Normal Cell Differentiation Research Articles

HER-2 low in breast cancer: A new perspective for anti-HER-2 therapy

HER-2 is a transmembrane receptor of the Epidermal Growth Factor Receptor (EGFR) subfamily that functions physiologically in normal cell proliferation and differentiation. HER-2 overexpression is found in 20–30% of breast cancer patients. Thus, HER-2 is established as a prognosis marker and therapeutic target for anti-HER-2. The American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) issued guidelines for HER-2 classification based on immunohistochemical (IHC) and in situ hybridization (ISH) examinations. Before ASCO/CAP issued the latest update to their guidelines, HER-2 classification was divided into HER-2 negative, equivocal, and positive. Only patients with HER-2 positive (HER-2 overexpression) received anti-HER-2 therapy. After the DESTINY-Breast04 trial demonstrated the efficacy of trastuzumab deruxtecan in breast cancer with low HER-2 levels, ASCO/CAP officially updated the guidelines by introducing a low HER-2 classification, which is HER-2 expression with an immunohistochemical (IHC) score of 1+ or 2+ without HER-2 gene amplification on in situ hybridization (ISH). Trastuzumab deruxtecan exerts a substantial cytotoxic burden on HER-2-expressing tumor cells, significantly improving progression-free survival and overall survival compared with conventional chemotherapy. Reclassification of low HER-2 tumors bridges a critical gap in breast cancer management, providing a new perspective for patients with low HER-2 expression with anti-HER-2 therapy, thus highlighting the importance of accurate identification of HER-2 for prognosis determination and therapeutic reference in breast cancer. This review highlights HER-2 classification, the importance of IHC and ISH assays for HER-2 expression, and anti-HER-2 therapy options for HER-2 positive and HER-2 low based on the latest guidelines.

Identification of a Novel RUNX1::STX2 Fusion in Mixed-Phenotype Acute Leukemia (MPAL) With BCR::ABL1.

Mixed phenotype acute leukemia (MPAL) is a rare type of acute leukemia (AL), MPAL with BCR::ABL1 fusion is the main subtype of MPAL, mainly affecting adult males. It is an acute leukemia with unique clinical and biological characteristics that involve both the myeloid and lymphatic systems. Gene fusion plays a crucial role in the pathogenesis, diagnosis, prognosis assessment, and treatment of leukemia. We present the first discovery of a novel fusion of RUNX1::STX2 in this subtype, which is co-expressed with BCR::ABL1 fusion. RUNX1 is a crucial transcription factor for hematopoietic differentiation, frequently found to be abnormal in AML, while STX2 may play a role in cancer progression. The RUNX1::STX2 fusion protein may act as the primary negative regulator of wild-type RUNX1, influencing normal cell differentiation and proliferation, consequently elevating the risk of leukemia. The gene fusion status of this patient is unique and complex, requiring further exploration to understand its functional significance in leukemia progression and treatment response.

Identification of novel transcription factors regulated by H3K27 acetylation in myogenic differentiation of porcine skeletal muscle satellite cells.

H3K27 acetylation (H3K27ac) is crucial in muscle development as it regulates gene expression. Dysregulation of H3K27ac level has been linked to muscle-related diseases such as Duchenne muscular dystrophy, yet the mechanisms through which H3K27ac influences myogenic differentiation are not fully understood. Here, we utilized the SGC-CBP30 drug, a CBP/p300 bromodomain inhibitor, to reduce H3K27ac level and investigated its effect on myogenic differentiation of porcine skeletal muscle satellite cells. The results demonstrated an increased H3K27ac level during normal muscle satellite cell differentiation. We found that the addition of SGC-CBP30 resulted in a reduced level of H3K27ac based on ATAC-seq and CUT&Tag data. Our analysis revealed that a cluster characterized by reduced levels of H3K27ac and increased levels of H3K27me3 was enriched with motifs corresponding to Bach2, MafK, and Fosl2 transcription factors. Furthermore, knockdown of Bach2, MafK, and Fosl2 produced a similar suppression effect on myogenic differentiation. Taken together, our study contributes to a better understanding of how H3K27ac influences myogenic differentiation.

TMOD-30. DISRUPTION OF NORMAL RADIAL GLIA DEVELOPMENT IN AN NF2-ALTERED NEUROEPITHELIAL STEM CELL MODEL

Abstract NF2-related schwannomatosis is a tumor predisposition syndrome caused by mutations in the NF2 gene and associated with spinal ependymomas (SP-EPN). SP-EPNs are suspected to originate from aberrations in the radial glia (RG) cell lineage. These tumors are only effectively treated through high-risk surgical resection, emphasizing the critical need for identification of targets for medical therapy. Yet, the role of NF2-dependent disruption in RG cell development is poorly understood. We hypothesize that this mutation may be halting normal RG cell differentiation, resulting in a RG-like stem cell that is driving SP-EPN formation. An NF2-knockout was generated in neuroepithelial stem (NES) cells using CRISPR/Cas9. Knockouts were validated using Western blot and Sanger sequencing. In vitro differentiation was induced with removal of growth factors. NF2-knockout phenotypes were assessed with real-time polymerase chain reaction and compared with wildtype NES cells. Preliminary data has shown that NF2-knockout cells express similar levels of early pan-neural and neural stem cell genes compared to wildtype after CRISPR editing. The NF2-knockout cells retain this stem cell-like gene expression following attempted differentiation, whereas wildtype cells take on a primarily neural phenotype. The knockout cells also form what appears to be pre-neoplastic spheres when allowed to differentiate. NF2-knockout NES cells fail to differentiate normally compared to wildtype NES cells. They retain early RG-like markers, including SOX2, BLBP, and GFAP. Furthermore, formation of spheres when growth factors were removed hints at NF2 loss being relevant to formation of pre-neoplastic growths. Future work will include investigating downstream effects of NF2 loss in this model.

Hyperactivation of the PI3K pathway in inborn errors of immunity: current understanding and therapeutic perspectives.

The phosphoinositide-3-kinase (PI3K) pathway function is crucial to the normal development, differentiation, and function of immune cells including B, T, and NK cells. Following the description of two cohorts of patients with an inboirn error of immunity(also known as primary immunodeficiency) with gain-of-function variants in the PIK3CD gene a decade ago, the disease entity activated PI3K delta syndrome (APDS) was named. Since then, many more patients with PIK3CD variants have been described, and loss-of-function variants in PIK3R1 and PTEN have also been linked to APDS. Importantly, the availability of small molecules that inhibit the PI3K pathway has enabled targeted treatment of APDS patients. In this review, we define (i) the PI3K pathway and its role in inborn errors of immunity; (ii) the clinical and immunological presentation of APDS1 (PIK3CD GOF), APDS2 (PIK3R1 LOF), and related disorders; (iii) Diagnostic approaches to identify and functionally validate the genetic causes of disease; (iv) therapeutic interventions to target PI3K hyperactivation; and finally (v) current challenges and future perspectives that require attention for the optimal treatment of patients with APDS and APDS-L diseases.

Fetal Cortical Abnormalities Identified on Ultrasound.

Normal neuronal cell differentiation and migration is critical to brain formation, is rapidly occurring as the fetal brain develops, and peaks at the time of the routine ultrasound anatomic survey. Abnormalities in cortical migration can signify an underlying genetic abnormality or other fetal injury that can have a profound impact on future development. Although cortical migration peaks at 20-22 weeks, cortical migration abnormalities are rarely diagnosed at the time of the anatomic survey. We describe three cases of fetal cortical abnormalities in which prenatal ultrasound imaging was instrumental to making a prompt and accurate diagnosis in the mid-trimester and for guiding clinical counseling.

Prognostic Impact of CD200 and CD56 Expression in Patients with Acute Myeloid Leukemia

Abstract Background Acute myeloid leukemia (AML) is a clonal malignant disease of hematopoietic tissue which results from a block of normal differentiation of hematopoietic progenitor cells along with uncontrolled proliferation of cells of myeloid origin with maturation arrest leading to infiltration of bone marrow and other tissues by myeloblasts. It escapes from immunosurveillance by induction of immunosuppression through expression of specific cell surface molecules with immune modulatory function. Novel immune-directed therapeutic approaches form a major focus of current and clinical research. Objective to assess the expression level of CD200 and CD56 in de-novo acute myeloid leukemia patients and evaluate the prognostic value of their positive expressions in patients with AML. Methods This Cohort study was conducted at Ain Shams University Hospitals, on 51 newly diagnosed adult AML patients attending the Hematology Oncology Unit of Ain Shams University Hospitals from February, 2022 until June, 2023. Results CD200+ expression was reported in 74.5% of patients while 9.8% of patients showed CD56+ expression. M1-M2 were found to be the most common FAB subtypes. CD200+ was higher among female patients (p = 0.045). On the other hand, CD56+ patients were younger in comparison to CD56- patients (p = 0.002). Total death was higher among CD200+ patients than CD200- patients (p = 0.037). Conclusion Our study reveals that CD200 expression is associated with higher incidence of mortality which suggests a negative impact of CD200 expression on survival rate while CD56 is not associated with a significant mortality.

Identification of a novel cryptic variant chromosomal rearrangement involving 9q34, 22q11.2, and 5q22 resulting in ins(9;22) and t(5;22) in chronic myeloid leukemia: a case report.

Chronic myeloid leukemia (CML) is a malignant clonal disorder of the hematopoietic stem cells characterized by the aberrant production and uncontrolled proliferation of mature granulocytes with normal cell differentiation. The Philadelphia (Ph) chromosome resulting from reciprocal translocation between chromosomes 9 and 22 is the main genetic molecular hallmark of CML seen in more than 90% of the patients. However, about 5-10% of CML patients show a variant genetic rearrangement, involving one or more chromosomes in addition to 9 and 22. Herein, we describe the results of hematological, cytogenetic, fluorescence in situ hybridization (FISH), and high-end molecular analysis in a 77-year-old man diagnosed with CML. The combination of conventional cytogenetic analysis along with metaphase FISH and whole chromosomal paint revealed a novel cryptic variant chromosomal rearrangement involving 9q34, 22q11.2, and 5q22, resulting in ins(9;22) and t(5;22). At the molecular level, using PCR, myeloid NGS panels, and whole transcriptome analyses, we showed that this complex rearrangement indeed resulted in the formation of the BCR::ABL1 e13a2 major fusion transcript. No additional somatic mutations or kinase domain mutations were identified, thereby suggesting that the current case is indeed genetically homogeneous. This study provided strong evidence to support the idea that insertion-derived BCR::ABL1 fusions often involve complex chromosomal abnormalities that are overlooked by conventional cytogenetics but can be identified by a combination of conventional, molecular cytogenetics, and high-end NGS studies.

Role of Oxidative Stress Signaling, Nrf2, on Survival and Stemness of Human Adipose-Derived Stem Cells Exposed to X-rays, Protons and Carbon Ions.

Some cancers have a poor prognosis and often lead to local recurrence because they are resistant to available treatments, e.g., glioblastoma. Attempts have been made to increase the sensitivity of resistant tumors by targeting pathways involved in the resistance and combining it, for example, with radiotherapy (RT). We have previously reported that treating glioblastoma stem cells with an Nrf2 inhibitor increases their radiosensitivity. Unfortunately, the application of drugs can also affect normal cells. In the present study, we aim to investigate the role of the Nrf2 pathway in the survival and differentiation of normal human adipose-derived stem cells (ADSCs) exposed to radiation. We treated ADSCs with an Nrf2 inhibitor and then exposed them to X-rays, protons or carbon ions. All three radiation qualities are used to treat cancer. The survival and differentiation abilities of the surviving ADSCs were studied. We found that the enhancing effect of Nrf2 inhibition on cell survival levels was radiation-quality-dependent (X-rays > proton > carbon ions). Furthermore, our results indicate that Nrf2 inhibition reduces stem cell differentiation by 35% and 28% for adipogenesis and osteogenesis, respectively, using all applied radiation qualities. Interestingly, the results show that the cells that survive proton and carbon ion irradiations have an increased ability, compared with X-rays, to differentiate into osteogenesis and adipogenesis lineages. Therefore, we can conclude that the use of carbon ions or protons can affect the stemness of irradiated ADSCs at lower levels than X-rays and is thus more beneficial for long-time cancer survivors, such as pediatric patients.

Proliferative arrest induces neuron differentiation and innate immune responses in control and Creutzfeldt-Jakob Disease agent infected rat septal neurons.

Rat post-mitotic septal (SEP) neurons, engineered to conditionally proliferate at 33°C, differentiate when arrested at 37.5°C and can be maintained for weeks without cytotoxic effects. Nine independent cDNA libraries were made to follow arrest-induced neural differentiation and innate immune responses in normal (Nl) uninfected and CJ agent infected SEP cells. Proliferating Nl versus latently infected (CJ-) cells showed few RNA-seq differences. However arrest induced major changes. Normal cells displayed a plethora of anti-proliferative transcripts. Additionally, known neuron differentiation transcripts, e.g., Agtr2, Neuregulin-1, GDF6, SFRP4 and Prnp were upregulated. These Nl neurons also displayed many activated IFN innate immune genes, e.g., OAS1, RTP4, ISG20, GTB4, CD80 and cytokines, complement, and clusterin (CLU) that binds to misfolded proteins. In contrast, arrested highly infectious CJ+ cells (10 logs/gm) downregulated many replication controls. Furthermore, arrested CJ+ cells suppressed neuronal differentiation transcripts, including Prnp which is essential for CJ agent infection. CJ+ cells also enhanced IFN stimulated pathways, and analysis of the 342 CJ+ unique transcripts revealed additional innate immune and anti-viral-linked transcripts, e.g., Il17, ISG15, and RSAD2 (viperin). These data show: 1) innate immune transcripts are produced by normal neurons during differentiation; 2) CJ infection can enhance and expand anti-viral responses; 3) latent CJ infection epigenetically imprints many proliferative pathways to thwart complete arrest. CJ+ brain microglia, white blood cells and intestinal myeloid cells with shared transcripts may be stimulated to educe latent CJD infections that can be clinically silent for >30 years.

Melatonin via MTNR1B regulates METTL3 to protect ileum cell differentiation.

Intestinal stem cells rapidly differentiate into various epithelial cells, playing a crucial role in maintaining intestinal homeostasis. Melatonin, a known endogenous molecule with anti-inflammatory and antioxidant properties, has its potential efficacy in ileum stem cells differentiation not fully understood to date. This study indicates that melatonin suppresses ileum inflammation and maintains normal differentiation of ileum stem cells through MTNR1B. Subsequent outcomes following treatment with MTNR1B inhibitors further substantiate these findings. Additionally, overexpression of METTL3 protein appears to be a potential instigator for promoting ileum inflammation and disruptions in cell differentiation. Treatment with the METTL3 inhibitor SAH significantly inhibits ileum inflammation and Wnt/β-catenin activity, thereby sustaining normal cellular differentiation functions. In summary, this study showed that melatonin may improve ileum inflammation and maintain cell differentiation functions by inhibiting abnormal METTL3 expression via MTNR1B.

Single-cell multiomics reveals ENL mutation perturbs kidney developmental trajectory by rewiring gene regulatory landscape

How disruptions to normal cell differentiation link to tumorigenesis remains incompletely understood. Wilms tumor, an embryonal tumor associated with disrupted organogenesis, often harbors mutations in epigenetic regulators, but their role in kidney development remains unexplored. Here, we show at single-cell resolution that a Wilms tumor-associated mutation in the histone acetylation reader ENL disrupts kidney differentiation in mice by rewiring the gene regulatory landscape. Mutant ENL promotes nephron progenitor commitment while restricting their differentiation by dysregulating transcription factors such as Hox clusters. It also induces abnormal progenitors that lose kidney-associated chromatin identity. Furthermore, mutant ENL alters the transcriptome and chromatin accessibility of stromal progenitors, resulting in hyperactivation of Wnt signaling. The impacts of mutant ENL on both nephron and stroma lineages lead to profound kidney developmental defects and postnatal mortality in mice. Notably, a small molecule inhibiting mutant ENL’s histone acetylation binding activity largely reverses these defects. This study provides insights into how mutations in epigenetic regulators disrupt kidney development and suggests a potential therapeutic approach.

ROR2 Regulates Cellular Plasticity in Pancreatic Neoplasia and Adenocarcinoma.

Cellular plasticity is a hallmark of pancreatic ductal adenocarcinoma (PDAC) starting from the conversion of normal cells into precancerous lesions, to the progression of carcinoma subtypes associated with aggressiveness and therapeutic response. We discovered that normal acinar cell differentiation, maintained by the transcription factor PDX1, suppresses a broad gastric cell identity that is maintained in metaplasia, neoplasia, and the classical subtype of PDAC in a mouse and human. We identified the receptor tyrosine kinase ROR2 as marker of a gastric metaplasia-like identity in pancreas neoplasms. Ablation of Ror2 in a mouse model of pancreatic tumorigenesis promoted a switch to a gastric pit cell identity that largely persisted through progression to the classical subtype of PDAC. In both human and mouse pancreatic cancer, ROR2 activity continued to antagonize the gastric pit cell identity, strongly promoting an epithelial to mesenchymal transition, conferring resistance to KRAS inhibition, and vulnerability to AKT inhibition. Significance: We discovered the receptor tyrosine kinase ROR2 as an important regulator of cellular identity in pancreatic precancerous lesions and pancreatic cancer. ROR2 drives an aggressive PDAC phenotype and confers resistance to KRAS inhibitors, suggesting that targeting ROR2 will enhance sensitivity to this new generation of targeted therapies. See related commentary by Marasco and Misale, p. 2018.

The Notch inhibitor, FLI-06, increases the chemosensitivity of head and neck Squamous cell carcinoma cells to taxanes-based treatment

Aberration of Notch signaling is one of the key events involved in the development and progression of head and neck squamous cell carcinoma (HNSCC). The Notch pathway controls the tissue-specific differentiation of normal squamous epithelial cells and is frequently altered in squamous carcinomas, thus affecting their proliferation, growth, survival, and chemosensitivity or resistance against anti-cancer agents. In this study, we show that the use of novel, small-molecule inhibitors of Notch signaling, such as FLI-06, can have a beneficial effect on increasing the chemosensitivity of HNSCC to taxane-based chemotherapy. Inhibition of Notch signaling by FLI-06 alone virtually blocks the proliferation and growth of HNSCC cells in both 2D and 3D cultures and the zebrafish model, which is accompanied by down-regulation of key Notch target genes and proteins. Mechanistically, FLI-06 treatment causes cell cycle arrest in the G1-phase and induction of apoptosis in HNSCC, which is accompanied by increased c-JunS63 phosphorylation. Combining FLI-06 with Docetaxel shows a synergistic effect and partially blocks the cell growth of aggressive HNSCC cells via enhanced apoptosis and modification of c-JunS243 phosphorylation via GSK-3β inhibition. In conclusion, inhibition of Notch signaling in HNSCC cells that retain active Notch signaling significantly supports taxane-based anticancer activities via modulation of both the GSK-3β and the c-Jun.

Abstract B026: APOBEC3 promotes squamous differentiation via IL1A/AP-1 signaling

Abstract The APOBEC family of cytidine deaminase enzymes catalyze the conversion of cytosine to uracil in ssDNA and RNA substrates. The resulting C to U transition has been noted in the innate immune response to viral infection, and somatic hypermutation. However, APOBEC family members APOBEC3A (hA3A) and APOBEC3B (hA3B) have been implicated as drivers of the APOBEC3 mutational signatures in numerous cancer types. Notably, approximately 70% of single nucleotide variant mutations in bladder cancer can be attributed to APOBEC3 induced mutagenesis. Studies have implicated various APOBEC3 family members to be drivers of tumorigenesis, disease progression, and therapeutic resistance. To investigate APOBEC3’s role in bladder cancer, we have generated a novel, cre-inducible, pten and p53 knockout, to overexpress mouse Apobec3(mA3) in Upk3a+ cells (UPPA), compared to a model that does not overexpress mA3 (UPP). Apobec3 expression was shown to accelerate bladder tumor formation, indicated by a shorter median time of tumor latency in the UPPA model (43.3 weeks) compared to the UPP model (53.6 weeks). While both tumor models had presence of squamous differentiation, the extensiveness was more profound in the UPPA tumors. Transcriptional analysis of UPP and UPPA tumors, via scRNA sequencing, revealed an enrichment of squamous gene expression in the UPPA tumors. Utilizing mouse syngeneic bladder cancer cell lines and normal bladder urothelial cells, we overexpressed mA3 in a doxycycline inducible manner. Overexpression of mA3 was shown to prevent luminal differentiation. Additionally, mA3 overexpression resulted in the increase of IL-1a production. IL-1a production was sufficient to drive squamous differentiation in BBN963 and normal bladder urothelial cells. Blocking cFOS and IL-1R, individually, prevented expression of squamous genes. These results suggest that DNA damage induced by mA3 is sufficient to drive squamous differentiation via signaling through IL-1a resulting in AP-1 transcription factor activation. We then analyzed bladder cancer samples from The Cancer Genome Atlas and found that hA3A was the only APOBEC family member to be significantly associated with squamous gene expression. Interestingly, hA3A expression was enriched in the basal/squamous consensus subtype. To further interrogate the potential of hA3A being a driver of squamous differentiation in bladder cancer, we have also generated doxycycline inducible expression of hA3A and hA3B in syngeneic bladder cancer cell lines. Targeting IL-1a in various autoimmune diseases has resulted in FDA approval of antibodies targeting IL-1a and IL-1R. Given the clinical utility of targeting IL-1a, it is plausible to target this signaling axis for therapeutic benefit in bladder cancers with ongoing hA3A activity. In aggregate, our work demonstrates the promotion of an aggressive tumor state, driven by APOBEC mutagenesis and implicates hA3A as a possible driver of squamous differentiation in urothelial carcinoma. Citation Format: Andrew S. Truong, Michael S. Sturdivant, Mi Zhou, Wolfgang A. Beckabir, John Raupp, Ujjawal Manocha, Elliot D. Toomer, Ibardo A. Zambrano, Hung-Jui Tan, Marc A. Bjurlin, Angela B. Smith, Tracy L. Rose, Matthew I. Milowsky, Sara E. Wobker, Kathryn H. Gessner, Jeffrey S. Damrauer, William Y. Kim. APOBEC3 promotes squamous differentiation via IL1A/AP-1 signaling [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B026.

G-quadruplex forming motifs in the promoter region of the B-MYB proto-oncogene

To combat cancer, a comprehensive understanding of the molecular mechanisms and behaviors involved in carcinogenesis is crucial, as tumorigenesis is a complex process influenced by various genetic events and disease hallmarks. The B-MYB gene encodes a transcription factor involved in cell cycle regulation, survival, and differentiation in normal cells. B-MYB can be transformed into an oncogene through mutations, and abnormal expression of B-MYB has been identified in various cancers, including lung cancer, and is associated with poor prognosis. Targeting this oncogene is a promising approach for anti-cancer drug design. B-MYB has been deemed undruggable in previous reports, necessitating the search for novel therapeutic options. In this study, we found that the B-MYB gene promoter contains several G/C rich motifs compatible with G-quadruplex (G4) formation. We investigated and validated the existence of G4 structures in the promoter region of B-MYB, first in vitro using a combination of bioinformatics, biophysical, and biochemical methods, then in cell with the recently developed G4access method.

Abstract PO1-24-06: Prolactin Hormone-Induced Mammary Differentiation and Anti-tumorigenic Role in Breast Cancer

Abstract The premise of differentiation therapy in cancer is a strategy that aims at engaging-forward differentiation and cellular reprograming restricting the proliferative, tumor repopulation, stemness, EMT and metastatic capacities of tumor cells leading to the cessation of the aggressive tumor phenotype and offering the cancer patients improved survival for decades. Therefore, deciphering molecular mechanisms deriving differentiation in normal mammary and breast cancer cells may allow the discovery of innovative differentiation-based biomarkers and therapeutics in breast cancer. Lactation is an intricate process that results in the ability of the breast cells to produce a complex nutritious biological fluid to nurse the new-born. While the beneficial effects of breastfeeding to the infant is irrefutable, its effects on maternal health are less investigated especially in relation to breast cancer that still affects 1 in 8 women in high income countries and 1 in 20 globally. Importantly, epidemiological studies have linked breastfeeding to reduced risk of breast cancer by promoting terminal differentiation of the breast epithelial cells. While breastfeeding process is regulated by multiple hormones, growth factors, and transcriptional regulators, the lactation hormone prolactin (PRL) is known to be directly implicated in the hormonal control of breastfeeding. Extensive research including our own work has shown that PRL/PRL receptor (PRLR) pathway derives mammary gland development and importantly mammary epithelial cell terminal differentiation allowing successful lactation. In contrast the role of PRL in breast cancer is still to be fully defined. Importantly, we have accumulated compelling evidence using in-silico publicly available patient data sets and molecular data implicating this pathway as a clinically relevant pro-differentiation pathway driving differentiation and cellular reprograming suppressing stemness, EMT, metastasis and tumorigenesis in breast cancer. To better characterize PRL signaling mediating its pro-differentiation effects, we used large-scale unbiased proteomics analysis of PRLR/interacting proteins in breast cancer cells. Our analyses revealed several novel PRLR-interactors. We have further confirmed these interactions through co-immunoprecipitations/western blotting analyses in breast cancer cells representative the different breast cancer subtypes. We also examined their functional contributions to mammary differentiation and tumorigenesis using in vitro and in vivo assays. Moreover, we defined their potential clinical relevance using bioinformatics in silico databases of breast cancer. Together our study delineates novel PRL/PRLR-downstream signaling mediators important for mammary differentiation and tumorigenesis and may thus be useful as biomarkers and/or therapeutic targets in breast cancer. Citation Format: Dana Hamam, Suhad Ali. Prolactin Hormone-Induced Mammary Differentiation and Anti-tumorigenic Role in Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-24-06.

Hyaluronidase 2 induces pathogenicity in Th17 cells

Abstract Autoreactive Th17 cells express high levels of inflammatory cytokine IL-17A promoting the development and progression of autoimmune diseases. Previous studies show that differentiation of Th17 cells with IL-1 and IL-23 or TLR2 activation drives their aggressive proliferation, making them pathogenic to induce experimental autoimmune encephalomyelitis (EAE). We aim to study a previously undefined role of hyaluronic acid (HA) and its modulation in influencing inflammatory potential and pathogenicity of Th17 cells in autoimmune diseases. Our in vitro differentiation experiments with HA and its modifying enzymes show that a baseline level of HA is essential for the normal differentiation and proliferation of Th17 cells. The overexpression of hyaluronidase 2 (Hyal2) that cleaves HA in Th17 cells decreases IL-17A production but increases cell proliferation in vitro, and adoptive transfer of these cells is sufficient to induce EAE in mice. Furthermore, flow cytometric analysis of infiltrated CD4+ T cells in the CNS of EAE mice indicates lower levels of inflammatory cytokines. Our findings suggest that Hyal2 itself exhibits a level of pathogenicity challenging the prevailing paradigm that these cells can induce the disease only when producing higher levels of encephalitogenic cytokines. Future experiments will delve into the regulation and mechanisms underlying the impact of HA on pathogenic Th17 cells, potentially identifying target molecules to treat autoimmune disorders.

Abstract 3306: RGT-M001, a first-in-class small molecule mRNA degrader of the oncogenic transcription factor c-Myb, demonstrated remarkable single agent anti-tumor efficacy in cancer patient-derived xenograft model

Abstract Dysregulated transcription factors (TFs) represent a unique class of drug targets that drive aberrant gene expression programs involved in the major hallmarks of cancers. However, developing drug-like small molecules targeting TF proteins for clinical purposes has proven to be extremely challenging. Here, we present a novel and innovative approach to degrade the RNA transcript of the master oncogenic transcription factor C-MYB, thereby preventing its undesirable expression, using potent and orally available small molecules. C-MYB is a transcription factor that regulates differentiation and proliferation programs in normal cells, including hematopoietic, stem and epithelial cells. In numerous cancer types, such as adenoid cystic carcinoma (ACC), leukemia, colorectal cancer, and breast cancer, C-MYB is a well-established oncogenic transcription factor, overactivated via different mechanisms, including chromosomal translocations and gene amplification. Here, we leveraged our integrative RNA-targeting platform to identify and validate actionable cryptic exon target sites in the human C-MYB gene. We identified RGT-M001, a potent small molecule that can selectively induce the inclusion of the cryptic exon into the final C-MYB transcripts, resulting in a robust decrease of C-MYB canonical transcripts and C-MYB protein in cells. In a functional assay, we demonstrated that RGT-M001 has potent cell-killing activity against a large panel of cancer cell lines overexpressing C-MYB (EC50 ~ 20 - 300nM), while sparing normal cells. To confirm RGT-M001's on-target effect, we demonstrated a robust correlation between RGT-M001 cell-killing activity and the knockdown of C-MYB RNA and protein. We further investigated the anti-tumor activity of RGT-M001 in an ACC patient-derived xenograft (PDx) mouse model harboring C-MYB-NFBI fusion. Recurrent or metastatic ACC is a malignant neoplasm of predominantly salivary gland origin for which effective approved therapies are lacking; the best reported ORR being 15.6% for lenvatinib. As a single agent, RGT-M001 reduced in vivo C-MYB transcript levels by >80% at peak drug exposure and induced a remarkable tumor growth inhibition response (~70% TGI) in the ACCX11 PDx mouse model, surpassing the therapeutic benchmark Lenvatinib (40% TGI). Importantly, the RGT-M001 regimen was well tolerated. Finally, we showed that the combination of RGT-M001 with the Notch Inhibitor AL-101 resulted in complete inhibition of tumor growth. In conclusion, these data demonstrate that small molecules targeting RNA are a safe and effective approach to address previously undruggable protein targets. Down-regulation of C-MYB by our RNA-targeting small molecules is an attractive therapeutic strategy to treat ACC and other cancers driven by C-MYB dysregulations. Citation Format: Norman Lu, Patricia Soulard, Kay Li, Heather Sadlish, Chris Yates, Xiubin Gu, Ibrahim Kays, Jae Lee, Sam Hasson, Zhiping Weng, Simon Xi, Travis Wager. RGT-M001, a first-in-class small molecule mRNA degrader of the oncogenic transcription factor c-Myb, demonstrated remarkable single agent anti-tumor efficacy in cancer patient-derived xenograft model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3306.

The Role of the L-Arginine-Nitric Oxide Molecular Pathway in Autosomal Dominant Polycystic Kidney Disease.

Recently, arginine has been proven to play an important role in ADPKD physiopathology. Arginine auxotrophy in ADPKD induces cell hyperproliferation, blocking the normal differentiation of renal tube cells and causing cyst formation. We explored the L-arginine (Arg)-nitric oxide (NO) molecular pathway in ADPKD, a multisystemic arginine auxotrophe disease. We developed a prospective case-control study that included a group of 62 ADPKD subjects with an estimated filtration rate over 60 mL/min/1.73 mp, 26 subjects with chronic kidney disease with an eGFR > 60 mL/min/1.73 mp, and a group of 37 healthy subjects. The laboratory determinations were the serum level of arginine, the enzymatic activity of arginase 2 and inducible nitric oxide synthase, the serum levels of the stable metabolites of nitric oxide (nitrate, direct nitrite, and total nitrite), and the endogenous inhibitors of nitric oxide synthesis (asymmetric dimethylarginine and symmetric dimethylarginine). In the ADPKD group, the levels of the arginine and nitric oxide metabolites were low, while the levels of the metabolization enzymes were higher compared to the control group. Statistical analysis of the correlations showed a positive association between the serum levels of Arg and the eGFR and a negative association between Arg and albuminuria. ADPKD is a metabolic kidney disease that is auxotrophic for arginine. Exploring arginine reprogramming and L-Arg-NO pathways could be an important element in the understanding of the pathogenesis and progression of ADPKD.