Laboratory of Molecular Design
Radiohybridization Imaging of HER2 Expression
Aggressive, invasive breast cancer will attack >180,000 women in the US in 2007, and will take the lives of >40,000 women. Mammograms detect lumps in breasts, »80% of which are benign, and »20% are malignant. Lumps are biopsied to determine whether they are benign or malignant. But biopsies do not determine which oncogenes are activated, and do not reliably diagnose estrogen-dependent vs. estrogen-independent breast cancer. The cells in malignant lumps divide frequently due to mutational activation of cancer genes. We have designed and demonstrated a novel technology to visualize hyperactive cancer gene mRNAs from outside the body. mRNA imaging scans the entire breast to find all sites of cancer gene activation, whether or not a lump has formed. RHI probes are peptide nucleic acid (PNA) sequences that hybridize specifically to messenger RNAs (mRNAs) copied from activated cancer genes. We added a small peptide analog to allow the mRNA imaging agents to be taken up by the breast cancer cells. Finally, we chelated radionuclides to permit external imaging by positron emission tomography (PET) scanning. mRNA imaging probes for CCND1, HER2, MYCC, and KRAS2 mRNAs, injected into animal models, enabled us to visualize breast cancer, pancreas cancer, and prostate cancer xenografts. High levels of human epidermal growth factor receptor 2 (Her2) protein are found in 25-30% of breast cancers, as well as other cancers, and are associated with aggressive, invasive, estrogen-independent metastasis. Measurements of HER2 mRNA demonstrated that Her2+ breast cancer cells express thousands of HER2 mRNAs per cell, while Her2- breast cancer cells express much less. We hypothesize that external radiohybridization imaging of HER2 oncogene expression will detect aggressive Her2+ breast cancers noninvasively, enabling faster, accurate, cost-effective diagnosis. Phase 1: Milestone 1: We will synthesize and purify a HER2 mRNA mRNA imaging agent and mismatch controls to =95% purity. Milestone 2: We will determine whether or not the HER2 mRNA imaging agent will show =3-fold greater accumulation in human Her2+ breast cancer cells in culture, vs. mismatch controls. Phase 2: Milestone 1: We will optimize the sensitivity of the HER2 mRNA imaging agent, vs. mismatch controls, in human Her2+ and Her2- breast cancer xenografts by varying the specific activity over a wide range, in order to achieve =3-fold greater PET image contrast in the xenografts, relative to normal contralateral tissue. Milestone 2: We will determine which agent, among macrocyclic chelators, oligolysines, and IGF1 analogs, will reduce nonspecific organ uptake by =2-fold. Milestone 3: We will determine whether radiohybridization imaging of HER2 mRNA following chemotherapy in Her2+ transgenic mice that develop spontaneous breast cancers will show =2-fold decrease in PET image contrast in the tumor, relative to normal contralateral tissue, vs. Her2- control mice, as a response to chemotherapeutic interdiction of proliferation. PET imaging measurement of HER2 mRNA levels will be compared with FDG measurement of metabolic activity over time.
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