Proteomic Studies of Primary Acute Myeloid Leukemia Cells Derived from Patients Before and during Disease-Stabilizing Treatment Based on All-Trans Retinoic Acid and Valproic Acid

SIMPLE SUMMARY: Acute myeloid leukemia (AML) is an aggressive hematological malignancy, and the only possibility of cure is intensive antileukemic treatment. Such treatment is only possible for relatively young and fit patients, but there is a large subset of elderly/unfit patients above 65–70 years of age who cannot receive intensive treatment. The low-toxicity combination of valproic acid (VP) plus all-trans retinoic acid (ATRA) has an AML-stabilizing effect for a subset of patients, even those with chemoresistant relapse. This response may be an indirect effect due to the modulation of the metabolic environment, but in this article, we describe that the in vivo treatment with ATRA/VP also has direct effects on the fundamental functions of human AML cells. Furthermore, new and less intensive antileukemic therapies are now available (i.e., venetoclax, azacitidine, decitabine), and the combination of these new agents with ATRA/VP may represent a new therapeutic strategy in AML. ABSTRACT: All-trans retinoic acid (ATRA) and valproic acid (VP) have been tried in the treatment of non-promyelocytic variants of acute myeloid leukemia (AML). Non-randomized studies suggest that the two drugs can stabilize AML and improve normal peripheral blood cell counts. In this context, we used a proteomic/phosphoproteomic strategy to investigate the in vivo effects of ATRA/VP on human AML cells. Before starting the combined treatment, AML responders showed increased levels of several proteins, especially those involved in neutrophil degranulation/differentiation, M phase regulation and the interconversion of nucleotide di- and triphosphates (i.e., DNA synthesis and binding). Several among the differentially regulated phosphorylation sites reflected differences in the regulation of RNA metabolism and apoptotic events at the same time point. These effects were mainly caused by increased cyclin dependent kinase 1 and 2 (CDK1/2), LIM domain kinase 1 and 2 (LIMK1/2), mitogen-activated protein kinase 7 (MAPK7) and protein kinase C delta (PRKCD) activity in responder cells. An extensive effect of in vivo treatment with ATRA/VP was the altered level and phosphorylation of proteins involved in the regulation of transcription/translation/RNA metabolism, especially in non-responders, but the regulation of cell metabolism, immune system and cytoskeletal functions were also affected. Our analysis of serial samples during the first week of treatment suggest that proteomic and phosphoproteomic profiling can be used for the early identification of responders to ATRA/VP-based treatment.