Abstract 1470: UGP2 is a critical regulator of protein glycosylation in pancreatic cancer

UDP-glucose pyrophosphorylase 2 (UGP2) is a lynchpin metabolic enzyme that rests at the convergence of multiple metabolic pathways regulating both glycogen synthesis and glycosylation modifications. Here we elucidated the essential role of UGP2-mediated glycosylation in the maintenance of KRAS-driven cancer using both in vitro and in vivo models. A key effector of KRAS oncogenic function is the transcription factor YAP. We identified the YAP/TEAD transcription factor complex as a major regulator of UGP2 mRNA expression and enzymatic activity using genomic perturbations, correlative protein immunohistochemistry in PDAC samples, and ChIP-seq and targeted ChIP-qPCR at the UGP2 promoter. Loss of YAP or UGP2 leads to a decrease in glycogen and defects in key glycosylation targets such as EGFR. In murine xenograft models using pancreatic cancer lines, knockdown of UGP2 prevented tumor growth and decreased expression of the critical glycosylation target EGFR. This essential role for UGP2 in cancer maintenance may lead to new avenues of therapy in otherwise intractable KRAS-driven cancers.

Citation Format: Andrew L. Wolfe, Jacqueline Galeas, Eneda Toska, Qing Zhou, Angel Ku, Richard P. Koche, Sourav Bandyopadhyay, Carlito B. Lebrilla, Maurizio Scaltriti, Frank McCormick, Sung Eun Kim. UGP2 is a critical regulator of protein glycosylation in pancreatic cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1470.

Abstract 5588: Clinical and pharmacodynamic responses to a modified whole tumor cell immunotherapy in patients with advanced breast cancer from two phase I-IIa trials

SV-BR-1-GM is a GM-CSF secreting breast cancer cell line that also expresses HLA class I & II antigens. Irradiated SV-BR-1-GM is used in a regimen including pre-dose low-dose cyclophosphamide and post-dose local interferon-α2b. The SV-BR-1-GM regimen has been used alone (“Monotherapy” study ClinicalTrials.gov NCT03066947) and in combination with immune checkpoint inhibitors (ongoing combination study ClinicalTrials.gov identifier NCT03328026). Here we report regression of metastatic breast cancer and pharmacodynamic analysis with immunologic correlates.

23 patients with advanced breast cancer refractory to standard therapies were treated with the SV-BR-1-GM regimen in the monotherapy trial with cycles every 2 weeks for the first month and then monthly. The combination study is evaluating the SV-BR-1-GM regimen with checkpoint inhibitors (PD-1 inhibitors pembrolizumab or INCMGA00012) with cycles every 3 weeks (11 patients have been dosed to date). Pharmacodynamic analyses include delayed-type hypersensitivity (DTH), antibodies against SV-BR-1 (precursor of SV-BR-1-GM), blood lymphocyte proliferation (determined using flow cytometry), circulating cytokines in sera and cytokine secretion (Luminex based assays) following stimulation with peptides of antigens expressed in SV-BR-1-GM cells (HER2 and PRAME).

In the monotherapy study, tumor regression was seen in 3 patients. 21 patients developed measurable DTH signifying cellular immunity. Blood lymphocytes from responders after treatment showed increased proliferation and cytokine secretion (GM-CSF, IL-2, IL-21) - following stimulation with HER2 and PRAME peptides. Differential serum cytokine levels were observed (CD40L, MCP-1, IL-1RA) in 5 patients. Increased antibody levels compared to baseline were observed in 6 of the 12 patients assessed. Patients with objective tumor regression had the most pronounced responses. In the combination therapy study, 2 patients have shown objective evidence of tumor regression, including one patient with liver metastases, which decreased by 25%, and one patient with adrenal and dural metastases (29% reduction in target lesion). Both patients had Grade II tumors, similar to the tumor from which SV-BR-1-GM was derived.

These observations confirm the ability of the SV-BR-1-GM regimen to elicit regression of far advanced refractory metastatic breast cancer. No serious toxicities clearly attributed to the SV-BR-1-GM regimen were observed. Pharmacodynamic analysis of humoral and cell-mediated immune responses showed notable upregulation, the strongest responses being seen in those with measurable clinical regression. Patients with Grade I or II tumors appeared more likely to respond.

Citation Format: Vivekananda G. Sunkari, Jacqueline Galeas, Shaker R. Dakhil, Jarrod Holmes, Saveri Bhattacharya, Carmen J. Calfa, Ajay Kundra, Daniel L. Adams, Diane DaSilva, George E. Peoples, Charles L. Wiseman, William V. Williams, Markus D. Lacher. Clinical and pharmacodynamic responses to a modified whole tumor cell immunotherapy in patients with advanced breast cancer from two phase I-IIa trials [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5588.

Abstract A39: The role of YAP in regulating glycogen metabolism in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is driven largely by oncogenic KRAS mutations, making KRAS and its downstream effectors, in theory, ideal candidates for therapeutic intervention. Unfortunately, attempts to directly inhibit KRAS or its effectors have either been unsuccessful or ineffective and, as a result, there is much interest in identifying novel downstream effectors of oncogenic KRAS signaling. Yes-associated protein (YAP) has been shown to be an essential mediator of oncogenic KRAS signaling during PDAC progression as well as a marker for poor prognosis in PDAC patients. YAP is required for tumor recurrence and is able to compensate for loss of oncogenic KRAS in several cancer types, suggesting interplay between these pathways. YAP is a transcriptional co-activator that partners with transcription factors to control organ size, and upregulation of YAP is frequently observed in human cancers. Downstream target genes of YAP include cyclins and growth factors involved in proliferation, but YAP also induces stem cell properties, drug resistance, and metastasis, suggesting the presence of additional targets that affect various cellular processes. As KRAS is a major regulator of cellular metabolism and can upregulate scavenging pathways, such as autophagy and macropinocytosis, we hypothesize that YAP may also play a role in metabolic reprogramming of pancreatic cancers based on its importance in tumor initiation and progression. Our data demonstrate that YAP depletion in PDAC cells leads to dysregulated glycogen metabolism through regulation of uridine diphosphate glucose (UDP-Glc), the direct glucosyl donor for glycogen synthesis. UDP-Glc is synthesized from glucose-1-phosphate and uridine triphosphate (UTP) by UDP-Glc pyrophorphorylase 2 (UGP2), the sole enzyme responsible for this reaction in mammalian cells. YAP-depleted cells showed corresponding decrease of UGP2 mRNA and protein levels in a panel of PDAC cell lines. TCGA provisional dataset analysis showed a statistically significant tendency towards co-occurrence (p<0.001) between YAP and UGP2 mRNA levels in PDAC patients, and immunohistochemistry of tissues samples showed high correlation between YAP and UGP2 expression patterns, suggesting this regulation also exists in PDAC patients. Cells depleted of UGP2 showed a marked decrease of cell growth in 2D and 3D cultures, suggesting that UGP2 plays an important role in PDAC cell survival and proliferation. Interestingly, cells expressing oncogenic KRAS or its direct downstream effector, BRAF, have increased UGP2 expression and glycogen levels that are YAP-dependent. This suggests that glycogen metabolism may be an integral part of YAP-dependent KRAS signaling and that this pathway has an important function in PDAC cells. This is a novel role of YAP that has not been previously reported, and here we seek to understand the mechanism of how YAP regulates this pathway and its function in PDAC cells.

Citation Format: Sung Eun (Monica) Kim, Jacqueline Galeas, Frank McCormick. The role of YAP in regulating glycogen metabolism in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr A39.

RIT1 oncoproteins escape LZTR1-mediated proteolysis

RIT1 oncoproteins have emerged as an etiologic factor in Noonan syndrome and cancer. Despite the resemblance of RIT1 to other members of the Ras small guanosine triphosphatases (GTPases), mutations affecting RIT1 are not found in the classic hotspots but rather in a region near the switch II domain of the protein. We used an isogenic germline knock-in mouse model to study the effects of RIT1 mutation at the organismal level, which resulted in a phenotype resembling Noonan syndrome. By mass spectrometry, we detected a RIT1 interactor, leucine zipper-like transcription regulator 1 (LZTR1), that acts as an adaptor for protein degradation. Pathogenic mutations affecting either RIT1 or LZTR1 resulted in incomplete degradation of RIT1. This led to RIT1 accumulation and dysregulated growth factor signaling responses. Our results highlight a mechanism of pathogenesis that relies on impaired protein degradation of the Ras GTPase RIT1.

Abstract 5520: Oncogenic RTK signaling inhibits Spred1/NF1 to sustain constitutive Ras/MAPK signaling

Spred proteins negatively regulate Ras/MAPK signaling following growth factor stimulation. Inhibition of Ras primary occurs through Spreds ability to bind and localize NF1, a RasGAP and major tumor suppressor, to the plasma membrane. Spred1 and NF1 loss-of-function mutations occur across multiple cancer types including non-small cell lung carcinoma, glioblastoma, melanoma, stomach carcinoma, and uterine carcinosarcoma. Here we demonstrate that oncogenic RTK signaling leads to phosphorylation of Spred1(S105) in the EVH domain, which disrupts Spred1-NF1 binding and function. Phosphomimetic Spred1 is unable to suppress Ras-GTP following growth factor stimulation and cancer cell proliferation. The Spred1(S105) kinase is likely to be a CDK based on in vitro kinase and in vivo cell line assays. Our findings provide one potential mechanism by which oncogenic RTK signaling disrupts negative feedback to sustain constitutive Ras signaling. Furthermore, this work may elucidate a novel therapeutic target for restoring NF1-mediated inhibition of Ras.

Citation Format: Evan Markegard, Ellen L. Mercado, Pau Castel, Jillian Silva, Jacqueline Galeas, Kathy Li, Anatoly Urisman, Frank McCormick. Oncogenic RTK signaling inhibits Spred1/NF1 to sustain constitutive Ras/MAPK signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5520.

Abstract B098: GPX4 is a broadly shared gene vulnerability among residual tumors

The heterogeneity of tumor cells underlies acquired drug resistance to a variety of therapeutic approaches. The advent of next-generation sequencing has facilitated a wave of studies identifying genetic mutations, which may be preexisting or acquired during treatment, that drive drug resistance and tumor relapse. However, it has recently become clear that non-mutational mechanisms of drug resistance, such as cell state switching from an epithelial to mesenchymal state, can also play an important role in the process of acquired drug resistance. Non-mutational drug resistance is relatively poorly understood and represents fertile ground for the discovery of novel therapeutic targets. Drug-tolerant “persister” cells are an experimental model of non-mutational cancer drug resistance in which small fractions (<5%) of cells within cancer cell lines survive cytotoxic drug exposure despite lacking resistance-conferring mutations. These residual surviving persister cells occupy a reversible quiescent state with a unique chromatin landscape. Persister cells regrow and become resensitized to drug, reminiscent of clinical observations of secondary responses from retreatment after a drug holiday. Persister cells also eventually obtain genetic mutations and reenter the cell cycle after weeks or months of continuous drug exposure, modeling the process of acquisition of resistance-conferring genetic mutations in patients during treatment. Here, we report on our efforts to identify a widely shared gene vulnerability in persister cells that transcends tissue lineage, genetic mutation background, and drug treatment regimens. Through a functional genomics approach entailing RNA-seq, pathway analysis, and a focused chemical inhibitor screen, we have identified a gene, glutathione peroxidase 4 (GPX4), that is specifically essential to persister cells. When GPX4 is chemically inhibited or genetically ablated, persister cells across a wide range of tissue lineages undergo ferroptosis–a recently discovered mechanism of non-apoptotic caspase-independent cell death. Ferroptosis occurs when lipid peroxides accumulate in cells, and as the only human enzyme capable of scavenging lipid peroxides, GPX4 plays a key role in preventing ferroptosis. Compared to drug-naïve parental cells or nontransformed normal cells, persister cells are strongly differentially sensitive to GPX4 inhibition and ferroptosis. This sensitivity is the result of a disabled antioxidant program in persister cells marked by a global downregulation of antioxidant genes including Nrf2 targets, and decreased levels of reducing cofactors glutathione and NADPH. As a first step toward raising GPX4 as a promising preclinical drug target in vivo, we also show that targeting GPX4 in residual melanoma xenograft tumors prevents tumor relapse. Therefore, GPX4 is an extremely promising drug target that may be exploited to prevent tumor relapse across a wide spectrum of tumor types and drug treatments.

Citation Format: Matthew J. Hangauer, Vasanthi S. Viswanathan, Matthew J. Ryan, Dhruv Bole, John K. Eaton, Alexandre Matov, Jacqueline Galeas, Harshil D. Dhruv, Michael E. Berens, Stuart L. Schreiber, Frank McCormick, Michael T. McManus. GPX4 is a broadly shared gene vulnerability among residual tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B098.

Drug-tolerant persister cancer cells are vulnerable to GPX4 inhibition

Acquired drug resistance prevents cancer therapies from achieving stable and complete responses.¹ Emerging evidence implicates a key role for nonmutational drug resistance mechanisms underlying the survival of residual cancer “persister” cells.^2-4 The persister cell pool constitutes a reservoir from which drug-resistant tumours may emerge. Targeting persister cells therefore presents a therapeutic opportunity to impede tumour relapse.⁵ In an earlier report, we found that cancer cells in a high mesenchymal therapy-resistant cell state are dependent on the lipid hydroperoxidase GPX4 for survival.⁶ Here, we describe the discovery that a similar therapy-resistant cell state underlies the behavior of persister cells derived from a wide range of cancers and drug treatments. Consequently, we show that persister cells acquire a dependency on GPX4. We demonstrate that loss of GPX4 function results in selective persister cell ferroptotic death in vitro and prevents tumour relapse in vivo. These findings support targeting GPX4 as a therapeutic strategy to prevent acquired drug resistance.

Abstract 1370: EGFR-mediated Spred1 phosphorylation inhibits NF1 to sustain constitutive Ras/MAPK signaling

Spred proteins negatively regulate Ras/MAPK signaling following growth factor stimulation. Inhibition of Ras primary occurs through Spreds ability to bind and localize NF1, a RasGAP and major tumor suppressor, to the plasma membrane. Spred1 and NF1 loss-of-function mutations occur across multiple cancer types including non-small cell lung carcinoma, glioblastoma, melanoma, stomach carcinoma, and uterine carcinosarcoma. Here we demonstrate that EGFR signaling disrupts Spred1-NF1 binding. Mass spectrometry was performed on cells overexpressing EGFRL858R to identify potential phosphorylation sites on Spred1 and NF1 that could disrupt Spred1-NF1 binding by steric hindrance. A serine phosphorylation site on Spred1 was identified in which a phosphomimetic and phosphodeficient mutant decreased or increased Spred1-NF1 binding, respectively. Phosphomimetic Spred1 is unable to suppress Ras-GTP following EGF stimulation. Therefore, phosphorylation of Spred1 at this site by a serine kinase downstream of EGFR may disrupt Spred1-NF1 binding. To identify the Spred1 kinase we are performing an in vitro kinase assay and an unbiased CRISPRa screen. Our findings provide one potential mechanism by which EGFR signaling disrupts negative feedback to sustain constitutive Ras signaling. Furthermore, this work may elucidate a novel therapeutic target for restoring NF1-mediated inhibition of Ras.

Citation Format: Evan Markegard, Ellen L. Mercado, Jillian M. Silva, Jacqueline Galeas, Marena I. Trinidad, Anatoly Urisman, Frank McCormick. EGFR-mediated Spred1 phosphorylation inhibits NF1 to sustain constitutive Ras/MAPK signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1370. doi:10.1158/1538-7445.AM2017-1370

Abstract 1874: Oncogenic EGFR signaling inhibits the Spred1-NF1 interaction to sustain constitutive Ras signaling

Spred proteins negatively regulate Ras/MAPK signaling following mitogen stimulation. Inhibition of Ras primary occurs through Spreds ability to bind and localize NF1, a RasGAP and major tumor suppressor, to the plasma membrane. Loss-of-function Spred1 and NF1 mutations occur across multiple cancer types including melanoma, non-small cell lung carcinoma, stomach carcinoma, and uterine carcinosarcoma. Here we demonstrate that oncogenic EGFR signaling disrupts Spred1-NF1 binding. Mass spectrometry was performed on cells overexpressing EGFRL858R to identify potential phosphorylation sites on Spred1 and NF1 that could disrupt Spred1-NF1 binding by steric hindrance. A serine phosphorylation site on Spred1 was identified in which a phosphomimetic and phosphodeficient mutant decreased or increased Spred1-NF1 binding, respectively. Therefore, phosphorylation of Spred1 at this site by a serine kinase downstream of oncogenic EGFR may disrupt Spred1-NF1 binding. Our findings provide one potential mechanism by which oncogenic EGFR signaling disrupts negative feedback to allow for constitutive Ras signaling. Furthermore, this work may elucidate a novel kinase therapeutic target for restoring NF1 mediated inhibition of Ras.

Citation Format: Evan Markegard, Ellen L. Mercado, Jacqueline Galeas, Marena I. Trinidad, Anatoly Urisman, Frank McCormick. Oncogenic EGFR signaling inhibits the Spred1-NF1 interaction to sustain constitutive Ras signaling. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1874.

K-Ras Promotes Tumorigenicity through Suppression of Non-canonical Wnt Signaling

K-Ras and H-Ras share identical effectors and have similar properties; however, the high degree of tumor-type specificity associated with K-Ras and H-Ras mutations suggests that they have unique roles in oncogenesis. Here, we report that oncogenic K-Ras, but not H-Ras, suppresses non-canonical Wnt/Ca(2+) signaling, an effect that contributes strongly to its tumorigenic properties. K-Ras does this by binding to calmodulin and so reducing CaMKii activity and expression of Fzd8. Restoring Fzd8 in K-Ras mutant pancreatic cells suppresses malignancy, whereas depletion of Fzd8 in H-Ras(V12)-transformed cells enhances their tumor initiating capacity. Interrupting K-Ras-calmodulin binding using genetic means or by treatment with an orally active protein kinase C (PKC)-activator, prostratin, represses tumorigenesis in K-Ras mutant pancreatic cancer cells. These findings provide an alternative way to selectively target this "undruggable" protein.

Enhanced MET Translation and Signaling Sustains K-Ras-Driven Proliferation under Anchorage-Independent Growth Conditions

Oncogenic K-Ras mutation occurs frequently in several types of cancers, including pancreatic and lung cancers. Tumors with K-Ras mutation are resistant to chemotherapeutic drugs as well as molecular targeting agents. Although numerous approaches are ongoing to find effective ways to treat these tumors, there are still no effective therapies for K-Ras mutant cancer patients. Here we report that K-Ras mutant cancers are more dependent on K-Ras in anchorage-independent culture conditions than in monolayer culture conditions. In seeking to determine mechanisms that contribute to the K-Ras dependency in anchorage-independent culture conditions, we discovered the involvement of Met in K-Ras-dependent, anchorage-independent cell growth. The Met signaling pathway is enhanced and plays an indispensable role in anchorage-independent growth even in cells in which Met is not amplified. Indeed, Met expression is elevated under anchorage-independent growth conditions and is regulated by K-Ras in a MAPK/ERK kinase (MEK)-dependent manner. Remarkably, in spite of a global downregulation of mRNA translation during anchorage-independent growth, we find that Met mRNA translation is specifically enhanced under these conditions. Importantly, ectopic expression of an active Met mutant rescues K-Ras ablation-derived growth suppression, indicating that K-Ras-mediated Met expression drives "K-Ras addiction" in anchorage-independent conditions. Our results indicate that enhanced Met expression and signaling is essential for anchorage-independent growth of K-Ras mutant cancer cells and suggests that pharmacological inhibitors of Met could be effective for K-Ras mutant tumor patients.

Abstract 2327: Oncogenic K-Ras and H-Ras differentially regulate cancer stem cell-like properties via repression of non-canonical Wnt signaling

Cancer stem cells (CSCs) can cause cancer treatment failures and tumor recurrence due to their stem cell-like properties, such as the unlimited self-renewal, tumorigenicity, and chemo-resistance. Ras is the most common oncogene in human cancers, but its roles in stem cell-like properties have not been convincingly demonstrated. With a high degree of sequence homology as well as common sets of downstream effectors and upstream affecters, the three isoforms of Ras, N-, H- and K-Ras, have long been assumed to be functionally redundant. However, knockout of K-Ras, not N- or H-Ras, in mice leads to embryonic lethality, suggesting a non-redundant role of K-Ras in embryonic development. Herein, we report that oncogenic K-Ras, differentially from H-Ras, causes CSC-like properties in transformed mouse fibroblast and pancreatic cancer cells. When compared to the NIH3T3 cells with H-RasV12, the cells transformed with K-RasV12 demonstrated significantly enhanced sphere forming efficiency, elevated resistance toward cisplatin, and heightened sensitivity to the CSC inhibitor, salinomycin, while the RasGTPase, p-Erk and p-Akt activities are comparable. In the comparison with H-RasV12 transformed cells, K-RasV12 transformed NIH3T3 cells possessed significantly increased tumor initiating frequency in limited cell transplantation and in vivo serial transplantation assays. Through stem cell signaling-related genes focusing PCRarray, we further identified Frizzled 8 (Fzd8), a Wnt receptor and potential activator of non-canonical Wnt/Ca2+ signaling, was significantly down-regulated in K-RasV12 transformed NIH3T3 cells when compared to normal cells or H-RasV12- transformed cells. In clinical human pancreatic tissues, Fzd8 was dramatically reduced in malignant specimens, whereas normal tissue showed high expressions of Fzd8. Knockdown of K-Ras in pancreatic cancer cells led to significant increases in Fzd8 at RNA and protein levels, suggesting oncogenic K-Ras repress the expression of Fzd8. TOPFlash assay revealed that K-RasV12 transformed NIH3T3 had dramatically enhanced canonical beta-catenin activity when compared to normal or H-RasV12- transformed cells. Human pancreatic cancer cells with K-Ras knocked down showed significantly reduced canonical beta-catenin activity. In a syngenic mouse model, over-expression of Fzd8 in oncogenic K-Ras driven mouse pancreatic cancer cells delayed the orthotropic tumor formation, and further decreased peritoneal metastatic spreads. Our data collectively suggest that oncogenic K-Ras regulates the stem cell-like properties of cancer cells, differentially from oncogenic H-Ras, through repression of Fzd8-mediated non-canonical Wnt/Ca2+ signaling. Restoration of Fzd8 suppressed oncogenic K-Ras induced pancreatic tumorigenesis, providing an alternative way to target this “undruggable” oncogene.

Citation Format: Man-Tzu Wang, Jacqueline Galeas, Cayde Ritchie, Frank McCormick. Oncogenic K-Ras and H-Ras differentially regulate cancer stem cell-like properties via repression of non-canonical Wnt signaling. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2327. doi:10.1158/1538-7445.AM2013-2327