Modulation of the haematopoietic stem cell niche by photo-triggerable nanoparticles

Abstract

The bone-marrow haematopoietic stem cell niche is a protective hard to reach microenvironment that is difficult to modulate in the context of HSC transplant and malignant haematopoietic disease. In this thesis we developed new strategies to tackle this by the use of a combination of nanomedicine tools and cell-mediated delivery systems. In the context of leukaemia, cells that are resistant to conventional therapies are thought to reside in protective niches. Here, we describe light-inducible polymeric retinoic acid (RA)-containing nanoparticles (NPs) with the capacity to accumulate in the cytoplasm of leukaemia cells for several days and release their RA payloads within a few minutes upon exposure to blue/UV light. Compared to NPs that are not activated by light exposure, these NPs more efficiently reduce the clonogenicity of bone marrow cancer cells from patients with AML and induce the differentiation of RA-low sensitive leukaemia cells. Importantly, we show that leukaemia cells transfected with light-inducible NPs containing RA can engraft into bone marrow in vivo in the proximity of other leukaemic cells, differentiate upon exposure to blue light and release paracrine factors that modulate nearby cells. This capacity of remotely modulating the leukaemic niche has been tested in an AML disease animal model with success. RA+NPs induced AML differentiation towards monocytic/macrophage lineage in the MLL-AF9 mouse model of AML. Also, we have shown in vitro that RA+NPs stimulate antitumoral M1 macrophage activation. This macrophage induced differentiation in vivo seems to have “systemic” anti-leukemic effect within the BM leukemic niche, as we observed a significant reduction of leukemic cells in the BM of animals treated with RA+NPs when compared with animals treated with empty NPs (RA-NPs). Finally, prospective studies on the use of healthy HSCs as carriers have shown that despite having a more sensitive behaviour UCB CD34+cells can be loaded with RA+NP and after light-activated release of RA, induce CD38 expression and differentiate. Towards the use of this type of tools in the context of HSC transplant engraftment modulation we were able to produce functional HOXB4, a pivotal transcription factor for HSC potency, that was able to induce G0 quiescence, but NP-functionalization with this molecule remains a challenge and is the subject of future work.