Novel Strategies to Treat Children with Refractory or Relapsed Acute Myeloid Leukemia

Background AML is an aggressive disease. Current pediatric protocols ensure a 60% survival rate (Pession A et al, Blood 2013), reaching a plateau of intensiveness. Nevertheless, patients with primary induction failure (PIF) (10%) or relapse (30%) after stem cell transplantation (SCT) still have a very poor outcome. Novel therapeutic strategies are needed.

Case 1. In January 2013, a 13 year-old female with FAB-M1-AML, presenting with chromosome 11 monosomy, was enrolled on AIEOP-AML-2002/01 protocol (Pession A et al, Blood 2013) and showed a PIF after two cycles of induction phase. Leukemic blasts arose in a low peripheral blood cell (PBC) count, even in response to second line treatment (I-BFM-AML-relapse2001 protocol). A third line experimental therapy, azacitidine (AZA) and rapamycin, failed to induce remission. Low PBC count with blasts still remained. Based on a bright expression of CD117/cKit, detected by flow cytometry, we designed a salvage therapy with AZA (75mg/mq/day for 7 days, every 21 days), in association with Imatinib Mesylate (375 mg/mq/day). We observed an increase of PBC count, with rapid disappearance of blasts. After two courses of AZA-Imatinib, the patient achieved complete remission. Subsequently she underwent SCT from an unrelated donor (UD) (Nov/2013). Nine months later, immune-suppressive therapy was withdrawn and we confirmed complete remission with a 100% donor engraftment. She is currently alive and in remission. Case 2. In October 2013, a 13 year-old male with FAB-M5-AML, presenting with a complex karyotype and specific molecular markers (FLT3-ITD and NSD1-NUP98), was enrolled on AIEOP-AML-2002/01 protocol. He achieved complete remission after induction phase. Nearby SCT-UD program, he presented colonization with two multi-resistant-gram-negative bacteria. For this reason, he was shifted to a haplo-identical SCT program. He received two haplo-SCT from his mother (April/2014) and his father (June/2014) respectively, after which he showed a bone marrow relapse (Sept/2014). Based on his low performance status, we designed a salvage therapy with cytosine arabinoside (100 mg/day i.v. in a total 8-days/cycle) Sorafenib (600 mg/day orally, already started before the first haplo-SCT), in association with PEG-Asparaginase (Oncaspar) at 3500 UI/i.v. weekly for 4 administrations. Surprisingly we observed an increasing signs of cutaneous grade II graft-versus-host-disease (GVHD), confirmed by flow cytometry analysis (high T-cell suppressors/NK cells), consistently with an increasing rate of donor's DNA (Dec/2014). Therefore, after a second cycle, the patient achieved the complete remission (Jan/2015) and a third haplo-SCT (Feb/2015) was given, using NK-alloreactive donor cells from his mother. Currently, the patient is alive and in complete remission with 100% donor.

Conclusion. Our experience suggests that innovative combinational therapies are able to rescue patients with PIF or relapsed AML after SCT, the worst candidates. Association of a tyrosine kinase inhibitor with a demethylating agent showed a synergistic effect on leukemic blasts. More interestingly, PEG-LASP combined an anti-leukemic effect to an immune-modulation on donor's lymphocytes, as shown by immunophenotypic analyses.