The inhibition of a tumour cell surface protease in vivo and its re-activation by oxidation

Fluorescent location of human colonic tumour cells by means of an enzyme-inhibitor complex

We studied the enzymic status of the tumour cell surface protease, guanidinobenzoatase (GB) in frozen sections of a human colonic tumour grown in nude mice and also in human colons. Active enzyme was demonstrated by the binding of a synthetic fluorescent probe for the active centre of guanidinobenzoatase (GB). It was observed that tissue derived inhibitors of GB blocked the binding of this fluorescent probe and that enzyme inhibitor complex formation could be controlled by lowering the pH of the medium with lactic acid. The presence of an inhibitor of GB in the mouse tumour extract was taken advantage of by making two fluorescent derivatives of this inhibitor; both of which located GB on colonic tumour cells in frozen sections of human colon.

The status of trypsin-like enzymes in squamous-cell carcinoma of the head and neck region

The activity of two proteases associated with tumour cells was studied using frozen sections of squamous-cell carcinoma and fluorescent probes for the enzymes. Four fluorescent probes were used to define the enzymic status of guanidinobenzoatase on the surface of the squamous carcinoma cells. Each of four probes demonstrated the location of cells possessing inactive guanidinobenzoatase, whereas adjacent cells of the same tumour exhibited active enzyme. It was shown that the inactive form of the enzyme was an inhibitor-enzyme complex that could be dissociated. In contrast, all of the squamous carcinoma cells possessed active trypsin-like enzymes that were recognised by fluorescent aprotinin molecules. The observed variation in enzymic status of these two tumour-associated enzyme systems is discussed in the context of a possible biological control mechanism for cell migration.

Studies on the activity of a protease associated with cells at the advancing edge of human tumour masses in frozen sections

A fluorescent probe has been employed to study the status of a tumour associated protease, guanidinobenzoatase, in frozen sections of human tumours obtained from the head and neck regions. The results indicate that in vivo a naturally occurring inhibitor of guanidinobenzoatase effectively controls the activity of this enzyme on the majority of cells in a tumour mass. This inhibitor can be artificially displaced by formaldehyde treatment of the frozen sections and this treatment reveals the extent of latent enzyme in the section. In the frozen sections it was noticed that at the advancing edges of the tumour mass, the tumour cells possessed uninhibited guanidinobenzoatase, an enzyme known to degrade the link peptide between cells and fibronectin. It was shown that a synthetic inhibitor of guanidinobenzoatase selectively inhibited the guanidinobenzoatase of the tumour cells at the advancing edge of the tumour mass. It is suggested that the guanidinobenzoatase on cells at the leading edge of the tumour mass plays an important role in the invasion of adjacent host tissue. This synthetic inhibitor of guanidinobenzoatase has no inhibitory action on other trypsin-like enzymes and might therefore be of value in limiting the growth of the tumour mass in vivo.