Prostate cancer presents a conundrum. On one hand, the vast majority of tumors are biologically indolent, and likely do not require treatment. On the other hand, tumors found to be locally advanced during surgery require aggressive treatment for cure. Even with this conundrum, molecular imaging has the potential to make an enormous impact on patient care. For staging, PET/MRI could identify tumors that are no longer organ-confined, and thus spare men from futile surgery. For men who are surgical candidates, optical imaging via near-infrared (NIR) fluorescence could provide real-time guidance during prostate resection, and importantly, highlight areas of extracapsular extension or in-transit metastases. To achieve both goals, though, a technology that improves cancer cell detection by at least 100-fold over conventional means is required. The hypothesis guiding this study is that zwitterionic contrast agents and radiotracers, defined as molecules with electrically-neutral and geometrically-balanced alternating positive and negative charges, will provide log-level improvements in molecular imaging. This hypothesis is based on observations from our group using small molecule, protein, and nanoparticle systems. In each case, zwitterionic molecules exhibited extremely low non-specific binding to normal tissues and organs. And, when engineered to exhibit rapid, renal- only clearance, unbound dose was eliminated completely from the body, resulting in high SBR. The focus of our study is prostate-specific membrane antigen (PSMA), a type II membrane receptor to which we have previously developed high affinity (2 and 9 nM) small molecule targeting ligands called GPI. We will create zwitterionic versions of GPI that have both optical (800 nm NIR fluorescence) and PET (deferoxamine chelation of Zr-89) functional groups (ZWGPI). Mathematical modeling of ZWGPI's performance in vivo reveals that the combination of constitutive endocytosis via PSMA, and the use of a long half-life isotope, such as Zr-89, will result in SBRs 100-fold higher than is currently possible.
Or specific aims i nclude chemical optimization of ZWGPI, in vivo validation, cGMP manufacture under 21 CFR 211/212, and a set of first-in-human trials in men undergoing prostate cancer staging and resection. To accomplish these ambitious aims, we have assembled an international team of experts. We also leverage a unique infrastructure at BIDMC. The newly opened Translational Cancer Imaging Facility (TCIF) is capable of manufacturing IND-eligible optical contrast agents and PET radiotracers under both 21 CFR 211 and 21 CFR 212 cGMP compliance. Of special note, ZW800-1, the zwitterionic NIR fluorophore on which this study is based, was also manufactured in the TCIF and has already been through the FDA IND process. Thus the regulatory path for ZWGPI is well defined at the outset and budgeted appropriately in our application. Completion of our specific aims has the potential to revolutionize prostate cancer care by providing improved PET/MRI staging and, if the chosen definitive treatment is surgery, real-time intraoperative guidance.
Prostate cancer needs improved treatment. In men whose tumor has spread beyond the confines of the prostate, surgery will be futile. We need technology that will identify such non-surgical candidates with much higher sensitivity than is available today. In men whose tumor is thought to be confined to the prostate, image- guidance using a special kind of light called near-infrared fluorescent light would permit the surgeon to see the tumor, even through blood and surrounding tissue, thus ensuring that none is left behind. In this grant application, we describe a new contrast agent/radiotracer technology based on a physicochemical property called zwitterionicity. By engineering molecules with zwitterionicity as well as rapid renal clearance we expect 100-fold or greater improvements in cancer detectability, both before and during human surgery.
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