Abstract 1948: A near-infrared, highly specific NQO1-activated turn-on fluorescent probe for the detection and imaging of cancer cellsin vivo

Biomedical imaging plays an important role in all phases of cancer management including screening, guidance for biopsy excisions, malignancy staging, prognosis, therapy planning, follow-up and therapeutic responses. Unfortunately, the present detection threshold for solid tumors is approximately 109 cells (1 g = 1 cm3) growing as a single mass. The Near-infrared Fluorescence (NIRF) molecular imaging of cancer is known to be superior in sensitivity and resolution compared to other imaging modalities because of insignificant absorption by macromolecules, deeper tissue penetration and less auto-fluorescence. NAD(P)H Quinone oxidoreductase 1 (NQO1) is expressed in many human solid tumors at levels >200-fold than in normal tissues and its elevated activity has been closely associated with tumor progression, aggressiveness, resistance to chemotherapy, and poor prognosis. Therefore, NQO1 has been recognized as a potential biomarker of malignant tumors, accurate detection of which is highly desirable to improve diagnosis, efficacy and predict drug responsiveness. Fast, selective, and noninvasive reporting of intracellular cancer-associated events and species will lead to a better understanding of tumorigenesis at the molecular level and development of precision medicine. Therefore, we synthesized an NQO1 activatable NIR fluorescent probe (NQ-DCI) by conjugating dicyanoisophorone (DCI) fluorophore with the NQO1 substrate quinone propionic acid (QPA). The probe remained non-fluorescent until activation by NQO1, whose expression is largely limited to malignant tissues. With a large Stokes shift (186 nm) and a prominent near-infrared emission (646 nm) in response to NQO1, NQ-DCI was capable of monitoring NQO1 activity in vitro and in vivo with a high specificity and selectivity. We successfully employed the NQ-DCI to differentiate cancer cells from normal cells based on NQO1 activity using fluorescence microscopy and flow cytometry. Chemical and genetic approaches involving the use of ES936, a specific inhibitor of NQO1 and siRNA and gene transfection procedures unambiguously demonstrated NQO1 to be the sole target activating the NQ-DCI in cell cultures. NQ-DCI was successfully used to detect and image the endogenous NQO1 in three live tumor-bearing mouse models (A549 lung cancer, Lewis lung carcinoma, and MDMAMB 231 xenografts) with a high signal-to-low noise ratiometric NIR fluorescence response. When the NQO1-proficient A549 tumors and NQO1-deficient MDA-MB-231 tumors were developed in the same animal, only the A549 malignancies activated the NQ-DCI probe with a strong signal within 10 minutes. No other host tissues revealed fluorescence signals at this time. Because of its high sensitivity, rapid activation, tumor selectivity and nontoxic properties, we suggest that the NQ-DCI is a promising probe with clinical applications (supported by CPRIT RP170207). Note: This abstract was not presented at the meeting. Citation Format: Surendra Reddy Punganuru, Viswanath Arutla, Kalkunte S. Srivenugopal. A near-infrared, highly specific NQO1-activated turn-on fluorescent probe for the detection and imaging of cancer cells in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1948.