Relationship between biodistribution of a novel thymidine phosphorylase (TP) imaging probe and TP expression levels in normal mice

Disturbance of bile acids profile aggravates the diarrhea induced by capecitabine through inhibiting the Wnt/β-catenin pathway

INTRODUCTION

Diarrhea is the primary dose-limiting side effect of capecitabine(Cap) hindering its clinical application, but the mechanism is unclear. Clarifying this mechanism may enhance the patient compliance and improve the treatment outcome.

OBJECTIVES

To assess if the endogenous metabolic profile could prodict the diarrhea induced by Cap and explore and validate underlying mechanisms.

METHODS

Untargeted and targeted bile acids(BAs) metabolomics were performed to analyzed the metabolic profile of baseline samples from colorectal cancer(CRC) patients and the association with the diarrhea induced by Cap was assessed. The toxicity of BAs and Cap and its metabolites alone or their combinations to the human normal intestinal epithelial cell(HIEC) was assessed, and the key genes that mediated the BAs-enhanced toxicity of Cap were discovered by RNA-seq and then validated. A mouse model with high exposure levels of BAs was constructed and then treated with Cap to verify the Cap-induced diarrhea enhanced by BAs.

RESULTS

The baseline endogenous metabolic profile showed obviously difference between diarrhea and non-diarrhea CRC patients, and the differential metabolites mainly enriched in BAs metabolism; the deoxycholic acid(DCA) and lithocholic acid(LCA) were selected to be the key BAs that enhanced the toxicity of Cap metabolite 5-FU to the HIEC cell; the DCA and LCA could inhibit the Wnt/β-catenin signaling pathway, which then suppressed the P-glycoprotein and increased the exposure level of 5-FU in the HIEC cell. The results of animal experiment verified that the excessive DCA and LCA could aggravate the Cap-induced diarrhea through inhibiting Wnt/β-catenin-P-glycoprotein pathway.

CONCLUSIONS

The disordered BAs metabolic profile showed close relationship with diarrhea induced by Cap, and excessive DCA and LCA were proved to be the key BAs, which could aggravate the Cap-induced diarrhea through inhibiting Wnt/β-catenin-P-glycoprotein pathway.

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.

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.