M. Eileen Dolan, Ph.D.

Modulation of DNA Repair to Enhance Chemotherapy

Research Summary

    Recent advances in genome research have suggested strong associations between genetic factors and complex human traits, such as an individual’s disease susceptibility, response to therapy, and gene expression levels. The objective of our work is to identify genetic determinants contributing to cellular susceptibility to chemotherapeutic agents. Most chemotherapeutic drugs exhibit serious toxicity; hence elucidating the genetic variants that alter their pharmacodynamic effects is an important but challenging project. Challenges include our inability to do family studies evaluating the effects of chemotherapy on individuals without cancer and the multigenic nature of drug response. Therefore, we have developed several cell based models to identify genetic variants important in chemotherapeutic-induced toxicity. The models employ EBV-transformed lymphoblastoid cell lines from related healthy Caucasians of European descent (CEPH) and Yorubans of African descent to evaluate chemotherapeutic-induced cytotoxicity and/or apoptosis. These family-based cell lines allow us to apply familial genetic strategies to determine the heritability and the genetic components contributing to complex phenotypes such as susceptibility to chemotherapy. The pedigrees have microsatellite and SNP data available for linkage mapping studies. Furthermore, the HapMap trios contained within these large pedigrees have over 3 million SNPs genotyped. We have performed expression array to allow for studies of population differences in gene expression and cellular susceptibility to chemotherapy.  Our laboratory was the first to demonstrate susceptibility to chemotherapy-induced cytotoxicity is significantly heritable and that susceptibility to chemotherapeutic toxicity in Caucasians and Africans is significantly different for certain drugs. Our long-term goal is to identify genetic variants and gene expression, including those in an underserved population that predict risk for adverse reactions to chemotherapeutic agents.

    Previous to my interest in whole genome studies to improve chemotherapy, my laboratory took a candidate gene approach to evaluate the contribution of a DNA repair protein (MGMT) to resistance to chemotherapeutic alkylating agents.  We developed O6-benzylguanine (BG), an inactivator of the MGMT protein based on our understanding of the substrate specificity of the repair protein and the SN2 bimolecular nature of the reaction. The preclinical and clinical development of BG has been a major focus of my laboratory. We incorporated biochemical, pharmacokinetic, pharmacodynamic and metabolic correlative studies into clinical trials. We identified the enzymes responsible for conversion of BG to its metabolites and studied drug-drug interactions. We recently found that BG enhances the toxicity of other bi-functional agents (i.e. cisplatin, carboplatin) not known to produce an O6-guanine adduct. Enhancement is independent of AGT status indicating a separate and novel mechanism that we are currently investigating.

Selected Papers

Long L, and Dolan ME. (2001).  Role of CYP450 isoenzymes in metabolism of O⁶-benzylguanine: Implications for dacarbazine activation.  Clinical Cancer Res., 7:4239-4244.

Fishel ML, Delaney SM, Friesen LD, Hansen RJ, Zuhowski EG, Moschel RC, Egorin MJ, and Dolan ME. (2003). Enhancement of platinum-induced cytotoxicity by O⁶-benzylguanine.  Molec Cancer Ther, 2:633-640.

Nagasubramanian R, Dolan ME. (2003). Pharmacogenomics: Racing toward personalized prescriptions. J Lab Med, 9:651-659.

Wu MH, Chen P, Wu X, Liu W, Strom S, Das S, Cook EH, and Dolan ME. (2004). Determination and analysis of single nucleotide prolymorphisms and haplotype structure of the human carboxylesterase 2 gene. Pharmacogenetics, 14:1-11.

Dolan ME, Newbold KG, Nagasubramanian R, Wu X, Ratain MJ, Cook EH, and Badner JA. (2004). Heritability and linkage analysis of sensitivity to cisplatin-induced cytotoxicity. Cancer Res 64(12):4353-4356.

Shukla SJ and Dolan ME. (2005). Use of CEPH and nonCEPH cells in pharmacogenetic studies. Pharmacogenomics, 6:303-310.

Hansen RJ, Nagasubramanian R, Delaney SM, Cherian MM, Kogan SC, Lin S, Dolan ME. (2005). Role of O⁶-alkylguanine-DNA alkyltransferase in protecting against BCNU-induced long-term toxicities.  JPET, 315:1247-1255.

Rabik CA, Njoku MC and Dolan ME. (2006). Inactivation of O⁶-alkylguanine DNA alkyltransferase as a means to enhance chemotherapy. Cancer Treatment Reviews, 32:261-276.

Rabik CA, Dolan ME. (2006). Molecular Mechanisms of Platinating Agents’ Reistance Toxicity. Cancer Treatment Reviews, 32: 261-276.

Huang RS, Kistner EO, Bleibel WK, Shukla SJ, Dolan ME. (2007). Effect of population and Gender on Chemotherapeutic Agent-Induced Cytotoxicity. Molecular Cancer Therapeutics, 6, 31-36.

Weingart J, Grossman SA, Carson KA, Fisher JD, Delaney SM, Rosenbum ML, Olivi A, Judy K, Tatter SB, Dolan ME. (2007). Phase I Trial of Polifeprosan 20 with Carmustine Implant Plus Continuous Infusion of Intravenous O⁶-Benzylguanine in Adults with Recurrent Malignant Glioma: A New Approaches to Brain Tumor Therapy CNS Consortium Trial, JCO 28(4); 399-404.