Abstract 1228: 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

[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.