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The purification and physico-chemical properties of the enactin congeners are concerned in this paper. We proposed the group name hydroxamic acid antimycotic antibiotics (HAAA) for enactin, neoenactin and the related antibiotics. Streptomyces roseoviridis, the enactin-producing microbe, was cultured to prepare an inoculum seed.

Thirteen heterocyclic quinones (5 quinoline quinones, 7 isoquinoline quinones, 1 indole quinone) were tested for their effects on avian myeloblastosis virus reverse transcriptase, growth of murine lymphoblastoma L5178Y cells, respiration of rat liver mitochondria and oxidation of NADH by Clostridium kluyveri diaphorase in comparison with those of streptonigrin, in which the quinoline quinone moiety is considered to play a crucial role. Most of the quinoline quinones and isoquinoline quinones inhibited reverse transcriptase to the same extent as streptonigrin with the ID50 values ranging between 1 and 5 micrograms/ml, whereas the ID50 value of the indole quinone derivative, 4,7-dihydro-2,3-dimethylindole-4,7-dione, was 80 micrograms/ml. The cytotoxicities of the quinones were much lower than that of streptonigrin; the ID50 values of the quinones were higher than 0.15 micrograms/ml. In particular, the ID50 value of the ortho-quinoline quinone derivative, 8-methoxy-7-methyl-5,6-dihydroquinoline-5,6-dione, was as high as 16 micrograms/ml, while the 50% inhibition of cell growth was seen in the presence of 0.0025 micrograms/ml streptonigrin. The membrane transport of the quinones was evaluated by comparing the effects on oxygen consumption by mitochondria and oxidation of NADH by bacterial diaphorase, being proven not to be responsible for their lower cytotoxicities.

Inhibition of avian myeloblastosis virus (AMV) reverse transcriptase by natural and synthetic quinones including antibiotics could be accounted for by an oxidation-reduction reaction. The quinones were shown to function as electron acceptors as revealed by the catalytic oxidation of NADH by Clostridium kluyveri diaphorase which was in excellent agreement with enzyme inhibition activity. The kinetics of inhibition of AMV reverse transcriptase by three synthetic quinones with different core structures, i.e., 6-methoxy-5, 8-dihydroquinoline-5, 8-dione, 5, 8-dihydroisoquinoline-5, 8-dione and 1, 4-naphthoqumone, were studied. These quinones inhibited reverse transcriptase in the same manner as streptonigrin (STN) and were shown to act at a single class of reaction site(s) on the enzyme molecule. In contrast, the quinones with bulky substituents, i.e., 7-(2-nitrophenethylamino)-5, 8-dihydroisoquinoline-5, 8-dione and 7-methoxy6-methyl-3-piperidino-5, 8-dihydroisoquinoline-5, 8-dione, were inactive as inhibitors of reverse transcriptase, whereas they retained competent catalytic activities in the oxidation of NADH by C. kluyveri diaphorase. Based on these observations, the existence of a specific site of interaction on the enzyme molecule, referred to as a quinone pocket, was proposed. The quinone pocket might play a crucial role in the early sequence of events leading to the inhibition of reverse transcriptase by quinones including STN and sakyomicin A (SKM). Access of SKM to a quinone pocket might be restricted due to its bulky structure in the vicinity of the quinone group. This is inferred from unsuccessful inhibition of reverse transcriptase by the quinones with bulky substituents, resulting in much poorer inhibition of reverse transcriptase in spite of more potent electron acceptor activity in the oxidationreduction system as compared with those of STN.

Antitumor antibiotic streptonigrin (STN-COOH) is a potent inhibitor of avian myeloblastosis virus (AMV) and human immunodeficiency virus reverse transcriptases. The carboxyl group at 2'-position of STN-COOH was modified to give esters, hydrazide, amides and amino acid derivatives for biological studies. Against AMV reverse transcriptase, the hydrazide, amides and amino acid derivatives showed inhibitory activity, which compared favorably to that of STN-COOH, with the ID50 values ranging 2-8 micrograms/ml. In contrast, the esters lacked this activity except for those having a dimethylamino group in the substituent. Splenomegaly caused by Friend leukemia virus infection was significantly inhibited by STN-COOH and STN-COO(CH2)3N(CH3)2, but not STN-CONH(CH2)3N(CH3)2. Doxorubicin-resistant murine lymphoblastoma L5178Y cells showed collateral sensitivity to both STN-COOH and STN-COO(CH2)3N(CH3)2 not only in vitro but also in vivo.

The naphthoquinone moiety was proven to be essential to the biological activities of sakyomicin A using various naphthoquinone derivatives. Among the naphthoquinones tested, juglone (5-hydroxy-1, 4-naphthoquinone) which resembles the partial structure of sakyomicin A was the most active in cytotoxicity against murine lymphosarcoma L5178Y cells, electron acceptor function in the oxidation of NADH by Clostridium kluyveri diaphorase or rat liver mitochondria and inhibition against avian myeloblastosis virus reverse transcriptase. The significantly lower cytotoxicity of sakyomicin A as compared with juglone was attributable to its poor membrane transport. The inhibition of reverse transcriptase activity may result from the interaction between a sulfhydryl group in the active center of the enzyme and quinone groups of the naphthoquinones and sakyomicin A.

Etude comparative de l'activite inhibitrice de differentes flavones et isoflavones vis-a-vis de la reverse transcriptase du virus de la myeloblastose aviaire. Une relation entre la structure et l'activite inhibitrice est mise en evidence

Antitumor antibiotic streptonigrin (STN-COOH) is a potent inhibitor of avian myeloblastosis virus (AMV) and human immunodeficiency virus reverse transcriptases. The carboxyl group at 2'-position of STN-COOH was modified to give esters, hydrazide, amides and amino acid derivatives for biological studies. Against AMV reverse transcriptase, the hydrazide, amides and amino acid derivatives showed inhibitory activity, which compared favorably to that of STN-COOH, with the ID50 values ranging 2-8 μg/ml. In contrast, the esters lacked this activity except for those having a dimethylamino group in the substituent. Splenomegaly caused by Friend leukemia virus infection was significantly inhibited by STN-COOH and STN-COO(CH2)3N(CH3)2, but not STN-CONH(CH2)3N(CH3)2. Doxorubicin-resistant murine lymphoblastoma L5178Y cells showed collateral sensitivity to both STN-COOH and STN-COO(CH2)3N(CH3)2 not only in vitro but also in vivo.