From Daffodils to Drug Leads: Amaryllidaceae Alkaloids Target Protein Translation in Chronic Lymphocytic Leukemia to Induce Selective Apoptosis

Abstract Targeting protein translation is a promising strategy in oncology, especially for malignancies dependent on short-lived survival factors. The clinical translation inhibitor homoharringtonine (HHT) was recently discontinued in the U.S. due to poor solubility and cardiotoxicity, creating an urgent need for new leads. We investigated structurally distinct Amaryllidaceae alkaloids, narciclasine (NCS), lycorine (LYC), and haemanthamine (HAEM), in models of chronic lymphocytic leukemia (CLL) and Richter transformation (RT). Using an optimized 10 L Soxhlet extraction of ’Carlton’ daffodil bulbs, an unprecedented NCS yield of 250 mg/kg was achieved, doubling previous laboratory records. NCS showed potent activity against primary CLL cells and the RT-derived HPRT1 line (IC50 = 50 nM), while normal T-cell viability remained largely unaffected at doses producing near-complete CLL cell depletion, indicating a favorable therapeutic window. O-Propargyl-puromycin incorporation and [3H]-leucine assays confirmed dose-dependent inhibition of de novo protein synthesis, triggering selective depletion of the short-lived anti-apoptotic protein Mcl-1 while leaving stable Bcl-2 unaffected. Mcl-1 loss induced mitochondrial depolarization, Annexin V/PI positivity, and PARP cleavage. Combination studies with the Bcl-2 inhibitor venetoclax revealed synergistic activity across all compounds, most pronounced for HAEM, consistent with its comparatively modest Mcl-1 depletion. These findings establish that Amaryllidaceae alkaloids exploit the ″translational addiction″ of leukemia cells to Mcl-1 and validate the isocarbostyril and phenanthridine scaffolds as mechanistically characterized leads. SAR-guided analogue optimization to improve pharmacokinetic properties while preserving the translational inhibition pharmacophore represents the planned next stage of this program.