Screening of radiotracer for diagnosis of colorectal cancer liver metastasis based on MACC1-SPON2

Abstract

Background: Metastasis-associated in colon cancer 1 (MACC1) and Spondin2 (SPON2) are newly discovered oncogenes, but little is known about their role in colorectal cancer(CRC) liver metastases. PET has become an important molecular imaging technology due to its high sensitivity and quantifiability. In particular, its targeted, specific molecular probes can detect biological behaviors. This study was designed to evaluate the different biological properties of ¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO PET. The value of the CRC liver metastasis model explores the correlation and potential mechanisms of three tracers uptakes with tumor-related biological characteristics.

Methods: Human CRC cell lines(LoVo and HCT8), were cultured for in vitro radionuclide uptake experiments to compare the molecular imaging features of colorectal cancer cells with different metastatic potentials. Two kinds of cells were injected into the spleen of nude mice to establish a liver metastasis model. After the tumor formation, three kinds of tracer PET images were performed to evaluate the characteristics of live PET imaging of high and low liver metastasis colorectal cancer models. The expression levels of MACC1 and SPON2 in tissues were detected by immunohistochemistry and Western blot. Correlation between tracer uptake and expression of MACC1 and SPON2 in liver metastases was assessed by linear regression analysis.

Results: The uptake rate of in vitro three tracers uptake experiments was LoVo > HCT8. Micro-PET scan showed no significant difference between the ¹⁸F-FDG SUV values of the two cells (P > 0.05); there was significant difference between the ¹⁸F-FLT and ¹⁸F-FMISO SUV values (P < 0.05). All in vivo FLT and FMISO SUV values were significantly higher in LoVo tumors than in HCT8 tumors. The results of Western blot and immunohistochemistry showed that the expression levels of MACC1 and SPON2 in LoVo liver metastasis were higher than those in HCT8 (P < 0.05). The ¹⁸F-FLT SUVmax ratio was significantly correlated with the expression of MACC1 and SPON2 in hepatic metastases (r = 0.737, P = 0.0026; r = 0.842, P = 0.0002). The ¹⁸F-FMISO SUVmax ratio was only significantly correlated with the expression of MACC1 in hepatic metastasis (r = 0.770, P = 0.0013).

Conclusions: Early screening with ¹⁸F-FLT and ¹⁸F-FMISO tracers has important clinical value for the efficient diagnosis and treatment of colorectal cancer liver metastases.

Keywords: 18F-FDG; 18F-FLT; 18F-FMISO; Biological characteristics; Colorectal cancer liver metastasis; PET.

Fig. 1

¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO PET images of LoVo and HCT8 liver metastasis models and their corresponding liver anatomical images after 8 weeks of spleen injection of tumor cells. Yellow arrows indicate uptake of ¹⁸F-FDG, ¹⁸F-FLT, and ¹⁸F-FMISO in LoVo and HCT8 liver metastasis lesions; white nodules indicate liver metastases. It can be seen that the edge of liver metastasis lesions in ¹⁸F-FMISO Micro-PET imaging is clear, and the boundary between the liver and the surrounding organs is clear, and the degree of recognition is high. The edge of liver metastasis lesions in ¹⁸F-FLT Micro-PET imaging is blurred, intestinal tube, bladder, etc. The organ intake was higher and the recognition was relatively low. In the ¹⁸F-FDG Micro-PET imaging, the liver and metastases were relatively insignificant due to the high intake of the mouse head and heart

Fig. 2

Between three tracer (¹⁸F-FDG, ¹⁸F-FLT, ¹⁸F-FMISO) PET parameter values (SUVmax, SUVmax ratio) in the LoVo (n = 9) and HCT8 (n = 7) liver metastasis models Compare, ****P < 0.0001

Fig. 3

Immunohistochemical staining of human colorectal cancer LoVo and HCT8 liver metastases reflecting the level of protein expression as a result of yellow staining. The results showed that MACC1 was mainly expressed in the cytoplasm of two kinds of cellular liver metastasis tissues; SPON2 was expressed in both cytoplasm and cell membrane. The expressions of MACC1 and SPON2 in LoVo liver metastasis were significantly higher than those in HCT8 (× 400)

Fig. 4

Western blot quantitative analysis of SPON2 and MACC1 in LoVo and HCT8 liver metastases, using independent sample t-test to analyze the differences between the two proteins (***P = 0.0003, ****P < 0.0001)

Fig. 5

Correlation analysis between MACC1 and SPON2 and three tracers in LoVo and HCT8 liver metastases (n = 14). a There was a significant positive correlation between MACC1 expression and expression of ¹⁸F-FLT SUVmax ratio and ¹⁸F-FMISO SUVmax ratio in liver metastasis. b There was a significant positive correlation between the expression of SPON2 in liver metastases and the expression of ¹⁸F-FLT SUVmax ratio

Fig. 6

Correlation between MACC1 and SPON2 protein expression. Linear regression analysis showed a significant positive correlation between MACC1 and SPON2 (r = 0.763, P = 0.0015)