Acute myeloid leukemia (AML) represents one of the most complex types of leukemia. It is a clinically and genetically heterogeneous disorder of hematopoietic progenitor cells, which have lost their ability to differentiate normally. Retinoids regulate vital biological processes including development, differentiation, proliferation, and cell death of hematopoietic progenitor cells. The natural retinoid all-trans retinoic acid (ATRA) became the paradigm for the treatment of acute promyelocytic leukemia (APL), an AML subtype. However, in non-APL AML patients, ATRA is possibly only effective in patients with Nucleophosmin-1 mutations without FMS-like tyrosine kinase 3 internal tandem duplication (FLT-3 ITD). Therefore, synthetic retinoids, specifically the adamantyl ST1926, emerged as potential alternatives. However, despite its lack of toxicity, ST1926 development in clinic was limited due to its rapid glucuroconjugation resulting in low plasma concentrations. Nanomedicine enables more efficient drug delivery and bioavailability. Here, we investigate the pre-clinical efficacy of ST1926 and polymer stabilized ST1926 nanoparticles in AML in vitro and in vivo models. We show that ST1926, at low sub-µM concentrations, potently inhibited the growth of human non-APL ATRA-resistant AML cell lines and AML patient cells while sparing resting and activated normal leukocytes at ten- to hundred-fold higher concentrations. ST1926 induced early DNA damage and massive apoptosis in all tested AML cell lines. To optimize the drug’s bioavailability burden, polymer stabilized ST1926 nanoparticles were developed using Flash NanoPrecipitation, and were shown to display comparable anti-growth activities to the naked drug in vitro. In murine AML xenograft model, ST1926 and ST1926 nanoparticles significantly prolonged survival. Strikingly, ST1926 encapsulated in nanoparticles extended survival in AML xenografted mice at four-fold lower concentrations than the naked drug. These results highlight the promise of ST1926 in AML therapy and warrant further clinical development of this adamantly retinoid.

Citation Format: Leeanna El-Houjeiri, Walid Saad, Berthe Hayar, Patrick Aouad, Nadim Tawil, Rana Abdel-Samad, Claudio Pisano, Ali Bazarbachi, Hiba El Hajj, Nadine Darwiche. Encapsulation of the atypical retinoid ST1926 in nanoparticles prolongs the survival of acute myeloid leukemia xenografted mice at multiple folds lower concentrations than the naked drug [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5140. doi:10.1158/1538-7445.AM2017-5140