Harnessing RARA signalling for curative AML therapies

In acute promyelocytic leukaemia (APL), retinoic acid (RA) and arsenic trioxide (ATO) bind the PML/RARA fusion to promote its degradation, derepressing unknown master regulatory genes and activating a PML/P53 checkpoint which is required for APL cure. APL initiation deregulates Retinoic Acid Receptor a (RARA) signalling. These deregulations are likely shared with a sizable subset of non-APL acute myeloid leukaemia (AML): the 30% that overexpress normal RARA and exhibit some RA-sensitivity ex vivo. Clinical trials have demonstrated some benefit of RA addition to conventional therapies in non-APL AML patients, but have not resulted in the incorporation of RA into standard therapies. Thus, modulation of RARA signalling is an unrealized target for treatment of non-APL AMLs. Of importance, RARA serves a dual function in APL by promoting leukemogenesis in the unliganded state, but also by enforcing RA-response. We made the striking observation that overexpression of RARA suffices to confer cell self-renewal ex vivo and RA-sensitivity in several AML models. We propose to i) define the actual effects (differentiation, self-renewal) and cellular mechanisms (senescence, apoptosis, growth arrest) underlying RA action on a variety of primary myeloid cells over-expressing RARA ii) delineate the mechanism(s) underlying RARA overexpression in some human AMLs iii) identify the RARA downstream targets that drive self-renewal iv) discover novel RA-containing drug combinations exhibiting synergies for AML clearance in RA-sensitive transformed myeloid cells. This proposal is based on our previous modelling of APL therapy and recent disruptive observations. This renewed exploration of RARA-driven progenitor self-renewal will allow us to define novel curative RA-containing strategies and biomarkers for many AML patients unfit for chemotherapy, who are currently not eligible for cure.