Acute myeloid leukemia (AML) is a heterogenous disease associated with distinct genetic and molecular abnormalities. Somatic mutations result in dysregulation of intracellular signaling pathways, epigenetics, and apoptosis of the leukemia cells. Understanding the basis for the dysregulated processes provides the platform for the design of novel targeted therapy for AML patients.
The effort to devise new targeted therapy has been helped by recent advances in methods for high-throughput genomic screening and the availability of computer-assisted techniques for the design of novel agents that are predicted to specifically inhibit the mutant molecules involved in these intracellular events. In this review, we will provide the scientific basis for targeting the dysregulated molecular mechanisms and discuss the agents currently being investigated, alone or in combination with chemotherapy, for treating patients with AML. Successes in molecular targeting will ultimately change the treatment paradigm for the disease.
Despite the advance of modern chemotherapy, the prognosis of patients with acute myeloid leukemia (AML) has remained poor and little progress has been made that improves long term outcome of these patients. For more than four decades since the combination of an anthracycline and cytarabine was first used for induction therapy, the “3 + 7” regimen has remained the standard therapy for AML. The long term disease-free survival of AML patients under age 60 remains around 40% , with minimal improvement over the past several decades, suggesting that the gains from conventional chemotherapy may have been maximized. New approaches are, therefore, needed if further improvement in the outcome for AML patients is desired.
AML is a clonal malignancy associated with a wide-spectrum of genetic alterations. In addition to well-described chromosomal abnormalities, a multitude of mutations occur and they contribute to AML pathogenesis, either due to their effects of tumor suppressor genes or as drivers of intracellular oncologic signaling pathways or modifiers of epigenetics. The magnitude and frequency of these abnormalities, and their pathologic implications, were not fully appreciated until the last decade as novel techniques for the analysis of whole genome sequencing have become available.
The molecular events associated with AML have long been used to predict prognosis . With an expanding understanding of the molecular genetic alterations underlying AML pathogenesis, recent efforts have concentrated on specific targeting of intracellular events driven by these abnormal proteins. Molecular targeting is a particularly attractive therapeutic approach for several reasons. First, the therapeutic efficacy of molecular targeting may complement the benefits provided by conventional chemotherapy. Second, the approach may be more specific to each patient’s molecular landscape and minimize systemic toxicity. Third, it may offer an increased likelihood of eradication of the malignant clones that drive the disease and often being responsible for disease relapse.
Here we will review the intracellular mechanisms and pathways that provide the platforms for molecular targeting in AML. Specifically, we will discuss therapies targeting FMS-like tyrosine kinase 3 (FLT3) and pathways associated with DNA methyltransferase (DNMT)3A, ten-eleven-translocation (TET)2, and IDH (isocitrate dehydrogenase) 1/2. We will also summarize the current status of utilizing histone deacetylase (HDAC), bromodomain and extra terminal (BET), and disruptor of telomeric silencing 1-like (DOT1L) inhibitors in AML. Finally, we will discuss the role of therapies targeting the anti-apoptotic protein, BCL (B-cell lymphoma)-2, as it has recently been shown that IDH1/2 mutation status may identify patients who are most likely to respond to therapeutic inhibition of BCL-2 . Since molecular therapy of the promyelocytic leukemia-retinoic acid receptor alpha (PML-RARα) in acute promyelocytic leukemia (APL) is well-established, we will limit our review to novel agents for non-APL AML. This review is not meant to be an exhaustive discussion of all emerging agents. Instead we will summarize the results of some of the clinical studies carried out so far.