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    Home > Research & Grants > Grants Program > Research Grants > Research Grants Awarded > Abstract
    Awarded Grants
    Development of Selective AP-Site Directed Drugs in Breast Cancer

    Scientific Abstract:
    Background: A common type of damage observed after radiation or chemotherapy is the removal of a base from the double stranded DNA to generate abasic (apurinic and apyrimidinic (AP)) site. The main pathway responsible for repairing this lesion is called base-excision repair (BER). Previously, we discovered that a plant protein, MAP30, with known anticancer activity cleaves DNA by a unique mechanism of DNA glycosylase and AP lyase. Furthermore, we identified the amino acid residues on its active site responsible for this activity. On the basis of the structure of this protein we designed a series of cyclic hexapeptides (CHPs) that selectively recognize and cleave AP sites on DNA. Unfortunately, MAP30 will not show efficacy in humans due to immunogenicity. In contrast, CHPs that mimic the active site of MAP30 are effective and non-immunogenic in vivo. Objectives/ Hypothesis: We hypothesize that a selective AP-binder is synergistic with radiation and chemotherapy. Our hypothesis is based on three recent observations: 1) The mechanism of MAP30-induced DNA cleavage resembles a class of proteins responsible for DNA repair. 2) MAP30 demonstrated activity against metastatic breast cancer in preclinical animal models. 3) A series of CHPs that we designed to mimic the active site of MAP30 selectively recognize AP sites on DNA. Specific Aims: 1: To evaluate antitumor activity of CHPs alone and in combination with radiation or doxorubicin in MDA-MB-231 cells. 2: To demonstrate in vivo efficacy and pharmacokinetics of the most potent CHP in mice by non-invasive microPET techniques. Study Design: We will study the synergistic activity of CHPs with DNA damaging agents in vitro using cytotoxicity and clonogenic assays. The best peptide will be tested against a preclinical animal model of breast cancer to determine maximum tolerated dose. We will use microPET to monitor activity, efficacy and distribution of these peptides in mice. Potential Outcomes and Benefits of the Research: Our approach of simplifying a 30kDa protein to a simple peptide based on the active site of MAP30 is highly innovative, easier and cheaper to prepare, will be non-immunogenic due to its size, and may therefore be used in combination with known chemotherapeutics. If successfully carried out, these drugs will be the first small molecules targeting the BER pathway. The success of this project will also provide the very first proof-of-principle that small-molecule drugs can be designed based on the structural architecture of the active site of a therapeutic protein.

    Lay Abstract:
    Background: A common type of damage observed after radiation or chemotherapy is the removal of a base from DNA to generate abasic sites. This type of DNA damage can be efficiently repaired but surviving cells will acquire resistance. Therefore, we propose that selective killing of tumor cells with extensive DNA damage is synergistic with anticancer drugs. Previously, we solved the 3D structure of an anticancer protein, MAP30, and showed that it cleaves DNA and generates abasic sites. Recently, it was shown that MAP30 exhibits remarkable activity in mice. Unfortunately, MAP30 has limited efficacy in human due to immunogenicity. On the basis of its 3D structure we identified the amino acid residues on its active site responsible for enzymatic activity. These residues are likely to be responsible for its anticancer activity. We designed a series of cyclic hexapeptides (CHPs) mimicking these residues and showed that they selectively recognize and break DNA at abasic sites. Objectives/ Hypothesis: We hypothesize that a compound designed to selectively bind to abasic sites within a DNA is synergistic with radiation and chemotherapy. Our hypothesis is based on three recent observations: 1) The mechanism of MAP30-induced DNA cleavage resembles a class of proteins responsible for DNA repair. 2) MAP30 demonstrated activity against breast cancer in animal models. 3) A series of CHPs that we designed to mimic the active site of MAP30 selectively recognize abasic sites within a DNA. Specific Aims: 1: To evaluate antitumor activity of CHPs alone and in combination with radiation or doxorubicin. 2: To demonstrate in vivo efficacy and pharmacokinetics of the most potent CHP in mice by non-invasive microPET techniques. Study Design: We will study the synergistic activity of CHPs with DNA damaging agents in vitro. We will demonstrate in vivo efficacy of these agents in a minimal number of mice by microPET imaging. Potential Outcomes and Benefits of the Research: The significance of this finding is that for the first time abasic site within DNA will be considered as a therapeutic target and that by effectively blocking this pathway we can improve upon the efficacy of existing drugs in cancer chemotherapy. The concept, design and execution of this proposal are highly innovative. If successfully carried out, these drugs will be the first in targeting DNA repair pathway. The success of this project will also provide the very first proof-of-principle that small-molecule drugs can be designed based on the structural architecture of the active site of a therapeutic protein.