Phenyl sulfur mustard derivatives of distamycin A.

The design, synthesis, and cytotoxic activity of novel benzoyl and cinnamoyl sulfur mustard derivatives of distamycin A are described and structure activity relationships are discussed. These sulfur mustards are more potent cytotoxics than corresponding nitrogen mustards in spite of the lower alkylating power, while their sulfoxide analogues are substantially inactive. Cinnamoyl sulfur mustard derivative (7) proved to be one of the most active distamycin-derived cytotoxics, about 1000 times more potent than melphalan.

Synthesis and antitumor activity of new benzoheterocyclic derivatives of distamycin A.

The design, synthesis, and in vivo and in vitro antileukemic activity of a novel series of compounds (13-22 and 34), in which different benzoheterocyclic rings, bearing a nitrogen mustard or a benzoyl nitrogen mustard or an alpha-bromoacryloyl group as alkylating moieties, are tethered to a distamycin frame, are reported, and structure-activity relationships are discussed. The new derivatives were prepared by coupling nitrogen mustard-substituted, benzoyl nitrogen mustard-substituted, or alpha-bromoacryloyl-substituted benzoheterocyclic carboxylic acids 23-32 with desformyldistamycin (33) or in one case with its two-pyrrole analogue 35. With very few exceptions, the activities of compounds bearing the same alkylating moiety are slightly affected by the kind of the heteroatom present on the benzoheterocyclic ring. All novel compounds, with one exception, showed in vitro activity against L1210 murine leukemia cell line comparable to or better than that of tallimustine. The compounds in which the nitrogen mustard and the alpha-bromoacryloyl moieties are directly linked to benzoheterocyclic ring showed potent cytotoxic activities (IC(50) ranging from 2 to 14 nM), while benzoyl nitrogen mustard derivatives of benzoheterocycles showed reduced cytotoxic activities, and one compound (16) of this cluster was the sole derivative devoid of significant activity. Compound 18, a 5-nitrogen mustard N-methylindole derivative of distamycin, showed the best antileukemic activity in vivo, with a very long survival time (%T/C = 457), significantly increased in comparison to tallimustine (%T/C = 133), and was selected for further extensive evaluation. Arrested polymerase chain reaction and direct DNA fragmentation assays were performed for compound 18 and the structurally related compounds 13-17 and 19. The results obtained have shown that both alkylating groups and oligopeptide frames play a crucial role in the sequence selectivity of these compounds.

Cytotoxic halogenoacrylic derivatives of distamycin A.

The design, synthesis, in vitro and in vivo activities of a series of halogenoacrylic derivatives of distamycin A are described. The structure-activity relationships indicate a key role of the reactivity of alpha-halogenoacrylic moiety. The reactivity and the putative alkylating mechanism of these compounds are different from those of the nitrogen mustards and possibly based on a Michael type reaction. This supports the hypothesis that these compounds represent a class of minor groove binders mechanistically different from tallimustine.

Cytotoxic alpha-bromoacrylic derivatives of distamycin analogues modified at the amidino moiety.

The design, synthesis, in vitro and in vivo activities of novel alpha-bromoacrylic derivatives of distamycin A, modified at the amidino moiety by the replacement with basic or non-basic groups are reported. In spite of the relevance of these modifications of distamycin frame, the new derivatives are potent cytotoxics. The presence of the amidino moiety, is, therefore; not an absolute requirement for the activity. In particular due to a favorable myelotoxicity/cytotoxicity ratio, guanidino derivative PNU 166196 was selected for clinical development.

Sequence-specific DNA alkylation of novel tallimustine derivatives.

Three different groups of analogs of the sequence-specific minor groove alkylator tallimustine (2) have been synthesized and investigated. Within group I, the dibromo nitrogen mustard (3) and the half-mustard (4) are more cytotoxic (IC50 = 0.6 and 40 ng/ml respectively) than tallimustine (IC50 = 50.3 ng/ml) against L1210 cells with high reactivity against the region 5'-TTTTGA. The diol derivative (6) and the difluoro nitrogen mustard (5) were not cytotoxic against L1210 cells and did not show any detectable DNA alkylation. The two compounds modified in the propionamidine terminus (7 and 8, group II), showed lower cytotoxic potency (IC50 = 130 and 94 ng/ml respectively) against L1210 cells than tallimustine (IC50 = 50.3 ng/ml) and a loss of in vitro sequence specificity for DNA alkylation. Considering the compounds in which the pyrrole rings were replaced by one (9) or two (10) pyrazole rings, compound 9 was not significantly cytotoxic against L1210 cell line and was apparently unable to produce alkylation on the DNA fragments tested, while compound 10 showed decreased cytotoxicity (IC50 = 114 ng/ml) and no modification in the pattern and intensity of DNA alkylation. The data obtained in this work suggest that it is possible to increase tallimustine potency by modifying the nitrogen mustard moiety. Moreover, the sequence specificity of DNA alkylation appears to be affected by the modification of the propionamidino moiety but not by the isosteric modification of the pyrrole rings. The correlation between cytotoxicity and alkylation pattern suggests that tallimustine exerts its cytotoxicity through DNA sequence-specific alkylation of the adenine located in the sequence 5'-TTTTGA.