Molecular Imaging Of Targeting VCAM-1 Expression And Monitoring Therapy Response In Tumor

Objectives:Vascular cell adhesion molecule 1(VCAM-1)is overexpressed in a group of cancers.This study aimed to evaluate the apply of 99mTc labeled single chain variable fragment(scFv)of VCAM-1(VCAM-1scFv)as a possible imaging agent in several tumors.Methods:The VCAM-1scFv was labeled with 99mTc using the succinimidyl 6-hydraziniumnicotinate hydrochloride(SHNH).VCAM-1 expression levels were evaluated in a number of cell lines by immunofluorescence staining.In-vitro cell binding assays,single photon emission computed tomography(SPECT)imaging and biodistribution studies with 99mTc-6-hydrazinonicotinamide(HYNIC)-VCAM-1scFv were carried out in a variety of cell lines or tumors.The immunofluorescence study was also performed in the kidneys,livers and different tumor tissues.Results:99mTc-HYNIC-VCAM-1scFv was synthetized with a high radiolabeling yield of 81.46±3.61%(n=5),and a radiochemical purity of 96.54±1.65%(n=5)after purification.In-vitro binding assays showed that different binding affinity of 99mTc-HYNIC-VCAM-1scFv in different tumor cell lines,and high cellular uptake was seen in B16F10 and HT1080 cells(6.07±0.55%,5.73±0.41%,n=3),which were consistent with immunofluorescence staining.In-vivo SPECT imaging demonstrated that B16F10 and HT1080 tumor images could be clearly delineated(4.93±0.52%ID/g,4.65±0.39%ID/g,4h),and a visible signal was observed in SKOV3.ip tumor(2.99±0.44%ID/g,4h)and weak uptake in A375m,MDA-MB-231,and 786-0 tumors(1.33±0.22%ID/g,1.49±0.23%ID/g and 1.47±0.31%ID/g,4h),which were confirmed by biodistribution studies.Moreover,the high uptake in B16F10 tumors could be inhibited by excess VCAM-1ScFv(5.51±0.37%ID/g,2.92±0.26%ID/g,p<0.001).The immunofluorescence intensity of the tumors was correlated well with the in vivo result(R2=0.875,p<0.001),and the kidneys and livers showed relatively low signals.Conclusion:99mTc-HYNIC-VCAM-1scFv,which selectively binds to VCAM-1,can visualize different expression levels of VCAM-1 and provide a qualitative and quantitative method for noninvasive evaluation of VCAM-1 in tumors.Objectives:Vascular cell adhesion molecule-1(VCAM-1)is becoming an attractive candidate for tumor targeting detection and therapy due to its involvement in tumourigenicity and metastasis.LY2409881,an IKK2 inhibitor,can trigger apoptosis of VCAM-1 positive melanoma cells.The aim of this study was to assess the use of the 68Ga-labeled single chain variable fragment(scFv)of VCAM-1 in detecting VCAM-1-positive tumor expression and monitoring the therapeutic effect of LY2409881.Methods:Melanoma cell lines,B16F10 and A375m,were selected as VCAM-1 overexpression and underexpression models,respectively.VCAM-1 scFv was labeled with 68Ga using 1,4,7-triazacyclononane-1,4,7-triacetic acid(NOTA).MicroPET/CT imaging,biodistribution,and autoradiography studies were performed in mice bearing B16F10 and A375m tumors after injection of 68Ga-NOTA-VCAM-1scFv to verify the targeting ability of the tracer.In-vitro cytotoxicity assays of LY2409881 were performed in B16F10 cells,and an in vivo study was performed in B16F10 tumor-bearing mice with intraperitoneal injection of LY2409881,using DMSO injection with same protocol as a control.Treatment monitoring was evaluated with 68Ga-NOTA-VCAM-1scFv microPET/CT imaging weekly.Results:68Ga-NOTA-VCAM-1scFv was successfully synthesized with high labeling efficiency.MicroPET/CT images,biodistribution,and autoradiography studies showed much higher uptake of the tracer in B16F10 tumors than that in A375m tumors.LY2409881 caused dose-and time-dependent growth inhibition and apoptosis in melanoma cellsin vitro,and suppressed B16F10 tumor growth in vivo.In the therapy monitoring group,microPET/CT imaging showed the reduced tumor uptake of 68Ga-NOTA-VCAM-1scFv at the first week of LY2409881 treatment,but increased to the initial uptake level afterward.The tumor uptake of 68Ga-NOTA-VCAM-lScFv in the control group remained relatively steady during the DMSO treatment.Conclusions:LY2409881,an IKK2 inhibitor,inhibits tumor growth and VCAM-1 expression.68Ga-NOTA-VCAM-1scFv,an easily-prepared probe,can be used to visualize VCAM-1 positive tumors and monitor the effect of LY2409881 therapy,suggesting its prospective clinical application.