The Use of PET Imaging for Prognostic Integrin α2β1 Phenotyping to Detect Non-Small Cell Lung Cancer and Monitor Drug Resistance Responses

PURPOSE: Growing evidence has demonstrated that aberrant expression of integrin 21 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin 21 targeting 68 Ga-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used 18 F-FDG PET tracer to see if 68 Ga-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 21, 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 18 F-FDG and a newly developed 68 Ga-labeled integrin 21 ( 68 Ga-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 68 Ga-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 68 Ga-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 18 F-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, 68 Ga-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 21 expression.