Description: Epidermal growth factor receptor (EGFR) expression is upregulated in many types of tumors, and the EGFR tyrosine kinase inhibitor gefitinib has high potential as an anticancer drug. However, accumulating clinical evidence has indicated that only a subset of patients benefit from gefitinib treatment. This study aimed to determine whether optical imaging of vascular endothelial growth factor (VEGF) expression can be an early biomarker for tumor response to gefitinib therapy. Methods: A VEGF-targeting fluorescent probe Dye-BevF(ab') 2 was prepared and tested in vivo. Longitudinal optical imaging studies using Dye-BevF(ab') 2 were performed in both 22B (gefitinib-resistant) and A549 (gefitinib-responsive) tumor models at different times (days 0, 2, and 5) before and after gefitinib treatment. The imaging results were validated by ex vivo immunofluorescence staining and enzyme-linked immunosorbent assay. Results: Dye-BevF(ab') 2 exhibited high specificity for VEGF in vivo. There was no significant change in the Dye-BevF(ab') 2 uptake in gefitinib-treated 22B tumors, compared with the control group. In contrast, the A549 tumor uptake of Dye-BevF(ab') 2 in the gefitinib-treated group was significantly lower on days 2 and 5 than that in the control group and at the baseline. An in vivo gefitinib treatment study confirmed that 22B tumors were gefitinib-resistant, whereas A549 tumors were gefitinib-responsive. Immunofluorescence staining and enzyme-linked immunosorbent assay confirmed that changes in the Dye-BevF(ab') 2 uptake were correlated with VEGF expression levels in tumors. Conclusion: Optical imaging of VEGF expression with Dye-BevF(ab') 2 can be used for the early assessment of tumor response to gefitinib therapy. This approach may also be valuable for preclinical high-throughput screening of novel antiangiogenic drugs.

Description: Integrin α v β 6 , a member of the integrin family, is specifically expressed in many malignancies but not in normal organs. Overexpression of integrin α v β 6 is usually correlated with malignant potential and poor prognosis. In this study, we describe the synthesis and evaluation of a 99m Tc-labeled integrin α v β 6 –targeting peptide as a SPECT radiotracer for the in vivo imaging of integrin α v β 6 expression. Methods: An integrin α v β 6 –targeting peptide (denoted as the HK peptide) was conjugated with 6-hydrazinonicotinyl (HYNIC) and radiolabeled with 99m Tc using tricine and TPPTS (trisodium triphenylphosphine-3,3',3''-trisulfonate) as coligands. The in vitro and in vivo characteristics of 99m Tc-HYNIC(tricine)(TPPTS)-HK ( 99m Tc-HHK) were investigated in BxPC-3 (integrin α v β 6 –positive) and HEK293 (integrin α v β 6 –negative) models. The ability of 99m Tc-HHK to detect liver metastasis of pancreatic cancer was evaluated using small-animal SPECT/CT. Results: 99m Tc-HHK showed high integrin α v β 6 –binding specificity both in vitro and in vivo. 99m Tc-HHK was cleared rapidly from the blood and normal organs except for the kidneys. The highest uptake (0.88 ± 0.12 percentage injected dose per gram) of 99m Tc-HHK in BxPC-3 tumors was observed at 0.5 h after injection. High-contrast images of integrin α v β 6 –positive tumors were obtained using 99m Tc-HHK. The minimum nonspecific activity accumulation in normal liver tissues rendered high-quality SPECT/CT images of metastatic lesions. Conclusion: 99m Tc-HHK is a promising SPECT radiotracer for the noninvasive imaging of integrin α v β 6 expression in vivo. SPECT/CT with 99m Tc-HHK could provide an effective approach for the noninvasive detection of primary and metastatic lesions of integrin α v β 6 –positive tumors.

Description: Previous in vitro studies demonstrated that treating tumors expressing both epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 with trastuzumab resulted in increased EGFR homodimerization and subsequent rapid downregulation of EGFR. We investigated whether molecular imaging using near-infrared fluorescence (NIRF) imaging and PET probes could sensitively detect trastuzumab-induced EGFR downregulation in vivo. Methods: The F(ab') 2 antibody fragment PaniF(ab') 2 was generated by digesting the anti-EGFR monoclonal antibody panitumumab. PaniF(ab') 2 was labeled with either a NIRF dye or 68 Ga, and optical imaging and small-animal PET imaging of Dye-PaniF(ab') 2 and 68 Ga-PaniF(ab') 2 , respectively, were performed in HT-29 tumor–bearing nude mice treated with trastuzumab or untreated control. Results: Longitudinal NIRF imaging studies revealed significantly reduced tumor uptake of Dye-PaniF(ab') 2 on days 5 and 7 in trastuzumab-treated HT-29 tumors, compared with control. Western blotting confirmed the downregulation of EGFR after treatment with trastuzumab. Small-animal PET on day 5 after trastuzumab treatment also demonstrated decreased 68 Ga-PaniF(ab') 2 uptake in trastuzumab-treated HT-29 tumors. The tumor uptake value of 68 Ga-PaniF(ab') 2 obtained from PET imaging had an excellent linear correlation with the uptake value measured using biodistribution. Conclusion: The downregulation of EGFR induced by trastuzumab treatment could be detected noninvasively using optical and PET imaging. This molecular imaging strategy could provide a dynamic readout of changes in the tumor signaling and may facilitate the noninvasive monitoring of the early tumor response to drug treatment.

Description: Existing respiratory motion-correction methods are applied only to static PET imaging. We have previously developed an event-by-event respiratory motion-correction method with correlations between internal organ motion and external respiratory signals (INTEX). This method is uniquely appropriate for dynamic imaging because it corrects motion for each time point. In this study, we applied INTEX to human dynamic PET studies with various tracers and investigated the impact on kinetic parameter estimation. Methods: The use of 3 tracers—a myocardial perfusion tracer, 82 Rb ( n = 7); a pancreatic β-cell tracer, 18 F-FP(+)DTBZ ( n = 4); and a tumor hypoxia tracer, 18 F-fluoromisonidazole ( 18 F-FMISO) ( n = 1)—was investigated in a study of 12 human subjects. Both rest and stress studies were performed for 82 Rb. The Anzai belt system was used to record respiratory motion. Three-dimensional internal organ motion in high temporal resolution was calculated by INTEX to guide event-by-event respiratory motion correction of target organs in each dynamic frame. Time–activity curves of regions of interest drawn based on end-expiration PET images were obtained. For 82 Rb studies, K 1 was obtained with a 1-tissue model using a left-ventricle input function. Rest–stress myocardial blood flow (MBF) and coronary flow reserve (CFR) were determined. For 18 F-FP(+)DTBZ studies, the total volume of distribution was estimated with arterial input functions using the multilinear analysis 1 method. For the 18 F-FMISO study, the net uptake rate K i was obtained with a 2-tissue irreversible model using a left-ventricle input function. All parameters were compared with the values derived without motion correction. Results: With INTEX, K 1 and MBF increased by 10% ± 12% and 15% ± 19%, respectively, for 82 Rb stress studies. CFR increased by 19% ± 21%. For studies with motion amplitudes greater than 8 mm ( n = 3), K 1 , MBF, and CFR increased by 20% ± 12%, 30% ± 20%, and 34% ± 23%, respectively. For 82 Rb rest studies, INTEX had minimal effect on parameter estimation. The total volume of distribution of 18 F-FP(+)DTBZ and K i of 18 F-FMISO increased by 17% ± 6% and 20%, respectively. Conclusion: Respiratory motion can have a substantial impact on dynamic PET in the thorax and abdomen. The INTEX method using continuous external motion data substantially changed parameters in kinetic modeling. More accurate estimation is expected with INTEX.