In vitro and in vivo evaluations of a radioiodinated thymidine phosphorylase inhibitor as a tumor diagnostic agent for angiogenic enzyme imaging

Thymidine Phosphorylase Imaging Probe for Differential Diagnosis of Metabolic dysfunction-associated Steatohepatitis

PURPOSE

Metabolic dysfunction-associated steatotic liver disease (MASLD) comprises simple steatosis (SS), which has a low risk of mortality, and metabolic dysfunction-associated steatohepatitis (MASH), which can progress to liver cirrhosis and hepatocellular carcinoma. Because differentiation between MASH and SS is the most important issue in the diagnosis of MASLD, the establishment of noninvasive diagnostic methods is urgently needed. In this study, we evaluated the potential of [123I]IIMU, a thymidine phosphorylase (TYMP) targeted SPECT imaging probe, for differential diagnosis of MASLD in a preclinical animal model.

PROCEDURES

SS and MASH mice were prepared by feeding db/db mice with a standard diet and a methionine/choline-deficient diet, respectively. Control mice were prepared by feeding m/m mice with a standard diet. TYMP expression in the liver was evaluated by RT-PCR, western blotting, and immunohistochemistry. The biodistribution of [125I]IIMU in the three model mice was evaluated at 30 min post-injection. SPECT/CT imaging studies of the three model mice were performed 30 min after injection of [123I]IIMU.

RESULTS

Hepatic TYMP expression level was the highest in the SS mice and the lowest in the MASH mice at both mRNA and protein levels. The immunohistochemistry experiment showed a patchy distribution of TYMP only in the liver of MASH mice. In the biodistribution study, the hepatic accumulation of [125I]IIMU was the highest in the SS mice and the lowest in the MASH mice. The SPECT/CT imaging study showed similar results to the biodistribution experiment.

CONCLUSION

Hepatic TYMP expression level may serve as a promising imaging biomarker for differential diagnosis of SS and MASH. SPECT imaging using [123I]IIMU potentially provides a novel noninvasive diagnostic method to differentiate MASH and SS.

Methods and Advances in the Design, Testing and Development of In Vitro Diagnostic Instruments

With the continuous improvement of medical testing and instrumentation engineering technologies, the design, testing and development methods of in vitro diagnostic instruments are developing rapidly. In vitro diagnostic instruments are also gradually developing into a class of typical high-end medical equipment. The design of in vitro diagnostic instruments involves a variety of medical diagnostic methods and biochemical, physical and other related technologies, and its development process involves complex system engineering. This paper systematically organizes and summarizes the design, testing and development methods of in vitro diagnostic instruments and their development in recent years, focusing on summarizing the related technologies and core aspects of the R&D process, and analyzes the development trend of the in vitro diagnostic instrument market.

Biodistribution and internal radiation dosimetry of a novel probe for thymidine phosphorylase imaging, [123I]IIMU, in healthy volunteers

OBJECTIVE

We evaluated the radiation dosage, biodistribution, human safety, and tolerability of the injection of a single dose of [¹²³I] 5-iodo-6-[(2-iminoimidazolidinyl)methyl]uracil (IIMU), a new radiotracer targeting thymidine phosphorylase (TP), in healthy volunteers.

METHODS

Potential participants were tested at our hospital to confirm their eligibility. Two healthy male adults passed the screening tests. They were injected with 56 and 111 MBq of [¹²³I]IIMU, respectively. Safety assessments were performed before and at 1, 3, 6, 9, 24, 48 h, and 1-week post-injection. Whole-body emission scans were conducted at 1, 3, 6, 24, and 48 h post-injection. Regions of interest were manually drawn to enclose the entire body at each time point, identifying high-uptake organs to obtain the time-activity curves. Urine and blood samples were collected at 1, 2, 3, 4, 5, 6, 9, 24, and 48 h post-injection. The radiation dose for each organ and the effective doses were estimated using OLINDA/EXM 1.1 software.

RESULTS

No adverse events were observed as of the follow-up visit > 1-week post-injection. In both subjects, the highest uptake of [¹²³I]IIMU occurred in the liver, with peak injected activity (%IA) values of 17.7% and 15.1%, respectively. The second highest uptake was in the thyroid (0.35% and 0.66% IA). The %IA decreased gradually toward the end of the study (48 h) in all organs except the liver and thyroid. By the end of the study, 52.5% and 51.5% of the injected activity of [¹²³I]IIMU had been excreted via the subjects' renal systems. The estimated mean effective doses of [¹²³I]IIMU were 9.19 μSv/MBq and 10.1 μSv/MBq, respectively.

CONCLUSION

In this preliminary study, [¹²³I]IIMU was safely administered to healthy adults, and its potential clinical use in TP imaging was revealed.

Preclinical investigation of potential use of thymidine phosphorylase-targeting tracer for diagnosis of nonalcoholic steatohepatitis

INTRODUCTION

Although liver biopsy is the gold standard for the diagnosis of nonalcoholic steatohepatitis (NASH), it has several problems including high invasiveness and sampling errors. Therefore, the development of alternative methods to overcome these disadvantages is strongly required. In this study, we evaluated the potential use of our tracer targeting thymidine phosphorylase (TYMP), 5-[¹²³I]iodo-6-[(2-iminoimidazolidinyl)methyl]uracil ([¹²³I]IIMU) for the diagnosis of NASH.

METHODS

The mice used as the NASH model (hereafter, NASH mice) were prepared by feeding a methionine- and choline-deficient diet for 4 weeks. A control group was similarly given a control diet. The expression levels of the TYMP gene and protein in the liver were examined by real-time reverse-transcription polymerase chain reaction and western blot analyses. The localizations of [¹²⁵I]IIMU and the TYMP protein in the liver were examined by autoradiography and immunohistochemical staining, respectively. Finally, the mice were injected with [¹²³I]IIMU and single-photon emission tomography (SPECT) imaging was conducted.

RESULTS

The hepatic expression levels of TYMP were significantly lower in the NASH mice than in the control mice at both mRNA and protein levels, suggesting that a decrease in TYMP level could be an indicator of NASH. [¹²⁵I]IIMU was uniformly distributed in the liver of the control mice, whereas it showed a patchy distribution in that of the NASH mice. The localization of [¹²⁵I]IIMU was visually consistent with that of the TYMP protein in the liver of the control and NASH mice. SPECT analysis indicated that the hepatic accumulation of [¹²³I]IIMU in the NASH mice was significantly lower than that in the control mice [SUV (g/ml): 4.14 ± 0.87 (Control) vs 2.31 ± 0.29 (NASH)].

CONCLUSIONS

[¹²³I]IIMU may provide a noninvasive means for imaging TYMP expression in the liver and may be applicable to the diagnosis of NASH.

Assessment of early changes in 3H-fluorothymidine uptake after treatment with gefitinib in human tumor xenograft in comparison with Ki-67 and phospho-EGFR expression

Background

The purpose of this study was to evaluate whether early changes in 3′-deoxy-3′-³H-fluorothymidine (³H-FLT) uptake can reflect the antiproliferative effect of gefitinib in a human tumor xenograft, in comparison with the histopathological markers, Ki-67 and phosphorylated EGFR (phospho-EGFR).

Methods

An EGFR-dependent human tumor xenograft model (A431) was established in female BALB/c athymic mice, which were divided into three groups: one control group and two treatment groups. Mice in the treatment groups were orally administered a partial regression dose (100 mg/kg/day) or the maximum tolerated dose of gefitinib (200 mg/kg/day), once daily for 2 days. Mice in the control group were administered the vehicle (0.1% Tween 80). Tumor size was measured before and 3 days after the start of treatment. Biodistribution of ³H-FLT and ¹⁸F-FDG (%ID/g/kg) was examined 3 days after the start of the treatment. Tumor cell proliferative activity with Ki-67 was determined. Immunohistochemical staining of EGFR and measurement of phospho-EGFR were also performed.

Results

High expression levels of EGFR and Ki-67 were observed in the A431 tumor. After the treatment with 100 and 200 mg/kg gefitinib, the uptake levels of ³H-FLT in the tumor were significantly reduced to 67% and 61% of the control value, respectively (0.39 ± 0.09, 0.36 ± 0.06, 0.59 ± 0.11%ID/g/kg for 100 mg/kg, 200 mg/kg, and control groups, respectively; p < 0.01 vs. control), but those of ¹⁸F-FDG were not. After the treatment with 100 and 200 mg/kg gefitinib, the expression levels of Ki-67 in the tumor were markedly decreased (4.6 ± 2.4%, 6.2 ± 1.8%, and 10.4 ± 5.7% for 100 mg/kg, 200 mg/kg, and control groups, respectively, p < 0.01 vs. control). The expression levels of the phospho-EGFR protein also significantly decreased (29% and 21% of the control value for 100, and 200 mg/kg, respectively p < 0.01 vs. control). There was no statistically significant difference in tumor size between pre- and post-treatments in each group.

Conclusion

In our animal model, ³H-FLT uptake levels significantly decreased after the treatment with two different doses of gefitinib before a significant change in tumor size was observed. These results were confirmed by the immunohistochemical staining of Ki-67 and phospho-EGFR protein immunoassay. Thus, it was indicated that early changes in ³H-FLT uptake may reflect the antiproliferative effect of gefitinib in a mouse model of a human epidermoid cancer.