The hepatocyte growth factor (HGF) and its receptor, c-Met, are actively involved in tumor progression/metastasis and associated closely with poor prognostic outcome of cancer patients. Thus developing positron emission tomography (PET) agents for assessing c-Met expression would be extremely useful for diagnosis of cancer and subsequent monitoring of responses to c-Met-targeted therapies. Here we report the characterization of recombinant human hepatocyte growth factor (rh-HGF) as a PET tracer for detection of c-Met expression in vivo.
Methods
rh-HGF was expressed in human embryonic kidney (HEK) 293 cells and purified by nickel-nitrilogriacetic acid (Ni-NTA) affinity chromatography. The concentrated rh-HGF was conjugated to 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) and labeled with 64Cu. c-Met binding evaluation by flow cytometry was performed in both U87MG and MDA-MB-231 cell lines, which have high and low level of c-Met, respectively. PET imaging and biodistribution studies were performed in nude mice bearing U87MG and MDA-MB-231 xenografted tumors.
Results
The rh-HGF expression yield was 150–200 µg protein per 5 × 106 cells after 48 h transfection with purity of 85% ~ 90%. Flow cytometry examination confirmed strong and specific binding capacity of rh-HGF to c-Met. After labeled with 64Cu, PET imaging revealed specific and prominent uptake of 64Cu-NOTA-rh-HGF in c-Met positive U87MG tumors (6.7 ± 1.8 %ID/g at 9 h post-injection) and significantly lower uptake in c-Met negative MDA-MB-231 tumors (1.8 ± 0.6 %ID/g at 9 h post-injection). The fact that sonicated-denatured rh-HGF (termed as dnrh-HGF) had significantly lower uptake in U87MG tumors, along with histology analysis, confirmed the c-Met specificity of 64Cu-NOTA-rh-HGF.
Conclusion
The study provided the initial evidence to confirm that 64Cu-NOTA-rh-HGF is applicable for visualizing c-Met expression in vivo, which may also find potential applications in treatment monitoring of c-Met-targeted cancer therapy.