In vivo detection of phospholipase C by enzyme-activated  near-infrared probes.
In this article, the characterization of the first near-infrared (NIR) phospholipase-activated molecular beacon is reported, and its utility for in vivo cancer imaging is demonstrated. The probe consists of three elements: a phospholipid (PL) backbone to which the NIR fluorophore, pyropheophorbide a (Pyro), and the NIR Black Hole Quencher 3 (BHQ) were conjugated. Because of the close proximity of BHQ to Pyro, the Pyro-PtdEtn-BHQ probe is self-quenched until enzyme hydrolysis releases the fluorophore. The Pyro-PtdEtn-BHQ probe is highly specific to one isoform of phospholipase C, phosphatidylcholine-specific phospholipase C (PC-PLC), responsible for catabolizing phosphatidylcholine directly to phosphocholine. Incubation of Pyro-PtdEtn-BHQ in vitro with PC-PLC demonstrated a 150-fold increase in fluorescence that could be inhibited by the specific PC-PLC inhibitor tricyclodecan-9-yl xanthogenate (D609) with an IC(50) of 34 ± 8 μM. Since elevations in phosphocholine have been consistently observed by magnetic resonance spectroscopy in a wide array of cancer cells and solid tumors, we assessed the utility of Pyro-PtdEtn-BHQ as a probe for targeted tumor imaging. Injection of Pyro-PtdEtn-BHQ into mice bearing DU145 human prostate tumor xenografts followed by in vivo NIR imaging resulted in a 4-fold increase in tumor radiance over background and a 2 fold increase in the tumor/muscle ratio. Tumor fluorescence enhancement was inhibited with the administration of D609. The ability to image PC-PLC activity in vivo provides a unique and sensitive method of monitoring one of the critical phospholipase signaling pathways activated in cancer, as well as the phospholipase activities that are altered in response to cancer treatment.
Department of Radiology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Theresa M
TM
Mawn
Anatoliy V
AV
Popov
Nancy J
NJ
Beardsley
Klara
K
Stefflova
Matthew
M
Milkevitch
Gang
G
Zheng
E James
EJ
Delikatny
D000818:Animals; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D018613:Microscopy, Confocal; D010743:Phospholipids / Q000737:chemistry; D011471:Prostatic Neoplasms / Q000201:enzymology*; D010738:Type C Phospholipases / Q000032:analysis / Q000378:metabolism*
D005456:Fluorescent Dyes; D010743:Phospholipids; D010738:Type C Phospholipases