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Thesis
Peer Reviewed

Parallels between stem cells, development and cancer have long been recognized, but few molecular links have been delineated. Here, we identify and characterize a population of fetal mammary stem cells (fMaSCs). fMaSC concentration peaked late in fetal development well after the emergence of the earliest mammary structures. Several characteristics of fMaSCs enabled more extensive purification than previously achieved using adult mammary. Single cells from the fMaSC-enriched population generated multi-lineage spheres. These cells also revealed properties often associated with cancers. For example, we observed cells co-expressing luminal, myoepithelial and mesenchymal markers. Gene expression profiling revealed significant similarities with archived breast cancer arrays. The ErbB Pathway was heavily represented and fMaSC derived spheres were sensitive to ErbB kinase inhibition. The fMaSC expression profile was associated with aggressive breast cancer subtypes and consisted of unique gene modules with relevance for prognosis and the potential to indicate new therapeutic targets. The parallels between development and cancer suggest that close relationships may exist between organ specific fetal stem cells and cancer. Here, we overcome the substantial technical challenges of such studies to identify, isolate and characterize fetal mammary stem cells (fMaSCs). We report the surprising finding that fMaSC activity is rare early and undergoes a significant increase late in fetal mammogenesis when the rudiments invade into the mesenchyme and fat pad. We find that regulatory pathways associated with fMaSCs are also differentially expressed in a subset of human breast cancers, suggesting that cancer cells may evolve to recapitulate the fetal stem cell state. Our characterization of the fetal mammary stem cell state provides a resource for generating new molecular hypotheses linking development and cancer, identifying candidate therapeutic targets, and developing new diagnostic and prognostic metrics

Cover page: Links between development and cancer : fetal mammary stem cells and human breast cancer

Thesis
Peer Reviewed

Oxidative Stress and Beyond: The Impacts of Tobacco Exposure on Pancreatic Cancer Initiation and Progression

Lin, Xiaoxue
Advisor(s): Engle, Dannielle D

UC San Diego Electronic Theses and Dissertations (2025)

Tobacco is a major risk factor for pancreatic tumorigenesis. While some of these effects have been attributed to the mutagenic properties of tobacco carcinogens, the role of xenobiotic stress and cell signaling changes in response to these agents in pancreatic cancer initiation is not well understood. This study investigates how tobacco carcinogens, specifically cadmium and beno(a)pyrene(BaP) 5, contribute to pancreatic cancer by inducing reactive oxygen species (ROS) and activating redox and inflammatory pathways. We hypothesize that carcinogens in tobacco induce ROS1, which elevates the Nrf2 redox pathway. We also posit that additional signaling responses are induced during long-term tobacco exposure. Together, these changes facilitate pancreatic ductal adenocarcinoma (PDAC) initiation and progression. To determine the proliferation kinetics and ROS elevation upon carcinogen exposure, our lab has generated mouse pancreatic ductal organoids from normal pancreas (wildtype: mN), pre-malignant Pancreatic Intraepithelial Neoplasms (PanIN, Pdx1-Cre; KrasLSL-G12D/+: mP) and malignant pancreatic ductal epithelial cells (tumor, Kras LSL-G12D/+ and Trp53 LSL-R172H/+ mutant: mT). Proliferation kinetics and EC50 values were determined using intracellular ATP assays. Acute exposure led to rapid ROS elevation, with distinct profiles across genotypes and treatments. We next assessed the impact on redox pathway from short to prolonged exposure. While Nrf2 activity was elevated during acute (24h-hour) exposure, surprisingly, its levels were suppressed during prolonged exposure. RNA-seq and cytokine profiling revealed progressive activation of the TNFa-NFkB pathway during prolonged exposure, with increased expression and secretion of IL1a, LIF, and TNF, alongside elevated p65 phosphorylation. To further understand the impact of reduced Nrf2 during carcinogen exposure, we generated Nrf2 knockdown (shNrf2) in mN and mP organoids, which exhibited reduced proliferation as previously reported2, as well as elevated ROS, but similar EC50 compared to controls. Upon chronic exposure, Nrf2 knockdown was maintained, NFkB activity increased further in shNrf2 organoids, supporting a potential compensatory role for Nrf2 signaling. In the long run, this study highlights tumor-initiating mechanisms driven by redox-dependent and -independent pathways under tobacco exposure. This organoid platform can help predict therapeutic responses in PDAC smokers, and provides insights for Nrf2 elevation during chemotherapy, offering a potential explanation for drug resistance.

Article
Peer Reviewed

Model organoids provide new research opportunities for ductal pancreatic cancer

UC Davis Previously Published Works (2016)

We recently established organoid models from normal and neoplastic murine and human pancreas tissues. These organoids exhibit ductal- and disease stage-specific characteristics and, after orthotopic transplantation, recapitulate the full spectrum of tumor progression. Pancreatic organoid technology provides a novel platform for the study of tumor biology and the discovery of potential biomarkers, therapeutics, and personalized medicine strategies.

Cover page: Model organoids provide new research opportunities for ductal pancreatic cancer

Article
Peer Reviewed

Altered glycosylation in pancreatic cancer and beyond

UC San Diego Previously Published Works (2022)

Pancreatic ductal adenocarcinoma (PDA) is one of the deadliest cancers and is projected to soon be the second leading cause of cancer death. Median survival of PDA patients is 6-10 mo, with the majority of diagnoses occurring at later, metastatic stages that are refractory to treatment and accompanied by worsening prognoses. Glycosylation is one of the most common types of post-translational modifications. The complex landscape of glycosylation produces an extensive repertoire of glycan moieties, glycoproteins, and glycolipids, thus adding a dynamic and tunable level of intra- and intercellular signaling regulation. Aberrant glycosylation is a feature of cancer progression and influences a broad range of signaling pathways to promote disease onset and progression. However, despite being so common, the functional consequences of altered glycosylation and their potential as therapeutic targets remain poorly understood and vastly understudied in the context of PDA. In this review, the functionality of glycans as they contribute to hallmarks of PDA are highlighted as active regulators of disease onset, tumor progression, metastatic capability, therapeutic resistance, and remodeling of the tumor immune microenvironment. A deeper understanding of the functional consequences of altered glycosylation will facilitate future hypothesis-driven studies and identify novel therapeutic strategies in PDA.

Cover page: Altered glycosylation in pancreatic cancer and beyond

Article
Peer Reviewed

The impact of extracellular matrix on the precision medicine utility of pancreatic cancer patient-derived organoids

UC San Diego Previously Published Works (2024)

The use of patient-derived organoids (PDOs) to characterize therapeutic sensitivity and resistance is a promising precision medicine approach, and its potential to inform clinical decisions is now being tested in several large multiinstitutional clinical trials. PDOs are cultivated in the extracellular matrix from basement membrane extracts (BMEs) that are most commonly acquired commercially. Each clinical site utilizes distinct BME lots and may be restricted due to the availability of commercial BME sources. However, the effect of different sources of BMEs on organoid drug response is unknown. Here, we tested the effect of BME source on proliferation, drug response, and gene expression in mouse and human pancreatic ductal adenocarcinoma (PDA) organoids. Both human and mouse organoids displayed increased proliferation in Matrigel compared with Cultrex and UltiMatrix. However, we observed no substantial effect on drug response when organoids were cultured in Matrigel, Cultrex, or UltiMatrix. We also did not observe major shifts in gene expression across the different BME sources, and PDOs maintained their classical or basal-like designation. Overall, we found that the BME source (Matrigel, Cultrex, UltiMatrix) does not shift PDO dose-response curves or drug testing results, indicating that PDO pharmacotyping is a robust approach for precision medicine.

Cover page: The impact of extracellular matrix on the precision medicine utility of pancreatic cancer patient-derived organoids

Creative Commons 'BY' version 4.0 license

Article
Peer Reviewed

Dual inhibition of KRASG12D and pan-ERBB is synergistic in pancreatic ductal adenocarcinoma

UC San Diego Previously Published Works (2023)

Pancreatic ductal adenocarcinoma (PDAC) is a lethal cancer with a low survival rate. Recently, new drugs that target KRASG12D, a common mutation in PDAC, have been developed. We studied one of these compounds, MRTX1133, and found it was specific and effective at low nanomolar concentrations in patient-derived organoid models and cell lines harboring KRASG12D mutations. Treatment with MRTX1133 upregulated the expression and phosphorylation of EGFR and HER2, indicating that inhibition of ERBB signaling may potentiate MRTX1133 antitumor activity. Indeed, the irreversible pan-ERBB inhibitor, afatinib, potently synergized with MRTX1133 in vitro, and cancer cells with acquired resistance to MRTX1133 in vitro remained sensitive to this combination therapy. Finally, the combination of MRTX1133 and afatinib led to tumor regression and longer survival in orthotopic PDAC mouse models. These results suggest that dual inhibition of ERBB and KRAS signaling may be synergistic and circumvent the rapid development of acquired resistance in patients with KRAS mutant pancreatic cancer.

Significance

KRAS-mutant pancreatic cancer models, including KRAS inhibitor-resistant models, show exquisite sensitivity to combined pan-ERBB and KRAS targeting, which provides the rationale for testing this drug combination in clinical trials.

Cover page: Dual inhibition of KRASG12D and pan-ERBB is synergistic in pancreatic ductal adenocarcinoma

Creative Commons 'BY-NC-ND' version 4.0 license

Article
Peer Reviewed

Cross-Species Single-Cell Analysis of Pancreatic Ductal Adenocarcinoma Reveals Antigen-Presenting Cancer-Associated Fibroblasts.

UC San Diego Previously Published Works (2019)

Cancer-associated fibroblasts (CAF) are major players in the progression and drug resistance of pancreatic ductal adenocarcinoma (PDAC). CAFs constitute a diverse cell population consisting of several recently described subtypes, although the extent of CAF heterogeneity has remained undefined. Here we use single-cell RNA sequencing to thoroughly characterize the neoplastic and tumor microenvironment content of human and mouse PDAC tumors. We corroborate the presence of myofibroblastic CAFs and inflammatory CAFs and define their unique gene signatures in vivo. Moreover, we describe a new population of CAFs that express MHC class II and CD74, but do not express classic costimulatory molecules. We term this cell population antigen-presenting CAFs and find that they activate CD4+ T cells in an antigen-specific fashion in a model system, confirming their putative immune-modulatory capacity. Our cross-species analysis paves the way for investigating distinct functions of CAF subtypes in PDAC immunity and progression. SIGNIFICANCE: Appreciating the full spectrum of fibroblast heterogeneity in pancreatic ductal adenocarcinoma is crucial to developing therapies that specifically target tumor-promoting CAFs. This work identifies MHC class II-expressing CAFs with a capacity to present antigens to CD4+ T cells, and potentially to modulate the immune response in pancreatic tumors.See related commentary by Belle and DeNardo, p. 1001.This article is highlighted in the In This Issue feature, p. 983.

Cover page: Cross-Species Single-Cell Analysis of Pancreatic Ductal Adenocarcinoma Reveals Antigen-Presenting Cancer-Associated Fibroblasts.

Article
Peer Reviewed

Inhibiting Stromal Class I HDACs Curbs Pancreatic Cancer Progression

UC San Diego Previously Published Works (2023)

Oncogenic lesions in pancreatic ductal adenocarcinoma (PDAC) hijack the epigenetic machinery in stromal components to establish a desmoplastic and therapeutic resistant tumor microenvironment (TME). Here we identify Class I histone deacetylases (HDACs) as key epigenetic factors facilitating the induction of pro-desmoplastic and pro-tumorigenic transcriptional programs in pancreatic stromal fibroblasts. Mechanistically, HDAC-mediated changes in chromatin architecture enable the activation of pro-desmoplastic programs directed by serum response factor (SRF) and forkhead box M1 (FOXM1). HDACs also coordinate fibroblast pro-inflammatory programs inducing leukemia inhibitory factor (LIF) expression, supporting paracrine pro-tumorigenic crosstalk. HDAC depletion in cancer-associated fibroblasts (CAFs) and treatment with the HDAC inhibitor entinostat (Ent) in PDAC mouse models reduce stromal activation and curb tumor progression. Notably, HDAC inhibition (HDACi) enriches a lipogenic fibroblast subpopulation, a potential precursor for myofibroblasts in the PDAC stroma. Overall, our study reveals the stromal targeting potential of HDACi, highlighting the utility of this epigenetic modulating approach in PDAC therapeutics.

Cover page: Inhibiting Stromal Class I HDACs Curbs Pancreatic Cancer Progression

Article
Peer Reviewed

Distinct populations of inflammatory fibroblasts and myofibroblasts in pancreatic cancer

UC Davis Previously Published Works (2017)

Pancreatic stellate cells (PSCs) differentiate into cancer-associated fibroblasts (CAFs) that produce desmoplastic stroma, thereby modulating disease progression and therapeutic response in pancreatic ductal adenocarcinoma (PDA). However, it is unknown whether CAFs uniformly carry out these tasks or if subtypes of CAFs with distinct phenotypes in PDA exist. We identified a CAF subpopulation with elevated expression of α-smooth muscle actin (αSMA) located immediately adjacent to neoplastic cells in mouse and human PDA tissue. We recapitulated this finding in co-cultures of murine PSCs and PDA organoids, and demonstrated that organoid-activated CAFs produced desmoplastic stroma. The co-cultures showed cooperative interactions and revealed another distinct subpopulation of CAFs, located more distantly from neoplastic cells, which lacked elevated αSMA expression and instead secreted IL6 and additional inflammatory mediators. These findings were corroborated in mouse and human PDA tissue, providing direct evidence for CAF heterogeneity in PDA tumor biology with implications for disease etiology and therapeutic development.

Cover page: Distinct populations of inflammatory fibroblasts and myofibroblasts in pancreatic cancer

Article
Peer Reviewed

Inhibiting stromal Class I HDACs curbs pancreatic cancer progression.

UC San Diego Previously Published Works (2023)

Oncogenic lesions in pancreatic ductal adenocarcinoma (PDAC) hijack the epigenetic machinery in stromal components to establish a desmoplastic and therapeutic resistant tumor microenvironment (TME). Here we identify Class I histone deacetylases (HDACs) as key epigenetic factors facilitating the induction of pro-desmoplastic and pro-tumorigenic transcriptional programs in pancreatic stromal fibroblasts. Mechanistically, HDAC-mediated changes in chromatin architecture enable the activation of pro-desmoplastic programs directed by serum response factor (SRF) and forkhead box M1 (FOXM1). HDACs also coordinate fibroblast pro-inflammatory programs inducing leukemia inhibitory factor (LIF) expression, supporting paracrine pro-tumorigenic crosstalk. HDAC depletion in cancer-associated fibroblasts (CAFs) and treatment with the HDAC inhibitor entinostat (Ent) in PDAC mouse models reduce stromal activation and curb tumor progression. Notably, HDAC inhibition (HDACi) enriches a lipogenic fibroblast subpopulation, a potential precursor for myofibroblasts in the PDAC stroma. Overall, our study reveals the stromal targeting potential of HDACi, highlighting the utility of this epigenetic modulating approach in PDAC therapeutics.