Targeted molecular imaging of c-Met in NSCLC using ⁶⁸Ga-labeled binding peptide

Objectives: c-Met is a receptor tyrosine kinase, implicating cellular processes including proliferation and apoptosis ^[1]. Abnormal activation of c-Met pathway plays important role in tumorigenesis, progressionin NSCLC andmediates acquired resistance to epidermal growth factor receptor (EGFR) targeted therapy in NSCLC ^[2]. Nevertheless, lacking accurate in vivo detection methods for c-Metchallenges the understanding of the underlying c-Met related EGFR-TKI resistance mechanismand overall efficacy of c-Met targeted treatment. In this study, we developed a novel PET tracer (⁶⁸Ga-NODAGA-cMBP) based on c-Met-specific peptide with favorable pharmacokinetics and smaller size (~2 kDa) than antibodies (~150 kDa) and successfully used to image c-Met in NSCLC.

Methods: cMBP (KSLSRHDHIHHH)is a c-Met-specific peptideidentified from phage display library ^[3], here, we synthesized and modified cMBP with a linker-NODAGA and purified with HPLC. Then 10 ug of NODAGA-cMBPwas added into ⁶⁸GaCl₃ (536.5 MBq in 1 mL) for chelation reaction. Stability of ⁶⁸Ga-NODAGA-cMBP in phosphate buffer was measured by radio-HPLCin incubation time of 0.5, 1, 2, 4 h. Subcutaneous transplanted human NSCLC xenograftswith overexpression of c-Met (H1993) were established to assess tracer efficiencyand normal physiological level of c-Met (H1299) as negative control groups. PET/CT scanning (Discovery790Elite, GE healthcare) was performed at 0.5 h, 1 h and 2h after tail vein injection of ⁶⁸Ga-NODAGA-cMBP (9.25 MBq in 150 uL saline,n=3). Image quantification was performed at AW4.6 software (GE Healthcare) with decay-corrected and calculated as %ID/g. Cell uptake and biodistribution of ⁶⁸Ga-NODAGA-cMBP will be further supplemented.

Results: ⁶⁸Ga-NODAGA-cMBP was prepared with labeling yield of ≥62%and radiochemical purity of ≥95%. Stability of ⁶⁸Ga-NODAGA-cMBPin phosphate buffer was expressed as radiochemical purity and always >95% in all incubation time.H1993 tumors could be clearly observed in PET images (figure 1) at early 0.5 h after injection with highest tumor uptake of 0.77±0.04 %ID/g, significantly higher than H1299 (0.38±0.06 %ID/g, P < 0.01). At 1 h and 2 h, tumor uptake was gradually decreased, but H1299 tumors were always obviously lower than H1993 tumors (P < 0.05). From sequential images, we also find that ⁶⁸Ga-NODAGA-cMBP can accumulate in c-Met-positive tumors quickly and specificly and be cleared through urinary system rapidly. As we know, imaging agents with rapid metabolism matching short half-life nuclide could provide favorable pharmacokinetics, and so did ⁶⁸Ga-NODAGA-cMBP (t_1/2=68.1 min).Conclution: We successfully develop a novel ⁶⁸Ga-NODAGA-cMBPradiotracer with specific for c-Met and in vivoresults indicated ⁶⁸Ga-NODAGA-cMBPwas feasible to quantitatively detect c-Met in NSCLC by PET/CT imaging.The ⁶⁸Ga-NODAGA-cMBPPET/CT imaging has potential to be used for understanding the c-Met related tumorigenesis, progression and EGFR-TKI resistance mechanismin the noninvasive way. REFERENCES: 1 Trusolino L, Bertotti A, Comoglio PM. MET signalling: principles and functions in development, organ regeneration and cancer. Nat Rev Mol Cell Biol. 2010;11:834-848.2 Engelman JA, Zejnullahu K, Mitsudomi T, et al. MET amplification leads to gefitinib resistance in lung cancer by activating ERBB3 signaling. Science. 2007;316:1039-1043.3 Kim K, Hur Y, Ryu EK, et al. A neutralizable epitope is induced on HGF upon its interaction with its receptor cMet. Biochem Biophys Res Commun. 2007;354:115-121.