Abstract 3935: The polymeric fluoropyrimidine CF10 overcomes limitations of 5-FU in pancreatic ductal adenocarcinoma cells through increased replication stress

Pancreatic ductal adenocarcinoma (PDA) is a lethal disease that will soon become the second leading cause of cancer deaths in the US. Beside surgery, current therapies have narrow clinical benefits for this devastating disease, and in the majority of cases, only improve survival by a few months. Moreover, systemic toxicities are a harsh reality of these treatments. FOLFIRINOX is the drug regimen of choice, one component of which is 5-Fluorouracil (5-FU) which causes serious gastrointestinal and hematopoietic toxicities and is vulnerable to resistance due, in part, to thymidylate synthase (TS) overexpression. The Gmeiner lab has pioneered the development of polymeric fluoropyrimidines, named F10 and CF10, which unlike 5-FU, are in principle completely converted to the TS inhibitory metabolite FdUMP, without generating appreciable levels of ribonucleotides that cause systemic toxicities and while displaying much stronger anti-cancer activity. Here, we further confirm the potency of CF10 and investigate enhancement of its efficacy through combination with inhibitors targeting replication stress, a hallmark of PDA cells. We show that, consistent with our previous studies in PDA cells, CF10 is much more potent as a single agent than 5-FU, by an average 308x fold, and was effective in the nM range (GI50 range 3.13 - 336 nM) in 5 PDA cell lines tested. We also found that CF10 induces increased replication stress as assessed by phosphorylation of ATR, which appears as early as 8 hours after treatment and increases in intensity over 48 hours, consistent with the kinetics of FdU being released from CF10 and incorporated into DNA, a process requiring several hours. Importantly, phosphorylation of ATR induced by CF10 was significantly higher than with 5-FU. This is especially striking because compounds for this assay were used at their IC50 concentrations, with for example MiaPaCA2 cells being exposed to 899 time more 5-FU than CF10, yet at this concentration 5-FU induced less ATR phosphorylation. Further, we find that the activity of CF10, but not 5-FU can be enhanced through combination with inhibitors of ATR and Wee1 that regulate the S and G2 damage checkpoints. Our results indicate CF10 has potential to supersede the established benefit of 5-FU in PDA treatment and indicate novel combination approaches that may be beneficial compared to well-established regimens used currently for 5-FU.

Citation Format: Roberto DiNiro, Alex O. Haber, Kang J. Jeong, Soon Y. Park, Gordon B. Mills, William H. Gmeiner, Jonathan R. Brody. The polymeric fluoropyrimidine CF10 overcomes limitations of 5-FU in pancreatic ductal adenocarcinoma cells through increased replication stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3935.

AraC-FdUMP[10] Is a Next-Generation Fluoropyrimidine with Potent Antitumor Activity in PDAC and Synergy with PARG Inhibition

AraC-FdUMP[10] (CF10) is a second-generation polymeric fluoropyrimidine that targets both thymidylate synthase (TS), the target of 5-fluorouracil (5-FU), and DNA topoisomerase 1 (Top1), the target of irinotecan, two drugs that are key components of FOLFIRNOX, a standard-of-care regimen for pancreatic ductal adenocarcinoma (PDAC). We demonstrated that F10 and CF10 are potent inhibitors of PDAC cell survival (in multiple cell lines including patient-derived lines) with IC₅₀s in the nanomolar range and are nearly 1,000-fold more potent than 5-FU. The increased potency of CF10 relative to 5-FU correlated with enhanced TS inhibition and strong Top1 cleavage complex formation. Furthermore, CF10 displayed single-agent activity in PDAC murine xenografts without inducing weight loss. Through a focused drug synergy screen, we identified that combining CF10 with targeting the DNA repair enzyme, poly (ADP-ribose) glycohydrolase, induces substantial DNA damage and apoptosis. This work moves CF10 closer to a clinical trial for the treatment of PDAC. IMPLICATIONS: CF10 is a promising polymeric fluoropyrimidine with dual mechanisms of action (i.e., TS and Top1 inhibition) for the treatment of PDAC and synergizes with targeting of DNA repair. VISUAL OVERVIEW: http://mcr.aacrjournals.org/content/molcanres/19/4/565/F1.large.jpg.

Improved Antitumor Activity of the Fluoropyrimidine Polymer CF10 in Preclinical Colorectal Cancer Models through Distinct Mechanistic and Pharmacologic Properties

Chemotherapy regimens that include 5-fluorouracil (5-FU) are central to colorectal cancer treatment; however, risk/benefit concerns limit 5-FU's use, necessitating development of improved fluoropyrimidine (FP) drugs. In our study, we evaluated a second-generation nanoscale FP polymer, CF10, for improved antitumor activity. CF10 was more potent than the prototype FP polymer F10 and much more potent than 5-FU in multiple colorectal cancer cell lines including HCT-116, LS174T, SW480, and T84D. CF10 displayed improved stability to exonuclease degradation relative to F10 and reduced susceptibility to thymidine antagonism due to extension of the polymer with arabinosyl cytidine. In colorectal cancer cells, CF10 strongly inhibited thymidylate synthase (TS), induced Top1 cleavage complex formation and caused replication stress, while similar concentrations of 5-FU were ineffective. CF10 was well tolerated in vivo and invoked a reduced inflammatory response relative to 5-FU. Blood chemistry parameters in CF10-treated mice were within normal limits. In vivo, CF10 displayed antitumor activity in several colorectal cancer flank tumor models including HCT-116, HT-29, and CT-26. CF10's antitumor activity was associated with increased plasma levels of FP deoxynucleotide metabolites relative to 5-FU. CF10 significantly reduced tumor growth and improved survival (84.5 days vs. 32 days; P < 0.0001) relative to 5-FU in an orthotopic HCT-116-luc colorectal cancer model that spontaneously metastasized to liver. Improved survival in the orthotopic model correlated with localization of a fluorescent CF10 conjugate to tumor. Together, our preclinical data support an early-phase clinical trial of CF10 for treatment of colorectal cancer.

Abstract 3058: Recharacterizing the FDA approved drug pyrvinium pamoate as a clinically relevant HuR inhibitor in pancreatic ductal adenocarcinoma

HuR is an RNA binding protein involved in a coordinated cellular survival response to stressors. Upon insults such as chemotherapy, HuR translocates from the nucleus to the cytoplasm where it binds the 3’UTR of target mRNAs. HuR’s interaction with target mRNAs leads to the upregulation of target genes and ultimately treatment resistance. This is particularly relevant in the case of pancreatic ductal adenocarcinoma (PDA). PDA is highly resistant to radiotherapy and standard chemotherapy such as FOLFIRINOX or gemcitabine/nab-paclitaxel. Using a tumor microarray (TMA), we found 79% of patient tumor samples (n=70) were positive for active cytoplasmic HuR, while little to no cytoplasmic localization was detected in normal tissue. In addition, HuR CRISPR knockout cell lines have a xenograft lethal phenotype. The aim of our current study is to target HuR by re-purposing the anti-helminthic, FDA approved small molecule pyrvinium pamoate (PP) to inhibit HuR’s translocation and sensitize PDA cells to concurrent therapies. PP has been shown in bladder cancer to inhibit the translocation of HuR in vitro and in vivo. We have reproduced this in multiple PDA cell lines and have shown impressive drug potency with IC50s as low as 38nM in 2D cultures of PDA cell lines and PDX lines and 16nM in a 3D mouse PDA organoid model. We have demonstrated that inhibition of HuR translocation is likely to occur through secondary effectors AMPK and CDK1. We have also demonstrated that PP’s inhibition of HuR function may be through direct inhibition of target binding. In comparison to other published HuR inhibitors PP inhibits the binding of HuR to targets more potentlt with nanomolar IC50’s. We confirmed this work through HuR RNA Immunoprecipitation experiments and determined that PP inhibited the ability of HuR to bind target mRNA. We generated HuR deficient CRISPR lines to and demonstrated that lack of HuR sensitizes PDA cells to various therapeutics, an effect which is exacerbated in physiologically relevant low glucose settings. We next demonstrated that PP can synergize with several therapeutics including the CDK4/6 inhibitors Abemaciclib and Palbociclib in PDA cells and that this synergy is increased in low glucose setting. This synergistic effect is ameliorated in HuR deficient CRISPR cell lines, indicating that PP achieves this synergistic potential through the inhibition of HuR. We performed targeted phosphoproteomics and found that PP robustly inhibited critical mTOR pathway members as well as validating previous reports that it can inhibit the WNT pathway. Finally, we have demonstrated that PP has a dose dependent effect on PDA tumor growth in vivo with IP and PO dosing regimens. This work supports the recharacterization of PP as a potentially effective therapeutic agent for the treatment of PDA. Early phase clinical trials of PP in human subjects are being planned for 2019.

Citation Format: Christopher W. Schultz, Teena Dhir, Samantha Z. Brown, Saswati Chand, Wei Jiang, Grace A. McCarthy, Alex O. Haber, Charles J. Yeo, Austin Goetz, Avinoam Nevler, Oloruntoba Bolaji, Jonathan R. Brody. Recharacterizing the FDA approved drug pyrvinium pamoate as a clinically relevant HuR inhibitor in pancreatic ductal adenocarcinoma [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 3058.