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Deborah M. Stephens, DO, and John C. Byrd, MD, stated in a review article published in Blood.
Among patients with B-cell malignancies – including chronic lymphocytic leukemia (CLL), Waldenström’s macroglobulinemia (WM), mantle cell lymphoma (MCL), and marginal zone lymphoma (MZL) – BTKis have substantial efficacy. The review article focuses mainly on extremely rare primary or more common acquired BTKi resistance, particularly among patients with acquired resistance to ibrutinib (11%-38% in large studies).
Primary resistance suggests an alternative diagnosis or transformation to a more aggressive lymphoma. Acquired ibrutinib resistance manifests either as progressive CLL (typically after 2 years of therapy) or as early transformation (within the first 2 years of therapy) to more aggressive entities such as diffuse large B-cell lymphoma, Hodgkin lymphoma, or prolymphocytic leukemia. Less studied than ibrutinib, acquired resistance to acalabrutinib and zanubrutinib has been in the 12%-15% range.
Acquired resistance has meant a reduction in expected overall survival, and while the introduction of new therapies like venetoclax has extended OS, short progression-free survival (PFS) provides a rationale for research into mechanisms of resistance and alternative treatments.
Acquired resistance
Most often acquired, resistance to ibrutinib monotherapy in CLL patients has been associated with high-risk genomic features: complex karyotype, TP53 mutation, del(17)p13.1, and heavy pretreatment. In the phase 3 RESONATE trial, patients with both TP53 mutation and del(17)p13.1 had shorter PFS than those with only one or the other genomic feature. This feature may have explained the fairly good ibrutinib monotherapy outcomes in treatment-naive patients with del(17p)13.1.
Through univariable and multivariable analysis, a machine-learning program consistently identified TP53 mutation, prior CLL therapy, beta-2 microglobulin of at least5 mg/L, and lactate dehydrogenase greater than250 U/L as four risk factors associated with impaired survival. A second survival factor program comparing ibrutinib with chemoimmunotherapy identified beta-2 microglobulin levels of at least5 mg/L, lactate dehydrogenase greater than ULN, hemoglobin less than 110 g/L for women or less than120 g/L for men, and time from initiation of last therapy less than 24 months as risk factors.
While the mechanisms leading to ibrutinib resistance are not clearly known for patients with these risk factors, some research suggests that survival of TP53-mutated CLL cells is less dependent on the BCR pathway, making this CLL type more prone to ibrutinib resistance. TP53-mutated CLL cells, compared with T53–wild-type CLL cells, demonstrate a down-regulation of BCR-related genes and an up-regulation of prosurvival and antiapototic genes.
BTK mutations
Mutation of the active kinase domain on the BTK enzyme (C481) is the most common BTKi resistance mechanism described in CLL. A thymidine to adenine mutation (nucleotide 1634) leads to a 25-fold decrease in drug potency. Other known gene or chromosome regions affected in BTKi resistance include PLCy2, Del(8p), CARD11, TRAF2&3, BIRC3, MAP3k14, ARID2, SMARCA2, SMARCA4, MYD88, KLH14, and TNFAIP3.
Multiple mutations of PLCy2, the next most common BTKi resistance mechanism, include mutations of arginine to tryptophan, leucine to phenylalanine, serine to tyrosine, and others. When activated, these gain-of-function mutations prolong BCR signaling.
Ibrutinib resistance has also been associated with deletion of the short arm of chromosome 8 (del[8p]), with CLL cells harboring del(8p) insensitive to TRAIL-induced apoptosis, leading to continuous cell growth. Ibrutinib resistance in patients with WM has also been associated with del(8p).
CARD11 mutations, which allow for BTK-independent activation of NFkB, have been documented in ibrutinib-resistant patients with CLL and other lymphoid malignancies, as detailed in this review.
Novel therapies suggest promise
Survival in CLL after BTKi resistance develops is quite short, according to the authors, and they expressed hope that continued research into novel agents would prolong this population’s survival.
Venetoclax, an oral inhibitor of the antiapoptotic protein BCL2, is approved for all patients with CLL, both as monotherapy and in combination with an anti-CD20 monoclonal antibody. Data support its use after BTKi resistance has been detected. Some evidence in CLL cell lines supports use of the oral phosphoinositide 3-kinases inhibitors idelalisib and duvelisib in relapsed CLL and the BTK C481S mutation. Early response data with third-generation BTKis, such as ARQ-531 and LOXO-305, suggest promise in this setting. Also, for young and healthy patients who have progressed on both BTKi and venetoclax therapy, allogeneic hematopoietic stem cell transplantation could be considered.
In patients with heavily pretreated CLL, early clinical data support chimeric antigen receptor T-cell therapy (CAR T), a novel therapy where patients’ own T cells are extracted, engineered, and reinfused. A related immunotherapy, using a similar process of retroviral vector insertion of an anti-CD19 CAR into donor NK cells before infusion into the patient, is termed CAR-NK cell therapy. It shows promise in early data from patients with CLL who all had previously been heavily treated with ibrutinib.
More research, more hope
Despite the significant advance that BTKis represent, BTKi resistance, with shortened survival, remains a clinical problem for patients with B-cell malignancies. BTKi resistance has been associated with several genetic and clinical risk factors, with mutations in BTK and PLCy2 the most common and most thoroughly researched. “Ongoing clinical trials of third-generation noncovalent BTKis and cellular therapies, such as CAR T, provide much hope for these patients. ... Continued additional research is needed to further prolong the survival of patients with BTKi-resistant B-cell malignancies.”
Dr. Stephens has received research funding and has served on advisory boards for a variety of pharmaceutical and biotechnology companies. Dr. Byrd has received research funding and has consulted for a variety of pharmaceutical and biotechnology companies.
Deborah M. Stephens, DO, and John C. Byrd, MD, stated in a review article published in Blood.
Among patients with B-cell malignancies – including chronic lymphocytic leukemia (CLL), Waldenström’s macroglobulinemia (WM), mantle cell lymphoma (MCL), and marginal zone lymphoma (MZL) – BTKis have substantial efficacy. The review article focuses mainly on extremely rare primary or more common acquired BTKi resistance, particularly among patients with acquired resistance to ibrutinib (11%-38% in large studies).
Primary resistance suggests an alternative diagnosis or transformation to a more aggressive lymphoma. Acquired ibrutinib resistance manifests either as progressive CLL (typically after 2 years of therapy) or as early transformation (within the first 2 years of therapy) to more aggressive entities such as diffuse large B-cell lymphoma, Hodgkin lymphoma, or prolymphocytic leukemia. Less studied than ibrutinib, acquired resistance to acalabrutinib and zanubrutinib has been in the 12%-15% range.
Acquired resistance has meant a reduction in expected overall survival, and while the introduction of new therapies like venetoclax has extended OS, short progression-free survival (PFS) provides a rationale for research into mechanisms of resistance and alternative treatments.
Acquired resistance
Most often acquired, resistance to ibrutinib monotherapy in CLL patients has been associated with high-risk genomic features: complex karyotype, TP53 mutation, del(17)p13.1, and heavy pretreatment. In the phase 3 RESONATE trial, patients with both TP53 mutation and del(17)p13.1 had shorter PFS than those with only one or the other genomic feature. This feature may have explained the fairly good ibrutinib monotherapy outcomes in treatment-naive patients with del(17p)13.1.
Through univariable and multivariable analysis, a machine-learning program consistently identified TP53 mutation, prior CLL therapy, beta-2 microglobulin of at least5 mg/L, and lactate dehydrogenase greater than250 U/L as four risk factors associated with impaired survival. A second survival factor program comparing ibrutinib with chemoimmunotherapy identified beta-2 microglobulin levels of at least5 mg/L, lactate dehydrogenase greater than ULN, hemoglobin less than 110 g/L for women or less than120 g/L for men, and time from initiation of last therapy less than 24 months as risk factors.
While the mechanisms leading to ibrutinib resistance are not clearly known for patients with these risk factors, some research suggests that survival of TP53-mutated CLL cells is less dependent on the BCR pathway, making this CLL type more prone to ibrutinib resistance. TP53-mutated CLL cells, compared with T53–wild-type CLL cells, demonstrate a down-regulation of BCR-related genes and an up-regulation of prosurvival and antiapototic genes.
BTK mutations
Mutation of the active kinase domain on the BTK enzyme (C481) is the most common BTKi resistance mechanism described in CLL. A thymidine to adenine mutation (nucleotide 1634) leads to a 25-fold decrease in drug potency. Other known gene or chromosome regions affected in BTKi resistance include PLCy2, Del(8p), CARD11, TRAF2&3, BIRC3, MAP3k14, ARID2, SMARCA2, SMARCA4, MYD88, KLH14, and TNFAIP3.
Multiple mutations of PLCy2, the next most common BTKi resistance mechanism, include mutations of arginine to tryptophan, leucine to phenylalanine, serine to tyrosine, and others. When activated, these gain-of-function mutations prolong BCR signaling.
Ibrutinib resistance has also been associated with deletion of the short arm of chromosome 8 (del[8p]), with CLL cells harboring del(8p) insensitive to TRAIL-induced apoptosis, leading to continuous cell growth. Ibrutinib resistance in patients with WM has also been associated with del(8p).
CARD11 mutations, which allow for BTK-independent activation of NFkB, have been documented in ibrutinib-resistant patients with CLL and other lymphoid malignancies, as detailed in this review.
Novel therapies suggest promise
Survival in CLL after BTKi resistance develops is quite short, according to the authors, and they expressed hope that continued research into novel agents would prolong this population’s survival.
Venetoclax, an oral inhibitor of the antiapoptotic protein BCL2, is approved for all patients with CLL, both as monotherapy and in combination with an anti-CD20 monoclonal antibody. Data support its use after BTKi resistance has been detected. Some evidence in CLL cell lines supports use of the oral phosphoinositide 3-kinases inhibitors idelalisib and duvelisib in relapsed CLL and the BTK C481S mutation. Early response data with third-generation BTKis, such as ARQ-531 and LOXO-305, suggest promise in this setting. Also, for young and healthy patients who have progressed on both BTKi and venetoclax therapy, allogeneic hematopoietic stem cell transplantation could be considered.
In patients with heavily pretreated CLL, early clinical data support chimeric antigen receptor T-cell therapy (CAR T), a novel therapy where patients’ own T cells are extracted, engineered, and reinfused. A related immunotherapy, using a similar process of retroviral vector insertion of an anti-CD19 CAR into donor NK cells before infusion into the patient, is termed CAR-NK cell therapy. It shows promise in early data from patients with CLL who all had previously been heavily treated with ibrutinib.
More research, more hope
Despite the significant advance that BTKis represent, BTKi resistance, with shortened survival, remains a clinical problem for patients with B-cell malignancies. BTKi resistance has been associated with several genetic and clinical risk factors, with mutations in BTK and PLCy2 the most common and most thoroughly researched. “Ongoing clinical trials of third-generation noncovalent BTKis and cellular therapies, such as CAR T, provide much hope for these patients. ... Continued additional research is needed to further prolong the survival of patients with BTKi-resistant B-cell malignancies.”
Dr. Stephens has received research funding and has served on advisory boards for a variety of pharmaceutical and biotechnology companies. Dr. Byrd has received research funding and has consulted for a variety of pharmaceutical and biotechnology companies.
Deborah M. Stephens, DO, and John C. Byrd, MD, stated in a review article published in Blood.
Among patients with B-cell malignancies – including chronic lymphocytic leukemia (CLL), Waldenström’s macroglobulinemia (WM), mantle cell lymphoma (MCL), and marginal zone lymphoma (MZL) – BTKis have substantial efficacy. The review article focuses mainly on extremely rare primary or more common acquired BTKi resistance, particularly among patients with acquired resistance to ibrutinib (11%-38% in large studies).
Primary resistance suggests an alternative diagnosis or transformation to a more aggressive lymphoma. Acquired ibrutinib resistance manifests either as progressive CLL (typically after 2 years of therapy) or as early transformation (within the first 2 years of therapy) to more aggressive entities such as diffuse large B-cell lymphoma, Hodgkin lymphoma, or prolymphocytic leukemia. Less studied than ibrutinib, acquired resistance to acalabrutinib and zanubrutinib has been in the 12%-15% range.
Acquired resistance has meant a reduction in expected overall survival, and while the introduction of new therapies like venetoclax has extended OS, short progression-free survival (PFS) provides a rationale for research into mechanisms of resistance and alternative treatments.
Acquired resistance
Most often acquired, resistance to ibrutinib monotherapy in CLL patients has been associated with high-risk genomic features: complex karyotype, TP53 mutation, del(17)p13.1, and heavy pretreatment. In the phase 3 RESONATE trial, patients with both TP53 mutation and del(17)p13.1 had shorter PFS than those with only one or the other genomic feature. This feature may have explained the fairly good ibrutinib monotherapy outcomes in treatment-naive patients with del(17p)13.1.
Through univariable and multivariable analysis, a machine-learning program consistently identified TP53 mutation, prior CLL therapy, beta-2 microglobulin of at least5 mg/L, and lactate dehydrogenase greater than250 U/L as four risk factors associated with impaired survival. A second survival factor program comparing ibrutinib with chemoimmunotherapy identified beta-2 microglobulin levels of at least5 mg/L, lactate dehydrogenase greater than ULN, hemoglobin less than 110 g/L for women or less than120 g/L for men, and time from initiation of last therapy less than 24 months as risk factors.
While the mechanisms leading to ibrutinib resistance are not clearly known for patients with these risk factors, some research suggests that survival of TP53-mutated CLL cells is less dependent on the BCR pathway, making this CLL type more prone to ibrutinib resistance. TP53-mutated CLL cells, compared with T53–wild-type CLL cells, demonstrate a down-regulation of BCR-related genes and an up-regulation of prosurvival and antiapototic genes.
BTK mutations
Mutation of the active kinase domain on the BTK enzyme (C481) is the most common BTKi resistance mechanism described in CLL. A thymidine to adenine mutation (nucleotide 1634) leads to a 25-fold decrease in drug potency. Other known gene or chromosome regions affected in BTKi resistance include PLCy2, Del(8p), CARD11, TRAF2&3, BIRC3, MAP3k14, ARID2, SMARCA2, SMARCA4, MYD88, KLH14, and TNFAIP3.
Multiple mutations of PLCy2, the next most common BTKi resistance mechanism, include mutations of arginine to tryptophan, leucine to phenylalanine, serine to tyrosine, and others. When activated, these gain-of-function mutations prolong BCR signaling.
Ibrutinib resistance has also been associated with deletion of the short arm of chromosome 8 (del[8p]), with CLL cells harboring del(8p) insensitive to TRAIL-induced apoptosis, leading to continuous cell growth. Ibrutinib resistance in patients with WM has also been associated with del(8p).
CARD11 mutations, which allow for BTK-independent activation of NFkB, have been documented in ibrutinib-resistant patients with CLL and other lymphoid malignancies, as detailed in this review.
Novel therapies suggest promise
Survival in CLL after BTKi resistance develops is quite short, according to the authors, and they expressed hope that continued research into novel agents would prolong this population’s survival.
Venetoclax, an oral inhibitor of the antiapoptotic protein BCL2, is approved for all patients with CLL, both as monotherapy and in combination with an anti-CD20 monoclonal antibody. Data support its use after BTKi resistance has been detected. Some evidence in CLL cell lines supports use of the oral phosphoinositide 3-kinases inhibitors idelalisib and duvelisib in relapsed CLL and the BTK C481S mutation. Early response data with third-generation BTKis, such as ARQ-531 and LOXO-305, suggest promise in this setting. Also, for young and healthy patients who have progressed on both BTKi and venetoclax therapy, allogeneic hematopoietic stem cell transplantation could be considered.
In patients with heavily pretreated CLL, early clinical data support chimeric antigen receptor T-cell therapy (CAR T), a novel therapy where patients’ own T cells are extracted, engineered, and reinfused. A related immunotherapy, using a similar process of retroviral vector insertion of an anti-CD19 CAR into donor NK cells before infusion into the patient, is termed CAR-NK cell therapy. It shows promise in early data from patients with CLL who all had previously been heavily treated with ibrutinib.
More research, more hope
Despite the significant advance that BTKis represent, BTKi resistance, with shortened survival, remains a clinical problem for patients with B-cell malignancies. BTKi resistance has been associated with several genetic and clinical risk factors, with mutations in BTK and PLCy2 the most common and most thoroughly researched. “Ongoing clinical trials of third-generation noncovalent BTKis and cellular therapies, such as CAR T, provide much hope for these patients. ... Continued additional research is needed to further prolong the survival of patients with BTKi-resistant B-cell malignancies.”
Dr. Stephens has received research funding and has served on advisory boards for a variety of pharmaceutical and biotechnology companies. Dr. Byrd has received research funding and has consulted for a variety of pharmaceutical and biotechnology companies.
FROM BLOOD