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Identification of gamma-glutamyl-Se-methylselenocysteine (γ-glutamyl-SeMC) in water-soluble yeast fractions was accomplished by on-line reversed-phase (RP) HPLC with ICP-MS and electrospray ionisation (ESI) tandem MS. The sample was leached with water using accelerated solvent extraction (ASE) and the aqueous extracts were directly analysed using on-line RP HPLC-ICP-MS. HPLC was carried out with 0.1% formic acid in methanol–water (2 + 98, v/v) solution. Se-specific detection of the chromatographic effluent by ICP-MS allowed identification of γ-glutamyl-SeMC on the basis of comparison of retention times with a matching standard. Aqueous extracts of three different Se–yeast supplements (1291, 1550 and 1983 μg g−1 Se in the dry sample) were analysed by HPLC-ICP-MS for their γ-glutamyl-SeMC content (as Se). A significant variation of the Se speciation in the water extracts appeared to occur with an increase in the total Se concentration from 1550 to 1983 μg g−1. Apparently, the contribution of water-soluble SeMC and selenomethionine (SeMet) increased whereas the contribution of Se incorporated into γ-glutamyl-SeMC decreased with the increasing total Se content. Verification of the presence of γ-glutamyl-SeMC in the water-soluble yeast extract, on the basis of molecular mass determination for the [M + H]+ 80Se ions (m/z 313) and detection of its product ions using on-line RP HPLC-ESI-MS/MS, is reported here for the first time. This was achieved without the need for a cleanup of the aqueous yeast extract. The presence of γ-glutamyl-SeMC might be relevant to the anticarcinogenic potential of selenised yeast since this species is believed to serve primarily as a carrier of SeMC, which appears to be easily converted in animals and possibly humans to methylselenol. This Se metabolite is thought to be an effective anticarcinogen.

Researchers worldwide with information about the Kirsten ras (Ki-ras) tumour genotype and outcome of patients with colorectal cancer were invited to provide that data in a schematized format for inclusion in a collaborative database called RASCAL (The Kirsten ras in-colorectal-cancer collaborative group). Our results from 2721 such patients have been presented previously and for the first time in any common cancer, showed conclusively that different gene mutations have different impacts on outcome, even when the mutations occur at the same site on the genome. To explore the effect of Ki-ras mutations at different stages of colorectal cancer, more patients were recruited to the database, which was reanalysed when information on 4268 patients from 42 centres in 21 countries had been entered. After predetermined exclusion criteria were applied, data on 3439 patients were entered into a multivariate analysis. This found that of the 12 possible mutations on codons 12 and 13 of Kirsten ras, only one mutation on codon 12, glycine to valine, found in 8.6% of all patients, had a statistically significant impact on failure-free survival (P = 0.004, HR 1.3) and overall survival (P = 0.008, HR 1.29). This mutation appeared to have a greater impact on outcome in Dukes’ C cancers (failure-free survival, P = 0.008, HR 1.5; overall survival P = 0.02, HR 1.45) than in Dukes’ B tumours (failure-free survival, P = 0.46, HR 1.12; overall survival P = 0.36, HR 1.15). Ki-ras mutations may occur early in the development of pre-cancerous adenomas in the colon and rectum. However, this collaborative study suggests that not only is the presence of a codon 12 glycine to valine mutation important for cancer progression but also that it may predispose to more aggressive biological behaviour in patients with advanced colorectal cancer. © 2001 Cancer Research Campaign http://www.bjcancer.com