A new class of antitumor agents, having structural analogy to amonafide, but differing by the addition of a fourth ring in the nucleus, was synthesized conveniently from anthracene. Compounds with a variety of substituents, containing a basic nitrogen atom and located on the imide nitrogen, were prepared. Thirteen of 19 new compounds had greater growth inhibitory potency than amonafide in a panel of cultured murine and human tumor cells using the sulforhodamine B and MTT dye assays. The most active agents were similarly more toxic than amonafide to normal neonatal rat myocytes in vitro, but they had better chemotherapeutic indexes. From these compounds, the one with a 2-(dimethylamino)ethyl side chain (named azonafide) was chosen for further study. It showed high potency against a panel of cultured human colon cancer cells and it was active against ip P388 leukemia and subcutaneous B16 melanoma in mice. Preliminary structure-activity correlations suggest that the basicity of the side-chain nitrogen and the length of side chain are important determinants of antitumor potency in vitro. Steric hindrance and rigidity of the side chains might be other determinants.

Tomaymycin is a member of the pyrrolo[1,4]benzodiazepine [P(1,4)B] antitumor antibiotic group. This antibiotic is proposed to react with the exocyclic 2-amino group (N2) of guanine to form a covalent adduct that lies snugly within the minor groove of DNA. While DNA-footprinting experiments using methidiumpropyl-EDTA have revealed the favored bonding sequences for tomaymycin and related drugs on DNA, the stereochemistry at the covalent bonding site (C-11) and orientation in the minor groove were not established by these experiments. In previous studies using a combined fluorescence, high-field NMR, and molecular modeling approach, we have shown that for tomaymycin there are two diastereomeric species (11R and 11S) on both calf thymus DNA and d(ATGCAT)2. Although we were able to infer the identity (stereochemistry at C-11 and orientation in the minor groove) of the two species on d(ATGCAT)2 by high-field NMR and fluorescence studies, in combination with molecular mechanics calculations, definitive experimental evidence was lacking. We have designed and synthesized a self-complementary 12-mer [d(CICGAATTCICG)2] based on the Dickerson dodecamer [d(CGCGAATTCGCG)2] that bonds identically two tomaymycin molecules, each having a defined orientation and stereochemistry. Thus the bis(tomaymycin)-12-mer adduct maintains the self-complementarity of the original duplex molecule. Two-dimensional proton J-correlated spectroscopy (COSY) of the bis(tomaymycin)-d(CICGAATTCICG)2 adduct (I = inosine) unequivocally shows that C-11 of tomaymycin covalently bonds through N2 of guanine with an 11S stereochemistry in the sequence 5'-CGA-3'.(ABSTRACT TRUNCATED AT 250 WORDS)

A set of 30 mitomycin C and mitomycin A analogues, including five new compounds, was screened against three different solid human tumor cell lines using the MTT tetrazolium dye assay. A statistically significant correlation among antitumor activity, quinone reduction potential (E1/2), and the logarithm of the partition coefficient (log P) was obtained, with the most easily reduced and the most lipophilic compounds being the most potent. When these analogues were separated into mitomycin C and mitomycin A subsets, the former gave a correlation only with E1/2, whereas the latter (which differ little in their E1/2 values) gave a correlation only with log P. These correlations are in contrast to those made in the P388 leukemia assay in mice wherein the most active mitomycin C and mitomycin A analogues were the most hydrophilic ones. When the same compounds were tested against P388 leukemia cells in the MTT assay, the results were the same as those of the solid tumor assays. Thus, the substantial differences in relative potencies of mitomycins are related not to the kind of tumor cell, but to the type of assay performed, cell culture versus whole animal. No correlation was found between antitumor potency in the cell culture systems and calculated relative DNA binding strengths, probably because the limiting factors in antitumor potency of mitomycins appear to be tumor cell uptake (log P) and/or bioreductive activation (E1/2).

Three new types of amonafide and azonafide analogues were synthesized and screened in a panel of human solid tumor cells and murine L1210 leukemia cells. The structural types included tetrahydroazonafides, which have the naphthalene chromophore of amonafide within the anthracene nucleus of azonafide; phenanthrene analogues, in which the linear anthracene nucleus is replaced by the bent phenanthrene nucleus; and azaphenanthrenes. The tetrahydroazonafides were generally intermediate in potencies between amonafide and azonafide against the tumor cells, but some of them had high potencies against the L1210 cells and were more potent against the MDR strain than the sensitive strain. The phenanthrene and azaphenanthrene analogues showed no improvement on the potencies of the anthracenes.

Tomaymycin is a member of the pyrrolo[1,4]benzodiazepine antitumor-antibiotic group that binds covalently to the exocyclic 2-amino group of guanine in DNA. Previous correlation of fluorescence and NMR data suggested that the 11R,11aS and the 11S,11aS diastereomers of tomaymycin could bind to DNA in two orientations relative to the covalently modified guanine (Barkley, M. D.; Cheatham, S.; Thurston, D. E.; Hurley, L. H. Biochemistry 1986, 25, 3021-3031). We now report on fluorescence, one- and two-dimensional proton NMR, and molecular modeling studies of the tomaymycin-d(ATGCAT)2 adduct, which corroborate these earlier observations. Fluorescence measurements show that there are two species of tomaymycin bound to d(ATGCAT)2, which are tentatively identified as the 11R,11aS and 11S,11aS diastereomers. Two distinct sets of signals for the tomaymycin molecule are present in the proton NMR spectrum of the tomaymycin-d(ATGCAT)2 duplex adduct. Two-dimensional correlation spectroscopy (2D-COSY) studies also show connectivities for four cytosine H5-H6 and eight thymine methyl-H6 protons and thus clearly establish the presence of two distinct species of tomaymycin-d(ATGCAT)2 adducts in solution. A single scalar 11-11a 1H NMR coupling in the 2D-COSY spectrum is indicative of an adduct species that has an S configuration at the C-11 position. Two-dimensional nuclear Overhauser effect (NOESY) spectra of the tomaymycin-d(ATGCAT)2 duplex adduct show that the adducts are relatively nondistortive. In a NOESY experiment, cross-peaks were identified between both the aromatic H9 proton and the ethylidine methyl protons of tomaymycin and two different adenine H2 protons of d(ATGCAT)2. Molecular mechanics calculations with AMBER show that the two species with the thermodynamically most favorable binding energies are the 11R,11aS and 11S,11aS isomers with their aromatic rings to the 5' and 3' sides of the covalently bound guanine, respectively. The NOEs observed between tomaymycin protons and adenine H2 protons are in accord with molecular modeling studies. Taken together, these results strongly suggest that the two forms of tomaymycin bound to d(ATGCAT)2 are the 11S,11aS and 11R,11aS species, oriented with their aromatic rings to the 3' and 5' sides, respectively, of the covalently modified guanines.