Sorafenib is tolerable and improves clinical outcomes in patients with FLT3-ITD acute myeloid leukemia prior to stem cell transplant and after relapse post-transplant

FLT3 inhibitors as maintenance therapy post allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia patients with FLT3 mutations: A meta‐analysis

BACKGROUND

Acute myeloid leukemia (AML) patients with a Fms-like tyrosine kinase 3 (FLT3) mutation have a high incidence of relapse despite allogeneic hematopoietic stem cell transplantation (allo-HSCT) and a subsequent poor prognosis. FLT3 inhibitors (FLT3i) have been suggested to reduce the post-transplant relapse risk in recent studies. As more evidence is accumulated, we perform the present meta-analysis to assess the efficacy and safety of FLT3i as post-transplant maintenance therapy in AML patients.

METHODS

Literature search was performed in public databases from inception to December 31, 2021. Overall survival (OS), relapse-free survival (RFS), cumulative incidence of relapse (CIR), non-relapse mortality (NRM), graft-versus-host disease (GVHD) and adverse events were compared between FLT3i and control groups. Pooled hazard ratio (HR) or relative risk (RR) with corresponding 95% confidence interval (CI) were calculated.

RESULTS

We identified 12 eligible studies with 2282 FLT3-mutated AML patients who had received HSCT. There was no between-study heterogeneity and a fix-effect model was used. Post-transplant FLT3i maintenance significantly prolonged OS (HR = 0.41, 95%CI: 0.32-0.52, p < 0.001) and RFS (HR = 0.39, 95%CI 0.31-0.50, p < 0.001), and reduced CIR (HR = 0.31, 95%CI 0.20-0.46, p < 0.001) as compared with control. There were no significant risk differences in NRM (RR = 0.69, 95%CI 0.41-1.17, p = 0.169), acute GVHD (RR = 1.17, 95%CI 0.93-1.47, p = 0.175), chronic GVHD (RR = 1.31, 95%CI 0.91-1.39, p = 0.276) and grade ≥3 adverse events between both groups, except for skin toxicity (RR = 5.86, 95%CI 1.34-25.57, p = 0.019).

CONCLUSION

Post-transplant FLT3i maintenance can improve survival and reduce relapse in FLT3-mutated AML patients and is tolerable.

Role of Biomarkers in FLT3 AML

Simple Summary

Genetically heterogeneous disorder acute myeloid leukemia (AML) is marked by recurring mutations in FLT3. Current FLT3 inhibitors and other emerging inhibitors have helped in the improvement of the quality of standard of care therapies; however, the overall survival of the patients remains static. This is due to numerous mutations in FLT3, which causes resistance against these FLT3 inhibitors. For effective treatment of AML patients, alternative approaches are required to overcome this resistance. Here, we will summarize the biomarkers for FLT3 inhibitors in AML, as well as the alternative measures to overcome resistance to the current therapies.

Abstract

Acute myeloid leukemia is a disease characterized by uncontrolled proliferation of clonal myeloid blast cells that are incapable of maturation to leukocytes. AML is the most common leukemia in adults and remains a highly fatal disease with a five-year survival rate of 24%. More than 50% of AML patients have mutations in the FLT3 gene, rendering FLT3 an attractive target for small-molecule inhibition. Currently, there are several FLT3 inhibitors in the clinic, and others remain in clinical trials. However, these inhibitors face challenges due to lack of efficacy against several FLT3 mutants. Therefore, the identification of biomarkers is vital to stratify AML patients and target AML patient population with a particular FLT3 mutation. Additionally, there is an unmet need to identify alternative approaches to combat the resistance to FLT3 inhibitors. Here, we summarize the current knowledge on the utilization of diagnostic, prognostic, predictive, and pharmacodynamic biomarkers for FLT3-mutated AML. The resistance mechanisms to various FLT3 inhibitors and alternative approaches to combat this resistance are also discussed and presented.

Post-Transplant Maintenance Therapy for Patients with Acute Myeloid Leukemia: Current Approaches and the Need for More Trials

Relapse rates following allogeneic stem cell transplantation for acute myeloid leukemia remain unacceptably high and a major cause of death. Maintenance therapies post-transplant administered either to patients with impending relapse or at high risk of relapse could present a strategy to improve survival and overall outcomes. With the increasing use of molecular and genomic characterization of the disease, more novel therapies became available as maintenance strategies. These options were, however, hindered by excessive toxicities, mostly hematologic, especially with the use of myeloablative conditioning regimens. Several key questions have also emerged including the efficacy of these therapies, the duration of maintenance, as well as the potential modulation of the graft and the immune microenvironment. These issues are further complicated by the paucity of well-designed prospective randomized clinical trials evaluating these agents. Future directions in this field should include better risk stratification and patient selection based on assays of minimal residual disease, as well as the incorporation of novel targets and pathways of leukemogenesis. In this article, we highlight the current evidence behind the use of post-transplant maintenance therapy, the optimal patient and disease selection, as well as the challenges faced by these strategies in an area that remains quite controversial. We will focus on therapies targeting leukemia stem cells that directly or indirectly modulate the allografted immune microenvironment and augment the graft-versus-leukemia impact.

Advances in Genomic Profiling and Risk Stratification in Acute Myeloid Leukemia

OBJECTIVE

To review the current state of molecular and genetic profiling of acute myeloid leukemia (AML) and its implications.

DATA SOURCE

Peer-reviewed journal articles.

CONCLUSION

Significant advances in the understanding of the pathology of acute myeloid leukemia have led to refined risk stratification of patients and application of novel targeted therapies based on genetic profiles. Minimal residual disease testing allows for highly sensitive disease surveillance that can be used to predict relapse and assess treatment response.

IMPLICATIONS FOR NURSING PRACTICE

Accurate prognostication and therapeutic decision-making for patients with acute myeloid leukemia is dependent on molecular profiling. Being knowledgeable of the implications of minimal residual disease testing is critical for patient-centered care.

A Prospective Study of Peritransplant Sorafenib for Patients with FLT3-ITD Acute Myeloid Leukemia Undergoing Allogeneic Transplantation

FLT3-ITD-mutated acute myeloid leukemia (AML) remains a therapeutic challenge. FLT3 inhibition in the setting of minimal residual disease and a new immune system via allogeneic transplantation offers a promise of improved survival for these patients. We performed a prospective study of patients with FLT3-ITD AML undergoing allogeneic transplant that was conducted to evaluate the safety, tolerability, and outcome of sorafenib administered peritransplant. Sorafenib dosing was individualized, starting at 200 mg twice a day (BID), and titrated based on tolerability or toxicities until a tolerable dose was identified. Forty-four patients, with a median age of 52 years, undergoing allogeneic transplant were started on sorafenib in the peritransplant period (21 pretransplant). The median duration of post-transplant follow-up was 27.6 months (range, 5.2 to 60.4). Overall survival was 76% at both 24 and 36 months. Event-free survival at 24 and 36 months was 74% and 64%, respectively. Ten patients died in the post-transplant period, with 6 deaths due to relapsed leukemia and 4 from transplant-associated toxicity. Tolerable doses ranged from 200 mg every other day to 400 mg BID with similar exposure. Correlative studies evaluating FLT3 inhibition via a plasma inhibitory activity assay showed consistent inhibition of FLT3 at all tolerability-determined dosing levels. Sorafenib is well tolerated in the peritransplant setting irrespective of the conditioning intensity or the donor source. Our findings indicate that sorafenib dosing can be individualized in the post-transplantation setting according to patient tolerability. This approach results in effective in vivo FLT3 inhibition and yields encouraging survival results.

Fungal Infections with Ibrutinib and Other Small-Molecule Kinase Inhibitors

Purpose of review

Small molecule kinase inhibitors (SMKIs) have revolutionized the management of malignant and autoimmune disorders. Emerging clinical reports point toward an increased risk for invasive fungal infections (IFIs) in patients treated with certain SMKIs. In this mini-review, we highlight representative examples of SMKIs that have been associated with or are expected to give rise to IFIs.

Recent findings

The clinical use of the Bruton's tyrosine kinase inhibitor ibrutinib as well as other FDA-approved SMKIs has been associated with IFIs. The fungal infection susceptibility associated with the clinical use of certain SMKIs underscores their detrimental effects on innate and adaptive antifungal immune responses.

Summary

The unprecedented development and clinical use of SMKIs is expected to give rise to an expansion of iatrogenic immunosuppressive factors predisposing to IFIs (and other opportunistic infections). Beyond increased clinical surveillance, better understanding of the pathogenesis of SMKI-associated immune dysregulation should help devising improved risk stratification and prophylaxis strategies in vulnerable patients.

Amino alkynylisoquinoline and alkynylnaphthyridine compounds potently inhibit acute myeloid leukemia proliferation in mice

BACKGROUND

Acute myeloid leukemia (AML) remains one of the most lethal, rarely cured cancers, despite decades of active development of AML therapeutics. Currently, the 5-year survival of AML patients is about 30% and for elderly patients, the rate drops to <10%. About 30% of AML patients harbor an activating mutation in the tyrosine kinase domain (TKD) of Fms-Like Tyrosine kinase 3 (FLT3) or a FLT3 internal tandem duplication (FLT3-ITD). Inhibitors of FLT3, such as Rydapt that was recently approved by the FDA, have shown good initial response but patients often relapse due to secondary mutations in the FLT3 TKD, like D835Y and F691 L mutations.

METHODS

Alkynyl aminoisoquinoline and naphthyridine compounds were synthesized via Sonogashira coupling. The compounds were evaluated for their in vitro and in vivo effects on leukemia growth.

FINDINGS

The compounds inhibited FLT3 kinase activity at low nanomolar concentrations. The lead compound, HSN431, also inhibited Src kinase activity. The compounds potently inhibited the viability of MV4-11 and MOLM-14 AML cells with IC50 values <1 nM. Furthermore, the viability of drug-resistant AML cells harboring the D835Y and F691 L mutations were potently inhibited. In vivo efficacy studies in mice demonstrated that the compounds could drastically reduce AML proliferation in mice.

INTERPRETATION

Compounds that inhibit FLT3 and downstream targets like Src (for example HSN431) are good leads for development as anti-AML agents. FUND: Purdue University, Purdue Institute for Drug Discovery (PIDD), Purdue University Center for Cancer Research, Elks Foundation and NIH P30 CA023168.

Second allogeneic hematopoietic cell transplantation enables long-term disease-free survival in relapsed acute leukemia

Allogeneic hematopoietic cell transplantation (HCT) is the treatment of choice for high-risk myeloid and lymphoid leukemias. Relapse after allogeneic HCT is associated with a dismal prognosis and further therapeutic options are limited. One potential curative approach is a second allogeneic HCT. However, there is no consensus about optimal transplant modalities, suitable patients, and entities. We performed a retrospective analysis of our institutional database to evaluate risk factors that influence survival after a second allogeneic HCT for the treatment of relapsed acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL). We identified 40 patients (AML, n = 29; ALL, n = 11) that received a second allogeneic HCT at our institution. At time of second HCT, 48% of patients were in complete remission (CR). Current overall survival (OS) was 14/40 patients with a median follow-up of 64 months (range 4-140) of patients alive resulting in a Kaplan-Meier estimated 2-year event-free survival (EFS) and OS of 32%, respectively. Cumulative incidence of non-relapse mortality (NRM) and relapse at 2 years was 31 and 37%, respectively. We identified several independent risk factors influencing OS: > 6 months from first to second transplant (p = 0.02), complete remission prior to transplant (p = 0.003), and the subsequent occurrence of chronic graft-versus-host disease (p = 0.003) were associated with a significantly improved OS. In conclusion, our data suggest that a second allogeneic HCT is a curative treatment option for relapsed acute leukemias in selected patients.

The role of FLT3 inhibitors as maintenance therapy following hematopoietic stem cell transplant

Activating mutations in FLT3 in acute myeloid leukemia (AML) portend a poor prognosis, and targeting FLT3 with a tyrosine kinase inhibitor has been an area of intense research recently. Most FLT3 mutated AML patients undergo hematopoietic stem cell transplantation (HSCT) as standard of care but a significant proportion of patients relapse. Although the use of FLT3 inhibitors in the pre-HSCT perspective is more clearly defined, its use in the post-HSCT scenario, when most relapses occur, remains unclear. In this review, we comprehensively present the data on the recent and ongoing studies evaluating the role of various FLT3 inhibitors in AML with a particular focus in the post-HSCT setting.

Protein Kinase Inhibitors as Therapeutic Drugs in AML: Advances and Challenges

Acute myeloid leukemia (AML) is a malignant blood disorder and the cure rate has been remarkably improved over the past decade. However, recurrent or refractory leu-kemia remains the major problem of the AML and no clearly effective therapy has been es-tablished so far. Traditional treatments such as chemotherapy and hematopoietic stem cell transplantation are both far dissatisfying the patients partly for their individual variety. Be-sides, conventional treatments usually have many side effects to result in poor prognosis. Therefore, an urgent need is necessary to update therapies of AML. To date, protein kinase inhibitors as new drugs offer hope for AML treatment and many of them are on clinical tri-als. Here, this review will provide a brief summary of protein kinase inhibitors investigated in AML thus far, mainly including tyrosine protein kinase inhibitors and serine/threonine kinase inhibitors. We also presented the sketch of signal pathways involving protein kinase inhibitors, as well as discussed the clinical applications and the challenges of inhibitors in AML treatment

Sorafenib Dose Recommendation in Acute Myeloid Leukemia Based on Exposure-FLT3 Relationship

Sorafenib administered at the approved dose continuously is not tolerated long-term in patients with acute myeloid leukemia (AML). The purpose of this study was to optimize the dosing regimen by characterizing the sorafenib exposure-response relationship in patients with AML. A one-compartment model with a transit absorption compartment and enterohepatic recirculation described the exposure. The relationship between sorafenib exposure and target modulation of kinase targets (FMS-like tyrosine kinase 3 (FLT3)-ITD and extracellular signal-regulated kinase (ERK)) were described by an inhibitory maximum effect (Emax ) model. Sorafenib could inhibit FLT3-ITD activity by 100% with an IC50 of 69.3 ng/mL and ERK activity by 84% with an IC50 of 85.7 ng/mL (both adjusted for metabolite potency). Different dosing regimens utilizing 200 or 400 mg at varying frequencies were simulated based on the exposure-response relationship. Simulations demonstrate that a 200 mg twice daily (b.i.d.) dosing regimen showed similar FLT3-ITD and ERK inhibitory activity compared with 400 mg b.i.d. and is recommended in further clinical trials in patients with AML.

Arsenic Trioxide and Sorafenib Induce Synthetic Lethality of FLT3-ITD Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) with Fms-related tyrosine kinase 3 internal tandem duplication (FLT3-ITD) mutation is notoriously hard to treat. We identified two drugs that together form an effective combination therapy against FLT3-ITD AML. One of the drugs, Sorafenib, an inhibitor of FLT3-ITD and other kinase activity, produces an impressive but short-lived remission in FLT3-ITD AML patients. The second, arsenic trioxide (ATO), at therapeutically achievable concentrations, reduces the level of FLT3-ITD and Mcl-1 proteins, and induces apoptosis in leukemic cell lines and in primary cells expressing FLT3-ITD. We linked this relative sensitivity to ATO to low levels of reduced glutathione. While producing proapoptotic effects, ATO treatment also has an unwanted effect whereby it causes the accumulation of the phosphorylated (inactive) form of glycogen synthase kinase 3β (GSK3β), a kinase necessary for apoptosis. When ATO is combined with Sorafenib, GSK3β is activated, Mcl-1 is further reduced, and proapoptotic proteins Bak and Bax are activated. Mice xenografted with FLT3-ITD MOLM13 cell line treated with the Sorafenib/ATO combination have significantly improved survival. This combination has potential to improve the therapeutic outcome of FLT3-ITD-targeted therapy of AML patients. Mol Cancer Ther; 17(9); 1871-80. ©2018 AACR.

Tyrosine kinase inhibitors and immune checkpoint blockade in allogeneic hematopoietic cell transplantation

Advances in the prevention of graft-versus-host disease (GVHD) and opportunistic infection have improved survival after allogeneic hematopoietic cell transplantation (allo-HCT) in the past decade. However, few inroads have been made into the treatment or prevention of relapse of the underlying malignancy for which allo-HCT is being performed. The introduction of US Food and Drug Administration-approved agents with significant activity in a variety of hematologic malignancies provides an opportunity to evaluate these interventions in the allo-HCT setting. Some of the most promising new agents include tyrosine kinase inhibitors (TKIs) directed at bcr-abl, kinase inhibitors targeting fms-like tyrosine kinase 3, and immune checkpoint inhibitors blocking both CTLA4 and PD-1. Data have emerged indicating potential efficacy of these agents in preventing or treating relapse, though definitive evidence remains elusive. However, potential toxicity can be considerable, highlighting the need for further clinical trials to define the therapeutic window. This review explores the immunologic and clinical consequence of treatment with both TKIs and checkpoint inhibitors in the peri- and post-allo-HCT setting.

Therapeutic targeting of leukemic stem cells in acute myeloid leukemia - the biological background for possible strategies

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive malignancy, caused by the accumulation of immature leukemic blasts in blood and bone marrow. There is a relatively high risk of chemoresistant relapse even for the younger patients who can receive the most intensive antileukemic treatment. Treatment directed against the remaining leukemic and preleukemic stem cells will most likely reduce the risk of later relapse. Areas covered: Relevant publications were identified through literature searches. The authors searched for original articles and recent reviews describing (i) the characteristics of leukemic/preleukemic stem cells; (ii) the importance of the bone marrow stem cell niches in leukemogenesis; and (iii) possible therapeutic strategies to target the preleukemic/leukemic stem cells. Expert opinion: Leukemia relapse/progression seems to be derived from residual chemoresistant leukemic or preleukemic stem cells, and a more effective treatment directed against these cells will likely be important to improve survival both for patients receiving intensive treatment and leukemia-stabilizing therapy. Several possible strategies are now considered, including the targeting of the epigenetic regulation of gene expression, proapoptotic intracellular signaling, cell metabolism, telomere activity and the AML-supporting effects by neighboring stromal cells. Due to disease heterogeneity, the most effective stem cell-directed therapy will probably differ between individual patients.

How I treat FLT3-mutated AML

FLT3-mutated acute myeloid leukemia (AML), despite not being recognized as a distinct entity in the World Health Organization (WHO) classification system, is readily recognized as a particular challenge by clinical specialists who treat acute leukemia. This is especially true with regards to the patients harboring the most common type of FLT3 mutation, the internal tandem duplication (FLT3-ITD) mutation. Here we present 4 patient cases from our institution and discuss how our management reflects what we have learned about this subtype of the disease. We also reflect on how we anticipate the management might change in the near future, with the emergence of clinically useful tyrosine kinase inhibitors.

Pharmacologic maintenance strategies following allogeneic hematopoietic cell transplantation for acute myeloid leukemia

The use of pharmacologic agents to maintain remission following allogeneic hematopoietic cell transplantation (HCT) is a topic of increasing interest and exploration for patients with high-risk acute myeloid leukemia (AML). This review details published and ongoing studies focused on post-transplant pharmacologic maintenance for AML. While early phase studies have demonstrated the safety and tolerability of various maintenance approaches following HCT, the results of several ongoing randomized prospective studies will be required to determine the clinical efficacy needed to expand this approach from experimental to standard of care.

High frequency of additional gene mutations in acute myeloid leukemia with MLL partial tandem duplication: DNMT3A mutation is associated with poor prognosis

The mutational profiles of acute myeloid leukemia (AML) with partial tandem duplication of mixed-lineage leukemia gene (MLL-PTD) have not been comprehensively studied. We studied 19 gene mutations for 98 patients with MLL-PTD AML to determine the mutation frequency and clinical correlations. MLL-PTD was screened by reverse-transcriptase PCR and confirmed by real-time quantitative PCR. The mutational analyses were performed with PCR-based assays followed by direct sequencing. Gene mutations of signaling pathways occurred in 63.3% of patients, with FLT3-ITD (44.9%) and FLT3-TKD (13.3%) being the most frequent. 66% of patients had gene mutations involving epigenetic regulation, and DNMT3A (32.7%), IDH2 (18.4%), TET2 (18.4%), and IDH1 (10.2%) mutations were most common. Genes of transcription pathways and tumor suppressors accounted for 23.5% and 10.2% of patients. RUNX1 mutation occurred in 23.5% of patients, while none had NPM1 or double CEBPA mutation. 90.8% of MLL-PTD AML patients had at least one additional gene mutation. Of 55 MLL-PTD AML patients who received standard chemotherapy, age older than 50 years and DNMT3A mutation were associated with inferior outcome. In conclusion, gene mutations involving DNA methylation and activated signaling pathway were common co-existed gene mutations. DNMT3A mutation was a poor prognostic factor in MLL-PTD AML.

Haematopoietic cell transplantation with and without sorafenib maintenance for patients with FLT3-ITD acute myeloid leukaemia in first complete remission

We performed a retrospective study analysing the effect of sorafenib, an oral fms-Like Tyrosine Kinase 3 (FLT3)/multikinase inhibitor, as post-transplant maintenance in adult patients with FLT3-internal tandem duplication (ITD) acute myeloid leukaemia (AML). We identified consecutive patients with FLT3-ITD AML diagnosed between 2008 and 2014 who received haematopoietic cell transplantation (HCT) in first complete remission (CR1). Post-HCT initiation of sorafenib (yes/no) was evaluated as a time-varying covariate in the overall survival/progression-free survival (OS/PFS) analysis and we performed a landmark analysis of controls alive without relapse at the median date of sorafenib initiation. We identified 26 sorafenib patients and 55 controls. Median follow-up was 27·2 months post-HCT for sorafenib survivors, and 38·4 months for controls (P = 0·021). The median time to initiating sorafenib was 68 days post-HCT; 43 controls were alive without relapse at this cut-off. Sorafenib patients had improved 2-year OS in the d+68 landmark analysis (81% vs. 62%, P = 0·029). Sorafenib was associated with improved 2-year PFS (82% vs. 53%, P = 0·0081) and lower 2-year cumulative incidence of relapse (8·2% vs. 37·7%, P = 0·0077). In multivariate analysis, sorafenib significantly improved OS [Hazard ratio (HR) 0·26, P = 0·021] and PFS (HR 0·25, P = 0·016). There was no difference in 2-year non-relapse mortality (9·8% vs. 9·3%, P = 0·82) or 1-year chronic graft-versus-host disease (55·5% vs. 37·2%, P = 0·28). These findings suggest potential benefit of post-HCT sorafenib in FLT3-ITD AML, and support further evaluation of post-HCT FLT3 inhibition.

The Successful Complete Remission Induction by Sorafenib Monotherapy in a FLT3-D835Y-Positive Patient with Refractory Acute Monocytic Leukemia

Sorafenib has been shown to be active in AML patients with FLT3-ITD. However, the effect of sorafenib in AML patients with FLT-TKD has never been well determined. Moreover, acquisition of secondary FLT3 TKD mutations, mainly at D835 (D835F/H/V/Y), are recognized as the major mechanisms of resistance of AML patients with FLT3-ITD to sorafenib. It has been reported that sorafenib induced death of cells that expressed the FLT3-ITD or FLT3-D835G but not cells that expressed the FLT3-D835Y point mutant or wild-type FLT3 in vitro. Here, we report the successful complete remission induction by sorafenib monotherapy in a FLT3-D835Y-positive patient with refractory AML-M5 followed by allogeneic stem cell transplantation.

Allogeneic Hematopoietic Stem Cell Transplantation in FLT3-ITD-Positive Acute Myelogenous Leukemia: The Role for FLT3 Tyrosine Kinase Inhibitors Post-Transplantation

In recent years, allogeneic hematopoietic stem cell transplantation (allo-HSCT) has become increasingly common in patients with acute myelogenous leukemia (AML) due to improved donor availability and the use of nonmyeloablative regimens. However, despite the potential clinical gains with allo-HSCT, the post-transplantation outcomes for many patients, especially those with high-risk disease, remain dismal. Patients with AML who have internal tandem duplication mutations in the tyrosine kinase receptor FLT3 (FLT3-ITD) face particularly poor outcomes, even after allo-HSCT, which appears to only partially mitigate the poor prognosis associated with this mutation. Experimental treatments to reduce the likelihood of relapse and improve survival following allo-HSCT include maintenance with FLT3-specific tyrosine kinase inhibitors (TKIs), several of which are currently being evaluated in clinical studies. Preliminary data and case reports suggest that FLT3 TKIs can be effective in the post-transplantation setting, particularly for patients with FLT3-ITD mutations. Improvements in donor matching, transplantation procedures, and supportive care have allowed a greater number of patients to undergo allo-HSCT than ever before. For these patients, it is essential to identify effective post-transplantation therapies to reduce the risk of relapse and improve disease-free survival.

Novel strategies to prevent relapse after allogeneic haematopoietic stem cell transplantation for acute myeloid leukaemia and myelodysplastic syndromes

PURPOSE OF REVIEW

Relapse of haematological neoplasms after allogeneic haematopoietic stem cell transplantation (HSCT) remains one of the leading causes of death. Treatment of relapse post-HSCT is frequently ineffective and outcomes are poor, necessitating preventive strategies that are reviewed below.

RECENT FINDINGS

Current strategies to prevent relapse after HSCT are geared towards four general principles: improving the antitumour effects of conditioning regimens prior to HSCT, improving graft selection and engineering to augment the graft-versus-leukaemia effect, post-HSCT chemotherapeutic interventions to impair growth of residual clonal cells and post-HSCT immune-mediated interventions to enhance the graft-versus-leukaemia effect. Strategies based on cell manipulation, namely natural killer (NK) cell enrichment and adoptive T cell transfer, are emerging. Targeted therapies including vaccinations, FLT3 inhibitors, mAbs and chimeric antigen receptor T cell therapy represent a new avenue of treating acute myeloid leukaemia (AML) and myelodysplastic syndromes (MDS). Studies are underway to incorporate all of these strategies in the clinical setting to determine their impact on relapse and survival after HSCT.

SUMMARY

The most recent evidence suggests that strategies using NK cell therapy and targeted immune therapies after HSCT may change the current landscape of HSCT for AML and MDS.

Current Approaches in the Treatment of Relapsed and Refractory Acute Myeloid Leukemia

The limited sensitivity of the historical treatment response criteria for acute myeloid leukemia (AML) has resulted in a different paradigm for treatment compared with most other cancers presenting with widely disseminated disease. Initial cytotoxic induction chemotherapy is often able to reduce tumor burden to a level sufficient to meet the current criteria for "complete" remission. Nevertheless, most AML patients ultimately die from their disease, most commonly as clinically evident relapsed AML. Despite a variety of available salvage therapy options, prognosis in patients with relapsed or refractory AML is generally poor. In this review, we outline the commonly utilized salvage cytotoxic therapy interventions and then highlight novel investigational efforts currently in clinical trials using both pathway-targeted agents and immunotherapy based approaches. We conclude that there is no current standard of care for adult relapsed or refractory AML other than offering referral to an appropriate clinical trial.