Specific staining of iododeoxyuridine and bromodeoxyuridine in tumors double labelled in vivo: a cell kinetic analysis.

The simultaneous and specific staining of iododeoxyuridine (IdUrd) and chlorodeoxyuridine (CldUrd) allows for more accurate estimates of potential doubling time (Tpot). Because CldUrd is not approved for human use, the procedure was adapted for the staining of IdUrd and bromodeoxy-uridine (BrdUrd). The fluorescein isothiocyanate-conjugated B44 antibody (B44-FITC) stained both IdUrd and BrdUrd in tumor nuclei labelled singly with one or the other pyrimidine analogue. However, when MCaK tumors in exponential growth in vivo were pulse labelled with both IdUrd and BrdUrd, the staining of BrdUrd was not seen, and the labelling pattern reflected specificity to IdUrd. These observations were confirmed using tumors pulse labelled with IdUrd and/or BrdUrd at 6 h and/or 0.3 h prior to tumor removal in all possible combinations. Simultaneous specific staining of BrdUrd by Br3 and of IdUrd by B44-FITC was documented by quantification of labelling indices (LIs) from double-labelled tumors. The specificity of B44-FITC for IdUrd in double-labelled tumors was due to a greater affinity of this antibody for IdUrd than for BrdUrd. This technique allowed for two independent estimates of LI and Tpot when tumors were double labelled for 3.0 and 5.5 h. Both IdUrd and BrdUrd are approved for clinical use, and this double-labelling technique should prove to be valuable for measuring the cell kinetics of solid tumors in vivo.