Eribulin induces micronuclei and enhances the nuclear localization of cGAS in triple-negative breast cancer cells

Eribulin's exclusive binding to microtubule plus ends results from discrimination between GTP and GDP forms of β-tubulin

The clinically approved anticancer agent eribulin (Halaven®) exerts cytotoxic antimitotic effects by binding to high affinity sites on exposed plus ends of growing microtubules (MT). Despite X-ray crystallographic mapping of eribulin's binding pocket within β-tubulin's vinca domain, the biophysical basis for eribulin's MT plus end binding exclusivity remains unknown. We performed surface plasmon resonance (SPR) studies of tubulin binding to biotinylated eribulin probes to ask if eribulin discriminates between GTP and GDP forms of β-tubulin, which characterize growing MT plus ends and MT sides, respectively. Tubulin binding to biotin-eribulin proceeded via a single state binding reaction, while binding to biotin-vinblastine occurred via a two-state reaction incorporating a conformational change. Biochemical approaches confirmed tubulin conformational changes induced by vinblastine but not eribulin. SPR competition studies using free eribulin and vinblastine confirmed tubulin binding specificity to cognate biotinylated probes, showing that eribulin binding within the β-tubulin vinca domain is physically and functionally distinct from vinblastine. SPR studies using tubulin containing only GTP or GDP forms of β-tubulin showed that while biotin-eribulin has only slightly higher overall affinity for GTP-tubulin, dissociation from GTP-tubulin was ∼7-fold slower than from GDP-tubulin, establishing that eribulin discriminates between GTP and GDP forms of β-tubulin. In contrast, vinblastine fails to discriminate between these two tubulin forms, consistent with its known binding to both MT ends and sides. Overall, our results establish, for the first time, the biophysical basis for eribulin's MT plus end binding exclusivity as resulting from the ability to discriminate between GTP and GDP forms of β-tubulin.

The role of cGAS in epithelial dysregulation in inflammatory bowel disease and gastrointestinal malignancies

The gastrointestinal tract is lined by an epithelial monolayer responsible for selective permeability and absorption, as well as protection against harmful luminal contents. Recognition of foreign or aberrant DNA within these epithelial cells is, in part, regulated by pattern recognition receptors such as cyclic GMP-AMP synthase (cGAS). cGAS binds double-stranded DNA from exogenous and endogenous sources, resulting in the activation of stimulator of interferon genes (STING) and a type 1 interferon response. cGAS is also implicated in non-canonical pathways involving the suppression of DNA repair and the upregulation of autophagy via interactions with PARP1 and Beclin-1, respectively. The importance of cGAS activation in the development and progression of inflammatory bowel disease and gastrointestinal cancers has been and continues to be explored. This review delves into the intricacies of the complex role of cGAS in intestinal epithelial inflammation and gastrointestinal malignancies, as well as recent therapeutic advances targeting cGAS pathways.