Pten-null Mice Research Articles

CDK12 loss drives prostate cancer progression, transcription-replication conflicts, and synthetic lethality with paralog CDK13

Biallelic loss of cyclin-dependent kinase 12 (CDK12) defines a metastatic castration-resistant prostate cancer (mCRPC) subtype. It remains unclear, however, whether CDK12 loss drives prostate cancer (PCa) development or uncovers pharmacologic vulnerabilities. Here, we show Cdk12 ablation in murine prostate epithelium is sufficient to induce preneoplastic lesions with lymphocytic infiltration. In allograft-based CRISPR screening, Cdk12 loss associates positively with Trp53 inactivation but negatively with Pten inactivation. Moreover, concurrent Cdk12/Trp53 ablation promotes proliferation of prostate-derived organoids, while Cdk12 knockout in Pten-null mice abrogates prostate tumor growth. In syngeneic systems, Cdk12/Trp53-null allografts exhibit luminal morphology and immune checkpoint blockade sensitivity. Mechanistically, Cdk12 inactivation mediates genomic instability by inducing transcription-replication conflicts. Strikingly, CDK12-mutant organoids and patient-derived xenografts are sensitive to inhibition or degradation of the paralog kinase, CDK13. We therein establish CDK12 as a bona fide tumor suppressor, mechanistically define how CDK12 inactivation causes genomic instability, and advance a therapeutic strategy for CDK12-mutant mCRPC.

Abstract 5328: Dual role of Kupffer cell secreted CXCL5 in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is hallmarked by inflammatory cell infiltration. Chemokines secreted during inflammation are crucial at directing immune cell infiltration during cancer development. We screened patient dataset from different etiologies including HBV, HCV, alcohol and non-alcoholic steatohepatitis (NASH) and identified CXCL5 as the only chemokine consistently upregulated in HCC. Immunohistochemistry (IHC) of patient liver tumor tissues further showed the production of CXCL5 by tumor surrounding non parenchymal cells. Using a mouse model (Pte loxP/loxP; Alb-Cre+, Pten null) which recapitulates human liver disease progression from non-alcoholic fatty liver disease (NAFLD) to NASH to liver cancer, we found that CXCL5 was expression was gradually increased during disease progression. Further analysis using IHC and flow cytometry analysis showed that CXCL5 is predominantly expressed by Kupffer cells in Pten null livers bearing tumors. Furthermore, we found that LPS stimulated the expression and secretion of CXCL5 in Kupffer cells, but not other macrophages including peritoneal macrophage and macrophage cell line Raw264.7 cells. We hypothesized that the Kupffer cell-secreted CXCL5 in response to LPS promotes tumor progression by promoting HCC cell proliferation and regulating HCC associated immune cell infiltration. To investigate whether CXCL5 increases tumor cell proliferation, we treated wild type and Pten null hepatocytes with various concentrations of CXCL5. Our results showed that CXCL5 increased hepatocytes viability in a dose dependent manner. BrdU incorporation assay further confirmed that CXCL5 treatments induces HCC cell proliferation through its receptor CXCR2. We further demonstrated that CXCR2 knockdown led to reduced xenograft tumor growth using HepG2 cells. Additionally, we injected Pten null mice with CXCR2 inhibitor to block CXCL5 signal and observed partial response. We analyzed the immune cell profile of the responder mice vs. non-responder mice and showed that tumor inhibition is correlated with T cell infiltration. To test whether Kupffer cells regulate T cells through CXCL5, we isolated primary Kupffer cells from murine livers. We performed transwell migration assay using immune cells from murine spleens. Our results indicate that LPS stimulation in Kupffer cells reduced the ratio of migrated CD4+ T cells, while blocking CXCL5 using a CXCL5 antibody significantly increased CD4+ T cell recruitment to the LPS-stimulated Kupffer cells and moderately decreased neutrophil recruitment. Consistently, we found that recombinant CXCL5 protein reduces CD4+ T cell migration independent of neutrophils. In summary, our study suggests that Kupffer cell secreted CXCL5 reduces liver CD4+ T cell recruitment and increases liver cancer cell proliferation. Citation Format: Taojian Tu, Handan Hong, Lina He, Mario Alba, Tang Qi, Curtis T. Okamoto, Bangyan L. Stiles. Dual role of Kupffer cell secreted CXCL5 in hepatocellular carcinoma [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 5328.

STAT3/LKB1 controls metastatic prostate cancer by regulating mTORC1/CREB pathway

Prostate cancer (PCa) is a common and fatal type of cancer in men. Metastatic PCa (mPCa) is a major factor contributing to its lethality, although the mechanisms remain poorly understood. PTEN is one of the most frequently deleted genes in mPCa. Here we show a frequent genomic co-deletion of PTEN and STAT3 in liquid biopsies of patients with mPCa. Loss of Stat3 in a Pten-null mouse prostate model leads to a reduction of LKB1/pAMPK with simultaneous activation of mTOR/CREB, resulting in metastatic disease. However, constitutive activation of Stat3 led to high LKB1/pAMPK levels and suppressed mTORC1/CREB pathway, preventing mPCa development. Metformin, one of the most widely prescribed therapeutics against type 2 diabetes, inhibits mTORC1 in liver and requires LKB1 to mediate glucose homeostasis. We find that metformin treatment of STAT3/AR-expressing PCa xenografts resulted in significantly reduced tumor growth accompanied by diminished mTORC1/CREB, AR and PSA levels. PCa xenografts with deletion of STAT3/AR nearly completely abrogated mTORC1/CREB inhibition mediated by metformin. Moreover, metformin treatment of PCa patients with high Gleason grade and type 2 diabetes resulted in undetectable mTORC1 levels and upregulated STAT3 expression. Furthermore, PCa patients with high CREB expression have worse clinical outcomes and a significantly increased risk of PCa relapse and metastatic recurrence. In summary, we have shown that STAT3 controls mPCa via LKB1/pAMPK/mTORC1/CREB signaling, which we have identified as a promising novel downstream target for the treatment of lethal mPCa.

AKT activation because of PTEN loss upregulates xCT via GSK3β/NRF2, leading to inhibition of ferroptosis in PTEN-mutant tumor cells

Here, we show that the tumor suppressor phosphatase and tensin homolog deleted from chromosome 10 (PTEN) sensitizes cells to ferroptosis, an iron-dependent form of cell death, by restraining the expression and activity of the cystine/glutamate antiporter system Xc- (xCT). Loss of PTEN activates AKT kinase to inhibit GSK3β, increasing NF-E2 p45-related factor 2 (NRF2) along with transcription of one of its known target genes encoding xCT. Elevated xCT in Pten-null mouse embryonic fibroblasts increases the flux of cystine transport and synthesis of glutathione, which enhances the steady-state levels of these metabolites. A pan-cancer analysis finds that loss of PTEN shows evidence of increased xCT, and PTEN-mutant cells are resistant to ferroptosis as a consequence of elevated xCT. These findings suggest that selection of PTEN mutation during tumor development may be due to its ability to confer resistance to ferroptosis in the setting of metabolic and oxidative stress that occurs during tumor initiation and progression.

S-palmitoylation of PCSK9 induces sorafenib resistance in liver cancer by activating the PI3K/AKT pathway.

Sorafenib is currently the first-line treatment for advanced hepatocellular carcinoma (HCC). However, sorafenib resistance remains a significant challenge. Aberrant AKT signaling activation is a crucial mechanism driving sorafenib resistance in HCC. Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays a vital role in antitumor immune responses. In this study, we demonstrate that aberrant PCSK9 upregulation promotes cell proliferation and sorafenib resistance in HCC by inducing AKT-S473 phosphorylation. After palmitoylation at cysteine 600, the binding affinity between PCSK9 and tensin homolog (PTEN) is dramatically increased, inducing lysosome-mediated PTEN degradation and subsequent AKT activation. We identify zinc finger DHHC-type palmitoyltransferase 16 (ZDHHC16) as a palmitoyltransferase that promotes PCSK9 palmitoylation at cysteine 600. We also develop a biologically active PCSK9-derived peptide that competitively inhibits PCSK9 palmitoylation, suppressing AKT phosphorylation and augmenting the antitumor effects of sorafenib in HCC.

Abstract 1760: Role of Batf-dependant Th17 immune response in PTEN-null mouse model

Abstract Basic leucine zipper transcription factor ATF-like (BATF) belongs to the activator protein 1 (AP-1) family of transcription factors and has been shown to be predominantly expressed in cells of hematopoietic origin, especially in T cells. Mice deficient for BATF were first described to lack T helper cell type 17 (Th17). Th17 cells are a distinct lineage of CD4+ T helper cells that provide protective immunity to infections but are also involved in chronic inflammation and autoimmunity. However, the role of Th17 response in prostate cancer remains controversial. In this study, we took a genetic approach to explore the role of BATF-dependent Th17 cells in prostate cancers by interbreeding BATF-deficient (Batf-/-) mice with mice that are conditionally mutant for PTEN, an established preclinical model for prostate cancer. Batf+/+;Pten-/- and Batf+/-;Pten-/- mice presented similar prostate phenotypes thus were put into one group (named Batf+), which were compared to the Batf-/-;Pten-/- group (named Batf-). We found that Batf- prostates were clearly smaller than Batf+ prostates at 30 weeks. The genitourinary bloc weight was significantly heavier in Batf+ mice than in Batf- mice at 12 and 30 weeks. Batf+ mice developed significantly higher percent of invasive adenocarcinomas in different prostate lobes at 9, 12, and 30 weeks, respectively compared to Batf- mice. Tumors in Batf- mice exhibited lower rates of cellular proliferation and higher apoptosis, as well as reduced inflammatory cell infiltration and angiogenesis in the prostatic stroma. Moreover, Batf- mice exhibited significantly reduced mRNA and protein levels of Th17 cytokines, AP-1 family members and IL-23R, and reduced NF-kB pathway activity in both spleen and prostate tissues. CD4+ T cells from Batf- mice cultured under Th17 conditions for 4 days, expressed reduced AP-1 family-regulated genes compared to Batf+ mice. Prostate cancer cells (LNCaP) with overexpression of BATF in vitro exhibited increased IL-23R expression. Prostate tissues from Batf- mice cultured under IL-6 or Th17 conditions for 4 days had reduced IL-23R expression compared to that from Batf+ mice. Taken together, our results suggest that Batf promotes the initiation and progression of prostate adenocarcinoma via Th17-mediated inflammatory immune responses and that the Batf-IL-23-IL-17 axis is a critical pathway that is needed for prostate adenocarcinoma development and progression. This work was supported by the NIH-National Institute of General Medical Sciences COBRE on Aging and Regenerative Medicine (P20GM103629, PD: S. Michal Jazwinski; PI: Q.Z.) and the Carol Lavin Bernick Faculty Grant from Tulane University (PI: Q.Z.). Citation Format: Qiuyang Zhang, Sen Liu, Bing Zhang. Role of Batf-dependant Th17 immune response in PTEN-null mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1760.

Transformation of SOX9+ cells by Pten deletion synergizes with steatotic liver injury to drive development of hepatocellular and cholangiocarcinoma

SOX9 (Sex-determining region Y Box 9) is a well-characterized transcription factor that is a marker for progenitor cells in various tissues. In the liver, cells delineated by SOX9 are responsible for regenerating liver parenchyma when cell proliferation is impaired following chronic injury. However, whether these SOX9+ cells play a role in liver carcinogenesis has not been fully understood, although high SOX9 expression has been linked to poor survival outcome in liver cancer patients. To address this question, we developed a liver cancer mouse model (PtenloxP/loxP; Sox9-CreERT+; R26RYFP) where tumor suppressor Pten (phosphatase and tensin homolog deleted on chromosome ten) is deleted in SOX9+ cells following tamoxifen injection. In this paper, we employ lineage-tracing to demonstrate the tumorigenicity potential of the Pten-, SOX9+ cells. We show that these cells are capable of giving rise to mixed-lineage tumors that manifest features of both hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (CCA). Our results suggest that PTEN loss induces the transformation of SOX9+ cells. We further show that to activate these transformed SOX9+ cells, the presence of liver injury is crucial. Liver injury, induced by hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) or high-fat diet (HFD), substantially increases tumor incidence and accelerates liver carcinogenesis from SOX9+ cells in Pten null mice but not in control mice. We further examine the mechanisms underlying tumor formation in this model to show that concurrent with the induction of niche signal (i.e., Wnt signaling), liver injury significantly stimulates the expansion of tumor-initiating cells (TICs). Together, these data show that (1) SOX9+ cells have the potential to become TICs following the primary transformation (i.e. Pten deletion) and that (2) liver injury is necessary for promoting the activation and proliferation of transformed SOX9+ cells, resulting in the genesis of mixed-lineage liver tumors.

Dual regulation of fatty acid synthase (FASN) expression by O-GlcNAc transferase (OGT) and mTOR pathway in proliferating liver cancer cells.

Fatty acid synthase (FASN) participates in many fundamental biological processes, including energy storage and signal transduction, and is overexpressed in many cancer cells. We previously showed in a context of lipogenesis that FASN is protected from degradation by its interaction with O-GlcNAc transferase (OGT) in a nutrient-dependent manner. We and others also reported that OGT and O-GlcNAcylation up-regulate the PI3K/AKT/mTOR pathway that senses mitogenic signals and nutrient availability to drive cell cycle. Using biochemical and microscopy approaches, we show here that FASN co-localizes with OGT in the cytoplasm and, to a lesser extent, in the membrane fraction. This interaction occurs in a cell cycle-dependent manner, following the pattern of FASN expression. Moreover, we show that FASN expression depends on OGT upon serum stimulation. The level of FASN also correlates with the activation of the PI3K/AKT/mTOR pathway in hepatic cell lines, and in livers of obese mice and in a chronically activated insulin and mTOR signaling mouse model (PTEN-null mice). These results indicate that FASN is under a dual control of O-GlcNAcylation and mTOR pathways. In turn, blocking FASN with the small-molecule inhibitor C75 reduces both OGT and O-GlcNAcylation levels, and mTOR activation, highlighting a novel reciprocal regulation between these actors. In addition to the role of O-GlcNAcylation in tumorigenesis, our findings shed new light on how aberrant activity of FASN and mTOR signaling may promote the emergence of hepatic tumors.

Inhibition of Estrogen-Related Receptor α Blocks Liver Steatosis and Steatohepatitis and Attenuates Triglyceride Biosynthesis

The estrogen-related receptor (ERR) family of orphan nuclear receptors are transcriptional activators for genes involved in mitochondrial bioenergetics and metabolism. The goal of this study was to explore the role of ERRα in lipid metabolism and the potential effect of inhibiting ERRα on the development of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). In the current study, three experimental mouse models: high-fat diet, high-carbohydrate diet, and a genetic model of hepatic insulin resistance where the liver hyperinsulinemia signal is mimicked via hepatic deletion of Pten (phosphatase and tensin homolog deleted on chromosome 10), the negative regulator of the insulin/phosphatidylinositol 3-kinase signaling pathway, were used. A recently developed small-molecule inhibitor for ERRα was used to demonstrate that inhibiting ERRα blocked NAFLD development induced by either high-carbohydrate diet or high-fat diet feeding. ERRα inhibition also diminished lipid accumulation and attenuated NASH development in the Pten null mice. Glycerolipid synthesis was discovered as an additional mechanism for ERRα-regulated NAFLD/NASH development and glycerophosphate acyltransferase 4 was identified as a novel transcriptional target of ERRα. In summary, these results establish ERRα as a major transcriptional regulator of lipid biosynthesis in addition to its characterized primary function as a regulator for mitochondrial function. This study recognizes ERRα as a potential target for NAFLD/NASH treatment and elucidates novel signaling pathways regulated by ERRα.

Age-Related Increased Onset and Progression of Prostate Cancer Is Revealed in Novel Pten-Null Mouse Models

Prostate cancer (PCa) is associated with advanced age. To better understand how age impacts PCa, it is critical to use PCa animal models generated at different ages (aged vs. non-aged). The PB-Cre4 driven phosphatase and tensin homolog (Pten) conditional knockout mouse model, which closely imitates human PCa initiation and progression. However, the Pten deletion is triggered in a 2-week-old prostate, when comparing the extent of PCa between aged and non-aged mice, it is difficult to distinguish the extent to which the onset and progression of PCa are due to the acceleration of the normal aging process or due to the manifestation of PCa pathologies over time. We present here a protocol to inject Cre-expressing adenovirus with luciferin tag intraductally into the prostate anterior lobes of Pten floxed mice, thus, the Pten-loss will be triggered at different ages post-Cre expression. The in vivo imaging of luciferin signals following viral infection was conducted to confirm the Cre expression and activity. Immunohistochemical staining was performed to confirm the Cre expression, Pten loss, and p-Akt and p-S6 activation. Prostate weight and histopathology were compared between aged and non-aged mice. The results showed that the virus infection was limited in the prostate glands and aged mice had significantly increased PCa onset and progression compared to young mice. Although technical skill is required to carry out this procedure and the success rate of viral infection is about 80%, this model of PCa is of great use to all investigators in the aging and cancer research field.

KDM5B Is Essential for the Hyperactivation of PI3K/AKT Signaling in Prostate Tumorigenesis

KDM5B (lysine[K]-specific demethylase 5B) is frequently upregulated in various human cancers including prostate cancer. KDM5B controls H3K4me3/2 levels and regulates gene transcription and cell differentiation, yet the contributions of KDM5B to prostate cancer tumorigenesis remain unknown. In this study, we investigated the functional role of KDM5B in epigenetic dysregulation and prostate cancer progression in cultured cells and in mouse models of prostate epithelium-specific mutant Pten/Kdm5b. Kdm5b deficiency resulted in a significant delay in the onset of prostate cancer in Pten-null mice, whereas Kdm5b loss alone caused no morphologic abnormalities in mouse prostates. At 6 months of age, the prostate weight of Pten/Kdm5b mice was reduced by up to 70% compared with that of Pten mice. Pathologic analysis revealed Pten/Kdm5b mice displayed mild morphologic changes with hyperplasia in prostates, whereas age-matched Pten littermates developed high-grade prostatic intraepithelial neoplasia and prostate cancer. Mechanistically, KDM5B governed PI3K/AKT signaling in prostate cancer in vitro and in vivo. KDM5B directly bound the PIK3CA promoter, and KDM5B knockout resulted in a significant reduction of P110α and PIP3 levels and subsequent decrease in proliferation of human prostate cancer cells. Conversely, KDM5B overexpression resulted in increased PI3K/AKT signaling. Loss of Kdm5b abrogated the hyperactivation of AKT signaling by decreasing P110α/P85 levels in Pten/Kdm5b mice. Taken together, our findings reveal that KDM5B acts as a key regulator of PI3K/AKT signaling; they also support the concept that targeting KDM5B is a novel and effective therapeutic strategy against prostate cancer. SIGNIFICANCE: This study demonstrates that levels of histone modification enzyme KDM5B determine hyperactivation of PI3K/AKT signaling in prostate cancer and that targeting KDM5B could be a novel strategy against prostate cancer.

Abstract PR13: PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas

Abstract Melanoma is one of the most highly mutated cancer types, harboring numerous alterations with unknown significance. To identify functional drivers of melanoma, we searched for cross-species conserved mutations utilizing a mouse melanoma model driven by loss of PTEN and CDKN2A, and identified mutations in Kras, Erbb3, and Ptpn11. PTPN11 encodes the SHP2 protein tyrosine phosphatase (PTP) that activates the RAS/RAF/MAPK pathway. Although PTPN11 is an oncogene in leukemia, lung, and breast cancers, its roles in melanoma are not clear. In this study, we found that PTPN11 is frequently activated in human melanoma specimens and cell lines and is required for full RAS/RAF/MAPK signaling activation in BRAF wild-type (either NRAS mutant or wild-type) melanoma cells. PTPN11 played oncogenic roles in melanoma by driving anchorage-independent colony formation and tumor growth. In Pten and Cdkn2a null mice, tet-inducible and melanocyte-specific PTPN11E76K expression significantly enhanced melanoma tumorigenesis. Melanoma cells derived from this mouse model showed doxycycline-dependent tumor growth in nude mice. Silencing PTPN11E76K expression by doxycycline withdrawal caused regression of established tumors by induction of apoptosis and senescence and suppression of proliferation. Moreover, the PTPN11 inhibitor (SHP099) also caused regression of NRASQ61K-mutant melanoma. Using a quantitative tyrosine phospho-proteomics approach, we identified GSK3α/β as one of the key substrates that were differentially tyrosine-phosphorylated in these experiments modulating PTPN11. This study demonstrates that PTPN11 plays oncogenic roles in melanoma and regulates RAS and GSK3α/β signaling pathways. This study also identifies PTPN11 as a novel and actionable therapeutic target for BRAF wild-type melanoma. This abstract is also being presented as Poster A14. Citation Format: Kristen S. Hill, Evan R. Roberts, Xue Wang, John M. Koomen, Jane L. Messina, Jamie K. Teer, Youngchul Kim, Jie Wu, Charles E. Chalfant, Minjung Kim. PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas [abstract]. In: Proceedings of the AACR Special Conference on Melanoma: From Biology to Target; 2019 Jan 15-18; Houston, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(19 Suppl):Abstract nr PR13.

KLF5-mediated COX2 upregulation contributes to tumorigenesis driven by PTEN deficiency

Tumor suppressor gene PTEN is frequently mutated in a wide variety of cancers. However, the downstream targets or signal transduction pathways of PTEN remain not fully understood. By analyzing Pten-null mouse embryonic fibroblasts (MEFs) cell lines and their isogenic counterparts, we showed that loss of PTEN led to increased cyclooxygenase2 (COX2) expression in an AKT-independent manner. Moreover, we demonstrated that PTEN deficiency promotes the transcription of COX2 via upregulation of the transcription factor Krüppel-like factor 5 (KLF5). Knocked down the expression of COX2 suppressed proliferation, migration and tumoral growth of Pten-null cells. Further experiments revealed that COX2 enhanced Pten-null MEFs growth and migration through upregulation of NADPH oxidase 4 (NOX4). In addition, MK-2206, a specific inhibitor of AKT, in combination with celecoxib, a COX2 inhibitor, strongly inhibited Pten-deficient cell growth. We concluded that KLF5/COX2/NOX4 signaling pathway is critical for cell growth and migration caused by the loss of PTEN, and the combination of MK-2206 and celecoxib may be an effective new approach to treating PTEN deficiency related tumors.

Abstract 1144: Novel prostate cancer mouse models for testing targeted chemopreventive potential of pterostilbene

Abstract Metastasis-associated protein 1 (MTA1) plays role in prostate cancer progression and metastasis. We have previously reported on the MTA1-targeted chemopreventive and therapeutic efficacy of pterostilbene (Pter) in the prostate-specific Pten heterozygous (Pten+/f; Pb-Cre+) and Pten null (Ptenf/f; Pb-Cre+) mice. To investigate the exact role of MTA1 in prostate cancer tumorigenesis and its early stages, we developed appropriate mouse models, namely prostate-specific MTA1-knocked in (MTA1-tg) and MTA1-tg on the background of prostate-specific Pten heterozygosity (MTA+/+, Pten+/f; Pb-Cre+). In the current project, we asked three major questions: 1) whether prostate MTA1 overexpression in the context of Pten loss promotes an earlier onset, greater total incidence and accelerated PIN or tumor growth rate; 2) what MTA1-associated molecules are involved in prostate cancer progression; and 3) whether Pter supplemented diet can provide beneficial effects. Identified from our ChIP-Seq data MTA1-associated molecules included CyclinD1, Notch2, and two neuroendocrine markers, namely CHGA and SYP. Using two prostate cancer cell lines, DU145 and PC3M and their corresponding MTA1 knockdown (shMTA1) clones, we validated the direct link between MTA1 and these markers on mRNA and protein levels. Further, we generated 28 prostate-specific MTA1+/+; Pten+/f; Pb-Cre+ mice and randomized them into two major groups: 1) mice on control diet (Ctrl-Diet) and 2) mice on Pter-Diet. After 5 months of feeding with corresponding diets (AIN-76A phytoestrogen free diets supplemented or not with Pter at 100 mg/kg/diet), mice were sacrificed and prostate tissues were isolated for histological, immunochemical and molecular analysis. Results demonstrated the contribution of MTA1 in more aggressive histological phenotype (Ki67, PCNA, p27, SMA, CK8), increased levels of oncogenic MTA1-guided molecules (CyclinD1, Notch2, CHGA, SYP, AR) and the potential for Pter in prostate cancer chemoprevention. Citation Format: Rutu Hemani, Ninad Inamdar, Avinash Kumar, Virginia Donovan, Anait S. Levenson. Novel prostate cancer mouse models for testing targeted chemopreventive potential of pterostilbene [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 1144.

Abstract 97: Analysis of Pten-null mouse astrocytes revealed overlapping transcribed genes with human glioblastoma transcriptome

Abstract Glioblastoma is an aggressive form of brain cancer with universally poor prognosis. Even with optimal therapy, the cancer recurs frequently. Phosphatase and tensin homolog (PTEN) is a tumor suppressor gene whose mutations are often found in multiple human cancers. PTEN encodes a lipid phosphatase and serves as a negative regulator of the phosphoinositide 3-kinase (PI3K) pathway. Cumulative evidence suggests that PTEN mutations play significant roles in tumorigenesis of glioblastoma as 60% of glioblastoma patients acquired mutations in this gene. Based on our preliminary data, transcriptomic profiling of primary astrocytes derived from Pten knockout mice revealed an overlapping enrichment of mitotic regulators and cell cycle related pathways with human GBM. 4 genes (RCC1, RCC2, NEK2, and CHK2) were validated to be significantly upregulated in PTEN KO astrocytes by qRT-PCR. Regulator of chromatin condensation 2 (RCC2) has been reported to be guanine-nucleotide exchange factor (GEF) for Rac1 and RalA GTPase and act as a regulator of cell cycle progression. Accumulating evidence revealed a pro-tumorigenic role of RCC2 in multiple cancers such as tumor growth and tumor metastasis. Via siRNA inhibition of RCC2, we demonstrated that knocking down of RCC2 in glioblastoma cell lines suppresses cell growth and RCC2 is essential for both G1-S and G2-M progression. Additionally, RCC2 knocking down and a PI3K inhibitor LY294002 inhibit glioblastoma cell viability in a synergistic manner. In summary, PTEN deficiency leads to the upregulation of RCC2, which may promote tumorigenesis of glioblastoma by dysregulating cell cycle progression.To further explore the RCC2 roles, we will find the potential downstream target of RCC2 in dysregulating cell cycle and its potential therapeutic effect in vivo. Funding: General Research Fund Grant #14113519 from The Research Grants Council of Hong Kong Citation Format: Tian Liu, Penelope Mei-Yu Or, Chi-Wai Wong, Stanley Kwok-Kuen Cheung, Yubing Wang, Yiwei Wang, Andrew M. Chan. Analysis of Pten-null mouse astrocytes revealed overlapping transcribed genes with human glioblastoma transcriptome [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 97.

PTEN deletion drives aberrations of DNA methylome and transcriptome in different stages of prostate cancer.

Phosphatase and tensin homolog located on chromosome 10 (PTEN) is a tumor suppressor gene and one of the most frequently mutated/deleted genes in human prostate cancer (PCa). However, how PTEN deletion would impact the epigenome and transcriptome alterations remain unknown. This hypothesis was tested in a prostate-specific PTEN-/- (KO) mouse prostatic adenocarcinoma model through DNA methyl-Seq and RNA-Seq analyses. Examination of cancer genomic datasets revealed that PTEN is expressed at lower levels in PTEN-deleted tumor samples than in normal solid tissue samples. Methylome and transcriptome profiling identified several inflammatory responses and immune response signaling pathways, including NF-kB signaling, IL-6 signaling, LPS/IL-1-mediated inhibition of RXR Function, PI3K in B lymphocytes, iCOS-iCOSL in T helper cells, and the role of NFAT in regulating the immune response, were affected by PTEN deletion. Importantly, a small subset of genes that showed DNA hypermethylation or hypomethylation was correlated with decreased or increased gene expression including CXCL1. quantitative polymerase chain reaction analyses of representative genes validated the RNA-Seq results. Histopathological examinations showed that the severity of prostatic intraepithelial neoplasia and inflammation development gradually increased as PTEN null mice aged. Collectively, these findings suggest that loss of PTEN drives global changes in DNA CpG methylation and transcriptomic gene expression and highly associated with several inflammatory and immune molecular pathways during PCa development. These biomarkers could be valuable molecular targets for cancer drug discovery and development against PCa.

Abstract LB-085: PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas

Abstract Melanoma is one of the most highly mutated cancer types. To identify functional drivers of melanoma, we searched for cross-species conserved mutations utilizing a mouse melanoma model driven by loss of PTEN and CDKN2A, and identified mutations in Kras, Erbb3, and Ptpn11. PTPN11 encodes the SHP2 protein tyrosine phosphatase (PTP) that activates the RAS/RAF/MAPK pathway. Although PTPN11 is an oncogene in leukemia, lung, and breast cancers, its roles in melanoma are not clear. In this study, we found that PTPN11 is frequently activated in human melanoma specimens and cell lines and is required for full RAS/RAF/MAPK signaling activation in BRAF wild-type (either NRAS mutant or wild-type) melanoma cells. PTPN11 played oncogenic roles in melanoma by driving anchorage-independent colony formation and tumor growth. In Pten and Cdkn2a null mice, tet-inducible and melanocyte-specific PTPN11 E76K expression significantly enhanced melanoma tumorigenesis. Melanoma cells derived from this mouse model showed doxycycline-dependent tumor growth in nude mice. Silencing PTPN11 E76K expression by doxycycline withdrawal caused regression of established tumors by induction of apoptosis and senescence, and suppression of proliferation. Moreover, the PTPN11 inhibitor (SHP099) also caused regression of NRAS Q61K-mutant melanoma. Using a quantitative tyrosine phosphoproteomics approach, we identified GSK3α/β as one of the key substrates that were differentially tyrosine-phosphorylated in these experiments modulating PTPN11. This study identifies PTPN11 as an oncogenic driver and a novel and actionable therapeutic target for BRAF wild-type melanoma. Citation Format: Kristen Hill, Jane Messina, Jie Wu, Charles E. Chalfant, Minjung Kim. PTPN11 plays oncogenic roles and is a therapeutic target for BRAF wild-type melanomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-085.

Abstract 3139: EphB4-EphrinB2 receptor-ligand are downstream effectors and novel targets of PTEN deficient prostate cancer

Abstract Background EphB4 is upregulated in prostate cancer in over half the cases, and correlates with stage and survival. EprhinB2, the ligand for EphB4 has not been well studied. Functional studies show EphB4 provides a survival signal through the PI3K/PTEN/Akt/pS6 pathway. A therapeutic agent, soluble EphB4-albumin fusion protein (sEphB4) which blocks bidirectional signaling is currently in clinical development. We thus wished to conduct detailed investigation into the role of EphB4 and EphrinB2 in genetic mouse model of prostate cancer, in tumor initiation and progression, by knockout of EphB4 and by pharmacological agent (sEphB4). Methods We studied the expression of Ephrinb2 in 180 samples of human prostate cancers and normal prostates using highly characterized, specific EphrinB2 mAb. We next used genetically engineered mouse model of prostate cancer condition deletion of PTEN in prostate epithelium, crossed with transgenic mouse line expressing luciferase. To test the role of EphB4-EphrinB2, we generated Floxed allele of Ephb4 to conditionally delete in prostate epithelium. PTENf/f, EphB4f/f and luciferase were crossed and imaged over time. Secondly, PTENf/f mice were treated with sEphB4 in prevention, established tumor and castration resistant prostate cancer (CRPC) cohorts. Prostate cell lines C4-2B, PC3 and 22RV1 were used to analyze the role of EphB4 in regulation of PI3K pathway and androgen receptor (AR). Results EphrinB2 is expressed in 50% of human prostate cancers, but not the normal tissues. PTEN null mouse prostate tumors had elevated EphB4 and EphrinB2, but not other family members. Conditional deletion of EphB4 in the context of PTEN deletion in prostate epithelium abolished tumor formation and caused inhibition of the PI3K pathway. Treatment with sEphB4 precluded tumor development and induced tumor regression in both early prostate cancer and CRPC mice. PI3K/AKT/pS6 activity nearly complete declined in the treatment group. Mechanistic studies using EphB4 knock down showed downregulation of PI3K alpha, beta, not gamma and delta. Most surprisingly, AR levels were markedly reduced in sEphB4 treated tumors. Further studies in vitro showed decline in AR with EphB4 knock down, which could be rescued with ectopic expression of PI3K beta, but not other PI3K isoforms. These changes were recapitulated in a patient with late stage CRPC treated in a single patient IND for sEphB4. Conclusions EphB4-EphrinB2, a receptor-ligand pair are expressed in prostate cancer and induced by loss of PTEN or activation of PI3K pathway. Genetic and pharmacological intervention validates the potential role as a downstream effectors through downregulation of PI3K signaling and AR. Drugs that can reduce AR levels and PI3Kβ inhibitors are potential candidates for prostate cancer therapy and sEphB4 holds therapeutic potential in prostate cancer. Citation Format: Grace X. Li, Binyun Ma, Valery G. Krasnoperov, Imran Siddiqi, Akash Sali, Gangning Liang, Inderbir S. Gill, Jacek K. Pinski, David I. Quinn, Sarmad Sadeghi, Parkash S. Gill. EphB4-EphrinB2 receptor-ligand are downstream effectors and novel targets of PTEN deficient prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3139.

Abstract 4621: Developing genetically modified homograft models of mouse prostate cancer for efficacy evaluation of combinatory immunotherapies

Abstract Despite the early approval of Sipuleucel-T for metastatic castration-resistant prostate cancer, which often perceived as a milestone achievement in cancer immunotherapy, subsequent progress in prostate cancer immunotherapy development has been limited by disappointing results with tumor vaccines and its resistance to immune checkpoint inhibitors, such as PD1 & PD-L1. It is now generally accepted that we need to tackle prostate cancer by combinatorial approaches of chemo-, targeted- and immuno-therapies. Highly relevant preclinical models are very much needed for proof of principle efficacy evaluation. Genetically engineered mouse models (GEMM) recapitulate key aspects of human prostate cancer in both histo- & molecular- pathology. Among those, PTEN loss of function (LOF) in prostate epithelium is one of the central events in human prostate cancer. PTEN haploinsufficiency in mice is sufficient to drive mouse prostatic intraepithelial neoplasia (PIN) formation, while loss of both alleles of PTEN in mouse prostate leads to hyperplasia at 4 weeks, PIN at 6 weeks, and fully invasive adenocarcinoma from 12 weeks of age. PTEN null tumors are also resistant to androgen depletion. In the meantime, although KRAS mutation are not often seen in human prostate cancer, activation of MAPK pathway often happens in advanced tumor. Mutant KRAS or BRAF can robustly promote mouse prostate cancer progression. Prostate specific Pten null and Kras G12D; Pten null mouse prostate cancer models have been well characterized by a number of labs. However, parental GEMM models are difficult to be used for pharmacological studies due to the spontaneous nature of tumor onset and progression. The compound mutant mice are also costly to breed. Here we report generation of transplantable mouse prostate cancer homograft models by passaging the primary tumor subcutaneously in the C57BL/6 mice. These mouse tumors featuring Pbsn-Cre;LSL-KrasG12D/+;Ptenflox/flox or Pbsn-Cre;Ptenflox/flox retain morphological similarity to moderate to poorly differentiated human prostate cancer. These homograft tumors show high levels of M2 macrophage infiltration. Growth of these mouse prostate tumors are resistant to androgen depletion. They are also resistant to the treatment of AR inhibitor enzalutamide, only marginally responsive to docetaxel, but sensitive to treatments with mTOR inhibitor everolimus. When treated with immune checkpoint antibodies, i.e. PD1 and CTLA4, these tumors showed increased T-cell infiltration, but very modest growth inhibition. We are now testing a variety of combinatory therapies with chemotherapies, immune modulators and immune checkpoint antibodies. The results will be presented at the meeting. Citation Format: Jessie Jingjing Wang, Yanrui Song, Annie Xiaoyu An, Likun Zhang, Henry Qixiang Li, Davy Xuesong Ouyang. Developing genetically modified homograft models of mouse prostate cancer for efficacy evaluation of combinatory immunotherapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4621.

Epigenetic Suppression of SERPINB1 Promotes Inflammation-Mediated Prostate Cancer Progression.

Granulocytic myeloid infiltration and resultant enhanced neutrophil elastase (NE) activity is associated with poor outcomes in numerous malignancies. We recently showed that NE expression and activity from infiltrating myeloid cells was high in human prostate cancer xenografts and mouse Pten-null prostate tumors. We further demonstrated that NE directly stimulated human prostate cancer cells to proliferate, migrate, and invade, and inhibition of NE in vivo attenuated xenograft growth. Interestingly, reduced expression of SERPINB1, an endogenous NE inhibitor, also correlates with diminished survival in some cancers. Therefore, we sought to characterize the role of SERPINB1 in prostate cancer. We find that SERPINB1 expression is reduced in human metastatic and locally advanced disease and predicts poor outcome. SERPINB1 is also reduced in Pten-null mouse prostate tumors compared with wild-type prostates, and treatment with sivelestat (SERPINB1 pharmacomimetic) attenuates tumor growth. Knockdown of highly expressed SERPINB1 in nonmalignant prostatic epithelial cells (RWPE-1) increases proliferation, decreases apoptosis, and stimulates expression of epithelial-to-mesenchymal transition markers. In contrast, stable SERPINB1 expression in normally low-expressing prostate cancer cells (C4-2) reduces xenograft growth in vivo. Finally, EZH2-mediated histone (H3K27me3) methylation and DNA methyltransferase-mediated DNA methylation suppress SERPINB1 expression in prostate cancer cells. Analysis of The Cancer Genome Atlas and pyrosequencing demonstrate hypermethylation of the SERPINB1 promoter in prostate cancer compared with normal tissue, and the extent of promoter methylation negatively correlates with SERPINB1 mRNA expression. IMPLICATIONS: Our findings suggest that the balance between SERPINB1 and NE is physiologically important within the prostate and may serve as a biomarker and therapeutic target in prostate cancer.