CDC25 inhibitors as anticancer agents are moving forward.

The identification of a CDC25 inhibitor to arrest the cell cycle closely followed the discovery of CDC25 by Russell and Nurse in 1986. Recent advances at the preclinical and clinical stages reinforce the rationale to consider CDC25 as a relevant target for a cancer treatment. Here, in order to exemplify recent drug discovery efforts, we present our own experience with various chemical series of CDC25 inhibitors. We discuss how we have progressed and how we are considering the next steps to define the clinical entry points and hopefully complete this target validation to generate a new class of therapeutic agents.

G2/M checkpoint stringency is a key parameter in the sensitivity of AML cells to genotoxic stress.

Acute myeloid leukemia (AML) cells exposed to genotoxic agents arrest their cell cycle at the G2/M checkpoint and are inherently chemoresistant. To understand the mechanism of this chemoresistance, we compared the ability of immature CD34+ versus mature CD34- AML cell lines (KG1a and U937, respectively) to recover from a DNA damage-induced cell cycle checkpoint in G2. Here, we report that KG1a cells have a more stringent G2/M checkpoint response than U937 cells. We show that in both cell types, the CDC25B phosphatase participates in the G2/M checkpoint recovery and that its expression is upregulated. Furthermore, we show that CHK1 inhibition by UCN-01 in immature KG1a cells allows checkpoint exit and induces sensitivity to genotoxic agents. Similarly, UCN-01 treatment potentializes genotoxic-induced inhibition of colony formation efficiency of primary leukemic cells from AML patients. Altogether, our results demonstrate that checkpoint stringency varies during the maturation process and indicate that targeting checkpoint mechanisms might represent an attractive therapeutic opportunity for chemoresistant immature AML cells.

Identification of potent non-peptide somatostatin antagonists with sst(3) selectivity.

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.

Novel non-peptide ligands for the somatostatin sst3 receptor.

A series of imidazole derivatives has been prepared using high throughput parallel synthesis. Several compounds showed high affinity (Ki in 10(-6)-10(-8) M range) and selectivity at recombinant human somatostatin receptor subtype 3 (hsst3).

Synthesis of sulfur-linked analogues of nigerose, laminarabiose, laminaratriose, gentiobiose, gentiotriose, and laminaran trisaccharide Y.

Sulfur-linked analogues of 3-O-alpha-D-glucopyranosyl-D-glucose (nigerose), 3-O-beta-D-glucopyranosyl-D-glucose (laminarabiose), 6-O-beta-D-glucopyranosyl-D-glucose (gentiobiose), O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->3)-D-glucos e (laminaratriose), O-beta-D-glucopyranosyl)-(1-->6)-O-beta-D-glucopyranosyl-(1-->6)-D-gluco se (gentiotriose) and 3,6-di-O-beta-D-glucopyranosyl-D-glucose (laminaran trisaccharide Y), namely, respectively, 3-thionigerose (6), 3-thiolaminarabiose (11), 6-thiogentiobiose (21), 3I,3II-dithiolaminaratriose (16), 6I,6II-dithiogentiotriose (29) and 3I,6I-dithiolaminaran trisaccharide Y (37) have been conveniently prepared by SN2 reactions of the corresponding anomer of D-glucopyranose 1-thiolate with suitably activated monosaccharide derivatives in N,N-dimethylformamide (for 6 and 21) or in tetrahydrofuran in the presence of a crown ether (for 11). A sequence involving the reaction of non-anomeric thiolates with 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide was alternatively used for the preparation of 11 and 21 but proved less satisfactory. The preparation of thiotrisaccharides 16, 29, and 37 involved a mixed approach.

Stereocontrolled synthesis of sulfur-linked analogues of the branched tetrasaccharide repeating-unit of the immunostimulant polysaccharide schizophyllan and of its beta-(1-->3)-branched, beta-(1-->6)-linked isomer.

The branched, sulfur-linked tetrasaccharide S-(beta-D-glucopyranosyl)-(1-->3)-S-[(6-S-beta-D-glucopyranosyl)-3,6-dit hio- beta-D-glucopyranosyl]-(1-->3)-S-3-thio-D-glucopyranose (9) has been conveniently prepared by SN2 displacement of the triflate group in 1,2:5,6-di-O-isopropylidene-3-O-trifluoromethylsulfonyl-alpha-D-++ +allofuranose with the sodium salt of 2,4-di-O-acetyl-3,6-di-S-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)- 1,3,6- trithio-beta-D-glucopyranose (5). Conversely, reaction of the sodium salt of 5 with 1,2,3,4-tetra-O-acetyl-6-deoxy-6-iodo-beta-D-glucopyranose afforded the positional isomer S-(beta-D-glucopyranosyl)-(1-->6)-S-[(3-S-beta-D-glucopyranosyl)-3,6-dit hio- beta-D-glucopyranosyl]-(1-->6)-S-6-thio-D-glucopyranose (12).