-Author name in bold denotes the presenting author
-Asterisk * with author name denotes a Non-ASH member
Clinically Relevant Abstract denotes an abstract that is clinically relevant.

PhD Trainee denotes that this is a recommended PHD Trainee Session.

Ticketed Session denotes that this is a ticketed session.

585 Mechanisms of Adaptation to Ibrutinib in High Risk Chronic Lymphocytic Leukemia

Program: Oral and Poster Abstracts
Type: Oral
Session: 641. CLL: Biology and Pathophysiology, excluding Therapy: Mechanisms of Action and Resistance to Targeted Agents
Hematology Disease Topics & Pathways:
Leukemia, Diseases, CLL, Biological Processes, Technology and Procedures, Lymphoid Malignancies, genomics, flow cytometry, NGS, molecular interactions
Monday, December 3, 2018: 7:30 AM
Grand Ballroom 5 (Marriott Marquis San Diego Marina)

Valeria Spina, PhD1, Gabriela Forestieri1*, Antonella Zucchetto2*, Alessio Bruscaggin, PhD1, Tamara Bittolo, PhD2*, Lodovico Terzi di Bergamo1*, Eva Szenes3*, Adalgisa Condoluci, MD1,4*, Erika Tissino, PhD2*, Lorenzo De Paoli, MD5*, Clara Deambrogi, PhD5*, Anna Maria Frustaci6*, Francesco Autore, MD7*, Michele Merli8*, Lydia Scarfo, MD9*, Claudia Cirillo Sanchez1*, Francesca Guidetti1*, Simone Favini5*, Fary Diop5*, Renzo Lucchini4*, Tanja N. Hartmann, Ph.D.3*, Giovanni Del Poeta, MD10, Roberto Marasca, MD11, Francesco Zaja12*, Bernhard Gerber4*, Emanuele Zucca, MD4, Georg Stussi, MD4, Jakob R. Passweg, MD, MS13, Paolo Ghia, MD, PhD14, Francesco Passamonti, MD15*, Michael Gregor, MD16*, Luca Laurenti, MD17*, Marco Montillo, MD6, Alessandra Tedeschi, MD6*, Franco Cavalli, MD4, Gianluca Gaidano, MD, PhD5, Valter Gattei, MD18 and Davide Rossi, MD, PhD1,4

1Institute of Oncology Research, Bellinzona, Switzerland
2Clinical and Experimental Onco-Hematology Unit, IRCCS Centro Di Riferimento Oncologico, Aviano, Italy
3Salzburg Cancer Research Institute, Salzburg, Salzburg, Austria
4Oncology Institute of Southern Switzerland, Bellinzona, Switzerland
5Department of Translational Medicine, University of Eastern Piedmont, Novara, Italy
6Department of Haematology, Niguarda Cancer Center, ASST Grande Ospedale Metropolitano Niguarda, Milan, Italy
7Hematology Department, Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy
8Department of Hematology,University of Insubria, Varese, Italy
9Università Vita-Salute San Raffaele and IRCCS Istituto Scientifico San Raffaele, Milano, Italy
10Hematology, Ospedale S. Eugenio Universita 'Tor Vergata', Rome, Italy
11Department of Medical and Surgical Sciences, University of Modena and Reggio Emilia, Modena, Italy
12Clinica Ematologica, DAME, University of Udine, Udine, Italy
13Hematology, University Hospital Basel, Basel, Switzerland
14Università Vita-Salute San Raffaele and IRCCS Istituto Scientifico San Raffaele, Milan, Italy
15University Hospital Ospedale Di Circolo E Fondazione Macchi, VARESE, Italy
16Division of Hematology, Cantonal Hospital of Lucerne, Lucerne, Switzerland
17Istituto di Ematologia, Fondazione Policlinico Universitario A. Gemelli, Università Cattolica del Sacro Cuore, Rome, Italy
18Clinical and Experimental Onco-Hematology Unit, Centro Di Riferimento Oncologico, Aviano, Italy

Introduction. Ibrutinib inhibits the BTK molecule downstream the B-cell receptor (BCR). Though highly active in high risk chronic lymphocytic leukemia (CLL), the most typical response achievable in patients is a minimal residual disease (MRD) positive partial remission (PR) which is maintained until the development of genetically driven resistance caused by the acquisition of mutations in the BTK or PLCG2 genes. The study aims at characterizing the adaptation process allowing residual CLL cells to persist despite BTK inhibition. Methods. The IOSI-EMA-001 study (NCT02827617) is an observational study consisting in the prospective and longitudinal collection of peripheral blood samples and clinical data from high risk CLL patients treated with ibrutinib. Peripheral blood CLL cells longitudinally drawn from patients before treatment start and at fixed timepoints under ibrutinib were monitored by: i) next generation flow cytometry approaches for changes in proliferation rate, surfaceome, and pathway activation; and ii) CAPP-seq targeted deep next generation (sensitivity ~10-3) for clonal evolution. Results. The study cohort comprised 31 high risk CLL patients, including 15 treatment naïve, 16 relapsed, 80% IGHV unmutated, 42% 17p deleted and 55% TP53 mutated. Median duration of ibrutinib treatment was 45 weeks (24-72 weeks). All patients obtained a MRD positive PR that was maintained in all but one who progressed with a PLCG2 mutation (VAF 3%). Compared to baseline, under ibrutinib therapy CLL cells slowed down their proliferation, as suggested by the decreased expression of Ki-67, the reduction of the proliferating fraction (CXCR4dimCD5bright), and the increase of the resting fraction (CXCR4brightCD5dim). Compared to baseline, under ibrutinib therapy CLL cells also upregulated BCR and adhesion/homing proteins, and decreased the expression of BCR inhibitor proteins. Upon stimulation of the BCR with anti-IgM, the downstream path through pBTK and pPLCG2 was inhibited by ibrutinib, while conversely the downstream path through pAKT and pERK was still inducible throughout all the assessed timepoints. The proportion of CLL cells harboring nuclear localization of NF-kB progressively increased over time under ibrutinib. NF-kB nuclear localization was inducible throughout all the assessed timepoints by CD40L stimulation of the non-canonical NF-kB pathway, but not by anti-IgM stimulation of the BCR/canonical NF-kB pathway. Overall, 880 individual mutations were longitudinally discovered and monitored across a total of 121 sequential timepoints collected during ibrutinib treatment. Clonal evolution was observed in (67.7%) cases, a proportion rate previously documented in CLL treated with chemoimmunotherapy. Clonal evolution appeared to be heterogeneous involving different genes without a stereotypic targeting. Consistently, none of the main driver gene mutations was homogeneously selected or suppressed by ibrutinib suggesting that the biological adaptation of CLL cells under ibrutinib is not genetically driven. Clonal evolution propensity was not associated with any of the biomarkers of the disease, and it did not decrease over time under ibrutinib. Conclusions. Taken together these results suggest that residual CLL cells persisting under ibrutinib therapy adapt their phenotype by upregulating adhesion molecules, chemokine receptors and BCR molecules, and by maintaining a competence of BCR signaling through the PI3K/AKT/ERK pathway. The progressive selection of CLL cells having NF-kB in the nucleus, likely due to the BTK independent non-canonical NF-kB pathway, might explain their survival despite ibrutinib therapy. Finally, clonal evolution is not suppressed by ibrutinib chemotherapy, and despite does not seem to be directly involved in such adaptation process, may ultimately favor the acquisition of BTK and PLCG2 ibrutinib resistance mutations.

Disclosures: Zucca: Celltrion: Consultancy; AstraZeneca: Consultancy. Ghia: Sunesis: Honoraria, Research Funding; BeiGene: Honoraria, Research Funding; Acerta: Honoraria, Research Funding; Gilead: Honoraria, Research Funding; AbbVie, Inc: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Janssen: Honoraria, Research Funding. Montillo: Gilead: Consultancy, Honoraria, Speakers Bureau; Roche: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Speakers Bureau; Janssen: Consultancy, Honoraria. Tedeschi: Janssen: Consultancy, Speakers Bureau; Gilead: Consultancy; AbbVie: Consultancy. Gaidano: AbbVie: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Morphosys: Honoraria; Roche: Consultancy, Honoraria. Rossi: Roche: Honoraria; MSD: Consultancy; Gilead: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria, Research Funding; Cellestia: Research Funding.

*signifies non-member of ASH