QSAR of acridines. II. Features of nitracrine analogs for high anti-tumor activity and selectivity on mice, searched by PCA and MRA methods.

A study of quantitative structure-activity relationships (QSAR) of 32 nitro-9-aminoacridine derivatives has been carried out. The results of the four biological tests in vitro, anti-tumor activity against S-180 and toxicity on healthy as well as on tumor bearing mice were subjected to principal component analysis (PCA). Two significant principal components PC1 and PC2 (containing 81.4% and 8.1% of total data set information, respectively) were extracted. The biological meaning of PCs was identified: PC1 corresponds to a general biological activity, PC2 mainly to selectivity. To obtain predictability of biological activities multiple regression analysis (MRA) for PC1 and PC2 were used. The general biological activity (PC1) is parabolically dependent on the lipophilicity (log P*) of the substituent on 9-amino group (R = 0.97); selectivity (PC2), however, on the shape index 2K and the indicator variable IN2N (R = 0.76). For high antitumor activity and improved therapeutic effectivity (LD50/ED50) 1-nitro-9-amino-acridines should be characterized by: (i) lipophilicity, expressed as log P*, between -1 and -2; (ii) three or more methylene spacers between proximal and distal nitrogen atoms in the side chain, if the distal nitrogen is present; (iii) high 2K value for the side chain, as for a large and preferably unbranched substituent on C9.