Isolated thyroid metastasis from benign phyllodes tumour.

We present a rare and interesting case of a 35-year-old woman who initially underwent an uneventful wide excision for a 13 cm left benign phyllodes tumour. She then noted a slowly growing left thyroid nodule 8 months postsurgery which on thyroidectomy 4 years later was shown to be a 6.9cm isolated thyroid metastasis from the phyllodes tumour. As this may be the first reported such case in the literature, implications on histological classification, predictive factors for disease progression, mechanisms of metastasis, and evaluation, management and surveillance of benign phyllodes tumours and thyroid nodule/s with a history of phyllodes tumour can thus be significantly impacted.

Methods for the design and analysis of oligodeoxynucleotide-based DNA (cytosine-5) methyltransferase inhibitors.

Several second-generation inhibitors of DNA (cytosine-5) methyltransferases based on studies of modified synthetic oligodeoxynucleoides have been described. As an aid to studies of these inhibitors, we present an electronic structure-based algorithm that can be used as a method for predicting the nature of the expected inhibition by any noncytosine nucleotide target. Targeting by the major human enzyme (hDnmt1) is governed by the presence of a three-nucleotide motif. In hemimethylated DNA, this motif consists of a 5-methylcytosine targeting signal that causes the enzyme to probe the opposite strand for a normally paired guanosine or inosine residue and attempt to methylate the residue 5' to that site. As a demonstration of the method, we apply these rules to the design and characterization of a novel oligodeoxynucleotide inhibitor of hDnmt1. This inhibitor takes advantage of the three-nucleotide recognition motif characteristic of hDnmt1 and shows that the enzyme is inhibited in vitro by non-CG methylation which targets the enzyme to normally basepaired but unproductive nucleotides such as dG, dA, and dT. Kinetic analysis at constant S-adenosyl-L-methionine concentration shows that representative inhibitory oligodeoxynucleotides are best viewed as weakly productive components of systems containing two DNA substrates. This model suggests that the most effective inhibitors are those with very low apparent Vmax and very low Km values. Oligodeoxynucleotides containing mispaired and unproductive targets such as dG, dA, dT, and dU are also inhibitory as secondary substrates for the human enzyme. Biologically, fail-safe mechanisms identified by the ab initio approach appear to be active in preventing potentially mutagenic deamination of dihydrocytosine and enzymatic methylation of dU.