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Supplementary Figure S3 describes the effects of distinct MEK inhibitors in combination with BCL-2/XL inhibition and contribution of BCL-2 vs. BCL-XL to apoptotic vulnerability of HGSOC PDX models

Supplementary Table 1 shows the p53 mutation in the PDX models

Most patients with late-stage high-grade serous ovarian cancer (HGSOC) initially respond to chemotherapy but inevitably relapse and develop resistance, highlighting the need for novel therapies to improve patient outcomes. The MEK/ERK pathway is activated in a large subset of HGSOC, making it an attractive therapeutic target. Here, we systematically evaluated the extent of MEK/ERK pathway activation and efficacy of pathway inhibition in a large panel of well-annotated HGSOC patient–derived xenograft models. The vast majority of models were nonresponsive to the MEK inhibitor cobimetinib (GDC-0973) despite effective pathway inhibition. Proteomic analyses of adaptive responses to GDC-0973 revealed that GDC-0973 upregulated the proapoptotic protein BIM, thus priming the cells for apoptosis regulated by BCL2-family proteins. Indeed, combination of both MEK inhibitor and dual BCL-2/XL inhibitor (ABT-263) significantly reduced cell number, increased cell death, and displayed synergy in vitro in most models. In vivo, GDC-0973 and ABT-263 combination was well tolerated and resulted in greater tumor growth inhibition than single agents. Detailed proteomic and correlation analyses identified two subsets of responsive models—those with high BIM at baseline that was increased with MEK inhibition and those with low basal BIM and high pERK levels. Models with low BIM and low pERK were nonresponsive. Our findings demonstrate that combined MEK and BCL-2/XL inhibition has therapeutic activity in HGSOC models and provide a mechanistic rationale for the clinical evaluation of this drug combination as well as the assessment of the extent to which BIM and/or pERK levels predict drug combination effectiveness in chemoresistant HGSOC.

Both, p38/MAPK, and ERK/MEK pathway contribute to MYC and YAP up-regulation in resistant cell lines.

Sensitivity Analyses For the Median-Center and Proliferation Normalization of Microarray Data.

Description of additional methods and procedures used in the study.

Gene Expression Signatures

Aberrant activation of the PI3K/mTOR pathway is a common feature of many cancers and an attractive target for therapy, but resistance inevitably evolves as is the case for any cancer cell–targeted therapy. In animal tumor models, chronic inhibition of PI3K/mTOR initially inhibits tumor growth, but over time, tumor cells escape inhibition. In this study, we identified a context-dependent mechanism of escape whereby tumor cells upregulated the proto-oncogene transcriptional regulators c-MYC and YAP1. This mechanism was dependent on both constitutive ERK activity as well as inhibition of the stress kinase p38. Inhibition of p38 relieved proliferation arrest and allowed upregulation of MYC and YAP through stabilization of CREB. These data provide new insights into cellular signaling mechanisms that influence resistance to PI3K/mTOR inhibitors. Furthermore, they suggest that therapies that inactivate YAP or MYC or augment p38 activity could enhance the efficacy of PI3K/mTOR inhibitors. Cancer Res; 76(24); 7168–80. ©2016 AACR.

Table S5: Somatic Sequence Alterations in parental tumor and xenograft DF149

Legends for Supplementary Figures S1-S4.

Table S4: Somatic Sequence Alterations in parental tumor and xenograft DF101

Purpose: To provide further insight into the role of proliferation and other cellular processes in chemosensitivity and resistance, we evaluated the association of a diverse set of gene expression signatures with response to neoadjuvant chemotherapy (NAC) in breast cancer.Experimental Design: Expression data from primary breast cancer biopsies for 1,419 patients in 17 studies prior to NAC were identified and aggregated using common normalization procedures. Clinicopathologic characteristics, including response to NAC, were collected. Scores for 125 previously published breast cancer–related gene expression signatures were calculated for each tumor.Results: Within each receptor-based subgroup or PAM50 subtype, breast tumors with high proliferation signature scores were significantly more likely to achieve pathologic complete response to NAC. To distinguish “proliferation-associated” from “proliferation-independent” signatures, we used correlation and linear modeling approaches. Most signatures associated with response to NAC were proliferation associated: 90.5% (38/42) in ER+/HER2− and 63.3% (38/60) in triple-negative breast cancer (TNBC). Proliferation-independent signatures predictive of response to NAC in ER+/HER2− breast cancer were related to immune activity, while those in TNBC comprised a diverse set of signatures, including immune, DNA damage, signaling pathways (PI3K, AKT, Ras, and EGFR), and “stemness” phenotypes.Conclusions: Proliferation differences account for the vast majority of predictive capacity of gene expression signatures in neoadjuvant chemosensitivity for ER+/HER2− breast cancers and, to a lesser extent, TNBCs. Immune activation signatures are proliferation-independent predictors of pathologic complete response in ER+/HER2− breast cancers. In TNBCs, significant proliferation-independent signatures include gene sets that represent a diverse set of cellular processes. Clin Cancer Res; 22(24); 6039–50. ©2016 AACR.

Purpose: Ovarian cancer is the leading cause of death from gynecologic malignancy in the United States, with high rates of recurrence and eventual resistance to cytotoxic chemotherapy. Model systems that allow for accurate and reproducible target discovery and validation are needed to support further drug development in this disease.Experimental Design: Clinically annotated patient-derived xenograft (PDX) models were generated from tumor cells isolated from the ascites or pleural fluid of patients undergoing clinical procedures. Models were characterized by IHC and by molecular analyses. Each PDX was luciferized to allow for reproducible in vivo assessment of intraperitoneal tumor burden by bioluminescence imaging (BLI). Plasma assays for CA125 and human LINE-1 were developed as secondary tests of in vivo disease burden.Results: Fourteen clinically annotated and molecularly characterized luciferized ovarian PDX models were generated. Luciferized PDX models retain fidelity to both the nonluciferized PDX and the original patient tumor, as demonstrated by IHC, array CGH, and targeted and whole-exome sequencing analyses. Models demonstrated diversity in specific genetic alterations and activation of PI3K signaling pathway members. Response of luciferized PDX models to standard-of-care therapy could be reproducibly monitored by BLI or plasma markers.Conclusions: We describe the establishment of a collection of 14 clinically annotated and molecularly characterized luciferized ovarian PDX models in which orthotopic tumor burden in the intraperitoneal space can be followed by standard and reproducible methods. This collection is well suited as a platform for proof-of-concept efficacy and biomarker studies and for validation of novel therapeutic strategies in ovarian cancer. Clin Cancer Res; 23(5); 1263–73. ©2016 AACR.

Table S2: Array CGH characterization of PDX models

Supplementary Figure 1 from Fibroblast Growth Factor Receptor 1–Transformed Mammary Epithelial Cells Are Dependent on RSK Activity for Growth and Survival

Supplementary Figure 2 from Fibroblast Growth Factor Receptor 1–Transformed Mammary Epithelial Cells Are Dependent on RSK Activity for Growth and Survival

Supplementary Figure 4 from Fibroblast Growth Factor Receptor 1–Transformed Mammary Epithelial Cells Are Dependent on RSK Activity for Growth and Survival

Supplementary Figure 3 from Fibroblast Growth Factor Receptor 1–Transformed Mammary Epithelial Cells Are Dependent on RSK Activity for Growth and Survival

Supplementary Figure 5 from Fibroblast Growth Factor Receptor 1–Transformed Mammary Epithelial Cells Are Dependent on RSK Activity for Growth and Survival

Fibroblast growth factor receptor 1 (FGFR1) is frequently amplified and highly expressed in lobular carcinomas of the breast. In this report, we evaluated the biological activity of FGFR1 in a wide range of in vitro assays. Conditional activation of FGFR1 in the nontransformed MCF10A human mammary cell line, MCF10A, resulted in cellular transformation marked by epidermal growth factor–independent cell growth, anchorage-independent cell proliferation and survival, loss of cell polarity, and epithelial-to-mesenchymal transition. Interestingly, small-molecule or small interfering RNA inhibition of ribosomal S6 kinase (RSK) activity induced death of the FGFR1-transformed cells, but not of the parental MCF10A cell line. The dependence of FGFR1-transformed cells on RSK activity was further confirmed in cell lines derived from mouse and human lobular carcinomas that possess high FGFR1 activity. Taken together, these results show the transforming activity of FGFR1 in mammary epithelial cells and identify RSK as a critical component of FGFR1 signaling in lobular carcinomas, thus implicating RSK as a candidate therapeutic target in FGFR1-expressing tumors. [Cancer Res 2009;69(6):2244–51]

SUMMARYCells rely on antioxidants to survive. The most abundant antioxidant is glutathione (GSH). The synthesis of GSH is non-redundantly controlled by the glutamate-cysteine ligase catalytic subunit (GCLC). GSH imbalance is implicated in many diseases, but the requirement for GSH in adult tissues is unclear. To interrogate this, we developed a series ofin vivomodels to induceGclcdeletion in adult animals. We find that GSH is essential to lipid abundancein vivo. GSH levels are reported to be highest in liver tissue, which is also a hub for lipid production. While the loss of GSH did not cause liver failure, it decreased lipogenic enzyme expression, circulating triglyceride levels, and fat stores. Mechanistically, we found that GSH promotes lipid abundance by repressing NRF2, a transcription factor induced by oxidative stress. These studies identify GSH as a fulcrum in the liver’s balance of redox buffering and triglyceride production.

Intratumoral heterogeneity has been described for various tumor types and models of human cancer, and can have profound effects on tumor progression and drug resistance. This study describes an in-depth analysis of molecular and functional heterogeneity among subclonal populations (SCPs) derived from a single triple-negative breast cancer cell line, including copy number analysis, whole-exome and RNA sequencing, proteome analysis, and barcode analysis of clonal dynamics, as well as functional assays. The SCPs were found to have multiple unique genetic alterations and displayed significant variation in anchorage independent growth and tumor forming ability. Analyses of clonal dynamics in SCP mixtures using DNA barcode technology revealed selection for distinct clonal populations in different in vitro and in vivo environmental contexts, demonstrating that in vitro propagation of cancer cell lines using different culture conditions can contribute to the establishment of unique strains. These analyses also revealed strong enrichment of a single SCP during the development of xenograft tumors in immune-compromised mice. This SCP displayed attenuated interferon signaling in vivo and reduced sensitivity to the antiproliferative effects of type I interferons. Reduction in interferon signaling was found to provide a selective advantage within the xenograft microenvironment specifically. In concordance with the previously described role of interferon signaling as tumor suppressor, these findings suggest that similar selective pressures may be operative in human cancer and patient-derived xenograft models.

Significance Factors stemming from the tumor microenvironment can modulate drug resistance. Therefore, rational approaches to design efficacious targeted therapies are needed. Here, we show that fibroblasts reduce lapatinib sensitivity in a subset of HER2+ breast cancer cells via paracrine signaling that can be reversed by targeting downstream survival programs such as MTOR and antiapoptotic proteins (BCL-XL and MCL-1). Our finding that fibroblasts derived from either primary tumor or metastatic sites limit lapatinib response has important implications for developing treatment strategies that can restore sensitivity in multiple drug-resistant microenvironments. Due to the diversity of microenvironmental factors between these sites, targeting downstream survival programs instead of individual factors released by fibroblasts represents a promising strategy to combat microenvironment complexity., Despite the implementation of multiple HER2-targeted therapies, patients with advanced HER2+ breast cancer ultimately develop drug resistance. Stromal fibroblasts represent an abundant cell type in the tumor microenvironment and have been linked to poor outcomes and drug resistance. Here, we show that fibroblasts counteract the cytotoxic effects of HER2 kinase-targeted therapy in a subset of HER2+ breast cancer cell lines and allow cancer cells to proliferate in the presence of the HER2 kinase inhibitor lapatinib. Fibroblasts from primary breast tumors, normal breast tissue, and lung tissue have similar protective effects on tumor cells via paracrine factors. This fibroblast-mediated reduction in drug sensitivity involves increased expression of antiapoptotic proteins and sustained activation of the PI3K/AKT/MTOR pathway, despite inhibition of the HER2 and the RAS-ERK pathways in tumor cells. HER2 therapy sensitivity is restored in the fibroblast cocultures by combination treatment with inhibitors of MTOR or the antiapoptotic proteins BCL-XL and MCL-1. Expression of activated AKT in tumor cells recapitulates the effects of fibroblasts resulting in sustained MTOR signaling and poor lapatinib response. Lapatinib sensitivity was not altered by fibroblasts in tumor cells that exhibited sustained MTOR signaling due to a strong gain-of-function PI3KCA mutation. These findings indicate that in addition to tumor cell-intrinsic mechanisms that cause constitutive PI3K/AKT/MTOR pathway activation, secreted factors from fibroblasts can maintain this pathway in the context of HER2 inhibition. Our integrated proteomic–phenotypic approach presents a strategy for the discovery of protective mechanisms in fibroblast-rich tumors and the design of rational combination therapies to restore drug sensitivity.

Recently, organoid technology has been used to generate a large repository of breast cancer organoids. Here we present an extensive evaluation of the ability of organoid culture technology to preserve complex stem/progenitor and differentiated cell types via long-term propagation of normal human mammary tissues. Basal/stem and luminal progenitor cells can differentiate in culture to generate mature basal and luminal cell types, including ER+ cells that have been challenging to maintain in culture. Cells associated with increased cancer risk can also be propagated. Single-cell analyses of matched organoid cultures and native tissues by mass cytometry for 38 markers provide a higher resolution representation of the multiple mammary epithelial cell types in the organoids, and demonstrate that protein expression patterns of the tissue of origin can be preserved in culture. These studies indicate that organoid cultures provide a valuable platform for studies of mammary differentiation, transformation, and breast cancer risk., Organoid technology has enabled the generation of several breast cancer organoids. Here, the authors combine propagation of normal human mammary tissues with mass cytometry to evaluate the ability of organoid culture technologies to preserve stem cells and differentiated cell types.

Background: While new treatments and improved subtyping schemas are anticipated to improve treatment response in triple-negative breast cancer (TNBC) patients, therapeutic resistance remains a significant challenge. Moreover, there is an urgent need for additional research model systems to study resistance and residual disease in breast cancer, including aggressive subtypes of breast cancer. Organoid culture is a promising technology used for growing breast cancer cells with high efficiency; however, the extent to which treatment resistance can be modeled using this system is unknown. This research used patient-derived organoid cultures in the context of computational analyses of large molecular and clinical datasets to study resistance mechanisms, biomarkers, and alternative treatment strategies to overcome drug resistance in early-stage TNBC. Methods: Organoid cultures were derived from breast tumor samples (taken from lumpectomy, mastectomy, or core biopsy samples), digested to the organoid level using collagenase, and grown in three dimensional cultures using a basement membrane extract and a fully-defined organoid medium (Dekkers et al. Nat Protoc 2021). An evaluation of all available I-SPY2 biomarker data (Wolf et al. Cancer Cell 2022) was performed focusing on genes, proteins, and pathways associated with resistance. These were then used to study whether resistance biomarkers identified in patient tumors are also present in organoids propagated from breast cancer post-treatment residual disease. To this end, bulk RNA sequencing data of organoids were normalized and merged with the TCGA dataset (Hoadley et al. Cell 2018) to enable analysis in a larger context, and immunofluorescence staining of organoids was performed. A high-throughput 386 anti-cancer drug compound screen and subsequent synergy testing with the most promising compounds were performed to identify and predict alternative treatment strategies. Additional assays to explore kinome activity in this organoid model are in progress. Results: A TNBC organoid biobank was established (n=31), which was enriched for inflammatory breast cancer (IBC; n=15), an aggressive form of breast cancer. Most organoids were derived from residual disease after neoadjuvant therapy. Bulk RNA sequencing analysis performed on 10 TNBC organoids revealed 3 subsets that were characterized predominantly by either normal-like/luminal androgen receptor or basal-like features or expressed distinct gene expression profiles, with IBC cases present in all 3 subsets. Intriguingly, the IBC organoids were characterized by higher expression of a number of immune-related signatures, despite an absence of clear immune cells in culture. A residual disease IBC/TNBC organoid resistant to chemotherapy was used to perform the 386-drug compound screen. The organoid model showed resistance to veliparib-cisplatin, consistent with the expression of gene/protein biomarkers predictive of drug resistance found in I-SPY2 (low PARPi7 levels and high pFOXO1 and pMEK1/2 expression). In addition, the screen identified multiple classes of inhibitors as promising synergistic/additive candidates for overcoming resistance to cisplatin. Conclusion: In this proof-of-principle study, we demonstrated the utility of matching I-SPY2 resistance biomarkers and signatures to residual disease tumor organoid cultures. We show that tumor organoid cultures modeling drug resistance states are a useful complement to existing research models of breast cancer and can be used for compound testing. We have developed a pipeline to propagate residual tumors from patients enrolled in I-SPY2 into organoid cultures to create a broader platform for preclinical drug testing informed by tumor biology with the ultimate goal of enabling faster, more successful translational studies and increased treatment options for resistant disease. Citation Format: Tam Binh V. Bui, Denise M. Wolf, Kaitlin Moore, Isaac S. Harris, Pravin Phadatare, Christina Yau, Lamorna A. Brown Swigart, Laura J. Esserman, Jean-Philippe Coppe, Julia Wulfkuhle, Emanuel F. Petricoin, Michael Campbell, Laura M. Selfors, Deborah A. Dillon, Beth Overmoyer, Filipa Lynce, Laura Van ’t Veer, Jennifer Rosenbluth. PD5-02 An Organoid Model System to Study Resistance Mechanisms, Predictive Biomarkers, and New Strategies to Overcome Therapeutic Resistance in Early-Stage Triple-Negative Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD5-02.

Akt produces reducing power The protein kinase Akt provides a link from growth factors to the production of metabolic reducing power within the cell. Hoxhaj et al. discovered that Akt directly phosphorylates nicotinamide adenine dinucleotide kinase (NADK). Catalytic activity of NADK is normally inhibited by its own amino-terminal domain, and phosphorylation by Akt relieved this inhibition. Active NADK produces nicotinamide adenine dinucleotide phosphate (NADP + ). NADP + in turn is required to produce the reduced form of NADP + (NADPH), which is the primary cofactor for reductive metabolism in the cell. Science , this issue p. 1088

Most patients with late-stage high-grade serous ovarian cancer (HGSOC) initially respond to chemotherapy but inevitably relapse and develop resistance, highlighting the need for novel therapies to improve patient outcomes. The MEK/ERK pathway is activated in a large subset of HGSOC, making it an attractive therapeutic target. Here, we systematically evaluated the extent of MEK/ERK pathway activation and efficacy of pathway inhibition in a large panel of well-annotated HGSOC patient–derived xenograft models. The vast majority of models were nonresponsive to the MEK inhibitor cobimetinib (GDC-0973) despite effective pathway inhibition. Proteomic analyses of adaptive responses to GDC-0973 revealed that GDC-0973 upregulated the proapoptotic protein BIM, thus priming the cells for apoptosis regulated by BCL2-family proteins. Indeed, combination of both MEK inhibitor and dual BCL-2/XL inhibitor (ABT-263) significantly reduced cell number, increased cell death, and displayed synergy in vitro in most models. In vivo, GDC-0973 and ABT-263 combination was well tolerated and resulted in greater tumor growth inhibition than single agents. Detailed proteomic and correlation analyses identified two subsets of responsive models—those with high BIM at baseline that was increased with MEK inhibition and those with low basal BIM and high pERK levels. Models with low BIM and low pERK were nonresponsive. Our findings demonstrate that combined MEK and BCL-2/XL inhibition has therapeutic activity in HGSOC models and provide a mechanistic rationale for the clinical evaluation of this drug combination as well as the assessment of the extent to which BIM and/or pERK levels predict drug combination effectiveness in chemoresistant HGSOC.

A major challenge of targeting metabolism for cancer therapy is pathway redundancy, in which multiple sources of critical nutrients can limit the effectiveness of some metabolism-targeted therapies. Here, we analyze lineage-dependent gene expression in human breast tumors to identify differences in metabolic gene expression that may limit pathway redundancy and create therapeutic vulnerabilities. We find that the serine synthesis pathway gene PSAT1 is the most depleted metabolic gene in luminal breast tumors relative to basal tumors. Low PSAT1 prevents de novo serine biosynthesis and sensitizes luminal breast cancer cells to serine and glycine starvation in vitro and in vivo. This PSAT1 expression disparity preexists in the putative cells of origin of basal and luminal tumors and is due to luminal-specific hypermethylation of the PSAT1 gene. Our data demonstrate that luminal breast tumors are auxotrophic for serine and may be uniquely sensitive to therapies targeting serine availability.

Our previous pre-clinical work defined BCL-2 induction as a critical component of the adaptive response to lapatinib-mediated inhibition of HER2. To determine whether a similar BCL-2 upregulation occurs in lapatinib-treated patients, we evaluated gene expression within tumor biopsies, collected before and after lapatinib or trastuzumab treatment, from the TRIO-B-07 clinical trial (NCT#00769470). We detected BCL2 mRNA upregulation in both HER2+/ER- as well as HER2+/ER+ patient tumors treated with lapatinib or trastuzumab. To address whether mRNA expression correlated with protein expression, we evaluated pre- and post-treatment tumors for BCL-2 via immunohistochemistry. Despite BCL2 mRNA upregulation within HER2+/ER- tumors, BCL-2 protein levels were undetectable in most of the lapatinib- or trastuzumab-treated HER2+/ER- tumors. BCL-2 upregulation was evident within the majority of lapatinib-treated HER2+/ER+ tumors and was often coupled with increased ER expression and decreased proliferation. Comparable BCL-2 upregulation was not observed within the trastuzumab-treated HER2+/ER+ tumors. Together, these results provide clinical validation of the BCL-2 induction associated with the adaptive response to lapatinib and support evaluation of BCL-2 inhibitors within the context of lapatinib and other HER2-targeted receptor tyrosine kinase inhibitors.

Our previous pre-clinical work defined BCL-2 induction as a critical component of the adaptive response to lapatinib-mediated inhibition of HER2. To determine whether a similar BCL-2 upregulation occurs in lapatinib-treated patients, we evaluated gene expression within tumor biopsies, collected before and after lapatinib or trastuzumab treatment, from the TRIO-B-07 clinical trial (NCT#00769470). We detected BCL-2 mRNA upregulation in both HER2+/ER- as well as HER2+/ER+ patient tumors treated with lapatinib or trastuzumab. To address whether mRNA expression correlated with protein expression, we evaluated pre- and post-treatment tumors for BCL-2 via immunohistochemistry. Despite BCL-2 mRNA upregulation within HER2+/ER- tumors, BCL-2 protein levels were undetectable in most of the lapatinib- or trastuzumab-treated HER2+/ER- tumors. BCL-2 upregulation was evident within the majority of lapatinib-treated HER2+/ER+ tumors and was often coupled with increased ER expression and decreased proliferation. Comparable BCL-2 upregulation was not observed within the trastuzumab-treated HER2+/ER+ tumors. Together, these results provide clinical validation of the BCL-2 induction associated with the adaptive response to lapatinib and support evaluation of BCL-2 inhibitors within the context of lapatinib and other HER2-targeted receptor tyrosine kinase inhibitors.

The breast is a dynamic organ whose response to physiological and pathophysiological conditions alters its disease susceptibility, yet the specific effects of these clinical variables on cell state remain poorly annotated. We present a unified, high-resolution breast atlas by integrating single-cell RNA-seq, mass cytometry, and cyclic immunofluorescence, encompassing a myriad of states. We define cell subtypes within the alveolar, hormone-sensing, and basal epithelial lineages, delineating associations of several subtypes with cancer risk factors, including age, parity, and BRCA2 germline mutation. Of particular interest is a subset of alveolar cells, termed basal-luminal (BL) cells, which exhibits poor transcriptional lineage fidelity, accumulates with age, and carries a gene signature associated with basal-like breast cancer. We further utilize a medium-depletion approach to identify molecular factors regulating cell subtype proportion in organoids. Together, these data are a rich resource to elucidate diverse mammary cell states.

The extent and importance of functional heterogeneity and crosstalk between tumor cells is poorly understood. Here, we describe the generation of clonal populations from a patient-derived ovarian clear cell carcinoma model which forms malignant ascites and solid peritoneal tumors upon intraperitoneal transplantation in mice. The clonal populations are engineered with secreted Gaussia luciferase to monitor tumor growth dynamics and tagged with a unique DNA barcode to track their fate in multiclonal mixtures during tumor progression. Only one clone, CL31, grows robustly, generating exclusively malignant ascites. However, multiclonal mixtures form large solid peritoneal metastases, populated almost entirely by CL31, suggesting that transient cooperative interclonal interactions are sufficient to promote metastasis of CL31. CL31 uniquely harbors ERBB2 amplification, and its acquired metastatic activity in clonal mixtures is dependent on transient exposure to amphiregulin, which is exclusively secreted by non-tumorigenic clones. Amphiregulin enhances CL31 mesothelial clearance, a prerequisite for metastasis. These findings demonstrate that transient, ostensibly innocuous tumor subpopulations can promote metastases via “hit-and-run” commensal interactions., Cooperative interactions among tumor cells may have important implications for metastasis. Here, the authors examined the spatio-temporal nature of interactions among clonal populations of ovarian carcinoma cells and found that transient interactions cells can promote metastases via commensal interactions.

SUMMARY Aging is closely associated with increased susceptibility to breast cancer, yet there have been limited systematic studies of aging-induced alterations in the mammary gland. Here, we leverage high-throughput single-cell RNA sequencing to generate a detailed transcriptomic atlas of young and aged murine mammary tissues. By analyzing epithelial, stromal, and immune cells, we identify age-dependent alterations in cell proportions and gene expression, providing evidence that suggests alveolar maturation and physiological decline. The analysis also uncovers potential pro-tumorigenic mechanisms coupled to the age-associated loss of tumor suppressor function and change in microenvironment. In addition, we identify a rare, age-dependent luminal population co-expressing hormone-sensing and secretory-alveolar lineage markers, as well as two macrophage populations expressing distinct gene signatures, underscoring the complex heterogeneity of the mammary epithelia and stroma. Collectively, this rich single-cell atlas reveals the effects of aging on mammary physiology and can serve as a useful resource for understanding aging-associated cancer risk., In Brief Using single-cell RNA-sequencing, Li et al. compare mammary epithelia and stroma in young and aged mice. Age-dependent changes at cell and gene levels provide evidence suggesting alveolar maturation, functional deterioration, and potential pro-tumorigenic and inflammatory alterations. Additionally, identification of heterogeneous luminal and macrophage subpopulations underscores the complexity of mammary lineages., Graphical Abstract

SUMMARYA major challenge of targeting metabolism for cancer therapy is pathway redundancy, where multiple sources of critical nutrients can limit the effectiveness of some metabolism-targeted therapies. Here, we analyzed lineage-dependent gene expression in human breast tumors to identify differences in metabolic gene expression that may limit pathway redundancy and create therapeutic vulnerabilities. We found that the serine synthesis pathway gene PSAT1 is the most depleted metabolic gene in luminal breast tumors relative to basal tumors. Low PSAT1 prevents de novo serine biosynthesis and sensitizes luminal breast cancer cells to serine and glycine starvation in vitro and in vivo. This PSAT1 expression disparity—which pre-exists in the putative cells-of-origin of basal and luminal tumors—is due to luminal-specific hypermethylation of the PSAT1 gene. Together, our data demonstrates that luminal breast tumors are auxotrophic for serine and may be uniquely sensitive to dietary serine starvation.

To interrogate functional heterogeneity and crosstalk between tumor cells, we generated clonal populations from a patient-derived ovarian clear cell carcinoma model which forms malignant ascites and solid peritoneal tumors upon intraperitoneal transplantation in mice. The clonal populations were engineered with secreted Gaussia luciferase to monitor tumor growth dynamics and tagged with a unique DNA barcode to track their fate in multiclonal mixtures during tumor progression. Only one clone, CL31, grew robustly, generating exclusively malignant ascites. However, multiclonal mixtures formed large solid peritoneal metastases, populated almost entirely by CL31, suggesting that transient cooperative interclonal interactions were sufficient to promote metastasis of CL31. CL31 uniquely harbored ERBB2 amplification, and its acquired metastatic trait was dependent on transient exposure to amphiregulin, which was exclusively secreted by non-tumorigenic clones. Amphiregulin enhanced CL31 mesothelial clearance, a prerequisite for metastasis. These findings demonstrate that transient, ostensibly innocuous tumor subpopulations can promote metastases via “hit- and-run” commensal interactions.

The lack of effective chemotherapies for high-grade serous ovarian cancers (HGS-OvCa) has motivated a search for alternative treatment strategies. Here, we present an unbiased systems-approach to interrogate a panel of 14 well-annotated HGS-OvCa patient-derived xenografts for sensitivity to PI3K and PI3K/mTOR inhibitors and uncover cell death vulnerabilities. Proteomic analysis reveals that PI3K/mTOR inhibition in HGS-OvCa patient-derived xenografts induces both pro-apoptotic and anti-apoptotic signaling responses that limit cell killing, but also primes cells for inhibitors of anti-apoptotic proteins. In-depth quantitative analysis of BCL-2 family proteins and other apoptotic regulators, together with computational modeling and selective anti-apoptotic protein inhibitors, uncovers new mechanistic details about apoptotic regulators that are predictive of drug sensitivity (BIM, caspase-3, BCL-XL) and resistance (MCL-1, XIAP). Our systems-approach presents a strategy for systematic analysis of the mechanisms that limit effective tumor cell killing and the identification of apoptotic vulnerabilities to overcome drug resistance in ovarian and other cancers., High-grade serous ovarian cancers (HGS-OvCa) frequently develop chemotherapy resistance. Here, the authors through a systematic analysis of proteomic and drug response data of 14 HGS-OvCa PDXs demonstrate that targeting apoptosis regulators can improve response of these tumors to inhibitors of the PI3K/mTOR pathway.

Background: In triple-negative breast cancers (TNBC), high proliferation is associated with greater chemosensitivity but, paradoxically, also associated with poor prognosis. We hypothesized that this subset of TNBC has distinct transcriptional features that contribute to poor prognosis. Approach: To evaluate transcriptional signatures associated with this 'proliferation paradox,' we identified 17 study cohorts of TNBC treated with neoadjuvant chemotherapy (NAC) that reported receptor status, pathologic response, and had expression data from biopsies obtained prior to NAC (n=446). In 6 studies, distant metastasis-free survival (DMFS) data was available for 235 patients with a median follow-up of 31.2 months. We calculated scores for 135 published gene expression signatures for each tumor and evaluated the association with response to chemotherapy and DMFS. Results: Using recursive partitioning to develop a model of response using a training set (n=340), six of the 135 expression signatures stratify primary tumors into four groups based on signatures of proliferation, BRCA1 mutation, immune, luminal, Ras, and PI3K phenotypes (Table 1.). Response to NAC ranged from 11% to 61% pCR/RCB-I and results were highly concordant when applied to a validation set (n = 106, p = 0.006). The group that was highly proliferative but chemoresistant ('resistant' group) had a distinct transcriptional profile, including lower 'BRCA-ness' and DNA damage expression signatures with higher Ras and stem cell signatures. The 'resistant' group had the poorest DMFS (HR 2.48 [1.52-4.06]; log-rank p=0.002) and this poor survival was validated among chemotherapy-treated TNBCs in a separate dataset, METABRIC. Analyses of only patients with residual disease after NAC demonstrated that the 'resistant' group remained poorest prognosis, with median DMFS of only 31 months from diagnosis. Conclusions: Using a novel approach to categorize primary TNBC tumors based on six signatures, we can effectively distinguish subgroups with higher versus lower pCR rates. One specific group demonstrated high proliferation but low response to chemotherapy and particularly poor survival. This group demonstrates expression signatures implicating DNA damage repair, stemness, and Ras pathway activity as potential mediators of the phenotype. We identify specific molecular characteristics for investigation in patients within a poor prognosis subgroup of TNBC. Table 1. Proportion Pathologic Complete Response or RCB-I and Survival Low ProlifHigh Prolif / ResistantHigh Prolif / SensitiveHigh ImmuneSignature StratificationLow GGI + High LuminalHigh GGI + Low BRCA1mut or High RasHigh GGI + High PI3K or Low RasHigh TNBC ImmunepCR/RCB-I rate: Training Set11/105 (10.5%)26/127 (20.5%)42/81 (51.9%)16/27 (59.3%)pCR/RCB-I rate: Validation Set3/23 (13.0%)11/45 (24.4%)13/29 (44.8%)6/9 (66.7%)pCR/RCB-I rate: TOTAL14/128 (10.9%)37/172 (21.5%)55/110 (50.0%)22/36 (61.1%)Overall Survival (n=235)Hazard Ratio (95% CI)1.62 (0.99-2.64)2.48 (1.52-4.06)(ref.)0.47 (0.29-0.77)Signatures GGI (Sotiriou, JNCI 2006); Luminal (Lim, Nat Med 2009); BRCA1 mutation (van't Veer, Nature 2002); Ras (Pratilas, PNAS 2009); PI3K (Gatza, PNAS 2010), TNBC Immune (Lehmann, JCI 2011) Citation Format: Stover DG, Selfors LM, Winer EP, Partridge AH, Barry WT. Integrated transcriptional analysis of the triple negative 'proliferation paradox': High proliferation, chemosensitivity, and poor prognosis [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-07-05.

Aging of the mammary gland is closely associated with increased susceptibility to diseases such as cancer, but there have been limited systematic studies of aging-induced alterations within this organ. We performed high-throughput single-cell RNA-sequencing (scRNA-seq) profiling of mammary tissues from young and old nulliparous mice, including both epithelial and stromal cell types. Our analysis identified altered proportions and distinct gene expression patterns in numerous cell populations as a consequence of the aging process, independent of parity and lactation. In addition, we detected a subset of luminal cells that express both hormone-sensing and alveolar markers and decrease in relative abundance with age. These data provide a high-resolution landscape of aging mammary tissues, with potential implications for normal tissue functions and cancer predisposition.

Background: Mutations in BRCA1 and BRCA2 are associated with a high risk of developing breast cancer, but the earliest molecular changes that lead to the transformation of mammary cells in the setting of BRCA1/2 heterozygosity remain unknown. We previously demonstrated that breast organoid cultures derived from histologically normal tissues can preserve all of the major mammary epithelial lineages for further study in vitro1. In addition, organoid culture medium is fully defined, enabling modulation of the medium to enhance the growth of distinct mammary subpopulations. Here, we undertook the development of a large biobank of breast organoids derived from patients with and without increased breast cancer risk, including patients with inherited mutations in BRCA1 and BRCA2. Methods: Breast samples with normal histology (taken from reduction mammoplasties or prophylactic mastectomies), were digested for ~2 hours using collagenase, embedded in basement membrane extract, and grown in a fully-defined organoid medium1. CyTOF profiling was performed using our previously published mammary-specific heavy metal-tagged antibody panel1. Lentiviral transduction was performed to knock-down BRCA1 and/or overexpress mutant p53. Murine engraftment of normal breast organoids was performed by intra-ductal injection of ~1,000 organoids into NCG mice using a modification of protocols for breast cancer cell lines2, with removal of mammary glands after 3 months for detailed immunohistochemistry analysis. Results: A living biobank of > 100 normal breast organoids derived from patients with and without inherited mutations in breast cancer predisposition genes, including BRCA1 and BRCA2, was established. Cultures were generated with high efficiency (>95%) and could be serially passaged with the longest cultures > 16 months. CyTOF profiling of organoids revealed the maintenance of multiple epithelial cell subtypes, with at least one subtype of luminal cells enriched in tissues and organoids from BRCA1/2 mutation carriers. Protein and RNA expression patterns of breast organoids were found to correlate with patient tissues analyzed using a combination of single-cell analyses (CyTOF, single-cell RNA sequencing, and immunohistochemistry). The impact of factors present in the organoid medium on distinct mammary epithelial cell subtypes was assessed by CyTOF, enabling identification of conditions that promote expansion of cell populations that are enriched in tissues from BRCA1/2 mutation carriers. Furthermore, normal breast cell types could be engrafted into the murine mammary gland, and could be modified by lentiviral transduction for gene transfer, enabling future studies of the tumorigenic potential of distinct normal and premalignant epithelial cell subtypes. Conclusion: We have shown that organoid cultures can be used to propagate normal breast tissues with high efficiency, preserve normal as well as potential premalignant breast epithelial cell types, and model methods to inhibit precancerous cells in vitro. Thus, organoids are a useful complement to murine and other models of breast cancer development, and can ultimately be used to identify potential cancer interception strategies for patients at high risk of developing breast cancer. References:1.Rosenbluth JM, Schackmann RCJ, Gray GK, et al: Organoid cultures from normal and cancer-prone human breast tissues preserve complex epithelial lineages. Nat Commun 11:1711, 20202.Zoeller JJ, Bronson RT, Selfors LM, et al: Niche-localized tumor cells are protected from HER2-targeted therapy via upregulation of an anti-apoptotic program in vivo. NPJ Breast Cancer 3:18, 2017 Citation Format: Jennifer M Rosenbluth, Carman Man-Chung Li, Kenneth G Gray, Walter Gao, Ron CJ Schackmann, Jason J Zoeller, Laura M Selfors, Kaitlin Moore, Deborah Dillon, Judy Garber, Joan S Brugge. A living biobank of normal mammary organoids derived from patients at low and increased risk of developing breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PD7-03.

Aberrant activation of the PI3K/mTOR pathway is a common feature of many cancers and an attractive target for therapy, but resistance inevitably evolves as is the case for any cancer cell-targeted therapy. In animal tumor models, chronic inhibition of PI3K/mTOR initially inhibits tumor growth, but over time, tumor cells escape inhibition. In this study, we identified a context-dependent mechanism of escape whereby tumor cells upregulated the proto-oncogene transcriptional regulators c-MYC and YAP1. This mechanism was dependent on both constitutive ERK activity as well as inhibition of the stress kinase p38. Inhibition of p38 relieved proliferation arrest and allowed upregulation of MYC and YAP through stabilization of CREB. These data provide new insights into cellular signaling mechanisms that influence resistance to PI3K/mTOR inhibitors. Furthermore, they suggest that therapies that inactivate YAP or MYC or augment p38 activity could enhance the efficacy of PI3K/mTOR inhibitors., National Institutes of Health (U.S.) (Grant R01CA103866), National Institutes of Health (U.S.) (Grant AI47389)

Purpose: To provide further insight into the role of proliferation and other cellular processes in chemosensitivity and resistance, we evaluated the association of a diverse set of gene expression signatures with response to neoadjuvant chemotherapy (NAC) in breast cancer. Experimental Design: Expression data from primary breast cancer biopsies for 1,419 patients in 17 studies prior to NAC were identified and aggregated using common normalization procedures. Clinicopathologic characteristics, including response to NAC, were collected. Scores for 125 previously published breast cancer–related gene expression signatures were calculated for each tumor. Results: Within each receptor-based subgroup or PAM50 subtype, breast tumors with high proliferation signature scores were significantly more likely to achieve pathologic complete response to NAC. To distinguish “proliferation-associated” from “proliferation-independent” signatures, we used correlation and linear modeling approaches. Most signatures associated with response to NAC were proliferation associated: 90.5% (38/42) in ER+/HER2− and 63.3% (38/60) in triple-negative breast cancer (TNBC). Proliferation-independent signatures predictive of response to NAC in ER+/HER2− breast cancer were related to immune activity, while those in TNBC comprised a diverse set of signatures, including immune, DNA damage, signaling pathways (PI3K, AKT, Ras, and EGFR), and “stemness” phenotypes. Conclusions: Proliferation differences account for the vast majority of predictive capacity of gene expression signatures in neoadjuvant chemosensitivity for ER+/HER2− breast cancers and, to a lesser extent, TNBCs. Immune activation signatures are proliferation-independent predictors of pathologic complete response in ER+/HER2− breast cancers. In TNBCs, significant proliferation-independent signatures include gene sets that represent a diverse set of cellular processes. Clin Cancer Res; 22(24); 6039–50. ©2016 AACR.

Background: Proliferation is the strongest predictor of response to neoadjuvant chemotherapy in estrogen receptor-positive (ER+) breast cancer. Evidence of immune activation has also been associated with improved response to neoadjuvant chemotherapy in breast cancer. We hypothesized that immune signatures may be associated with response independent of proliferation in ER+ breast cancers. Approach: We compiled microarray expression data from breast cancer biopsies obtained prior to neoadjuvant chemotherapy on 465 ER-positive/HER2-negative patients by reported pathologic receptor status. We evaluated the association of 118 published gene expression signatures with response to neoadjuvant chemotherapy, based on study-defined pathologic complete response (pCR) versus residual disease (RD). Results: Overall, 42 of 118 signatures were significantly associated with response to neoadjuvant chemotherapy in ER+ breast cancer (FDR-corrected p0.30, p0.4, p Conclusions: Gene expression signatures associated with "immune activation" identify a subset of ER+ breast cancers with higher rates of pCR to neoadjuvant chemotherapy. These "immune activation" signatures appear to be proliferation-independent and may provide additional predictive information to existing gene expression-based approaches for ER+ breast cancer. Citation Format: Stover DG, Waks AG, Erica ML, Brugge JS, Winer EP, Selfors LM. Immune activation signatures identify a subset of ER+ breast cancers with increased pathologic complete response to neoadjuvant chemotherapy. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-31.