Huiyun Zhao

Two (90)Y-Labeled Multimeric RGD Peptides RGD4 and 3PRGD2 for Integrin Targeted Radionuclide Therapy

We have recently developed a series of new Arg-Gly-Asp (RGD) dimeric peptides for specific targeting of integrin α(v)β₃ with enhanced tumor uptake and improved pharmacokinetics. In this study, we investigated ⁹⁰Y-labeled RGD tetramer (RGD4) and the new type of RGD dimer (3PRGD2), for the radionuclide therapy of integrin α(v)β₃-positive tumors. Biodistribution and gamma imaging studies of ¹¹¹In labeled RGD4 and 3PRGD2 were performed. Groups of nude mice were used to determine maximum tolerated dose (MTD) of ⁹⁰Y-DOTA-RGD4 and ⁹⁰Y-DOTA-3PRGD2. The radionuclide therapeutic efficacy of ⁹⁰Y-DOTA-RGD4 and ⁹⁰Y-DOTA-3PRGD2 was evaluated in U87MG tumor-bearing nude mice. The U87MG tumor uptake of ¹¹¹In-DOTA-3PRGD2 was slightly lower than that of the ¹¹¹In-DOTA-RGD4 (e.g., 6.13 ± 0.82%ID/g vs 6.43 ± 1.6%ID/g at 4 h postinjection), but the uptake of ¹¹¹In-DOTA-3PRGD2 in normal organs, such as liver and kidneys, was much lower than that of ¹¹¹In-DOTA-RGD4, which resulted in much higher tumor-to-nontumor ratios and lower toxicity. The MTD of ⁹⁰Y-DOTA-RGD4 in nude mice is less than 44.4 MBq, while the MTD of ⁹⁰Y-DOTA-3PRGD2 in mice is more than 55.5 MBq. ⁹⁰Y-DOTA-3PRGD2 administration exhibited a similar tumor inhibition effect as compared with ⁹⁰Y-DOTA-RGD4 at the same dose. The tumor vasculature in the ⁹⁰Y-DOTA-3PRGD2 treatment group was much less than the control groups. Radionuclide therapy studies exhibited that both ⁹⁰Y-DOTA-RGD4 and ⁹⁰Y-DOTA-3PRGD2 caused significant tumor growth delay in the U87MG tumor model. Compared to ⁹⁰Y-DOTA-RGD4, the low accumulation of ⁹⁰Y-DOTA-3PRGD2 in normal organs led to lower toxicity and higher MTD in nude mice, which would make it more suitable for high dose or multiple-dose regimens, in order to achieve maximum therapeutic efficacy.

Epidermal Growth Factor Receptor–Targeted Radioimmunotherapy of Human Head and Neck Cancer Xenografts Using 90Y-Labeled Fully Human Antibody Panitumumab

Panitumumab (ABX-EGF or Vectibix), the first fully human monoclonal antibody targeting epidermal growth factor receptor (EGFR), was approved by the Food and Drug Administration for treatment of patients with metastatic colorectal cancer. Here, we report for the first time the radioimmunotherapy (RIT) of EGFR-positive human head and neck cancer in a nude mouse model using pure β− emitter 90Y-labeled panitumumab. Biodistribution and planar γ-imaging studies were carried out with 111In-DOTA-panitumumab. The RIT efficacy of 90Y-DOTA-panitumumab was evaluated in UM-SCC-22B tumor model. CD31, Ki67, terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling, and H&E staining were done on UM-SCC-22B tumor sections after treatment. The tumor uptake of 111In-DOTA-panitumumab in UM-SCC-22B tumor-bearing nude mice was 26.10 ± 4.93, 59.11 ± 7.22, 44.57 ± 9.80, 40.38 ± 7.76, and 14.86 ± 7.23 % injected dose per gram of tissue at 4, 24, 72, 120, and 168 hours after injection, respectively. Immunotherapy with cold panitumumab (four doses of 10 mg/kg) did not cause significant antitumor effect. RIT with a single dose of 100 μCi 90Y-DOTA-panitumumab caused significant tumor growth delay and improved the survival in UM-SCC-22B tumor model. A single dose of 200 μCi 90Y-DOTA-panitumumab led to almost complete tumor regression (tumor volumes were 34.83 ± 11.11 mm3 and 56.02 ± 39.95 mm3 on days 0 and 46 after treatment, respectively). Histopathologic analysis of tumors and normal organs further validated the therapeutic efficacy and limited systemic toxicity of 90Y-DOTA-panitumumab. The high tumor uptake and prolonged tumor retention, as well as effective therapy, reveal that 90Y-DOTA-panitumumab may be a promising radioimmunotherapeutic agent to treat EGFR-positive solid tumors. Mol Cancer Ther; 9(8); 2297–308. ©2010 AACR.

PET imaging of neovascularization with (68)Ga-3PRGD2 for assessing tumor early response to Endostar antiangiogenic therapy.

Antiangiogenic therapy is an effective strategy to inhibit tumor growth. Endostar, as an approved antiangiogenesis agent, inhibits the newborn vascular endothelial cells, causing the decrease of integrin αvβ3 expression. Radiolabeled 3PRGD2, a novel PEGlayted RGD dimer probe (PEG4-E[PEG4-c(RGDfK)]2) showed highly specific targeting capability to integrin αvβ3, which could be used for monitoring the efficacy of Endostar antiangiogenic therapy. In this study, (68)Ga-3PRGD2 PET imaging was performed in Endostar treated/untreated Lewis Lung Carcinoma (LLC) mice on days 3, 7, 14, and 21 post-treatment for monitoring the tumor response to Endostar treatment, with the (18)F-FDG imaging as control. As a result, (68)Ga-3PRGD2 PET reflected the tumor response to Endostar antiangiogenic therapy much earlier (day 3 post-treatment vs day 14 post-treatment) and more accurately than that of (18)F-FDG metabolic imaging, which provides new opportunities to develop individualized therapeutic approaches, establish optimized dosages and dose intervals for effective treatment that improve the survival rate of patients.

Radioimmunotherapy of Human Colon Cancer Xenografts with 131I-Labeled Anti-CEA Monoclonal Antibody

Radioimmunotherapy (RIT) is a promising approach for the treatment of a wide variety of malignancies. The aim of this study was to investigate the therapeutic efficacy of (131)I-labeled anticarcinoembryonic antigen (CEA) monoclonal antibody CL58 in a human colon cancer mouse model. In vitro and in vivo characteristics of (125)I-CL58 were evaluated in LS180 human colon cancer cells and the nude mouse model. (131)I-CL58 was prepared and its in vivo therapeutic efficacy was tested. (125)I-CL58 showed high affinity to LS180 cells, as well as high tumor uptake and long tumor retention in LS180 tumor xenografts. (131)I-CL58 exhibited dose-dependent inhibition of LS180 tumor growth. With the excellent in vitro and in vivo characteristics, and the effective therapy for colon cancer in animal model, (131)I-CL58 is a promising agent for RIT of CEA-positive tumors including colon cancer.

Serial in vivo imaging using a fluorescence probe allows identification of tumor early response to cetuximab immunotherapy.

Cetuximab is an antiepidermal growth factor receptor (EGFR) monoclonal antibody that has received the approval of the Food and Drug Administration (FDA) for cancer treatment. However, most clinical studies indicate that cetuximab can only elicit positive effects on a subset of cancer patients. In this study, we investigated whether near-infrared fluorescence (NIRF) imaging of tumor vascular endothelial growth factor (VEGF) expression could be a biomarker for tumor early response to cetuximab therapy in preclinical wild-type and mutant tumor models of the KRAS gene. The treatment efficacy of cetuximab was determined in both HT-29 (wild-type KRAS) and HTC-116 (mutant KRAS) human colon cancer models. A VEGF-specific optical imaging probe (Dye755-Ran) was synthesized by conjugating ranibizumab (an anti-VEGF antibody Fab fragment) with a NIRF dye. Serial optical scans with Dye755-Ran were performed in HT-29 and HTC-116 xenograft models. By using longitudinal NIRF imaging, we were able to detect early tumor response on day 3 and day 5 after initiation of cetuximab treatment in the cetuximab-responsive HT-29 tumor model. Enzyme-linked immunosorbent assay (ELISA) confirmed that cetuximab treatment inhibited human VEGF expression in the KRAS wild-type HT-29 tumor but not in the KRAS mutant HCT-116 tumor. We have demonstrated that the antitumor effect of cetuximab can be noninvasively monitored by serial fluorescence imaging using Dye755-Ran. VEGF expression detected by optical imaging could serve as a sensitive biomarker for tumor early response to drugs that directly or indirectly act on VEGF.

Anti-tumor effect of integrin targeted (177)Lu-3PRGD2 and combined therapy with Endostar.

Purpose: Targeted radiotherapy (TRT) is an emerging approach for tumor treatment. Previously, 3PRGD2 (a dimeric RGD peptide with 3 PEG4 linkers) has been demonstrated to be of advantage for integrin αvβ3 targeting. Given the promising results of 99mTc-3PRGD2 for lung cancer detection in human beings, we are encouraged to investigate the radiotherapeutic efficacy of radiolabeled 3PRGD2. The goal of this study was to investigate and optimize the integrin αvβ3 mediated therapeutic effect of 177Lu-3PRGD2 in the animal model. Experimental Design: Biodistribution, gamma imaging and maximum tolerated dose (MTD) studies of 177Lu-3PRGD2 were performed. The targeted radiotherapy (TRT) with single dose and repeated doses as well as the combined therapy of TRT and the anti-angiogenic therapy (AAT) with Endostar were conducted in U87MG tumor model. The hematoxylin and eosin (H&E) staining and immunochemistry (IHC) were performed post-treatment to evaluate the therapeutic effect. Results: The U87MG tumor uptake of 177Lu-3PRGD2 was relatively high (6.03 ± 0.65 %ID/g, 4.62 ± 1.44 %ID/g, 3.55 ± 1.08 %ID/g, and 1.22 ± 0.18 %ID/g at 1 h, 4 h, 24 h, and 72 h postinjection, respectively), and the gamma imaging could visualize the tumors clearly. The MTD of 177Lu-3PRGD2 in nude mice (>111 MBq) was twice to that of 90Y-3PRGD2 (55.5 MBq). U87MG tumor growth was significantly delayed by 177Lu-3PRGD2 TRT. Significantly increased anti-tumor effects were observed in the two doses or combined treatment groups. Conclusion: The two-dose TRT and combined therapy with Endostar potently enhanced the tumor growth inhibition, but the former does not need to inject daily for weeks, avoiding a lot of unnecessary inconvenience and suffering for patients, which could potentially be rapidly translated into clinical practice in the future.

Early Assessment of Tumor Response to Gefitinib Treatment by Noninvasive Optical Imaging of Tumor Vascular Endothelial Growth Factor Expression in Animal Models

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.

SPECT/NIRF Dual Modality Imaging for Detection of Intraperitoneal Colon Tumor with an Avidin/Biotin Pretargeting System

We describe herein dual-modality imaging of intraperitoneal colon tumor using an avidin/biotin pretargeting system. A novel dual-modality probe, 99mTc-HYNIC-lys(Cy5.5)-PEG4-biotin, was designed, synthesized and characterized. Single-photon emission computed tomography/ computed tomography (SPECT/CT) imaging and near infrared fluorescence (NIRF) imaging were developed using intraperitoneal LS180 human colon adenocarcinoma xenografts. Following avidin preinjection for 4 hours, 99mTc-HYNIC-lys(Cy5.5)-PEG4-biotin could successfully detect colon tumors of different sizes inside the abdominal region using both modalities, and the imaging results showed no differences. Biodistribution studies demonstrated that the tumors had a very high uptake of the probe 99mTc-HYNIC-lys(Cy5.5)-PEG4-biotin (12.74 ± 1.89% ID/g at 2 h p.i.), and the clearance from blood and other normal tissues occured very fast. The low tumor uptake in the non-pretargeted mice (1.63 ± 0.50% ID/g at 2 h p.i.) and tumor cell staining results showed excellent tumor binding specificity of the pretargeting system. The ability of the novel probe to show excellent imaging quality with high tumor-to-background contrast, a high degree of binding specificity with tumors and excellent in vivo biodistribution pharmacokinetics should prove that the avidin/biotin based dual-modality pretargeting probe is a promising imaging tool during the entire period of tumor diagnosis and treatment.

Small-Animal SPECT/CT of the Progression and Recovery of Rat Liver Fibrosis by Using an Integrin αvβ3-targeting Radiotracer.

PURPOSE To assess the potential utility of an integrin αvβ3-targeting radiotracer, technetium 99m-PEG4-E[PEG4-cyclo(arginine-glycine-aspartic acid-D-phenylalanine-lysine)]2 ((99m)Tc-3PRGD2), for single photon emission computed tomography (SPECT)/computed tomography (CT) for monitoring of the progression and prognosis of liver fibrosis in a rat model. MATERIALS AND METHODS All animal experiments were performed by following the protocol approved by the institutional animal care and use committee. (99m)Tc-3PRGD2 was prepared and longitudinal SPECT/CT was performed to monitor the progression (n = 8) and recovery (n = 5) of liver fibrosis induced in a rat model by means of thioacetamide (TAA) administration. The mean liver-to-background radioactivity per unit volume ratio was analyzed for comparisons between the TAA and control (saline) groups at different stages of liver fibrosis. Data were compared by using Student t and Mann-Whitney tests. Results:of SPECT/CT were compared with those of ex vivo biodistribution analysis (n = 5). RESULTS Accumulation of (99m)Tc-3PRGD2 in the liver increased in proportion to the progression of fibrosis and TAA exposure time; accumulation levels were significantly different between the TAA and control groups as early as week 4 of TAA administration (liver-to-background ratio: 32.30 ± 3.39 vs 19.01 ± 3.31; P = .0002). Results of ex vivo immunofluorescence staining demonstrated the positive expression of integrin αvβ3 on the activated hepatic stellate cells, and the integrin αvβ3 levels in the liver corresponded to the results of SPECT/CT (R(2) = 0.75, P < .0001). (99m)Tc-3PRGD2 uptake in the fibrotic liver decreased after antifibrotic therapy with interferon α2b compared with that in the control group (relative liver-to-background ratio: 0.45 ± 0.05 vs 1.01 ± 0.05; P < .0001) or spontaneous recovery (relative liver-to-background ratio: 0.56 ± 0.06 vs 1.01 ± 0.05; P < .0001). CONCLUSION (99m)Tc-3PRGD2 SPECT/CT was successfully used to monitor the progression and recovery of liver fibrosis and shows potential applications for noninvasive diagnosis of early stage liver fibrosis.

68Ga-Labeled 3PRGD2 for Dual PET and Cerenkov Luminescence Imaging of Orthotopic Human Glioblastoma

β-Emitters can produce Cerenkov radiation that is detectable by Cerenkov luminescence imaging (CLI), allowing the combination of PET and CLI with one radiotracer for both tumor diagnosis and visual guidance during surgery. Recently, the clinical feasibility of CLI with the established therapeutic reagent Na(131)I and the PET tracer (18)F-FDG was demonstrated. (68)Ga possesses a higher Cerenkov light output than (18)F and (131)I, which would result in higher sensitivity for CLI and improve the outcome of CLI in clinical applications. However, the research on (68)Ga-based tumor-specific tracers for CLI is limited. In this study, we examined the use of (68)Ga-radiolabeled DOTA-3PRGD2 ((68)Ga-3PRGD2) for dual PET and CLI of orthotopic U87MG human glioblastoma. For this purpose, the Cerenkov efficiencies of (68)Ga and (18)F were measured with the IVIS Spectrum system (PerkinElmer, USA). The CLI signal intensity of (68)Ga was 15 times stronger than that of (18)F. PET and CLI of (68)Ga-3PRGD2 were performed in U87MG human glioblastoma xenografts. Both PET and CLI revealed a remarkable accumulation of (68)Ga-3PRGD2 in the U87MG human glioblastoma xenografts at 1 h p.i. with an extremely low background in the brain when compared with (18)F-FDG. Furthermore, (68)Ga-3PRGD2 was used for dual PET and CLI of orthotopic human glioblastoma. The orthotopic human glioblastoma was clearly visualized by both imaging modalities. In addition, the biodistribution of (68)Ga-3PRGD2 was assessed in normal mice to estimate the radiation dosimetry. The whole-body effective dose is 20.1 ± 3.3 μSv/MBq, which is equal to 3.7 mSv per whole-body PET scan with a 5 mCi injection dose. Thus, (68)Ga-3PRGD2 involves less radiation exposure in patients when compared with (18)F-FDG (7.0 mSv). The use of (68)Ga-3PRGD2 in dual PET and CLI shows great promise for tumor diagnosis and image-guided surgery.