Cellectar Biosciences (CLRB) Study update summary

Platform overview and scientific rationale

• Phospholipid ether (PLE) platform targets remodeled, cholesterol-rich lipid rafts common to many cancers, enabling broad application across hematologic and solid tumors.

• Tumor targeting is antigen-independent, relying on raft-mediated, biophysical partitioning rather than ligand-receptor docking, overcoming limitations of traditional antibody or peptide targeting.

• High protein binding, especially to albumin, enhances tumor microenvironment accumulation and retention, with pharmacokinetics characterized by membrane-driven distribution, minimal metabolism, slow elimination, and prolonged tumor retention.

• The PLE scaffold is metabolically stable, resists enzymatic degradation, and supports modular payload conjugation, including radiopharmaceuticals, small molecules, mRNA, siRNA, degraders, and peptides.

• The tumor microenvironment amplifies lipid raft abundance, further enhancing selective uptake and retention of PLE-based therapeutics.

Preclinical and clinical validation

• Over 180 tumor types tested in vitro, all showing significant lipid raft presence and PLE uptake.

• Lead asset iopofosine I-131 (CLR 131) demonstrated high overall (98.2%) and major (61.8%) response rates in pivotal Phase 2b CLOVER-WaM study for relapsed/refractory Waldenström macroglobulinemia, with durable responses and manageable hematologic toxicity.

• Clinical studies in Waldenstrom's macroglobulinemia show 84% overall response rate and 18-month median duration in refractory patients.

• Activity observed in multiple myeloma (32% ORR at >60 mCi; 50% ORR in quad-class refractory), diffuse large B-cell lymphoma (30% ORR), other NHLs (50% ORR), pediatric high-grade glioma (PFS ~8.1 months, OS ~11.5 months), and head and neck cancers.

• CLR 125 (Auger emitter), CLR 225 (alpha emitter), and CLR 212 (lead-212) showed significant tumor uptake, growth inhibition, and survival benefit in preclinical models, with minimal off-target toxicity.

Pipeline and modality expansion

• The PLE scaffold enables delivery of diverse payloads, including radiopharmaceuticals, small molecules, mRNA, siRNA, peptides, PROTACs, and molecular glues, with tumor-selective cytoplasmic delivery.

• Small-molecule and peptide conjugates showed broad in vitro and in vivo activity, with full tumor regression and no regrowth post-treatment in breast cancer models.

• mRNA and siRNA conjugates achieved tumor-restricted expression and knockdown of target genes, with no off-target effects in non-tumor cells.

• Oligonucleotide delivery is a future priority due to specificity and robust intellectual property.

• Design principles emphasize preserving scaffold biophysics, engineering linkers for stability and release, and re-mapping biodistribution for each payload.