Impact Of Baseline (BL) Mutations, Including Low-Level and Compound Mutations, On Ponatinib Response and End Of Treatment (EOT) Mutation Analysis In Patients (Pts) With Chronic Phase Chronic Myeloid Leukemia (CP-CML)

In CML, the presence of BCR-ABL kinase domain (KD) mutations, including low-level mutations, can predict clinical responses to 2^nd line BCR-ABL tyrosine kinase inhibitors (TKIs). In addition, sequential treatment with TKIs can lead to development of compound mutations (≥2 mutations in the same BCR-ABL allele) that can be highly TKI-resistant. Ponatinib is a potent BCR-ABL TKI that, preclinically, has demonstrated activity against all BCR-ABL mutations tested and suppresses the emergence of any single mutation at clinically achievable concentrations (40 nM with ≥30 mg/d). In vitro, higher ponatinib concentrations were required to suppress emergence of certain compound mutations on a background of T315I or E255V single mutations. We evaluated the impact of single, low-level, and compound mutations at BL on responses to ponatinib and EOT mutations in CP-CML pts in the phase 2 PACE trial.

Pts with CP-CML (93% received ≥2 prior TKIs, 60% ≥3) resistant or intolerant to dasatinib and/or nilotinib (N=203) or with T315I confirmed at BL (N=64) were enrolled. The primary endpt was major cytogenetic response (MCyR) by 12 mos. Median follow-up at analysis (1 Apr 2013) was 20 (0.1-28) mos, with a minimum follow-up of 18 mos for pts remaining on study. Next generation sequencing (NGS) and Sanger sequencing (SS) were done at a central laboratory. NGS was conducted on all BL samples (N=267) with the Ion Torrent PGM using chemistry that enabled read lengths up to 400 bp for detection of compound mutations; mutations observed at a frequency ≥1% are reported. SS was conducted on both BL and EOT samples.

By NGS at BL, 267 mutations (amino acid substitutions in the ABL KD [M237-E507]) were detected among 163 (61%) pts; 106 (40%) mutations were low level mutations not detected by SS. 75 unique single mutations were observed: 27 were detected by SS and NGS, all 27 have been associated with resistance to TKIs other than ponatinib; 48 were low level mutations detected only by NGS, 5 have been associated with resistance to TKIs other than ponatinib. 12% of pts had only low level mutations. Overall, no mutations were detected in 39% of pts, 1 mutation in 37%, and ≥2 mutations in 24%. Compound mutations were detected in 65% of pts who had ≥2 mutations, representing 15% of pts overall (10% with 1, 5% with 2 to 4 compound mutations). 48 unique compound mutations were observed; T315I, F317L, and F359C/I/V were the most commonly observed mutations within compound mutations.

Responses were seen in pts with each of the 20 unique single mutations present in >1 pt at BL by NGS, including Y253H, E255V/K, T315I, M351T, F359V. Responses were observed regardless of overall NGS BL mutation status (table). The high response rates and durability of response in pts with compound mutations suggest that, in general, the presence of compound mutations at BL did not adversely affect the activity of ponatinib.

Of the 109 pts who discontinued, 84 had successful mutation assessments by SS at or near the EOT visit. 4 pts had mutations at EOT that were not detected by NGS at BL; all 4 involved compound mutations (T315I/F359V [100%/90%], T315I/M351T [100%/40%], Y253H/F359V [100%/100%; n=2]), with one or both of the involved mutations detected individually at BL or by history. Overall, 12 pts lost MCyR (none with T315I at BL); 6 of the 12 discontinued and had EOT mutations assessed, no changes from BL were observed.

Responses to ponatinib were observed regardless of BL mutation status. Interestingly, responses tended to be lower in pts without mutations, suggesting that BCR-ABL independent mechanisms may be involved. No single mutation conferring resistance to ponatinib in CP-CML has been observed to date. In general, ponatinib activity was not adversely affected by the presence of compound mutations at BL. Rarely, the development of compound mutations was observed at EOT in pts with one of the involved mutations at BL or by history. Early introduction of ponatinib may suppress the emergence of single BCR-ABL mutations, and, as a result, the development of compound mutations. NCT01207440

Deininger:BMS, ARIAD, NOVARTIS: Consultancy; BMS, NOVARTIS, CELGENE, GILEAD: Research Funding; ARIAD, NOVARTIS: Advisory Boards, Advisory Boards Other. Shah:Ariad, Bristol-Myers Squibb: Consultancy, Research Funding. Cortes:Ariad, Pfizer, Teva: Consultancy; Ariad, BMS, Novartis, Pfizer, Teva: Research Funding. Kim:BMS, Novartis, IL-Yang: Consultancy; BMS, Novartis, Pfizer, ARIAD, IL-Yang: Research Funding; BMS, Novartis, Pfizer, IL-Yang: Honoraria; BMS, Novartis, Pfizer: Speakers Bureau; BMS, Pfizer: Membership on an entity’s Board of Directors or advisory committees. Nicolini:Novartis, ARIAD, Teva: Consultancy; Novartis, BMS: Research Funding; Novartis, BMS, Teva, Pfizer, ARIAD: Honoraria; Novartis, BMS, TEva: Speakers Bureau; Novartis, ARIAD, Teva, Pfizer: Membership on an entity’s Board of Directors or advisory committees. Talpaz:Ariad, BMS, Sanofi, INCYTE: Research Funding; Ariad, Novartis: Speakers Bureau; Ariad, Sanofi, Novartis: Membership on an entity’s Board of Directors or advisory committees. Baccarani:ARIAD, Novartis, BMS: Consultancy; ARIAD, Novartis, BMS, Pfizer, Teva: Honoraria; ARIAD, Novartis, BMS, Pfizer, Teva: Speakers Bureau. Muller:Novartis, BMS, ARIAD: Consultancy; Novartis, BMS: Research Funding; Novartis, BMS, ARIAD: Honoraria. Lustgarten:ARIAD: employees of and own stock/stock options in ARIAD Pharmaceuticals, Inc Other, Employment. Clackson:ARIAD: employees of and own stock/stock options in ARIAD Pharmaceuticals, Inc Other, Employment. Turner:ARIAD: Employment. Haluska:ARIAD: employees of and own stock/stock options in ARIAD Pharmaceuticals, Inc Other, Employment. Hodgson:ARIAD: Employment, Equity Ownership. Rivera:ARIAD: Employment, Equity Ownership. Goldman:ARIAD: Honoraria. Kantarjian:ARIAD, Novartis, BMS, Phizer: Research Funding. Soverini:Novartis, BMS, ARIAD: Consultancy. Hochhaus:Ariad, Novartis, BMS, MSD, Pfizer: Research Funding; Novartis, BMS, Pfizer: Honoraria. Hughes:Novartis, BMS, ARIAD: Honoraria, Research Funding. Branford:Novartis, BMS, ARIAD: Research Funding; Novartis, BMS, ARIAD: Honoraria.