Comparative investigations of the action of two nitrogen mustard derivatives on the early stages of development of chick embryos.

CYTOTOXIC compounds act by combining with the biochemical constituents of cells. Because of the complexity of living matter, the cytotoxic activity is highly complicated in nature and is therefore far from being thoroughly understood. In order to analyse the cytotoxicity of any chemical compound, many biological variables concerned in determining the mode of action of the compound and its selectivity for any particular range of cells have to be taken into account (Danielli, 1952,1954). Cells of the early embryonic stages are a suitable material for cytotoxic investigations. Although not completely differentiated, they soon arrange themselves into a few embryonic tissues originating directly from the three fundamental germ layers. These tissues consist of cells which may be regarded as the precursors of all the cells of the adult organ. It is interesting to inquire whether they show in these early stages a specific selectivity to cytotoxic compounds which is similar to the selectivity of tumour cells, and which may later be derived indirectly from different germ layers. One of many biological variables which should be taken into account in cytotoxic investigations is the presence or absence of particular enzymes causing the cells to be more sensitive or more resistant to the cytotoxic drugs concerned. So far, very little information is available on the enzymatic constitution of the germ layers (Steinbach & Moog, 1955). The experiments reported here aimed at comparing the cytotoxic activity of two related derivatives of nitrogen mustard, one of which is an acetyl derivative of the other. Their formulas are as follows: