Para-nitroacetophenone (PNAP) selectively sensitizes hypoxic mammalian cells to ionizing radiation. The growth of Chinese hamster V79 cells as multicellular spheroids provides a convenient tumor model to test this drug. When irradiated, cells from these spheroids exhibit a multicomponent survival curve. The resistant portion of the curve is primarily due to hypoxic, noncycling cells near the center of the spheroid. However, radiation survival data indicates that these cells are as resistant as the most resistant cycling cells when the latter are made hypoxic. Addition of 500 μM PNAP prior to and during irradiation under oxic conditions decreases the survival on the resistant portion of the spheroid survival curve although the dose-modification is not as large as in hypoxic, monolayer systems. The analog, m-nitroacetophenone, acts in a similar fashion in spheroids.

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