Analysis of radiation effects in two irradiated tumor spheroid models.

Multicellular spheroids have proven suitable as three-dimensional in vivo-like models of non-vascularized micrometastases. Unlike monolayer-based models, spheroids mirror the cellular milieu and the pathophysiological gradients inside tumor nodules. However, there is limited knowledge of the radiation effects at the molecular level in spheroids of human origin. The present study is a presentation of selected cell biological processes that may easily be analyzed with methods available at routine pathology laboratories. Using gamma irradiated pancreatic neuroendocrine BON1 and colonic adenocarcinoma HCT116 spheroids as model systems, the present study assessed the radiobiological response in these models. Spheroid growth after irradiation was followed over time and molecular responses were subsequently assessed with immunohistochemistry (IHC) staining for descriptive analyses and semi-automatic grading of apoptosis, G2-phase and senescence in thin sections of the spheroids. Growth studies demonstrated the BON1 spheroids were slower growing and less sensitive to radiation compared with the HCT116 spheroids. IHC staining for G2-phase was primarily observed in the outer viable P-cell layers of the spheroids, with the 6 Gy irradiated HCT116 spheroids demonstrating a very clear increase in staining intensity compared with unirradiated spheroids. Apoptosis staining results indicated increased apoptosis with increasing radiation doses. No clear association between senescence and radiation exposure in the spheroids were observed. The present results demonstrate the feasibility of the use of multicellular spheroids of human origin in combination with IHC analyses to unravel radiobiological responses at a molecular level. The present findings inspire further investigations, including other relevant IHC-detectable molecular processes in time- and radiation dose-dependent settings.

Evaluation of a novel type of imaging probe based on a recombinant bivalent mini-antibody construct for detection of CD44v6-expressing squamous cell carcinoma.

We have developed the CD44v6-targeting human bivalent antibody fragment AbD19384, an engineered recombinant human bivalent Fab antibody formed via dimerization of dHLX (synthetic double helix loop helix motif) domains, for potential use in antibody-based molecular imaging of squamous cell carcinoma in the head and neck region. This is a unique construct that has, to the best of our knowledge, never been assessed for molecular imaging in vivo before. The objective of the present study was to evaluate for the first time the in vitro and in vivo binding properties of radio-iodinated AbD19384, and to assess its utility as a targeting agent for molecular imaging of CD44v6-expressing tumors. Antigen specificity and binding properties were assessed in vitro. In vivo specificity and biodistribution of 125I-AbD19384 were next evaluated in tumor-bearing mice using a dual-tumor setup. Finally, AbD19384 was labeled with 124I, and its imaging properties were assessed by small animal PET/CT in tumor bearing mice, and compared with 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG). In vitro studies demonstrated CD44v6-specific binding with slow off-rate for AbD19384. A favorable biodistribution profile was seen in vivo, with tumor-specific uptake. Small animal PET/CT images of 124I-AbD19384 supported the results through clearly visible high CD44v6-expressing tumors and faintly visible low expressing tumors, with superior imaging properties compared to 18F-FDG. Tumor-to-blood ratios increased with time for the conjugate (assessed up to 72 h p.i.), although 48 h p.i. proved best for imaging. Biodistribution and small-animal PET studies demonstrated that the recombinant Fab-dHLX construct AbD19384 is a promising tracer for imaging of CD44v6 antigen expression in vivo, with the future aim to be used for individualized diagnosis and early detection of squamous cell carcinomas in the head and neck region. Furthermore, this proof-of-concept research established the feasibility of using recombinant Fab-dHLX constructs for in vivo imaging of tumor biomarkers.

Targeted radionuclide therapy in head and neck cancer.

There is great potential for targeted radionuclide therapy (TRT) in the treatment of head and neck cancer. In recent years, developments in fields such as antigen screening, protein engineering, and cancer biology have facilitated the rational design of targeted pharmaceuticals, with monoclonal antibodies forming the most rapidly expanding category. TRT may be a promising way to improve targeted treatment, especially in head and neck cancer, because of the intrinsic radiosensitivity of this tumor type. TRT may also provide a good foundation on which to build rational biologic combination therapies. In the next few years the use of TRT may offer new opportunities for further improvement of the therapeutic ratio that potentially may obviate or reduce the need for conventional cytotoxics.