Models of human adamantinomatous craniopharyngioma tissue: Steps toward an effective adjuvant treatment

Abstract

Even though ACP is a benign tumor, treatment is challenging because of the tumor's eloquent location. Today, with the exception of surgical intervention and irradiation, further treatment options are limited. However, ongoing molecular research in this field provides insights into the pathways involved in ACP pathogenesis and reveal a plethora of druggable targets. In the next step, appropriate models are essential to identify the most suitable and effective substances for clinical practice. Primary cell cultures in low passages provide a proper and rapid tool for initial drug potency testing. The patient-derived xenograft (PDX) model accommodates ACP complexity in that it shows respect to the preserved architecture and similar histological appearance to human tumors and therefore provides the most appropriate means for analyzing pharmacological efficacy. Nevertheless, further research is needed to understand in more detail the biological background of ACP pathogenesis, which provides the identification of the best targets in the hierarchy of signaling cascades. ACP models are also important for the continuous testing of new targeting drugs, to establish precision medicine.

Keywords: EGFR; PDX model; craniopharyngioma; primary cell cultures; radioresistance.

Figure 1

Craniopharyngioma research facets. Based on the most important source of this research, the patient‐derived native tumor tissue obtained during surgical treatment, molecular analyses reveal druggable targets (gray arrows). Both in vitro and in vivo models are indispensable for the functional analysis of identified targets. Primary cell cultures and patient‐derived xenograft (PDX) models were established from native ACP tissue. The efficacy of drugs could be examined using both models. Because of the limits of cell cultures, gene regulatory events based on the inhibition of a specific target should be verified by histology, for example, utilizing double immunofluorescence to analyze the target, as well as the expression of the identified gene (green arrow). In contrast to cell cultures, the PDX model consistently conserves molecular tumor appearances, as seen in the patient. Therefore, this model seems to be most suitable for translating results into humans. Tumor screening using MRI and the development of radiotherapy protocols, adapted for the clinical course, not only allow the further investigation of mechanisms leading to recurrence even after irradiation, but also drug primed enhancement of radiosensitivity. Using these models, our prospective goal is the identification of patient precision adjuvant therapy (broken arrow).

Figure 2

Subcellular characterization of ACP based on immunohistochemistry. Double immunohistochemistry (A) showing budding ACP tumor (line) into adjacent brain tissue (asterisk) with beta‐catenin accumulating cell clusters (red) at the tip of the finger‐shaped tumor protrusion. Detection of activated EGFR (EGFR‐P, green) reveals co‐localization within the beta‐ catenin accumulating cells (yellow) in the merged view, demonstrating co‐activation of Wnt signaling and EGFR signaling pathway within the same cells at the invasion front. Solid ACP areas reveal a different marker expression (B). The beta‐catenin accumulating cells are marked in red with the corresponding marker profile summarized in the red box. Cells surrounding the mostly whirl‐shaped beta‐catenin enriched cells (light blue) express enhanced levels of claudin‐1, involved in tight junction formation and the epithelial cell adhesion molecule EpCAM.

Figure 3

PDX model. (A) Intracranial lesion of transplanted patient‐derived ACP tissue is detectable on T2‐weigted and after contrast media administration T1‐weigted MR images. Hematoxylin & Eosin staining reveal histological appearance of a tumor transplanted into the mouse brain (asterisk), showing typical histological hallmarks in magnification, for example, palisading cells (1), stellate reticulum cells (2), wet keratin (3), calcification (4) and solid cells (5) of ACP. (B) Xenotransplanted tumors also exhibit digitate tumor protrusions into adjacent brain tissue (asterisk) with beta‐catenin accumulating cells (arrow) also showing EGFR activation (EGFR‐P) with nuclear localization (arrow). (C) In order to evaluate the impact of radiation therapy on ACP tissue, PDX model irradiation planning was performed in accordance with the standard clinical approach. Colored isodose lines correspond to the dose levels shown in the coronal, sagittal and axial view (adapted from Hartmann et al).