RF07 | PSUN384 Hepatocyte Deletion of IGF2 Prevents DNA Damage and Tumor Formation in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide with a 18% 5-year survival rate. Mice lacking the splicing factor SRSF3 in hepatocytes (SKO mice) overexpress IGF2 and are predisposed to developing HCC with age. Loss of Igf2 in the SKO background prevented hepatic fibrosis and inflammation, and completely prevented tumor formation. This was associated with decreased proliferation, apoptosis and DNA damage, and restored DNA repair enzyme expression. Mechanistically, IGF2 treatment of HepG2 cells in vitro caused DNA damage and decreased DNA repair enzyme expression, and tumors from the SKO mice show mutational signatures consistent with double strand break and defective mismatch repair. Looking at human data, HCC patients with high IGF2 mRNA expression had worse survival compared to patients with normal IGF2 expression. The patients also showed a switch in IGF2 promoter usage that correlated with increased expression. HCC patients having high SRSF3 mRNA expression also showed poor survival as did patients with alterations in known SRSF3-dependent splicing events. The level of SRSF3 protein was decreased 6-fold in human HCC tissues compared with normal liver tissues. The results indicate that IGF2 overexpression in conjunction with reduced SRSF3 splicing activity could be a major cause of DNA damage and driver of liver cancer.

Presentation: Saturday, June 11, 2022 1:18 p.m. - 1:23 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

A MYC-ZNF148-ID1/3 regulatory axis modulating cancer stem cell traits in aggressive breast cancer

The MYC proto-oncogene (MYC) is one of the most frequently overexpressed genes in breast cancer that drives cancer stem cell-like traits, resulting in aggressive disease progression and poor prognosis. In this study, we identified zinc finger transcription factor 148 (ZNF148, also called Zfp148 and ZBP-89) as a direct target of MYC. ZNF148 suppressed cell proliferation and migration and was transcriptionally repressed by MYC in breast cancer. Depletion of ZNF148 by short hairpin RNA (shRNA) and CRISPR/Cas9 increased triple-negative breast cancer (TNBC) cell proliferation and migration. Global transcriptome and chromatin occupancy analyses of ZNF148 revealed a central role in inhibiting cancer cell de-differentiation and migration. Mechanistically, we identified the Inhibitor of DNA binding 1 and 3 (ID1, ID3), drivers of cancer stemness and plasticity, as previously uncharacterized targets of transcriptional repression by ZNF148. Silencing of ZNF148 increased the stemness and tumorigenicity in TNBC cells. These findings uncover a previously unknown tumor suppressor role for ZNF148, and a transcriptional regulatory circuitry encompassing MYC, ZNF148, and ID1/3 in driving cancer stem cell traits in aggressive breast cancer.

MON-314 Insulin-like Growth Factor 2 Drives Hepatocellular Carcinoma In Hepatocyte Srsf3 Ko Mice

Background: Hepatocellular Carcinoma (HCC) is the most common liver cancer and is the second highest cause of cancer-related death worldwide. Previously we demonstrated that hepatocyte-specific deletion of serine/arginine rich splicing factor 3 (SRSF3-HKO) caused spontaneous hepatocellular carcinoma in aging with very high tumor expression of insulin-like growth factor 2 (IGF2). Elevated IGF2 has been reported in human HCC and we have also shown loss of SRSF3 occurs in human HCC, so the SRSF3HKO mouse represents a useful model for human HCC. Whether the elevated IGF2 is involved in HCC development or growth remains to be determined however. Here, we aimed to test whether IGF2 drives tumor development in the SRSF3HKO mouse by creating a double hepatocyte deletion of SRSF3 and IGF2. Methods: We generated hepatocyte specific SRSF3-IGF2-DKO mice to assess the role of IGF2 in tumor growth in the SRSF3-HKO mice over 12 months. Proliferation, apoptosis, steatosis, fibrosis and tumor phenotype were assessed by immunohistochemistry and immunoblot. We measured IGF1, Insulin, IGF2 and growth hormone levels in plasma. In addition we measured gene expression of lipid storage, oxidation, transportation, and inflammation. Results: None of the SRSF3-IGF2-DKO mice developed tumors over 12 months while all SRSF3-HKO mice developed HCC. Histology of livers showed (1) nuclear morphology in the SRSF3-IGF2-DKO mice resembling that of the SRSF3-HKO mice, (2) reduced fibrosis as indicated by decreased collagen staining in SRSF3-IGF2-DKO mice livers at 6 and 12 month of age, (3) SRSF3-IGF2-DKO mice livers have greater steatosis than SRSF3-HKO, and (4) SRSF3-IGF2-DKO mice livers have lower inflammation than SRSF3-HKO. Gene expression by qRT-PCR suggested (1) higher expression of lipid synthesis and accumulation in SRSF3-IGF2-DKO livers, (2) lower levels of inflammation in SRSF3-IGF2-DKO livers. Immunohistochemistry showed more Ki67-positive staining for proliferation and also for apoptosis (TUNEL and caspase3) in SRSF3-HKO mice compared to WT and SRSF3-IGF2-DKO mice. ELISA data showed the elevated levels of IGF1 and insulin in plasma of SRSF3-IGF2-DKO.We also confirmed over expression of IGF2 in human early liver diseases as has been shown in HCC. We furthermore showed that H19 expression was high in both SRSF3 HKO and SRSF3-IGF2-DKO mice livers suggesting altered epigenetic imprinting of the IGF2-H19 locus. Conclusion: IGF2 over expression is essential for HCC formation in SRSF3HKO mice. References: (1)Sen et al., Nature Communication. 2013,4:1336 (2)Sen et al., Hepatology. 2015, Jan;61(1):171-83. Sources of Research support: VA Merit Review grants I01BX000130, and NIH Grants CA196853, CA155435, CA023100, HD012303 awarded to NJW. Key Words: IGF2, SRSF3, HCC

SAT-336 Time Restricted Feeding Delays Breast Cancer Initiation and Growth in a Mouse Model of Postmenopausal Obesity

Background: The prevalence of obesity and the metabolic syndrome (MetS) has increased dramatically in developed countries over the last three decades (Flegal et al., 2012). Numerous studies indicate that adiposity and the MetS are independent risk factors for multiple diseases including cancer, particularly postmenopausal breast cancer (Kim et al., 2018). Therefore improving the metabolic health of obese postmenopausal women may mitigate their risk for breast cancer. Accumulating evidence suggests that time-restricted feeding (TRF), a form of intermittent fasting in which food intake is limited to a defined period during the normal active phase, can have a positive influence on metabolic health. Importantly, interventional studies in obese mice and small clinical studies in humans have demonstrated that TRF can improve metabolic health even though obesity is maintained (Sutton et al., 2018). Time restriction rather than calorie restriction is thus a promising method to control the negative sequelae of obesity, due to the hunger and irritability that reduces compliance with long-term calorie restriction. The objective of this study was to investigate whether TRF attenuates breast cancer in a mouse model of postmenopausal obesity and whether this effect is mediated by reducing the hyperinsulinemia associated with obesity. Methods: Ovariectomized mice were used as postmenopausal mice model. The ovariectomized mice were initially made obese by feeding 60% high fat diet (HFD) for 10 weeks and then grouped into a continued ad libitum group (24 h access to food) or a TRF group (8 h access to food during active phase). For an orthotopic tumor model, mice were injected with E0771 breast cancer cells into four mammary fat pads per mouse three weeks following the start of TRF. As a tumor initiation model, transgenic PyMT mice were used to assess tumor onset and growth following the same TRF or AL access to the HFD. The insulin dependency of tumor growth was studied by increasing insulinemia using an implanted insulin pump, or by reducing insulin secretion using diazoxide. Insulin effects on tumor cell proliferation and migration was further validated in vitro. Results and Conclusion: TRF had a dramatic effect, reducing tumor growth in obese mice fed a high fat diet (HFD) to levels seen in lean mice. Tumor growth and initiation was also delayed in the transgenic PyMT model of mammary tumorigenesis. Our results further suggest that the antitumor effect of TRF is at least partially mediated by reducing hyperinsulinemia, suggesting that this intervention may be effective in breast cancer prevention and therapy. References: • Flegal, K. M. et al., (2012), JAMA 307, 491-497. • Kim, N. H. et al. (2018). Dig Dis Sci 63, 3126-3133. • Sutton, E. F. et al. (2018). Cell Metab 27, 1212-1221 e1213.

Abstract 377: Time-restricted feeding: A dietary intervention to treat breast cancer in postmenopausal obese mice

Background: Abundant evidence indicates that obesity increases risk for breast cancer and the incidence further increases by 40% in obese postmenopausal women. Therefore it is envisioned by diverse research groups that the risk of breast cancer in obese postmenopausal women is an ever-increasing menace that needs to be curbed soon with effective practical strategies that could have a far-reaching impact. In this setting, time-restricted feeding (TRF), the practice of consuming ad libitum energy during the normal active phase, has been demonstrated to reinforce normal metabolic regulation, thereby attenuating obesity-driven

metabolic deregulation. Although studies have assessed the effect of TRF on metabolism, no investigations have been carried out in human or mouse exploring TRF in cancer remission. Therefore, the present work is to understand the efficacy of TRF for improved breast cancer remission in postmenopausal obese female mice. Further, the work explores the mechanistic link of TRF for reduced tumor growth.

Methods: Ovariectomized and 4-vinylcyclohexene diepoxide (VCD) treated mice were used as a postmenopausal model. Both ovariectomized and VCD mice were made obese by feeding them with 60% high-fat diet (HFD) and then grouped into ad libitum group (24 h access to food) and TRF group (8 hr access to food at night) to assess metabolic and tumor growth effect of TRF. To develop breast tumor, mice were injected with py230 breast cancer cell line into the mammary fat pad. The metabolic effect of TRF was assessed by glucose tolerance test, insulin tolerance test, body weight measurement, food intake, lipid accumulation in liver by HE staining and measurement of different tissue weight. Measuring the tumor volume over time and tumor weight assessed TRF effect on tumor growth. Performing a tumor growth study in mice fed with HFD and HFD containing diazoxide assessed insulin dependency of tumor growth in ad libitum group. Insulin-dependent tumor growth was validated by tumor growth study in normal chow-fed mice implanted with insulin pump or without pump (control).

Results: The preliminary studies in ovariectomized and VCD-treated postmenopausal mice suggest that restricting access to Western-style HFD in active night phase improves insulin resistance, glucose tolerance, and hepatic steatosis. Further, TRF exhibited reduced tumor growth compared to ad libitum group. More importantly, the results from tumor growth study in mice fed with HFD with/without diazoxide or normal chow mice with/without insulin pump, suggest that the tumor growth is insulin dependent and TRF may be acting through attenuating insulin signaling.

Conclusion: Experimental and animal model data corroborate that TRF improves metabolic deregulation and reduces breast tumor growth in HFD-fed obese mice. The results suggest putative application of such therapeutic intervention for breast cancer therapy.

Citation Format: Manasi Das, Emilie Gross, Deepak Kumar, Consuelo Sauceda, Hyun-Tae Park, Dorothy D. Sears, Lesley Ellies, Nicholas Webster. Time-restricted feeding: A dietary intervention to treat breast cancer in postmenopausal obese mice [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 377.

Expression of cationic amino acid transporter 2 is required for myeloid derived suppressor cell-mediated control of T cell immunity (IRC4P.460)

Myeloid derived suppressor cells (MDSC) are a heterogeneous population of immature cells that expand during benign and cancer-associated inflammation. MDSC regulate innate and adaptive immunity, notably by inhibiting T cell functions. Increased metabolism of L-Arginine (L-Arg), through arginase 1 (ARG1) and nitric oxide synthase 2 (NOS2), is well documented as a major MDSC suppressive mechanism. However, the mechanism by which extracellular L-Arg is transported into MDSC is not defined. Using murine models of prostate specific inflammation and cancer, we show that MDSC recruited to localized inflammation and tumor sites upregulate cationic amino acid transporter 2 (Cat2) coordinately with Arg1 and Nos2. CAT2 contributes to the transport of L-Arg in MDSC and acts as an important regulator of MDSC suppressive function. MDSC that lack CAT2 have significantly reduced suppressive ability ex vivo and display impaired capacity for regulating T cell responses in vivo as evidenced by increased T cell expansion and decreased tumor growth in Cat2-/- mice. The abrogation of suppressive function is due to lower L-Arg uptake, which leads to the impaired ability of NOS2 to catalyze L-Arg metabolic processes. These findings demonstrate that CAT2 is an important regulator of MDSC suppressive function. In the absence of CAT2 MDSC display diminished capacity for controlling T cell immunity in prostate inflammation and cancer models, where the loss of CAT2 results in enhanced antitumor activity.

Endothelial cell HIF-1α and HIF-2α differentially regulate metastatic success

The hypoxia inducible transcription factors (HIFs) control many mediators of vascular response, including both angiogenic factors and small molecules such as nitric oxide (NO). In studying how endothelial HIF response itself affects metastasis, we found that loss of HIF-1α in endothelial cells reduces NO synthesis, retards tumor cell migration through endothelial layers, and restricts tumor cell metastasis, and that loss of HIF-2α has in each case the opposite effect. This results from differential regulation of NO homeostasis that in turn regulates vascular endothelial growth factor expression in an NO-dependent feedback loop. These opposing roles for the two HIF factors indicate that both they and endothelial cells regulate metastasis as malignancy progresses.