Meeting News

BCL2 mutation confers resistance to venetoclax in chronic lymphocytic leukemia

Piers Blombery, MBBS
Piers Blombery

SAN DIEGO — Researchers characterized a recurrent mutation in the BCL2 protein that offered new insights into the pathobiology of venetoclax resistance among patients with progressive chronic lymphocytic leukemia and could be a biomarker of impending relapse, according to study results presented during the late-breaking abstract session at ASH Annual Meeting and Exposition.

The recurrent Gly101Val mutation in BCL2 conferred resistance to venetoclax (Venclexta; AbbVie, Genentech) in patient leukemia cells and engineered cell lines, and provided a selective growth advantage over wild-type cells in the presence of venetoclax in vitro.

“This is the first BCL2 mutation that’s been described ... with CLL that had [resistance] with venetoclax,” Piers Blombery, MBBS, clinical and laboratory hematologist and medical lead of the molecular hematology laboratory at Peter MacCallum Cancer Centre in Melbourne, Australia, said during a press conference. “It seems to work by markedly reducing the affinity of venetoclax with BCL2.”

Venetoclax, a BCL2 inhibitor, induces high rates of response — including complete remission — in patients with pretreated CLL. However, researchers say the molecular mechanisms that create resistance to the agent are largely unknown.

Researchers evaluated CLL-type progressions among a group of 67 patients with relapsed CLL treated with venetoclax during three early-phase clinical trials. Twenty-one of these patients experienced CLL progression after median 36 months (range 6-73), 18 experienced Richter’s transformation and 28 had no disease progression.

Fifteen of the patients with CLL progression had suitable samples for genomic analysis. Researchers performed targeted amplicon next-generation sequencing on these samples with a panel of 33 genes recurrently mutated in lymphoid malignancy.

Researchers detected the mutation Gly101Val — a single heterozygous nucleotide variant — in BCL2 in progression samples from seven of the 15 patients. Researchers further confirmed the mutation through a droplet digital polymerase chain reaction assay.

Researchers first detected the mutation at low variant allele fraction after 19 to 42 months on venetoclax, which is up to 25 months earlier than when standard disease progression criteria were met.

This group of patients did not harbor the mutation prior to venetoclax treatment, and researchers did not detect it in samples from patients treated at a Melbourne institution without venetoclax for CLL (n = 74), non-Hodgkin lymphoma (n = 198) or myeloma (n = 103). The mutation had not been described in cancer or population databases.

“We also tested almost 400 patients with CLL and other blood cancers who had never been treated with venetoclax, and we did not find this mutation in any of those patients,” Blombery said in a press release. “This is evidence that the mutation only develops during venetoclax treatment, so it is something that patients can be screened for. In patients who develop this mutation at a low level, it would be prudent for the hematologist to begin to look for other therapies to use instead.”

Researchers expressed Gly101Val in two B-lineage cell lines — RS4;11 and KMS-PE-12 — and found that cells with the mutation were 30-fold less sensitive to venetoclax than cells expressing wild-type BCL2.

The mutation conferred a selective advantage when continuously exposed to sublethal concentrations of venetoclax in 3-week cultures, and in primary patient mutant cells in both short-term survival assays and when cultured.

Researchers noted not all CLL cells at progression had the mutation, and one patient in the study had subclones with and without the mutation at progression. The subclone with wild-type BCL 2 had elevated BCL-xL by mass cytometry, whereas the mutated clone had minimal BCL-xL expression.

“We don’t know what caused the cancer to relapse in the eight patients in whom we did not find the BCL2 mutation,” Blombery said. “Moreover, in the seven patients who had the mutation, we found it in only some of their cancer cells — and yet the cells that did not carry the mutation were still contributing to the cancer’s growth. So, clearly, even among patients who have the mutation, other factors are at play in causing resistance to venetoclax therapy.”

Researchers plan to conduct additional genomic analyses of patients who did not develop the BCL2 mutation to identify other mechanisms of venetoclax resistance. They also plan to gather more data on the time to acquisition of the mutation. – by John DeRosier

Reference:

Blombery, et al. Abstract LBA-7. Presented at: ASH Annual Meeting and Exposition; Dec. 1-4, 2018; San Diego.

Disclosures : Blombery reports no relevant financial disclosures. Please see the abstract for all other authors’ relevant financial disclosures.

Piers Blombery, MBBS
Piers Blombery

SAN DIEGO — Researchers characterized a recurrent mutation in the BCL2 protein that offered new insights into the pathobiology of venetoclax resistance among patients with progressive chronic lymphocytic leukemia and could be a biomarker of impending relapse, according to study results presented during the late-breaking abstract session at ASH Annual Meeting and Exposition.

The recurrent Gly101Val mutation in BCL2 conferred resistance to venetoclax (Venclexta; AbbVie, Genentech) in patient leukemia cells and engineered cell lines, and provided a selective growth advantage over wild-type cells in the presence of venetoclax in vitro.

“This is the first BCL2 mutation that’s been described ... with CLL that had [resistance] with venetoclax,” Piers Blombery, MBBS, clinical and laboratory hematologist and medical lead of the molecular hematology laboratory at Peter MacCallum Cancer Centre in Melbourne, Australia, said during a press conference. “It seems to work by markedly reducing the affinity of venetoclax with BCL2.”

Venetoclax, a BCL2 inhibitor, induces high rates of response — including complete remission — in patients with pretreated CLL. However, researchers say the molecular mechanisms that create resistance to the agent are largely unknown.

Researchers evaluated CLL-type progressions among a group of 67 patients with relapsed CLL treated with venetoclax during three early-phase clinical trials. Twenty-one of these patients experienced CLL progression after median 36 months (range 6-73), 18 experienced Richter’s transformation and 28 had no disease progression.

Fifteen of the patients with CLL progression had suitable samples for genomic analysis. Researchers performed targeted amplicon next-generation sequencing on these samples with a panel of 33 genes recurrently mutated in lymphoid malignancy.

Researchers detected the mutation Gly101Val — a single heterozygous nucleotide variant — in BCL2 in progression samples from seven of the 15 patients. Researchers further confirmed the mutation through a droplet digital polymerase chain reaction assay.

Researchers first detected the mutation at low variant allele fraction after 19 to 42 months on venetoclax, which is up to 25 months earlier than when standard disease progression criteria were met.

This group of patients did not harbor the mutation prior to venetoclax treatment, and researchers did not detect it in samples from patients treated at a Melbourne institution without venetoclax for CLL (n = 74), non-Hodgkin lymphoma (n = 198) or myeloma (n = 103). The mutation had not been described in cancer or population databases.

“We also tested almost 400 patients with CLL and other blood cancers who had never been treated with venetoclax, and we did not find this mutation in any of those patients,” Blombery said in a press release. “This is evidence that the mutation only develops during venetoclax treatment, so it is something that patients can be screened for. In patients who develop this mutation at a low level, it would be prudent for the hematologist to begin to look for other therapies to use instead.”

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Researchers expressed Gly101Val in two B-lineage cell lines — RS4;11 and KMS-PE-12 — and found that cells with the mutation were 30-fold less sensitive to venetoclax than cells expressing wild-type BCL2.

The mutation conferred a selective advantage when continuously exposed to sublethal concentrations of venetoclax in 3-week cultures, and in primary patient mutant cells in both short-term survival assays and when cultured.

Researchers noted not all CLL cells at progression had the mutation, and one patient in the study had subclones with and without the mutation at progression. The subclone with wild-type BCL 2 had elevated BCL-xL by mass cytometry, whereas the mutated clone had minimal BCL-xL expression.

“We don’t know what caused the cancer to relapse in the eight patients in whom we did not find the BCL2 mutation,” Blombery said. “Moreover, in the seven patients who had the mutation, we found it in only some of their cancer cells — and yet the cells that did not carry the mutation were still contributing to the cancer’s growth. So, clearly, even among patients who have the mutation, other factors are at play in causing resistance to venetoclax therapy.”

Researchers plan to conduct additional genomic analyses of patients who did not develop the BCL2 mutation to identify other mechanisms of venetoclax resistance. They also plan to gather more data on the time to acquisition of the mutation. – by John DeRosier

Reference:

Blombery, et al. Abstract LBA-7. Presented at: ASH Annual Meeting and Exposition; Dec. 1-4, 2018; San Diego.

Disclosures : Blombery reports no relevant financial disclosures. Please see the abstract for all other authors’ relevant financial disclosures.

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