Imatinib-Loaded Polyelectrolyte Microcapsules for Sustained Targeting of BCR-ABL⁺ Leukemia Stem Cells

Abstract

Aim: The lack of sensitivity of chronic myeloid leukemia (CML) stem cells to imatinib mesylate (IM) commonly leads to drug dose escalation or early disease relapses when therapy is stopped. Here, we report that packaging of IM into a biodegradable carrier based on polyelectrolyte microcapsules increases drug retention and antitumor activity in CML stem cells, also improving the ex vivo purging of malignant progenitors from patient autografts. Materials & methods: Microparticles/capsules were obtained by layer-by-layer (LbL) self-assembly of oppositely charged polyelectrolyte multilayers on removable calcium carbonate (CaCO₃) templates and loaded with or without IM. A leukemic cell line (KU812) and CD34⁺ cells freshly isolated from healthy donors or CML patients were tested. Results & discussion: Polyelectrolyte microcapsules (PMCs) with an average diameter of 3 µm, fluorescently labelled multilayers sensitive to the action of intracellular proteases and 95–99% encapsulation efficiency of IM, were prepared. Cell uptake efficiency of such biodegradable carriers was quantified in KU812, leukemic and normal CD34⁺ stem cells (range: 70–85%), and empty PMCs did not impact cell viability. IM-loaded PMCs selectively targeted CML cells, by promoting apoptosis at doses that exert only cytostatic effects by IM alone. More importantly, residual CML cells from patient leukapheresis products were reduced or eliminated more efficiently by using IM-loaded PMCs compared with freely soluble IM, with a purging efficiency of several logs. No adverse effects on normal CD34⁺ stem-cell survival and their clonogenic potential was noticed in long-term cultures of hematopoietic progenitors in vitro.Conclusion: This pilot study provides the proof-of-principle for the clinical application of biodegradable IM-loaded PMC as feasible, safe and effective ex vivo purging agents to target CML stem cells, in order to improve transplant outcome of resistant/relapsed patients or reduce IM dose escalation.

Keywords::

• chronic myeloid leukemia
• drug delivery system
• drug resistance
• imatinib mesylate
• layer-by-layer
• microcapsules
• polyelectrolytes
• stem cell

Financial & competing interests disclosure

This research was supported by the Italian Association for Cancer Research (AIRC) through a MFAG project No. 6189 to AMC. Financial support of the Italian Ministry of University and Research (MIUR) through a FIRB project no. RBLA03ER38 ‘Con il contributo del Ministero degli Affari Esteri, Direzione Generale per la promozione e la Cooperazione Sociale’ (Large Scale ITA –USA Bilateral Project ‘Nano-trasportatori per la terapia del cancro‘) is also acknowledged. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Acknowledgements

We are grateful to V Vergaro, A della Torre and E Perrone from National Nanotechnology Laboratory (NNL) for atomic force microscopy and scanning electron microscope results. U Reibetanz and E Donath (University of Leipzig, Germany) are also gratefully acknowledged for introducing us to layer-by-layer encapsulation techniques, polymer labelling and for useful discussions.

Additional information

Funding

This research was supported by the Italian Association for Cancer Research (AIRC) through a MFAG project No. 6189 to AMC. Financial support of the Italian Ministry of University and Research (MIUR) through a FIRB project no. RBLA03ER38 ‘Con il contributo del Ministero degli Affari Esteri, Direzione Generale per la promozione e la Cooperazione Sociale’ (Large Scale ITA –USA Bilateral Project ‘Nano-trasportatori per la terapia del cancro‘) is also acknowledged. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.