Selection of potential targets for stratifying congenital pulmonary airway malformation patients with molecular imaging: is MUC1 the one?

Abstract

Currently there is a global lack of consensus about the best treatment for asymptomatic congenital pulmonary airway malformation (CPAM) patients. The somatic KRAS mutations commonly found in adult lung cancer combined with mucinous proliferations are sometimes found in CPAM. For this risk of developing malignancy, 70% of paediatric surgeons perform a resection for asymptomatic CPAM. In order to stratify these patients into high- and low-risk groups for developing malignancy, a minimally invasive diagnostic method is needed, for example targeted molecular imaging. A prerequisite for this technique is a cell membrane bound target. The aim of this study was to review the literature to identify potential targets for molecular imaging in CPAM patients and perform a first step to validate these findings.A systematic search was conducted to identify possible targets in CPAM and adenocarcinoma in situ (AIS) patients. The most interesting targets were evaluated with immunofluorescent staining in adjacent lung tissue, KRAS⁺ CPAM tissue and KRAS^- CPAM tissue.In 185 included studies, 143 possible targets were described, of which 20 targets were upregulated and membrane-bound. Six of them were also upregulated in lung AIS tissue (CEACAM5, E-cadherin, EGFR, ERBB2, ITGA2 and MUC1) and as such of possible interest. Validating studies showed that MUC1 is a potential interesting target.This study provides an extensive overview of all known potential targets in CPAM that might identify those patients at risk for malignancy and conducted the first step towards validation, identifying MUC1 as the most promising target.

FIGURE 1

Schematic overview of the principle of tumour-targeted positron emission tomography imaging. A suitable tracer will be administered into the subject (e.g. a baby with a congenital pulmonary airway malformation). Depending on the size of the tracer, the tracer can target the cancer at multiple locations, e.g. intravascular, receptors on the cell membrane or intracellular. Figure created using BioRender.com.

FIGURE 2

Preferred Reporting Items for Systematic reviews and Meta-Analyses flowchart. CPAM: congenital pulmonary airway malformation; AIS: adenocarcinoma in situ; LTE: letter to the editor; CLM: congenital lung malformation.

FIGURE 3

Flowchart describing the congenital pulmonary airway malformation target selection process.

FIGURE 4

KRAS-related targets. Upregulated targets related to the RAS pathway: all potential plasma membrane targets related to the RAS pathway found in the literature search (therefore CEACAM5 is not shown). EGFR: epidermal growth factor receptor; MUC1: mucin 1; ERBB2: Erb-B2 tyrosine kinase 2; CDH1: E-cadherin; ITGA2: integrin-α2; →: activation; ⊥: inhibition.

FIGURE 5

Single-cell RNA expression of pulmonary cell types according to Guo et al. [36] and the RNA expression of our selected interesting targets in these cells. Red indicates high RNA expression of the target, blue indicates low expression of the target. AEC: arterial endothelial cell; AF: alveolar fibroblast; AM: alveolar macrophage; ASMC: airway smooth muscle cell; AT: alveolar type cell; CAP: capillary cell; ILC: innate lymphoid cell; IM: interstitial macrophage; IMON: inflammatory monocyte; LEC: lymphatic endothelial cell; maDC: mature dendritic cell subset; MEC: myoepithelial cell; NK: natural killer cell; pDC: plasmacytoid dendritic cell; pMON: patrolling monocyte; PNEC: pulmonary neuroendocrine cell; SCMF: secondary crest myofibroblast; SMG: submucosal gland; VEC: venous endothelial cell; VSMC: vascular smooth muscle cell.

FIGURE 6

Immunofluorescent staining of adjacent “normal lung” tissue, KRAS⁻ congenital pulmonary airway malformation tissue (CPAM) and KRAS⁺ CPAM tissue with a) E-cadherin (CDH1), b) Erb-B2 receptor tyrosine kinase 2 (ERBB2) and c) cell adhesion molecule 5 (CEACAM5). DAPI: 4′,6-diamidino-2-phenylindole. Arrows point to positive signal. Scale bars=50 µm.

FIGURE 7

a) Haematoxylin and eosin (H&E) staining of adjacent “normal” lung tissue, congenital pulmonary airway malformation (CPAM) tissue without KRAS mutations (KRAS⁻), CPAM tissue with KRAS mutations (KRAS⁺) and areas with mucinous proliferations (MP) found in only KRAS⁺ CPAM tissue. Scale bars=100 µm. b) Immunofluorescent staining of KRAS⁻ CPAM tissue, KRAS⁺ CPAM tissue and MP within KRAS⁺ CPAM tissue with mucin 1 (MUC1), sex-determining region Y-box 2 (SOX2) and 4′,6-diamidino-2-phenylindole (DAPI). Scale bars=100 µm (top row), 50 µm (bottom rows). c) H&E staining of MPs, and immunofluorescent staining of MUC1, SOX2 and DAPI. Scale bars=50 µm. Arrows point to positive signals.