Despite the advent of potent tyrosine kinase inhibitors (TKI), resistance and disease persistence remain significant clinical challenges in chronic myeloid leukemia. This review aims to synthesize concepts derived from recent advances in single-cell and multi-omics analyses, which have revealed profound heterogeneity among leukemic stem cells (LSC). These findings augment traditional models that focus solely on clonal selection and resistance-conferring mutations. We discuss how LSC, like normal hematopoietic stem cells, exist in a spectrum of transcriptionally and epigenetically defined cell states, each governed by distinct gene regulatory networks (GRN) that confer unique lineage biases and responses to therapy. Incorporating recent insights from single-cell analyses, our review highlights evidence for a conserved chronic phase LSC state characterized by lineage skewing, altered metabolic and environmental responsiveness, and epigenetic dysregulation, features that are likely to be underpinned by specific GRN configurations that collectively contribute to intrinsic TKI resistance. We explore how both intrinsic factors (such as germline polymorphisms and lineage bias) and extrinsic cues (including microenvironmental signals, immune interactions, and hypoxia) are likely to modulate GRN activity and LSC states, thereby affecting apoptotic thresholds, primary resistance, and the potential for treatment-free remission. Emerging data support the concept of GRN-defined LSC states at diagnosis that are predictive of TKI responses. Furthermore, multiple studies suggest that blast crisis converges on a common high-risk transcriptomic and GRN state that is agnostic to mutational diversity, and driven by polycomb and DNA methylation-dependent epigenetic reprogramming. Given that BCR::ABL1-independent mechanisms, regulated at the level of GRN, may contribute to resistance and LSC persistence, these observations support placing greater emphasis in the management of chronic myeloid leukemia on addressing GRN-defined cell-state vulnerabilities, with the goal of lowering the risk of blast crisis in high-risk patients and improving control of therapy-resistant chronic phase LSC.

Aspartame (APM), a widely used sweetener, has been linked to cancers, yet its molecular impact on metabolic dysfunction-associated steatotic liver disease (MASLD) and subsequent hepatocellular carcinoma (HCC) remains undefined. We integrated network toxicology, bulk RNA-seq and docking to map the mechanism. APM targets were retrieved from ChEMBL, STITCH and SwissTargetPrediction. MASLD and HCC RNA-seq data from GEO were used to call differentially expressed genes(DEGs). WGCNA identified disease modules and hub genes. Intersection of APM targets, DEGs and hubs defined core genes for GO/KEGG and PPI analyses. CytoHubba (DMNC, EPC, Degree, MCC), LASSO, RF and SVM-RFE shortlisted key genes, and docking verified APM binding. Twelve genes intersected across APM, MASLD and HCC datasets. Enrichment supports a "dual-track" mechanism: APM-MASLD targets suppress bile-acid export, impair lipid clearance and fuel steatosis; MASLD-HCC targets jointly activate TNF/IL-17 and chemical-carcinogenesis pathways, indicating chronic inflammation bridges steatosis to cancer; APM-HCC targets map to p53, nuclear-receptor and xenobiotic-response networks, revealing APM hijacks receptor signalling to impose proliferative stress that, coupled with p53 loss, drives clonal selection. Machine-learning nominated EGR1 and PTGS2 as top diagnostic genes (AUC > 0.7); docking showed high-affinity APM binding (-7.1 and-7.9kcal mol⁻¹, respectively), identifying them as key relays in APM-induced HCC. EGR1 and PTGS2 are central nodes through which APM precipitates MASLD and accelerates progression to HCC. We propose a "dual-track" oncogenic paradigm: Track A follows the canonical MASLD-HCC axis (bile-acid retention - lipid deposition - TNF/IL-17-driven ROS-mutational amplification), whereas Track B allows APM, via PTGS2/EGR1, to usurp gate-keeper proteins governing proliferation and apoptosis, initiating malignant programming before overt steatosis develops. These findings provide mechanistic insight into APM-related hepatocarcinogenesis, nominate tractable diagnostic biomarkers and therapeutic targets, and inform future re-evaluation of APM carcinogenicity classifications.

Listeria monocytogenes is a ubiquitous Gram-positive bacterium responsible for listeriosis, a foodborne zoonotic disease affecting humans and animals. Although infection in immunocompetent individuals is often asymptomatic or limited to mild self-limiting gastroenteritis, Listeria monocytogenes may cause severe invasive disease in vulnerable groups, including pregnant women, neonates, elderly individuals, and immunocompromised patients. Although the incidence of listeriosis is relatively low compared with many other foodborne pathogens, the high hospitalization and mortality rates associated with clinical cases make this bacterium a major concern for food safety and public health. The evolutionary success of L. monocytogenes reflects the interaction between a conserved core genome and a dynamic accessory genome shaped by horizontal gene transfer (HGT), ecological selection, and expansion of specific clones. Transient intestinal carriage in humans and animals, potentially influenced by gut microbiome composition, creates ecological interfaces where plasmids, transposons, prophages, and integrative conjugative elements contribute to the exchange of antimicrobial resistance determinants, virulence factors, and stress tolerance systems. Virulence diversification is further influenced by the differential distribution of pathogenicity islands such as LIPI-1, LIPI-3, and LIPI-4 across specific clonal lineages. These evolutionary processes occur across interconnected farm, food-production, environmental, and clinical ecosystems consistent with the One Health framework. Advances in whole-genome sequencing have clarified lineage-specific gene flow, expansion of specific clones, and the dynamics of the resistome and mobilome in L. monocytogenes populations. This narrative review aims to synthesize current knowledge on the mobile genetic elements and ecological interfaces that shape horizontal gene transfer in L. monocytogenes. Its novelty lies in integrating antimicrobial resistance, virulence-associated genomic islands, stress adaptation, and gut microbiome-mediated selection within a One Health and metapopulation framework. The main message of this review is that HGT should be interpreted as a context-dependent contributor to L. monocytogenes adaptation, acting together with clonal background, ecological selection, and mobile genetic elements.

Clonal selection drives cancer development, but quantifying selection on noncoding somatic mutations remains largely unexplored. Here, we introduce dNdS-Fun, an extension of the dN/dS framework to quantify selection of both coding and noncoding somatic mutations, thereby enhancing the discovery of driver genes. Applying dNdS-Fun to whole-genome sequencing data from 14,886 cancer patients across 31 cancer types, we identify 175 genes under positive selection across multiple cancer types or datasets, as well as 20 previously known driver genes detected through noncoding mutations. Of these, 69 are previously unrecognized as drivers, and 30 are identified solely through noncoding mutations. Furthermore, we observe evidence of negative selection throughout the genome, with significant enrichment in essential and cancer-dependent genes. Sixteen genes exhibit an overall signature of negative selection but show positive selection in noncoding elements, indicating both their conserved functions and adaptive regulatory roles in tumorigenesis. Our study reveals evidence consistent with negative selection of noncoding mutations, providing important insights for future research on their roles in cancer progression.

Fish mucosal tissues lack the organized lymphoid structures present in mammals. Although this is also true for the gills, with the gill-associated lymphoid tissue (GIALT) being mainly composed of B and T cells scattered throughout the epithelium and the lamellae, in some species such as rainbow trout (Oncorhynchus mykiss) or Atlantic salmon (Salmo salar), a more organized structure designated as the interbranchial lymphoid tissue (ILT) is also identified. Yet, although many studies have investigated the immune response of the gill to stimulation or pathogen encounter, which have revealed the activation of both innate and adaptive immune elements, how the gills respond to secondary stimulation or whether memory responses are locally orchestrated is still unknown. To provide insights into this matter, in the current study, we have infected rainbow trout by bath with Lactococcus petauri and then re-infected or mock-infected the survivor fish as well as mock-infected controls. At day 4 after the last infection, the fish were sacrificed and gills used to perform an RNAseq transcriptomic analysis and an IgM and IgT repertoire analysis. The number of cells secreting total and specific IgM in gills was also established by ELISpot. Our results demonstrate that memory responses are locally organized in the rainbow trout gills, given that re-infected fish did not up-regulate genes related to inflammation (as happens in the primary infection), but preferentially modified genes related to adaptive immunity, mainly to B cell function, experiencing a significant IgM and IgT clonal expansion. Accordingly, re-infected fish produced increased levels of specific IgM both locally and in serum, although no clonal selection was apparent. These findings advance our understanding of mucosal immunological memory in teleost fish and reveal the gills as a site of localized adaptive immune regulation during secondary responses.

The identification of the cancer cell of origin is a fundamental question in cancer biology. We used fluorescent lineage tracing of independent mouse skin stem cell populations, single cell transcriptomics, and Duplex sequencing, to identify the origin of chemically induced skin tumors. Tumors arose predominantly from Lgr6+ and / or Lrig1+ stem cells of the upper hair follicle, but only very rarely from the Lgr5+ and Krt19+ hair follicle bulge. Lgr6+ stem cells initiated by dimethylbenzanthracene responded to tumor promoter treatment resulting in clonal expansion of initiated cells carrying the canonical Hras Q61L mutation. Spontaneous mutations in Kras also clonally expanded, but did not generate tumors unless the Hras gene was deleted, thus revealing a competitive interaction between Hras and Kras pathways that influences clonal selection.

Prions are self-templating assemblies of the host prion protein in which conformational templating encodes heritable "strain" information. Human prion diseases, including Creutzfeldt-Jakob disease (CJD), are rare but uniformly fatal neurodegenerative disorders with established public-health relevance through epidemic and iatrogenic transmission and provide a paradigm for conformational templating in neurodegeneration. Mechanistic analysis of human prion propagation and development of infectivity assays for public health surveillance have been limited by the absence of mammalian cell systems that replicate authentic infectious human prions. Here, we establish a humanized neural cell system that enables propagation of variant CJD (vCJD) prions and reveals that prion replication is constrained by strain-compatible cellular states. The platform was generated using a silencing-followed-by-reconstitution strategy analogous to that used in transgenic mouse models of human prion disease, combined with high-throughput clonal selection. These cells propagate brain-derived vCJD prions and support chronic infection. Prions propagated in vitro transmit disease to humanized transgenic and wild-type mice while preserving defining biochemical and strain-specific neuropathological features, demonstrating faithful propagation. Propagation is strain specific: The cells are permissive to vCJD but refractory to sporadic CJD isolates, indicating that prion replication is constrained by strain-compatible cellular states. These humanized cells enable quantitative detection of infection at high dilution, support systematic genetic manipulation, and are readily adaptable to automation. By overcoming a longstanding barrier of propagating authentic human prions, this platform enables mechanistic dissection of the cellular determinants of prion replication and strain specificity and provides a scalable system for genetic analysis and sensitive detection of infectious human prions.

Clonal hematopoiesis (CH) is the age-related expansion of mutated hematopoietic stem cells without hematologic abnormalities. In patients with solid tumors, CH is associated with higher mortality and may evolve to therapy-related myeloid neoplasms; however, the mechanisms by which cancer treatments promote CH dynamics remain largely unknown. Here, we analyzed 392 serial samples from a prospective cohort of breast cancer patients and showed that cytotoxic treatments led to strong therapeutic bottlenecks, resulting in significant reductions in hematopoietic allelic populations and differential clonal selection. Positively selected CH that expanded through dose-dependent therapeutic bottlenecks harbored mutations in TP53, PPM1D, SRCAP, DNMT3A, and YLPM1. Patients with positively selected CH during treatment had the shortest progression-free and overall survival compared to patients with unchanging or negatively selected CH across all therapies. These findings, validated in independent breast cancer and pan-cancer cohorts, provide strong evidence for clinical relevance of monitoring CH during cancer treatment.

Aplastic anemia (AA) and paroxysmal nocturnal hemoglobinuria (PNH) are closely related bone marrow (BM) failure syndromes linked by shared immunological mechanisms. The frequent emergence of PNH-type blood cells during AA, together with the co-occurrence of the disorders and their overlapping therapeutic responses, supports the concept that they represent a spectrum of immune-mediated hematopoietic injury rather than distinct disease entities.AA is a prototypical immune-mediated BM failure characterized by cytotoxic T-cell-driven suppression of hematopoietic stem and progenitor cells. Within this immune-hostile environment, glycosylphosphatidylinositol (GPI)-anchor-deficient PNH clones commonly emerge and persist, a phenomenon best explained by immune selection rather than intrinsic proliferative advantage. Although most PNH clones detected in AA remain small and clinically silent, their presence reflects ongoing or past immune pressure within the BM microenvironment.Advances in high-sensitivity flow cytometry have revealed that minor PNH populations are frequent in AA, indicating that immune-driven clonal selection occurs at an early stage of hematopoiesis. Longitudinal studies further demonstrate that clonal dynamics parallel changes in immune activity, supporting their relevance for risk-adapted monitoring.In this review, we highlight immune-mediated BM failure as the common soil from which PNH clones arise and discuss implications for diagnosis, monitoring, and phenotype-driven management.

Clonal tracing of blood stem cells across mouse and human lifespans.

Dynamic genetic and nongenetic RAS pathway activation drives resistance to FLT3 and BCL2 inhibitor therapy.

An exploratory study of environmental and nutritional determinants of early-stage clonal hematopoiesis in the elderly.

Prostate cancer (PCa) is the second leading cause of cancer-related mortality in men, with bone representing the predominant metastatic site. Progress in treating bone metastatic disease is hindered by lack of preclinical models that faithfully recapitulate the bone microenvironment while reducing animal use. Biomaterial-based platforms offer a powerful alternative, enabling controlled reconstruction of bone composition, metabolic cues, and tumour-matrix interactions. A defining feature of PCa progression is citrate-centred metabolic reprogramming. While healthy prostate epithelial cells accumulate and secrete citrate, aggressive PCa cells import and oxidise it to sustain growth. Given the citrate-rich nature of prostate tissue and bone, we hypothesised that bone-derived citrate may be exploited by metastatic PCa cells to support bone colonisation. We developed a bone-mimetic platform by functionalising hydroxyapatite nanocrystals with citrate (HA-Nc-Cit) and incorporating them into collagen-based 3D matrices within a microfluidic chip. HA-Nc-Cit were characterised and citrate release quantified. Metastatic PCa cells were analysed for migration, viability, clonogenicity, metabolic reprogramming, and citrate transporter expression. HA-Nc-Cit released physiologically relevant citrate levels. Citrate exposure enhanced migration of androgen-independent PC3 cells and, within collagen type I-enriched matrices, increased clonogenicity, upregulated plasma membrane citrate transporter, suppressed glycolysis, and promoted lactate fermentation and mitochondrial biogenesis, without affecting respiratory chain or lipid metabolism. Citrate buffering supported PC3 clonal survival under acidic stress mimicking tumour acidification. In conclusion, citrate-functionalised HA-Nc promotes bone tropism of aggressive PCa by enhancing migratory potential, modulating tumour metabolism, and buffering extracellular acidification, underscoring the value of biomaterial-based models for studying bone-tumour interactions and guiding therapeutic development. STATEMENT OF SIGNIFICANCE: PCa often spreads to bone, but current models fail to capture the complexity of bone environment, limiting progress in treatment development. In this study, we created a 3D bone-mimicking system by binding citrate, a key bone metabolite, to hydroxyapatite nanocrystals mimicking bone mineral and embedding them in collagen-based matrices. This platform shows how citrate not only fuels PCa cells but also buffers the acidic conditions they create, making bone more prone to tumour growth. Unlike traditional models, such biomaterial-based approach combines mineral chemistry, metabolism, and pH regulation in a controlled setting. This work introduces a tool to study bone-tumour interactions and guide future therapies for metastatic PCa.

Extrachromosomal DNA (ecDNA) is a structural variant linked to poor prognosis in pediatric cancers. Patient-derived xenograft (PDX) models are crucial tools for cancer research, as they are believed to recapitulate the molecular features and intratumoral heterogeneity in patient tumors. However, ecDNA demonstrates unique evolutionary dynamics under selective pressure, and its behavior during PDX development remains largely uncharacterized. This study investigates the fidelity of PDX models in representing ecDNA from primary tumors. By analyzing ecDNA sequence composition and copy number conservation across pediatric solid cancers, we assess how well PDX models recapitulate the ecDNA landscape observed in human tumors. AmpliconArchitect was used to analyze whole-genome sequencing (WGS) of 338 PDX models and 127 corresponding primary tumors. ecDNA status, sequence, copy number, and associated genes were compared between PDX models and their matched human tumors. Additionally, multiome RNA and ATAC single-cell sequencing of a PDX tumor enabled comparison of ecDNA intratumoral heterogeneity relative to similar data from the primary tumor. ecDNA in PDX models largely recapitulated oncogene amplifications observed in human tumors, with MYCN being the most frequently amplified. ecDNA status remained unchanged for a majority of the PDX models (105/127, 83%) compared to primary tumors, with 20% of previously ecDNA-negative cases acquiring ecDNA during PDX development. Consequently, ecDNA was more prevalent in the PDX models than in their corresponding human tumors (McNemar's test, p = 0.00086). Detailed examination of ecDNA sequences in tumor-PDX pairs showed substantial conservation (67% with > 90% sequence overlap) but variable breakpoint concordance. Single-cell analysis demonstrated that rare ecDNA-positive cells from the primary tumor preferentially drive PDX tumor development. This study highlights the prevalence, oncogenic content, and conservation of ecDNA in PDX models relative to pediatric patient tumors. We observed that ecDNA frequently recapitulates oncogene amplifications found in human cancers, is generally preserved during PDX establishment, and reflects subtype-specific patterns across tumor types. These findings support the utility of PDX models in studying ecDNA biology in pediatric cancer progression and therapy. Longitudinal sampling during PDX tumor growth and under therapeutic pressure could provide insights into molecular evolution, clonal selection, and ecDNA-driven therapy resistance.

Clonal reproduction represents a fundamental strategy in plant propagation, enabling the formation of extensive genetically identical populations through persistent asexual growth. Understanding the spatial-temporal dynamics of these clonal systems, particularly with regard to their age, size, and somatic mutation patterns, is crucial for unravelling the evolutionary ecology of long-lived plant species. While such investigations have been conducted in woody perennials, herbaceous clonal systems remain markedly understudied. We address this knowledge gap through an integrated genomic study (including de novo assembly of a gap-free reference genome and whole-genome resequencing of 72 spatially distributed samples) of Typha latifolia, a rhizomatous perennial inhabiting a 103.2 ha alpine wetland in Sichuan, China. We identify this population as a clonal population and estimated the clone's age to be ~1900 ( ± 100) years, with a species-level mutation rate and radiocarbon. Somatic mutations are significantly enriched in transposable elements (TEs), 71% occurring in TEs with one-third genomic coverage ( ~ 33% of callable sites and ~34% of total genome), and are significantly fixed in TEs in 50 out of 72 sampled ramets. This study provides insights into both clonal persistence and clonal expansion capacity and somatic mutation accumulation in herbaceous plants, advancing understanding of clonal plant survival and evolution.

Targeting Oncomucin-driven Immunosuppression Improves the Efficacy of K-rasG12D Inhibition in Pancreatic Cancer.

Intensified fed-batch processes are becoming increasingly prevalent among biomanufacturers due to their superior space-time yields relative to traditional, non-intensified fed-batch processes. However, the shift towards intensified manufacturing has unexpectedly made optimal clone selection more challenging. Clone selection, traditionally an empirical screening of candidates on the basis of productivity, has been complicated by the observation that clonal productivity rankings can vary substantially between intensified and non-intensified processes. In the absence of a small-scale intensified empirical screen, clones destined for intensified manufacturing are selected based on their performance in the non-intensified process. This mismatch risks selection of suboptimal clones, representing a missed opportunity to generate additional product at no extra cost. This study presents a machine learning approach to improve clone selection for intensified processes by predicting and ranking clonal productivity. Models were trained on non-intensified clone performance data routinely collected during cell line development to facilitate seamless integration into existing capabilities. To evaluate generalizability and simulate real-world application, independent clone panels expressing two distinct monoclonal antibodies were withheld from model training and used in comparative testing against the legacy clone selection method. The ranking model identified the most productive clone of those expressing the first mAb, representing a 68.5% higher titer than the clone selected by the legacy method. For the second mAb, the ranking model identified the second most productive clone, resulting in a marginally lower titer. These results demonstrate the potential of machine learning models as practical tools for improving the selection of high productivity clones in intensified bioprocessing.

Lawson ARJ, et al. Somatic mutation and selection at the population scale. Nature. 2025;647(8089):411-420. https://doi.org/10.1038/s41586-025-09584-w . A cross-sectional observational cohort study using advanced genomic sequencing to map somatic mutations and clonal selection in normal human tissues at the population level1. The authors used targeted NanoSeq, a duplex sequencing method achieving exceptionally low error rates (fewer than five errors per billion base pairs). The technique was applied to targeted capture of a 239-gene panel (0.9 Mb) in 1042 non-invasive buccal swab samples (median donor age 68 years, 79% female, 37% smokers) and 371 blood samples from the TwinsUK registry. Mutation calling required strict duplex consensus filters. Gene-level selection was quantified using dNdScv, while site-level dN/dS analyses were used to identify recurrent hotspots and selected sites. Mutational signatures were deconvolved with sigfit, and multivariate mixed-effects regression modelled associations with age, smoking (pack-years), alcohol (drink-years), missing teeth, and other covariates. In the oral epithelium, single nucleotide variants (SNVs) accumulated at 18.0 per cell per year and indels (insertions or deletions in the genome) at 2.0 per cell per year. Across all 1,042 participants, the authors detected 341,682 somatic mutations, including approximately 62,000 estimated driver mutations across 46 positively selected genes (e.g., NOTCH1 mutant cells reaching approximately 10% by ages 65-85 years, TP53 ~ 3%). Nine genes showed negative selection. Two dominant mutational signatures emerged: a clock-like signature A (resembling SBS1 and SBS5) and an alcohol associated signature B (resembling SBS16). The authors reported that smoking and alcohol were associated with higher mutation burdens, and that some effects on clonal selection were inferred from regression analyses; missing teeth (a marker of poor oral health) were independently associated with higher overall driver density. Driver frequencies for NOTCH1 were similar in normal epithelium and head and neck squamous cell carcinoma (HNSCC), whereas TP53 was enriched in cancer. The authors concluded that optimised NanoSeq enables population-scale mutational epidemiology in polyclonal tissues, revealing an extraordinarily rich landscape of positive and negative selection in normal oral epithelium. Environmental exposures shape mutagenesis and may also influence clonal selection, supporting a plausible mechanistic link between smoking, alcohol, and oral cancer risk.

Prostate cancer (PCa) is immunologically "cold" and resistant to immune checkpoint blockade (ICB), yet bulk analyses show low, non-prognostic PD-L1 expression. We hypothesised that this paradox reflects two overlooked dimensions: basal heterogeneity (static engine) and IFN-γ-driven adaptive resistance (adaptive engine). Using TCGA-PRAD data (n=554) to parameterise an agent-based model, we simulated clonal selection and extended it to a hybrid discrete-continuum framework with reaction-diffusion IFN-γ. Bulk PD-L1 was low (median 1.48 TPM) and non-prognostic (HR =1.15, p=0.621). The static engine alone produced weak immunoediting (1.10-fold enrichment), whereas the adaptive engine drove a 2.95-fold enrichment of PD-L1-high clones via protective sanctuary formation, without increasing final tumour burden. Induction knockout (Pmax=0) abrogated this advantage, while diffusion knockout (D=0) had no effect. The cold tumour paradox is resolved by a hierarchical twin engine: rare genomic outliers permit initial persistence, but local IFN-γ/PD-L1 feedback dominates resistance, identifying induction capacity as the primary therapeutic target for JAK/STAT inhibition combined with ICB.

Temozolomide (TMZ) can be an effective medical treatment for aggressive pituitary tumors. In case of disease recurrence following TMZ treatment, however, treatment with the drug generally does not control tumor regrowth. This work aimed to better understand the mechanisms of resistance of corticotroph tumors to TMZ in the context of heterogeneity of methylguanine-DNA methyltransferase (MGMT) expression. We performed immunohistochemical analysis of the MGMT expression pattern in 25 corticotroph tumors to evaluate intratumoral heterogeneity. In addition, we created in vitro models of AtT20 corticotroph tumor cells with acquired TMZ-resistance after exposure to high- and low-dose TMZ, the latter representing a clinically achievable TMZ level. MGMT immunostaining in corticotroph tumors showed a considerable heterogeneous intertumoral and intratumoral distribution pattern in 80% of tumors. In the in vitro model, high- and low-dose TMZ challenges induced a 6.3- and 3.4-fold decreased sensitivity to the growth inhibitory effect of TMZ. TMZ-induced changes in cell cycle phases were lower in TMZ-resistant cells than in vehicle-challenged cells. TMZ-resistant cells had higher Mgmt messenger RNA and protein expression and 1.8-fold higher number of Mgmt-positive cells. No difference was observed in the level of Mgmt promoter methylation. Corticotroph pituitary tumors demonstrate a high intertumoral and intratumoral heterogeneity in MGMT expression. In an acquired TMZ-resistant corticotroph pituitary tumor cell model, TMZ resistance was associated with strong increase in MGMT expression and percentage of MGMT-positive cells. We hypothesize that clonal selection of high MGMT-expressing cells is involved in this acquired TMZ resistance.