A Bioengineered Peptide that Localizes to and Illuminates Medulloblastoma: A New Tool with Potential for Fluorescence-Guided Surgical Resection

Cyclic Ruthenium-Peptide Prodrugs Penetrate the Blood-Brain Barrier and Attack Glioblastoma upon Light Activation in Orthotopic Zebrafish Tumor Models

The blood-brain barrier (BBB) presents one of the main obstacles to delivering anticancer drugs in glioblastoma. Herein, we investigated the potential of a series of cyclic ruthenium-peptide conjugates as photoactivated therapy candidates for the treatment of this aggressive tumor. The three compounds studied, Ru-p(HH), Ru-p(MH), and Ru-p(MM) ([Ru(Ph2phen)2 (Ac-X1RGDX2-NH2)]Cl2 with Ph2phen = 4,7-diphenyl-1,10-phenanthroline and X1, X2 = His or Met), include an integrin-targeted pentapeptide coordinated to a ruthenium warhead via two photoactivated ruthenium-X1,2 bonds. Their photochemistry, activation mechanism, tumor targeting, and antitumor activity were meticulously addressed. A combined in vitro and in vivo study revealed that the photoactivated cell-killing mechanism and their O2 dependence were strongly influenced by the nature of X1 and X2. Ru-p(MM) was shown to be a photoactivated chemotherapy (PACT) drug, while Ru-p(HH) behaved as a photodynamic therapy (PDT) drug. All conjugates, however, showed comparable antitumor targeting and efficacy toward human glioblastoma 3D spheroids and orthotopic glioblastoma tumor models in zebrafish embryos. Most importantly, in this model, all three compounds could effectively cross the BBB, resulting in excellent targeting of the tumors in the brain.

Integrin-Targeting Knottin Peptide-Drug Conjugates Are Potent Inhibitors of Tumor Cell Proliferation

Antibody-drug conjugates (ADCs) offer increased efficacy and reduced toxicity compared to systemic chemotherapy. Less attention has been paid to peptide-drug delivery, which has the potential for increased tumor penetration and facile synthesis. We report a knottin peptide-drug conjugate (KDC) and demonstrate that it can selectively deliver gemcitabine to malignant cells expressing tumor-associated integrins. This KDC binds to tumor cells with low-nanomolar affinity, is internalized by an integrin-mediated process, releases its payload intracellularly, and is a highly potent inhibitor of brain, breast, ovarian, and pancreatic cancer cell lines. Notably, these features enable this KDC to bypass a gemcitabine-resistance mechanism found in pancreatic cancer cells. This work expands the therapeutic relevance of knottin peptides to include targeted drug delivery, and further motivates efforts to expand the drug-conjugate toolkit to include non-antibody protein scaffolds.