TAS3681, an androgen receptor antagonist, prevents drug resistance driven by aberrant androgen receptor signaling in prostate cancer.

Second-generation androgen receptor (AR) signaling inhibitors (ARSIs), such as abiraterone and enzalutamide, prolong the life of patients with castration-resistant prostate cancer (CRPC). However, patients receiving ARSIs ultimately develop resistance through various complex mechanisms, including AR mutations, constitutively active AR-splice variants (AR-Vs), and AR overexpression. Here, we characterized a novel AR pure antagonist, TAS3681, which inhibits AR transcriptional activity and downregulates AR-full length (AR-FL) and AR-Vs. TAS3681 reduced the protein levels of AR-FL and AR-Vs including AR-V7 in enzalutamide-resistant cells (SAS MDV No. 3-14), in vitro and in vivo, showing strong antitumor efficacy in an AR-V7-positive xenograft model. In AR-overexpressing VCaP (prostate cancer) cells, conversely to enzalutamide, TAS3681 effectively suppressed cell proliferation and downregulated AR expression. Importantly, TAS3681 blocked the transcriptional activity of various mutant ARs, including mutations F877L/T878A and H875Y/T878A, which confer resistance to enzalutamide, and V716M and H875Y mutations, which confer resistance to darolutamide. Our results demonstrate that TAS3681 suppresses the reactivation of AR signaling, which causes resistance to ARSIs, via a newly identified mechanism of action. Therefore, TAS3681 could be a new therapeutic option for CRPC treatment.

Genome editing of Nf1, Pten, and Trp53 in neonatal mice induces glioblastomas positive for oligodendrocyte lineage transcription factor 2.

To generate a mouse glioblastoma model by genome editing, we introduced Cas9 protein and guide RNAs specific for Nf1, Pten, and Trp53 into the neonatal mouse forebrain by electroporation. We found a high incidence (approximately 90%) of glial tumor development, including glioblastomas, 15 weeks later. The histological features of the tumors were similar to those of diffuse gliomas and, in some cases, similar to human glioblastomas, with microvascular proliferation (glomeruloid structure). In addition, unlike glial fibrillary acidic protein (GFAP)-positive glioblastomas generated using a similar method in a previous model, the majority of tumor cells were positive for oligodendrocyte lineage transcription factor 2, but negative for GFAP and neurofilaments. One base pair insertions identical to those seen in a previous model were found around the target sequences in Nf1, Pten, and Trp53, and additional deletions were found only in Pten. Considering that the histological characteristics were different from those seen in the previous model, our new model provides an additional research tool to investigate the early stages of glioblastoma development.

dUTPase inhibition confers susceptibility to a thymidylate synthase inhibitor in DNA-repair-defective human cancer cells.

Deficiency in DNA repair proteins confers susceptibility to DNA damage, making cancer cells vulnerable to various cancer chemotherapies. 5-Fluorouracil (5-FU) is an anticancer nucleoside analog that both inhibits thymidylate synthase (TS) and causes DNA damage via the misincorporation of FdUTP and dUTP into DNA under the conditions of dTTP depletion. However, the role of the DNA damage response to its antitumor activity is still unclear. To determine which DNA repair pathway contributes to DNA damage caused by 5-FU and uracil misincorporation, we examined cancer cells treated with 2'-deoxy-5-fluorouridine (FdUrd) in the presence of TAS-114, a highly potent inhibitor of dUTPase that restricts aberrant base misincorporation. Addition of TAS-114 increased FdUTP and dUTP levels in HeLa cells and facilitated 5-FU and uracil misincorporation into DNA, but did not alter TS inhibition or 5-FU incorporation into RNA. TAS-114 showed synergistic potentiation of FdUrd cytotoxicity and caused aberrant base misincorporation, leading to DNA damage and induced cell death even after short-term exposure to FdUrd. Base excision repair (BER) and homologous recombination (HR) were found to be involved in the DNA repair of 5-FU and uracil misincorporation caused by dUTPase inhibition in genetically modified chicken DT40 cell lines and siRNA-treated HeLa cells. These results suggested that BER and HR are major pathways that protect cells from the antitumor effects of massive incorporation of 5-FU and uracil. Further, dUTPase inhibition has the potential to maximize the antitumor activity of fluoropyrimidines in cancers that are defective in BER or HR.

TAS0314, a novel multi-epitope long peptide vaccine, showed synergistic antitumor immunity with PD-1/PD-L1 blockade in HLA-A*2402 mice.

Cancer peptide vaccines are a promising cancer immunotherapy that can induce cancer-specific cytotoxic T lymphocytes (CTLs) in tumors. However, recent clinical trials of cancer vaccines have revealed that the efficacy of the vaccines is limited. Targeting single antigens and vaccination with short peptides are partly the cause of the poor clinical outcomes. We synthesized a novel multi-epitope long peptide, TAS0314, which induced multiple epitope-specific CTLs in HLA knock-in mice. It also showed superior epitope-specific CTL induction and antitumor activity. We also established a combination treatment model of vaccination with PD-1/PD-L1 blockade in HLA-A*2402 knock-in mice, and it showed a synergistic antitumor effect with TAS0314. Thus, our data indicated that TAS0314 treatment, especially in combination with PD-1/PD-L1 blockade, is a promising therapeutic candidate for cancer immunotherapy.

TAS-114, a First-in-Class Dual dUTPase/DPD Inhibitor, Demonstrates Potential to Improve Therapeutic Efficacy of Fluoropyrimidine-Based Chemotherapy.

5-Fluorouracil (5-FU) is an antimetabolite and exerts antitumor activity via intracellularly and physiologically complicated metabolic pathways. In this study, we designed a novel small molecule inhibitor, TAS-114, which targets the intercellular metabolism of 5-FU to enhance antitumor activity and modulates catabolic pathway to improve the systemic availability of 5-FU. TAS-114 strongly and competitively inhibited deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase), a gatekeeper protein preventing aberrant base incorporation into DNA, and enhanced the cytotoxicity of fluoropyrimidines in cancer cells; however, it had little intrinsic activity. In addition, TAS-114 had moderate and reversible inhibitory activity on dihydropyrimidine dehydrogenase (DPD), a catabolizing enzyme of 5-FU. Thus, TAS-114 increased the bioavailability of 5-FU when coadministered with capecitabine in mice, and it significantly improved the therapeutic efficacy of capecitabine by reducing the required dose of the prodrug by dual enzyme inhibition. Enhancement of antitumor efficacy caused by the addition of TAS-114 was retained in the presence of a potent DPD inhibitor containing oral fluoropyrimidine (S-1), indicating that dUTPase inhibition plays a major role in enhancing the antitumor efficacy of fluoropyrimidine-based therapy. In conclusion, TAS-114, a dual dUTPase/DPD inhibitor, demonstrated the potential to improve the therapeutic efficacy of fluoropyrimidine. Dual inhibition of dUTPase and DPD is a novel strategy for the advancement of oral fluoropyrimidine-based chemotherapy for cancer treatment. Mol Cancer Ther; 17(8); 1683-93. ©2018 AACR.

Repeated oral dosing of TAS-102 confers high trifluridine incorporation into DNA and sustained antitumor activity in mouse models.

TAS-102 is a novel oral nucleoside antitumor agent containing trifluridine (FTD) and tipiracil hydrochloride (TPI). The compound improves overall survival of colorectal cancer (CRC) patients who are insensitive to standard chemotherapies. FTD possesses direct antitumor activity since it inhibits thymidylate synthase (TS) and is itself incorporated into DNA. However, the precise mechanisms underlying the incorporation into DNA and the inhibition of TS remain unclear. We found that FTD-dependent inhibition of TS was similar to that elicited by fluorodeoxyuridine (FdUrd), another clinically used nucleoside analog. However, washout experiments revealed that FTD-dependent inhibition of TS declined rapidly, whereas FdUrd activity persisted. The incorporation of FTD into DNA was significantly higher than that of other antitumor nucleosides. Additionally, orally administered FTD had increased antitumor activity and was incorporated into DNA more effectively than continuously infused FTD. When TAS-102 was administered, FTD gradually accumulated in tumor cell DNA, in a TPI-independent manner, and significantly delayed tumor growth and prolonged survival, compared to treatment with 5-FU derivatives. TAS-102 reduced the Ki-67-positive cell fraction, and swollen nuclei were observed in treated tumor tissue. The amount of FTD incorporation in DNA and the antitumor activity of TAS-102 in xenograft models were positively and significantly correlated. These results suggest that TAS-102 exerts its antitumor activity predominantly due to its DNA incorporation, rather than as a result of TS inhibition. The persistence of FTD in the DNA of tumor cells treated with TAS-102 may underlie its ability to prolong survival in cancer patients.

1,2,3-Triazole-containing uracil derivatives with excellent pharmacokinetics as a novel class of potent human deoxyuridine triphosphatase inhibitors.

Deoxyuridine triphosphatase (dUTPase) has emerged as a potential target for drug development as a 5-fluorouracil-based combination chemotherapy. We describe the design and synthesis of a novel class of human dUTPase inhibitors, 1,2,3-triazole-containing uracil derivatives. Compound 45a, which possesses 1,5-disubstituted 1,2,3-triazole moiety that mimics the amide bond of tert-amide-containing inhibitor 6b locked in a cis conformation showed potent inhibitory activity, and its structure-activity relationship studies led us to the discovery of highly potent inhibitors 48c and 50c (IC(50) = ~0.029 µM). These derivatives dramatically enhanced the growth inhibition activity of 5-fluoro-2'-deoxyuridine against HeLa S3 cells in vitro (EC(50) = ~0.05 µM). In addition, compound 50c exhibited a markedly improved pharmacokinetic profile as a result of the introduction of a benzylic hydroxy group and significantly enhanced the antitumor activity of 5-fluorouracil against human breast cancer MX-1 xenograft model in mice. These data indicate that 50c is a promising candidate for combination cancer chemotherapies with TS inhibitors.

Discovery of highly potent human deoxyuridine triphosphatase inhibitors based on the conformation restriction strategy.

Human deoxyuridine triphosphatase (dUTPase) inhibition is a promising approach to enhance the efficacy of thymidylate synthase (TS) inhibitor based chemotherapy. In this study, we describe the discovery of a novel class of human dUTPase inhibitors based on the conformation restriction strategy. On the basis of the X-ray cocrystal structure of dUTPase and its inhibitor compound 7, we designed and synthesized two conformation restricted analogues, i.e., compounds 8 and 9. These compounds exhibited increased in vitro potency compared with the parent compound 7. Further structure-activity relationship (SAR) studies identified a compound 43 with the highest in vitro potency (IC(50) = 39 nM, EC(50) = 66 nM). Furthermore, compound 43 had a favorable oral PK profile and exhibited potent antitumor activity in combination with 5-fluorouracil (5-FU) in the MX-1 breast cancer xenograft model. These results suggested that a dUTPase inhibitor may have potential for clinical usage.

Discovery of a novel class of potent human deoxyuridine triphosphatase inhibitors remarkably enhancing the antitumor activity of thymidylate synthase inhibitors.

Inhibition of human deoxyuridine triphosphatase (dUTPase) has been identified as a promising approach to enhance the efficacy of 5-fluorouracil (5-FU)-based chemotherapy. This study describes the development of a novel class of dUTPase inhibitors based on the structure-activity relationship (SAR) studies of uracil derivatives. Starting from the weak inhibitor 7 (IC(50) = 100 µM), we developed compound 26, which is the most potent human dUTPase inhibitor (IC(50) = 0.021 µM) reported to date. Not only does compound 26 significantly enhance the growth inhibition activity of 5-fluoro-2'-deoxyuridine (FdUrd) against HeLa S3 cells in vitro (EC(50) = 0.075 µM) but also shows robust antitumor activity against MX-1 breast cancer xenograft model in mice when administered orally with a continuous infusion of 5-FU. This is the first in vivo evidence that human dUTPase inhibitors enhance the antitumor activity of TS inhibitors. On the basis of these findings, it was concluded that compound 26 is a promising candidate for clinical development.