KFERQ sequence in ribonuclease A-mediated cytotoxicity

Area of Science:

• Biochemistry
• Molecular Biology
• Oncology

Background:

• Onconase (ONC), an amphibian ribonuclease, is under clinical investigation as a cancer chemotherapeutic agent.
• ONC is structurally similar to human ribonuclease A (RNase A).
• RNase A can be engineered for cytotoxicity against cancer cells by altering specific amino acid residues.

Purpose of the Study:

• To investigate the role of the KFERQ sequence in RNase A-mediated cytotoxicity and inhibition.
• To compare the cytotoxic potential of modified RNase A variants to Onconase.
• To determine if lysosomal degradation pathways influence the efficacy of RNase A variants.

Main Methods:

• Site-directed mutagenesis was used to create RNase A variants, including G88R RNase A and K7A/G88R RNase A.
• Cytotoxicity assays were performed to measure the efficacy of these variants against cancer cells.
• Enzyme kinetics and binding assays were used to assess the affinity of variants for ribonuclease inhibitor protein (RI).

Main Results:

• The KFERQ sequence in RNase A targets it for lysosomal degradation.
• Substitution of Arg(10) in the KFERQ sequence did not significantly alter G88R RNase A cytotoxicity or RI affinity.
• The K7A/G88R RNase A variant exhibited a nearly 10-fold increase in cytotoxicity and a >10-fold decrease in RI affinity compared to G88R RNase A.
• Modulating the KFERQ-mediated lysosomal pathway did not impact the cytotoxicity of the tested RNase A variants.
• The K7A and G88R substitutions endowed RNase A with cytotoxic activity comparable to Onconase.

Conclusions:

• KFERQ-mediated lysosomal degradation does not limit the cytotoxic activity of RNase A variants.
• Two specific amino acid substitutions (K7A and G88R) are sufficient to confer potent anti-cancer activity to RNase A, similar to Onconase.
• Engineered RNase A variants represent promising candidates for cancer chemotherapy.