Current inhibitors of checkpoint kinase 2.

Checkpoint kinase 2 is a serine/threonine protein which functions as an important transducer in apoptosis or DNA repair following activation by DNA damage. Inhibition of checkpoint kinase 2 is thought to sensitize p53-mutated or p53-deficient cancerous cells but protect normal tissue following DNA-damage caused by ionizing radiation or chemotherapeutic agents. The development of checkpoint kinase inhibitors for the treatment of cancer has therefore been a major objective in drug discovery over the past decade. Several inhibitors have been co-crystallized in the active site of checkpoint kinase 2 revealing important features of effective inhibitors. Some of these inhibitors have entered clinical trials in the last decade. This review describes and discusses the most recent inhibitors of checkpoint kinase 2 as reported in the literature, including an evaluation of biological activity.

Preparation of hymenialdisine, analogues and their evaluation as kinase inhibitors.

The natural product hymenialdisine was first isolated in 1980 from the marine sponges of the genera Hymeniacidon, Acanthella, Axinella and Pseudaxinyssa. The structure was elucidated on the basis of X-ray crystallography demonstrating a structurally interesting pyrrole-azepin-8-one ring system bonded to a glycocyamidine ring. Great interest has been taken in synthesizing this type of scaffold due to its potent activity in competitive kinase inhibition. In addition, several patents have claimed pharmacological use of these compounds for prevention and treatment of different diseases. The challenging syntheses of hymenialdisine and its analogues are described in this review as well as their evaluation as kinase inhibitors.

FR900482 class of anti-tumor drugs cross-links oncoprotein HMG I/Y to DNA in vivo.

BACKGROUND: Overexpression of the high-mobility group, HMG I/Y, family of chromatin oncoproteins has been implicated as a clinical diagnostic marker for both neoplastic cellular transformation and increased metastatic potential of several human cancers. These minor groove DNA-binding oncoproteins are thus an attractive target for anti-tumor chemotherapy. FR900482 represents a new class of anti-tumor agents that bind to the minor groove of DNA and exhibit greatly reduced host toxicity compared to the structurally related mitomycin C class of anti-tumor drugs. We report covalent cross-linking of DNA to HMG I/Y by FR900482 in vivo which represents the first example of a covalent DNA-drug-protein cross-link with a minor groove-binding oncoprotein and a potential novel mechanism through which these compounds exert their anti-tumor activity. RESULTS: Using a modified chromatin immunoprecipitation procedure, fragments of DNA that have been covalently cross-linked by FR900482 to HMG I/Y proteins in vivo were polymerase chain reaction-amplified, isolated and characterized. The nuclear samples from control cells were devoid of DNA fragments whereas the nuclear samples from cells treated with FR900482 contained DNA fragments which were cross-linked by the drug to the minor groove-binding HMG I/Y proteins in vivo. Additional control experiments established that the drug also cross-linked other non-oncogenic minor groove-binding proteins (HMG-1 and HMG-2) but did not cross-link major groove-binding proteins (Elf-1 and NFkappaB) in vivo. Our results are the first demonstration that FR900482 cross-links a number of minor groove-binding proteins in vivo and suggests that the cross-linking of the HMG I/Y oncoproteins may participate in the mode of efficacy as a chemotherapeutic agent. CONCLUSIONS: We have illustrated that the FR class of anti-tumor antibiotics, represented in this study by FR900482, is able to produce covalent cross-links between the HMG I/Y oncoproteins and DNA in vivo. The ability of this class of compounds to cross-link the HMG I/Y proteins in the minor groove of DNA represents the first demonstration of drug-induced cross-linking of a specific cancer-related protein to DNA in living cells. We have also demonstrated that FR900482 cross-links other minor groove-binding proteins (HMG-1 and HMG-2 in the present study) in vivo; however, since HMG I/Y is the only minor groove-binding oncoprotein presently known, it is possible that these non-histone chromatin proteins are among the important in vivo targets of this family of drugs. These compounds have already been assessed as representing a compelling clinical replacement for mitomycin C due to their greatly reduced host toxicity and superior DNA interstrand cross-linking efficacy. The capacity of FR900482 to cross-link the HMG I/Y oncoprotein with nuclear DNA in vivo potentially represents a significant elucidation of the anti-tumor efficacy of this family of anticancer agents.

Structure-activity relationship for DNA topoisomerase II-induced DNA cleavage by azatoxin analogues.

Eighteen analogues of the nonintercalative DNA topoisomerase II (topo II)-active epipodophyllotoxin-ellipticine hybrid, azatoxin, were synthesized and evaluated for their ability to induce topo II-mediated DNA strand breaks in vitro. In general, the SAR profile of the azatoxins showed more homology with that of the epipodophyllotoxins than with the ellipticines. Of the compounds studied, only fluoro substitution at the 8-, 9, and 10-positions of azatoxins enhanced activity, with 9-fluoroazatoxin being the most active compound in this series.

Inhibition of DNA topoisomerase II by azaelliptitoxins functionalized in the variable substituent domain.

A series of novel C11-substituted derivatives of azaelliptitoxin (azatoxin) have been synthesized and tested for their inhibitory activity against human DNA topoisomerase II. Incorporation of a C11 polyamine or amine resulted in an increase in the intercalation properties of the drug and a decrease of topoisomerase II activity. The structure-activity relationship (SAR) profile of the nonintercalating C11 anilino azatoxin class follows the SAR of the (anilino)acridine family. 11-(4-Cyanoanilino)azatoxin (14) was found to be the most active analog in this series, exhibiting approximately 10-fold higher activity than azatoxin 12 and etoposide.