First Line Treatment with Nilotinib 800 Mg Daily Results In Unprecedentedly High Rate of Rapid, “Deep” and Stable Molecular Responses as Assessed by a High Sensitive Nanofluidic Array for the Detection of Rare Copies of BCR-ABL1 Transcript: Results of a Phase 2 Trial of the GIMEMA CML Working Party.

Treatment strategies based on second generation tyrosine kinase inhibitors such as Nilotinib, have improved overall chronic myeloid leukemia (CML) treatment results, with a rapid and major molecular remission (MCR), at 12 months rate ranging 75%. Therefore, the detection of residual leukemic cells by measuring BCR-ABL1 transcript level is absolutely required to monitor minimal residual disease. To investigate the molecular therapeutic efficacy of nilotinib 400 mg BID in previously untreated, ECP, Philadelphia-positive CML patients, the Italian GIMEMA CML Working Party is conducting an multicenter phase II study (ClinicalTrials.gov NCT00481052). The primary endpoint is the CCgR rate at 1 year. The kinetic of molecular response is being studied by Q-PCR at baseline and after 1, 2, 3, 6, 9, 12, 18 and 24 months from treatment start by a TaqMan absolute quantitative PCR (Applied Biosystems 7900HT Fast Real-Time PCR System) and by the 12.765 Digital array (Fluidigm) which is is a nanofluidic biochip consisting in twelve panels, each containing 765 individual reaction chambers of 6 nL volume. Fluidigm analysis was done in parallel on same samples (at diagnosis,1, 2, 3, 6, 9, 12, and were possible at 18 and 24 months). Patient with longest follow up was 727 days. A Major Molecular Response, defined as a BCR-ABL:ABL ratio <0.1% according to the International Scale, and obtained by conventional RT-PCR was already achieved in 52% at 3 months, 66% at 6 months 73% at 9 months and 85% at 12 months. The median BCR-ABL transcripts level at 3, 6, 9 and 12 months was 0.063, 0.018, 0.018 and 0.006, respectively. On 73 patients with the longest follow up, a complete molecular response (CMR) defined as a BCR-ABL:ABL ratio <0.0032%IS and a negative nested PCR, was achieved in 7 patients at 12 months. The log-reduction in BCR-ABL/ABL level at 3 months was predictive of the probability of MMR at 12 months. Probability to obtain a MMR at 12 months was of 42%, 62% and 95%, respectively. The molecular results achieved in our study strongly support the notion that in early chronic phase CML patients molecular responses to nilotinib are substantially faster and “deeper” than those to IM. More rapid reduction of residual disease might help to reduce failures and to improve the late outcome of therapy.