Synthesis and evaluation of novel pyrimido-acridone, -phenoxadine, and -carbazole as topoisomerase II inhibitors.

As part of a series of studies to discover new topoisomerase II inhibitors, novel pyrimidoacridones, pyrimidophenoxadines, and pyrimidocarbazoles were synthesized, and in vitro and in vivo antitumor activities and DNA-protein and/or DNA-topoisomerase II cross-linking activity as an indicator of topoisomerase II-DNA cleavable complex formation were evaluated. The pyrimidocarbazoles possessed high in vitro and in vivo potencies. Compound 26 (ER-37326), 8-acetyl-2-[2-(dimethylamino)ethyl]-1H-pyrimido[5,6,1-jk]carbazole-1,3(2H)-dione, showed in vitro growth inhibitory activity with respective IC(50) values of 0.049 microM and 0.35 microM against mouse leukemia P388 and human oral cancer KB. In vivo, this compound inhibited the tumor growth of mouse sarcoma M5076 implanted into mice with T/C values of 42% and 13% at 3.13 and 6.25 mg/kg/d respectively without significantly affecting the body weight. In addition, compound 26 (ER-37326) increased the formation of DNA-topoisomerase II cross-linking in P388 cells.

A novel carbazole topoisomerase II poison, ER-37328: potent tumoricidal activity against human solid tumors in vitro and in vivo.

We have discovered a novel topoisomerase II (topo II) poison, ER-37328 (12,13-dihydro-5-[2-(dimethylamino)ethyl]-4H-benzo[c]pyrimido[5,6,1-jk]carbazole-4,6,10(5H,11H)-trione hydrochloride), which shows potent tumor regression activity against Colon 38 cancer inoculated s.c. Here, we describe studies on the cell-killing activity against a panel of human cancer cell lines and the antitumor activity of ER-37328 against human tumor xenografts. In a cell-killing assay involving 1-h drug treatment, ER-37328 showed more potent cell-killing activity (50% lethal concentrations (LC50s) ranging from 2.9 to 20 microM) than etoposide (LC50s>60 microM) against a panel of human cancer cell lines. ER-37328 induced double-stranded DNA cleavage, an indicator of topo II-DNA cleavable complex formation, within 1 h in MX-1 cells, and the extent of cleavage showed a bell-shaped relationship to drug concentration, with the maximum at 2.5 microM. After removal of the drug (2.5 microM) at 1 h, incubation was continued in drug-free medium, and the amount of cleaved DNA decreased. However, at 10 microM, which is close to the LC50s against MX-1 cells, DNA cleavage was not detected immediately after 1-h treatment, but appeared and increased after drug removal. This result may explain the potent cell-killing activity of ER-37328 in the 1-h treatment. In vivo, ER-37328 showed potent tumor regression activity against MX-1 and NS-3 tumors. Moreover, ER-37328 had a different antitumor spectrum from irinotecan or cisplatin against human tumor xenografts. In conclusion, ER-37328 is a promising topo II poison with strong cell killing activity in vitro and tumor regression activity in vivo, and is a candidate for the clinical treatment of malignant solid tumors.

Antitumor activity of ER-37328, a novel carbazole topoisomerase II inhibitor.

DNA topoisomerase II has been shown to be an important therapeutic target in cancer chemotherapy. Here, we describe studies on the antitumor activity of a novel topoisomerase II inhibitor, ER-37328 [12,13-dihydro-5-[2-(dimethylamino)ethyl]-4H-benzo[c]pyrimido[5,6,1- jk]carbazole-4,6,10(5H,11H)-trione hydrochloride]. ER-37328 inhibited topoisomerase II activity at 10 times lower concentration than etoposide in relaxation assay and induced double-strand DNA cleavage within 1 h in murine leukemia P388 cells, in a bell-shaped manner with respect to drug concentration. The maximum amount of DNA cleavage was obtained at 2 microM. Like etoposide, ER-37328 (2 microM) induced topoisomerase II-DNA cross-linking in P388 cells. A spectroscopic study of ER-37328 mixed with DNA demonstrated that ER-37328 has apparent binding activity to DNA. ER-37328 showed potent growth-inhibitory activity against a panel of 21 human cancer cell lines [mean (50% growth-inhibitory concentration) GI50 = 59 nM]. COMPARE analysis according to the National Cancer Institute screening protocol showed that the pattern of the growth-inhibitory effect of ER-37328 was similar to that of etoposide, but different from that of doxorubicin. Studies on etoposide-, amsacrine [4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA)]-, and camptothecin-resistant P388 cell lines showed that: (a) etoposide- and m-AMSA-resistant P388 cell lines were partially resistant to ER-37328 compared with the parental cell line; and (b) a camptothecin-resistant cell line showed no cross-resistance to ER-37328. In addition, ER-37328 overcame P-glycoprotein-mediated resistance. In vivo, ER-37328 produced potent tumor regression of Colon 38 carcinoma inoculated s.c., and its activity was superior to that of etoposide or doxorubicin. These results indicate that ER-37328 inhibits topoisomerase II activity through the formation of topoisomerase II-DNA cleavable complex and has potent antitumor activity both in vitro and in vivo.