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

PURPOSE

Growing evidence has demonstrated that aberrant expression of integrin α2β1 might contribute to the invasion, metastasis and drug resistance of non-small cell lung cancer (NSCLC). Thus, the integrin α2β1 targeting Ga-DOTA-A2B1 tracer was validated in NSCLC in contrast to accumulation of the clinically used F-FDG PET tracer to see if 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 α2β1, several quantitative and functional 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-FDG and a newly developed Ga-labeled integrin α2β1 (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 Ga-DOTA-A2B1 tracers. Treatment responses were monitored by injecting animals with metastatic bone tumors with 5 mg/kg doxorubicin. All 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-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; < 0.05). The xenograft tumors were all clearly visible. In contrast, the accumulation of 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; < 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-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, = 0. 015) 6 h post-treatment with doxorubicin. The elevated intensity of tracer uptake was in accordance with the results of Western blot and integrin staining, demonstrating elevated integrin α2β1 expression.

CONCLUSION

In this study, integrin α2β1 was identified as a biomarker of aggressive malignant NSCLC. Thus, efforts should be devoted to validating integrin α2β1 as a potential target for non-invasive diagnosis and as a predictive marker for monitoring treatment responses using a preclinical PET imaging system.