Blocking Wnt Signaling Boosts Daratumumab's Power Against Multiple Myeloma

Multiple myeloma is a bone-marrow cancer of plasma cells that, despite major therapeutic advances, remains largely incurable. Daratumumab, a monoclonal antibody that binds the surface protein CD38, has transformed myeloma treatment, but resistance is common and frequently linked to declining CD38 expression on tumor cells. Understanding what controls CD38 abundance is therefore a priority for improving outcomes. This study from investigators at Jiangnan University and Amsterdam UMC set out to test whether the aberrantly active Wnt/β-catenin pathway in myeloma regulates CD38 through a crosstalk with the STAT3 signaling axis.

The researchers used two complementary genetic tools — ectopic expression of a dominant-negative TCF4 mutant (dnTCF4) and CRISPR/Cas9 knockout of β-catenin — to shut down canonical Wnt signaling in three human myeloma cell lines (U266, H929, and MM1.S). Both approaches consistently reduced phosphorylated STAT3 (Ser727) and lowered mRNA levels of the Wnt target genes c-MYC and CCND1, as well as the pro-survival cytokine IL-6. These findings established a mechanistic link: active Wnt signaling sustains STAT3 activity in myeloma, at least in part by maintaining autocrine IL-6 production.

With the Wnt–STAT3 axis established, the team examined downstream consequences for CD38. Flow cytometry showed that dnTCF4 expression and β-catenin deletion both significantly increased CD38 surface density on myeloma cell lines (p ≤ 0.001 to p ≤ 0.0001 in multiple comparisons). Treatment with the small-molecule Wnt inhibitor ICG-001 at 5 µM for 48 hours recapitulated these genetic findings, boosting CD38 expression in all three cell lines. To confirm that STAT3 mediates the CD38 effect, the authors overexpressed a STAT3-GFP construct and demonstrated that forced STAT3 activation blunted the ICG-001-induced rise in CD38, placing STAT3 causally between Wnt signaling and CD38 regulation.

Functional anti-tumor effects were measured in antibody-dependent cellular cytotoxicity (ADCC) assays using NK92MI-CD16 effector cells at a 5:1 effector-to-target ratio. ICG-001 pretreatment followed by daratumumab produced significantly greater myeloma cell lysis than either agent alone across all three cell lines (p ≤ 0.001–0.0001). The combination was also tested with cord-blood-derived primary NK cells at a 25:1 ratio and in four patient-derived primary myeloma samples — including two from daratumumab-experienced patients — yielding similarly enhanced killing. In the in vivo arm, CB17 SCID mice bearing subcutaneous H929 xenografts were randomized into four groups (n = 5 each): vehicle, ICG-001 alone (100 mg/kg i.p. daily), daratumumab alone (8 mg/kg i.p. weekly), or the combination. Tumor volumes in the combination group were significantly smaller than in either monotherapy group, and immunohistochemistry of excised tumors confirmed higher CD38 protein staining in ICG-001-treated animals, consistent with the in vitro mechanistic data.

These findings present a coherent therapeutic rationale: myeloma cells use active Wnt signaling to maintain STAT3 activity, which suppresses CD38 and thereby limits daratumumab's reach. Blocking Wnt reverses this suppression, re-exposes CD38, and makes tumors more vulnerable to immune-mediated killing. Because ICG-001 is an established pharmacological tool and Wnt inhibitors are under active clinical investigation in hematologic malignancies, the combination strategy described here is clinically tractable. The main caveats are the preclinical nature of the evidence, small animal group sizes, and the absence of daratumumab-resistant cell line models specifically engineered for low CD38; clinical validation will be needed.