tumor tracer IUdR lead to advantageous properties regarding uptake into brain tumor tissue and metabolic stability.

Induction of lethal bystander effects in human breast cancer cell cultures by DNA-incorporated Iodine-125 depends on phenotype

PURPOSE

This study uses a three-dimensional cell culture model to investigate lethal bystander effects in human breast cancer cell cultures (MCF-7, MDA-MB-231) treated with (125)I-labeled 5-iodo-2 -deoxyuridine ((125)IdU). These breast cancer cell lines respectively form metastatic xenografts in nude mice in an estrogen-dependent and independent manner.

MATERIALS AND METHODS

In the present study, these cells were cultured in loosely-packed three-dimensional architecture in a Cytomatrix™ carbon scaffold. Cultures were pulse-labeled for 3 h with (125)IdU to selectively irradiate a minor fraction of cells, and simultaneously co-pulse-labeled with 0.04 mM 5-ethynyl-2'-deoxyuridine (EdU) to identify the radiolabeled cells using Click-iT(®) EdU and flow cytometry. The cultures were then washed and incubated for 48 h. The cells were then harvested, serially diluted, and seeded for colony formation. Aliquots of cells were subjected to flow cytometry to determine the percentage of cells labeled with (125)IdU/EdU. Additional aliquots were used to determine the mean (125)I activity per labeled cell. The percentage of labeled cells was about 15% and 10% for MCF-7 and MDA cells, respectively. This created irradiation conditions wherein the cross-dose to unlabeled cells was small relative to the self-dose to labeled cells. The surviving fraction relative to EdU-treated controls was measured.

RESULTS

Survival curves indicated significant lethal bystander effect in MCF-7 cells, however, no significant lethal bystander effect was observed in MDA-MB-231 cells.

CONCLUSIONS

These studies demonstrate the capacity of (125)IdU to induce lethal bystander effects in human breast cancer cells and suggest that the response depends on phenotype.

Highly efficient syntheses of [methyl-11C]thymidine and its analogue 4'-[methyl-11C]thiothymidine as nucleoside PET probes for cancer cell proliferation by Pd(0)-mediated rapid C-[11C]methylation

Pd(0)-mediated rapid couplings of CH(3)I (and then [(11)C]CH(3)I) with excess 5-tributylstannyl-2'-deoxyuridine and -4'-thio-2'-deoxyuridine were investigated for the syntheses of [methyl-(11)C]thymidine and its stable analogue, 4'-[methyl-(11)C]thiothymidine as PET probes for cancer diagnosis. The previously reported conditions were attempted using Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3) (1 : 4 in molar ratio) at 130 °C for 5 min in DMF, giving desired products only in 32 and 30% yields. Therefore, we adapted the current reaction conditions developed in our laboratory for heteroaromatic compounds. The reaction using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1 : 25 : 1 : 32 : 2 : 5) at 80 °C gave thymidine in 85% yield. Whereas, CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuBr/CsF (1 : 25 : 1 : 32 : 2 : 5) including another CuBr/CsF system promoted the reaction at a milder temperature (60 °C), giving thymidine in 100% yield. Chemo-response of thiothymidine-precursor was different from thymidine system. Thus, the above optimized conditions including CuBr/CsF system gave 4'-thiothymidine only in 40% yield. The reaction using 5-fold amount of CuBr/CsF at 80 °C gave much higher yield (83%), but unexpectedly, the reaction was accompanied by a considerable amount of undesired destannylated product. Such destannylation was greatly suppressed by changing to a CuCl/K(2)CO(3) system using CH(3)I/stannane/Pd(2)(dba)(3)/P(o-CH(3)C(6)H(4))(3)/CuCl/K(2)CO(3) (1 : 25 : 1 : 32 : 2 : 5) at 80 °C, giving the 4'-thiothymidine in 98% yield. The each optimized conditions were successfully applied to the syntheses of the corresponding PET probes in 87 and 93% HPLC analytical yields. [(11)C]Compounds were isolated by preparative HPLC after the reaction conducted under slightly improved conditions, exhibiting sufficient radioactivity of 3.7-3.8 GBq and specific radioactivity of 89-200 GBq µmol(-1) with radiochemical purity of ≥99.5% for animal and human PET studies.

Auger processes in the 21st century

PURPOSE

The extreme radiotoxicity of Auger electrons and their exquisite capacity to irradiate specific molecular sites has prompted scientists to extensively investigate their radiobiological effects. Their efforts have been punctuated by quadrennial international symposia that have focused on biophysical aspects of Auger processes. The latest meeting, the 6th International Symposium on Physical, Molecular, Cellular, and Medical Aspects of Auger Processes, was held 5-6 July 2007 at Harvard Medical School in Boston, Massachusetts, USA. This article provides a review of the research in this field that was published during the years 2004-2007, the period that has elapsed since the previous meeting.

CONCLUSION

The field has advanced considerably. A glimpse of the potential of this unique form of ionizing radiation to contribute to future progress in a variety of fields of study is proffered.

The preparation of clinical grade 5-[123I]iodo-2'-deoxyuridine and 5-[125I]iodo-2'-deoxyuridine with high in vitro stability and the potential for early proliferation scintigraphy

BACKGROUND AND METHODS

5-Iodo-2'-deoxyuridine (IdUrd) radiolabelled with the positron emitter I or with the gamma and Auger electron emitters I or I has been proposed for cancer diagnosis and therapy. We modified the synthesis to reliably obtain [I]IdUrd and [I]IdUrd by using an Iodogen supported destannylation reaction of 5-(tri-n-butylstannyl)-2'-deoxyuridine (Bu3SndUrd) which meets the requirements for good laboratory practice (GLP) and good clinical practice (GCP). A method of purification was developed to eliminate by-products as well as any unreacted starting material.

RESULTS

[I]IdUrd, which originated from a trace of iodide in the Bu3SndUrd precursor, was identified as the unknown by-product reported for this method. This trace could be eliminated by modified purification of Bu3SndUrd. Stabilization of pH was essential for unequivocal identification of radiolabelled IdUrd and possible degradation products in the different systems tested for quality control. Biodistribution in tumour bearing nude mice was measured as early as 3 and 6 h after i.v. injection of [I]IdUrd. This compound showed high and specific activity uptake in tumour and dividing tissues when combined with 5-fluoro-2'-deoxyuridine pre-treatment. Uptake was specifically inhibited by injection of excess thymidine.

5-[125]iodo-2'-deoxyuridine in the radiotherapy of solid CNS tumors in rats

We have been investigating the therapeutic efficacy of the thymidine analog 5-iodo-2'-deoxyuridine (IUdR) when radiolabeled with the Auger electron emitter 125I in rats bearing intrathecal (i.t.) or intracerebral (i.c.) 9L gliosarcoma solid tumors. [125I]IUdR was infused i.t. (via subarachnoid catheters) or intracerebrally over a 5- or 2-day period; equimolar concentrations of [127I]IUdR were infused into control animals. Hind-leg paralysis and/or survival were followed over time. The results indicate that compared with [127I]IUdR, rats bearing intrathecal tumors and infused i.t. with [125I]IUdR showed significant prolongation of the onset of median paralysis (15.2 versus 9 days). Similarly, the median survival of rats bearing intracerebral tumors and infused i.c. with [125I]IUdR was significantly increased (24 versus 17 days). The data substantiate the antineoplastic potential of [125I]IUdR and indicate a promising role for this radiopharmaceutical in the treatment of CNS cancers.

Biochemical modulation by 5-fluorouracil and 1-folinic acid of tumor uptake of intra-arterial 5-[123I]iodo-2'deoxyuridine in patients with liver metastases from colorectal cancer

In previous studies we demonstrated a high tumor-targeting value of the 123I-labeled thymidine analogue 5-iodo-2'-deoxyuridine (IUdR) infused intra-arterially in patients with liver metastases from colorectal cancer. In the present study we have explored the possibility of enhancing tumor uptake of [123I]IUdR, by biochemical modulation with 5-fluorouracil (5-FU) and 1-folinic acid (FA), a drug combination known to inhibit thymidylate synthetase in tumor cells. The investigation was carried out employing diagnostic imaging doses of [123I]IUdR, much lower than possible therapeutic levels. In the baseline study, [123I]IUdR was infused into the hepatic artery of patients with inoperable liver metastases from colorectal cancer, and a second infusion was performed one week later, after intra-arterial administration of 5-FU and FA. The effect was evaluated by comparing tumor uptake of [123I]IUdR in the second study with that of the baseline study. The average tumor uptake immediately after [123I]IUdR infusion was 9.1% ID in the baseline study, increasing to 14.9% ID after pretreatment with 5-FU and FA. The average enhancement in early tumor uptake of [123I]IUdR induced by biochemical modulation was 72%. This enhancement was sustained at 18 and 42 hours after infusion (stable uptake). The results encourage the pretreatment of patients with 5-FU and FA prior to radioiodinated IUdR administration and suggest its inclusion in therapeutic protocols employing IUdR labeled with 123I or 125I as a source of highly cytotoxic Auger electrons.