Polystyrene micro- and nanoplastics (PS-MNPs) are emerging environmental pollutants with potential implications for human health. This study investigated the cytotoxic effects of PS particles by using two different sizes of PS-MNPs (0.25 µm and 1 µm) on non-small cell lung cancer (A549, H460), small cell lung cancer (DMS53, H372), and normal lung epithelial (BEAS-2B) cells as well as on human-derived lung organoids. Neither PS-MPs nor PS-NPs interfered with cell viability or proliferation at lower concentrations (< 30 µg/cm², equivalent to 50 µg/ml). Intracellular kinetic assays revealed that non-malignant (BEAS-2B) lung cells had the strongest turnover of PS-NPs compared to malignant cells. Since PS-NPs exhibited more pronounced cellular effects, additional analyses focused on their impact. Furthermore, we observed significantly increased migration, prolonged S-phase arrest with induced DNA damage, and oxidative stress in non-malignant (BEAS-2B) lung cells. Thus, our data suggest that BEAS-2B cells exhibit the highest sensitivity to PS-NPs. These cells displayed decreased base excision repair capacity and increased activation of survival pathways including AKT and ERK phosphorylation after PS-NP treatment. PS-NP internalization and increase of signal pathways were validated in a physiological lung organoid setting. Our findings suggest that while PS-NPs do not significantly affect the malignant behavior of cancer cells, they could promote malignant features in normal lung cells through the induction of survival pathways, migration, and altered stress response mechanisms.

Malignant pleural mesothelioma (MPM) is an aggressive malignancy with very limited therapeutic options. Fibroblast growth factor (FGF) signals play important roles in mesothelioma cell growth. Several FGFs and FGF receptors (FGFRs) are predicted targets of the miR‐15/16 family, which is downregulated in MPM. The aim of this study was to explore the link between the miR‐15/16 family and the FGF axis in MPM. Expression analyses via RT‐qPCR showed downregulation of the FGF axis after transfection with miR‐15/16 mimics. Direct interaction was confirmed by luciferase reporter assays. Restoration of miR‐15/16 led to dose‐dependent growth inhibition in MPM cell lines, which significantly correlated with their sensitivity to FGFR inhibition. Treatment with recombinant FGF2 prevented growth inhibition and further reduced the levels of FGF/R‐targeting microRNAs, indicating a vicious cycle between miR‐15/16 down‐ and FGF/FGFR signaling upregulation. Combined inhibition of two independent miR‐15/16 targets, the FGF axis and Bcl‐2, resulted in additive or synergistic activity. Our data indicate that post‐transcriptional repression of FGF‐mediated signals contributes to the tumor suppressor function of the microRNA‐15/16 family. Inhibiting hyperactivated FGF signals and Bcl‐2 might serve as a novel therapeutic combination strategy in MPM.

Purpose: Acquired chemoresistance is a frequent event in small cell lung cancer (SCLC), one of the deadliest human malignancies. Histone deacetylase inhibitors (HDACi) have been shown to synergize with different chemotherapeutic agents including cisplatin. Accordingly, we aimed to investigate the dual targeting of HDAC inhibition and chemotherapy in SCLC. Experimental Design: The efficacy of HDACi and chemotherapy in SCLC was investigated both in vitro and in vivo. Synergistic drug interactions were calculated based on the HSA model (Combenefit software). Results from the proteomic analysis were confirmed via ICP-MS, cell-cycle analysis, and comet assays. Results: Single entinostat- or chemotherapy significantly reduced cell viability in human neuroendocrine SCLC cells. The combination of entinostat with either cisplatin, carboplatin, irinotecan, epirubicin, or etoposide led to strong synergy in a subset of resistant SCLC cells. Combination treatment with entinostat and cisplatin significantly decreased tumor growth in vivo. Proteomic analysis comparing the groups of SCLC cell lines with synergistic and additive response patterns indicated alterations in cell-cycle regulation and DNA damage repair. Cell-cycle analysis revealed that cells exhibiting synergistic drug responses displayed a shift from G1 to S-phase compared with cells showing additive features upon dual treatment. Comet assays demonstrated more DNA damage and decreased base excision repair in SCLC cells more responsive to combination therapy. Conclusions: In this study, we decipher the molecular processes behind synergistic interactions between chemotherapy and HDAC inhibition. Moreover, we report novel mechanisms to overcome drug resistance in SCLC, which may be relevant to increasing therapeutic success.

Malignant pleural mesothelioma (MPM) is a devastating malignancy with limited therapeutic options. Fibroblast growth factor receptors (FGFR) and their ligands were shown to contribute to MPM aggressiveness and it was suggested that subgroups of MPM patients could benefit from FGFR-targeted inhibitors. In the current investigation, we determined the expression of all four FGFRs (FGFR1–FGFR4) by immunohistochemistry in tissue samples from 94 MPM patients. From 13 of these patients, we were able to establish stable cell lines, which were subjected to FGFR1–4 staining, transcript analysis by quantitative RT-PCR, and treatment with the FGFR inhibitor infigratinib. While FGFR1 and FGFR2 were widely expressed in MPM tissue and cell lines, FGFR3 and FGFR4 showed more restricted expression. FGFR1 and FGFR2 showed no correlation with clinicopathologic data or patient survival, but presence of FGFR3 in 42% and of FGFR4 in 7% of patients correlated with shorter overall survival. Immunostaining in cell lines was more homogenous than in the corresponding tissue samples. Neither transcript nor protein expression of FGFR1–4 correlated with response to infigratinib treatment in MPM cell lines. We conclude that FGFR3 and FGFR4, but not FGFR1 or FGFR2, have prognostic significance in MPM and that FGFR expression is not sufficient to predict FGFR inhibitor response in MPM cell lines.

Background: Small cell lung cancer (SCLC) is an aggressive malignancy with distinct molecular subtypes defined by transcription factors and inflammatory characteristics. This follow-up study aimed to validate the unique metabolic phenotype in achaete-scute homologue 1 (ASCL1)-driven SCLC cell lines and human tumor tissue. Methods: Metabolic alterations were analyzed using proteomic data. Structural and functional differences of mitochondria were investigated using qPCR, flow cytometry, confocal imaging, and transmission electron microscopy and seahorse assays. Several metabolic inhibitors were tested using MTT-based and clonogenic assays. Single-cell enzyme activity assays were conducted on cell lines and tumor tissue samples of SCLC patients. Results: We found increased mitochondrial numbers correlating with higher oxidative phosphorylation activity in ASCL1-dominant cells compared to other SCLC subtypes. Metabolic inhibitors targeting mitochondrial respiratory complex-I or carnitine palmitoyltransferase 1 revealed higher responsiveness in SCLC-A. Conversely, we demonstrated that non-ASCL1-driven SCLCs with lower oxidative signatures show dependence on glutaminolysis as evidenced by the enhanced susceptibility to glutaminase inhibition. Accordingly, we detected increased glutamate-dehydrogenase activity in non-ASCL1-dominant cell lines as well as in human SCLC tissue samples. Conclusions: Distinct SCLC subtypes exhibit unique metabolic vulnerabilities, suggesting potential for subtype-specific therapies targeting the respiratory chain, fatty acid transport, or glutaminolysis. Graphical