Daily oral treatment with venetoclax induced substantial responses with manageable adverse effects in patients with relapsed chronic lymphocytic leukemia or small lymphocytic lymphoma in a first-in-human phase I dose-escalation study.

The promising effects of the highly selective investigational inhibitor of BCL2 – a protein central to the survival of CLL cells – were noted even in patients with poor prognostic features, who comprised 89% of the cohort, reported Dr. Andrew W. Roberts of Royal Melbourne Hospital, Australia, and his colleagues. The study was published online Jan. 28 in The New England Journal of Medicine.

In the dose escalation phase of the study, 56 patients received active treatment at doses raging from 150 to 1,200 mg daily, and 60 additional patients received weekly stepwise ramp-up with doses beginning at 20 mg daily with weekly increases to 50 mg, 100 mg, and 200 mg daily up to the target dose of 400 mg daily. The patients had received a median of 3 previous therapies (range, 1-11).

Of 116 treated patients, 92 (79%) had a response, and 20% achieved complete remission, including 5% with no minimal residual disease on flow cytometry, the investigators said ( N Engl J Med. 2016;374:311-22 ).

Venetoclax was active at all doses used in the study, and no maximum tolerated dose was identified.

Tumor lysis syndrome occurred in 10 patients, but clinically important sequelae occurred in only 3 of those patients, 2 of whom had severe sequelae. After adjustments were made to dosing schedule, no further cases occurred.

Other side effects included mild diarrhea, upper respiratory tract infection, nausea, and grade 3 or 4 neutropenia, which occurred in 41%-52% of patients. Serious adverse events included febrile neutropenia in 6% of patients, pneumonia in 4%, upper respiratory tract infection in 3%, and immune thrombocytopenia in 3%.

Among the patients with an adverse prognosis, treatment response rates ranged from 71% to 79%, depending on the subgroup. For example, the response rate was 79% in 70 patients with resistance to fludarabine, and 71% in 31 patients with chromosome 17p deletions.

New treatments, including ibrutinib monotherapy and idelalisib in combination with rituximab, have improved outcomes for patients with relapsed CLL, but despite these advances, complete remissions remain uncommon, the authors said.

“This first trial of venetoclax showed the potential of BCL2 antagonism as an additional therapeutic avenue for patients with relapsed CLL,” they wrote, adding that the 79% overall response rate in this study – including deep responses and complete responses without minimal residual disease in patients up to age 86 years and patients with poor prognostic factors – “provides support for further development of venetoclax as a treatment option for patients with heavily pretreated relapsed or refractory CLL or SLL.”

Of note, the Food and Drug Administration on Jan. 28 – the date this study was released – granted venetoclax Breakthrough Therapy Designation for use in combination with hypomethylating agents for the treatment of acute myeloid leukemia patients who aren’t eligible for standard induction chemotherapy. The designation – the third for the agent – is supported by data from a single study of untreated patients aged 65 years or older with AML. Prior venetoclax Breakthrough Therapy Designations were granted in April 2015 for its use as monotherapy in patients with refractory CLL who have the 17p deletion genetic mutation, and in January for its use with rituximab for the treatment of relapsed/refractory CLL.

AbbVie and Genentech supported the study. Dr. Roberts reported receiving grant support and study drugs form AbbVie, serving as an investigator in trials sponsored by Genentech, AbbVie, Janssen, and Beigene, and receiving institutional research funding from Genentech for the development of venetoclax. His coauthors reported ties to various pharmaceutical companies.


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