Prodrug esters of the indolocarbazole CEP-751 (KT-6587)

Design and synthesis of N-methylmaleimide indolocarbazole bearing modified 2-acetamino acid moieties as Topoisomerase I inhibitors

A novel series of N-methylmaleimide indolocarbazole derivatives bearing modified 2-acetamino acid moieties are first reported. The cytotoxic effects of these compounds were tested in five human tumor cell lines. The potent compounds 9a, 9b, 9d, and 9e have been further evaluated for their effect on Topoisomerase I (TOPO I) and cancer cell cycle. It is concluded that the indolocarbazoles with alkyl piperazine or morpholine substituent groups instead of esters or glycosyl residues would have better activities against tumors.

Indolocarbazole natural products: occurrence, biosynthesis, and biological activity

The indolocarbazole family of natural products, including the biosynthetically related bisindolylmaleimides, is reviewed (with 316 references cited). The isolation of indolocarbazoles from natural sources and the biosynthesis of this class of compounds are thoroughly reviewed, including recent developments in molecular genetics, enzymology and metabolic engineering. The biological activities and underlying modes of action displayed by natural and synthetic indolocarbazoles is also presented, with an emphasis on the development of analogs that have entered clinical trials for its future use against cancer or other diseases.

Phase I trial of orally administered CEP-701, a novel neurotrophin receptor-linked tyrosine kinase inhibitor

PURPOSE

A phase I clinical trial in patients with advanced carcinomas was conducted using the orally available neurotrophin receptor-linked tyrosine kinase receptor inhibitor, CEP-701. The objectives were to determine the maximum tolerated dose (MTD), dose-limiting toxicities, and pharmacokinetic profile of this orally administered agent.

PATIENTS AND METHODS

A total of 30 patients were accrued to receive escalating BID doses of CEP-701 in cycles lasting 28 days. Between 3 and 6 patients were enrolled at each dose level. Once the MTD was determined, nine de novo patients were recruited to receive that level of drug. Pharmacokinetic studies were performed after the first dose, with additional sampling to assess intraindividual variability.

RESULTS

The dosages ranged from 5 mg BID to 160 mg BID. While the criteria for MTD were not met at the dose levels administered, DLTs were observed at 80 and 120 mg BID. Treatment related adverse events, especially of the gastrointestinal system, made CEP-701 poorly tolerated at dosages above 40 mg BID. While CEP-701 did not produce an objective tumor response in any patient, 7 of the 30 patients received treatment for 3 months or more, including 3 who were on study with stable disease for more than 6 months. Orally administered CEP-701 was rapidly absorbed, with a mean t(max) between 1 and 3 hours. At higher dose levels, serum drug levels showed greater than dose-proportional increases by Day 28 versus Day 1.

CONCLUSION

CEP-701 40 mg BID was well tolerated by patients with advanced malignancy and is the recommended dose level for planned phase II trials. Further study is necessary to determine the clinical efficacy of this novel new chemotherapeutic agent.

Synthesis, Modeling, and In Vitro Activity of (3‘S)-epi-K-252a Analogues. Elucidating the Stereochemical Requirements of the 3‘-Sugar Alcohol on trkA Tyrosine Kinase Activity

Utilizing our recently published semisynthetic approach to the (3'S)-K-252a diastereomer, we report the first synthesis of the (3'R)-10 diastereomer and a set of related epimers, with the goal of defining the stereochemical role of the 3'-sugar hydroxyl group on trkA tyrosine kinase activity and selectivity. (3'R)-10 displayed potent trkA inhibitory activity with an IC50 value of 4 nM. The corresponding deshydroxy epimer (3'S)-14 was 7-fold more potent than its 3'R counterpart (natural stereochemistry) with a trkA IC50 value of 3 nM and demonstrated >280-fold selectivity over PKC (IC50 = 850 nM). In cells, (3'S)-14 displayed potent inhibition of trkA autophosphorylation with an IC50 < 10 nM. Molecular modeling studies revealed that the 3'-OH, due to the inverted geometry, forms significant H-bonding interactions with Glu27 and Arg195, an interaction that is not attainable with the natural isomers.

Synthesis and Target Identification of Hymenialdisine Analogs

Hymenialdisine (HMD) is a sponge-derived natural product kinase inhibitor with nanomolar activity against CDKs, Mek1, GSK3beta, and CK1 and micromolar activity against Chk1. In order to explore the broader application of the pyrrolo[2,3-c]azepine skeleton of HMD as a general kinase inhibitory scaffold, we searched for additional protein targets using affinity chromatography in conjunction with the synthesis of diverse HMD analogs and profiled HMD against a panel of 60 recombinant enzymes. This effort has led to nanomolar to micromolar inhibitors of 11 new targets including p90RSK, KDR, c-Kit, Fes, MAPK1, PAK2, PDK1, PKCtheta, PKD2, Rsk1, and SGK. The synthesis of HMD analogs has resulted in the identification of compounds with enhanced and/or dramatically altered selectivities relative to HMD (28n) and in molecules with antiproliferative activities 30-fold higher than HMD (28p).

A New Class of Potent Vascular Endothelial Growth Factor Receptor Tyrosine Kinase Inhibitors: Structure−Activity Relationships for a Series of 9-Alkoxymethyl-12-(3-hydroxypropyl)indeno[2,1-a]pyrrolo[3,4-c]carbazole-5-ones and the Identification of CEP-5214 and Its Dimethylglycine Ester Prodrug Clinical Candidate CEP-7055

A series of potent vascular endothelial growth factor R2 (VEGF-R2) tyrosine kinase inhibitors from a new indenopyrrolocarbazole template is reported. The structure-activity relationships for a series of 9-alkoxymethyl-12-(3-hydroxypropyl)indeno[2,1-a]pyrrolo[3,4-c]carbazole-5-ones revealed an optimal R9 substitution with ethoxymethyl 19 (VEGF-R2 IC(50) = 4 nM) and isopropoxymethyl 21 (VEGF-R2 IC(50) = 8 nM) being the most potent inhibitors in the series. The VEGF-R2 activity was reduced appreciably by increasing the size of the R9 alkoxy group or by alpha-methyl branching adjacent to the ring. The combined R9 alkoxymethyl and N12 hydroxypropyl substitutions were required for potent VEGF-R2 activity, and the corresponding thioether analogues were weaker than their ether counterparts. Compound 21 (R9 isopropoxymethyl, CEP-5214) was identified as a potent, low-nanomolar pan inhibitor of human VEGF-R tyrosine kinases, displaying IC(50) values of 16, 8, and 4 nM for VEGF-R1/FLT-1, VEGF-R2/KDR, and VEGF-R3/FLT-4, respectively, with cellular activity equivalent to the isolated enzyme activity. Compound 21 exhibited good selectivity against numerous tyrosine and serine/threonine kinases including PKC, Tie2, TrkA, CDK1, p38, JNK, and IRK. To increase water solubility and oral bioavailability, the N,N-dimethylglycine ester 40 was prepared. In pharmacokinetic studies in mice and rats, increased plasma levels of 21 were observed after oral administration of 40. Compound 21 demonstrated significant in vivo antitumor activity in numerous tumor models and was advanced into phase I clinical trials as the water-soluble N,N-dimethylglycine ester prodrug 40 (CEP-7055).

ATP site-directed competitive and irreversible inhibitors of protein kinases

Several tyrosine and serine/threonine protein kinases have emerged in the last few years as attractive targets in the search for new therapeutic agents being applicable in many different disease indications. Initially, inhibition of these protein kinases by ATP site-directed inhibitors was considered less prone to success, but medicinal chemists from both academia and industry have been able to impart potency and selectivity to a limited number of scaffolds by modulating and fine-tuning the interactions of the modified template with the ATP binding site of the selected kinase. The chemical templates that have been used in the synthesis of ATP site-directed protein kinase inhibitors are reviewed with emphasis on the kinase inhibitors that have entered or are about to enter clinical trials. Examples have been selected to illustrate how structure-based design approaches and new methods to increase compound diversity have had an impact on this area of research.