New triene-ansamycins, thiazinotrienomycins F and G and a diene-ansamycin, benzoxazomycin.

New triene-ansamycins designated thiazinotrienomycins F (TT-F) and G (TT-G) and a new diene-ansamycin, benzoxazomycin, were isolated from a culture broth of Streptomyces sp. MJ672-m3 and their structures were elucidated by spectroscopic analyses. The Mean Graphs of TT-G suggests that the tumor growth inhibitory activities are almost as strong as TT-B, in respect of GI50 and TGI against several human cancer cell lines.

ABC transporter genes, kasKLM, responsible for self-resistance of a kasugamycin producer strain.

We previously reported that a 7.6-kb DNA fragment from Streptomyces kasugaensis M338-M1, a kasugamycin (KSM) producer, included KSM acetyltransferase gene (kac338) and some other genes possibly involved in KSM biosynthesis. As an extension of that study, a 10-kb SacI-KpnI DNA fragment, located approximately 5-15-kb upstream of kac33, was cloned and a 4.2-kb SacI-EcoRI fragment therefrom was sequenced, revealing one incomplete (designated ORF J) and three complete open reading frames (designated kasK, kasL and kasM). The coding frames of kasK, L and M overlap one another with terminator/initiator ATGA sequence. RT-PCR analysis of a DNA region including kasKLM indicated the presence of one transcript that is long enough to span the three genes. The kasK gene potentially encodes an ATP-binding protein of the ATP-binding cassette (ABC) transporter superfamily. Homology search for the deduced KasK protein shows similarity to other ABC transporters involved in self-resistance of a mithramycin and possibly doxorubicin producer strain. The kasL and kasM genes encode different integral membrane proteins, both having six putative transmembrane helices. An expression plasmid for kasKLM (pTV-KLM) was constructed and these genes were expressed in E. coli JM 109, which had been sensitive to KSM. The transformant acquired resistance to KSM, suggesting that KasK, L and M proteins as a set in S. kasugaensis M338-M1 pump out KSM to protect the producer from its toxic metabolite.

Futalosine and its derivatives, new nucleoside analogs.

Futalosine, a new nucleoside analog, was isolated from a fermentation broth of Streptomyces sp. MK359-NF1. Some chemical derivatives of futalosine were prepared. 6-O-Methylfutalosine methylester inhibited growth of HeLa-S3 cells in vitro (IC50 = 19.5 micrograms/ml) in contrast to the weak activity of futalosine. 6-O-Methylfutalosine methylester at concentrations higher than 10 micrograms/ml inhibited incorporation of 3H-TdR and 3H-UR but not 3H-Leu in the acid-soluble fractions of HeLa-S3 cells.

Effect of thiazinotrienomycin B, an ansamycin antibiotic, on the function of epidermal growth factor receptor in human stomach tumor cells.

Thiazinotrienomycin B (TT-B), an ansamycin isolated from fermentation broths of Streptomyces sp. MJ672-m3, inhibited the growth in vitro of human stomach tumor SC-6 cells over 10 times more strongly than the growth of other human tumor cells, such as HeLa (cervix), T24 (bladder) and LX-1 (lung). The extent of growth inhibition by TT-B of SC-6, but not of LX-1 nor T24, was lowered in a competitive manner by raising serum concentrations in the culture medium. TT-B inhibited the cell cycle progression of SC-6 at an early stage of the progression from G0/G1 to S. The inhibition was again competitive with serum concentrations in the culture medium. No direct inhibition of DNA synthesis was observed at the concentration range which caused the cell cycle arrest. TT-B and anti-epidermal growth factor receptor (anti-EGFR) were antagonistic to each other in inhibiting the cell cycle progression of SC-6 from G0/G1 to S, suggesting that the two compounds share the same target, EGFR. The kinase activity of EGFR was little inhibited by TT-B in a cell-free system.

Inhibition of anchorage-independent growth of tumor cells by IT-62-B, a new anthracycline.

IT-62-B, a new anthracycline isolated from fermentation broths of Streptomyces sp. IT-62, reversed certain tumor cell phenotypes in vitro including some of human origin. The observed normal phenotypes were anchorage dependence of cell growth, flattened cell morphology and restoration of actin stress fibers. The extent of the anchorage dependence of cell growth induced by IT-62-B was generally greater than that by doxorubicin or pirarubicin. The cell-flattening effect of IT-62-B on cells of T24 (human bladder), but not on C-33A (human cervix), accompanied inhibition of fos gene expression. T24 cells, once flattened by IT-62-B, retained their flat morphology even in drug-free, fresh medium and eventually died in several days. IT-62-B, unlike doxorubicin, only slightly inhibited the topoisomerase II reaction in vitro and DNA synthesis in isolated cell nuclei.

A new anthracycline antibiotic, IT-62-B, converts the morphology of ras-transformed cells back to normal: taxonomy, fermentation, isolation, structure elucidation and biological characterization.

A new antibiotic, IT-62-B was isolated from the culture broth of Streptomyces sp. IT-62 by extraction with acetone and then with ethyl acetate, followed by conventional column chromatography using silica gel, Sephadex LH-20 and silica ODS. Its structure (C39H47NO15, MW 769) was determined by 1H, 13C NMR, MS, IR and UV spectrometric techniques to be a new member of the baumycin-group anthracyclines. It showed moderate activity against Gram-positive bacteria and had antitumor activity against various tumor cell lines. Further, antibiotic IT-62-B converted the morphology of ras-transformed NIH3T3 cells and T-cells back to normal at concentrations inhibiting cell growth by 30% or more.

Use of transcriptional-enhancer elements responsive to ras, protein kinase A and protein kinase C to evaluate inhibitors of specific signal transduction pathways.

To evaluate ras-mediated signal transduction, we constructed a transient transfection assay system that measures chloramphenicol acetyl transferase activity expressed under the transcriptional-enhancer elements responsive to ras, protein kinase C, and protein kinase A in NIH3T3 cells. Characterization of the assay system with several known activators and inhibitors of signal transduction pathways proved that our system could reliably evaluate agents that affect individual pathways. Pirarubicin ((2"R)-4'-tetrahydropyranyladriamycin, THP), which has recently been found able to reverse ras-transformed cells, appeared to selectively inhibit the ras signal transduction pathway.

Phenotypic reversion induced by anthracyclines in ras oncogene-expressed cells; structure-activity relationships.

Several antitumor anthracyclines, including those in preclinical stages, were examined for their action in reversing tumorous phenotypes of H- or K-ras 3T3 cells (NIH3T3 cells transformed by human H- or K-ras oncogene) into normal phenotypes, such as flattened cell morphology, anchorage dependent cell growth, etc. (referred to as anti-ras activity). The study elucidated relationships between the chemical structure of anthracyclines and the anti-ras activity. The human tumor cell line T24, which has a mutated H-ras gene, responded to the anthracyclines, as did K- or H-ras 3T3 cells, in respect to the phenotypic alterations. Pirarubicin was more than 4 times as active as aclarubicin in inhibiting the growth of solid tumors of K-ras 3T3 cells in nude mice, possibly reflecting a difference in anti-ras activity between the two antibiotics.

Distinct effects of clinically used anthracycline antibiotics on ras oncogene-expressed cells.

Doxorubicin, pirarubicin, and FAD-104, but not aclarubicin or MX 2, flattened the morphology of NIH3T3 cells that had been transformed by human H-ras and K-ras. The effect appeared on almost all cells, as early as 2 d following exposure to the antibiotics at concentrations inhibiting cell growth by 50% or more. The morphological alteration accompanied other normal cell phenotypes, such as the restoration of actin stress fibers, anchorage dependence of cell growth and an increase in nucleoside diphosphate (NDP) kinase activity. NIH3T3 cells transformed by src and other tumor cell lines responded less prominently, if at all.

Aminopeptidase activity of an antitumor antibiotic, C-1027.

An antitumor antibiotic C-1027, a complex protein consisting of an apoprotein and a non-covalently bound chromophore, showed some aminopeptidase activity, 1/15 (on the basis of activity per mg protein) that of porcine kidney enzyme [E.C. 3.4.11.2] by use of L-phenylalanyl 4-methyl-coumaryl-7-amide as the substrate. Neither the apoprotein alone nor the chromophore alone were active. Amastatin and bestatin but not leupeptin inhibited the activity. The enzyme activity of the holo-antibiotic, as opposed to that of the porcine kidney enzyme, was readily lost by UV irradiation, indicating that the intact structure of the chromophore was needed to maintain the native conformation of the holo-antibiotic. The cytotoxicity of the holo-antibiotic, but not that of the chromophore, to Ehrlich carcinoma cells in vitro was reduced to 1/5 by 1 microgram/ml of amastatin which alone had no effect on cell growth. The porcine aminopeptidase was not cytotoxic at all even at higher concentrations (higher enzyme activities/ml). Amastatin possibly occupied the catalytic domain of the holo-antibiotic, interfering with the binding of the holo-antibiotic with some cell-surface protein(s). Amastatin did not inhibit the holo-antibiotic to cleave isolated DNA.