Targeted imaging of cancer by fluorocoxib C, a near-infrared cyclooxygenase-2 probe

Abstract

Cyclooxygenase-2 (COX-2) is a promising target for the imaging of cancer in a range of diagnostic and therapeutic settings. We report a near-infrared COX-2-targeted probe, fluorocoxib C (FC), for visualization of solid tumors by optical imaging. FC exhibits selective and potent COX-2 inhibition in both purified protein and human cancercell lines. In vivo optical imaging shows selective accumulation of FC in COX-2-overexpressing human tumor xenografts [1483 head and neck squamous cell carcinoma (HNSCC)] implanted in nude mice, while minimal uptake is detectable in COX-2-negative tumor xenografts (HCT116)or 1483 HNSCC xenografts preblocked with the COX-2-selective inhibitor celecoxib. Time course imaging studies conducted from 3 h to 7-day post-FC injection revealed a marked reduction in nonspecific fluorescent signals with retention of fluorescence in 1483 HNSCC tumors. Thus, use of FC in a delayed imaging protocol offers an approach to improve imaging signal-to-noise that should improve cancer detection in multiple preclinical and clinical settings.

Fig. 1

Structures of (a) indomethacin, (b) celecoxib (Cel), (c) NIR664 (NIR), and (d) fluorocoxib A (FA).

Fig. 2

(a) Structure of fluorocoxib C (FC). (b) Steady state fluorescence excitation and emission spectra were determined for FC in water pH 7 using a Spex 1681 Fluorolog spectrofluorometer, equipped with a 450 W xenon arc lamp. The excitation and emission monochromator slit widths were 1 to 2 mm. FC exhibited excitation and emission maxima of ${\lambda }_{\mathrm{ex}}=672\mathrm{nm}$ and ${\lambda }_{\mathrm{em}}=692\mathrm{nm}$, respectively.

Fig. 3

In vivo and ex vivo prompt imaging of COX-2 in 1483 HNSCC xenograft tumors. FC ($0.2\mathrm{mg}/\mathrm{kg}$, r.o.) or NIR664 ($0.2\mathrm{mg}/\mathrm{kg}$, r.o.) were injected into nude mice bearing 1483 HNSCC or HCT116 xenograft tumors and imaged at 4 h postinjection under a Xenogen IVIS 200 optical imaging system. In vivo image of (a) 1483 HNSCC xenograft with FC; (b) celecoxib pretreated 1483 HNSCC xenograft with FC; (c) HCT116 xenograft with FC; and (d) 1483 HNSCC xenograft with NIR664. After imaging, tumors were collected by dissection and imaged under a Xenogen IVIS 200 optical imaging system. Ex vivo image of (e) 1483 HNSCC tumor shown in (a); (f) 1483 HNSCC tumor shown in (b); (g) HCT116 tumor shown in (c); and (h) 1483 HNSCC tumor shown in (d). (i) Quantification of tumor uptake of FC by ex vivo image analysis using AMIDE software ($n=4$, $p<0.003$).

Fig. 4

In vivo and ex vivo delayed optical imaging of COX-2 in 1483 HNSCC xenograft tumors. FC was injected into nude mice bearing 1483 HNSCC xenograft tumor on the left hip ($0.2\mathrm{mg}/\mathrm{kg}$, r.o.). The animal was imaged from 3 h to 7 days postinjection of FC under a Xenogen IVIS 200 optical imaging system: (a)–(f) Fluorescence images of a nude mice bearing 1483 HNSCC xenograft at 3 h to 7 days postinjection of FC. (g)–(j) Fluorescence images of tumor, liver, kidney, and muscle from an uninjected animal. (k)–(n) Fluorescence images of tumor, liver, kidney, and muscle from a 3 h animal. (o)–(r) Fluorescence images of tumor, liver, kidney, and muscle from a 7-days animal. (s) Quantification of signals in tumor, liver, kidney, and muscle from uninjected control, 3 h and 7-days animals by AMIDE software ($n=4$, $p=0.004$).