Abstract. Elastic scattering spectroscopy (ESS), in the form of wavelength-dependent backscattering measurements, can be used to monitor apoptosis in cell cultures. Early changes in backscattering upon apoptosis induction are characterized by an overall decrease in spectral slope and begin as early as 10 to 15 min post-treatment, progressing over the next 6 to 8 h. The timescale of early scattering changes is consistent with reports of the onset of apoptotic volume decrease (AVD). Modeling cellular scattering with a fixed distribution of sizes and a decreasing index ratio, as well as an increased contribution of the whole cell to cellular scattering, resulting from increased cytoplasmic density, is also consistent with observed spectral changes. Changes in ESS signal from cells undergoing osmotically-induced volume decrease in the absence of apoptosis were similar, but smaller in magnitude, to those of apoptotic cells. Further, blockage of Cl − channels, which blocks AVD and delays apoptosis, blocked the early scattering changes, indicating that the early scattering changes during apoptosis result, at least partially, from AVD. Work continues to identify the additional sources of early spectral scattering changes that result from apoptosis induction. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).

Abstract. Apoptosis, a form of programmed cell death with unique morphological and biochemical features, is dysregulated in cancer and is activated by many cancer chemotherapeutic drugs. Noninvasive assays for apoptosis in cell cultures can aid in screening of new anticancer agents. We have previously demonstrated that elastic scattering spectroscopy can monitor apoptosis in cell cultures. In this report we present data on monitoring the detailed time-course of scattering changes in a Chinese hamster ovary (CHO) and PC-3 prostate cancer cells treated with staurosporine to induce apoptosis. Changes in the backscattering spectrum are detectable within 10 min, and continue to progress up to 48 h after staurosporine treatment, with the magnitude and kinetics of scattering changes dependent on inducer concentration. Similar responses were observed in CHO cells treated with several other apoptosis-inducing protocols. Early and late scattering changes were observed under conditions shown to induce apoptosis via caspase activity assay and were absent under conditions where apoptosis was not induced. Finally, blocking caspase activity and downstream apoptotic morphology changes prevented late scattering changes. These observations demonstrate that early and late changes in wavelength-dependent backscattering correlate with the presence of apoptosis in cell cultures and that the late changes are specific to apoptosis. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).