PB1649 EXOSOMES‐MEDIATED DELIVERY OF RNA OLIGOS DIRECTED TO CHE‐1/AATF IMPAIRS BCP‐ALL VITALITY

Background: Precursor B cell acute lymphoblastic leukemia (BCP‐ALL) is the most common childhood malignancy and represents the leading cause of cancer‐related death in children and young adults. BCP‐ALL arises from a monoclonal or oligoclonal expansion of malignant B cell precursors in the bone marrow and despite the overall progress in treatment relapse occurs across the whole spectrum of all subtypes with an overall survival of 30%. We recently found that Che‐1/AATF, an important RNA polymerase II binding protein involved in the regulation of gene transcription with anti‐apoptotic activity in different tumour contests, exerts a pivotal role in BCP‐ALL. Che‐1 is highly expressed in a cohort of BCP‐ALL patients at the onset of disease and at time of relapse, irrespective of genetic heterogeneity, but were barely detectable when patients obtained leukemia remission. Notably, Che‐1 depletion strongly affected growth of BCP‐ALL cells and sensitized to Adriamycin. Aims: With the aim to therapeutically inhibit Che‐1 expression, overcoming the difficulty of the nuclear localization, and to find a technical approach available in in vivo models we focused on exosome‐mediated delivery of RNA oligos. Methods: To test this hypothesis, peripheral blood obtained from healthy donors was used for monocytes isolation and differentiation to immature dendritic cells. Supernatants were harvested and submitted to exosomes extraction procedure. Vesicles were electroporated with FITC‐conjugated oligos to set up experimental conditions. We observed high oligos loading and a 100% efficiency of oligo delivery in BCP‐ALL cell lines and in primary blast cells upon cellular co‐culture. In the same experimental conditions, we tested the efficacy of a panel of FITC‐conjugate oligo targeting Che‐1. Results: The exosome‐mediated delivery of combination of two oligos resulted in downregulation of Che‐1 expression in BCP‐ALL cell lines. The obtained result produced also an increase in PARP cleavage and an higher amount of cells in subG0‐1 phase. Summary/Conclusion: Since part of this procedure is an already approved GMP‐grade procedure, we will test the cooperation between exosome‐mediated Che‐1 downregulation and the current therapeutic treatments with the aim to develop a new applicable clinical approach, particularly in BCP‐ALL relapsed patients.