From bench to bedside: Improving the clinical safety of GalNAc-siRNA conjugates using seed-pairing destabilization.

Preclinical mechanistic studies have pointed towards RNA interference-mediated off-target effects as a major driver of hepatotoxicity for GalNAc-siRNA conjugates. Here, we demonstrate that a single glycol nucleic acid or 2'-5'-RNA modification can substantially reduce small interfering RNA (siRNA) seed-mediated binding to off-target transcripts while maintaining on-target activity. In siRNAs with established hepatotoxicity driven by off-target effects, these novel designs with seed-pairing destabilization, termed enhanced stabilization chemistry plus (ESC+), demonstrated a substantially improved therapeutic window in rats. In contrast, siRNAs thermally destabilized to a similar extent by the incorporation of multiple DNA nucleotides in the seed region showed little to no improvement in rat safety suggesting that factors in addition to global thermodynamics play a role in off-target mitigation. We utilized the ESC+ strategy to improve the safety of ALN-HBV, which exhibited dose-dependent, transient and asymptomatic alanine aminotransferase elevations in healthy volunteers. The redesigned ALN-HBV02 (VIR-2218) showed improved specificity with comparable on-target activity and the program was reintroduced into clinical development.

Selection of GalNAc-conjugated siRNAs with limited off-target-driven rat hepatotoxicity.

Small interfering RNAs (siRNAs) conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand are being evaluated in investigational clinical studies for a variety of indications. The typical development candidate selection process includes evaluation of the most active compounds for toxicity in rats at pharmacologically exaggerated doses. The subset of GalNAc-siRNAs that show rat hepatotoxicity is not advanced to clinical development. Potential mechanisms of hepatotoxicity can be associated with the intracellular accumulation of oligonucleotides and their metabolites, RNA interference (RNAi)-mediated hybridization-based off-target effects, and/or perturbation of endogenous RNAi pathways. Here we show that rodent hepatotoxicity observed at supratherapeutic exposures can be largely attributed to RNAi-mediated off-target effects, but not chemical modifications or the perturbation of RNAi pathways. Furthermore, these off-target effects can be mitigated by modulating seed-pairing using a thermally destabilizing chemical modification, which significantly improves the safety profile of a GalNAc-siRNA in rat and may minimize the occurrence of hepatotoxic siRNAs across species.

Pten-null tumors cohabiting the same lung display differential AKT activation and sensitivity to dietary restriction.

PTEN loss is considered a biomarker for activated phosphoinositide 3-kinase (PI3K)/AKT, a pathway frequently mutated in cancer, and was recently shown to confer resistance to dietary restriction. Here, we show that Pten loss is not sufficient to drive AKT activation and resistance to dietary restriction in tumors with low growth factor receptor levels. We describe a murine Pten-null Kras-driven lung cancer model that harbors both dietary restriction-resistant, higher-grade, bronchiolar tumors with high AKT activity, and dietary restriction-sensitive, lower-grade, alveolar tumors with low AKT activity. We find that this phenotype is cell autonomous and that normal bronchiolar cells express higher levels of insulin-like growth factor-I receptor (IGF-IR) and of ectonucleoside triphosphate diphosphohydrolase 5 (ENTPD5), an endoplasmic reticulum enzyme known to modulate growth factor receptor levels. Suppression of ENTPD5 is sufficient to decrease IGF-IR levels and sensitize bronchiolar tumor cells to serum in vitro and to dietary restriction in vivo. Furthermore, we find that a significant percentage of human non-small cell lung carcinomas (NSCLC) have low AKT activity despite PTEN loss.