The Use Of Pet Imaging For Prognostic Integrin Alpha(2)Beta(1) Phenotyping To Detect Non-Small Cell Lung Cancer And Monitor Drug Resistance Responses

PURPOSE: Growing evidence has demonstrated that aberrant expression of integrin alpha 2 beta 1 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin alpha 2 beta 1 targeting Ga-68-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used F-18-FDG PET tracer to see if Ga-68-DOTA-A2B1-PET imaging can offer a valuable and critical diagnostic imaging criterion for the identification of phenotypes of aggressive lung cancer.METHODS: To verify the prognostic value of integrin alpha 2 beta 1, several quantitative and functional in vitro assays were validated in different NSCLC cell lines (CL1-0, CL1-5, A549 and selected A549(++) cells). Positron emission tomography (PET) imaging studies using both standard F-18-FDG and a newly developed Ga-68-labeled integrin alpha 2 beta 1 (Ga-68-DOTA-A2B1) tracer were sequentially performed on mice with lung tumor xenografts in different anatomic locations (subcutaneous, orthotopic and osseous) to validate the targeting capability of the Ga-68-DOTA-A2B1 tracers. Treatment responses were monitored by injecting animals with metastatic bone tumors with 5 mg/kg doxorubicin. All in vivo treatment responses in each treatment subgroup were monitored with a PET imaging system to evaluate the up-regulation of integrin expression at the earliest stage of treatment (6 h).RESULTS: The PET and computed tomography (CT) images from NSCLC xenograft animals unambiguously demonstrated accumulation of the integrin tracer Ga-68-DOTA-A2B1 in the tumor lesions at all locations. The average tumor uptake and tumor-to-normal (T/N) ratio were 2.51 +/- 0.56 % ID/g and T/N = 2.82, 3.40 +/- 0.42 % ID/g and T/N = 1.52, and 1.58 +/- 0.108 % ID/g and T/N = 2.31 in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). The xenograft tumors were all clearly visible. In contrast, the accumulation of F-18-FDG reached 3.6 +/- 0.76 % ID/g, 1.39 +/- 0.075 % ID/g and 3.78 +/- 0.73 % ID/g in subcutaneous, orthotopic and osseous tumors, respectively (n = 5; p < 0.05). However, due to the high background uptake by normal tissue, the T/N values were less than or close to 1, making the tumors almost indistinguishable in the PET imaging analysis. Furthermore, Ga-68-DOTA-A2B1-PET imaging of the treated osseous tumor model demonstrated more than 19% tracer uptake in A549 lesions (1.72 +/- 0.95 % ID/g vs. pretreatment 1.44 +/- 0.12 % ID/g, p = 0. 015) 6 h post-treatment with doxorubicin. The elevated intensity of tracer uptake was in accordance with the results of in vitroWestern blot and ex vivo integrin staining, demonstrating elevated integrin alpha 2 beta 1 expression.CONCLUSION: In this study, integrin alpha 2 beta 1 was identified as a biomarker of aggressive malignant NSCLC. Thus, efforts should be devoted to validating integrin alpha 2 beta 1 as a potential target for non-invasive diagnosis and as a predictive marker for monitoring treatment responses using a preclinical PET imaging system.