Translational research in radiation oncology

Flow cytometry analysis of single-strand DNA damage in neuroblastoma cell lines using the F7-26 monoclonal antibody

The F7-26 monoclonal antibody (Mab) has been reported to be specific for single-strand DNA damage (ssDNA) and to also identify cells in apoptosis. We carriedout studies to determine if F7-26 binding measured by flow cytometry was able to specifically identify exogenous ssDNA as opposed to DNA damage from apoptosis. Neuroblastoma cells were treated with melphalan (L-PAM), fenretinide, 4-hydroperoxycyclophosphamide (4-HC)+/-pan-caspase inhibitor BOC-d-fmk, topotecan or with 10Gy gamma radiation+/-hydrogen peroxide (H2O2) and fixed immediately postradiation. Cytotoxicity was measured by DIMSCAN digital imaging fluorescence assay. The degree of ssDNA damage was analyzed by flow cytometry using Mab F7-26, with DNA visualized by propidium iodide counterstaining. Flow cytometry was used to measure apoptosis detected by terminal deoxynucleotidyltransferase (TUNEL) assay and reactive oxygen species (ROS) by carboxy-dichlorofluorescein diacetate. Irradiated and immediately fixed neuroblastoma cells showed increased ssDNA, but not apoptosis by TUNEL (TUNEL-negative). 4-HC or L-PAM+/-BOC-d-fmk increased ssDNA (F7-26-positive), but BOC-d-fmk prevented TUNEL staining. Fenretinide increased apoptosis by TUNEL but not ssDNA damage detected with F7-26. Enhanced ssDNA in neuroblastoma cells treated with radiation+H2O2 was associated with increased ROS. Topotecan increased both ssDNA and cytotoxicity in 4-HC-treated cells. These data demonstrate that Mab F7-26 recognized ssDNA due to exogenous DNA damage, rather than apoptosis. This assay should be useful to characterize the mechanism of action of antineoplastic drugs.

Radiation therapy

RT is an indispensable part of current treatment approaches of locally advanced and metastatic NSCLC. It can be used alone or in combination with surgery or CHT. Because RT can potentially cure some patients, prolong the life of others, and reduce symptoms in the majority of them, it is a unique treatment modality in this disease. Radiation oncologists have learned how to deal with RT-induced toxicities and how to improve quality of life of lung cancer patients. Although recent technologic advances made sophisticated RT somewhat more expensive than before (demanding more manpower and being more time-consuming), it is still an inexpensive treatment modality, which is important in the era of focusing on cost-effectiveness. Although newer RT technologies are used to enable effective dose-escalation-a clear must for the community of radiation oncologists--optimization of RT must also include clear identification of various pretreatment, patient, and tumor-related characteristics that may influence treatment outcome. Regardless of the current therapeutic/technologic potential, we still lack some basic knowledge to better understand the process of, for example, combining RT and CHT. There is recognized need for better translational research that ultimately should be seen as a "two-way road," from laboratory to clinic and vice versa, preferably in a continuous way. The National Cancer Institute in the United States recently organized a workshop on translational research in radiation oncology, which has identified RT-CHT interactions as one of its major areas of research. Research topics include development of the methods of imaging the results of RT/ CHT interactions (confirmed by biopsy), development of new radiation modifiers, and identification of factors other than genetic ones that may influence the response of tumors to RT/CHT interactions. Tumor microenvironment was also clearly addressed as one of the targets for research, indicating as special tasks the development of new, microenvironmentally activated cytotoxic or cytostatic drugs, development and validation of more user-friendly methods for determining tumor oxygenation, and answering whether hypoxia predicts for radioresistance to CHT in treatment and whether it causes increased tumor aggression and metastasis. The future may, therefore, be quite simple: technology meets biology.

Novel techniques in the delivery of radiation in pediatric oncology

The field of radiation oncology continues to develop at a rapid pace, due to concurrent progress in high speed computing, improved sensitivity in diagnostic imaging (both anatomic and physiologic), and the introduction of rational new therapeutics built on solid radiobiologic principles. These innovations will become critically important in the field of pediatric oncology, as they will allow for an increased therapeutic ratio in the developing child. Maximizing the benefit of lower dose radiation through the use of radiation modifiers (hypoxic cell sensitizers, signal transduction pathway inhibitors, concurrent chemotherapy), increasing the tolerance of normal tissues (radioprotectors) and tailoring the target area more closely to the desired critical tissues (IMRT, functional simulation with PET and MRS, radiolabeled monoclonal antibodies) will lessen the short and long term toxicity of radiation and increase its effectiveness.