No abstract

Using a solution-phase parallel synthesis strategy, a series of non-peptide somatostatin analogues were prepared, and their binding affinities to the five human somatostatin receptor subtypes (sst(1-5)) were determined. Imidazolyl derivatives 2 were found to bind with moderate affinity but with high selectivity to the sst(3) receptor subtype. Further modifications of these structures led to a more potent class of ligands, the tetrahydro-beta-carboline derivatives 4. Among these, compounds 4k (BN81644) and 4n (BN81674) bind selectively and with high affinity to the sst(3) receptor subtype (K(i) = 0.64 and 0.92 nM, respectively). Furthermore, 4k and 4n reverse the inhibition of cyclic AMP accumulation induced by 1 nM somatostatin via sst(3) receptors, with IC(50) = 2.7 and 0.84 nM, respectively. The most potent compound 4n was shown to be a competitive antagonist of human sst(3) receptors by increasing the EC(50) of SRIF-14-mediated inhibition of cAMP accumulation with a K(B) of 2.8 nM (where K(B) is the concentration of antagonist that shifts the agonist dose-response 2-fold). These new derivatives are, to our knowledge, the first potent and highly selective non-peptide human sst(3) antagonists known and, as such, are useful tools for investigating the physiological role of sst(3) receptors.

Cell cycle regulators, such as the CDC25 phosphatases, are potential targets for the development of new anticancer drugs. Here we report the identification and the characterization of BN82685, a quinone-based CDC25 inhibitor that is active in vitro and in vivo. BN82685 inhibits recombinant CDC25A, B, and C phosphatases in vitro. It inhibits the growth of human tumor cell lines with an IC 50 in the submicromolar range, independently of their resistance to chemotherapeutic agents. This inhibitory effect is irreversible on both the purified CDC25 enzyme in vitro and on tumor cell proliferation. The specificity of BN82685 towards the CDC25 phosphatases is shown by an increase in cyclin-dependent kinase 1 tyrosine 15 phosphorylation, by the reversion of the mitosis-inducing effect of CDC25B overexpression in HeLa cells, and by the lack of a growth inhibitory effect in an assay based on the use of a CDC25-independent fission yeast model. Finally, when administered p.o.,

CDC25 phosphatases are key actors in cyclin-dependent kinases activation whose role is essential at various stages of the cell cycle. CDC25 expression is upregulated in a number of human cancers. CDC25 phosphatases are therefore thought to represent promising novel targets in cancer therapy. Here, we report the identification and the characterization of IRC-083864, an original bis-quinone moiety that is a potent and selective inhibitor of CDC25 phosphatases in the low nanomolar range. IRC-083864 inhibits cell proliferation of a number of cell lines, regardless of their resistance to other drugs. It irreversibly inhibits cell proliferation and cell cycle progression and prevents entry into mitosis. In addition, it inhibits the growth of HCT-116 tumor spheroids with induction of p21 and apoptosis. Finally, IRC-083864 reduced tumor growth in mice with established human prostatic and pancreatic tumor xenografts. This study describes a novel compound, which merits further study as a potential anticancer agent. ' 2008 Wiley-Liss, Inc.Key words: CDC25 phosphatase; cell cycle; cancer; pharmacology CDC25 phosphatases dephosphorylate and hence, activate cyclin-dependent kinases (CDKs), thus participating as major actors in the control of cell cycle progression. Their function is also tightly linked to the maintenance of genomic integrity as targets of the checkpoint machinery activated upon DNA injury. 1During the past decade, an increasing body of evidence suggests that CDC25 phosphatases are key players in cell transformation and in cancer progression.2 For instance, when specifically targeted to the mammary gland, overexpression of CDC25B, in association with the carcinogen DMBA (9,10-dimethyl-1,2-benzanthracene), has been shown to induce neoplasia. 3,4 Further, hemizygous disruption of CDC25A inhibits cellular transformation and mammary tumorigenesis in mice, suggesting that a low level of CDC25A protein plays a rate-limiting role in transformation and tumor initiation mediated by oncogene such as H-ras 12 and neu. 5,6 Finally, overexpression of CDC25A and CDC25B proteins has been observed in a wide variety of human tumors (see ref. 2 and 7 for review), and these observations have often been linked to a poor prognosis, suggesting an important role in tumor behavior.A limited number of small molecule inhibitors of the CDC25 phosphatases have been identified (see ref. 1,8 for review), but little is known about either their metabolism or efficacy in xenograft tumor models. These compounds are mainly quinones but also phosphate surrogates or electrophilic entities.9-22 Several mechanisms of action have been proposed for these inhibitors such as oxidization of the catalytic site cysteine, Michael acceptors capable of reacting with the activated thiolate or other electrophilic entities. Initial results support the view that CDC25 is an interesting and important anticancer target, 12,13,23 and considerable effort is currently directed to the identification additional candidate drugs. Here, we describe a novel small molecule...

The effects of cell adhesion on leukemia cell proliferation remain poorly documented and somehow controversial. In this work, we investigated the effect of adhesion to fibronectin on the proliferation of acute myeloid leukemia (AML) cell lines (U937 and KG1a) and CD34 + normal or leukemic primary cells. We observed an increased rate of proliferation of AML cells when adhered to fibronectin, concomitant with accelerated S-phase entry and accumulation of CDC25A. Conversely, normal CD34+ cell proliferation was decreased by adhesion to fibronectin with a concomitant drop in CDC25A expression. Importantly, we showed that both small interfering RNA (siRNA)-mediated CDC25A down-regulation and a recently developed CDC25 pharmacologic inhibitor impaired this adhesion-dependent proliferation, establishing a functional link between CDC25A accumulation and adhesion-dependent proliferation in leukemic cells. CDC25A accumulation was found only slightly dependent on transcriptional regulation and essentially due to modifications of the proteasomal degradation of the protein as shown using proteasome inhibitors and reverse transcription-PCR. Interestingly, CDC25A regulation was Chk1 dependent in these cells as suggested by siRNA-mediated down-regulation of this protein. Finally, we identified activation of the phosphatidylinositol 3-kinase/ Akt pathway as an adhesion-dependent regulation mechanism of CDC25A protein expression. Altogether, our data show that in leukemic cells adhesion to fibronectin increases CDC25A expression through proteasome-and Chk1-dependent mechanisms, resulting in enhanced proliferation. They also suggest that these adhesion-dependent proliferation properties of hematopoietic cells may be modified during leukemogenesis.