The Evolving Role of Molecular Imaging in Non–Small Cell Lung Cancer Radiotherapy

Evolution of treatment strategies for oligometastatic NSCLC patients - A systematic review of the literature

BACKGROUND

The concept of oligometastatic disease (OMD) has expanded the scope of potentially curative therapy for metastatic NSCLC. However, large uncertainties remain regarding its definition and optimal management strategies. We therefore conducted a systematic review to investigate the value of various multimodality treatment concepts.

METHODS

We searched the available literature in Pubmed, Medline and EMBASE using the terms "oligomet*", "synchron*", "oligorec*", "metachr*" "NSCLC", "lung cancer" and "stage IV" and included studies reporting treatment regimens and outcomes on radically treated patients with either "synchronous", "metachronous" or "mixed" OMD. Only de-novo diagnosis of OMD was considered. The impact of patient and treatment characteristics on overall survival (OS) and time trends in patterns of care were investigated.

RESULTS

54 studies published between 1987 and 2018 were included. Despite a wide range of OMD definitions, 90.1% of patients were treated for a single metastasis. Systemic therapy was used as backbone treatment for most patients. Although surgery was the preferred local treatment in earlier studies, the use of stereotactic radiotherapy increased rapidly after 2011. No OS difference was observed between surgery or radiotherapy as the treatment of primary tumor or metastases, respectively. A time trend towards improved OS after 2011 could be detected.

CONCLUSIONS

While evidence in favor of radical treatment is emerging, most studies remain retrospective and mainly evaluate patients with singular metastases. While surgery, stereotactic radiotherapy and chemotherapy are the cornerstones of current treatment strategies, future clinical trials need to address the high risk of distant metastases by integrating targeted or immunotherapy.

Noninvasive assessment and quantification of tumor vascularization using [18F]FDG-PET/CT and CE-CT in a tumor model with modifiable angiogenesis-an animal experimental prospective cohort study

Background

This study investigated the noninvasive assessment of tumor vascularization with clinical F-18-fluorodeoxyglucose positron emission tomography/computed tomography and contrast-enhanced computed tomography ([18F]FDG-PET/CT and CE-CT) in experimental human xenograft tumors with modifiable vascularization and compared results to histology. Tumor xenografts with modifiable vascularization were established in 71 athymic nude rats by subcutaneous transplantation of human non-small-cell lung cancer (NSCLC) cells. Four different groups were transplanted with two different tumor cell lines (either A549 or H1299) alone or tumors co-transplanted with rat glomerular endothelial (RGE) cells, the latter to increase vascularization. Tumors were assessed noninvasively by [18F]FDG PET/CT and contrast-enhanced CT (CE-CT) using clinical scanners. This was followed by histological examinations evaluating tumor vasculature (CD-31 and intravascular fluorescent beads).

Results

In both tumor lines (A549 and H1299), co-transplantation of RGE cells resulted in faster growth rates [maximal tumor diameter of 20 mm after 22 (± 1.2) as compared to 45 (± 1.8) days, p < 0.001], higher microvessel density (MVD) determined histologically after CD-31 staining [171.4 (± 18.9) as compared to 110.8 (± 11) vessels per mm², p = 0.002], and higher perfusion as indicated by the number of beads [1.3 (± 0.1) as compared to 1.1 (± 0.04) beads per field of view, p = 0.001]. In [18F]FDG-PET/CT, co-transplanted tumors revealed significantly higher standardized uptake values [SUVmax, 2.8 (± 0.2) as compared to 1.1 (± 0.1), p < 0.001] and larger metabolic active volumes [2.4 (± 0.2) as compared to 0.4 (± 0.2) cm³, p < 0.001] than non-co-transplanted tumors. There were significant correlations for vascularization parameters derived from histology and [18F]FDG PET/CT [beads and SUVmax, r = 0.353, p = 0.005; CD-31 and SUVmax, r = 0.294, p = 0.036] as well as between CE-CT and [18F]FDG PET/CT [contrast enhancement and SUVmax, r = 0.63, p < 0.001; vital CT tumor volume and metabolic PET tumor volume, r = 0.919, p < 0.001].

Conclusions

In this study, a human xenograft tumor model with modifiable vascularization implementable for imaging, pharmacological, and radiation therapy studies was successfully established. Both [18F]FDG-PET/CT and CE-CT are capable to detect parameters closely connected to the degree of tumor vascularization, thus they can help to evaluate vascularization in tumors noninvasively. [18F]FDG-PET may be considered for characterization of tumors beyond pure glucose metabolism and have much greater contribution to diagnostics in oncology.

ImmunoPET Imaging of CTLA-4 Expression in Mouse Models of Non-small Cell Lung Cancer

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is expressed on the surface of activated T cells and some tumor cells, and is the target of the clinically approved monoclonal antibody ipilimumab. In this study, we investigate specific binding of radiolabeled ipilimumab to CTLA-4 expressed by human non-small cell lung cancer cells in vivo using positron emission tomography (PET). Ipilimumab was radiolabeled with ⁶⁴Cu (t_1/2 = 12.7 h) through the use of the chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to formulate ⁶⁴Cu-DOTA-ipilimumab. CTLA-4 expression in three non-small cell lung cancer (NSCLC) cell lines (A549, H460, and H358) was verified and quantified by Western blot and enzyme-linked immunosorbent assays (ELISA). A receptor binding assay was utilized to monitor the binding and internalization of ⁶⁴Cu-DOTA-ipilimumab in the NSCLC cell lines. Next, the biodistribution of ⁶⁴Cu-DOTA-ipilimumab was mapped by longitudinal PET imaging up to 48 h after injection. Ex vivo biodistribution and histological studies were employed to verify PET results. By in vitro analysis, CTLA-4 was found to be expressed on all three NSCLC cell lines with A549 and H358 showing the highest and lowest level of expression, respectively. PET imaging and quantification verified these findings as the tracer accumulated highest in the A549 tumor model (9.80 ± 0.22%ID/g at 48 h after injection; n = 4), followed by H460 and H358 tumors with uptakes of 9.37 ± 0.26%ID/g and 7.43 ± 0.05%ID/g, respectively (n = 4). The specificity of the tracer was verified by injecting excess ipilimumab in A549 tumor-bearing mice, which decreased tracer uptake to 6.90 ± 0.51%ID/g at 48 after injection (n = 4). Ex vivo analysis following the last imaging session also corroborated these findings. ⁶⁴Cu-DOTA-ipilimumab showed enhanced and persistent accumulation in CTLA-4-expressing tissues, which will enable researchers further insight into CTLA-4 targeted therapies in the future.