Dissecting the Complexity of Philadelphia-Positive Mutated Populations by Ultra-Deep Sequencing of the Bcr-Abl Kinase Domain: Biological and Clinical Implications
Authors: Soverini Simona , De Benedittis Caterina , Polakova Katerina Machova , Brouckova Adela , Castagnetti Fausto , Papayannidis Cristina , Gugliotta Gabriele , Palandri Francesca , Klamova Hana , Iacobucci Ilaria , Venturi Claudia , Cattina Federica , Bresciani Paola , Coluccio Valeria , Salvucci Marzia , Tiribelli Mario , Binotto Gianni , Intermesoli Tamara , Luppi Mario , Bochicchio Maria Teresa , Ottaviani Emanuela , Russo Domenico , Rosti Gianantonio , Baccarani Michele , Martinelli Giovanni 
Published: October 2019

Abstract
Abstract 692

Background and Aims:
In chronic myeloid leukemia (CML) and Philadelphia-positive acute lymphoblastic leukemia (ALL), tyrosine kinase inhibitor (TKI) therapy may select for drug-resistant Bcr-Abl mutants. Mutation status of resistant patients is usually investigated by Sanger sequencing (SS) of the Bcr-Abl kinase domain (KD). Novel ultra-deep sequencing (UDS) technologies allow to conjugate higher sensitivity with the unprecedented possibility to perform instant cloning of thousands of DNA molecules. We thus decided to take advantage of an UDS-based approach in order to:

Methods:
We retrospectively performed a longitudinal analysis of a total of 111 samples from 35 CML or Ph+ ALL patients who had received sequential treatment with multiple TKIs (two to four TKIs among imatinib, dasatinib, nilotinib, ponatinib) and had experienced sequential relapses accompanied by selection of TKI-resistant mutations. All samples had already been scored by SS; 74/111 (67%) were positive for one (n=33) or multiple (n=41) mutations. UDS of the Bcr-Abl KD was done using Roche 454 technology. UDS allowed to achieve a lower detection limit of at least 0.1% – as compared to 20% of SS.

Results:
Bcr-Abl KD mutation status was found to be more complex than SS had previously shown in 85/111 (77%) samples (representative examples are detailed in Table 1). In 33/74 (44%) samples known to harbour one or more mutations by SS, UDS revealed that up to four ‘minor’ mutations with 1–20% abundance were present in addition to the ‘dominant’ one(s). The type of mutations could easily be accounted for by TKI exposure history, since the majority were known to be poorly sensitive either to the current or to the previous TKI received. The higher degree of complexity was evident also when the clonal relationships of multiple mutations were reconstructed (Table 1). This revealed that identical mutations may be acquired in parallel by independent populations (e.g., one wild-type and one already harboring a mutation), via the same or different nucleotide changes leading to the same amino acid substitution (convergent evolution). In addition, longitudinal quantitative follow-up of mutated populations revealed that:

Conclusions:

Disclosures:
Soverini: ARIAD: Consultancy; Bristol-Myers Squibb: Consultancy; Novartis: Consultancy. Castagnetti:Novartis: Honoraria; Bristol Myers Squibb: Honoraria. Luppi:CELGENE CORPORATION: Research Funding. Rosti:Bristol Myers Squibb: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding. Baccarani:ARIAD, Novartis, Bristol Myers-Squibb, and Pfizer: Consultancy, Honoraria, Speakers Bureau. Martinelli:NOVARTIS: Consultancy, Honoraria, Speakers Bureau; BMS: Consultancy, Honoraria, Speakers Bureau; PFIZER: Consultancy; ARIAD: Consultancy.