Prognostic significance of lysosomal cysteine proteases in the estimation of the effectiveness of the antitumor therapy

The influence of the antitumor drugs, cyclophosphamide (CPA) and nitrosomethylurea (NMU) on the activity of lysosomal cysteine proteases cathepsin B and L in tumor tissue has been investigated using CPA-sensitive (LS) and CPA-resistant mouse lymphosarcomas (RLS). (These drugs exhibit high and low antitumor efficiency towards LS and RLS mouse lymphosarcomas, respectively). Regression or reduction in the growth rate of LS and RLS lymphosarcomas caused by CPA or NMU administration was accompanied by the increase in the activity of cysteine proteases cathepsin B and L in the tumor tissue. The increase of cathepsin B and L activity in tumor tissue correlated with the therapeutic effect of these drugs. Data obtained suggest that activity of cathepsin B and L in tumor tissue has a prognostic significance for the estimation of the effectiveness of antitumor therapy.