Glutathione-Mediated Metabolism of Technetium-99m SNS/S Mixed Ligand Complexes: A Proposed Mechanism of Brain Retention

Two series of [99mTc](SNS/S) mixed ligand complexes each carrying the N-diethylaminoethyl or the N-ethyl-substituted bis(2-mercaptoethyl)amine ligand (SNS) are produced at tracer level using tin chloride as reductant and glucoheptonate as transfer ligand. The identity of [99mTc](SNS/S) complexes is established by high-performance liquid chromatographic (HPLC) comparison with authentic rhenium samples. The para substituent R on the phenylthiolate coligand (S) ranges from electron-donating (−NH2) to electron-withdrawing (−NO2) groups, to study complex stability against nucleophiles as a result of N- and R-substitution. The relative resistance of [99mTc](SNS/S) complexes against nucleophilic attack of glutathione (GSH), a native nucleophilic thiol of 2 mM intracerebral concentration, is investigated in vitro by HPLC. The reaction of [99mTc](SNS/S) complexes with GSH is reversible and advances via substitution of the monothiolate ligand by GS- and concomitant formation of the hydrophilic [99mTc](SNS/GS) daughter compound. The N-diethylaminoethyl complexes are found to be more reactive against GSH as compared to the N-ethyl ones. Complex reactivity as a result of R-substitution follows the sequence −NO2 ≫ −H > −NH2. These in vitro findings correlate well with in vivo distribution data in mice. Thus, brain retention parallels complex susceptibility to GSH attack. Furthermore, isolation of the hydrophilic [99mTc](SNS/GS) metabolite from biological fluids and brain homogenates provides additional evidence that the brain retention mechanism of [99mTc](SNS/S) complexes is GSH-mediated

Tumour histology in sporadic ovarian cancer cases compared to that of <i>BRCA1</i> carriers in each group. Histological type was known for 26/27 <i>BRCA1</i> carriers and 450/592 in total.

<p>Tumour histology in sporadic ovarian cancer cases compared to that of <i>BRCA1</i> carriers in each group. Histological type was known for 26/27 <i>BRCA1</i> carriers and 450/592 in total.</p

Age of onset distribution in familial and sporadic cases.

<p>A) Age of onset distribution among the total of 106 familial patients with ovarian cancer and 41 patients with a <i>BRCA1</i> mutation. B) Age of onset distribution among 492/592 of sporadic patients and 27/27 patients with a <i>BRCA1</i> mutation.</p

Pedigree of a family with the <i>BRCA1</i> p.V1833M variant of uncertain significance (VUS).

<p>Pink circles indicate women with ovarian cancer. The plus sign indicates the presence of the variant in the indicated person, while the minus sign indicates the absence of the variant. OvCa = ovarian cancer.</p

<i>BRCA1</i> pathogenic mutations identified in familial cases.

*<p>Unclassified variant.</p>**<p>Splicing variant causing exon 23 skipping <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0058182#pone.0058182-Gaildrat1" target="_blank">[47]</a>.</p><p>N.A. Non Applicable.</p

Showing the characteristics of patients carrying the <i>BRCA1</i> p.V1833M variant.

<p>Showing the characteristics of patients carrying the <i>BRCA1</i> p.V1833M variant.</p

<i>BRCA1</i> pathogenic mutations identified in sporadic cases.

<p><i>BRCA1</i> pathogenic mutations identified in sporadic cases.</p

Tumour histology in familial ovarian cancer cases compared to that of <i>BRCA1</i> carriers in each group. Histological type was known for 33/43 <i>BRCA1</i> carriers and 62/106 in total.

<p>Tumour histology in familial ovarian cancer cases compared to that of <i>BRCA1</i> carriers in each group. Histological type was known for 33/43 <i>BRCA1</i> carriers and 62/106 in total.</p

Frequencies and ORs for the SNPs rs2588809, rs1314913, and rs999737 for all breast cancer cases, familial cases and ER-positive and -negative cases in the BCAC dataset.

Frequencies and ORs for the SNPs rs2588809, rs1314913, and rs999737 for all breast cancer cases, familial cases and ER-positive and -negative cases in the BCAC dataset.</p

Estimated haplotype frequencies and haplotype-specific ORs among the BCAC dataset.

The haplotypes are based on genotypes for SNPs rs2588809, rs1314913, and rs999737.</p