Single-Agent Regimens Fall Short in DLBCL

Sharon Worcester

October 22, 2021

Targeted agents for the treatment of diffuse large B-cell lymphoma (DLBCL) should be used in the context of oncogenic addictions within the lymphoma cells, and a thorough molecular analysis should be conducted prior to using specific agents, a review of the relevant literature suggests.

"In addition ... single-agent regimens are most likely not efficient enough to substantially improve the outcome of patients with DLBCL," Wendan Xu and colleagues at University Hospital Munster, Germany, concluded, based on their review.

Indeed, novel combinations that include B-cell receptor (BCR) signaling and phosphatidylinositol 3-kinase (PI3K) inhibitors are needed for DLBCL treatment, and treatment should also include conventional chemoimmunotherapeutic regimens as well as other targeted agents and novel immunologic approaches, they wrote. Such novel combinations could overcome mechanisms of resistance and increase cure rates in individuals with DLBCL, they contended.

The authors' observations are based on a search of the available data, from which they summarized the "current understanding of BCR signaling with a special focus on the PI3K pathway and its role in the pathogenesis of DLBCL."

The addition of the anti-CD20 antibody rituximab to the CHOP regimen (cyclophosphamide, doxorubicin, vincristine, and prednisone) significantly improved outcomes for patients with DLBCL, but about a third of patients are not cured by the rituximab-CHOP (R-CHOP) regimen and subsequent therapies, they said, explaining their rationale for the review.

"A better understanding of the molecular pathogenesis is warranted to use novel targeted agents in an optimal manner," they said.

The authors also addressed clinical implications of the findings, and mechanisms of resistance to PI3k inhibitors. For example, they noted that:

Bruton's tyrosine kinase (BTK) inhibitors may be beneficial when added to R-CHOP.

In the randomized phase 3 PHOENIX trial, ibrutinib plus R-CHOP versus R-CHOP alone in patients with non–germinal center B-cell (non-GCB) DLBCL showed a survival benefit in patients over 60 years of age, which suggests a possible role for "an intensified R-CHOP regimen that includes a BTK inhibitor" in these patients, they said. They added that confirmatory trials are under way, including the ESCALADE trial looking at the second-generation BTK inhibitor acalabrutinib combined with R-CHOP versus R-CHOP alone in patients with untreated DLBCL.

Results have been mixed with PI3K inhibitors.

Various PI3K inhibitors have been evaluated for the treatment of patients with DLBCL.

Idelalisib, a first-in-class PI3K-specific inhibitor approved for treatment of relapsed/refractory (r/r) follicular lymphoma, small lymphocytic lymphoma, and chronic lymphocytic leukemia (CLL), showed only modest activity in preclinical DLBCL models, and no responses were detectable in a small trial of patients with r/r DLBCL, the authors said. "Severe toxic side effects and treatment-related deaths occurred in several clinical trials that tested idelalisib in combination with antibodies alone or with antibodies and chemotherapy, leading to the premature discontinuation of some of these studies," they noted.

Other studies investigating idelalisib plus lenalidomide and rituximab or the spleen tyrosine kinase (SYK) inhibitor entospletinib in patients with r/r CLL or lymphoma were also halted because of "overwhelming, immune-mediated pulmonary and/or hepatic toxicities."

Copanlisib, an intravenous pan-class I PI3K inhibitor with preferential inhibition of PI3Ka and PI3Kd, showed some promise as monotherapy in a phase 2 trial of patients with r/r DLBCL. The overall response rate was about 20%, and response was "numerically higher" in activated B-cell like (ABC) DLBCL, compared with GCB DLBCL (32% vs. 13%), confirming preclinical data that showed PI3Ka/d inhibition effectiveness mainly in ABC DLBCL.

"Compared with idelalisib, copanlisib appears to have a more favorable toxicity profile, with a lower incidence of severe complications," they said, adding that a phase 2 trial of copanlisib plus R-CHOP as first-line therapy for patients with DLBCL is under way.

Further, monotherapy with buparlisib, a pan-class I PI3K inhibitor, was associated with a low response rate of 11.5% in a DLBCL subcohort in a phase 2 study, whereas parsaclisib, a next-generation inhibitor with specificity to the PI3Kd isoform, showed efficacy as a monotherapy in patients with r/r DLBCL in a phase 2 study (overall response rate, 25.5%), they said, adding that other PI3K inhibitors with additional inhibitory effects are under clinical development.

Various molecular mechanisms of resistance to PI3K inhibitors have been described preclinically and clinically.

In an unbiased exploratory analysis of samples from patients treated with copanlisib, a 16-gene mutation signature that separated responders from nonresponders was identified, the authors said.

The finding suggests that genetic aberrations dictate response to PI3K inhibitors, they noted.

"This 16-gene signature included TNFAIP3, CREBBP, and PRDM1, which are known to be important in the molecular pathogenesis of DLBCL," they wrote. A composite score was developed to reflect the numerical presence or absence of mutations in the gene set, they explained, adding that patients with a high composite score had a significantly higher overall response rate and longer progression-free survival than did patients with a lower score.

In addition, idelalisib treatment resulted in a feedback activation of PI3Ka in ABC DLBCL cells.

"This rebound of PI3K activity was overcome by subsequent PI3Ka inhibition in preclinical DLBCL models, further underscoring the necessity of inhibiting both PI3Ka and PI3Kd to achieve responses in ABC DLBCL," they wrote, adding that "[i]n ABC DLBCL models treated with the PI3Ka/PI3Kd inhibitor AZD8835, activated CARD11 mutations were identified as a mechanism of resistance."

Investigations looking at various treatment combinations to overcome resistance to PI3K inhibition and improve the efficacy of targeted approaches are under way, they said.

For example, copanlisib plus the BCL-2 inhibitor venetoclax showed "synergistic activity in BCR-dependent DLBCLs, with genetic bases for BCL-2 dysregulation in vitro and in vivo," and combination treatment with umbralisib and the proteasome inhibitor carfilzomib showed synergistic cytotoxicity in B-cell lymphoma, they said, noting that the latter combination is currently being evaluated in patients with DLBCL.

This work was supported by a research grant from the Deutsche Krebshilfe. Xu reported having no financial disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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