From the Journals

Bortezomib may unlock resistance in WM with mutations



The use of bortezomib may help overcome treatment resistance in patients with Waldenström macroglobulinemia (WM) with CXCR4 mutations, according to new research.

Romanos Sklavenitis-Pistofidis, MD, of the Dana-Farber Cancer Institute in Boston, and his colleagues compared the effects of treatment with bortezomib/rituximab in patients with WM based on their CXCR4 mutation status. They found no significant difference in progression-free survival (Log-rank, P = .994) or overall survival (Log-rank, P = .407) when comparing patients who have CXCR4 mutations with those who have CXCR4 wild type.

“We report for the first time that a bortezomib-based combination is impervious to the impact of CXCR4 mutations in a cohort of patients with WM,” the researchers wrote in Blood. “Previously, we had shown this to be true in WM cell lines, whereby genetically engineering BCWM.1 and MWCL-1 to overexpress CXCR4 had no impact on bortezomib resistance.”

The researchers noted, however, that the mechanism at work may be different than that seen with bortezomib in other cancers.

“Different experiments have linked CXCR4 expression and bortezomib in a variety of ways in other hematological malignancies, including multiple myeloma. However, despite the complicated association in those cancer types, in WM there seems to be a consistently neutral effect of CXCR4 mutations on bortezomib resistance in both cell line and patient data,” they wrote.

The researchers recommended that the theory be tested in a prospective trial of bortezomib-based therapy in WM patients with CXCR4 mutations. Another question to be investigated, they pointed out, is the role of rituximab in the survival results seen in the current analysis.

The study included 63 patients with WM who were treated with bortezomib/rituximab either as upfront treatment or in the relapsed/refractory setting as part of a phase 2 trial.

Bortezomib was given by IV weekly at 1.6 mg/m2 for six cycles and rituximab was given at 375 mg/m2 during cycles one and four. Patients were taken off therapy after two cycles if they had progressive disease.

The researchers excluded 20 patients from the study because of a lack of material for genotyping. However, they noted that their clinical characteristics were not different from those patients who were included.

Out of 43 patients who were genotyped for CXCR4, 17 patients had a mutation. All patients who carried a CXCR4 mutation also had MYD88 L265P. Ten patients had frameshift mutations, one patient had a nonsense mutation, and six patients had missense mutations. The median follow-up of the analysis was 90.7 months.

The researchers repeated the analysis after excluding six patients with missense mutations and accounting for different treatment settings and found that survival remained unchanged.

The study was supported by the National Institutes of Health, the Leukemia and Lymphoma Society, and the International Waldenström Macroglobulinemia Foundation. One of the authors reported consulting and research funding from Takeda, which markets bortezomib, and other companies.

SOURCE: Sklavenitis-Pistofidis R et al. Blood. 2018 Oct 26. doi: 10.1182/blood-2018-07-863241.

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