Targeting mesotrypsin in breast, prostate and pancreatic cancers

Optimization of two amino acids (green) of the natural trypsin inhibitor BPTI (gray ribbon, top) produces an improved inhibitor with structural complementarity to mesotrypsin (beige).

Inhibition of breast cancer cell malignant growth in 3-D culture is enhanced in treatment with prototype mesotrypsin inhibitor (filled circles) compared with BPTI (open diamonds).

In Matrigel Transwell invasion assays, prostate cancer cells assayed in the presence of prototype mesotrypsin inhibitor showed a dose-dependent reduction in invasion relative to control cells; 100 nM inhibitor was similar in effect to shRNA knockdown of PRSS3 (KD).

Mesotrypsin, encoded by the PRSS3 gene, is a human serine protease whose upregulation has been implicated in promoting tumor progression. Mesotrypsin inhibitors could offer valuable tools for deciphering the pathological role of this enzyme and could also form the basis for novel therapeutic strategies targeting mesotrypsin.

The Proteases in Cancer Laboratory is developing mesotrypsin inhibitors and evaluating their therapeutic potential in preclinical models of breast, pancreatic and prostate cancers.

Mesotrypsin inhibitors could offer a new approach to slowing cancer cell malignant growth, invasion and metastasis.

But targeting mesotrypsin specifically is a challenge because mesotrypsin is one enzyme among a large family of proteases with similar structure and specificity. In addition, mesotrypsin has proved notoriously resistant to inhibition by many inhibitors of other trypsins.

By using site-directed mutagenesis, biochemical assays and X-ray crystallography to define features of mesotrypsin specificity that are distinct from other serine proteases, the Radisky Proteases in Cancer Laboratory has created a prototype mesotrypsin inhibitor with stronger affinity than any other natural or artificial inhibitor yet studied.

This new engineered inhibitor shows striking anti-cancer activity in physiologically relevant assays of breast cancer cell malignant growth, pancreatic cancer cell invasion and prostate cancer cell invasion. Further engineering of this and other polypeptide inhibitors for enhanced mesotrypsin specificity may generate targeted therapeutics capable of suppressing cancer progression in patients.

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