Single-agent inhibition of Chk1 is antiproliferative in human cancer cell lines in vitro and inhibits tumor xenograft growth in vivo

Chk1 is a serine/threonine kinase that plays several important roles in the cellular response to genotoxic stress. Since many current standard-of-care therapies for human cancer directly damage DNA or inhibit DNA synthesis, there is interest in using small molecule inhibitors of Chk1 to potentiate their clinical activity. Additionally, Chk1 is known to be critically involved in cell cycle progression of unperturbed cells. Therefore, it is plausible that treatment with a Chkl inhibitor alone could also be an efficacious cancer therapy. Here we report that Chk1-A, a potent and highly selective small molecule inhibitor of Chk1, is antiproliferative as a single agent in a variety of human cancer cell lines in vitro. The inhibition of proliferation is associated with collapse of DNA replication and apoptosis. Rapid decreases in inhibitory phosphorylation of CDKs and a concomitant increase in CDK kinase activity and chromatin loading of Cdc45 suggest that the antiproliferative and proapoptotic activity of Chk1-A is at least in part due to deregulation of DNA synthesis. We extend these in vitro studies by demonstrating that Chk1-A inhibits the growth of tumor xenografts in vivo in a treatment regimen that is well tolerated. Together, these results suggest that single-agent inhibition of Chk1 may be an effective treatment strategy for selected human malignancies.

Abstract 3874: Single-agent Chk1 inhibition is anti-proliferative in leukemia cells in vitro and in vivo

Chk1 is a serine/threonine kinase that plays important roles in the cellular response to genotoxic stress. For this reason, there is a great deal of interest in using inhibitors of Chk1 to potentiate the effects of DNA-damaging chemotherapeutics. In addition, multiple studies have demonstrated that Chk1 activity is essential during an unperturbed cell cycle to ensure proper DNA replication and maintain genomic integrity. Therefore, it is plausible that a Chk1 inhibitor could also be efficacious as a single-agent therapeutic for human cancer. Here we show that treatment with Chk1-A, a potent and selective inhibitor of Chk1, alone is anti-proliferative against a wide array of cancer cell lines with varying degrees of potency. We sought to understand the mechanisms by which Chk1 inhibition derives the observed anti-proliferative effect. Employing the human leukemia cell line HEL92.1.7, a line particularly sensitive to Chk1 inhibition in terms of proliferation, we characterized the biochemical and functional effects of Chk1-A treatment. We observed concentration-dependent increases in phosphorylation of H2A. X, Chk1, and Chk2, which are markers of DNA damage and cell-cycle checkpoint activation. These biochemical events correlated with S-phase accumulation and eventual apoptosis. In vivo, we found that HEL92.1.7 tumor xenografts were sensitive to oral administration of Chk1-A at a dose that was well tolerated. Together, these studies suggest that inhibition of Chk1 results in DNA damage that induces apoptosis and that use of a Chk1 inhibitor as a single-agent could be an effective strategy to treat certain types of human cancers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3874.

Abstract B254: Extended target-coverage by selective Chk1 inhibitors enhances pharmacodynamic inhibition of Chk1 signaling and antitumor activity in vivo

Loss of coordination between cell cycle checkpoints and DNA damage repair is a fundamental feature tumor cells rely on for unregulated growth and developing chemotherapeutic resistance. The protein kinase Checkpoint kinase 1 (Chk1) is a sentinel molecule essential for cell cycle arrest at the S and G2M checkpoints, as well as regulating homologous recombination DNA repair. In tumor cells exposed to chemotherapy, Chk1 inhibition overrides cell cycle arrest and DNA repair functions, effectively driving tumor cells into a state of mitotic catastrophe and, ultimately, cell death. We have previously reported in schedule-dependence studies, using Chk1 inhibitors and irinotecan (CPT-11), that oral administration of Chk1 inhibitors allows for multi-day target-coverage, and thus continuous inhibition of Chk1 for a finite period of time, which maximizes anti-tumor efficacy. Here, we extend these studies and investigate the pharmacodynamic relationship to efficacy, as well as the specific biomarkers that are predictive of an anti-tumor effect, when Chk1 inhibitors are administered on a multi-day dosing schedule. Utilizing potent (IC50=24–27nM), selective, and orally bio-available small molecule Chk1 inhibitors of which Chk1-A and Chk1-C are representative, we find only modest inhibition of the functional biomarker phospho-cdc2, following a single dose of a Chk1 inhibitor. Alternatively, on multi-day Chk1 inhibitor dose schedules, we find dose-related pharmacodynamic inhibition of Chk1 signaling that is maximized at doses where we see significant tumor growth inhibition in efficacy experiments. Furthermore, multi-day dosing of Chk1 inhibitors induces marked inhibition of phospho-cdc2 and Rad51 protein levels, suggesting tumoricidal activity related to Chk1 inhibition is due to both checkpoint override and impairment of DNA damage repair. In human tumor xenografts administered combination therapy with gemcitabine, an orally-delivered Chk1 inhibitor dosed on a multi-day schedule shows superior efficacy over an IV administered compound. Taken together, our findings show a clear correlative relationship between pharmacodynamic target inhibition and anti-tumor activity that is exclusively achieved on multi-day dose schedules. These results demonstrate the need for prolonged Chk1 inhibition to provide robust pharmacodynamic inhibition and maximal anti-tumor efficacy.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B254.

Glyoxylic Acid and MP-Glyoxylate: Efficient Formaldehyde Equivalents in the 3-CC of 2-Aminoazines, Aldehydes, and Isonitriles

[reaction: see text] Glyoxylic acid, either in solution or immobilized on MP-carbonate (MP-glyoxylate), participates in an uncatalyzed 3-CC with 2-aminoazines and isonitriles to afford novel 2-unsubstituted-3-amino-imidazoheterocycles. MP-glyoxylate serves as a particularly efficient and experimentally convenient formaldehyde equivalent and readily liberates products through decarboxylation/self-release from the resin. These examples furthermore constitute the first application in which MP-CO3 serves as a solid support for transformations involving carboxylic acids.

Small molecule modulators of endogenous and co-chaperone-stimulated Hsp70 ATPase activity

The molecular chaperone and cytoprotective activities of the Hsp70 and Hsp40 chaperones represent therapeutic targets for human diseases such as cancer and those that arise from defects in protein folding; however, very few Hsp70 and no Hsp40 modulators have been described. Using an assay for ATP hydrolysis, we identified and screened small molecules with structural similarity to 15-deoxyspergualin and NSC 630668-R/1 for their effects on endogenous and Hsp40-stimulated Hsp70 ATPase activity. Several of these compounds modulated Hsp70 ATPase activity, consistent with the action of NSC 630668-R/1 observed previously (Fewell, S. W., Day, B. W., and Brodsky, J. L. (2001) J. Biol. Chem. 276, 910-914). In contrast, three compounds inhibited the ability of Hsp40 to stimulate Hsp70 ATPase activity but did not affect the endogenous activity of Hsp70. Two of these agents also compromised the Hsp70/Hsp40-mediated post-translational translocation of a secreted pre-protein in vitro. Together, these data indicate the potential for continued screening of small molecule Hsp70 effectors and that specific modulators of Hsp70-Hsp40 interaction can be obtained, potentially for future therapeutic use.

Dual-specificity phosphatases as targets for antineoplastic agents

Dual-specificity protein phosphatases are a subclass of protein tyrosine phosphatases that are uniquely able to hydrolyse the phosphate ester bond on both a tyrosine and a threonine or serine residue on the same protein. Dual-specificity phosphatases have a central role in the complex regulation of signalling pathways that are involved in cell stress responses, proliferation and death. Although this enzyme family is increasingly the target of drug discovery efforts in pharmaceutical companies, a summary of the salient developments in the biology and medicinal chemistry of dual-specificity phosphatases has been lacking. We hope that this comprehensive overview will stimulate further progress in the development of small-molecule inhibitors that could form the basis for a new class of target-directed therapeutic agents.

Teaching social workers to use psychological assessment data

Psychological assessments of children and parents are frequently used by social service caseworkers when making case planning decisions. Often, however, the two disciplines--psychology and social work--have difficulty collaborating in and coordinating their respective work. Caseworkers may lack formal training in how to understand and use psychological reports. Psychologists may lack formal training in forensic assessment and in understanding the constraints of the social service and child welfare systems. This article describes how caseworkers may become more sophisticated consumers of psychological assessments, and how collaborative relationships between evaluating psychologists and caseworkers can be fostered.

A validity study of the social skills rating system-teacher version with disabled and nondisabled preschool children

This study examined the differences among social skills and problem behaviors of disabled (n = 22) and nondisabled (n = 27) preschoolers on Social Skills Rating System-Teacher Version. Significant differences were found between the two groups on all measures of social skills and all but one measure (internalizing problems) of problem behaviors. Also, correlations with a measure of social competence and 8 teachers' ratings strongly supported the validity of this measure of social skills for preschool children. Implications for designing early intervention programs are discussed.

A comparison between WISC-III and WISC-R scores for learning disabilities reevaluations

This study examined differences between Wechsler Intelligence Scale for Children-Third Edition (WISC-III) and Wechsler Intelligence Scale for Children-Revised (WISC-R) scores for 40 students with learning disabilities (LD) at the time of their triennial reevaluations. WISC-III Full Scale, Verbal, and Performance IQs were significantly lower than comparable WISC-R IQs by approximately one-third to one-half of a standard deviation. Correlations among the IQ scores were moderate to moderately strong. Implications of these findings for LD reevaluations are discussed.

A confluent model of outcomes for adult children of alcoholics: implications for assessment, treatment, and research

Current conceptions of adult children of alcoholics do not account for recent suggestions that characteristics used to describe them are not valid. These conceptions do not explain the documented heterogeneity with regard to life and therapeutic outcomes. In this paper, an alternative model of outcomes is formulated. This model is based on self-schema theory, behavioral self-regulation and self-efficacy, the influences of the "ecological environment," and objective signs and subjective symptoms of dysfunction. It is argued that the model provides a better "fit" to the empirical data concerning outcomes and carries implications for assessment, treatment, and research.

Academic self-concept as a predictor of achievement for a sample of elementary school students

This study examined the relationship of academic self-concept scores of 122 children with their achievement in Grade 6 as compared to general self-concept and locus of control. Academic self-concept correlated significantly higher with teachers' grades and standardized measures of achievement than either general self-concept or locus of control. A multiple regression analysis also confirmed the potential usefulness of academic self-concept for predicting students' achievement. Academic self-concept may be a more useful construct in helping understand students' achievement than frequently administered measures of general self-concept.

Comparison of K-ABC performance between at-risk and normal preschool children

This study examined differences in K-ABC performance between at-risk (n = 44) and normal (n = 49) preschool children. For the group at-risk, all of the mean global scores on the K-ABC clustered around a standard score of approximately 90. The normal group's mean scores were 15 to 21 standard-score points higher and clustered near 110. The results of t tests for independent samples indicated that the normal group's scores on both the global scales and K-ABC subtests were significantly higher than the at-risk group's scores in nearly every instance. Correlations among scores were consistent with previous findings for preschoolers on the K-ABC. For the normal group, correlations obtained among the global scales were nearly identical to those reported for the standardization sample. For the at-risk group, however, the correlation of .75 between Sequential processing and Achievement was higher than that (.58) between Simultaneous processing and Achievement.

The premenstrual syndrome. A survey of current treatment practices

Interest in the premenstrual syndrome (PMS) has increased rapidly in both the lay and professional communities during the past few years. Research on the causes, diagnosis and treatment of the disorder continues to expand. An area that has received little attention, however, is the current treatment practices of physicians who recognize PMS as a treatable disorder. Our study was a survey of 502 physicians from the United States and Canada regarding diagnostic and treatment services provided to their PMS patients. Descriptive results of the survey, as well as breakdowns by medical specialty and region, were obtained. The results have implications for current practice and future research.