Cell cycle alterations, apoptosis, and response to low-dose-rate radioimmunotherapy in lymphoma cells

Int J Radiat Oncol Biol Phys. 1993 Oct 20;27(3):643-50. doi: 10.1016/0360-3016(93)90391-8.


Purpose: In an attempt to elucidate some aspects of the radiobiological basis of radioimmunotherapy, we have evaluated the in vitro cellular response patterns for malignant lymphoma cell lines exposed to high- and low-dose-rate radiation administered within the physiological context of antibody cell-surface binding.

Methods and materials: We used two different malignant lymphoma cell lines, a Thy1.2+ murine T-lymphoma line called EL-4 and a CD20+ human B-lymphoma line called Raji. Cells were grown in suspension cultures and exposed to high-dose-rate gamma radiation from an external 137Cs source or low-dose-rate beta radiation from DTPA-solubilized 90Y in solution. In some experiments, cells were pre-incubated with an excess of nonradioactive antibody in order to assess the effects of immunoglobulin surface binding during radiation exposure. Irradiated cells were evaluated for viability, cell-cycle changes, patterns of post-radiation morphologic changes, and biochemical hallmarks of radiation-associated necrosis and programmed cell death.

Results: The EL-4 line was sensitive to both high-dose-rate and low-dose-rate irradiation, while the Raji showed efficient cell kill only after high-dose-rate irradiation. Studies of radiation-induced cell cycle changes demonstrated that both cell lines were efficiently blocked at the G2/M interface by high-dose-rate irradiation, with the Raji cells appearing somewhat more susceptible than the EL-4 cells to low-dose-rate radiation-induced G2/M block. Electron microscopy and DNA gel electrophoresis studies showed that a significant proportion of the EL-4 cells appeared to be dying by radiation-induced programmed cell death (apoptosis) while the Raji cells appeared to be dying primarily by classical radiation-induced cellular necrosis.

Conclusion: We propose that the unusual clinical responsiveness of some high and low grade lymphomas to modest doses of low-dose-rate radioimmunotherapy may be explained in part by the induction of apoptosis. The unusual dose-response characteristics observed in some experimental models of radiation-induced apoptosis may require a reappraisal of standard linear quadratic and alpha/beta algorithms used to predict target tissue cytoreduction after radioimmunotherapy.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apoptosis / radiation effects*
  • Cell Cycle / radiation effects
  • DNA, Neoplasm / metabolism
  • Dose-Response Relationship, Radiation
  • Humans
  • Lymphoma / pathology
  • Lymphoma / radiotherapy*
  • Mice
  • Radioimmunotherapy*
  • Tumor Cells, Cultured


  • DNA, Neoplasm