Design, implementation and multisite evaluation of a system suitability protocol for the quantitative assessment of instrument performance in liquid chromatography-multiple reaction monitoring-MS (LC-MRM-MS)

Multiple reaction monitoring (MRM) mass spectrometry coupled with stable isotope dilution (SID) and liquid chromatography (LC) is increasingly used in biological and clinical studies for precise and reproducible quantification of peptides and proteins in complex sample matrices. Robust LC-SID-MRM-MS-based assays that can be replicated across laboratories and ultimately in clinical laboratory settings require standardized protocols to demonstrate that the analysis platforms are performing adequately. We developed a system suitability protocol (SSP), which employs a predigested mixture of six proteins, to facilitate performance evaluation of LC-SID-MRM-MS instrument platforms, configured with nanoflow-LC systems interfaced to triple quadrupole mass spectrometers. The SSP was designed for use with low multiplex analyses as well as high multiplex approaches when software-driven scheduling of data acquisition is required. Performance was assessed by monitoring of a range of chromatographic and mass spectrometric metrics including peak width, chromatographic resolution, peak capacity, and the variability in peak area and analyte retention time (RT) stability. The SSP, which was evaluated in 11 laboratories on a total of 15 different instruments, enabled early diagnoses of LC and MS anomalies that indicated suboptimal LC-MRM-MS performance. The observed range in variation of each of the metrics scrutinized serves to define the criteria for optimized LC-SID-MRM-MS platforms for routine use, with pass/fail criteria for system suitability performance measures defined as peak area coefficient of variation <0.15, peak width coefficient of variation <0.15, standard deviation of RT <0.15 min (9 s), and the RT drift <0.5min (30 s). The deleterious effect of a marginally performing LC-SID-MRM-MS system on the limit of quantification (LOQ) in targeted quantitative assays illustrates the use and need for a SSP to establish robust and reliable system performance. Use of a SSP helps to ensure that analyte quantification measurements can be replicated with good precision within and across multiple laboratories and should facilitate more widespread use of MRM-MS technology by the basic biomedical and clinical laboratory research communities.

The treatment of intravenously implanted Lewis lung carcinoma with two sustained release forms of 1-β-d-arabinofuranosylcytosine

Liposomes have been used in recent years as carriers for drugs and molecules of biological importance. In cancer chemotherapy, however, the advantages of liposome encapsulation of antitumor drugs remain uncertain, with the possible exception of the usefulness of encapsulated 1-beta-D-arabinofuranosyl-cytosine (ara-C), an antitumor drug of a very short half-life. Liposome-encapsulated ara-C has been shown by others to enhance significantly the survival time of mice bearing leukemia, and the enhancement may be attributable to the role of liposomes as a slow release system for ara-C. We now further explore the advantages of two sustained release systems for ara-C, namely the liposome-encapsulated ara-C and 1-beta-D-arabinofuranosylcytosine-5'-diphosphate-L-1,2-dipalmitin (ara-CDP-L-dipalmitin, a prodrug of ara-C). Intravenously implanted Lewis lung carcinoma is used as a solid tumor model. The therapeutic effectiveness of the two slow release forms of ara-C given by either i.v. or i.p. injections is examined. Viable tumor cells (1.0 X 10(5) cells/mouse) were inoculated i.v. and treatment was initiated 24 hr later using three schedules of multiple treatments for liposomal ara-C and single or multiple injections of ara-CDP-L-dipalmitin. Liposomal ara-C given by the i.p. route consistently increased the number of cures (greater than 120 days survival). For example, when nine small doses (10 mg/kg) were given on consecutive days by i.p. injections, 50% of mice given liposomal ara-C were cured, compared with 10% cures in the group given ara-C liposomes by i.v. and no cures in mice receiving free ara-C given according to the same schedules. On the other hand, ara-CDP-L-dipalmitin given at a single dose is more effective than an equal dose divided in five injections. However, no cures have been obtained by treatments with ara-CDP-L-dipalmitin. These results have further demonstrated the advantage of liposomes as carriers for antitumor drugs of short half-life.