RSPO3 Furin domain-conjugated liposomes for selective drug delivery to LGR5-high cells.

The transmembrane receptor LGR5 potentiates Wnt/ß-catenin signaling by binding both secreted R-spondin (RSPOs) and the Wnt tumor suppressors RNF43/ZNRF3, directing clearance of RNF43/ZNRF3 from the cell surface. Besides being widely used as a stem cell marker in various tissues, LGR5 is overexpressed in many types of malignancies, including colorectal cancer. Its expression characterizes a subpopulation of cancer cells that play a crucial role in tumor initiation, progression and cancer relapse, known as cancer stem cells (CSCs). For this reason, ongoing efforts are aimed at eradicating LGR5-positive CSCs. Here, we engineered liposomes decorated with different RSPO proteins to specifically detect and target LGR5-positive cells. Using fluorescence-loaded liposomes, we show that conjugation of full-length RSPO1 to the liposomal surface mediates aspecific, LGR5-independent cellular uptake, largely mediated by heparan sulfate proteoglycan binding. By contrast, liposomes decorated only with the Furin (FuFu) domains of RSPO3 are taken up by cells in a highly specific, LGR5-dependent manner. Moreover, encapsulating doxorubicin in FuFuRSPO3 liposomes allowed us to selectively inhibit the growth of LGR5-high cells. Thus, FuFuRSPO3-coated liposomes allow for the selective detection and ablation of LGR5-high cells, providing a potential drug delivery system for LGR5-targeted anti-cancer strategies.

Anti-LRP5/6 VHHs promote differentiation of Wnt-hypersensitive intestinal stem cells.

Wnt-induced ß-catenin-mediated transcription is a driving force for stem cell self-renewal during adult tissue homeostasis. Enhanced Wnt receptor expression due to mutational inactivation of the ubiquitin ligases RNF43/ZNRF3 recently emerged as a leading cause for cancer development. Consequently, targeting canonical Wnt receptors such as LRP5/6 holds great promise for treatment of such cancer subsets. Here, we employ CIS display technology to identify single-domain antibody fragments (VHH) that bind the LRP6 P3E3P4E4 region with nanomolar affinity and strongly inhibit Wnt3/3a-induced ß-catenin-mediated transcription in cells, while leaving Wnt1 responses unaffected. Structural analysis reveal that individual VHHs variably employ divergent antigen-binding regions to bind a similar surface in the third ß-propeller of LRP5/6, sterically interfering with Wnt3/3a binding. Importantly, anti-LRP5/6 VHHs block the growth of Wnt-hypersensitive Rnf43/Znrf3-mutant intestinal organoids through stem cell exhaustion and collective terminal differentiation. Thus, VHH-mediated targeting of LRP5/6 provides a promising differentiation-inducing strategy for treatment of Wnt-hypersensitive tumors.