A Peptide Delivery System That Guides a Cancer Drug Directly to Tumors, Sparing Healthy Organs

Researchers created DiWB-1, a peptide-drug conjugate that links an LHRH-receptor-targeting peptide to the PI3K inhibitor buparlisib. DiWB-1 was more potent than buparlisib alone against LHRH-receptor-positive breast cancer cells (IC50 of 1.8 μM vs 2.4 μM) while being less toxic to normal cells. In mice, DiWB-1 suppressed tumors effectively while avoiding the liver damage, kidney damage, and blood sugar spikes caused by buparlisib alone. The conjugate also showed favorable metabolic stability with a half-life of 5.6 hours, slightly longer than the established peptide drug triptorelin (4.2 hours).

The researchers developed the LHRH-targeting peptide IV-6, characterized its receptor affinity and metabolic stability, then conjugated it to buparlisib to form DiWB-1. They tested anti-cancer activity in vitro against LHRH-receptor-positive MDA-MB-231 breast cancer cells and normal cells. In vivo efficacy was assessed in a mouse xenograft tumor model, with toxicity evaluated via organ histology and blood chemistry. Pharmacokinetic studies measured half-life and metabolic stability.

PI3K inhibitors are effective against certain cancers but cause serious side effects because they hit healthy cells too. By attaching buparlisib to a peptide that homes in on LHRH receptors — which are overexpressed on many cancer types — the researchers created a drug that preferentially accumulates in tumors. This peptide-drug conjugate approach could make potent but toxic cancer drugs safer and more effective by delivering them directly to cancer cells.

Peptide-drug conjugates (PDCs) are an emerging class of targeted cancer therapy positioned between small-molecule drugs and the larger antibody-drug conjugates (ADCs). PDCs are smaller, cheaper to manufacture, and can penetrate tumors more easily than antibodies. LHRH-receptor targeting is particularly versatile because these receptors are overexpressed in breast, prostate, ovarian, and endometrial cancers. DiWB-1 demonstrates the practical promise of this approach — taking a drug with known efficacy but problematic toxicity and making it tumor-selective.

This is preclinical research using a single cancer cell line (MDA-MB-231) and mouse xenograft models. The improvement in IC50 over buparlisib alone is modest (1.8 vs 2.4 μM). The study only tested LHRH-receptor-positive tumors; efficacy against receptor-negative cancers is unknown. Human pharmacokinetics and safety are not established. Manufacturing complexity and cost of the PDC are not discussed.