Looking beyond the SRM to high-resolution MS paradigm shift for DMPK studies

Kean University, New Jersey Center for Science, Technology & Mathematics, 1000 Morris Avenue, Union, NJ 07033, USA Tel.: +1 908 737 7217 E-mail: ramanatd@kean.edu A 1900 statement from Lord Kelvin to British physicists stated the following: “There is nothing new to be discovered in physics now. All that remains is more and more precise measurement” [101]. In a nutshell the SRM to HRMS paradigm shift revolves around precise or accurate measurement of mass using highresolution MS (HRMS). Over the last few years, HRMS systems facilitated by new technological advances and userfriendly software have evolved from a specialist to a generalist analytical tool. The HRMS-based methods are now routinely used in most discovery DMPK bioanalytical and biotransformation laboratories and they are also slowly infiltrating some of the regulated bioanalytical laboratories. New additions to the HRMS workflow, such as MS (where e represents collision energy) and sequential window acquisition of all theoretical fragments (SWATH) technologies, have started to pave the way to improved selectivity, specificity and signal-to-noise ratio of DMPK assays and are poised to help the paradigm shift come to completion. Success in drug R&D is critical for meeting the needs of medicine and patient care with the demands of running a growing, profitable business. For new drugs to be beneficial to patients, they must show improved efficacy and safety over existing treatments. For a drug to enter clinical trials and to become a product for patients, four separate but somewhat interrelated processes influence a drug’s movement in the body: absorption (A), distribution (D), metabolism (M) and excretion (E). A drug’s ADME properties are studied and optimized by pre-clinical and clinical drug metabolism and DMPK scientists. Over the past 20 years, LC–MS-based techniques have grown to replace every other technique and become the gold standard analytical technique for DMPK studies. The crystallization of the LC–MS technique as the gold standard DMPK analytical tool happened with the introduction of atmospheric pressure ionization (API) techniques, specifically, ESI and atmospheric-pressure chemical ionization (APCI). API techniques facilitated efficient coupling of LC separation technologies, which simplifies complex biological samples, before MS analysis. Since routine DMPK assays involve measuring m/z ratios of drugs and/or their metabolites present in complex biological samples, adequate sample clean-up and chromatographic separation are essential for quantification and characterization of these components. Two major chromatographic separation techniques used in DMPK studies are HPLC and UHPLC. Over the last 3–5 years, major developments in columns based on sub-2 μm porous particles, monoliths, and wide pore core-shell particles (2–3 μm) combined with the introduction of rugged UHPLC systems have improved the speed and throughput of small-molecule separations. Along with the developments in sample separation and preparation technologies, the evolutions of MS technologies have streamlined how DMPK studies are conducted. If you had to pinpoint it, the last paradigm shift in the bioanalytical sciences in support of DMPK studies happened in the late 1980s and early 1990s. And it revolved around shifting from LC–UV to LC–MS/MS for PK and TK quantitation [1] and the combined use of benchtop quodrupole ion trap and triple quadrupole for metabolite detection and characterization [2]. These shifts allowed DMPK scientists to bring bioanalysis into drug metabolism laboratories rather than be dependent on centralized MS facilities operated by a specialist. Furthermore, during this shift the ability to couple LC with sensitive MS/MS-based SRM methods allowed bioanalysts to improve the detection