Ronald G. Blasberg: Overview
These reporter systems can be used noninvasively to study and image tumor biology, oncogenesis, and metastases, as well as to track and monitor adoptive T cell and stem-cell therapies sequentially over time in single animals and in patients. In addition, reporter-gene imaging can be used to assess the effect of drug therapy on specific endogenous molecules and signaling pathways in living animals, and to determine the pharmacodynamic and pharmacokinetic profile of a drug’s effect on a specific molecular target(s), repetitively over time in single animals. This technology can provide a novel, low-cost “molecular readout” of drug efficacy.
Our current reporter systems include: p53 (oncogenesis and apoptosis); HRE (hypoxia); HIF-1α degradation (hypoxia); E2F (cell cycle, proliferation); FOXO (PI3K-AKT pathway); SMAD4/RUNX2 (TGFβ pathway); NFAT (nuclear factor of activated T cells); HSP70 (heat shock factor, HSF1); Gli-1 (hedgehog pathway signaling); and BMI1 (cell differentiation and oncogenesis).
Currently we focus on the impact of changes in lactic acid metabolism on disease evolution and progression and development of metastases. This application focuses on two components of an abnormal metabolic phenotype in breast and prostate cancer involving lactate dehydrogenase A (LDH-A) and monocarboxylate transporter 4 (MCT4). We’ve chosen these components because LDH-A is a bridge between several metabolic pathways and MCT-4 is primarily involved in the export of lactate from cancer cells.
We propose to show that cells and tumors with high lactate secretion and/or tissue concentrations express high levels of LDH-A and MCT4, and that they are prone to be more invasive and to develop metastases. The expression of LDH-A and MCT4 are very highly correlated with the duration of metastasis-free survival in human breast cancer, and expression of these genes is expected to be highly correlated with tumor lactate concentrations. In addition, the product of LDH-A activity (lactate) can be assessed noninvasively and quantitatively using magnetic resonance spectroscopic (MRS) imaging (MRSI), which is being performed in collaboration with Jason Koutcher’s laboratory.
Oxygen-dependent and Independent Regulation of HIF-1
The level of HIF-1α protein determines the level and activity of a transcription factor (HIF-1), which regulates the expression of at least 70 other genes, including those involved in blood vessel formation (angiogenesis), cell proliferation, cell viability, glucose metabolism, and other functions. Suppression of HIF-1α gene expression has been shown to reduce tumor growth, and drugs that directly or indirectly inhibit HIF-1 activity have demonstrable benefit. Therefore, there is great interest in identifying new inhibitors.
Molecular imaging techniques developed in our lab over the past ten years are being used to study the effect of established and potential new drugs that inhibit or downregulate HIF-1α and HIF-1 transcription factor in preclinical assays, with the goal of identifying candidate drugs for clinical trials.
Heat Shock Protein Responses in Cancer and Treatment
Heat shock proteins are elevated in most cancer cells and are an integral component of a cell’s stress response. We have developed a multimodality reporter system regulated by the HSP70 enhancer element and sensitive to the Hsf1 transcription factor. We have shown that this reporter system is sensitive to and can image cell and tissue responses to heat shock and the effects of HSP90 targeted drugs, such as 17AAG.
Translational Reporter-gene Imaging
Using human reporter genes, including hNIS (sodium-iodide symporter), hNET (norepinephrine transporter), and hSTR2 (somatostatin receptor, subtype 2), developed in our lab, studies are in progress to image the trafficking and localization, as well as functional status of T cells in animals and in patients, (This work is in collaboration with physician-scientist Vladimir Ponomarev and medical oncologist Susan Slovin).
A series of vectors encoding both constitutive and inducible reporter genes is being developed to distinguish subpopulations of T cells during their specific antigen-induced activation.