Randall R. Rossman

Discovery of Dinaciclib (SCH 727965): A Potent and Selective Inhibitor of Cyclin-Dependent Kinases

Inhibition of cyclin-dependent kinases (CDKs) has emerged as an attractive strategy for the development of novel oncology therapeutics. Herein is described the utilization of an in vivo screening approach with integrated efficacy and tolerability parameters to identify candidate CDK inhibitors with a suitable balance of activity and tolerability. This approach has resulted in the identification of SCH 727965, a potent and selective CDK inhibitor that is currently undergoing clinical evaluation.

SCH529074, a Small Molecule Activator of Mutant p53, Which Binds p53 DNA Binding Domain (DBD), Restores Growth-suppressive Function to Mutant p53 and Interrupts HDM2-mediated Ubiquitination of Wild Type p53

Abrogation of p53 function occurs in almost all human cancers, with more than 50% of cancers harboring inactivating mutations in p53 itself. Mutation of p53 is indicative of highly aggressive cancers and poor prognosis. The vast majority of mutations in p53 occur in its core DNA binding domain (DBD) and result in inactivation of p53 by reducing its thermodynamic stability at physiological temperature. Here, we report a small molecule, SCH529074, that binds specifically to the p53 DBD in a saturable manner with an affinity of 1–2 μm. Binding restores wild type function to many oncogenic mutant forms of p53. This small molecule reactivates mutant p53 by acting as a chaperone, in a manner similar to that previously reported for the peptide CDB3. Binding of SCH529074 to the p53 DBD is specifically displaced by an oligonucleotide with a sequence derived from the p53-response element. In addition to reactivating mutant p53, SCH529074 binding inhibits ubiquitination of p53 by HDM2. We have also developed a novel variant of p53 by changing a single amino acid in the core domain of p53 (N268R), which abolishes binding of SCH529074. This amino acid change also inhibits HDM2-mediated ubiquitination of p53. Our novel findings indicate that through its interaction with p53 DBD, SCH529074 restores DNA binding activity to mutant p53 and inhibits HDM2-mediated ubiquitination.

Discovery of pyrazolo[1,5-a]pyrimidine-based CHK1 inhibitors: A template-based approach-Part 2.

Previous efforts by our group have established pyrazolo[1,5-a]pyrimidine as a viable core for the development of potent and selective CDK inhibitors. As part of an effort to utilize the pyrazolo[1,5-a]pyrimidine core as a template for the design and synthesis of potent and selective kinase inhibitors, we focused on a key regulator in the cell cycle progression, CHK1. Continued SAR development of the pyrazolo[1,5-a]pyrimidine core at the C5 and C6 positions, in conjunction with previously disclosed SAR at the C3 and C7 positions, led to the discovery of potent and selective CHK1 inhibitors.

Effects of SCH 59228, an orally bioavailable farnesyl protein transferase inhibitor, on the growth of oncogene-transformed fibroblasts and a human colon carcinoma xenograft in nude mice

Abstract The products of the Ha-, Ki-, and N-ras proto-oncogenes comprise a family of 21 kDa guanine nucleotide-binding proteins which play a crucial role in growth factor signal transduction and in the control of cellular proliferation and differentiation. Activating mutations in the ras oncogenes occur in a wide variety of human tumors. Ras proteins undergo a series of posttranslational processing events. The first modification is addition of the 15-carbon isoprene, farnesyl, to a Cys residue near the carboxy-terminus of Ras. Prenylation allows the Ras oncoprotein to localize to the plasma membrane where it can initiate downstream signalling events leading to cellular transformation. Inhibitors of the enzyme which catalyzes this step, farnesyl protein transferase (FPT), are a potential class of novel anticancer drugs which interfere with Ras function. SCH 59228 is a tricyclic FPT inhibitor which inhibits the farnesylation of purified Ha-Ras with an IC50 of 95 nM and blocks the processing of Ha-Ras in Cos cells with an IC50 of 0.6 M. SCH 59228 has favorable pharmacokinetic properties upon oral dosing in nude mice. The in vivo efficacy of SCH 59228 was evaluated using a panel of tumor models grown in nude mice. These included several rodent fibroblast lines expressing mutationally-activated (val12) forms of the Ha-Ras oncogene. In some cases, these proteins contain their native C-terminal sequence (CVLS) which directs farnesylation. In one model, the C-terminal sequence was altered to CVLL, making the expressed protein a substrate for a distinct prenyl transferase, geranylgeranyl protein transferase-1. When dosed orally at 10 and 50 mg/kg (four times a day, 7 days a week) SCH 59228 significantly inhibited tumor growth of cells expressing farnesylated Ha-Ras in a dose-dependent manner; over 90% growth inhibition was observed at the 50 mg/kg dose. Tumor growth of cells expressing the geranylgeranylated form of Ha-Ras was less potently inhibited. Growth of tumors derived from a rodent fibroblast line expressing activated Ki-Ras containing its native C-terminal sequence (CVIM), which preferentially directs farnesylation, was also inhibited by SCH 59228. Inhibition in the Ki-Ras model was less than that observed in the Ha-Ras model. In contrast, tumors derived from cells transformed with the mos oncogene were not significantly inhibited even at the highest dose level. SCH 59228 also significantly and dose-dependently inhibited the growth of human colon adenocarcinoma DLD-1 xenografts (which express activated Ki-ras). These results indicate that SCH 59228 possesses in vivo antitumor activity upon oral dosing in tumor models expressing activated ras oncogenes. This is the first report of oral antitumor activity with an FPT inhibitor. These results are discussed in light of recent observations on alternative prenylation of some Ras isoforms.

Antitumor 8-chlorobenzocycloheptapyridines: a new class of selective, nonpeptidic, nonsulfhydryl inhibitors of ras farnesylation.

Ras farnesylation by farnesyl protein transferase (FPT) is an intracellular event that facilitates the membrane association of the ras protein and is involved in the signal transduction process. FPT inhibition could be a novel, noncytotoxic method of treating ras dependent tumor growth. We report here three structural classes of 8-chlorobenzocycloheptapyridines as novel, nonpeptidic, nonsulfhydryl FPT inhibitors having antitumor activity in mice when dosed orally. We discuss structural and conformational aspects of these compounds in relation to biological activities as well as a comparison to the conformation of a bound tetrapeptide FPT inhibitor.

Kijanimicin. Part 3. Structure and absolute stereochemistry of kijanimicin

Kijanimicin, a novel antibiotic from Actinomadura kijaniata nov. sp. SCC1256 (ATCC 31588), has been shown by chemical degradation, spectroscopic studies, and X-ray crystallographic studies to have a unique tetronic acid structure. The molecule contains a branched chain tetrasaccharide moiety consisting of three units of 2,6-dideoxy-α-L-ribo-hexopyranose and one unit of 2,6-dideoxy-4-O-methyl-β-L-ribo-hexopyranose. The molecule also contains a novel nitrosugar, namely 2,3,4,6-tetradeoxy-4-methoxy-carbonylamino-3-C-methyl-3-nitro-β-D-xylo-hexopyranose (D-kijanose), which is the third nitrosugar to be isolated from an antibiotic. The structure of L-rubranitrose is revised to D-rubranitrose. Evidence for the total structure, the absolute stereochemistry, and the solution conformation of kijanimicin is presented.

Novel 3-O-α-L-cladinosyl sixteen-membered macrolide antibacterials

A novel series of 3-O-α-L-cladinosyl sixteen-membered macrolide antibacterials has been synthesized by glycosidation of the 3-hydroxy group of 12,13-de-epoxy-12,13-didehydrorosaramicin, 12,13-de-epoxy-12,13-didehydro-20-deoxorosaramicin, desmycosin, 20-deoxodesmycosin, and 19-deformyldesmycosin. The glycosidation was effected by reaction of the suitably protected macrolide substrates with the 1-S-pyridyl derivative of L-cladinose in the presence of either anhydrous silver perchlorate or anhydrous silver trifluoromethanesulphonate to afford the 3-O-α-glycosides in good yield.

5-Benzothiazole substituted pyrimidine derivatives as HCV replication (replicase) inhibitors

Based on a previously identified HCV replication (replicase) inhibitor 1, SAR efforts were conducted around the pyrimidine core to improve the potency and pharmacokinetic profile of the inhibitors. A benzothiazole moiety was found to be the optimal substituent at the pyrimidine 5-position. Due to potential reactivity concern, the 4-chloro residue was replaced by a methyl group with some loss in potency and enhanced rat in vivo profile. Extensive investigations at the C-2 position resulted in identification of compound 16 that demonstrated very good replicon potency, selectivity and rodent plasma/target organ concentration. Inhibitor 16 also demonstrated good plasma levels and oral bioavailability in dogs, while monkey exposure was rather low. Chemistry optimization towards a practical route to install the benzothiazole moiety resulted in an efficient direct C-H arylation protocol.

Semisynthetic macrolide antibacterials derived from tylosin. Synthesis of 3-O-acetyl-23-O-demycinosyl-4″-O-isovaleryltylosin and related compounds, as well as the 12,13-epoxy derivatives

Selective acylation techniques have been developed that enable the synthesis of 3-O-acetyl-4″-O-isovaleryltylosin and 3-O-acetyl-23-O-demycinosyl-4″-O-isovaleryltylosin to be carried out in an efficient manner starting from tylosin. The syntheses of the 2′-O-acetyl, 23-O-acetyl, and 2′,23-di-O-acetyl derivatives of the latter are also described. The synthesis of key hydrazones is also described. The regio- and stereo-selective epoxidation of tylosin and its acyl derivatives afforded the 12,13-epoxy analogues, which were used to synthesize novel acylated 12,13-epoxy derivatives of 23-O-demycinosyltylosin.

Novel semisynthetic oxo and alkyl macrolide antibacterials and related derivatives

An efficient method of protecting the 10,11-double bond in dienone and epoxy enone 16-membered macrolides has been developed. This involves Michael addition of thioacetic S-acid to the 10,11-ene to give exclusively the 11 -acetylthio derivatives, which can be smoothly deprotected by treatment with fluoride ion. The protected intermediates have been used to prepare a novel class of macrolide antibacterials in which the aldehyde group has been converted into an alkyl ketone by reaction with the appropriate diazoalkane. Thus 20-oxo analogues of rosaramicin, 12,13-de-epoxy-12,13-dehydrorosaramicin, tylosin, and desmycosin have been prepared. The reaction of diazomethane with unprotected macrolides has also been studied including the synthesis of 18-C-methyl-3″-O-propionyll-eucomycin A5. Derivatives in which the 20-formyl group has been replaced by methyl and by halogeno groups, as well as derivatives having a 2,3-ene are described. A number of base-catalyzed rearrangement products including desmycosin 8β,20α-aldol and desmycoin 8α,20β-aldol are also described.