High and Early Rates of Cytogenetic and Molecular Response with Nilotinib 800 Mg Daily as First Line Treatment of Ph-Positive Chronic Myeloid Leukemia in Chronic Phase: Results of a Phase 2 Trial of the GIMEMA CML Working Party

Imatinib (IM) 400 mg daily is the standard treatment for chronic myeloid leukemia in early chronic phase (ECP): the results of the IRIS trial have shown a 72 months overall survival of 95%; EFS and PFS were 83% and 93%, respectively; the cumulative rate of complete cytogenetic response (CCgR) for the IM 400 mg arm was 25% at 3 months (at 6, 12, 18 and 60 months it was 51%, 69%, 76% and 87%, respectively). Nilotinib, a second generation TKI, has a higher binding affinity and selectivity for Abl with respect to IM, being 20 to 50 times more active in IM-sensitive cell lines and is highly effective in IM resistant patients, across every disease phase. To investigate the therapeutic efficacy and the safety of nilotinib 400 mg BID in untreated, ECP, Ph-pos CML patients, the italian GIMEMA CML Working Party is conducting an open-label, single stage, multicentric, phase II study trial (ClinicalTrials.gov. NCT00481052); all patients provided written informed consent. The primary endpoint is the CCgR rate at 1 year; the kinetic of molecular response is studied by Q-PCR baseline and after 1, 2, 3, 6, 9 and 12 months from treatment start. PATIENTS Seventy-three patients have been enrolled from 20 Centres between June, 2007 and February, 2008. The median age was 51 years (range 18–83), 45% low, 41% intermediate and 14% high Sokal risk. Median follow-up is currently 210 days (range 68–362).

RESULTS All 73 patients and 48/73 (66%) completed 3 and 6 months on treatment, respectively. Response at 3 and 6 months (ITT): the CHR rate was 100% and 98%, the CCgR rate 78% and 96%, respectively. A MMR, defined as a BCR-ABL:ABL ratio < 0.1% according to the International Scale, was achieved by 3% of all treated patients after 1 month on treatment, but this proportion rapidly increased to 22% after 2 months, 59% after 3 months and 74% after 6 months. One patient progressed at 6 months to accelerated-blastic phase with the T315I mutation. NILOTINIB DOSE AND COMPLIANCE No dose escalation was permitted in case of resistance; the median daily average dose was close to the intended dose, 789 mg (range 261 – 800); 34/73 patients (47%) interrupted nilotinib at least once, with a median duration of dose interruption of 15 days (range 2–98). The dose of nilotinib at the last visit was 400 mg BID for 52 patients (71%), 400 mg daily for 20 patients (27%) and 200 mg daily for 1 patient (1%).

ADVERSE EVENTS: AEs (grade III/IV) were manageable with appropriate dose adaptations: hematologic toxicity was recorded so far in 4 pts (5% - only 1 event grade IV neutropenia); the most frequent biochemical laboratory abnormalities (grade III) were total bilirubin increase (15%), GOT/GPT increase (11%) and lipase increase (4%). Only 1 episode of grade IV lipase increase was recorded. It is noteworthy, considering the 48 cases with at least 6 months of follow-up, that the incidence of any grade II and III nonhematologic adverse event, decreased from 50% and 8% (first 3 months) to 23% and 6% (second trimester), respectively. ECG monitoring: in 16 patients (22%), transient and not clinically relevant ECG abnormalities have been recorded; 2 more patients (3%) revealed a transient and uneventful QTc prolongation (>450 but <499 msec).

CONCLUSIONS: The results that have been achieved in these unselected patients and within a multicentric trial, strongly support the notion that in ECP Ph-pos CML patients both cytogenetic and molecular responses to nilotinib are substantially faster than the responses to IM. Acknowledgments: Work supported by European LeukemiaNet, COFIN, University of Bologna and BolognAIL.