Interactions between Ibrutinib and Anti-CD20 Antibodies: Competing Effects on the Outcome of Combination Therapy.
OBJECTIVE
Clinical trials of ibrutinib combined with anti-CD20 monoclonal antibodies (mAb) for chronic lymphocytic leukemia (CLL) report encouraging results. Paradoxically, in preclinical studies, in vitro ibrutinib was reported to decrease CD20 expression and inhibit cellular effector mechanisms. We therefore set out to investigate effects of in vivo ibrutinib treatment that could explain this paradox.


METHODS
Patients received single-agent ibrutinib (420 mg daily) on an investigator-initiated phase II trial. Serial blood samples were collected pretreatment and during treatment for ex vivo functional assays to examine the effects on CLL cell susceptibility to anti-CD20 mAbs.


RESULTS
We demonstrate that CD20 expression on ibrutinib was rapidly and persistently downregulated (median reduction 74%, day 28, P < 0.001) compared with baseline. Concomitantly, CD20 mRNA was decreased concurrent with reduced NF-κB signaling. An NF-κB binding site in the promoter of MS4A1 (encoding CD20) and downregulation of CD20 by NF-κB inhibitors support a direct transcriptional effect. Ex vivo, tumor cells from patients on ibrutinib were less susceptible to anti-CD20 mAb-mediated complement-dependent cytotoxicity than pretreatment cells (median reduction 75%, P < 0.001); however, opsonization by the complement protein C3d, which targets cells for phagocytosis, was relatively maintained. Expression of decay-accelerating factor (CD55) decreased on ibrutinib, providing a likely mechanism for the preserved C3d opsonization. In addition, ibrutinib significantly inhibited trogocytosis, a major contributor to antigen loss and tumor escape during mAb therapy.


CONCLUSIONS
Our data indicate that ibrutinib promotes both positive and negative interactions with anti-CD20 mAbs, suggesting that successfully harnessing maximal antitumor effects of such combinations requires further investigation.
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Martin
M
Skarzynski
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Carsten U
CU
Niemann
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Yuh Shan
YS
Lee
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Sabrina
S
Martyr
Department of Laboratory Medicine, Clinical Center, NIH, Bethesda, Maryland.
Irina
I
Maric
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Dalia
D
Salem
Flow Cytometry Unit, Laboratory of Pathology, Center for Cancer Research, NCI, NIH, Bethesda, Maryland.
Maryalice
M
Stetler-Stevenson
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Gerald E
GE
Marti
Department of Laboratory Medicine, Clinical Center, NIH, Bethesda, Maryland.
Katherine R
KR
Calvo
Flow Cytometry Unit, Laboratory of Pathology, Center for Cancer Research, NCI, NIH, Bethesda, Maryland.
Constance
C
Yuan
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Janet
J
Valdez
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Susan
S
Soto
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Mohammed Z H
MZ
Farooqui
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland.
Sarah E M
SE
Herman
Hematology Branch, National Heart, Lung, and Blood Institute, NIH, Bethesda, Maryland. wiestnera@mail.nih.gov.
Adrian
A
Wiestner
D000225:Adenine / Q000031:analogs & derivatives; D018951:Antigens, CD20 / Q000235:genetics / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001706:Biopsy; D001853:Bone Marrow / Q000473:pathology; D018958:CD55 Antigens / Q000235:genetics / Q000378:metabolism; D017322:Clinical Trials, Phase II as Topic; D003165:Complement System Proteins / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D004347:Drug Interactions; D015973:Gene Expression Regulation, Leukemic / Q000187:drug effects; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000175:diagnosis / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D010880:Piperidines; D011720:Pyrazoles / Q000494:pharmacology / Q000627:therapeutic use*; D011743:Pyrimidines / Q000494:pharmacology / Q000627:therapeutic use*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000069283:Rituximab / Q000187:drug effects* / Q000494:pharmacology
D018951:Antigens, CD20; D000970:Antineoplastic Agents; D018958:CD55 Antigens; D016328:NF-kappa B; D010880:Piperidines; D011720:Pyrazoles; D011743:Pyrimidines; D012333:RNA, Messenger; C551803:ibrutinib; D000069283:Rituximab; D003165:Complement System Proteins; D000225:Adenine