Subadditive interaction of radiation and Taxol in vitro

Int J Radiat Oncol Biol Phys. 1997 Mar 15;37(5):1139-44. doi: 10.1016/s0360-3016(96)00629-3.


Purpose: To examine the dependency of Taxol-radiation interactions on the scheduling of the two agents.

Methods and materials: The human laryngeal squamous cell carcinoma line SCC20 was used for this study. Cells were irradiated as subconfluent cultures using Cs-137 gamma rays at a dose rate of 1.75 Gy/min. Cultures were pretreated with Taxol (7.5 nM for 12 h, S.F. = 0.4) and then irradiated with graded doses followed by either immediate plating or holding for 6 h either in the absence or presence of 7.5 nM Taxol prior to plating for colony-forming ability. Experiments in which cells were irradiated and then exposed to 7.5 nM Taxol for both 12 and 18 h were also performed. Parallel-flow cytometric analyses of cell-cycle distribution of the various treated populations were carried out.

Results: The results indicate that pretreatment with Taxol induced a G2 block which was maintained during 6 h postirradiation holding either in the presence or absence of Taxol. No modification of radiosensitivity in the low-dose region was seen for cells treated with Taxol, irradiated, and plated immediately, with the resulting survival being compatible with an additive effect. However, for Taxol-pretreated cells held for 6 h postirradiation, either in the absence or presence of Taxol, the resulting survival reproducibly demonstrated a marked less than additive effect. This was particularly prominent for cells held in the presence of Taxol. Subsequent experiments in which Taxol was added to cells immediately postirradiation again demonstrated a less than additive effect of the two modalities.

Conclusion: The results of this study are consistent with a dual mechanism of action involving Taxol-induced radiation resistance, possibly as a consequence of postirradiation holding in G2, and radiation-induced Taxol resistance through an as-yet-undefined mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / administration & dosage
  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Carcinoma, Squamous Cell / pathology
  • Cell Survival / drug effects
  • Cell Survival / radiation effects
  • Drug Administration Schedule
  • Drug Screening Assays, Antitumor
  • G2 Phase / drug effects*
  • G2 Phase / radiation effects*
  • Humans
  • Laryngeal Neoplasms / pathology
  • Paclitaxel / administration & dosage
  • Paclitaxel / pharmacology*
  • Radiation Tolerance
  • Radiotherapy Dosage
  • Tumor Cells, Cultured / drug effects
  • Tumor Cells, Cultured / radiation effects


  • Antineoplastic Agents, Phytogenic
  • Paclitaxel