A central hypothesis of this project is that elevated levels of homologous recombinational (HR) DNA repair cause human tumors to be resistant to certain chemotherapies and radiotherapy, and that specific inhibition of HR may help overcome this resistance. Our on-going research plan involves a multistep screen for identifying small molecule inhibitors of human RAD51, which is the central protein involved in HR. An initial developmental portion of this project (funded by 1R21CA124557-01A1) has identified several lead compounds that block RAD51 filament formation, inhibit RAD51-mediated recombination in a purified system, and reduce HR in cells. This work also successfully validated RAD51 as a target for cancer therapy, and it facilitated optimization of assay techniques. The current proposal builds on this work in several ways including the support of medicinal chemistry, HR-specific cell-based assays, and in-vivo testing in a mouse model. The goal is to generate pharmacologic agents capable of sensitizing human tumors to common oncologic therapies.
In Aim 1, we propose to screen a library of 6800 very pharmacologically favorable compounds, using improved assay substrates and conditions. Titrations of hit compounds will identify those with highest activities, which will be determined based on their ability to inhibit RAD51 filament formation and based on their binding affinity to RAD51 protein.
In Aim 2, lead compounds will be tested for the ability to inhibit various aspects of HR in a purified system in-vitro system. The most active compounds in these biochemical assays will advance to cell-based assays, to determine which can specifically inhibit in-vivo HR at low concentrations while not affecting other DNA repair pathways. Active compounds will subsequently be tested for the ability to sensitize cancer cells to cross-linking chemotherapeutic drugs and/or ionizing radiation (IR). These cell-based assays will be performed on both cancer cell lines and non-immortalized normal cells, to identify which exert tumor-specific effects.
In Aim 3 (which will be performed at UIC), the chemical sub-structures of lead compounds from earlier aims and from existing lead compounds will be optimized. Chemically-related compounds that are commercially available will first be tested. The highest priority candidate compounds will be optimized via targeted chemical modifications aimed at improving both RAD51-inhibitory activity and pharmacologic properties. ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties will be measured for the most promising candidates.
In Aim 4, we will test the highest priority candidate compounds candidate compounds further in a mouse model. First, the maximal tolerated dose (MTD) of compounds will be determined in mice. Second, compounds will be tested for the ability to sensitize human tumor xenografts to treatment with cisplatin or radiation.

Public Health Relevance

Compounds are being developed to specifically sensitize cancer cells to DNA damaging therapies, particularly to radiation and chemotherapeutic agents that introduce inter-strand cross links. Our long-term goal is to generate novel pharmacologic compounds that can improve the therapeutic index of these common oncology treatments. Given that our therapeutic target (RAD51) is over-expressed in such a wide range of malignancies, this approach could potentially improve treatment efficacy for a very large group of cancer patients.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA142642-03
Application #
8213676
Study Section
Drug Discovery and Molecular Pharmacology Study Section (DMP)
Program Officer
Misra, Raj N
Project Start
2010-03-16
Project End
2015-01-31
Budget Start
2012-02-01
Budget End
2013-01-31
Support Year
3
Fiscal Year
2012
Total Cost
$432,769
Indirect Cost
$102,172
Name
University of Chicago
Department
Radiation-Diagnostic/Oncology
Type
Schools of Medicine
DUNS #
005421136
City
Chicago
State
IL
Country
United States
Zip Code
60637
Mason, Jennifer M; Logan, Hillary L; Budke, Brian et al. (2014) The RAD51-stimulatory compound RS-1 can exploit the RAD51 overexpression that exists in cancer cells and tumors. Cancer Res 74:3546-55
Pitroda, Sean P; Pashtan, Itai M; Logan, Hillary L et al. (2014) DNA repair pathway gene expression score correlates with repair proficiency and tumor sensitivity to chemotherapy. Sci Transl Med 6:229ra42
Budke, Brian; Chan, Yuen-Ling; Bishop, Douglas K et al. (2013) Real-time solution measurement of RAD51- and RecA-mediated strand assimilation without background annealing. Nucleic Acids Res 41:e130
Budke, Brian; Kalin, Jay H; Pawlowski, Michal et al. (2013) An optimized RAD51 inhibitor that disrupts homologous recombination without requiring Michael acceptor reactivity. J Med Chem 56:254-63
Connell, Philip P; Weichselbaum, Ralph R (2013) Small molecule derived from a natural product that mitigates radiation injury. Proc Natl Acad Sci U S A 110:18355-6
Liauw, Stanley L; Connell, Philip P; Weichselbaum, Ralph R (2013) New paradigms and future challenges in radiation oncology: an update of biological targets and technology. Sci Transl Med 5:173sr2
Cosnefroy, O; Tocco, A; Lesbats, P et al. (2012) Stimulation of the human RAD51 nucleofilament restricts HIV-1 integration in vitro and in infected cells. J Virol 86:513-26