Immunotargeting of tumor vasculature: preclinical development of novel antibody-based imaging and therapy against TEM1/CD248

The success of antibody-based theranostics depends on the identification of tumor specific biomarkers and the development of corresponding antibodies with high-affinity and specificity. Tumor endothelial marker-1 (TEM1) is highly expressed in tumor vasculature of multiple cancers but not in normal organs. The expression of TEM1 was first evaluated and confirmed by immunohistochemistry from 53 cases of metastatic serous ovarian cancer at HUP. TEM1 positive tumor stroma was observed in >95% of the cases studied. Hence, developing sensitive and effective theranostic agents against TEM1 are of utmost significance in improving diagnosis and treatment of ovarian cancer. Our goals are: 1) engineer TEM1-specific antibodies; 2) evaluate these engineered antibodies in imaging and immunotherapies in preclinical models. To generate TEM1-targeting agents, we designed a panel of multivalent fusion proteins from scFv78, a previously isolated single chain variable fragment specifically recognizing the extracellular domain of TEM1. scFv78 was fused with different huIgG1 Fc region (CH2-, CH3-, or hinge). Proteins were expressed in 293F cells and purified by affinity chromatography. All scFv78 variants exhibited comparable thermo and serum stability in vitro. Among them, the scFv78-Fc fusion (78Fc) has the highest affinity to TEM1 (Kd = 0.15nM, 15X higher than scFv78). Pharmacokinetics (PK) and biodistribution of the protein panel were evaluated in naïve and TEM1+ tumor bearing animals. 78Fc has a t1/2 of 5.1hr, which is suitable for in vivo therapeutic and imaging applications. Therefore, 78Fc was further developed as imaging tool and antibody-drug conjugate (ADC) based on its favorable affinity, stability, half-life and PK profile. In pilot studies with preclinical animal models of tumor vasculature, fluorophore- and [124-I]-labeled 78Fc demonstrated specific enrichment in TEM1+ grafts, but not in control tumor or other organs, by both optical and immunoPET imaging. In addition, 78Fc-MMAE conjugate exerted specific killing of TEM1+ cells. In summary, we have developed a panel of innovative theranostics agents targeting TEM1 on the vasculature of ovarian cancer and several other solid tumors. Our long term goal is to translate such combined approach into the clinic: Using TEM1-antibody as imaging tools to select, and monitor patients for TEM1-antibody based targeted therapies

Pilot study of PET imaging of 124I-iodoazomycin galactopyranoside (IAZGP), a putative hypoxia imaging agent, in patients with colorectal cancer and head and neck cancer

Background: Hypoxia within solid tumors confers radiation resistance and a poorer prognosis. 124I-iodoazomycin galactopyranoside (124I-IAZGP) has shown promise as a hypoxia radiotracer in animal models. We performed a clinical study to evaluate the safety, biodistribution, and imaging characteristics of 124I-IAZGP in patients with advanced colorectal cancer and head and neck cancer using serial positron emission tomography (PET) imaging. Methods: Ten patients underwent serial whole-torso (head/neck to pelvis) PET imaging together with multiple whole-body counts and blood sampling. These data were used to generate absorbed dose estimates to normal tissues for 124I-IAZGP. Tumors were scored as either positive or negative for 124I-IAZGP uptake. Results: There were no clinical toxicities or adverse effects associated with 124I-IAZGP administration. Clearance from the whole body and blood was rapid, primarily via the urinary tract, with no focal uptake in any parenchymal organ. The tissues receiving the highest absorbed doses were the mucosal walls of the urinary bladder and the intestinal tract, in particular the lower large intestine. All 124I-IAZGP PET scans were interpreted as negative for tumor uptake. Conclusions: It is safe to administer 124I-IAZGP to human subjects. However, there was insufficient tumor uptake to support a clinical role for 124I-IAZGP PET in colorectal cancer and head and neck cancer patients. Trial registration: ClinicalTrials.gov NCT0058827

Molecular Imaging of Pulmonary Cancer and Inflammation

Molecular imaging (MI) may be defined as imaging in vivo using molecules that report on biologic function. This review will focus on the clinical use of radioactive tracers (nonpharmacologic amounts of compounds labeled with a radioactive substance) that permit external imaging using single photon emission computed tomography (planar, SPECT) or positron emission tomography (PET) imaging. Imaging of lung cancer has been revolutionized with the use of fluorine-18–labeled fluorodeoxyglucose (18F-FDG), an analog of glucose that can be imaged using PET. The ability to carry out whole body imaging after intravenous injection of 18F-FDG allows accurate staging of disease, helping to determine regional and distant nodal and other parenchymal involvement. Glycolysis is increased in nonmalignant conditions, including inflammation (e.g., sarcoidosis), and 18F-FDG PET is a sensitive method for evaluation of active inflammatory disease. Inflammatory disease has been imaged, even before the advent of PET, with planar and SPECT imaging using gallium-67, a radiometal that binds to transferrin. Metabolic alteration in pulmonary pathology is currently being studied, largely in lung cancer, primarily with PET, with a variety of other radiotracers. Prominent among these is thymidine; fluorine-18–labeled thymidine PET is being increasingly used to evaluate proliferation rate in lung and other cancers. This overview will focus on the clinical utility of 18F-FDG PET in the staging and therapy evaluation of lung cancer as well as in imaging of nonmalignant pulmonary conditions. PET and SPECT imaging with other radiotracers of interest will also be reviewed. Future directions in PET imaging of pulmonary pathophysiology will also be explored

Whole-Body Low-Dose Computed Tomography and Advanced Imaging Techniques for Multiple Myeloma Bone Disease

Detection of lytic bone lesions is crucial in the workup for multiple myeloma and very often dictates the decision to start treatment. Conventional radiography, despite decades of use, is often insufficient for detection of bone disease in multiple myeloma. Modern imaging techniques such as MRI, PET, and CT offer superior detection of myeloma bone disease and extramedullary manifestations of plasma cell dyscrasias. Novel whole-body low-dose computed tomography (WBLDCT) protocols allow for collection of superior image detail of the skeleton at doses of radiation similar to those used for conventional planar radiography. Several studies have shown that WBLDCT has a superior detection rate for lytic bone lesions compared with whole-body X-ray (WBXR), potentially leading to restaging and changes in therapy. MRI and PET provide imaging data important for assessing disease activity and prognostication. Because of several advantages over WBXR, WBLDCT is already the standard imaging technique for use in patients with multiple myeloma in many European institutions. However, the radiographic skeletal survey or WBXR is still the initial study of choice used to screen for myeloma bone disease in many institutions. In this review, we aim to explore the changing landscape of imaging for myeloma bone disease through use of modern imaging techniques

Evaluation of a semi-automated approach for FDG PET image analysis for routine clinical application in patients with multiple myeloma

Background: FDG PET/CT is a tool for assessing response to therapy in various cancers, and may provide an earlier biomarker of clinical response. We developed a novel semi-automated approach for analyzing FDG PET/CT images in patients with multiple myeloma (MM) to standardize FDG PET application. Methods: Patients (n = 8) with relapsed/refractory MM from the Phase 2 study (NCT02899052) of venetoclax plus carfilzomib and dexamethasone underwent FDG PET/CT at baseline and up to two timepoints during treatment. Images were processed using an established automated segmentation algorithm, with the modification that a red marrow region in an unaffected lumbar vertebra was used to define background standardized uptake value normalized to lean body mass (SUL) threshold above which uptake was considered disease-specific uptake. This approach was compared to lesion segmentation, and to International Myeloma Working Group (IMWG) response criteria, including minimal residual disease (MRD). Results: The two FDG PET analysis techniques agreed on evaluation of patient-level SULpeak for 67% of scans. In the metabolic response assessment per PET Response Criteria in Solid Tumors (PERCIST), the two techniques agreed in 75% of patients. Differences between techniques occurred in low-uptake lesions due to greater reader sensitivity to lesions with uptake marginally above background. PERCIST outcomes were generally in agreement with IMWC and MRD. Conclusions: This semi-automated analysis was in high agreement with standard approaches for detecting response to MM therapy. This proof-of-concept study suggests that larger studies should be conducted to confirm how FDG PET analysis may aid early response detection in MM