Human Cancer Antigen Globo H Is a Cell-Surface Ligand for Human Ribonuclease 1

Area of Science:

• Biochemistry
• Oncology
• Immunology

Background:

• Pancreatic-type ribonucleases, like RNase A and human RNase 1, are secretory enzymes involved in RNA cleavage.
• Recent studies have shown that engineered ribonuclease variants exhibit selective toxicity towards cancer cells, prompting clinical trials.
• The underlying mechanism for this selective cytotoxicity against cancerous versus noncancerous cells remained largely undefined.

Purpose of the Study:

• To elucidate the molecular basis for the selective toxicity of ribonuclease variants against cancer cells.
• To identify specific molecular targets on cancer cells that interact with these ribonuclease enzymes.
• To explore the potential link between ribonuclease activity, tumor-associated antigens, and cancer treatment strategies.

Main Methods:

• A screen for RNase A ligands was performed using an array of mammalian cell-surface glycans.
• Binding affinity studies were conducted for RNase A and RNase 1 against immobilized Globo H.
• Cell-based assays were used to assess the toxicity of an RNase 1 variant upon reduction of Globo H expression.
• Heteronuclear single quantum coherence (HSQC) NMR spectroscopy was employed to characterize the interaction between RNase 1 and Globo H.

Main Results:

• A hexasaccharide, Globo H, a known tumor-associated antigen, was identified as a high-affinity ligand for RNase A.
• RNase A and RNase 1 demonstrated binding affinities in the low micromolar to high nanomolar range for immobilized Globo H.
• Decreasing Globo H expression on human breast adenocarcinoma cells reduced the toxicity of an RNase 1 variant.
• NMR spectroscopy revealed that RNase 1 interacts with Globo H using residues located away from the enzyme's active site.

Conclusions:

• The systemic human ribonuclease RNase 1 binds to Globo H, a moiety prominently displayed on human cancer cells.
• This interaction provides a mechanistic explanation for the selective toxicity of ribonuclease variants against cancer.
• The findings link ribonuclease-based cancer therapy with cancer vaccines targeting Globo H, suggesting a potential mechanism for innate cancer resistance.