Type I interferons (IFN) – IFN-α and IFN-β, which share the same receptor (Platanias, 2005) – have antiproliferative activity in vitro against acute myeloid leukaemia (AML) cell lines, e.g. K562, HL-60, U937 (Geng et al, 1995; Benjamin et al, 2007; Zhang et al, 2007). IFN-α has been investigated for the treatment of AML, where it had modest effects (Rohatiner et al, 1983). Preclinical studies revealed that a continuous exposure to type I IFN was required to durably suppress AML. Enforced constitutive expression of type I IFN suppressed the malignant behaviour of K562 (Geng et al, 1995). IFN-α inhibited proliferation and induced apoptosis of U937 in a dose- and time-dependent fashion (Zhang et al, 2007). In a mouse xenograft model, proliferation of HL-60 and of primary human AML cells was inhibited only when there was continuous stable expression of type I IFN (Benjamin et al, 2007). Subcutaneous or intravenous injections had no antileukaemic effect and were not associated with detectable or stable plasma levels of type I IFN. This can be accounted for by the short half-life of IFN and provides an explanation for the dichotomy between the marked antileukaemic effects of IFN-αin vitro and the disappointing effects in AML patients in vivo.
The polyethylene glycol-conjugated (pegylated) formulation of IFN-α allows for stable continuous release of IFN, resulting in improved therapeutic efficacy and fewer side effects (Matthews & McCoy, 2004). Pegylated IFN-α-2a (Peg-IFN-α-2a) has a high therapeutic activity in the chronic phase of the myeloproliferative neoplasms polycythemia vera (Kiladjian et al, 2008) and primary myelofibrosis (PMF) (Ianotto et al, 2009), higher than its non-pegylated counterpart. We report here on the induction of complete remission by Peg-IFN-α-2a of AML occurring in transformed PMF.
The diagnosis of a PMF type myeloproliferative neoplasm was made in 1994 in a 49-year-old man. In 2006, a control marrow examination demonstrated worsening of myelofibrosis, but no signs of AML. There were no BCR/ABL1 fusion transcripts or JAK2 V617F mutation. In 2008, blood and marrow demonstrated evolution to AML (Figs 1 and 2A) with a CD45low CD117+ CD34+/− CD33+ CD13+ immunophenotype. Intensive polychemotherapy and allogeneic stem cell transplantation were turned down by the patient. After informed consent, a treatment with Peg-IFN-α-2a (Pegasys®; Roche, Basel, Switzerland) was initiated.
Figure 1 summarises the clinical evolution. After 5 months of treatment, marrow analysis showed complete remission of AML (Fig 1B). This finding was confirmed by marrow histology, which revealed suppression of myeloid cell proliferation and CD34+ myeloblast infiltration (Fig 2). The AML-associated FLT3 D835 point mutation, which appeared at leukaemic transformation, was no longer demonstrable after starting Peg-IFN-α-2a (Fig 1B). Wilms tumour WT1 mRNA, a tumour marker in AML (Ogawa et al, 2003), that sharply increased at leukaemic transformation, decreased significantly during treatment (Fig 1A), confirming the antileukaemic activity of Peg-IFN-α-2a. At more than 10 months of follow-up and while on a maintenance dose of 180 μg/week, the patient is alive and well with peripheral blood counts indicative of continued complete remission of AML.
The dose of Peg-IFN-α-2a was determined on a pragmatic basis by taking into account blood and marrow findings. A weekly dose of 180 μg of Peg-IFN-α-2a usually results in stable serum IFN-α concentrations of around 25 ng/ml, corresponding to 6000 iu/ml (Matthews & McCoy, 2004). An antileukaemic effect is reached in vitro at concentrations of 1000–4000 iu/ml (Zhang et al, 2007) and in vivo at 3000 iu/ml (Benjamin et al, 2007). In general, the treatment was well tolerated, there were no infections and there was no need for hospitalisation. Three weeks after starting Peg-IFN-α-2a, the patient had mild transient arthralgias. Sporadic complaints of fatigue and palpitations were related to anaemia as they disappeared after transfusions. The loss of around 10% of the body weight, that started 3 months before the diagnosis of AML, presumably as a result of the leukaemic transformation, stopped 2 weeks after initiating Peg-IFN-α-2a.
As AML occurred while the patient was on hydroxycarbamide and this drug was stopped before reaching remission, there is little doubt that antileukaemic activity was brought about by Peg-IFN-α-2a. The antileukaemic effect of Peg-IFN-α-2a was considerably more pronounced than the limited clinical results of non-pegylated IFN-α in a small minority of AML patients (Rohatiner et al, 1983). This is congruent with the preclinical xenograft model, where control of AML was not obtained with subcutaneous or intravenous injections of type I IFN, which did not lead to stable plasma levels of IFN (Benjamin et al, 2007). They are also in sharp contrast to the failure to reach complete remission in any of the PMF patients in AML transformation treated with standard conventional chemotherapy (Mesa et al, 2005). Median survival time from diagnosis was 2·6 months and chemotherapy in this group of patients was associated with a 33% mortality rate.
The mechanisms by which IFN controls AML have been studied. Type I IFN induced JAK-1 and STAT-1 phosphorylation in HL-60 cells in vitro (Benjamin et al, 2007), compatible with IFN-mediated signalling (Platanias, 2005). There was increased apoptosis of AML cell lines in vitro and in the xenograft model in vivo following continuous exposure to type I IFN (Geng et al, 1995; Benjamin et al, 2007; Zhang et al, 2007). In general, type I IFNs induce apoptosis in different cell types through activation of IFN-stimulated response elements (ISRE) found in promoters of genes linked to apoptosis and/or antiviral immunity (Platanias, 2005). IFN-α treatment of leukaemic cells led to decreased cyclin E expression (Zhang et al, 2007) and to cell cycle arrest in S-phase (Geng et al, 1995), inhibiting cell proliferation.
In conclusion, this is the first report on the successful treatment of a poor prognosis AML using Peg-IFN-α-2a, without major side effects, hospital admission and/or administration of aggressive chemotherapy. It is the clinical proof-of-principle that Peg-IFN-α-2a not only has activity in the chronic phase of myeloproliferative neoplasms but also in acute myeloid malignancy. The low toxicity seen in this study supports conducting clinical trials in order to assess the place of Peg-IFN-α-2a in the treatment of primary AML and of AML transformation of myeloproliferative neoplasms.