Hayato Ogasawara

Intracellular carboxyl esterase activity is a determinant of cellular sensitivity to the antineoplastic agent KW-2189 in cell lines resistant to cisplatin and CPT-11

KW‐2189, a novel antitumor antibiotic belonging to the duocarmycins, possesses marked DNA‐binding activity upon activation by carboxyl esterase to its active form, DU‐86. Three duocarmycins, KW‐2189, DU‐86 and duocarmycin SA, were active against the cisplatin (CDDP)‐resistant human non‐small cell lung cancer cell lines PC‐9/CDDP and PC‐14/CDDP, and the multidrug‐resistant human small cell lung cancer cell line H69/VP. However, HAC2/0.1, a CDDP‐resistant human ovarian cancer cell line which is also resistant to CPT‐11 because of decreased intracellular activation of CPT‐11, was about 12.8‐fold more resistant to KW‐2189. HAC2/0.1 was not resistant to other duocarmycins as compared to its parental cell line, HAC2. There was no difference between HAC2 and HAC2/0.1 with regard to the intracellular accumulation of KW‐2189. Addition of 130 mU/ml of carboxyl esterase to the culture medium did not influence the sensitivity of HAC2 cells to KW‐2189. However, the sensitivity of HAC2/0.1 cells to KW‐2189 was enhanced to the level of HAC2. These results suggest that HAC2/0.1 is less potent than HAC2 in activating KW‐2189. The carboxyl esterase activity of whole‐cell and microsomal extracts from HAC2/0.1 was approximately 60% of that from HAC2. The cell‐free experiment revealed that KW‐2189 bound to DNA more efficiently in the presence of HAC2 than HAC2/0.1 cell extract. It was concluded that decreased intracellular carboxyl esterase activity in HAC2/0.1 cells caused decreased intracellular conversion of KW‐2189 to its active form, thus producing resistance to KW‐2189. The decreased conversion of CPT‐11 to SN‐38 in HAC2/0.1 cells might be explained by decreased carboxyl esterase activity.

A novel antitumor antibiotic, KW-2189 is activated by carboxyl esterase and induces DNA strand breaks in human small cell lung cancer cells.

KW‐2189 has been selected as a lead compound for clinical trial among duocarmycin derivatives with structural similarity to CC‐1065, a cyclopropylpyrroloindole. The purpose of this study was to examine the DNA‐binding potency and the mechanisms of cytotoxicity of KW‐2189. In order to analyze DNA‐binding activity of KW‐2189, plasmid pBR322 was treated with KW‐2189 with or without pretreatment with carboxyl esterase, which we demonstrated to be an activating enzyme, and the products were examined by agarose gel electrophoresis and restriction enzyme analysis. Cytotoxic activity was examined by exposing a human small cell lung cancer cell line, NCI‐H69 to KW‐2189 with or without carboxyl esterase. Alkaline elution was performed to examine whether KW‐2189 induces DNA strand breaks. DNA treated with KW‐2189 and carboxyl esterase migrated faster than KW‐2189‐treated DNA, which migrated at the same rate as untreated DNA. In addition DNA treated with esterase‐activated KW‐2189 was protected from digestion by some restriction enzymes. KW‐2189 showed concentration‐ and time‐dependent growth inhibitory effect with IC50 values (drug concentration required for 50% growth inhibition) of 58 nM (96 h) to 1900 nM (1 h) in H69 cells. The IC50 values of 4‐h exposure of H69 to KW‐2189 with 0, 26, 130, 650 mU/ml carboxyl esterase were 460, 120, 30, and 7 nM, respectively. Time‐dependent enhancement of cytotoxicity by carboxyl esterase was also observed. KW‐2189 induced DNA strand breaks in H69 cells in a concentration‐dependent manner around the IC50 value. We conclude that 1) KW‐2189 is activated by carboxyl esterase to its active form(s), 2) activated KW‐2189 has a stronger DNA‐binding activity and cytotoxicity than KW‐2189, 3) DNA cleavage is one of the major mechanisms of KW‐2189‐mediated cytotoxicity.

Improvement by eicosanoids in cancer cachexia induced by LLC-IL6 transplantation.

Cachexia frequently occurs in the late stages of cancer, and is difficult to manage. We previously reported that interleukin-6 (IL-6) cDNA transfection into Lewis lung carcinoma (LLC-IL6) induced cachexia-like symptoms in C57BL/6 mice. This was thought to be a useful experimental model of cancer cachexia. We have examined the effects of two eicosanoids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), in order to evaluate whether they could relieve cachexia. LLC-IL6-bearing animals were divided into three treatment groups receiving DHA, EPA or water as the control; 80-μl samples of these compounds (purity>95%) were administered orally by catheter daily starting 7 days after tumor transplantation. Tumor growth curves were similar in the three groups. There were no differences in water or food intake in the three groups. However, body weight, a marker of cachexia, was significantly higher in treated mice than in the control group. Sixteen days after tumor transplantation, the mean body weight was 17.45 g (P<0.05), 17.2 g and 16.41 g in the groups receiving DHA, EPA and water respectively. The eicosanoids did not affect serum levels of IL-6. Ubiquitination of muscle protein, a marker of proteolysis coupled to cachexia, was compared in LLC-IL6-and LLC-transplanted mice. The eicosanoids prevented the ubiquitination of approximately 180 kDa protein. These results suggest that eicosanoids may prevent the cachexia mediated by IL-6.

In vitro and in vivo growth of B16F10 melanoma cells transfected with interleukin-4 cDNA and gene therapy with the transfectant

In an attempt to develop the most effective cytokine gene therapy, we transfected mouse interleukin(IL)-2, mouse IL-4, and human IL-6 cDNAs into mouse melanoma cells, B16F10. Transfection with IL-4 cDNA decreased the tumorigenicity of B16F10 most strongly. We investigated whether gene therapy with IL-4-transfected B16F10 cells was possible. Flowcytometric analysis showed that major histocompatibility complex class I and II expression in B16F10 and IL-4-cDNA-transfected B16F10 (B16F10-IL4) cells did not differ. Doubling times of B16F10 and B16F10-IL4 were 20.1 and 21.1 h respectively. The growth of B16F10 cells was retarded if C57BL/6 mice were inoculated with B16F10-IL4 at the contralateral sides. When 5×105 B16F10 cells were transplanted subcutaneously into the flanks of C57BL/6 mice, they all developed a tumor mass, whereas no tumor masses formed in those transplanted with B16F10-IL4 cells within 60 days. No nude, severe combined immunodeficient or beige mice were able to reject parental B16F10 or B16F10-IL4 cells, although, B16F10-IL4 tumor growth in all these immunodeficient mice was slower than that of B16F10. Therefore, we concluded that T and natural killer cells are necessary for rejection of B16F10-IL4 tumor cells.

Characterization of an etoposide-resistant human ovarian cancer cell line.

Etoposide (VP-16) is one of the most important anticancer agents available and is used in many chemotherapeutic regimens. To characterize resistance to this drug, we established a VP-16-resistant human ovarian cancer cell line, SKOV3/VP, by continuous stepwise exposure of SKOV3 cells to VP-16. The degree of resistance to VP-16 of SKOV3/VP was about 25 times that of the parent cell line (SKOV3), and SKOV3/VP showed crossresistance to teniposide, adriamycin, CPT-11, and vincristine. The accumulation of [3H]-VP-16 observed in SKOV3/VP cells was about half that seen in SKOV3 cells, and the accumulation of Adriamycin by this resistant cell line was also lower than that of its parent. Overexpression of neither the multidrug resistance genemdr-1, the multidrug-resistance-associated protein (mrp) gene, nor P-glycoprotein was detected using reverse transcriptase-polymerase chain reaction analysis and flow cytometry with MRK-16, a monoclonal antibody against P-glycoprotein. The topoisomerase II activity of nuclear extracts from SKOV3/VP cells was lower than that from the parental cells, as was the amount of DNA topoisomerase II, demonstrated by immunoblotting. These results suggest that the mechanism responsible for the multidrug resistance of this cell line may be attributable to changes on its DNA topoisomerase II and to its reduced accumulation of the drugs as compared with the parental line SKOV3.

In vivo screening models of cisplatin-resistant human lung cancer cell lines using SCID mice

In vivo screening models of a cisplatin (CDDP)-resistant human small-cell lung cancer cell (SCLC) line, H69/CDDP, and a non-small-cell lung cancer cell (NSCLC) line, PC-14/CDDP, were evaluated. The transplantability of the tumor xenografts to SCID mice was more than 90%. Tumor xenografts of H69/CDDP and PC-14/CDDP showed CDDP resistance during in vivo treatment. The novel anticancer agent 254-S showed only a partial effect on the growth of H69/CDDP and PC-14/CDDP while ormaplatin showed no cross resistance to CDDP. The in vivo results correlated well with the results of the in vitro MTT assay. In this in vivo sensitivity test, H69/CDDP and PC-14/CDDP were more sensitive to ormaplatin than its parental cell lines. In vivo sensitivity testing using SCID mice bearing transplanted CDDP-resistant tumors was shown to be useful for evaluating the effects of new anti-cancer drugs, especially those that might overcome CDDP resistance.

In vitro enhancement of antitumor activity of a water-soluble duocarmycin derivative, KW-2189, by caffeine-mediated DNA-repair inhibition in human lung cancer cells

Duocarmycins, including KW‐2189, bind in the minor groove of double‐stranded DNA at A‐T‐rich sequences, followed by covalent bonding with N‐3 of adenine in preferred sequences. We examined the effect of DNA‐repair modulators, such as caffeine and aphidicolin, on the cytotoxicity of duocarmycins towards human lung cancer cells, as determined by dye formation assay. Caffeine (0.5 or 1 mM), but not aphidicolin, enhanced the growth‐inhibitory activity of KW‐2189, DU‐86, and duocarmycin SA. Caffeine inhibited repair of DNA strand breaks induced by KW‐2189, as assayed by the alkaline elution technique. This suggests that duocarmycin‐induced DNA strand breaks, which are potentially lethal to cells, are repaired through a caffeine‐sensitive pathway.

Hypersensitivity of NIH3T3 cells transformed by H-ras gene to DNA-topoisomerase-I inhibitors.

We examined the effects of the introduction of H‐ras oncogene into murine cell line NIH3T3 on growth inhibition by topoisomerase‐I (topo‐I) inhibitors. The H‐ras‐transformed cells (pT22‐3) showed approximately 12‐fold increased sensitivity to a novel topo‐I inhibitor, NB‐506 [6‐N‐formylamino‐12, 13‐dihydro‐I, II‐dihydroxy‐13‐(β‐D‐glucopyranosyl)‐5H‐indolo(2,3‐a)pyrrolo(3,4‐c) carbazole‐5,7(6H)‐dione], compared with the parental NIH3T3 cells. pT22‐3 also showed increased sensitivity to other topo‐I inhibitors such as camptothecin (approx. 3.0‐fold) and CPT‐II (irinotecan, approx. 3.0‐fold). Transformation of NIH3T3 by another oncogene (erb82) did not affect their sensitivity to these topo‐I inhibitors. pT22‐3 had approximately 32‐fold higher topo‐I activity than NIH3T3, but the same topo‐I content. In a cell‐free system, topo‐I activity was increased 2‐fold by addition of the H‐ras protein precipitated from pT22‐3 cells. Topo I in the nuclear extract of pT22‐3 was eluted easily by low concentrations of NaCl compared with that of NIH3T3, suggesting a qualitative change in pT22‐3 topo I. Increased phosphorylation of topo I was observed in pT22‐3. Furthermore, NB‐506 decreased the amount of the GTP‐bound form of the H‐ras product in pT22‐3 cells. These results suggest that the high growth‐inhibitory effect of a topo‐I inhibitor, NB‐506, on H‐ras‐transformed NIH3T3 cells is due to the H‐ras‐mediated signal‐transduction pathway.