Early Passage Cells Research Articles

A cell state-specific metabolic vulnerability to GPX4-dependent ferroptosis in glioblastoma

Glioma cells hijack developmental programs to control cell state. Here, we uncover a glioma cell state-specific metabolic liability that can be therapeutically targeted. To model cell conditions at brain tumor inception, we generated genetically engineered murine gliomas, with deletion of p53 alone (p53) or with constitutively active Notch signaling (N1IC), a pathway critical in controlling astrocyte differentiation during brain development. N1IC tumors harbored quiescent astrocyte-like transformed cell populations while p53 tumors were predominantly comprised of proliferating progenitor-like cell states. Further, N1IC transformed cells exhibited increased mitochondrial lipid peroxidation, high ROS production and depletion of reduced glutathione. This altered mitochondrial phenotype rendered the astrocyte-like, quiescent populations more sensitive to pharmacologic or genetic inhibition of the lipid hydroperoxidase GPX4 and induction of ferroptosis. Treatment of patient-derived early-passage cell lines and glioma slice cultures generated from surgical samples with a GPX4 inhibitor induced selective depletion of quiescent astrocyte-like glioma cell populations with similar metabolic profiles. Collectively, these findings reveal a specific therapeutic vulnerability to ferroptosis linked to mitochondrial redox imbalance in a subpopulation of quiescent astrocyte-like glioma cells resistant to standard forms of treatment.

Leveraging Cell Migration Dynamics to Discriminate Between Senescent and Presenescent Human Mesenchymal Stem Cells

PurposeThe suboptimal clinical performance of human mesenchymal stem cells (hMSCs) has raised concerns about their therapeutic potential. One major contributing factor to this issue is the heterogeneous nature of hMSCs. Senescent cell accumulation during stem cell expansion is a key driver of MSC heterogeneity. Current methodologies to eradicate senescent hMSCs have either shown limited success or lack clinical relevance. This study leverages the inherent capacity of hMSCs to migrate toward damaged tissues as a means to discern senescent from presenescent stem cells. Given the established deficiency of senescent cells to migrate through physiologically relevant environments, we hypothesized that a microfluidic device, designed to emulate key facets of in vivo cell motility, could serve as a platform for identifying presenescent cells.MethodsWe employed a Y-shaped microchannel assay, which allows fine-tuning of fluid flow rates and the degree of confinement.ResultsHighly migratory hMSCs detected by the device not only demonstrate increased speed, smaller size, and higher proliferative capacity but also manifest reduced DNA damage and senescence compared to non-migratory cells. Additionally, this assay detects presenescent cells in experiments with mixed early and late passage cells. The introduction of fluid flow through the device can further increase the fraction of highly motile stem cells, improving the assay's effectiveness to remove senescent hMSCs.ConclusionsCollectively, this assay facilitates the detection and isolation of a highly potent stem cell subpopulation. Given the positive correlation between the migratory potential of administered MSCs and the long-term clinical outcome, delivering homogeneous, highly motile presenescent hMSCs may benefit patient outcomes.

Changes in Stemness Properties of Human Adenoid-Derived Mesenchymal Stem Cells by in Vitro Aging

Mesenchymal stem cells (MSCs) have significant therapeutic potential in gene therapy. In vitro replicative senescence causes slow proliferation capacity of MSCs and changes in stem cell properties. In this study, the stem cell properties and proliferation potential of MSCs obtained from adenoid tissue, a new source of MSC, were investigated after long-term in vitro replicative senescence. Adenoid-derived MSCs (A-MSCs) were cultured up to passage 20 and were analyzed for cell morphology, proliferative capacity, differentiation potential and surface marker expression. In addition, the expression profile of cell cycle, apoptosis and senescence-related genes were evaluated. After in vitro replicative senescence, A-MSCs did not show significant morphological differences. The proliferation potential of A-MSCs was rapid up to passage 16, and a reduction in the proliferation potential of senescent cells in vitro was observed depending on the passage number. The differentiation potential of late-passage A-MSCs was also reduced compared to early-passage cells. A-MSCs also provided significant closure at the 8th hour in early passages in terms of closure of the scratch area, while late passage A-MSCs exhibited a similar closure profile at the 24th hour. In conclusion, A-MSCs have significant potential for clinical use due to the sustainability of MSC properties and their ability to proliferate and migrate with long-term culture.

Identification of Periostin Positive Cell Population During the Long-Term Culture of Mouse Tendon-Derived Cells in Late Passage.

Tendon-derived cells exhibit phenotypic changes and gradually lose their proliferative capacity during serial passages in vitro. This study aimed to characterize the changes in the growth and stem cell characteristics of tendon-derived cells over a long-term culture. Mouse flexor digitorum profundus tendon-derived cells were obtained by enzymatic digestion and seeded at an initial density of 5,000/cm2. Cells were characterized by morphology, growth, senescence staining, trilineage differentiation assays, real-time polymerase chain reaction, immunocytochemistry, flow cytometry, and RNA sequencing analysis. Tendon-derived cells underwent a proliferative stage in the first three passages, followed by a gradual senescence. However, a novel cell population expressing periostin (Postn+) emerged during the long-term culture from passages 5-8, which possessed a high rate of proliferation without significant senescence over successive passages. Compared to early passage cells, Postn+ cells exhibited enhanced osteogenic differentiation potential and attenuated chondrogenic differentiation potential, decreased expression of SSEA-1, Oct3/4, tenomodulin, scleraxis, CD90.2, CD73, CD105, Sca-1, and CD44, and increased expression of collagen III and CD34. RNA-sequencing analysis of Postn+ and early passage cells identified 908 differentially expressed genes, with extracellular matrix-receptor interaction and focal adhesion as the top pathways, and integrins as hub genes. This study highlights the dynamics of tendon-derived cells during serial passages. We identify a Postn+ cell population during long-term culture in late passages, with high proliferative ability and prominent osteogenic differentiation potential. Further investigations are needed to elucidate the origin and potential applications of Postn+ tendon-derived cells.

Expansion and Storage of Insect Cells and Virus Stocks.

Healthy insect cell cultures are critical for any method described in this book, including making productive baculovirus banks, protein or AAV expression, and determining viral titers. This chapter describes cell maintenance in shake flasks using serum-free conditions and the expansion of virus stocks from a single plaque purified virus. Insect cells can be passaged over multiple generations, but as the cells may undergo changes over multiple passages, limiting the use of your cells to a defined number of passages such as 50 passages is recommendable. Baculovirus stocks once created using serum-free media are not very stable at 4-8°C. This chapter also includes a simple method to store cells from an early cell passage and your virus stock in liquid nitrogen.

Biological Effects of "Inflammageing" on Human Oral Cells: Insights into a Potential Confounder of Age-Related Diseases.

The term "inflammageing" describes the process of inflammation-induced aging that leads living cells to a state of permanent cell cycle arrest due to chronic antigenic irritation. This in vitro study aimed to shed light on the mechanisms of "inflammageing" on human oral cells. Primary cultures of human gingival fibroblasts (hGFs) were exposed to variable pro-inflammatory stimuli, including lipopolysaccharide (LPS), Tumor Necrosis Factor-alpha (TNFa), and gingival crevicular fluid (GCF) collected from active periodontal pockets of systemically healthy patients. Inflammageing was studied through two experimental models, employing either late-passage ("aged") cells (p. 10) that were exposed to the pro-inflammatory stimuli or early-passage ("young") cells (p. 1) continuously exposed during a period of several passages (up to p. 10) to the above-mentioned stimuli. Cells were evaluated for the expression of beta-galactosidase activity (histochemical staining), senescence-associated genes (qPCR analysis), and biomarkers related to a Senescence-Associated Secretory Phenotype (SASP), through proteome profile analysis and bioinformatics. A significant increase (p < 0.05) in beta-galactosidase-positive cells was observed after exposure to each pro-inflammatory stimulus. The senescence-associated gene expression included upregulation for CCND1 and downregulation for SUSD6, and STAG1, a profile typical for cellular senescence. Overall, pro-inflammatory priming of late-passage cells caused more pronounced effects in terms of senescence than long-term exposure of early-passage cells to these stimuli. Proteomic analysis showed induction of SASP, evidenced by upregulation of several pro-inflammatory proteins (IL-6, IL-10, IL-16, IP-10, MCP-1, MCP-2, M-CSF, MIP-1a, MIP-1b, TNFb, sTNF-RI, sTNF-RII, TIMP-2) implicated in cellular aging and immune responses. The least potent impact on the induction of SASP was provoked by LPS and the most pronounced by GCF. This study demonstrates that long-term exposure of hGFs to various pro-inflammatory signals induced or accelerated cellular senescence with the most pronounced impact noted for the late-passage cells. The outcome of these analyses provides insights into oral chronic inflammation as a potential confounder of age-related diseases.

Putative Cancer Stem Cell Markers are Frequently Expressed by Melanoma Cells in Vitro and in Situ but are also Present in Benign Differentiated Cells.

Currently, there remains an incomplete view of cancer stem cells (CSCs) in solid tumours. We studied a panel of putative CSC surface markers (ALDH1A1, ABCG2, CD44v7/8, CD44v10, CD133, CD271, and Nestin) in 40 established melanoma cell lines and four early-passage melanoma strains by flow cytometry. We additionally examined 40 formalin-fixed paraffin-embedded melanoma tissues using immunofluorescence microscopy. This was compared with their expression in healthy skin, normal differentiated melanocytes and fibroblasts. Most of the putative CSC markers were expressed by both melanoma cell lines and tissues. When present, these proteins were expressed by the majority of cells in the population. However, the expression of these markers by cells in healthy skin sections, normal differentiated melanocytes, and fibroblasts revealed that differentiated non-malignant cells also expressed CSC markers indicating that they lack of specificity for CSCs. Culturing cell lines under conditions more characteristic of the tumour microenvironment upregulated CSC marker expressions in a proportion of cell lines, which correlated with improved cell growth and viability. The testing of melanoma cell lines (n = 40), early-passage cell strains (n = 4), and melanoma tissues (n = 40) showed that several putative CSC markers (ALDH1A1, ABCG2, CD44v7/8, CD44v10, CD133, CD271, and Nestin) are commonly present in a large proportion of melanoma cells in vitro and in situ. Further, we showed that these putative markers lack specificity for CSCs because they are also expressed in differentiated non-malignant cell types (melanocytes, fibroblasts, and skin), which could limit their use as therapeutic targets. These data are consistent with the emerging notion of CSC plasticity and phenotype switching within cancer cell populations.

Analysis of Somatic Mutations in Senescent Cells Using Single-Cell Whole-Genome Sequencing.

Somatic mutations accumulate in multiple organs and tissues during aging and are a known cause of cancer. Cellular senescence is a possible cause of functional decline in aging, yet also acts as an anticancer mechanism in vivo. Here, we compared somatic mutation burden between early passage and deeply senescent human fibroblasts using single-cell whole-genome sequencing. The results show that single-nucleotide variants (SNVs) and small insertions and deletions (INDELs) are increased in senescent cells by about twofold but have the same mutational signature as early passage cells. The increase in SNVs and INDELs can be explained by increased replication errors due to the increased number of cell divisions senescent cells are likely to have undergone. By contrast, a stark increase of aneuploidies was observed in deeply senescent cells, with about half of all senescent cells affected but none of the early passage cells analyzed. These results indicate that large chromosomal events rather than small base substitutions or insertions and deletions could be mechanistically linked to cellular senescence.

Abstract 2577: Pre-cancerous ovarian cells harboring a familial SMARCA4 mutation acquire in vitro phenotypes associated with transformation in SSCOHT

Abstract Introduction: Small Cell Carcinoma of the Ovary, Hypercalcemic Type (SCCOHT) is an extremely rare but deadly ovarian cancer associated with mutations in the SMARCA4 gene. Using a unique population of ovarian cells derived from a familial carrier of an SCCOHT-associated SMARCA4 mutation, we sought to determine if non-cancerous cells would spontaneously transform during in vitro culture, thereby providing a model system for studying formation of SCCOHT. Methods: Ovarian cells derived from a familial carrier of a SMARCA4 mutation (P590, SMARCA4. c.3081+1G&amp;gt;T) were serially passaged in vitro and interrogated for acquisition of phenotypes consistent with cellular transformation. Loss of contact-dependent inhibition was interrogated with focus-forming assays in confluent monolayers. The ability of cells to escape anoikis and grow independently as spheroids was tested in attachment-free growth conditions using both single and aggregate spheroid growth assays. Senescence-associated β-galactosidase (SA-β-gal), cellular necrosis, and cellular apoptosis was also measured. All experiments were conducted in parallel with an age-matched cell population derived from a benign ovarian surgery (P583). In experiments to determine if these differences could be attributed to loss of functional SMARCA4, non-mutant P583 cells were cultured in the presence of the SWI/SNF inhibitor BRM014 and interrogated in focus-forming and attachment-free growth assays. Results: P590 cells passaged over 12 twelve times (approx. 40 cell divisions) continued to proliferate in culture. In contrast, non-mutant P583 cells failed to grow beyond 11-12 passages. With prolonged culture, P590 cells lost expression of SMARCA4 protein, while P583 cells retained SMARCA4 expression. P590 cells grown to confluency spontaneously formed foci of multicellular aggregates, while P583 cells did not. In attachment-free culture conditions, P590 cells readily formed spheroids from both early-passage and late-passage cells. In contrast, P583 formed small spheroids that failed to expand in culture. Surprisingly, both P590 and P583 cells displayed elevated SA-β-gal staining, with neither cell populations showing elevated necrosis or apoptosis markers. Treating P583 cells with BRM014 increased focus formation and spheroid growth similar to that of mutant cells. Conclusions: SCCOHT is extremely rare, with very few representative samples useful for developing early-stage markers or improved therapeutics. Long-term culture of ovarian cells harboring inactivated forms of SMARCA4 result in the acquisition of several phenotypes consistent with early stages of cellular transformation. Our data suggest that mutating or inactivating SMARCA4 in non-transformed ovarian cells may be a way to create novel research tools for studying formation of SCCOHT. This work was supported by DoD award W81XWH-21-1-0512 Citation Format: Sonali Joshi, Shawn Campbell, Yukie Bean, Tanja Pejovic, Adam Krieg. Pre-cancerous ovarian cells harboring a familial SMARCA4 mutation acquire in vitro phenotypes associated with transformation in SSCOHT [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 2577.

Nanomechanical Signatures in Glioma Cells Depend on CD44 Distribution in IDH1 Wild-Type but Not in IDH1R132H Mutant Early-Passage Cultures

Atomic force microscopy (AFM) recently burst into biomedicine, providing morphological and functional characteristics of cancer cells and their microenvironment responsible for tumor invasion and progression, although the novelty of this assay needs to coordinate the malignant profiles of patients' specimens to diagnostically valuable criteria. Applying high-resolution semi-contact AFM mapping on an extended number of cells, we analyzed the nanomechanical properties of glioma early-passage cell cultures with a different IDH1 R132H mutation status. Each cell culture was additionally clustered on CD44+/- cells to find possible nanomechanical signatures that differentiate cell phenotypes varying in proliferative activity and the characteristic surface marker. IDH1 R132H mutant cells compared to IDH1 wild-type ones (IDH1wt) characterized by two-fold increased stiffness and 1.5-fold elasticity modulus. CD44+/IDH1wt cells were two-fold more rigid and much stiffer than CD44-/IDH1wt ones. In contrast to IDH1 wild-type cells, CD44+/IDH1 R132H and CD44-/IDH1 R132H did not exhibit nanomechanical signatures providing statistically valuable differentiation of these subpopulations. The median stiffness depends on glioma cell types and decreases according to the following manner: IDH1 R132H mt (4.7 mN/m), CD44+/IDH1wt (3.7 mN/m), CD44-/IDH1wt (2.5 mN/m). This indicates that the quantitative nanomechanical mapping would be a promising assay for the quick cell population analysis suitable for detailed diagnostics and personalized treatment of glioma forms.

An in vitro carcinogenesis model for cervical cancer harboring episomal form of HPV16.

Deregulated expression of viral E6 and E7 genes often caused by viral genome integration of high-risk human papillomaviruses (HR-HPVs) into host DNA and additional host genetic alterations are thought to be required for the development of cervical cancer. However, approximately 15% of invasive cervical cancer specimens contain only episomal HPV genomes. In this study, we investigated the tumorigenic potential of human cervical keratinocytes harboring only the episomal form of HPV16 (HCK1T/16epi). We found that the HPV16 episomal form is sufficient for promoting cell proliferation and colony formation of parental HCK1T cells. Ectopic expression of host oncogenes, MYC and PIK3CAE545K, enhanced clonogenic growth of both early- and late-passage HCK1T/16epi cells, but conferred tumor-initiating ability only to late-passage HCK1T/16epi cells. Interestingly, the expression levels of E6 and E7 were rather lower in late-passage than in early-passage cells. Moreover, additional introduction of a constitutively active MEK1 (MEK1DD) and/or KRASG12V into HCK1T/16epi cells resulted in generation of highly potent tumor-initiating cells. Thus an in vitro model for progression of cervical neoplasia with episomal HPV16 was established. In the model, constitutively active mutation of PIK3CA, PIK3CAE545K, and overexpression of MYC, in the cells with episomal HPV16 genome were not sufficient, but an additional event such as activation of the RAS-MEK pathway was required for progression to tumorigenicity.

Raman Spectroscopy Revealed Cell Passage-Dependent Distinct Biochemical Alterations in Radiation-Resistant Breast Cancer Cells.

Recapitulating radioresistant cell features in pertinent cell line models is essential for deciphering fundamental cellular mechanisms. The limited understanding of passage and cell cycle phases on radioresistant cells revived post-cryopreservation led us to investigate the effect of sub-culturing in parental and radioresistant MCF-7 cells. In this study, the radioresistant cells showed high-intensity nucleic acid and cytochrome bands, which are potentially a radiation-induced spectral marker. Raman spectroscopy data showed dynamic biochemical alterations in revived radioresistant G2/M synchronized cells at early cell passages 1 and 3 with stabilization at a latter cell passage, 5. The study highlights the importance of cell passaging and cell cycle phases in potentially changing the biochemical parameters during in vitro experiments after the revival of radioresistant cells post-cryopreservation.

14 In vitro transformation of ovarian surface epithelium links a mutation in SWI/SNF Related, Matrix Associated, Actin Dependent Regulator Of Chromatin, Subfamily A, Member 4 to familial small carcinoma of the ovary hypercalcemic type

Using a unique population of cells derived from a familial carrier of an SCCOHT-associated SMARCA4 mutation (SMARCA4. c.3081+1G>T), we sought to determine if non-cancerous cells would spontaneously transform during in vitro culture, thereby providing a model system for studying the formation of SCCOHT. Ovarian surface epithelium (OSE) derived from a familial carrier of a SCCOHT-associated mutation in the SMARCA4 gene (P590, SMARCA4. c.3081+1G>T, prophylactic oophorectomy) were serially passaged in vitro, and interrogated for their ability to acquire characteristics of cellular transformation. Cells were grown for multiple passages to determine if cells would spontaneously immortalize. Loss of contact-dependent inhibition was interrogated with focus-forming assays of confluent monolayers. The ability of cells to escape anoikis and grow independently as spheroids was interrogated in attachment-free growth conditions. Senescenceassociated beta-galactosidase (SA-beta-gal), cellular necrosis, and cellular apoptosis was also measured. All experiments were conducted in parallel with an age-matched OSE population derived from a benign ovarian surgery, P590 cells that were passaged over 12 twelve times, representing at least 40 cellular doublings, continued to proliferate in culture. In contrast, non-mutant P583 cells failed to grow beyond 11–12 passages. P590 cells grown to confluency spontaneously formed foci of multicellular aggregates, while P583 cells did not. In attachment-free culture conditions, P590 cells readily formed spheroids from both early-passage and late-passage cells. In contrast, P583 formed small spheroids that failed to expand in culture. Surprisingly, both P590 and P583 cells displayed elevated SA-betagal staining, with neither cell populations showing elevated necrosis or apoptosis markers. OSE harboring a SMARCA4 mutation associated with familial SCCOHT display several phenotypes consistent with early stages of cellular transformation. In contrast, non-mutant cells failed to display signs of transformation. Our data suggest that OSE may represent a unique cell population for studying the early stages of SCCOHT formation, providing a useful tool for developing improved diagnostic and therapeutic approaches.

End9: an early-passage cell line defective in master HLA-I transcriptional coordinators

Disruption in the HLA class I (HLA-I), β2-microglobulin (β2M) and/or Antigen Processing and Presentation Machinery (APPM) structural genes is believed to favor tumor immune escape, whereas purely regulatory mutants are few and poorly characterized. The endometrial carcinoma End9 was the extreme HLA-I/APPM-low outlier in a panel of >100 early-passage tumor cell lines established in culture by us from essentially all major tumor histotypes. The defect arose in vivo, was retained in culture, and remained stable for >100 passages. End9 was found to express no constitutive or IFN-responsive HLA-A, -B, -F, and-G, little HLA-C and β2m, ‘normal‘ HLA-E, and barely detectable TAP, tapasin, LMP2, LMP7, ERAP1 and ERAP2, as evaluated by protein and nucleic acid biochemistry. Lacking evidence for genomic damage, we used a reporter construct to assess the 3 major upstream HLA-I regulatory boxes (EnhA, ISRE and SXY), and attempted phenotypic rescue by transduction with missing trans-acting function(s). The NF-KB:EnhA interplay was apparently conserved, whereas the ISRE and SXY modules were simultaneously shut off due to (a) a complete JAK1 absence, (b) a physiological lack of CIITA, and (c) an epigenetic (5-Azacitidine-reversible) suppression of an intact (as per sequencing) NLRC5. The near-zero HLA-I/APPM phenotype of End9 highlighted several features of HLA-I regulation, including: (a) SXY-independent HLA-C transcription; (b) subordination of the EnhA and ISRE boxes (IFN and TNFα responsiveness) to promoter opening by CIITA/NLRC5; and (c) marginal HLA-I/APPM transactivation by residual NLRC5 at baseline and even upon >100X overexpression. End9 is the first regulatory mutant defective in a hierarchically high set of transacting functions operating upstream to most HLA-I/APPM members, resulting in a trophoblast-like, presumably immunoevasive phenotype. The defect involves NLRC5 but NLRC5 refractoriness implies a shortage of other transcriptional co-activators, making End9 a suitable recipient for complementation cloning to discover novel HLA-A/-B/APPM master coordinators.

Pro-cancerogenic effects of spontaneous and drug-induced senescence of ovarian cancer cells in vitro and in vivo: a comparative analysis

BackgroundClinical outcomes of cancer cell senescence are still elusive. Here, we reveal and compare pro-cancerous activity of spontaneously and drug-inducible senescent ovarian cancer cells. Experiments were performed on tumors and tumor-derived primary epithelial ovarian cancer cells (pEOCs) that were obtained from chemotherapy-naïve patients and from patients who received carboplatin (CPT) and paclitaxel (PCT) before cytoreduction.ResultsThe analysis of tumors showed that senescent cancer cells are present in patients from both groups, albeit most frequently and covering a greater area in tissues from chemotherapy-positive women. This in vivo senescence of pEOCs translated to an expression of senescence markers in early-passage cells in vitro. A conditioned medium from senescent pEOCs fueled the cancer progression, including adhesion of non-senescent pEOCs to normal peritoneal cells, and their increased proliferation, migration, invasion, and EMT. Senescent pEOCs’ secretome promoted angiogenic activity of vascular endothelium, induced senescence of normal peritoneal cells, reprogrammed their secretome towards hypersecretion of cancer-promoting proteins, and stimulated motility of cancer cells subjected to a mesothelium- and fibroblast-derived medium. The most striking finding was, however, that spontaneously senescent pEOCs supported all the above pro-cancerous effects more efficiently than drug-inducible senescent cells, which was plausibly related to augmented release of several cancer spread mediators by these cells. The prevalence of spontaneously senescent pEOCs was most evident in experiments on mice when they were able, unlike the drug-inducible cells, to promote the development of drug-sensitive i.p. xenografts.ConclusionsOur study shows that spontaneous senescence of pEOCs should be treated as an independent pathogenetic factor of cancer progression.

Role of H4K16 acetylation in 53BP1 recruitment to double-strand break sites in in vitro aged cells

Increased frequency of DNA double strand breaks (DSBs) with aging suggests an age-associated decline in DSB repair efficiency, which is also influenced by the epigenetic landscape. H4 acetylation at lysine 16 (H4K16Ac) has been related to DSB repair since deacetylation of this mark is required for efficient 53BP1 recruitment to DSBs. Although age-associated changes in H4K16Ac levels have been studied, their contribution to age-related DSB accumulation remains unknown. In vitro aged Human Dermal Fibroblasts (HDFs) display lower levels of H4K16A that correlate with reduced recruitment of 53BP1 to basal DSBs. Following DNA damage induction, early passage (EP) cells suffered from a transient H4K16 deacetylation that allowed proper 53BP1 recruitment to DSBs. In contrast, to reach this specific and optimum level, aged cells responded by increasing their overall lower H4K16Ac levels. Induced hyperacetylation of late passage (LP) cells using trichostatin A increased H4K16Ac levels but did not ameliorate 53BP1 recruitment. Instead, deacetylation induced by MOF silencing reduced H4K16Ac levels and compromised 53BP1 recruitment in both EP and LP cells. Age-associated decrease of H4K16Ac levels contributes to the repair defect displayed by in vitro aged cells. H4K16Ac responds to DNA damage in order to reach a specific, optimum level that allows proper 53BP1 recruitment. This response may be compromised with age, as LP cells depart from lower H4K16Ac levels. Variations in H4K16Ac following the activation of the DNA damage response and aging point at this histone mark as a key mediator between DNA repair and age-associated chromatin alterations.

Abstract 5333: Pancreatic cancer enhances HER2 signaling through DUSP6 to circumvent therapeutic MAPK inhibition

Abstract Background: Oncogenic KRAS is present in almost all cases of pancreatic ductal adenocarcinoma (PDAC). However, targeting KRAS or its canonical signaling cascades, especially the mitogen-activated protein kinase (MAPK) pathway, remains clinically unsuccessful. Targeting ERK kinases has recently emerged as a promising therapeutic strategy and combinatorial strategies should be developed. Aim: Identify adaptive mechanisms to ERK inhibition that can be co-targeted to achieve effective tumor inhibition in multiple patient-derived xenograft (PDX) models. Methods: Reverse-phase protein array (RPPA) was used in early-passage patient-derived cell lines (PDCLs) to identify potential resistance mechanisms. These were confirmed using RNA interference and overexpression in PDAC cell lines and PDCLs. The promising combinations were tested in 30 early-passaged PDAC PDXs. Results: RPPA showed dramatic downregulation of DUSP4 and DUSP6 phosphatases following MEK and ERK inhibition, which coincided with upregulation of phospho-HER2 and -HER3. Knockdown of DUSP6, but not DUSP4, was sufficient in phosphorylation of HER2. Conversely, overexpression of DUSP6 curbed HER2 and ERK activation. Downregulation of DUSP4 and DUSP6 induced by ulixertinib, an ERK inhibitor now in clinical development, was reversed by bortezomib, suggesting DUSP4 and DUSP6 are proteosomally degraded. Combined ulixertinib plus PI3K inhibitor copanlisib, or pan-HER inhibitor afatinib slowed but did not arrest PDX tumor growth in vivo, and addition of gemcitabine was required to achieve tumor regression or durable growth arrest. Alternatively, ulixertinib or MEK inhibitor (trametinib) in combination with trastuzumab deruxtecan (DS-8201a), an anti-HER2 conjugated topoisomerase I inhibitor, were extremely effective, leading to complete and durable tumor regression for all tested PDX models. We showed that upregulation of HER2 expression following MEK or ERK inhibitor treatment provides a conduit for enhanced internalization of DS-8201a. Conclusions: Our study provided novel mechanistic insight on how PDAC cells evade MAPK inhibition via enhancing HER2 signaling. We demonstrated that the combination of MEK or ERK inhibitor plus DS-8201a is extremely effective, leading to complete tumor regression in multiple PDAC PDX models. This combination should be advanced as a clinical trial for PDAC patients. Keys: DS-8201a, DUSP6, HER2, KRAS, ulixertinib, pancreatic ductal adenocarcinoma Citation Format: Ashenafi Shiferaw Bulle, Kuljeet Seehar, Sapana Bansod, Yali Chen, Chen Hung-Po, Paarth B. Dodhiawala, Lin Li, Vikas Somani, Jacqueline Mudd, Ryan C. Fields, Deborah Knoerzer, Andrea Wang-Gillam, Lim Kian-Huat. Pancreatic cancer enhances HER2 signaling through DUSP6 to circumvent therapeutic MAPK inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5333.

Abstract 1674: FGF8 as a modulator of Wilms' tumor in vitro growth and longevity

Abstract Wilms’ tumor is the most common pediatric renal tumor accounting for 6-7% of all childhood cancers. Development of faithful Wilms’ tumor cell lines is needed to identify novel therapeutics. Currently, established Wilms’ tumor cell lines that are suitable for high throughput studies only represent anaplastic Wilms, a rare subtype. In contrast, cell lines representing the more common favorable histology Wilms’ tumor (FHWT) often have poor proliferative capacity and are unable to passage long-term (e.g. &amp;gt;20 passages). For this reason, there is a need to establish robust cell lines representing FHWT. We hypothesize that there are core factors missing from the cell culture medium which prevent proper growth signaling and proliferation. We first performed bulk RNA-sequencing from patients and associated cell lines at Aflac Cancer and Blood Disorders Center with an underlying diagnosis of FHWT. Transcriptomic analyses showed that the reduced growth and proliferation in these FHWT cell lines may be due to reduced presence of the mitogenic fibroblast growth factor 8 (FGF8) in the cell culture environment as compared to the tumor environment. Wilms’ tumor has notably high FGF8 expression levels compared to all other pediatric tumors, implicating FGF8 as a potential driving factor in tumor maintenance. To characterize the phenotypic effects of FGF8 reintroduction in short term FHWT cell lines, we both endogenously overexpressed FGF8 via a lentiviral vector and ectopically added recombinant FGF8 to the cell culture medium. Qualitatively, endogenous overexpression of FGF8 induced distinct morphological changes in cells, converting the enlarged and flattened cells into more focal cells resembling proliferative early passage cells. Quantitatively, overexpression of FGF8 in one favorable histology cell line led to an increased rate of cellular proliferation and extended the cellular longevity by seven passages (47% above baseline). RNA-sequencing analysis of these FGF8 overexpressing cells implicated the anti-apoptotic gene, NTSR1, and an extracellular matrix protein, SNED1, as potential downstream targets of FGF8 overexpression. However, ectopic addition of recombinant FGF8 protein to the cellular medium had less pronounced effects, with seemingly cell-line specific effects. These data demonstrate FGF8 as possibly being required for survival in certain Wilms’ tumor cell lines that can be modulated to influence in vitro proliferation and longevity. Citation Format: Garrett Cooper, Benjamin Lee, Nate Smyth, Karuna Mittal, Taylor Lawrence, Hunter Jonus, Jenny Shim, Kelly Goldsmith, Andrew Hong. FGF8 as a modulator of Wilms' tumor in vitro growth and longevity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1674.

Reduced IRF4 expression promotes lytic phenotype in Type 2 EBV-infected B cells.

Humans are infected with two types of EBV (Type 1 (T1) and Type 2 (T2)) that differ substantially in their EBNA2 and EBNA 3A/B/C latency proteins and have different phenotypes in B cells. T1 EBV transforms B cells more efficiently than T2 EBV in vitro, and T2 EBV-infected B cells are more lytic. We previously showed that both increased NFATc1/c2 activity, and an NFAT-binding motif within the BZLF1 immediate-early promoter variant (Zp-V3) contained in all T2 strains, contribute to lytic infection in T2 EBV-infected B cells. Here we compare cellular and viral gene expression in early-passage lymphoblastoid cell lines (LCLs) infected with either T1 or T2 EBV strains. Using bulk RNA-seq, we show that T2 LCLs are readily distinguishable from T1 LCLs, with approximately 600 differentially expressed cellular genes. Gene Set Enrichment Analysis (GSEA) suggests that T2 LCLs have increased B-cell receptor (BCR) signaling, NFAT activation, and enhanced expression of epithelial-mesenchymal-transition-associated genes. T2 LCLs also have decreased RNA and protein expression of a cellular gene required for survival of T1 LCLs, IRF4. In addition to its essential role in plasma cell differentiation, IRF4 decreases BCR signaling. Knock-down of IRF4 in a T1 LCL (infected with the Zp-V3-containing Akata strain) induced lytic reactivation whereas over-expression of IRF4 in Burkitt lymphoma cells inhibited both NFATc1 and NFATc2 expression and lytic EBV reactivation. Single-cell RNA-seq confirmed that T2 LCLs have many more lytic cells compared to T1 LCLs and showed that lytically infected cells have both increased NFATc1, and decreased IRF4, compared to latently infected cells. These studies reveal numerous differences in cellular gene expression in B cells infected with T1 versus T2 EBV and suggest that decreased IRF4 contributes to both the latent and lytic phenotypes in cells with T2 EBV.

Establishment of four head and neck squamous cell carcinoma cell lines: importance of reference DNA for accurate genomic characterisation.

There is significant interest in developing early passage cell lines with matched normal reference DNA to facilitate a precision medicine approach in assessing drug response. This study aimed to establish early passage cell lines, and perform whole exome sequencing and short tandem repeat profiling on matched normal reference DNA, primary tumour and corresponding cell lines. A cell culture based, in vitro study was conducted of patients with primary human papillomavirus positive and human papillomavirus negative tumours. Four early passage cell lines were established. Two cell lines were human papillomavirus positive, confirmed by sequencing and p16 immunoblotting. Short tandem repeat profiling confirmed that all cell lines were established from their index tumours. Whole exome sequencing revealed that the matched normal reference DNA was critical for accurate mutational analysis: a high rate of false positive mutation calls were excluded (87.6 per cent). Early passage cell lines were successfully established. Patient-matched reference DNA is important for accurate cell line mutational calls.