Targeted Therapy For Acute Myeloid Leukemia: Retinoic Acid, Actinomycin D, and Everolimus

Abstract

Acute Myeloid Leukemia (AML) is a heterogeneous malignancy of myeloid origin and one of the most common adult leukemias. Despite all therapeutic advances, AML still associates with poor prognosis, high relapse rates, and resistance to chemotherapy. Personalized medicine based on predicted response or risk of disease, is gaining major interest in AML management. This includes targeted therapies of specific mutations or disrupted pathways in AML. Everolimus (EV), an mTOR inhibitor, improved the treatment of AML patients when combined with other therapeutic agents. Actinomycin D (ActD), an anti-tumor antibiotic, inhibited AML cell growth in vitro, yet presents an unambiguous clinical efficacy in some relapsed/refractory AMLs. Retinoic acid (RA), a hormone playing a major role in differentiation, proved beneficial, alone or combined to other agents on some subtypes of AML. In this study, we explored the effect of simultaneous administration of RA, EV, ActD or the sequential administration of RA first, followed by EV and/or ActD on AML. In vitro, we used OCI-AML2, OCI-AML3, THP-1 and MOLM-13, presenting different mutations and reflecting some heterogeneous groups of AML. In vivo, xenograft mice were injected with OCI-AML2 or OCI-AML3 and treated with either RA followed by EV and/or ActD, or simultaneously with RA/Act/EV. Mice were monitored for survival, or humanely sacrificed 2 weeks post-treatment. Liver weight was recorded, and leukemic burden was assessed by immunophenotyping. We demonstrated that OCI-AML2, OCI-AML3, and MOLM-13 are sensitive to ActD alone or to EV/ActD combination and RA addition to these treatments did not confer any additional advantage in OCI-AML2 and OCI-AML3. THP-1 cells lacking p53, were less sensitive to ActD alone, yet the addition of EV to ActD resulted in a more pronounced cell death. This phenotype which remained less prominent than that observed in cells with intact p53. Adding RA to EV demonstrated some beneficial effect in all tested cells, but this effect was not as prominent as ActD or EV/ActD. Accordingly, we restricted our molecular analysis to EV/ActD. We revealed a p53-dependent apoptosis in OCI-AML2 and OCI-AML3, 48 h post-treatment. Similar to in vitro results, sequential treatment with RA first, followed by EV/ActD did not yield any beneficial in vivo antitumor effect. Indeed, mice presented with sustained hepatomegaly and high even more exacerbated tumor burden in bone marrow for some conditions. However, our preliminary results showed that EV single agent, or EV/RA/ActD for 5 days following initial administration of RA prolonged survival of OCI-AML3 xenografted mice, while EV and ActD single agents, and RA prior to EV/ActD prolonged survival of OCI-AML2 mice. In conclusion, our preliminary study demonstrated that an original treatment with RA before EV and/or ActD may not be of great beneficial efficacy and is dependent on the AML subtype, but these results require a confirmation.