Effect of Nilotinib (NIL) on Molecular Response in Chronic Myelogenous Leukemia - Chronic Phase (CML-CP) Patients (pts) with a Suboptimal Molecular Response to Imatinib (IM)–ENABL Study Update

NIL is a potent, highly selective Bcr-Abl kinase inhibitor approved for newly diagnosed adult pts with Philadelphia-chromosome positive (Ph+) CML-CP and in Ph+ CML-CP and accelerated-phase pts who are resistant or intolerant to IM. Achieving complete cytogenetic response (CCyR) and major molecular response (MMR, 3-log reduction of Bcr-Abl transcript level from the baseline mean) are favorable prognostic factors for CML. This multicenter, open-label study (ENABL) was designed to explore nilotinib Bcr-Abl effects in pts with CCyR but who have suboptimal molecular response to IM.

This study evaluates change in Bcr-Abl trends in 2 groups of CML-CP pts (total n = 18) who achieved CCyR but have suboptimal molecular response to IM defined as: (Group 1) treated ≥ 1 year with IM, but Bcr-Abl transcript levels did not reach ≤ 0.1% on the international scale (IS) (MMR); or (Group 2) > 1-log increase in Bcr-Abl transcript levels from best response regardless of IM treatment duration. Pts are treated with NIL 300 mg twice daily for ≥ 1 year. RQ-PCR analysis is performed by a central lab at screening, then every 3 months (mos) for Group 1. Group 2 pts are monitored by RQ-PCR monthly for the first 3 mos, then every 3 mos. The 1° end point is change in Bcr-Abl transcript levels from a standardized baseline value by RQ-PCR at 12 mos. The data cutoff date for this analysis was June 30, 2011.

Eighteen pts (Group 1, n = 17; Group 2, n = 1) have been treated with NIL for a median of 17 mos on study (range 3–34 mos). Thirteen pts have been treated for ≥ 6 mos and 10 for ≥ 12 mos. One pt was deemed ineligible due to lack of evidence of CCyR at baseline but is included in the analysis because there was at least 1 post-baseline evaluation performed. The remaining 17 pts had CCyR at baseline. Before enrollment, pts were treated with at least 400 mg once-daily IM; the mean dose of prior IM treatment was 487 mg/day (range 342–786 mg/day). Median duration of prior IM treatment was 3.4 yrs (range 1.3–10.2 yrs). Three pts had prior interferon treatment.

All 18 pts were treated for ≥ 3 mos and had ≥ 1 post-baseline RQ-PCR result. Overall, 15 of 18 evaluable pts (83%) achieved MMR during treatment; 10 pts by 3 mos, 1 pt by 4.5 mos (measured at end of study), 1 pt by 6 mos, 2 pts by 9 mos, and 1 pt by 30 mos (Figure 1). The 3 pts who did not reach MMR at any point were only followed for up to 3 mos before discontinuing from the trial but showed a decreasing Bcr-Abl trend. Overall, pts achieved a median log reduction of PCR transcript levels of 3.1 (0.08% IS) at 3 mos; median 3.3-log reduction (0.05% IS) at 6 mos, and median 3.5-log reduction (0.035% IS) at 9 mos. Four pts had > 4-log (≤ 0.01% IS) reduction in Bcr-Abl; of these, 2 pts reached > 4.5-log (≤ 0.0032% IS) reduction in Bcr-Abl at least once during the study.

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Median Bcr-Abl transcript log reduction at 12 mos was 3.6 (0.025% IS, 1° end point) for 10 evaluable pts. All these pts reached MMR during NIL treatment; 9 pts by 12 mos, 1 pt after 30 mos.

NIL was well tolerated and brief dose interruptions were sufficient to manage most adverse events (AEs). Seven of 18 pts were dose reduced for NIL-related AEs and re-escalated if the patient recovered from the AEs. Patients were permitted to dose escalate to 400 mg b.i.d. per physician's discretion if MMR was not achieved after 6 mos (n = 1). The Grade 3 AEs reported include 2 cases of rash and 1 case each of pneumonia, squamous cell carcinoma, bladder prolapse, uterine prolapse, bradycardia, hypertension, hyperbilirubinemia and hypophosphatemia. The rashes and bradycardia were suspected to be related to NIL. No Grade 4 AEs were reported. The median dose intensity was 600 mg/day (range 300–683 mg/day). Five pts were discontinued from the study (3 due to abnormal laboratory values, 1 due to an AE, and 1 due to protocol violation). No pts who experienced QTcF changes had differences > 33 msec from baseline. No QTcF prolongation > 500 msec was observed.

NIL treatment results in high molecular response rates in CML-CP pts with suboptimal molecular responses to IM. Overall 83% of pts who switched to NIL achieved MMR, and the median Bcr-Abl log reduction for pts who reached 12 mos on study was 3.6 (0.025% IS). The IRIS study has shown that MMR rates increase with time in pts treated with IM (Hughes Blood 2010); however, this study appears to demonstrate that MMR is achieved relatively quickly in suboptimal molecular IM-treated pts when switched to NIL.

Ailawadhi:Novartis Pharmaceuticals: Consultancy, Speakers Bureau. Miller:Incyte: Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau. Akard:Eisai: Speakers Bureau; Bristol Myers-Squibb: Speakers Bureau; Novartis: Speakers Bureau; Millenium: Speakers Bureau; Chemgenex: Consultancy. Ericson:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership. Lin:Novartis: Employment, Equity Ownership. Radich:Novartis: Consultancy, Research Funding, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Speakers Bureau. DeAngelo:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy.