Small cell lung cancer (SCLC) is an aggressive thoracic disease characterized by rapid proliferation and early metastatic spread. The survival outcomes for patients with SCLC remain notoriously poor, underlining that only modest improvements have been achieved in clinical settings to date. However, insights gained from human tumors and preclinical models in recent years have shed light on the heterogeneous molecular profile of SCLC. Numerous research groups have, therefore, begun to stratify SCLC into subgroups based on differential transcription factor expression, the tumor immune microenvironment, and other criteria. As SCLC subtypes show major differences in their molecular landscape and biological behavior, they may offer unique therapeutic vulnerabilities and serve as a framework for future personalized clinical trials. Here, we summarize impactful classification attempts from the past 10 years, highlighting discrepancies and connections between the nomenclature of each study, and expound upon relevant factors of SCLC biology influencing subtype composition and plasticity. This review delves into the implications of subgrouping for understanding and treating SCLC, as well as potential future directions for SCLC research.

Abstract Small cell lung cancer (SCLC) is one of the most aggressive solid malignancies with limited treatment options. Access to clinically relevant SCLC tissue is restricted because surgical resection is rare in metastatic disease, making this cancer type difficult to study. Through our multicenter rapid research autopsy (RRA) program, however, we are able to collect not only primary tumors but also multiple metastatic lesions, providing a unique and rare collection of SCLC specimens. In this program, rapid autopsies are performed within four hours after death to ensure optimal tissue quality for downstream analyses. In the current project, we analyzed samples from seven patients with histologically confirmed SCLC, including clinical and metastatic lesions, as well as their corresponding patient-derived tumor xenografts (PDTXs) serially passaged through three generations. To assess whether the original tissue architecture and intratumoral heterogeneity are preserved across PDTX generations, we performed immunohistochemical and proteomic analyses, comparing molecular profiles between the original tumors and their corresponding PDTX models. A subset of SCLC clinical specimens, including matched PDTX-clinical pairs, confirmed that the histologic landscape of the tumors of origin is preserved in the derivative PDTX models. Samples were grouped by patient and anatomical site, and pairwise Pearson correlations of global protein abundance profiles were computed within each group. The mean within-lineage correlation was high (typically >0.8), and correlation heatmaps showed tight clustering across PDTX generations from the same lineage. Across all patients, the only pathways consistently and significantly downregulated in PDTX models compared with the original tumors were the ECM-receptor interaction and Complement and Coagulation Cascade pathways. When analyzing metastatic PDTX samples, we compared liver and lymph node metastases with their corresponding primary patient tumors across PDTX generations. In lymph node metastases, proteins involved in ECM-receptor interaction and EMT pathways were upregulated. In contrast, liver metastases showed upregulation of fatty acid metabolism and peroxisome proliferator-activated receptor signaling pathways, with downregulation of EMT, ECM-receptor interaction, E2F targets, and G2M checkpoint. These findings demonstrate that the proteomic identity of SCLC tumors is largely preserved during serial passaging in PDTX models, while site-specific adaptations emerge in distinct metastatic microenvironments. Citation Format: Sára Surguta, Laura Svajda, Zsolt Megyesfalvi, Bence Ferencz, Ildikó Kovács, Vivien Téglás, Lilla Horváth, Szilvia Török, Balázs Döme, Melinda Rezeli, Jozsef Tovari. Proteomic insights into metastatic small cell lung cancer using patient derived xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2108.

Patients with lung metastases frequently receive anti-angiogenic (AA) therapies based on the histological characteristics of the primary tumor. However, clinical benefit remains limited, suggesting the presence of therapeutic resistance. The contribution of intratumoral drug distribution to this limited therapeutic benefit remains insufficiently understood.We aimed to determine whether differences in therapeutic response are associated with differences in intratumoral drug distribution in matched primary and lung metastasis models of breast and renal cell carcinoma.Matched primary and lung metastasis models were established using 4T1, MDA-MB-231, and RENCA cells. Mice received sunitinib or vehicle, and therapeutic response was evaluated by complementary histopathological analyses of tumor growth, microvessel area (MVA), hypoxia, and necrosis, together with matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) assessment of intratumoral sunitinib distribution.Sunitinib significantly inhibited tumor growth and reduced MVA in all primary tumor models. In metastasis models, MVA was also significantly reduced, whereas therapeutic response varied between tumor types. MALDI-MSI demonstrated higher normalized intratumoral sunitinib signal in metastases than in corresponding primary tumors, particularly in the breast cancer models. Drug signal also differed between viable, necrotic, and hypoxic tumor regions, demonstrating substantial intratumoral heterogeneity.These findings demonstrate that integrating MALDI-MSI with histopathological analyses enables comparative assessment of intratumoral drug distribution in matched primary and metastatic tumor models. Despite consistent anti-vascular effects and detectable intratumoral drug signal, additional mechanisms beyond inadequate drug delivery are likely to contribute to the limited response observed in breast cancer lung metastases.

Proteomic analysis resulting from the comparison of SCLC cell lines showing synergistic or additive responses to entinostat and cisplatin therapy

Proteomic analysis resulting from the comparison of entinostat sensitive versus resistant cell lines

BackgroundNo targeted drugs are currently available against small cell lung cancer (SCLC). BCL-2 family members are involved in apoptosis regulation and represent therapeutic targets in many malignancies.MethodsExpression of BCL-2 family members in 27 SCLC cell lines representing all known four SCLC molecular subtypes was assessed by qPCR, Western blot and mass spectrometry-based proteomics. BCL-2 and MCL-1 inhibition (venetoclax and S63845, respectively) was assessed by MTT assay and flow cytometry and in mice bearing human SCLC tumours. Drug interactions were calculated using the Combenefit software. Ectopic BAX overexpression was achieved by expression plasmids.ResultsThe highest BCL-2 expression levels were detected in ASCL1- and POU2F3-driven SCLC cells. Although sensitivity to venetoclax was reflected by BCL-2 levels, not all cell lines responded consistently despite their high BCL-2 expression. MCL-1 overexpression and low BAX levels were both characteristic for venetoclax resistance in SCLC, whereas the expression of other BCL-2 family members did not affect therapeutic efficacy. Combination of venetoclax and S63845 resulted in significant, synergistic in vitro and in vivo anti-tumour activity and apoptosis induction in double-resistant cells; however, this was seen only in a subset with detectable BAX. In non-responding cells, ectopic BAX overexpression sensitised to venetoclax and S63845 and, furthermore, induced synergistic drug interaction.ConclusionsThe current study reveals the subtype specificity of BCL-2 expression and sheds light on the mechanism of venetoclax resistance in SCLC. Additionally, we provide preclinical evidence that combined BCL-2 and MCL-1 targeting is an effective approach to overcome venetoclax resistance in high BCL-2-expressing SCLCs with intact BAX.

AbstractPurpose: 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.

Small cell lung cancer (SCLC) represents for 15% of all lung cancers. Although SCLC is initially highly sensitive to chemotherapy (CHT), almost all patients acquire resistance within the course of the disease. A promising class of compounds to overcome drug resistance comprises histone deacetylase inhibitors (HDACi), which have been shown to synergize with several CHT agents such as cisplatin. In this study, we addressed whether entinostat exhibits anti-cancer activity as single-therapy or in combination with CHT in SCLC. The efficacy of entinostat alone or in combination with CHT was determined using MTT-based viability assays and a mouse xenograft model. Synergistic drug interactions were evaluated using the combenefit software. Analysis of our previously published proteomic dataset comprised 1D annotation enrichment, DAVID functional annotation and ToppCluster analysis. Hypothetic mechanisms were also examined using ICP-MS and FACS-based cell cycle analysis. Class I HDAC inhibition by entinostat resulted in significantly stronger effects in neuroendocrine (NE) SCLC cell lines. Subsequent proteomic analysis revealed differentially expressed proteins and pathways that coincide with NE and non-NE characteristics. Since “platinum drug resistance” appeared in the corresponding pathway analysis, cell lines were exposed to cisplatin. A significant correlation was observed between entinostat and cisplatin responsiveness (r=0.8079, p=0.0003). With combination therapy, a strong synergism was detected in a subset of SCLC cell lines and validated in a mouse model. Importantly, similar effects were also found when entinostat was combined with etoposide, epirubicin or irinotecan. To address the underlying mechanism of the observed effects, another proteomic evaluation comparing cell lines with synergistic and additive features indicated changes in cell cycle regulation and DNA damage repair. Cell cycle analysis revealed similar distributions in control, entinostat and cisplatin conditions. However, synergistic cell lines displayed a shift from G1 to S-phase compared to additive cell lines upon combination treatment. Results from ICP-MS analysis revealed that although basal platinum levels were significantly higher in the synergistic subgroup, all SCLC cell lines showed increased intracellular platinum levels in the presence of entinostat. Here, we report that high NE expression profiles in SCLC cell lines are associated with increased sensitivity to HDAC inhibition and, moreover, that combinational therapy using entinostat and CHT results in strong synergism in a subset of SCLC cell lines featuring dysregulated cell cycle and DNA damage repair, according to proteomic analyses. Especially in SCLC, efficient therapeutic options in relapsed patients are missing, and deciphering the molecular basis of synergism between chemotherapy and entinostat might lead to more effective therapy for patients. Citation Format: Anna Schwendenwein, Kristiina Boettiger, Ildiko Kovacs, Nandor Barany, Christian Lang, Zsolt Megyesfalvi, Michael Grusch, Walter Berger, Christian Kowol, Melinda Rezeli, Konrad Hoetzenecker, Balazs Döme, Karin Schelch. Entinostat potentiates chemotherapeutic efficacy in small cell lung cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2230.

The effect of nintedanib treatment on the migratory activity of the SPC212 cells

Mutational status of tumor suppressor genes of MPM cell lines

The understanding of small cell lung cancer (SCLC) biology has increased dramatically in recent years, but the processes that allow SCLC to progress rapidly remain poorly understood. Here, we advocate the integration of rapid autopsies and preclinical models into SCLC research as a comprehensive strategy with the potential to revolutionize current treatment paradigms.

Small cell lung cancer (SCLC) accounts for approximately 15% of all lung cancer cases and is associated with a poor survival rate. SCLC is a tremendously lethal disease characterized by rapid growth and a high propensity to metastasize. Hitherto, platinum-based chemotherapy is one of the key components of the standard first-line therapeutic regimen of SCLC. Despite the known initial chemosensitivity of SCLC, the prospect of therapeutic success is limited by early relapse and acquired resistance in almost all patients.

Background The microanatomical steps of malignant pleural mesothelioma (MPM) vascularization and the resistance mechanisms to anti-angiogenic drugs in MPM are unclear. Methods We investigated the vascularization of intrapleurally implanted human P31 and SPC111 MPM cells. We also assessed MPM cell’s motility, invasion and interaction with endothelial cells in vitro. Results P31 cells exhibited significantly higher two-dimensional (2D) motility and three-dimensional (3D) invasion than SPC111 cells in vitro. In co-cultures of MPM and endothelial cells, P31 spheroids permitted endothelial sprouting (ES) with minimal spatial distortion, whereas SPC111 spheroids repealed endothelial sprouts. Both MPM lines induced the early onset of submesothelial microvascular plexuses covering large pleural areas including regions distant from tumor colonies. The development of these microvascular networks occurred due to both intussusceptive angiogenesis (IA) and ES and was accelerated by vascular endothelial growth factor A (VEGF-A)-overexpression. Notably, SPC111 colonies showed different behavior to P31 cells. P31 nodules incorporated tumor-induced capillary plexuses from the earliest stages of tumor formation. P31 cells deposited a collagenous matrix of human origin which provided “space” for further intratumoral angiogenesis. In contrast, SPC111 colonies pushed the capillary plexuses away and thus remained avascular for weeks. The key event in SPC111 vascularization was the development of a desmoplastic matrix of mouse origin. Continuously invaded by SPC111 cells, this matrix transformed into intratumoral connective tissue trunks, providing a route for ES from the diaphragm. Conclusions Here, we report two distinct growth patterns of orthotopically implanted human MPM xenografts. In the invasive pattern, MPM cells invade and thus co-opt peritumoral capillary plexuses. In the pushing/desmoplastic pattern, MPM cells induce a desmoplastic response within the underlying tissue which allows the ingrowth of a nutritive vasculature from the pleura.

Spitzoid melanoma is a rare malignancy with histological characteristics similar to Spitz nevus. It has a diverse genetic background and in adults, a similarly grim clinical outcome as conventional malignant melanoma. We established a spitzoid melanoma cell line (PF130) from the pleural effusion sample of a 37-year-old male patient. We found that the cell line carries a rare MEK1 mutation (pGlu102_Lys104delinsGln) that belongs to the RAF- and phosphorylation-independent subgroup of MEK1 alternations supposedly insensitive to allosteric MEK inhibitors. The in vivo tumorigenicity was tested in three different models by injecting the cells subcutaneously, intravenously or into the thoracic cavity of SCID mice. In the intrapleural model, macroscopic tumors formed in the chest cavity after two months, while subcutaneously and intravenously delivered cells showed limited growth. In vitro, trametinib-but not selumentinib-and the ATP-competitive MEK inhibitor MAP855 strongly decreased the viability of the cells and induced cell death. In vivo, trametinib but not MAP855 significantly reduced tumor growth in the intrapleural model. To the best of our knowledge, this is the first patient-derived melanoma model with RAF- and phosphorylation-independent MEK mutation and we demonstrated its sensitivity to trametinib.

Apelin, a ligand of the APJ receptor, is overexpressed in several human cancers and plays an important role in tumor angiogenesis and growth in various experimental systems. We investigated the role of apelin signaling in the malignant behavior of cutaneous melanoma. Murine B16 and human A375 melanoma cell lines were stably transfected with apelin encoding or control vectors. Apelin overexpression significantly increased melanoma cell migration and invasion in vitro, but it had no impact on its proliferation. In our in vivo experiments, apelin significantly increased the number and size of lung metastases of murine melanoma cells. Melanoma cell proliferation rates and lymph and blood microvessel densities were significantly higher in the apelin-overexpressing pulmonary metastases. APJ inhibition by the competitive APJ antagonist MM54 significantly attenuated the in vivo pro-tumorigenic effects of apelin. Additionally, we detected significantly elevated circulating apelin and VEGF levels in patients with melanoma compared to healthy controls. Our results show that apelin promotes blood and lymphatic vascularization and the growth of pulmonary metastases of skin melanoma. Further studies are warranted to validate apelin signaling as a new potential therapeutic target in this malignancy.

Malignant pleural mesothelioma (MPM) has an overall poor prognosis and unsatisfactory treatment options. MPM nodules, protruding into the pleural cavity may have growth and spreading dynamics distinct that of other solid tumors. We demonstrate that multicellular aggregates can develop spontaneously in the majority of tested MPM cell lines when cultured at high cell density. Surprisingly, the nodule-like aggregates do not arise by excessive local cell proliferation, but by myosin II-driven cell contractility. Prominent actin cables, spanning several cells, are abundant both in cultured aggregates and in MPM surgical specimens. We propose a computational model for in vitro MPM nodule development. Such a self-tensioned Maxwell fluid exhibits a pattern-forming instability that was studied by analytical tools and computer simulations. Altogether, our findings may underline a rational for targeting the actomyosin system in MPM.

Aims Malignant pleural mesothelioma (MPM) is a rare malignancy with a dismal prognosis. While the epithelioid type is associated with a more favourable outcome, additional factors are needed to further stratify prognosis and to identify patients who can benefit from multimodal treatment. As epithelioid MPM shows remarkable morphological variability, the prognostic role of the five defined morphologies, the impact of the nuclear grading system and the mitosis-necrosis score were investigated in this study. Methods and results Tumour specimens of 192 patients with epithelioid MPM from five European centres were histologically subtyped. Nuclear grading and mitosis-necrosis score were determined and correlated with clinicopathological parameters and overall survival (OS). Digital slides of 55 independent cases from The Cancer Genome Atlas (TCGA) database were evaluated for external validation. Histological subtypes were collapsed into three groups based on their overlapping survival curves. The tubulopapillary/microcystic group had a significantly longer OS than the solid/trabecular group (732 days versus 397 days, P = 0.0013). Pleomorphic tumours had the shortest OS (173 days). The solid/trabecular variants showed a significant association with high nuclear grade and mitosis-necrosis score. The mitosis-necrosis score was a robust and independent prognostic factor in our patient cohort. The prognostic significance of all three parameters was externally validated in the TCGA cohort. Patients with tubulopapillary or microcystic tumours showed a greater improvement in OS after receiving multimodal therapy than those with solid or trabecular tumours. Conclusions Histological subtypes of epithelioid MPM have a prognostic impact, and might help to select patients for intensive multimodal treatment approaches.