New strategies in acute promyelocytic leukemia: moving to an entirely oral, chemotherapy-free upfront management approach

Therapeutic Approaches for Acute Promyelocytic Leukaemia: Moving Towards an Orally Chemotherapy-Free Era

The treatment of acute promyelocytic leukaemia (APL) has evolved dramatically over the past several decades, making the disease a highly curable form of acute leukaemia. The discoveries of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) were landmark events, leading to historic revolutions in the treatment of APL. One major change was from chemotherapy-based to chemotherapy-free treatment regimens, and the combination of ATRA plus ATO without chemotherapy has been recommended as the standard therapy for non-high-risk APL. The other major change was from the intravenous administration of medicine in the hospital to a largely home-based oral approach, which is a more cost-effective and convenient treatment model. In this review, we focus on the evolution of therapeutic approaches for APL, as well as the challenges that remain with the current approaches.

Retinoic acid and arsenic trioxide induce lasting differentiation and demethylation of target genes in APL cells

Acute promyelocytic leukemia (APL) is characterized by arrested differentiation of promyelocytes. Patients treated with all-trans retinoic acid (ATRA) alone experience relapse, while patients treated with ATRA and arsenic trioxide (ATO) are often relapse-free. This suggests sustained changes have been elicited by the combination therapy. To understand the lasting effects of the combination therapy, we compared the effects of ATRA and ATO on NB4 and ATRA-resistant NB4-MR2 APL cells during treatment versus post treatment termination. After treatment termination, NB4 cells treated with ATRA or ATO reverted to non-differentiated cells, while combination-treated cells remained terminally differentiated. This effect was diminished in NB4-MR2 cells. This suggests combination treatment induced more permanent changes. Combination treatment induced higher expression of target genes (e.g., transglutaminase 2 and retinoic acid receptor beta), which in NB4 cells was sustained post treatment termination. To determine whether sustained epigenetic changes were responsible, we quantified the enrichment of histone modifications by chromatin immunoprecipitation, and CpG methylation by bisulfite-pyrosequencing. While ATRA and combination treatment induced similar histone acetylation enrichment, combination treatment induced greater demethylation of target genes, which was sustained. Therefore, sustained demethylation of target genes by ATRA and ATO combination treatment is associated with lasting differentiation and gene expression changes.

The simpler, the better: oral arsenic for acute promyelocytic leukemia

Arsenic trioxide and all-trans retinoic acid have become the frontline treatments for patients with acute promyelocytic leukemia (APL). Despite the long wait for an oral arsenic drug, a commercially available agent, realgar-indigo naturalis formula (RIF), was not launched in China until 2009. Since then, over 5000 APL patients have been treated with oral RIF in China. Oral arsenic not only shows a clinical efficacy comparable to that of IV formulations but also displays a better safety profile, improved quality of life, and lower medical costs for patients. The promising results promote incorporating an outpatient postremission therapy model into clinical practice for both low-risk and high-risk APL patients in China. In this review, we discuss the evolution of oral arsenic RIF in the treatment of APL, with a special focus on how to address the related complications during induction therapy.

Natural variation in C. elegans arsenic toxicity is explained by differences in branched chain amino acid metabolism

We find that variation in the dbt-1 gene underlies natural differences in Caenorhabditis elegans responses to the toxin arsenic. This gene encodes the E2 subunit of the branched-chain α-keto acid dehydrogenase (BCKDH) complex, a core component of branched-chain amino acid (BCAA) metabolism. We causally linked a non-synonymous variant in the conserved lipoyl domain of DBT-1 to differential arsenic responses. Using targeted metabolomics and chemical supplementation, we demonstrate that differences in responses to arsenic are caused by variation in iso-branched chain fatty acids. Additionally, we show that levels of branched chain fatty acids in human cells are perturbed by arsenic treatment. This finding has broad implications for arsenic toxicity and for arsenic-focused chemotherapeutics across human populations. Our study implicates the BCKDH complex and BCAA metabolism in arsenic responses, demonstrating the power of C. elegans natural genetic diversity to identify novel mechanisms by which environmental toxins affect organismal physiology.

Editorial note: This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Therapy-related myelodysplastic syndrome after successful treatment of acute promyelocytic leukemia: case report and literature review

In the 2016 revision of the World Health Organization classification the term therapy-related myeloid neoplasia (t-MN) defines a subgroup of acute myeloid leukemia (AML) comprising patients who develop myelodysplastic syndrome (MDS-t) or acute myeloid leukemia (AML-t) after treatment with cytotoxic and/or radiation therapy for various malignancies or autoimmune disorders. We report the case of a 36 year old patient with t-MN (t-MDS) after achieving complete remission (CR) of a PML-RARA positive acute promyelocytic leukemia (APL) at 32 months after diagnosis. Initially classified as low risk APL and treated according to the AIDA protocol - induction and 3 consolidation cycles - the patient achieved a complete molecular response in September 2013 and started maintenance therapy. On follow-up PML-RARA transcript remained negative. In January 2016 leukopenia and thrombocytopenia developed and a peripheral blood smear revealed hypogranular and agranular neutrophils. Immunophenotyping in the bone marrow aspirate identified undifferentiated blast cells that did not express cytoplasmic myeloperoxidase. The cytogenetic study showed normal karyotype. The molecular biology tests not identified PMLRARA transcript. A diagnosis of t-MDS (AREB-2 - WHO 2008) was established. Treatment of AML was started with 2 “3+7” regimens and 1 MEC cycle. Two months from diagnosis, while in CR, an allogeneic HSCT from an unrelated HLA compatible donor was performed after myeloablative regimen. An unfavorable clinical evolution was followed by death on day 9 after transplantation. The occurrence of t-MNs during CR of APL represents a particular problem in terms of follow-up and differential diagnosis of relapse and constitutes a dramatic complication for a disease with a favorable prognosis.

This work was supported by the grants PN 41-087 /PN2-099 from the Romanian Ministry of Research and Technology

Fighting against hematological malignancy in China: from unique system to global impact

During recent decades, substantial progress has been made in clinical strategies for treating hematological malignancies. Not only did China benefit from the global progression in the management of acute promyelocytic leukemia, risk-stratification-directed strategies for acute or chronic leukemia and haploidentical hematopoietic stem cell transplantation, the unique system developed by Chinese doctors has also become inspiration for refining global clinical practice. The multicenter trials and collaborations adhering to international standards might further strengthen the global impact and lead the way in specific fields of research worldwide.

Acute promyelocytic leukemia: where did we start, where are we now, and the future

Historically, acute promyelocytic leukemia (APL) was considered to be one of the most fatal forms of acute leukemia with poor outcomes before the introduction of the vitamin A derivative all-trans retinoic acid (ATRA). With considerable advances in therapy, including the introduction of ATRA initially as a single agent and then in combination with anthracyclines, and more recently by development of arsenic trioxide (ATO)-containing regimens, APL is now characterized by complete remission rates of 90% and cure rates of ∼80%, even higher among low-risk patients. Furthermore, with ATRA-ATO combinations, chemotherapy may safely be omitted in low-risk patients. The disease is now considered to be the most curable subtype of acute myeloid leukemia (AML) in adults. Nevertheless, APL remains associated with a significant incidence of early death related to the characteristic bleeding diathesis. Early death, rather than resistant disease so common in all other subtypes of AML, has emerged as the major cause of treatment failure.

Real-life experience of a brief arsenic trioxide-based consolidation chemotherapy in the management of acute promyelocytic leukemia: favorable outcomes with limited anthracycline exposure and shorter consolidation therapy

BACKGROUND

Anthracyclines have activity against acute promyelocytic leukemia (APL) but can cause cardiac toxicity and secondary malignancy. The all-trans retinoic acid (ATRA)-arsenic trioxide (ATO) combination is an effective noncytotoxic approach for APL. However, its efficacy against high-risk APL (white blood cell count > 10,000/μL) has not been documented. Also, it requires ≥ 8 months to complete therapy.

PATIENTS AND METHODS

We report a retrospective analysis of 63 patients with APL given one cycle of ATO-based consolidation chemotherapy.

RESULTS

The 5-year overall survival, event-free survival, and leukemia-free survival was 93% (95% confidence interval [CI], 82%-97%), 89% (95% CI, 77%-95%), and 92% (95% CI, 80%-97%), respectively.

CONCLUSION

These data have confirmed that an abbreviated ATO-based chemotherapy regimen is an effective consolidation therapy for APL, including high-risk APL, and can be completed within 4 months.