Deficiencies in DNA repair (mismatch repair deficiencies in colon cancers, nucleotide excision repair in ovarian and testicular cancers, and in melanomas), deficiencies in cell cycle checkpoints (Rb, p53, BRCA1, BRCA2, and Chk2 deficiencies in solid tumors), and apoptosis (APC mutations in colon cancers, Bcr-Abl recombinations in leukemia, Bcl-2 overexpression in lymphomas) promote cancers. They also contribute to therapeutic responses and resistance to chemotherapy by precluding normal apoptotic response of tumor cells.To integrate these alterations within the emerging cellular network of molecular pathways, we have developed a mapping convention that can be visually represented as molecular interaction maps (MIMs). These maps are being presented by different members of the LMP (Dr. Kohn, Dr. Aladjem, and Dr. Pommier) at different meetings. They are published in international journals with high impact factors and we have developed an interactive Website in collaboration with the LMP Bioinformatic group (Dr. Weisntein) (http://discover.nci.nih.gov/mim).We are studying several new drugs in preclinical and early clinical development including agents from the NCI-Developmental Therapeutics Program (DTP). We are focusing on drugs that alter chromatin and cell cycle progression such as methanesulfonate derivatives, benzothiazole, tetrandrine, aminoflavone, and FdUMP[10]. Methanesulfonates, benzothiazole, and aminoflavone induce DNA-protein crosslinks. FdUMP[10] induces Top1 cleavage complexes as a result of thymidine depletion. Aminoflavone also induces replication double-strand breaks and histone H2AX phosphorylation (gamma-H2AX). Hence, gamma-H2AX can be used as a biomarker to monitor aminoflavone activity in tumor samples. We are currently using the NCI 60 cell line database to find genes that are correlated with aminoflavone activity and can be used to select patients who should benefit from aminoflavone. We are continuing our studies with ecteinascidin 743 (Et743 - Yondelis) (NSC 648766). Clinical responses to Et743 have been observed in sarcomas, which are notoriously resistant to therapy, as well as in ovarian and breast cancer. Et743 differs from other clinically used anticancer agents because it forms covalent adducts at specific guanines in the DNA minor groove and because it selectively Et743 traps the transcription-coupled NER (TC-NER). Thus, Et743 defines a novel class of anticancer drugs in which enhanced antiproliferative activity parallels enhanced cellular DNA-repair capability. The complementary between the activities of Et-743 and cisplatin with respect to TC-NER suggests the use of Et743 in cisplatin-resistant tumors and vice-versa. A clinical protocol has been proposed for a Phase I clinical trial of Et743 in ovarian cancers resistant to cisplatin (Collaboration with Dr. Elise Kohn, Pathology Branch, CCR, NCI). Further molecular studies are planned to determine the transcription- and the strand-specific-dependence of the DNA single-strand breaks induced by Et-743. We are also looking at TC-NER-dependent transcription inhibition by microarray analyses using NER-deficient, XPD, and XPD-complemented cells and Ewing sarcoma cell lines.Because most cancers have alterations in the cell cycle checkpoint pathways (p53, pRb) and cell cycle machinery (cyclins, cyclin-dependent kinase inhibitors - such as p16), we are exploring inhibitors of cell cycle checkpoints as novel anticancer agents. 7-hydroxystaurosporine (UCN-01) is a novel anticancer agent in phase II/III clinical trials. We found that UCN-01 is synergistic with DNA damaging agents such as topoisomerase inhibitors and drugs that act during the S-phase of the cell cycle. This synergism has been related to an abrogation of the S-phase checkpoint, which is controlled by 2 protein kinases, Chk1 and Chk2.
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