Response of human neuroblastoma and melanoma multicellular tumor spheroids (MTS) to single dose irradiation

The growth characteristics of 6 human cell line derived multicellular tumor spheroids (MTS) were studied. Melanoma MTS (C32, HML-A, HML-B) were slow growing with baseline growth rates of 13.9 to 27.3 microns diameter/day. Neuroblastoma MTS (Lan-1, NB-100, NB-134) grew rapidly, with baseline growth rates of 32.1 to 40.3 microns diameter/day, that is, 1.2 to 2.9 times as fast as the melanomas. Delay constants were calculated for all six lines. The neuroblastomas were more sensitive to radiation than melanomas, as reflected in a greater value for the radiation-induced growth delay constant. One neuroblastoma line, Lan-1, was highly radioresponsive; that is, after a subcurative dose of radiation, the MTS diameter decreased beyond the original diameter, which was followed by recovery and regrowth. Irrespective of these initial changes in diameter, growth delay sensitivity (value of delay constant) was the same for Lan-1 and NB-100, an MTS line that did not show the responsive pattern.