The cell cycle regulator p21 interacts with and inhibits the DNA replication and repair factor proliferating cell nuclear antigen (PCNA). We have defined a 39 amino acid fragment of p21 which is sufficient to bind PCNA with high affinity (Kd 10-20 nM). This peptide can inhibit DNA replication in vitro and microinjection of a GST fusion protein containing this domain inhibited S phase in vivo. Despite its high affinity for PCNA, the free 39 amino acid peptide does not have a well-defined structure, as judged from circular dichroism and nuclear magnetic resonance measurements, suggesting an induced fit mechanism for the PCNA-p21 interaction. The association of the small peptide with PCNA was thermolabile, suggesting that portions of p21 adjoining the minimal region of contact stabilize the interaction. In addition, a domain containing 67 amino acids from the N-terminus of PCNA was defined as both necessary and sufficient for binding to p21.
Endocrine therapy is the ideal treatment choice for estrogen receptor alpha (ERalpha)-positive breast cancer patients. Principal used therapies target either the ERalpha e.g. by selective ERalpha modulators (SERMs) such as tamoxifen or target estrogen biosynthesis with aromatase inhibitors. Steroid sulfatase (STS) plays a crucial role in formation of compounds with estrogenic properties, converting inactive sulfate-conjugated steroids to active non-conjugated forms. Steroid sulfates are considered as a reservoir for active steroids due to their prolonged half-life and increased concentration in plasma. STS is present in several tissues including the breast, and the STS the mRNA level and enzyme activity is significantly increased in ERalpha-positive breast tumors. Inhibition of STS is therefore a new approach for decreasing estrogenic steroids that stimulate breast cancer. The novel dual-acting compound SR 16157 is designed as a sulfamate-containing STS inhibitor that releases a tissue-selective SERM SR 16137. Use of a dual-target STS inhibitor and SERM represents a new strategy in the treatment of hormone-dependent breast cancer. In this study, we tested the potential of SR 16157 and SR 16137 on STS activity, cell growth and ERalpha function in MCF-7 breast cancer cells. We confirmed that the dual-target compound SR 16157 exerts STS inhibition and antiestrogenic effects. SR 16157 was a highly effective growth inhibitor, being 10 times more potent than the antiestrogens SR 16137 and tamoxifen. Relative to tamoxifen, SR 16137 displays profoundly improved ERalpha binding affinity and antiestrogenic effects on expression of estrogen-regulated genes. Thus, the dual-target SR 16157 is possibly a promising new treatment alternative, superior to tamoxifen.
A number of mono-and di-vinyl sulphones and sulphonamides have been prepared and the kinetics of their reaction with alcohols in the presence of a basic catalyst have been studied. In a series of pure alcohols, the reaction is of the first order with respect to both vinyl compound and catalyst; its rate at first increases and then becomes practically constant on ascending the homologous series from methanol to n-decanol. The rate of the reaction with ethanol is increased by the addition of dioxan. These results accord with the view that the mechanism of the reaction consists in the addition of the nucleophilic alkoxide ion to the vinyl compound followed by rapid protonation of the intermediate carbanion so formed.In dimethyl sulphoxide the reaction between equivalent amounts of vinyl compound and alcohol does not go to completion because the intermediate carbanion is stabilised sufficiently to be present in appreciable concentration.The addition of 2-hydroxyethanethiol to N-methyl-N-phenylvinylsulphonamide was studied in the course of devising an analytical method for the determination of activated vinyl groups. It proved to be of the first order in vinyl compound and catalyst and of zero order in thiol. This independence of thiol concentration of the reaction rate is ascribed to the relatively high acidity of this compound.
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