Isolation and in vitro culture of rare cancer stem cells from patient-derived xenografts of pancreatic ductal adenocarcinoma.

Described is the construction of a large array of releasable microstructures (micropallets) along with screening and isolation protocols for sorting rare, approximately 1 in 10,000, cancer stem cells (CSCs) from a heterogeneous cell population. A 10.1 × 7.1 cm array of micropallets (50 × 50 × 75 μm structures and 25 μm micropallet gap) was fabricated on a large glass substrate, providing an array of approximately 1.3 million releasable microstructures. Image analysis algorithms were developed to permit array screening for identification of fluorescently labeled cells in less than 15 minutes using an epifluorescent wide-field microscope with a computer controlled translational stage. Device operation was tested by culturing HeLa cells transfected with green fluorescent protein (GFP) admixed with wild-type HeLa cells at ratios of 1:104 to 1:106 on the array followed by screening to identify flourescent cells. Micropallets containing cells of interest were then selectively released by a focused laser pulse and collected on a numbered poly(dimethylsiloxane (PDMS) substrate with high viability. A direct comparison of this technology with fluorescence-activated cell sorting (FACS) demonstrated that micropallet arrays offered enhanced post sorting purity (100%), yield (100%) and viability (94 – 100%) for rare cell isolation. As a demonstration of the technology’s value, pancreatic tumor cells from Panc-1 cell lines and patient-derived xenografts were screened for the presence of CD24, CD44 and CD326; surface markers of pancreatic CSCs. Following cell isolation and culture, 63 ± 23% of the isolated Panc-1 cells and 35% of sorted human xenograft cells formed tumor spheroids retaining high expression levels of CD24, CD44 and CD326. The ability to isolate rare cells from relatively small sample sizes will facilitate our understanding of cell biology and the development of new therapeutic strategies.