Prof.  Jieqing  Liu
Huaqiao University,  China

Title: Transforming Weakly Active Natural Products into Potent Protein Degraders: The PROTAC-Based Strategy for Regulation in Cancer

Abstract:

Natural products are an important source of anticancer drugs, yet their development has long been constrained by weak activity and undefined targets. PROTACs (proteolysis-targeting chimeras) replace "occupancy-driven" inhibition with "event-driven" catalytic degradation, offering an entirely new paradigm for revitalizing weakly active natural products: the natural product scaffold only needs to bring the target protein into proximity with an E3 ligase, and does not itself require potent inhibitory activity. Drawing on two unpublished works from our group, this lecture presents the complete research workflow of "PROTACification of natural products."

Case 1 (lung cancer): Using the abietane diterpene dehydroabietic acid (DHA) as the POI ligand, we constructed a 30-molecule library and identified TO3, which showed an 18.85-fold improvement in potency over DHA in A549 cells (IC₅₀ 4.83 μM vs 91.04 μM), with a safety window of ~17.9-fold toward normal lung cells. TMT-based proteomics (3,000 differentially expressed proteins) combined with a four-tier filtering strategy pinpointed the dual targets KDM5B / CRIM1. MG132/MLN4924 rescue assays, SPR (K_D = 2.78×10⁻³ M), CETSA/DARTS, and competition experiments confirmed UPS-dependent direct binding. Mechanistically, TO3 acts through PTEN restoration and P-AKT downregulation, a finding reproduced in H460 cells. At 60 mg/kg, TO3 reduced A549 xenograft tumor volume by approximately 32%, with no overt toxicity in major organs.

Case 2 (breast cancer): Using artesunate (ART) as the ligand, we synthesized 15 PROTACs; Q2 enhanced antiproliferative activity by 8.7–14.7-fold. Integrating clues from prior pHDPP probe studies with docking, PPI analysis, and BLI/CETSA/DARTS validation, HMGB1 was confirmed as a direct target of artemisinin-class compounds. Through CRBN recruitment, Q2 degrades HMGB1 in a UPS-dependent, dose- and time-dependent manner reaching maximal degradation at 48 h; 100-ns molecular dynamics simulations showed that the CRBN–Q2–HMGB1 ternary complex remains stable throughout (MM-PBSA −375.26 kJ/mol). Downstream, Q2 coordinately activates p53 while downregulating MAPK and CDK1, inducing apoptosis and G2/M arrest. At 120 mg/kg, Q2 suppressed MCF-7 xenograft growth significantly better than an equidose of ART, with good tolerability.

Together, these two cases demonstrate that PROTACification not only boosts the cellular potency of weakly active natural products by an order of magnitude, but the PROTAC itself can also serve as a "molecular probe" for target discovery—providing a reproducible, dual-value pathway for mechanistic investigation and translational development of natural products.

Keywords: natural products; PROTAC; dehydroabietic acid; artesunate; KDM5B/CRIM1; HMGB1; cancer therapy

Biography: