Abstract B51: Regulation of HIF1α under hypoxia by APE1/Ref-1 impacts CA9 expression: Dual-targeting in patient-derived 3D pancreatic cancer models

Half of all patients diagnosed with pancreatic ductal adenocarcinoma (PDAC) die within a year despite extensive surgery and/or a highly aggressive chemotherapy regimen. Several mechanisms are proposed to play a role in PDAC therapeutic resistance, including reactive stroma and hypoxia. Cancer-associated fibroblasts (CAFs) contribute to tumor signaling, fibrosis, inflammation, and hypoxia. Hypoxia signaling creates a more aggressive phenotype with increased potential for metastasis and impairs therapeutic efficacy. Carbonic anhydrase IX (CA9) functions as part of the cellular response to hypoxia to regulate intracellular pH to promote cell survival. Apurinic/Apyrimidinic Endonuclease-1-Reduction/oxidation Effector Factor 1 (APE1/Ref-1) is a multi-functional protein that possesses two major activities: an endonuclease function in DNA base excision repair and a redox signaling function that reduces oxidized transcription factors, enabling them to bind to their DNA target sequences. APE1/Ref-1 regulates several transcription factors involved in survival mechanisms, tumor growth, and hypoxia signaling. We explored the mechanisms underlying PDAC cell responses to hypoxia and modulation of APE1/Ref-1 redox signaling control of hypoxia inducible factor 1 alpha (HIF1α), a critical factor in hypoxia-induced CA9 transcription. We hypothesized that obstructing the HIF-CA9 axis at two points via APE1/Ref-1 inhibition and CA9 inhibition will result in enhanced PDAC cell killing under hypoxic conditions.

Methods: We performed qRT-PCR and Western Blots to confirm changes in CA9 expression in PDAC cells and CAFs following APE1/Ref-1 inhibition and hypoxia exposure. We evaluated the effects of dual-targeting APE1/Ref-1 and CA9 on acidification of tumor cells with an intracellular pH indicator. Proliferation assays were used to assess cell killing following inhibition of APE1/Ref-1 and CA9 under hypoxia. Ex vivo 3-Dimensional co-culture models including both tumor and CAFs were used to examine whether we could enhance the efficacy of APE1/Ref-1 and/or CA9 inhibition with a dual-targeting approach to kill tumor spheroids. To delineate which function of APE1/Ref-1 is critical for observed effects, we used the APE1/Ref-1 redox signaling inhibitor, APX3330, an APE1/Ref-1 repair inhibitor, ARI-3, and an APX3330 analog that does not block APE1/Ref-1 redox activity, RN7-58. To inhibit CA9, we used the sulfonamide derivative, SLC-0111 (Clinical Trial NCT02215850).

Results: HIF1α-mediated induction of CA9 is significantly diminished in PDAC cells following APE1/Ref-1 redox inhibition or knock-down in both patient-derived and established cell lines, as well as pancreatic CAFs. Additionally, dual-targeting of APE1/Ref-1 redox signaling and CA9 results in acidification of PDAC cells and reduces PDAC tumor cell growth under hypoxic conditions as well as in a 3D tumor co-culture model.

The results presented here demonstrate potential clinical utility of blocking APE1/Ref-1 and CA9 function for novel PDAC therapeutic treatment. Ongoing experiments will determine the role of APE1/Ref-1 and CA9 in invasion of tumor cells exposed to hypoxic conditions, as well as the efficacy of dual-targeting APE1/Ref-1 and CA9 in in vivo models of PDAC.

Consequently, our findings further demonstrate a combination approach for blocking important signaling pathways in tumor cells. Our results support our previously published studies using APX3330 and STAT3 inhibition as a dual hit strategy in PDAC cells (Cardoso, Jiang et al. 2012) and APX3330 and Avastin (bevacizumab) for HIF1α-VEGF-signaling inhibition as an anti-angiogenesis combination strategy (Luo, Delaplane et al. 2008, Jiang, Gao et al. 2011, Li, Liu et al. 2014). Continued studies centering on the APE1/Ref-1 redox signaling axis and potential clinical partners for pathway inhibition are ongoing in our laboratories. This approach is supported by the planned phase 1 clinical trial for APX3330 scheduled to begin in mid-2016.

Citation Format: Derek P. Logsdon, Michelle Grimard, Safi Shahda, Nicholas Zyromski, Ernestina Schipani, Fabrizio Carta, Claudiu T. Supuran, Murray Korc, Mircea Ivan, Mark R. Kelley, Melissa L. Fishel.{Authors}. Regulation of HIF1α under hypoxia by APE1/Ref-1 impacts CA9 expression: Dual-targeting in patient-derived 3D pancreatic cancer models. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B51.

Regulation of HIF1α under Hypoxia by APE1/Ref-1 Impacts CA9 Expression: Dual Targeting in Patient-Derived 3D Pancreatic Cancer Models

Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related mortality in the United States. Aggressive treatment regimens have not changed the disease course, and the median survival has just recently reached a year. Several mechanisms are proposed to play a role in PDAC therapeutic resistance, including hypoxia, which creates a more aggressive phenotype with increased metastatic potential and impaired therapeutic efficacy. AP Endonuclease-1/Redox Effector Factor 1 (APE1/Ref-1) is a multifunctional protein possessing a DNA repair function in base excision repair and the ability to reduce oxidized transcription factors, enabling them to bind to their DNA target sequences. APE1/Ref-1 regulates several transcription factors involved in survival mechanisms, tumor growth, and hypoxia signaling. Here, we explore the mechanisms underlying PDAC cell responses to hypoxia and modulation of APE1/Ref-1 redox signaling activity, which regulates the transcriptional activation of hypoxia-inducible factor 1 alpha (HIF1α). Carbonic anhydrase IX (CA9) is regulated by HIF1α and functions as a part of the cellular response to hypoxia to regulate intracellular pH, thereby promoting cell survival. We hypothesized that modulating APE1/Ref-1 function will block activation of downstream transcription factors, STAT3 and HIF1α, interfering with the hypoxia-induced gene expression. We demonstrate APE1/Ref-1 inhibition in patient-derived and established PDAC cells results in decreased HIF1α-mediated induction of CA9. Furthermore, an ex vivo three-dimensional tumor coculture model demonstrates dramatic enhancement of APE1/Ref-1-induced cell killing upon dual targeting of APE1/Ref-1 and CA9. Both APE1/Ref-1 and CA9 are under clinical development; therefore, these studies have the potential to direct novel PDAC therapeutic treatment. Mol Cancer Ther; 15(11); 2722-32. ©2016 AACR.

Abstract 4740: Targeting Ref-1/APE1 pathway inhibition in pancreatic cancer using APX3330 for clinical trials

Pancreatic ductal adenocarcinoma (PDAC) is the 4th leading cause of cancer-related mortality in the US. Most patients present with advanced disease and ∼95% die within five years, with most surviving less than six months. Targeted therapies including Gemcitabine (GemzarTM), FOLFIRINOX (5-FU/leucovorin/irinotecan/oxaliplatin), and sustained release, nab-paclitaxel (AbraxaneTM) offer modest improvement in survival, albeit at an increase in side effects and unwanted toxicities. Data is presented on redox factor-1 (Ref-1) and specific Ref-1 inhibitor APX3330.

Ref-1 regulates multiple transcription factors involved in pancreatic cancer survival signaling due to its redox-coactivator activity on HIF-1α, NFkB, NRF2 and STAT3. High expression levels of Ref-1 indicate decreased survival in PDAC as well as other cancers. APX3330 has been shown in multiple in vitro and in vivo pancreatic cancer models to be effective in reducing tumor growth and metastases as a single agent. The mechanism of action has been extensively investigated and characterized for its specific activity on Ref-1, as well as its preclinical PK/PD and ADME. The safety and dose administration of APX3330 have been established by Eisai pharmaceutical company through a previous development program including toxicology, phase I, and phase II clinical evaluation in non-cancer patients in Japan. We have partnered with ApeX Therapeutics to develop APX3330 for cancer treatment (phase I trial anticipated start date early 2016).

While developing APX3330 for single agent use, we studied interactions of Ref-1, APX3330, convergent pathways; i.e. HIF-1 α and STAT3, and downstream targets like CAIX. Initially, we performed in vivo studies demonstrating single and combination effects of APX3330 with Gemcitabine (Gem) showing significantly decreased tumor volume in the APX3330 and Gem combination treatments compared to the single-agents alone. We also tested single and combination studies of APX3330 in an ex vivo 3-D tumor-stroma model system using patient derived tumor cells along with patient derived cancer-associated fibroblasts (CAFs). We used the CAIX inhibitor SLC-0111 and JAK2 inhibitor, Ruxolitinib; both agents in clinical trials. In our ex vivo 3D co-culture system, APX3330 decreases the tumor area and intensity in a dose-dependent manner. The combination of APX3330 with Gem demonstrated an additive enhancement effect in the tumor. Blocking both Ref-1 redox-signaling activity with APX3330 and CAIX activity via SLC-0111 demonstrated enhanced tumor killing in our models. APX3330 along with Ruxolitinib also demonstrated enhanced tumor killing.

These data demonstrate APX3330 single agent efficacy in our 3D patient PDAC model and enhanced tumor killing when pathways regulated by Ref-1, HIF-1 α and STAT3 are blocked. Additional drug combinations focused on pathways that are dependent on Ref-1 signaling will also be presented.

Citation Format: Melissa L. Fishel, Derek P. Logsdon, Michelle L. Grimard, Claudiu T. Supuran, Nicholas Zyromski, Mircea Ivan, Mark R. Kelley, Fenil Shah. Targeting Ref-1/APE1 pathway inhibition in pancreatic cancer using APX3330 for clinical trials. [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 4740.

Apurinic/apyrimidinic endonuclease/redox factor-1 (APE1/Ref-1) redox function negatively regulates NRF2

Apurinic/apyrimidinic endonuclease/redox factor-1 (APE1/Ref-1) (henceforth referred to as Ref-1) is a multifunctional protein that in addition to its base excision DNA repair activity exerts redox control of multiple transcription factors, including nuclear factor κ-light chain enhancer of activated B cells (NF-κB), STAT3, activator protein-1 (AP-1), hypoxia-inducible factor-1 (HIF-1), and tumor protein 53 (p53). In recent years, Ref-1 has emerged as a promising therapeutic target in cancer, particularly in pancreatic ductal carcinoma. Although a significant amount of research has centered on Ref-1, no wide-ranging approach had been performed on the effects of Ref-1 inhibition and transcription factor activity perturbation. Starting with a broader approach, we identified a previously unsuspected effect on the nuclear factor erythroid-related factor 2 (NRF2), a critical regulator of cellular defenses against oxidative stress. Based on genetic and small molecule inhibitor-based methodologies, we demonstrated that repression of Ref-1 potently activates NRF2 and its downstream targets in a dose-dependent fashion, and that the redox, rather than the DNA repair function of Ref-1 is critical for this effect. Intriguingly, our results also indicate that this pathway does not involve reactive oxygen species. The link between Ref-1 and NRF2 appears to be present in all cells tested in vitro, noncancerous and cancerous, including patient-derived tumor samples. In particular, we focused on understanding the implications of the novel interaction between these two pathways in primary pancreatic ductal adenocarcinoma tumor cells and provide the first evidence that this mechanism has implications for overcoming the resistance against experimental drugs targeting Ref-1 activity, with clear translational implications.

Research from the bedside to the lab bench & back

Transgenic mice represent a unique opportunity in biomedical research to discover the genes underlying disease and understand how manipulating the function of single genes and proteins alters physiology in a whole animal system. These advances in biomedical research may accelerate the time between when basic discoveries are made and when the research can be 'translated', that is, when the research will positively impact the lives of patients. The purpose of this article is to present some examples of promising mouse models of human diseases.

Mutation in erythroid specific transcription factor KLF1 causes Hereditary Spherocytosis in the Nan hemolytic anemia mouse model

KLF1 regulates definitive erythropoiesis of red blood cells by facilitating transcription through high affinity binding to CACCC elements within its erythroid specific target genes including those encoding erythrocyte membrane skeleton (EMS) proteins. Deficiencies of EMS proteins in humans lead to the hemolytic anemia Hereditary Spherocytosis (HS) which includes a subpopulation with no known genetic defect. Here we report that a mutation, E339D, in the second zinc finger domain of KLF1 is responsible for HS in the mouse model Nan. The causative nature of this mutation was verified with an allelic test cross between Nan/+ and heterozygous Klf1(+/-) knockout mice. Homology modeling predicted Nan KLF1 binds CACCC elements more tightly, suggesting that Nan KLF1 is a competitive inhibitor of wild-type KLF1. This is the first association of a KLF1 mutation with a disease state in adult mammals and also presents the possibility of being another causative gene for HS in humans.

Hematologic characterization and chromosomal localization of the novel dominantly inherited mouse hemolytic anemia, neonatal anemia (Nan)

One of the most commonly inherited anemias in man is Hereditary Spherocytosis (HS) with an incidence of 1 in 2000 for persons of Northern European descent. Mouse models of HS include spontaneous inherited hemolytic anemias and those generated by gene targeting. The Neonatal anemia (Nan) mouse is a novel model of HS generated by N-ethyl-N-nitrosurea mutagenesis and suffers from a severe neonatal anemia. Adult Nan mice have a lifelong hemolytic anemia with decreased red blood cell numbers, hematocrit, and hemoglobin, but elevated zinc protoporphyrin levels. Blood smears taken from Nan mice show a hypochromic anemia characterized by poikilocytosis, anisocytosis and polychromasia. The Nan phenotype can be transferred by bone marrow transplantation indicating that the defect is intrinsic to bone marrow. The hemolytic anemia in adult Nan mice can be identified by osmotic fragility testing. Examination of the erythrocyte membrane skeleton proteins (EMS) reveals a global deficiency of these proteins with protein 4.1a being completely absent. The Nan locus maps to mouse Chromosome 8 and does not co-localize with any known EMS genes. The identification of the Nan gene will likely uncover a novel protein that contributes to the stability of the EMS and may identify a new mutation for HS.