Our laboratory was the first to isolate and purify an intact mammalian cell multiprotein DNA replication complex, termed the synthesome, from a variety of human cell types that was both stable and fully functional. Subsequent work revealed that the synthesome of malignant breast epithelial cells exhibits a more error-prone synthesis process than that of nonmalignant breast epithelial cells. We recently correlated the low replication fidelity of malignant cells was due at least in part to a post-translational modification of a specific protein component of the synthesome: proliferating cell nuclear antigen, or PCNA. Our laboratory developed an antibody (cancer-associated or caPCNAab) specific to the cancer-associated PCNA isoform (cancer-associated or caPCNA), providing hope of an effective diagnostic marker of malignancy. Additionally, peptides were derived from the caPCNA sequence (caPeptides) and these peptides were shown to augment the action of doxorubicin (DOX) in leukemia cells while leaving nonmalignant cells intact. caPeptides may possess anti-cancer therapeutic potential through blocking the association of caPCNA with its binding partners involved in DNA replication and repair. The objective of this study was to determine the mechanism by which caPeptides directed against caPCNA induced cancer cell cytotoxicity. Breast cancer cells from a patient harboring a hereditary mutation in BRCA1, a major component of DNA double strand break repair (HCC1937 cells), were used in this study. As a genetically matched control, the wild-type breast cancer 1 early onset gene (BRCA1) was transduced into HCC1937 cells (referred to as HCC1937 + wild-type BRCA1). MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays were conducted with caPeptides at a variety of timepoints both alone and in combination with DNA damaging agent cisplatin in HCC1937 and HCC1937 + wild-type BRCA1 cells. The data suggests cells lacking wild-type BRCA1 show increased sensitivity to caPeptides in comparison to isogenic controls transduced with wild-type BRCA1. We show that caPeptides augment the action of DNA damaging agent cisplatin. Furthermore, caPeptides containing amino acid substitutions in specific sites within the peptide show enhanced cytotoxicity over wild-type caPeptides. This work may provide information useful in a clinical setting as caPeptides could benefit a particular subset of breast cancer patients. Additionally, caPeptide studies may shed light on the deregulated replication and repair processes common in cancer.

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 683.