Creating synergy between established histology methods and newer spatial analysis modalities using fresh frozen tissues

Formalin-fixed paraffin embedded tissues are a mainstay in contemporary histology and pathology practice and represent the most readily available and widely used sample format that has guided early studies and set standards for a new field of spatial biology. However, fixed tissues are not always suitable for all molecular applications and detection of certain molecular targets can be suppressed by these practices. There is a greater diversity of analysis techniques that are commercially available to researchers today, and pathologists and core services are now engaging with groups that prefer fresh-frozen samples more than ever before. Some of these analysis techniques can be characterized as ‘label-free’ and access unique classes of molecular targets in situ. Our team has developed tools and procedures to facilitate a synergy between the realm of label-free spatial biology and the histology laboratory for biomedical discovery programs. Herein, we discuss the development of 3D printed cassette holders for use in a variety of commercially available cryostats. This apparatus was tested using fresh frozen tissue slices embedded in hydroxypropyl methylcellulose polyvinylpyrrolidone for subsequent analyses. Based on our tests, we propose this protocol as an option to better preserve sample history during the lifetime of a specimen and curtail the decomposition of any lower abundance endogenous chemical moieties for spatial ‘omics’ analysis using mass spectrometry.