Ordinarily, materials analyzed by mass spectrometry are crude or partially purified samples. Expression Pathology, however, has introduced technology for direct isolation and evaluation of formalin-fixed histological specimens, according to David Krizman, Ph.D., CSO.
The technology uses a laser-based microdissection technology termed Director® to collect specific cells from slides, which are then introduced into a protein buffer. Samples in the range of 30,000 cells are prepared for mass spectrometry using Liquid Tissue® MS reagents, which bring about complete solubilization and capture of the entire protein content in a mass spec friendly format, Dr. Krizman said.
When tissues at various stages of malignant transformation were analyzed for increasing levels of the Her2 peptide with the Director and Liquid Tissue technologies, there was a virtually perfect quantitative agreement with comparable data obtained using both immunohistochemistry and FISH measurements, he added.
The approach can also be used in biomarker discovery, according to the company, which has analyzed eight primary cutaneous melanomas and 16 metastatic brain lesions by LC/MS/MS global profiling of Liquid Tissue lysates. The team observed 120 significant protein changes in metastatic tumors as compared to the primary melanomas.
“We offer SRM assays on a collaborative/fee-for-service basis,” Dr. Krizman noted. “We are willing to undertake collaborative protein biomarker discovery and validation collaborations either for clinical or basic research purposes.” At present the company is gearing up to move assays based on its collection of putative biomarker proteins into clinical trials.
The disciplines of mass spectrometry and sample preparation are intimately bound together, since MS cannot be an effective analytical tool without the specialized methods for removing trace contaminants that might otherwise create unmanageable noise. Interfering materials including protein aggregates, protein fragments, and low molecular weight compounds can all render the technology ineffective. So sample preparation must be effectively married to mass spectrometry instrumentation to optimize performance. The procedures described in this article, while incremental in scope, make mass spectrometry an option for analytical tasks that would not otherwise be available.