Expression of biologically active kringle 5 domain of human plasminogen in Escherichia coli

Rhenium-188 labeled recombinant human plasminogen kringle5 (rhk5) and preliminary biodistribution. Evaluation in mice bearing A549 tumours

AIM

Angiogenesis plays a critical role in tumour formation and metastasis. Suitable radiolabeled angiogenesis inhibitor can be used for noninvasive imaging of angiogenesis and radionuclide therapy. Here we prepare rhenium-188 labeled recombinant human plasminogen kringle5 (188Re-rhk5) in a convenient manner than evaluate its properties in A549 lung adenocarcinoma.

METHODS

188Re-rhk5 was obtained by conjugating His group at the C end of rhk5 with fac-[188Re(H2O)3(CO)3]+. Chelating efficiency of fac-[188Re(H2O)3(CO)3]+ and radiolabeling efficiency of 188Re-rhk5 were measured by radio thin-layer chromatography (RTLC). In vitro stability of 188Re-rhk5 was determined in human serum at 37°C and analyzed by RTLC. Competition test was also performed to verify the specificity of binding. A biodistribution study was carried out in nude mice bearing A549 lung adenocarcinoma.

RESULTS

188Re-rhk5 was obtained with a radiolabel efficiency of 66.1%, the radiochemical purity (RCP) can reach 95.2% after purification. 188Re-rhk5 showed high stability in human serum, the RCP was more than 80% even 12 h after incubation. Competition test showed a high binding specificity. Furthermore, this radio-complex was excreted mainly through kidneys and showed specific tumour uptake in mice bearing A549 tumours.

CONCLUSION

188Re-rhk5 was prepared by a simple method. Preliminary biodistribution results showed its potential as an agent for possible tumour imaging, therapy and encouraged further investigation.

Evaluation of biodistribution and antitumor effects of (188)Re-rhk5 in a mouse model of lung cancer

Targeting drugs to receptors involved in tumor angiogenesis is considered to be a novel and promising approach to improve cancer treatment. This study aimed to evaluate the anti-tumor efficacy of (188)Re-labeled recombinant human plasminogen kringle 5 ((188)Re‑rhk5) through [18F]-fluorodeoxyglucose (FDG) micro-positron emission tomography (PET). Radiolabeled rhk5 was obtained by conjugating the hystidine (6 x His) group at the carbon end of rhk5 with fac-[(188)Re(H(2)O)(3)(CO)(3)](+). The biodistribution study of (188)Re-rhk5 showed that (188)Re-rhk5 had a high initial tumor uptake and prolonged tumor retention. The highest tumor uptake of (188)Re-rhk5 (3.65±0.82% ID/g) was found 2 h after injection which decreased to 0.81±0.14% ID/g 12 h after injection. Following therapy, tumor size measurement indicated that (188)Re-rhk5-treated tumors were smaller than (188)Re-, rhk5- and saline-treated controls 6 days after the treatment. In vivo 18F-FDG micro-PET imaging showed significantly reduced tumor metabolism in the (188)Re-rhk5-treated mice vs. those treated with rhk5, (188)Re and saline control, 1 day after treatment. Moreover, the number of microvessels was significantly reduced after (188)Re-rhk5 treatment as determined by CD31 staining. Our results demonstrate that specific delivery of (188)Re-rhk5 allows preferential cytotoxicity to A549 lung cancer cells and tumor vasculature. (18)F-FDG micro-PET is a non-invasive imaging tool that can be utilized to assess early tumor responses to (188)Re-rhk5 therapy.