Dactinomycin in Acute Myeloid Leukemia with NPM1 Mutations

NPM1 mutations are frequent in acute myeloid leukemia (AML) and define a distinct entity according to the 2016 WHO classification. NPM1 mutations are generally associated with chemosensitivity and a favorable prognosis. However, outcome may vary according to co-mutational events, and still approximately 40% of patients relapse after achieving complete response. Wild-type NPM1 is mainly located in the nucleolus where it plays a key role in the regulation of ribosome biogenesis, protein synthesis and tumor suppression through TP53 activation. Mutated NPM1 loses its predominant nucleolar location and accumulates in cytoplasm contributing to leukemogenesis (Falini B, Blood 2011). Moreover, this mutational event leads to haploinsufficiency and cytoplasmic retention of wild type NPM1 creating a vulnerability to nucleolar stress. Indeed, complete responses have been observed in NPM1-mutated AML patients with dactinomycin, a nucleolar stress-inducing drug (Falini B, NEJM 2015). Here, we report our experience of off-label dactinomycin in untreated or relapsed/ refractory NPM1-mutated AML.

Inclusion criteria for this retrospective study were: age ≥ 18 years-old, AML with NPM1 mutation, relapsed or refractory disease as well as treatment-naive patients unfit for intensive chemotherapy. Patients should also have completed one cycle of dactinomycin 12.5 µg/kg/day for 5 days every 28 days.

From September 2015 to February 2019, 26 patients received dactinomycin. Median age was 62.5y, WBC count was > 50 giga/L in 8 patients (31%), 13 patients (50%) had FLT3-ITD mutation whereas 10 (38%) and 11 (42%) patients were classified as favorable or intermediate-I according to the ELN-2010 classification. There were 7 (27%) relapses post-allogeneic transplantation. Median number of dactinomycin cycle was 1 (1-8) and 7 patients (27%) received more than 3 cycles. Sorafenib was added in 6 patients with associated FLT3-ITD mutations whereas 2 others patients received ATRA in combination with dactinomycin. Dactinomycin was administered in different situations: front-line treatment in 4 unfit patients (16%); morphologic (n=16, 62%) or molecular relapses (n=4, 16%) following intensive chemotherapy, refractory disease (n=1, 13%) or post remission therapy in second complete response (CR) following salvage chemotherapy (n=1, 13%).

Three out of 17 patients (18%) in morphologic relapse or refractory to chemotherapy reached complete remission after the first cycle of dactinomycin. The duration of response was 4 and 6 months in 2 patients whereas the third patient is still in CR 3 years after dactinomycin. One out of 4 patients in molecular relapses achieved a complete molecular remission with dactinomycin. None of the 4 patients unfit for intensive chemotherapy responded to dactinomycin as front-line therapy. The only patient treated in post-CR2 with dactinomycin achieved a complete molecular remission before allogeneic transplantation. Overall, 5 patients (19%) appeared to benefit from dactinomycin treatment.

Grade 3-4 adverse events were thrombocytopenia (n=11, 42%), neutropenia (n=11, 42%), GI toxicity (n=6, 23%), mucositis (n=5, 19%), lung infection (n=5, 19%) and skin rash (n=2, 7.6%).

Dactinomycin is an inexpensive and easily available drug that may induce significant responses in AML patients with NPM1 mutations with an acceptable safety profile. Prospective and controlled clinical trials are mandatory to clearly define the role of this agent in AML with NPM1 mutations.