The effect of cyclophosphamide on the growth and cellular kinetics of a transplantable rat fibrosarcoma

Fractional incorporation of [3H]thymidine and DNA specific activity as assays of inhibition of tumour growth

The Fractional Incorporation (FI) of [3H] thymidine ([3H]TdR) has been examined in small lung tumours after cyclophosphamide (CY) treatment in vivo and compared to the DNA specific activity (SA) at different times after treatment. FI was found to correlate with the incidence of labelled cells after treatment, whereas SA did not, due to the loss of DNA from drug-killed cells 72 h after treatment. The FI is independent of the precursor concentration in the tissue, and therefore may give a better index of DNA synthesis in irregularly perfused tissues than SA. Following either CY or 60Co radiation treatment, the time necessary for FI to reach the pretreatment level is quite similar to the growth delay measured for the FI depression 45 h after treatment and growth delay has been established in the Lewis lung tumour, which would allow the prediction of growth delay induced by another agent to be made within 2 days of treatment.

A quantitative morphological analysis of the response of a transplantable rat fibrosarcoma to cyclophosphamide

The response of a transplantable rat fibrosarcoma, RIB(5), to a single injection of 100 mg/kg body weight of cyclophosphamide, 0·5, 1, 2 and 3 days after treatment, has been studied by means of a morphometric analysis of tumour sections and has been compared to the changes occurring in untreated tumours. The results showed a transitory increase in thymidine labelling index 12 hours after drug injection accompanied by a low mitotic index which persisted for a further 12 hours. These observations are compared with, and confirm, a previous study involving analysis of smear preparations from tumour cell suspensions. The changes in the proportion of the tumour occupied by erythrocytes and necrotic elements are described. The results of the morphometric analysis have shown the changes occurring in the outer, intermediate and inner zones of the tumour. In all control tumours, and tumours up to 2 days after cyclophosphamide treatment, necrosis was predominant in the inner zone and tumour cell proliferation was most marked in the outer zone. In contrast, 3 days after cyclophosphamide treatment proliferation was predominant in the inner zone and the amount of necrosis was approximately the same in each zone.