Nitrobenzylthioinosine-binding protein overexpression in human breast, liver, stomach and colorectal tumour tissues.

Using high-affinity [3H]nitrobenzylthioinosine (NBMPR) equilibrium binding assays, fresh human tumour tissues were consistently found to be over expressing NBMPR binding proteins at levels 1.5 to 5-fold higher than in corresponding normal tissues. The mean Bmax values for breast (n = 6), liver (n = 2) and stomach (n = 4) tumour tissues were 2.89 +/- 0.76, 0.5I +/- 0.03 and 1.38 +/- 0.43 fmol/micrograms of plasma membrane protein, respectively. These values were all significantly higher (p < 0.05, student paired t-test) than those for the normal tissues (Bmax's = 0.97 +/- 0.05, 0.20 +/- 0.02 and 0.51 +/- 0.05 fmol/microgram of protein for breast, liver and stomach, respectively). For colorectal tissues (n = 10), the mean Bmax value for the tumour specimens (1.36 +/- 0.24 fmol/microgram of protein) was also significantly higher (p < 0.005, student paired t-test) than those for the normal specimens taken 5 cm (0.42 +/- 0.03 fmol/microgram of protein) and 10 cm (0.47 +/- 0.04 fmol/(g of protein) away from tumour site. There were no consistent and significant differences in the binding affinities between tumour and normal tissues in these four tissue types (Kd values ranged from 0.07 to 1.0 nM, p > 0.05, student paired t-test).