166 CHAPTER 6 method. These findings confirm that the novel snap freezer preserves high-quality biospecimen and allows identification of individual patients’ molecular profiles. The commercial development and wide availability of a mobile, electrically powered snap freezer would greatly benefit precision medicine by placing molecular diagnostics for routine oncology practice within reach in all hospitals. Tissue preservation for complex multi-layer molecular analysis will no longer be confined to the academic hospitals by removing the obstacle of the logistical requirements posed by LN2. Obviously, the analyses of tissues still need to be performed in expert laboratories that have experience with the techniques and interpretation of the results. But ultimately, by simplifying and standardizing tissue preservation, more patients will have access to molecular profiling of their tumors and may benefit from precision oncology. Optimal preservation of human cancer tissue samples for immediate diagnostic evaluation and also for tissue biobanking has been a hot topic for decades. In the past, local operating procedures for tissue preservation differed per pathology department and were established to ensure optimal morphologic preservation, which does not necessarily correlate with optimal molecular preservation. Around the year 2000, many new biobanks were developed around the world, implementing more stringent standard operating procedures (SOPs) to reduce variability in pre-analytical handling of tissue specimens for research60. Early on, the need for rapid cooling of tissues (snap freezing) was recognized. Throughout the years, various methods of fixation and conservation of tissues have been developed58. Fixation methods that require a storage medium, such as formalin-fixed paraffin-embedding (FFPE), RNAlater or Optimal Cutting Temperature (OCT) compound, render the tissue useless for some analytical methods such as phosphoproteomics61, although new techniques are being developed to enable MS-based proteomics62-64. Medium-free snap freezing methods conserve the tissue for molecular analysis of all layers of biology, but all are laborious and have specific disadvantages, sometimes even damaging the tissue58. Examples are snap freezing in pre-cooled (-80 °C) isopentane, carbon dioxide quick-freeze method and the current golden standard of immersion in liquid nitrogen65. There is an unmet need for a standardized, widely available, straightforward snap freezing method to circumvent the limitations of the current methods used in pathology labs and biobanks. Kennedy et al. have developed a portable prototype Quick-Freeze Collection Device, using dimethyl ether/propane as an aerosol cooling system. The device was tested using a melanoma patient derived xenograft (PDX) model and global phosphoproteome profiles were comparable to profiles of samples processed in LN2. The results however reported an uneven release of coolant, which interfered with the results of the prototype data. The cooling performance of this device is less impressive than that of our snap freezer, as it cools slower, has a higher and non-adjustable maximum cold sink temperature (-30 °C) and the inability to maintain low freezing temperatures for more than 70 minutes66.
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