Abstract 3619: The absence of cleaved caspase-3 in circulating tumor cells detected using a non-enrichment-based assay

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Background: The role of cleaved caspase-3 as an integral player in the apoptotic process of mammalian cells has prompted the investigation of an assay to detect cleaved caspase-3 in circulating tumor cells (CTCs) as one way to assess CTC viability. Methods: Using a previously developed non-enrichment based assay, nucleated blood cells and CTCs are adhered to a single slide. An antibody for cleaved caspase-3 was incorporated into the assay in addition to the existing antibodies for cytokeratin (to identify tumor cells) and CD45 (to identify white blood cells), as well as a nuclear stain (DAPI). The modified assay was initially tested on cultured MCF 10a cells spiked into normal donor blood. Before spiking, apoptosis was induced in these cells using staurosporine. Following validation of the assay in cell lines, the assay was performed using blood samples from 9 different breast cancer patients, as well as 3 different normal donor samples. Results: CTCs were detected in the patient samples as single cells, as well as clusters. The results of the assay showed that only 1 out of 896 detected CTCs was positive for cleaved caspase-3 (0.11%). Of these CTCs, 134 of them were found to be in clusters, and all 134 were negative for cleaved caspase-3, indicating that whether in clusters or as single cells, the vast majority of CTC's detected with this assay are not undergoing irreversible apoptotic processes via cleaved caspase-3. The results also showed that 0.40% of white blood cells in healthy donors expressed cleaved caspase-3, compared to 0.51% of the white cells in cancer patients, indicating that healthy donors and cancer patients express cleaved caspase-3 in their white blood cells at nearly the same rate. Conclusions: The morphologic characterization used in this platform to select healthy-appearing cells identifies a population of circulating tumor cells with virtually no evidence of caspase-related ongoing apoptosis, a finding that supports the morphologic impression of viability. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3619. doi:1538-7445.AM2012-3619