111In-cetuximab-F(ab')2 SPECT imaging for quantification of accessible epidermal growth factor receptors (EGFR) in HNSCC xenografts

Advances in nuclear medicine-based molecular imaging in head and neck squamous cell carcinoma

Head and neck squamous cell carcinomas (HNSCCs) are often aggressive, making advanced disease very difficult to treat using contemporary modalities, such as surgery, radiation therapy, and chemotherapy. However, targeted therapy, e.g., cetuximab, an epidermal growth factor receptor inhibitor, has demonstrated survival benefit in HNSCC patients with locoregional failure or distant metastasis. Molecular imaging aims at various biomarkers used in targeted therapy, and nuclear medicine-based molecular imaging is a real-time and non-invasive modality with the potential to identify tumor in an earlier and more treatable stage, before anatomic-based imaging reveals diseases. The objective of this comprehensive review is to summarize recent advances in nuclear medicine-based molecular imaging for HNSCC focusing on several commonly radiolabeled biomarkers. The preclinical and clinical applications of these candidate imaging strategies are divided into three categories: those targeting tumor cells, tumor microenvironment, and tumor angiogenesis. This review endeavors to expand the knowledge of molecular biology of HNSCC and help realizing diagnostic potential of molecular imaging in clinical nuclear medicine.

Novel Receptor Tyrosine Kinase Pathway Inhibitors for Targeted Radionuclide Therapy of Glioblastoma

Glioblastoma (GB) remains the most fatal brain tumor characterized by a high infiltration rate and treatment resistance. Overexpression and/or mutation of receptor tyrosine kinases is common in GB, which subsequently leads to the activation of many downstream pathways that have a critical impact on tumor progression and therapy resistance. Therefore, receptor tyrosine kinase inhibitors (RTKIs) have been investigated to improve the dismal prognosis of GB in an effort to evolve into a personalized targeted therapy strategy with a better treatment outcome. Numerous RTKIs have been approved in the clinic and several radiopharmaceuticals are part of (pre)clinical trials as a non-invasive method to identify patients who could benefit from RTKI. The latter opens up the scope for theranostic applications. In this review, the present status of RTKIs for the treatment, nuclear imaging and targeted radionuclide therapy of GB is presented. The focus will be on seven tyrosine kinase receptors, based on their central role in GB: EGFR, VEGFR, MET, PDGFR, FGFR, Eph receptor and IGF1R. Finally, by way of analyzing structural and physiological characteristics of the TKIs with promising clinical trial results, four small molecule RTKIs were selected based on their potential to become new therapeutic GB radiopharmaceuticals.

Targeted molecular imaging of head and neck squamous cell carcinoma: a window into precision medicine

Tumor biomarkers play important roles in tumor growth, invasion, and metastasis. Imaging of specific biomarkers will help to understand different biological activities, thereby achieving precise medicine for each head and neck squamous cell carcinoma (HNSCC) patient. Here, we describe various molecular targets and molecular imaging modalities for HNSCC imaging. An extensive search was undertaken in the PubMed database with the keywords including “HNSCC,” “molecular imaging,” “biomarker,” and “multimodal imaging.” Imaging targets in HNSCC consist of the epidermal growth factor receptor, cluster of differentiation 44 variant 6 (CD44v6), and mesenchymal-epithelial transition factor and integrins. Targeted molecular imaging modalities in HNSCC include optical imaging, ultrasound, magnetic resonance imaging, positron emission tomography, and single-photon emission computed tomography. Making the most of each single imaging method, targeted multimodal imaging has a great potential in the accurate diagnosis and therapy of HNSCC. By visualizing tumor biomarkers at cellular and molecular levels in vivo, targeted molecular imaging can be used to identify specific genetic and metabolic aberrations, thereby accelerating personalized treatment development for HNSCC patients.

Analysis of Progress and Challenges of EGFR-Targeted Molecular Imaging in Cancer With a Focus on Affibody Molecules

Epidermal growth factor receptor (EGFR)-targeted cancer therapy requires an accurate estimation of EGFR expression in tumors to identify responsive patients, monitor therapeutic effect, and estimate prognosis. The EGFR molecular imaging is an optimal method for evaluating EGFR expression in vivo accurately and noninvasively. In this review, we discuss the recent advances in EGFR-targeted molecular imaging in cancer, with a special focus on the development of imaging agents, including epidermal growth factor (EGF) ligand, monoclonal antibodies, antibody fragments, Affibody, and small molecules. Each substrate or probe, whether it is an endogenous ligand, antibody, peptide, or small molecule labeled with fluorochrome or radionuclide, has unique advantages and limitations. Antibody-based probes have high affinity but a long metabolic cycle and therefore offer poor imaging quality. Affibody molecules promise to surpass antibody-based probes due to their small size, stable chemical properties, and high affinity to the target. Small-molecule probes are safe, have favorable pharmacokinetics, and show high affinity and specificity, in addition to having an ideal size, but are inadequate for delayed imaging after injection due to their fast clearance.

Radiolabeled F(ab')2-cetuximab for theranostic purposes in colorectal and skin tumor-bearing mice models

PURPOSE

This study aimed to investigate theranostic strategies in colorectal and skin cancer based on fragments of cetuximab, an anti-EGFR mAb, labeled with radionuclide with imaging and therapeutic properties, ¹¹¹In and ¹⁷⁷Lu, respectively.

METHODS

We designed F(ab')₂-fragments of cetuximab radiolabeled with ¹¹¹In and ¹⁷⁷Lu. ¹¹¹In-F(ab')₂-cetuximab tumor targeting and biodistribution were evaluated by SPECT in BalbC nude mice bearing primary colorectal tumors. The efficacy of ¹¹¹In-F(ab')₂-cetuximab to assess therapy efficacy was performed on BalbC nude mice bearing colorectal tumors receiving 17-DMAG, an HSP90 inhibitor. Therapeutic efficacy of the radioimmunotherapy based on ¹⁷⁷Lu-F(ab')₂-cetuximab was evaluated in SWISS nude mice bearing A431 tumors.

RESULTS

Radiolabeling procedure did not change F(ab')₂-cetuximab and cetuximab immunoreactivity nor affinity for HER1 in vitro. ¹¹¹In-DOTAGA-F(ab')₂-cetuximab exhibited a peak tumor uptake at 24 h post-injection and showed a high tumor specificity determined by a significant decrease in tumor uptake after the addition of an excess of unlabeled-DOTAGA-F(ab')₂-cetuximab. SPECT imaging of ¹¹¹In-DOTAGA-F(ab')₂-cetuximab allowed an accurate evaluation of tumor growth and successfully predicted the decrease in tumor growth induced by 17-DMAG. Finally, ¹⁷⁷Lu-DOTAGA-F(ab')₂-cetuximab radioimmunotherapy showed a significant reduction of tumor growth at 4 and 8 MBq doses.

CONCLUSIONS

¹¹¹In-DOTAGA-F(ab')₂-cetuximab is a reliable and stable tool for specific in vivo tumor targeting and is suitable for therapy efficacy assessment. ¹⁷⁷Lu-DOTAGA-F(ab')₂-cetuximab is an interesting theranostic tool allowing therapy and imaging.

Preclinical validation of 111In-girentuximab-F(ab')2 as a tracer to image hypoxia related marker CAIX expression in head and neck cancer xenografts

BACKGROUND AND PURPOSE

Hypoxia is a major cause of radio- and chemoresistance. Carbonic anhydrase IX (CAIX) is an endogenous hypoxia-related marker and an important prognostic marker. Assessment of CAIX expression may allow patient selection for hypoxia or CAIX-targeted treatment. The radioactive tracer ¹¹¹In-girentuximab-F(ab')₂ targets CAIX and can be used for SPECT imaging. Aim of this study was to validate and optimize ¹¹¹In-girentuximab-F(ab')₂ for imaging of CAIX expression in head and neck tumor xenografts.

MATERIAL AND METHODS

Affinity and internalization kinetics of ¹¹¹In-girentuximab-F(ab')₂ were determined in vitro using CAIX-expressing SK-RC-52 cells. Tumor targeting characteristics were determined in athymic mice with six different head and neck squamous cell carcinoma (SCCNij) xenografts. Tracer uptake was measured by ex vivo radioactivity counting. Intratumoral distribution of tracer uptake was measured using autoradiography and CAIX expression was determined immunohistochemically.

RESULTS

26% of the tracer was internalized into the SK-RC-52 cells within 24h. The half maximal inhibitory concentration (IC₅₀) was 0.69±0.08nM. In biodistribution studies SCCNij153 tumors showed the highest tracer uptake: 4.1±0.8ID/g at 24h p.i. Immunohistochemical and autoradiographic analyses of the xenografts showed a distinct spatial correlation between localization of the tracer and CAIX expression.

CONCLUSION

¹¹¹In-girentuximab-F(ab')₂ has a high affinity for CAIX. In vivo tumor uptake correlated strongly with CAIX expression in different head and neck xenografts. These results suggest that ¹¹¹In-girentuximab-F(ab')₂ is a promising tracer for imaging of hypoxia-related CAIX expression.

PET imaging of zirconium-89 labelled cetuximab: A phase I trial in patients with head and neck and lung cancer

BACKGROUND AND PURPOSE

PET imaging of cetuximab uptake may help selecting cancer patients with the highest chance of benefit. The aim of this phase I trial was to determine the safety of the tracer ⁸⁹Zr-cetuximab and to assess tumour uptake.

METHODS

Two dose schedules were used; two consecutive doses of 60MBq ⁸⁹Zr-cetuximab or a single dose of 120MBq, both preceded by 400mg/m² of unlabelled cetuximab. Toxicity (CTCAE 3.0) was scored twice weekly. PET-CT scans were acquired on days 4, 5 and 6 (step 1) or 5, 6, 7 (step 2). Because tumour uptake could not be assessed satisfactorily, a third step was added including EGFR overexpressing tumours.

RESULTS

Nine patients were included (6 NSCLC; 3 HNC). No additional toxicity was associated with administration of ⁸⁹Zr-cetuximab compared to standard cetuximab. A tumour to blood ratio (TBR)>1 was observed in all but one patient, with a maximum of 4.56. TBR was not different between dose schedules. There was a trend for higher TBR at intervals>5days after injection.

CONCLUSIONS

Both presented ⁸⁹Zr-cetuximab administration schedules are safe. The recommended dose for future trials is 60MBq, with a minimum time interval for scanning of 6days.

111In-cetuximab as a diagnostic agent by accessible epidermal growth factor (EGF) receptor targeting in human metastatic colorectal carcinoma

Colorectal adenocarcinoma is a common cause death cancer in the whole world. The aim of this study is to define the 111In-cetuximab as a diagnosis tracer of human colorectal adenocarcinoma. In this research, cell uptake, nano-SPECT/CT scintigraphy, autoradiography, biodistribution and immunohitochemical staining of EGF receptor were included. HCT-116 and HT-29 cell expressed a relatively high and moderate level of EGF receptor, respectively. The nano-SPECT/CT image of 111In-cetuximab showed tumor radiation uptake of subcutaneous HCT-116 xenograft tumor was higher than SW-620. Autoradiography image also showed that tumor of HCT-116 had high 111In-cetuximab uptake. Mice that bearing CT-26 in situ xenograft colorectal tumors showed similar high uptake in vivo and ex vivo through nano-SPECT/CT imaging at 72 hours. Metastatic HCT-116/Luc tumors demonstrated the highest uptake at 72 hours after the injection of 111In-cetuximab. Relatively, results of 111In-DTPA showed that metabolism through urinary system, especially in the kidney. The quantitative analysis of biodistribution showed count value of metastatic HCT-116/Luc tumors that treated with 111In-cetuximab had a significant difference (P < 0.05) compared with that treated with 111In-DTPA after injection 72 hours. Result of immunohistologic staining of EGF receptor also showed high EGF receptor expression and uptake in metastatic colorectal tumors. In summary, we suggested that 111In-cetuximab will be a potential tool for detecting EGF receptor expression in human metastatic colorectal carcinoma.

Epidermal growth factor receptor imaging in human head and neck cancer xenografts

Molecular imaging of specific biomarkers can have prognostic, predictive or monitoring value in head and neck squamous cell carcinoma (HNSCC). The epidermal growth factor receptor (EGFR) is involved in various radiation resistance mechanisms as it steers the pathways related to DNA damage repair, proliferation, hypoxia and apoptosis. Radiolabeled labeled F(ab')2 fragments of the EGFR antibody cetuximab can be applied for non-invasive imaging of this receptor. Preclinical studies have shown that radioresistant tumors had a higher tracer uptake after irradiation, probably due to upregulation of membranous EGFR, thereby increasing target availability possibly as a compensation mechanism. Tumors with increased EGFR availability were also more responsive to the EGFR inhibitor cetuximab. Potentially, radionuclide imaging of the EGFR can be applied for monitoring treatment regimens in clinical practice.

PET of EGFR with (64) Cu-cetuximab-F(ab')2 in mice with head and neck squamous cell carcinoma xenografts

Overexpression of the epidermal growth factor receptor (EGFR) is linked to an adverse outcome in various solid tumors. Cetuximab is an EGFR inhibitor, which in combination with radiotherapy improves locoregional control and survival in a subgroup of patients with head and neck squamous cell carcinomas (HNSCCs). The aim of this study was to develop and characterize an EGFR-directed PET tracer, (64) Cu-cetuximab-F(ab')2, to determine the systemic accessibility of EGFR. Mice with HNSCC xenografts, UT-SCC-8 (n = 6) or UT-SCC-45 (n = 6), were imaged 24 h post injection with (64) Cu-NODAGA-cetuximab-F(ab')2 using PET/CT. One mouse for each tumor model was co-injected with excess unlabeled cetuximab 3 days before radiotracer injection to determine non-EGFR-mediated uptake. Ex vivo biodistribution of the tracer was determined and tumors were analyzed by autoradiography and immunohistochemistry. The SUVmax of UT-SCC-8 tumors was higher than that of UT-SCC-45: 1.5 ± 1.0 and 0.8 ± 0.2 (p < 0.05), respectively. SUVmax after in vivo blocking of EGFR with cetuximab was 0.4. Immunohistochemistry showed that UT-SCC-8 had a significantly higher EGFR expression than UT-SCC-45: 0.50 ± 0.19 versus 0.12 ± 0.08 (p < 0.005), respectively. Autoradiography indicated that (64) Cu-cetuximab-F(ab')2 uptake correlated with EGFR expression in both tumors: r = 0.86 ± 0.06 (UT-SCC-8) and 0.90 ± 0.06 (UT-SCC-45). (64) Cu-cetuximab-F(ab')2 is a promising PET tracer to determine expression of EGFR in vivo. Clinically, this tracer has the potential to be used to determine cetuximab targeting of tumors and possibly to non-invasively monitor the response to EGFR-inhibitor treatment.

111In-cetuximab-F(ab')2 SPECT and 18F-FDG PET for prediction and response monitoring of combined-modality treatment of human head and neck carcinomas in a mouse model

Treatment of head and neck squamous cell carcinomas with radiotherapy and the epidermal growth factor receptor (EGFR) inhibitor cetuximab shows an improved response in a subgroup of patients. The aim of this study was to noninvasively monitor treatment response by visualizing systemically accessible EGFR with (111)In-cetuximab-F(ab')2 while simultaneously evaluating tumor metabolism with (18)F-FDG PET during combined-modality treatment.

METHODS

Eighty mice with patient-derived head and neck squamous cell carcinomas xenografts, SCCNij202 or SCCNij185, were imaged with SPECT/CT using (111)In-cetuximab-F(ab')2 (5 μg, 28 ± 6.1 MBq, 24 h after injection), followed by PET imaging with (18)F-FDG (9.4 ± 2.9 MBq, 1 h after injection). Scans were acquired on mice 10 d before treatment with either single-dose irradiation (10 Gy), cetuximab alone, or cetuximab-plus-irradiation combined or on untreated control mice. Scans were repeated 18 d after treatment. Tumor growth was monitored up to 120 d after treatment. EGFR expression was evaluated immunohistochemically.

RESULTS

SCCNij202 responded to combined treatment (P < 0.01) and cetuximab treatment alone (P < 0.05) but not to irradiation alone (P = 0.13). SCCNij185 responded to combined treatment (P < 0.05) and irradiation (P < 0.05) but not to cetuximab treatment alone (P = 0.34). (111)In-cetuximab-F(ab')2 uptake (tumor-to-liver ratio, scan 2 - scan 1) predicted response to therapy. A positive response to treatment significantly correlated with a reduced tracer uptake in the tumor in the second SPECT scan, compared with the first scan (P < 0.005 and <0.05 for SCCNij202 and SCCNij185, respectively). Resistance to therapy was characterized by a significantly increased (111)In-cetuximab-F(ab')2 tumor uptake; tumor-to-liver ratio was 2.2 ± 0.6 to 3.5 ± 1.2, P < 0.01, for (irradiated) SCCNij202 and 1.4 ± 0.4 to 2.0 ± 0.3, P < 0.05, for (cetuximab-treated) SCCNij185, respectively. (18)F-FDG PET tumor uptake (maximum standardized uptake value, scan 2 - scan 1) correlated with tumor response for SCCNij202 (P < 0.01) but not for SCCNij185 (P = 0.66). EGFR fractions were significantly different: 0.9 ± 0.1 (SCCNij202) and 0.5 ± 0.1 (SCCNij185) (P < 0.001). The EGFR fraction was significantly lower for irradiated SCCNij202 tumors than for controls (P < 0.005).

CONCLUSION

(111)In-cetuximab-F(ab')2 predicted and monitored the effects of EGFR inhibition or irradiation during treatment in both head and neck carcinoma models investigated, whereas (18)F-FDG PET only correlated with tumor response in the SCCNij202 model. Thus, the additional value of the (111)In-cetuximab-F(ab')2 tracer is emphasized and the tracer can aid in evaluating future treatments with EGFR-targeted therapies.

Matching the decay half-life with the biological half-life: ImmunoPET imaging with (44)Sc-labeled cetuximab Fab fragment

Scandium-44 (t_1/2 = 3.9 h) is a relatively new radioisotope of potential interest for use in clinical positron emission tomography (PET). Herein, we report, for the first time, the room-temperature radiolabeling of proteins with ⁴⁴Sc for in vivo PET imaging. For this purpose, the Fab fragment of Cetuximab, a monoclonal antibody that binds with high affinity to epidermal growth factor receptor (EGFR), was generated and conjugated with N-[(R)-2-amino-3-(para-isothiocyanato-phenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N′,N″,N″-pentaacetic acid (CHX-A″-DTPA). The high purity of Cetuximab-Fab was confirmed by SDS-PAGE and mass spectrometry. The potential of the bioconjugate for PET imaging of EGFR expression in human glioblastoma (U87MG) tumor-bearing mice was investigated after ⁴⁴Sc labeling. PET imaging revealed rapid tumor uptake (maximum uptake of ∼12% ID/g at 4 h postinjection) of ⁴⁴Sc–CHX-A″-DTPA–Cetuximab-Fab with excellent tumor-to-background ratio, which might allow for same day PET imaging in future clinical studies. Immunofluorescence staining was conducted to correlate tracer uptake in the tumor and normal tissues with EGFR expression. This successful strategy for immunoPET imaging of EGFR expression using ⁴⁴Sc–CHX-A″-DTPA–Cetuximab-Fab can make clinically translatable advances to select the right population of patients for EGFR-targeted therapy and also to monitor the therapeutic efficacy of anti-EGFR treatments.

Early response monitoring with 18F-FDG PET and cetuximab-F(ab')2-SPECT after radiotherapy of human head and neck squamous cell carcinomas in a mouse model

Only a subset of patients with head and neck squamous cell carcinomas (HNSCCs) benefit from radiotherapy and concurrent epidermal growth factor receptor (EGFR) inhibitor therapy with cetuximab, indicating the need for patient selection. The aim of this study was to visualize the change in systemically accessible EGFR with (111)In-cetuximab-F(ab')2 SPECT before and after radiotherapy, while simultaneously evaluating (18)F-FDG PET uptake.

METHODS

Mice with HNSCC xenografts, cetuximab-sensitive SCCNij202 and cetuximab-resistant SCCNij167, were imaged with SPECT/CT using (111)In-cetuximab-F(ab')2 as a tracer, directly followed by PET imaging with (18)F-FDG. Scans were acquired 7 d before radiotherapy (10 Gy) and 1, 7, and 14 d after treatment. Intratumoral localization of (111)In-cetuximab-F(ab')(2) was evaluated by autoradiography and histologic markers evaluated by immunofluorescence staining in the same tumor sections.

RESULTS

Growth of irradiated SCCNij202 and SCCNij167 tumors was significantly delayed, compared with controls (P < 0.05). No changes in uptake of (18)F-FDG were observed in either of the xenografts after radiotherapy. SPECT images of tumor-bearing mice showed a significant increase in uptake of (111)In-cetuximab-F(ab')(2) in the SCCNij202 tumors after irradiation (tumor-to-liver ratio, 4.3 ± 1.1 vs. 10.5 ± 3.3, 7 d before and 14 d after treatment, respectively, P < 0.01) but not in SCCNij167 tumors. Immunohistochemical EGFR staining showed a translocation of the EGFR from the cytoplasm to the cell membrane in irradiated SCCNij202 xenografts. Intratumoral distribution of (111)In-cetuximab-F(ab')(2) as determined by autoradiography correlated well with the distribution of EGFR as determined immunohistochemically (r = 0.85; range, 0.69-0.95).

CONCLUSION

EGFR accessibility can be visualized with (111)In-cetuximab-F(ab')(2). (111)In-cetuximab-F(ab')(2) uptake increased after irradiation only in cetuximab-sensitive SCCNij202 xenografts, implying that the tracer can be used to measure irradiation-induced changes of EGFR expression and can monitor the compensatory response of tumors to radiotherapy.

Radiolabeled Cetuximab Conjugates for EGFR Targeted Cancer Diagnostics and Therapy

The epidermal growth factor receptor (EGFR) has evolved over years into a main molecular target for the treatment of different cancer entities. In this regard, the anti-EGFR antibody cetuximab has been approved alone or in combination with: (a) chemotherapy for treatment of colorectal and head and neck squamous cell carcinoma and (b) with external radiotherapy for treatment of head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab in combination with the specific targeting properties of this antibody might increase its therapeutic efficiency. This review article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and/or treatment of different tumor models. A particularly promising approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important challenge is the reduction of nonspecific uptake of the radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized cancer treatment.