Novel spirocyclic dimer, SpiD3, targets critical tumor survival pathways and displays potent preclinical activity in B-cell chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) cell survival and growth is fueled by aberrant activation of various pro-survival signaling pathways within tumor niches. Specifically, B-cell receptor (BCR) signaling, toll-like receptor signaling, and supportive cellular interactions drive constitutive activation of NF-κB signaling and transcription of proliferative/pro-survival genes. Directly targeting the NF-κB pathway has been a challenge, however, herein, we investigated SpiD3, a spirocyclic dimer and novel NF-κB pathway inhibitor in preclinical models of CLL. Through cross-linking NF-κB proteins, SpiD3 attenuated NF-κB signaling in CLL cells independent of microenvironmental signals. Our integrated multi-omics and functional analyses revealed BCRNF-κB signaling, endoplasmic reticulum stress, oxidative stress, and activation of the unfolded protein response among the top pathways modulated by SpiD3 treatment. This was accompanied by marked inhibition of global protein synthesis, cumulating in profound anti-tumor properties in CLL cells. SpiD3 also modulated tumor microenvironment interactions shown by decreased chemokine and cytokine gene expression as well as decreased CLL chemotaxis towards CXCL-12 and CXCL-13. Moreover, SpiD3 induced apoptosis of stroma-protected primary CLL cells comparable to the BCR-targeting agent, ibrutinib. SpiD3 strikingly demonstrated selective cytotoxicity towards CLL cells compared to healthy lymphocytes, synergized with ibrutinib, and retained its anti-tumor effects in ibrutinib-resistant CLL cells. Altogether, our findings provide preclinical evidence for SpiD3 as an attractive therapeutic agent for CLL, especially in the context of relapsed/refractory disease.