[Introduction] FF-10850, a novel liposomal topotecan, has shown superior anti-tumor effects and a favorable safety profile compared with topotecan or doxorubicin HCl liposome injection (lipo-dox). In the present study, we evaluated the tissue distribution, pharmacodynamics, and payload release of FF-10850 to further characterize mechanisms for enhanced activity and improved safety. [Methods] ES-2 ovarian cancer cells were inoculated into nude mice by subcutaneous or intraperitoneal injection. Topotecan concentration and the ratio of p-H2AX/H2AX were measured by LC-MS/MS in tumor and bone marrow, respectively. FF-10850-internalized cell types in tumor were classified by flow cytometry using fluorescent-labeled FF-10850. Topotecan released from FF-10850-internalized cells was quantified in cell culture supernatants by LC-MS/MS. Payload released from the liposomal membranes of either FF-10850 or lipo-dox was quantified by ultracentrifugation/LC-MS/MS following incubation in tumor interstitial fluid and ammonia-containing buffer. [Results] Kinetic analysis of topotecan concentration and p-H2AX/H2AX ratio in tumor and bone marrow, after FF-10850 or topotecan injection, revealed that FF-10850 exerted profound drug exposure and DNA damage, preferentially in tumor. These findings were consistent with superior anti-tumor effects and a favorable safety profile of FF-10850 previously observed in both subcutaneous tumor models and in a clinically relevant intraperitoneally disseminated tumor model. Immunophenotyping revealed internalization of FF-10850 by tumor associated phagocytes. Evaluation of payload release confirmed topotecan was released from FF-10850-internalized cells into the extracellular space, and additionally from FF-10850 but not lipo-dox liposomal membranes during incubation in tumor interstitial fluid. A higher concentration of ammonia detected in the tumor interstitial fluid compared to that in plasma. Ammonia-containing buffer was shown to induce payload release from FF-10850 but not from lipo-dox membranes. [Conclusions] These data suggest that FF-10850 preferentially accumulates in tumor, presumably via the enhanced permeability and retention effect, and efficiently releases payload through dual mechanisms in tumor. One mechanism is mediated by tumor associated phagocytes, which internalize FF-10850 and release payload into the extracellular space. An additional mechanism is mediated by ammonia, which is reported to be a metabolite in glutaminolysis activated by the metabolic shift in tumor cells. These characteristics of FF-10850 distribution and release may translate to enhanced anti-tumor effects of FF-10850 as observed in subcutaneous as well as intraperitoneally disseminated tumor models closely resembling clinical conditions. Citation Format: Susumu Shimoyama, Ken Okada, Toshifumi Kimura, Noriyuki Kasagi, Shinji Nakayama, Keiko Makita-Suzuki, Shun Matsuda, Mikinaga Mori, Kiyohito Takada, Shinji Hagiwara, Takefumi Hara. FF-10850, a novel liposomal topotecan, achieved superior anti-tumor effects and a favorable safety profile via preferential distribution followed by dual payload release mechanisms in tumor [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 1228.
Although several liposomal drugs, including liposomal doxorubicin, have been approved, the etiology of the pathological responses caused by their physicochemical properties remains unknown. Herein, we investigated the pathological changes in the liver and the gallbladder of dogs following a single injection of liposomal doxorubicin (1 or 2.5 mg/kg) or an empty liposomal formulation (i.e., liposomal formulation without doxorubicin, ca. 21 mg/kg as lipid content). Injection of liposomal doxorubicin or the empty liposomal formulation induced hemorrhagic changes in the liver and the gallbladder. These changes were accompanied by minimal cellular infiltration with no obvious changes in the blood vessels. As there were no differences in the incidence and severity of hemorrhage between the groups administered comparable amounts of total lipid, the physicochemical properties of the liposomal formulation rather than an active pharmacological ingredient, doxorubicin, were associated with the hemorrhagic changes. Furthermore, decreased cytoplasmic granules with low electron density in mast cells beneath the endothelium of the hepatic vein were observed in the liver of dogs treated with liposomal doxorubicin or empty liposomal formulation. Injection of compound 48/80, a histamine releaser induced comparable hemorrhage in dogs, implying that hemorrhage caused by injection of liposomal doxorubicin or the empty liposomal formulation could be attributed to the histamine released from mast cells. The absence of similar hemorrhagic lesions in other species commonly used in toxicology studies (i.e., rats and monkeys), as well as humans, is due to the lack of mast cells beneath the endothelium of the hepatic vein in these species.
Cancer initiating cells (CIC) are suggested to be responsible for drug resistance and cancer relapse that are associated with poor prognosis. Therefore, drugs effective for CIC could fulfill an unmet clinical need. We performed a drug screen with chemical libraries to find out new compounds which specifically eradicated CIC established in the previous report (Yamashita et al., Cancer Research, 2015). We obtained compounds with a carboxylic acid skeleton as hit compounds. Interestingly, FF1215T, one of the hit compounds, was shown to inhibit growths of CIC by decreasing intracellular pyrimidine nucleotide levels. Finally, we identified dihydroorotate dehydrogenase (DHODH), which was essential for de novo pyrimidine synthesis as the target of the hit compounds in a ligand fishing assay. FF1215T inhibited DHODH enzymatic activity with the 50% inhibitory concentration value of 9 nM, which showed greater potency than well-known DHODH inhibitors brequinar (12 nM), teriflunomide (262 nM), and vidofludimus (141 nM). Growing evidence suggests that DHODH is considered to be a promising target to overcome a differentiation blockade of acute myeloid leukemia (AML) cells (Sykes et al., Cell, 2016).Therefore, we explored the effect of FF1215T on AML growth and differentiation. FF1215T demonstrated growth inhibitory effect in multiple human AML cell lines such as U937, MOLM13, HL60, and MV4-11 with the 50% growth inhibition values of 90-170 nM. FF1215T decreased intracellular pyrimidine nucleotide levels, induced DNA damage marker γ-H2AX possibly due to the replication stress, and finally led to apoptosis in HL60 cells. Cell cycle analysis revealed that FF1215T treatment arrested HL60 and THP1 cells at S phase and increased sub-G1 population in these cells. In addition, our DHODH inhibitors induced upregulation of cell-surface CD11b and CD86, which are monocyte and macrophage differentiation markers, morphological changes, and phagocytic activities in several AML cells, indicating differentiation of AML cells toward monocyte and macrophage by DHODH inhibition. FF1215T also depleted UDP-GlcNAc, a substrate for Protein O-GlcNAcylation, and diminished global O-GlcNAcylation and O-GlcNAcylated protein expressions such as c-Myc, SOX2, and OCT4, which play important roles in maintenance and self renewal of stem cells. We also found that our DHODH inhibitors induced CD11b and CD86, and increased the ratio of macrophage-like cells in primary patient-derived AML cells and these effects were rescued by uridine supplementation (Fig). Inhibitions of colony formations of primary AML cells were also shown after 14 days of FF1215T treatment. In exploring the value of DHODH inhibitors in the clinic, we identified that our DHODH inhibitors worked to overcome the resistance of standard therapy Ara-C. Our DHODH inhibitors were effective against Ara-C-resistant models of HL60 cells as well as HL60 parental cells. Notably, our DHODH inhibitors synergistically inhibited growths of Ara-C-resistant THP1 cells and enhanced CD11b upregulation of THP1 cells when combined with Ara-C by activating conversion of Ara-C to its active form Ara-CTP. Next, we optimized the hit compounds and identified an orally available DHODH inhibitor FF14984T that achieved high and prolonged plasma concentrations in vivo. Oral administration of 10 and 30 mg/kg FF14984T once daily for 10 days exhibited significant anti-tumor effects in mice xenografted with HL60 cells. These treatments showed strong reduction of CTP in tumor and induction of DHO in tumor and plasma. When 30 mg/kg FF14984T was orally administrated to orthotropic MOLM13-xenografted mice once daily for 12 days, hCD45+ cells proportions in bone marrow were decreased whereas hCD11bhigh/hCD45+ ratio increased, indicating that FF14984T induced AML differentiation in vivo. Finally, oral administration of 30 mg/kg FF14984T once daily significantly prolonged survival of mice in U937 orthotropic models. Taken together, we developed a novel potent DHODH inhibitor FF14984T that induced cellular differentiation and anti-leukemic effects on cell lines and primary AML cells. FF14984T is possibly a promising therapeutic option for Ara-C-resistant AML patients that can also benefit from the combination therapy of FF14984T and Ara-C. Identifying the precise mechanism of AML differentiation by DHODH inhibitor and its effects on CIC are currently ongoing. Disclosures Kitazawa: FUJIFILM Corporation: Employment. Ishii:FUJIFILM Corporation: Employment. Makita-Suzuki:FUJIFILM Corporation: Employment. Saito:FUJIFILM Corporation: Employment. Takayanagi:FUJIFILM Corporation: Employment. Sugihara:FUJIFILM Corporation: Employment. Matsuda:FUJIFILM Corporation: Employment. Yamakawa:FUJIFILM Corporation: Employment. Tsutsui:FUJIFILM Corporation: Employment. Tanaka:FUJIFILM Corporation: Employment. Hatta:FUJIFILM Corporation: Research Funding. Natsume:FUJIFILM Corporation: Research Funding. Kondo:FUJIFILM Corporation: Research Funding. Hagiwara:FUJIFILM Coporation: Employment. Kiyoi:FUJIFILM Corporation: Research Funding; Astellas Pharma Inc.: Honoraria, Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; Bristol-Myers Squibb: Research Funding; Daiichi Sankyo Co., Ltd: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; Otsuka Pharmaceutical Co.,Ltd.: Research Funding; Eisai Co., Ltd.: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding; Pfizer Japan Inc.: Honoraria; Perseus Proteomics Inc.: Research Funding.
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