[3H]thymidine labels less than half of the DNA-synthesizing cells in the mouse tumour, carcinoma NT

In vivo-like drug responses of human tumors growing in three-dimensional gel-supported primary culture

An in vitro test of cell sensitivity to drugs that indicates in vivo response is an important need in cancer therapy and cancer drug development. Toward this end, we previously developed a collagen gel-supported culture system for growth of human tumors. This three-dimensional culture system is general and grows tumors at high frequency directly from surgery or biopsy that maintain important in vivo properties in vitro, including tissue architecture. We report here that with autoradiographic techniques measuring cellular DNA synthesis the drug responses of individual cells within the tissue structure of in vitro-grown tumors can be determined. Twenty tumor classes, including all the major ones, have been measured in toto at greater than 50% frequency. Quantitative and qualitative results show increasing cell kill with rising cytotoxic drug concentration, differential drug sensitivities of multiple cell types within individual cultured tumors, differential sensitivities of a series of tumors of the same histopathological classification to a single drug, differential sensitivities of individual tumors to a series of drugs, and sensitivity patterns of various tumor types similar to the sensitivities found in vivo. Therefore, the results indicate that potentially important therapeutic data can be obtained from tumor specimens growing in vitro for the individual cancer patient as well as for rational and relevant screening for new agents active against human solid tumors.

The validity of the labelling index in tumour studies

The distribution of labelled cells through 5 different mouse tumours was measured after a single injection of [3H]-thymidine [( 3H]-TdR) or [3H]-deoxyuridine [( 3H]-UdR). All the tumours had areas where the percentage of labelled cells (the labelling index, LI) was high and areas where the LI was very low. The total area with a low LI was greater after [3H]-TdR than after [3H]-UdR injection in all 5 tumours. In one of the tumours, carcinoma NT, repeated injections of [3H]-UdR at 2 h intervals caused the areas of high LI to spread, eliminating all areas of low LI in many specimens. When 5-fluorodeoxyuridine (FUdR) was injected, to block de novo DNA synthesis in carcinoma NT, [3H]-TdR was incorporated by many more cells. The LI was increased throughout the tumour and no area had a LI below 20% after FUdR plus [3H]-TdR. After flash-labelling with [3H]-TdR alone, nearly half the tumour had a LI below 20%. We conclude that the labelling seen after FUdR plus [3H]-TdR represented the true distribution of S phase cells in carcinoma NT. Routine flash-labelling with [3H]-TdR or [3H]-UdR left nearly half the S phase cells unlabelled and gave an erroneously low value for the proportion of DNA synthesising cells in the tumour. The results suggest that many tumour cells have very large endogenous nucleotide pools which cannot be flooded by a single injection, even of [3H]-UdR.

Do cells of continually renewing populations and those stimulated from quiescence respond similarly to HU and Ara-C?

The cytocidal and cytostatic effects of a single dose of either hydroxyurea (HU) or cytosine arabinoside (Ara-C) have been studied in a variety of tissues, from both rats and mice, by autoradiographic and histological methods. The necrogenic effects of the drugs on DNA-synthesising cells from continually renewing populations have been compared with the effects on cells induced to enter DNA synthesis from a formerly quiescent state. Four models of stimulated proliferation have been studied; the isoprenaline-stimulated salivary glands, the testosterone-stimulated seminal vesicle in the castrate, the regenerating liver after two-thirds partial hepatectomy, and a model of diethylnitrosamine (DEN)-induced hepatocyte proliferation. The time course of the cytokinetic response in each tissue was followed for a period of 24 h after drug treatment. The cytostatic effects of the drugs were similar in all tissues investigated, DNA synthesis being inhibited for a 4- to 5-h period. However, the sensitivity to the lethal effects showed both tissue and species variability.