Influence of gangliosides or LPS-like gangliosides on the tumoricidal activity of adherent leukocytes

Hyperradiosensibilité aux très faibles doses: impact en radiothérapie des micrométastases

Radiobiologists have pointed out a novel radiobiological phenomenon observed in many tumor and normal cell lines: hyper-radiosensitivity to very low-dose (HRS) followed by induced radioresistance (IRR) after a threshold dose of 0.1-0.3 Gy that depends on the cell line. Radioresistance at high dose (i.e. higher than 0.5 Gy) and metastatic potential of tumor cells are likely major factors of failure in radiotherapy. A careful review of literature suggests that: 1) radiotherapy does not increase the metastatic potential of tumor cells; 2) radioresistance at high dose and metastatic potential are not related. However, inside a given tumor cell line, highly metastatic clones may elicit more cells showing HRS or are more radiosensitive at high dose than poorly metastatic ones. Recent data obtained from molecular techniques (comet and immunofluorescence assays) applied to single cells irradiated at very low radiation doses (1-100 mGy) suggest that DNA single-strand breaks (SSB) and double-strand breaks (DSB) may be the key-lesions responsible for the HRS phenomenon. These data suggest that the HRS phenomenon may find application in radiotherapy for micrometastasis. These early disseminated and probably unvascularised cells may escape the influence of high-dose chemotherapy after excision of the primary tumor. Considering the link between metastatic potential and HRS, we have previously proposed to apply very low-dose total body irradiation (TBI) at M(0) stage that may prevent the development of micrometastases. Literature data suggest that the smallest radiation dose that can produce HRS without increasing the risk of cancer may be in the milliGrays range.

Radio-prevention of micrometastases

In developed countries, the cancer incidence is about 150,000 cases per year and half of people with cancer may die from the extension of the primary tumour in secondary deposits. This disaster costs more than 2 billion euro per year. People with cancer are often treated with surgery and/or radiotherapy of localized primary tumour and chemo-prevention of occult disseminated micrometastases. Since chemotherapy essentially targets cycling tumour cells, quiescent micrometastases which may contain only one cell may escape. We previously reported that human melanoma clones with high metastatic potential and low gangliosides content appeared very radiosensitive to low-dose ionizing radiation both in culture and in immunosuppressed animals. This exquisite radiosensitivity was observed with the highly metastatic single cells which were resting at the time of irradiation. These data are consistent with the dose-response relationship for the radiotherapy of secondary deposits which appears linear with no threshold. Highly metastatic cells at an early stage of growth also appear very sensitive to chemicals and activated immune cells. We propose the medical hypothesis according to which the spread of resting micrometastases should be prevented by a single fraction of total-body irradiation delivered at a dose sufficiently low (below 0.2 Gy) to avoid normal tissue radiotoxicity. Radio-prevention may complement standard treatments for patients with metastases and may be delivered even for patients in whom no distant metastases were detected on tumour diagnosis (M0 stage).