Abstract 2480: A more sensitive approach to cancer imaging using cancer-activated PET reporters
Authors: Harwig Alex , Wang Morgan , Tong Ling , Nieu Regina , Nguyen Vy , Felsher Dean , Suhy David 
Published: June 2022

Abstract
Early detection and localization of primary cancers has been shown to improve clinical outcomes and overall survival. While liquid biopsy may indicate the presence of cancer and possibly provide the tissue of origin, it cannot pinpoint the exact location of cancer and its metastases. Furthermore, current imaging techniques lack the sensitivity to locate early-stage tumors, diminishing the ability for early clinical intervention. Current imaging approaches using 18F-FDG rely on increased metabolic rates of tumors vs. surrounding non-tumor tissue, often resulting in high background and inability to detect low-metabolic tumors. Earli is developing a highly sensitive, orthogonal approach that uses genetic constructs to usurp dysregulated cancer pathways to force the tumor to produce a synthetic biomarker used to detect and localize the malignancy. We previously demonstrated the utility of cancer-activated expression of blood-based biomarkers in preclinical cancer models, which are currently in an ongoing clinical study.
EARLI-201 is novel genetic imaging probe comprised of a DNA construct containing a cancer-activated promoter to drive the expression of a PET Reporter Gene (PRG). The HSV-sr39TK PRG product specifically sequesters the 18F-FHBG tracer inside the cell, enabling detection by PET imaging. Initial studies for sensitivity combined H1299 lung cancer cells engineered with only two copies of the PRG were implanted subcutaneously into immunocompromised mice followed by the administration of the 18F-FHBG tracer. Results demonstrate a robust signal from as few as 62,000 injected cells. Given that a 1 mm3 tumor contains ~1,000,000 cells, suggests that we can localize tumors as small as 6.25mm3 with only a 1% transfection efficiency. EARLI-201 was tested in a variety of murine models including the metastatic “Lung Trap” and spontaneous HCC-MYC/Twist1, which produce discrete tumor nodules in the lungs or liver, respectively. A single intravenous injection of EARLI-201 given at Day 1 results in cancer-activated expression and accumulation of the PRG in tumors. 18F-FHBG PET imaging three days post dosing revealed distinct tumor foci that co-register with tumors detected by CT. Additional ex vivo techniques confirmed PRG expression only in tumor-containing tissues and not in healthy tissue. Imaging the same animals with 18F-FDG failed to produce any appreciable signal in the same tumors, likely because they are of low metabolic nature.
These pre-clinical results clearly demonstrate the potential of Earli’s approach to detect and localize very small tumors currently outside the sensitivity of existing imaging modalities. Additional experiments to evaluate EARLI-201 in companion dogs diagnosed with cancer are currently in progress and provides the ability to validate the platform in larger body masses with spontaneously formed tumors.
Citation Format: Alex Harwig, Morgan Wang, Ling Tong, Regina Nieu, Vy Nguyen, Dean Felsher, David Suhy. A more sensitive approach to cancer imaging using cancer-activated PET reporters [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2480.