Sjoerd van Helvert

Mesenchymal neoplasms driven by protein kinases represent an increasing group with a broad clinicopathologic and genetic spectrum. Recently, tumors harboring a GAB1::ABL1 fusion have been reported, resulting in constitutive activation of the non-receptor tyrosine kinase ABL1. We describe six cases (one previously reported) investigated by fusion gene analysis and DNA-methylation profiling. Tumors were from three males and three females aged 7–71 years and arose in the neck, axilla, lower back, thigh, and digits. Lesions were excised. Available follow-up was uneventful. Neoplasms were circumscribed but unencapsulated, with infiltration of the surrounding tissue, and characterized by haphazardly arranged monomorphous spindle cells. There was a fibromyxoid stroma and staghorn-like vessels were present. Immunohistochemically, expression of CD34 (3/6), S100 (1/6), EMA (2/6), and GLUT1 (3/3) was observed. All cases harbored a GAB1::ABL1 fusion. RNA expression profile (n = 2) showed high-confidence similarity to dermatofibrosarcoma protuberans (DFSP). DNA-methylation profiling demonstrated that all cases clustered together in close proximity to DFSP. Application of the latest Heidelberg methylation sarcoma classifier did not confidentially classify these neoplasms. However, four showed low-confidence matches to NTRK-rearranged spindle cell neoplasms. GAB1::ABL1 spindle cell neoplasms represent a distinct member of the family of kinase-driven mesenchymal tumors with an indolent clinical course, while the activating ABL1 fusion raises the possibility of targeted therapy in selected cases.

Tumor cell invasion into heterogenous interstitial tissues consisting of network-, channel- or rift-like architectures involves both matrix metalloproteinase (MMP)-mediated tissue remodeling and cell shape adaptation to tissue geometry. Three-dimensional (3D) models composed of either porous or linearly aligned architectures have added to the understanding of how physical spacing principles affect migration efficacy; however, the relative contribution of each architecture to decision making in the presence of varying MMP availability is not known. Here, we developed an interface assay containing a cleft between two high-density collagen lattices, and we used this assay to probe tumor cell invasion efficacy, invasion mode and MMP dependence in concert. In silico modeling predicted facilitated cell migration into confining clefts independently of MMP activity, whereas migration into dense porous matrix was predicted to require matrix degradation. This prediction was verified experimentally, where inhibition of collagen degradation was found to strongly compromise migration into 3D collagen in a density-dependent manner, but interface-guided migration remained effective, occurring by cell jamming. The 3D interface assay reported here may serve as a suitable model to better understand the impact of in vivo-relevant interstitial tissue topologies on tumor invasion patterning and responses to molecular interventions.

Introduction: Salivary gland cancer (SGC) is a rare cancer for which systemic treatment options are limited. Therefore, it is important to characterize its genetic landscape in search for actionable aberrations, such as NTRK gene fusions. This research aimed to identify these actionable aberrations by combining NGS-based analysis of RNA (gene fusions) and DNA (single and multiple nucleotide variants, copy number variants, microsatellite instability and tumor mutational burden) in a large cohort of SGC patients. Methods: RNA and DNA were extracted from archival tissue of 121 patients with various SGC subtypes. Gene fusion analysis was performed using a customized RNA-based targeted NGS panel. DNA was sequenced using a targeted NGS panel encompassing 523 cancer-related genes. Cross-validation of NGS-based NTRK fusion detection and pan-TRK immunohistochemistry (IHC) was performed. Results: Fusion transcripts were detected in 50% of the cases and included both known (MYB-NFIB, MYBL1-NFIB, CRTC1-MAML2) and previously unknown fusions (including transcripts involving RET, BRAF or RAD51B). Only one NTRK fusion transcript was detected, in a secretory carcinoma case. Pan-TRK IHC (clone EPR17341) was false positive in 74% of cases. The proportion of patients with targets for genetically matched therapies differed among subtypes (salivary duct carcinoma: 82%, adenoid cystic carcinoma 28%, mucoepidermoid carcinoma 50%, acinic cell carcinoma 33%). Actionable aberrations were most often located in PIK3CA (n = 18, 15%), ERBB2 (n = 15, 12%), HRAS and NOTCH1 (both n = 9, 7%). Conclusions: Actionable genetic aberrations were seen in 53.7% of all SGC cases on the RNA and DNA level, with varying percentages between subtypes.

Cell migration is an adaptive process that depends on and responds to physical and molecular triggers. Moving cells sense and respond to tissue mechanics and induce transient or permanent tissue modifications, including extracellular matrix stiffening, compression and deformation, protein unfolding, proteolytic remodelling and jamming transitions. Here we discuss how the bi-directional relationship of cell–tissue interactions (mechanoreciprocity) allows cells to change position and contributes to single-cell and collective movement, structural and molecular tissue organization, and cell fate decisions.

The multistep process of cell migration requires cells to dynamically couple to extracellular interfaces and generate traction force or friction for displacement of the cell body. When deformed, biopolymer networks, including fibrillar collagen and fibrin, undergo a nonlinear elasticity change that is termed strain stiffening and is commonly measured by bulk rheology. It remains poorly characterized, however, whether forces generated by moving cells suffice to induce strain stiffening. To detect strain stiffening at the leading edge of normal and tumor cells moving across fibrillar type I collagen, we combined AFM nanoindentation and differential field probing with confocal reflection microscopy. In different cell models, gradient-like fiber realignment, densification, and elevation of Young’s modulus ahead of the leading edge were observed, with peak increases of up to 1.15 kPa near the leading edge. Moving fibroblasts generated a larger anterograde strain field with a higher amplitude and up to 6-fold increased cumulative strain stiffening (52 kPa) compared with mesenchymal HT1080 fibrosarcoma cells (8.8 kPa) and epithelial SCC38 cancer cells (9.8 kPa). Collectively moving SCC38 cells produced 4-fold increased cumulative strain stiffening (38 kPa) compared with individually moving SCC38 cells in a β1 integrin- and actomyosin-dependent manner. This indicates that the extent of strain stiffening by the leading edge of moving cells scales with cell type, multicellular cooperativity, integrin availability, and contractility. By straining, migrating cells realign and densify fibrillar extracellular matrix and thus adopt an autonomous strategy to move on a “traveling wave” of stiffened substrate, which reaches levels sufficient for mechanosensory activation and self-steering of migration.

Tumor hypoxia, by elevating hypoxia-inducible factors (HIFs), is an established inducer of epithelial-to-mesenchymal transition (EMT) and subsequent cancer cell invasion and metastasis. Using epithelial carcinoma spheroids in 3D fibrillar collagen, we characterized the invasion patterns as well as cellular and molecular mechanisms of hypoxia-induced cancer cell migration modes. While epithelial cancer cells show collective invasion under normoxic conditions, hypoxia or pharmacological stabilization of HIF-1 using the prolyl hydroxylase inhibitor dimethyloxalylglycine (DMOG) induced EMT-like detachment and migration of single cells. Besides mesenchymal movement, most epithelial cells converted to amoeboid migration with characteristic actin-rich filopodal or distinctive blebby protrusions towards the direction of migration. Whereas mesenchymal migrating cells moved with low velocities in a directionally persistent manner, amoeboid migrating cells generated a broad spectrum of low to high velocities, but with less persistent invasion paths. Sub-cellular molecular analysis showed typical amoeboid features particularly in hypoxic blebby single cell migration, including low to lacking collagen degradation along the migration path and insensitivity to broad-spectrum matrix metalloproteinase (MMP)-inhibitor GM6001, non-focalized cortical actin cytoskeleton within blebs that interacted with collagen structures and low-beta1 integrin expression with lack of integrin focalization. Thus, tumor hypoxia induces a diversity of single-cancer cell invasion modes, including blebby amoeboid migration, thereby enhancing predominantly MMP- and integrin-independent amoeboid dissemination in parallel to EMT induction.