Description

Tumor Radiosensitization by Expanded T lymphocytes: NO and CO as Molecular Determinants of Radioresponse through the IFN-? Signalling Pathway

A. Tumor immunity and radioresponse. The hypoxic tumor microenvironment is caused by poor vascularization, and displays both radioprotective and immunosuppressive properties. Besides traditional tools, such as bacteria-derived adjuvant CpG ODN and dendritic/tumor cells-based vaccines, radiotherapy has emerged as a novel approach to correct the immune anergy, by generating a pro-inflammatory environment and a release of tumor-associated antigens. In a mouse sarcoma model, combining CpG ODN with radiotherapy resulted in enhanced radioresponse and tumor rejection through adaptive T-cell immunity.It remains, however, unclear whether cytotoxic T lymphocytes were implicated in tumor cell radiosensitization.

B. NO-induced radiosensitization. Our laboratory has previously demonstrated the radiosensitizing effect of nitric oxide (NO) generated either by NO donors or by iNOS, a hypoxia/LPS/cytokine-inducible isoform of NO synthase. Consistently, other teams described an increased radiosensitivty of iNOS-overexpressing tumor cells, and a chemosensitizing potential for iNOS activation.The iNOS-mediated radiosensitization may require 0.3-1% oxygen which is essential for NO generation from L-arginine. We have recently shown that clinical immunoadjuvant lipid A and its synthetic derivate OM-174 reveal radiosensitizing activity through immune cells, which boost high output of NO in tumor cells 6-8. These lipopolysaccharide (LPS)-derived immunoadjuvants, however, interact with TLR4 receptors located on antigen-presenting dendritic but not T cells. We hypothesized that (a) TLR4 signaling was transmitted to T lymphocytes through the IL-2/IL-12/IL-18 cytokine cascade, and (b) activated T cells were responsible for tumor cell radiosensitization through the IFN-? signaling to iNOS.Our recent data suggests that purified mouse CD8 + T cells, following limited expansion and activation by immobilized anti-CD3/CD28 antibodies, display both an IFN-?+ phenotype and radiosensitizing effects 9.2

C. NO signaling to heme oxygenase-1 (HO-1).The stress-responsive gene HO-1 that generates carbon monoxide (CO) and biliverdin from heme, is frequently activated downstream to iNOS, thus reflecting a self defence mechanism against NO/nitrosative injury 10. Similar protective effects are shown for CORMs, which are chemical CO donors 11. Interestingly, HO-1 is sustained by hypoxia-reoxygenation, which is relevant to the intermittent hypoxia in tumours that is induced by sporadic blood vessel occlusions and by perturbations in oxygen consumption along radiotherapy. Although suspected but not proven, CO/biliverdin may protect aerobic cells from radiation through an antiapoptotic mechanism. We speculate that in hypoxia, CO may have an opposite effect and radiosensitize tumor cells through inhibition of mitochondrial respiration and sparing of oxygen, as the latter effect was described in 1% oxygen.

D. Colorectal carcinoma: relevant background and clinical trials Preoperative (chemo)radiotherapy has become standard of care in stage II-III rectal cancer, but is associated with acute and late grade 3 or 4 toxic effects in 27% and 14% of patients respectively. One way to decrease toxicity is by creating dose distributions that tightly match the shape of the planning target volume using intensity-modulated radiotherapy (IMRT) 12. Image-guided radiotherapy (IGRT) may further decrease the irradiated volume of nearby organs, as it allows smaller safety margins to compensate for daily setup errors and internal motion of organs 13. Our ongoing phase II trial of helical tomotherapy explores how far implementation of IMRT-IGRT in daily practice may reduce toxicity and whether a simultaneous integrated radiation boost on the gross tumor volume is equivalent to the radiosensitizing effects of 5-FU 14. Another way to improve the therapeutic index may be to exploit specific features of the tumor microenvironment, such as hypoxia or the pro-inflammatory tumor infiltrate. A comprehensive analysis of the surgical specimens from the Dutch TME trial revealed that patients with an extensive inflammatory tumor infiltrate had significantly lower recurrence colorectal cancer are tightly associated with iNOS expression, probably as a result of chronic exposure to luminal bacterial LPS 16.

E. Hypothesis. Recent developments demonstrated that polyclonal stimulation through CD3-TCR (T-cell receptor), accessory CD28 molecule and growth factor IL-2 provides an efficient approach for large scale exvivo expansion of T cells, aiming at adaptive immunotherapy 17,18. Moreover, commercially available CD3/CD28 beads (surrogate of immobilized antibodies) are suitable for both mouse and human T-cell expansion, and may be combined with priming against tumor-specific antigens. Once re-stimulated, both CD4+ and CD8+ expanded T cells display the IFN-?+ phenotype next to granzyme B/perforin, common markers of cytotoxicity.
AcronymFWOAL553
StatusFinished
Effective start/end date1/01/1031/12/13

    Research areas

  • image processing techniques, SPECT, image modelling and medical science, PET, small animal imaging, radiopharmaceuticals

    Flemish discipline codes

  • Physical sciences
  • Electrical and electronic engineering
  • Basic sciences
  • (Bio)medical engineering

ID: 3347756