Recent advances in pharmacologic study of natural anticancer agents in China

In this paper a number of anticancer agents of natural origin will be presented. Hydroxycamptothecin (HCPT) was found to produce a strong inhibitory action on a variety of animal tumors. It is also effective for treatment of patients with gastric carcinoma, liver carcinoma, tumor of head and neck or leukemia. Pharmacologic studies showed that it could depress S phase of tumor cells significantly and cause formation of cellular chromatid breaks. By means of alkaline elution and nick translation methods it has been proved that HCPT induced DNA single strand breaks remarkably. Homoharringtonine (HHRT) was shown to be effective against acute leukemia. Recent experiments in tumor-bearing mice indicated that (HHRT) could diminish tumor metastasis. Using molecular hybridization technique it was demonstrated that (HHRT) decreased the content of c-myc RNA in the cytoplasm but not in the nuclei. Lycobetaine (LBT) possessed strong inhibitory effects on a number of ascites tumors. In clinical trials it was effective against ovarian and gastric carcinomas. It is able to intercalate into DNA. Oxalysine (OXL) is a new antibiotic and shown to be effective against tumor metastatis. When used in combination with 5-FU, its anticancer action could be enhanced. Other natural compounds such as indirubin, beta-elemene, irisquinone, oridonine, norcantharidin and PSP have been also found to possess antitumor action.

Effects of lycobetaine on chromatin structure and activity of murine hepatoma cells

The effects of lycobetaine (LBT) on DNA single strand break and chromatin conformation were examined by in-situ nick translation method. It was found that LBT did not cause DNA single strand break. After 2-h incubation of murine hepatoma cells with 1-50 micrograms/ml LBT in vitro, the chromatin transcription activity was inhibited gradually. This effect was time- and dose-dependent. Actinomycin D produced a similar effect; 10-hydroxycamptothecin not only caused DNA single strand break, but also altered chromatin conformation; homoharringtonine had no marked influence on either. By molecular hybridization technique, it was found that the effect of LBT on individual genes was somewhat different. After 2-h incubation of the cells with LBT, the sensitivities of c-myc, N-ras, and beta 2-microglobulin genes to DNase I were decreased from 75 +/- 6, 66 +/- 4, 70 +/- 8% to 28 +/- 8, 25 +/- 5, 28 +/- 7%, respectively, while that of c-myb and beta-globin genes (8 + 6%, 6 + 5%) did not change obviously.

[Demonstration of the presence of Methanobrevibacter in a colon cancer Chinese patient]

A fecal specimen from a Chinese patient (85-year-old man) suffering from colonic cancer was examined for the presence of methane-producing bacteria. As a result, a Methanobrevibacter organism was isolated. Our isolate did not grow in the presence of bile salts, a result different from Methanobrevibacter from healthy Americans' feces by Miller et al.

[Modulation of norepinephrine release in sympathetic nerve endings in renal hypertensive dogs]

Experimental renal hypertensive and normal dogs with femoral arteries constantly perfused were studied. Cocaine was used to block the presynaptic norepinephrine (NE) reuptake and tyramine to initiate the release of NE in sympathetic nerve endings. NE spillover and infusion pressure were measured under basic conditions and during intraarterial infusion of cocaine, tyramine and in combination with alpha 1 and alpha 2 adrenoceptor antagonists. The extent of NE spillover increase induced by infusion of tyramine, the increased infusion pressure by cocaine and tyramine, and the reduced infusion pressure by prazosin were all greater in hypertensive dogs than those in normal dogs, but adrenoceptor antagonist idazoxan further increased tyramine-induced NE spillover in normal dogs only. It was suggested that reduced-regulation of presynaptic alpha 2 adrenoceptors to NE release and increased responsiveness of postsynaptic alpha 1 adrenoceptors to NE were present in hypertensive dogs.

[Analgesic and antipyretic effects of cyproheptadine]

Cyproheptadine-HCl raised the pain thresholds during hot plat test and writhing test in mice and tail flick test in rats, strengthened the hypnotic action by subthreshold dosage of sodium pentobarbital and chloral hydrate. The ED50 were 4.4 (3.2-5.7) and 12.4 (8.4-18.2) mg/kg 30 min after ip cyproheptadine in mice and rats, respectively. The ED50 was 0.14 (0.12-0.18) mg/kg 90 min after icv cyproheptadine in mice. Cyproheptadine po 20, 40 mg/kg and ip 10, 20 mg/kg showed significant antipyretic effects on yeast-induced pyrexia in rats.

[A new therapy of hemophilia with ranitidine]

20 cases of hemophilia, including ten of hemophilia A , nine of hemophilia B and one of von Willebrand's disease (VWD), were treated with ranitidine. The results revealed that the levels of both factor VIII and IX were increased and the clinical symptoms of bleeding were ameliorated. The level of factor VIII in hemophilia A ranged from 5.27 +/- 3.94% before treatment and rose to 14.68 +/- 4.70% during the treatment period (P less than 0.001). The level of the factor IX in the patients with hemophilia B increased from 4.42 +/- 3.01% before treatment to 20.33 + 9.31% under treatment (P less than 0.001). Tn the patient with VWD the level of the factor VIII rose but the level of von Willebrand factor did not change. The drug has no side effect. The results of our study suggests that ranitidine therapy is effective and safe in hemophilia.

Biological response modifier enhances the activity of natural killer cell against human cytomegalovirus-infected cells

Peripheral blood lymphocytes (PBL) from two human cytomegalovirus (CMV)-seronegative donors and eight CMV-seropositive donors were cultured for 3 days with or without the biological response modifier OK-432 and examined for lysis of K562 cells and CMV-infected MRC-5 cells. OK-432-stimulated PBL exhibited significantly greater natural killer (NK) activity than did unstimulated PBL. There was no difference in activity of NK cells in PBL prepared from CMV-seronegative and -seropositive donors. Antibody-complement depletion studies suggested that OK-432-stimulated NK activity was associated with Leu-7-positive cells. The ability of OK-432 to sustain the NK activity in PBL was decreased when the CD4-positive population of lymphocytes was eliminated by antibody-complement depletion prior to OK-432 stimulation. The ability of OK-432 to sustain the NK activity of PBL was also significantly decreased in the presence of monoclonal antibody against recombinant human interleukin-2. The results suggest that the activity of human NK cells against K562 and CMV-infected MRC-5 target cells can be sustained in vitro by OK-432-stimulated T-helper cells and that the effect of the T-helper cells is mediated, at least in part, by interleukin-2.

Characteristics of the interaction of lycobetaine with DNA

The characteristics of the interaction of lycobetaine (LBT) with DNA were examined by fluorescence spectrometer, disc electrophoresis and restriction enzyme analysis. The apparent binding constant of LBT with calf thymus DNA has been determined as 1.67 x 10(6) L/mol by ethidium bromide displacement method. Based on electrophoresis titration, the mode of DNA binding was found to be through intercalation. Fluorescence quenching assay showed that the intrinsic association constant and the binding site size of LBT to calf thymus DNA were 0.26 x 10(6) L/mol and 2.6 base pairs, respectively. Selective inhibition of LBT on action of some restriction enzymes showed that LBT intercalate preferentially into GC base pairs. Neither DNA strand break nor interstrand cross-link was produced by LBT. LBT did not bind to DNA covalently and did not cause DNA alkylation.

[Influence of zinc deprivation on thymus, spleen development and adenosine deaminase activity in young rats]

This study on the thymus and spleen development and ADA activity was done in young rats with zinc deprivation and supplementation. The serum zinc level, body weight, absolute and relative weight, and ADA activity of the thymus and spleen were compared between the experimental rats and the control group. Above indications were all decreased; especially both the thymus weight and the thymus ADA activity were markedly decreased in the zinc deficient group. The averages of thymic absolute weight, relative weight and ADA activity were dropped by 61.32%, 54.54% and 47.59%, respectively. After zinc supplementation for one month, all the body weight, weight of the thymus and spleen, and ADA activity of the spleen were recovered to the control group's level, while ADA activity of the thymus was 33.03% higher than that of the control group. Our data suggested that zinc was not only an important trace element in maintaining the growth of the body, the development of the thymus and spleen, but it may be an important agent to activate the ADA or to prompt synthesis of ADA.

Nephrotoxicity and hepatotoxicity of 1,1-dichloro-2,2-difluoroethylene in the rat. Indications for differential mechanisms of bioactivation

1,1-Dichloro-2,2-difluoroethylene (DCDFE) produced marked nephrotoxicity in rats upon an i.p. dose of 150 mumole/kg. At doses higher than 375 mumole/kg, DCDFE also produced hepatotoxicity. Aminooxyacetic acid, an inhibitor of cysteine conjugate beta-lyase, appeared to be slightly nephrotoxic in Wistar rats. Nevertheless it exerted an inhibitory effect on the nephrotoxicity of DCDFE. The N-acetylcysteine conjugate of DCDFE was identified as a major urinary metabolite of DCDFE. When administered as such, this conjugate appeared to be a potent nephrotoxin, without any effect on the liver, indicating that glutathione conjugation of DCDFE is most likely a bioactivation step for nephrotoxicity. The appearance of traces of chlorodifluoroacetic acid in urine of rats treated with higher doses of DCDFE indicates the existence of an oxidative pathway of metabolism of DCDFE, probably involving epoxidation by hepatic mixed-function oxidases. It is speculated that the latter route might account for the hepatotoxicity at higher doses of DCDFE. The nephro- and hepatotoxicity of DCDFE, therefore, most likely are the result of two different mechanisms of bioactivation.

[Transplantation model of human lung oat cell carcinoma in nude mice]

A human lung oat cell carcinoma from a surgical specimen was successfully transplanted into nude mice and has been maintained for over four years through 14 passages. This transplanted tumor had a long latent period of more than one month, slowly growing in the initial inoculation and the following passages. The interval between two passages was about four months. 5 months after the inoculation, the transplanted tumor in nude mice grew to 2 cm in diameter. It was demonstrated that the transplanted tumor possessed the human isoenzyme pattern and human chromosome karyotype. The original human tumor and its transplanted counterparts in the nude mice were strikingly similar by histopathology. Besides, specific neuro-secretory granules in cytoplasm of the transplanted tumor were observed under transmission electron microscope.

[Ultrastructural study on the model of human lung adenocarcinoma heterotransplanted to nude mice]

A human lung adenocarcinoma from surgical biopsy specimen was successfully heterotransplanted into nude mice and has been maintained for 40 generations. The experiments were made on 6-8 week old male or female nude mice with Swiss genetic background cultivated in specific pathogen-free condition. The electron microscopic observation on transplanted tumor of passages 2, 6, 12, 18 and 23 revealed that the ultrastructural features of this tumor were strictly maintained and no obvious change of differentiation was found. But there was a potential prone to regional squamous epithelial metaplasia in the transplanted tumor. The nude mice model of human lung adenocarcinoma so established can be used as a good experimental system of the homologous and reproducible human cancer for the study of basic medical sciences and chemotherapy of human lung carcinoma.

[Changes in protein in bile excretion from rat liver inoculated with BERH-2 hepatoma]

Rocket immunoelectrophoresis was used to assay the change in alpha fetoprotein (AFP) and albumin (Alb) in bile of rats 10 to 14 days after intrahepatic or intraperitoneal inoculation of BERH-2 hepatoma. The bile was collected from the common bile duct cannula. Total protein was determined by the Lowry method. The results showed that the excretion of total protein and Alb was reduced to 54% and 24% of the control in the intrahepatic group, and 65% and 56% of the control in the intraperitoneal group. Bile-AFP can be detected in rats in both groups and its concentration increased gradually during the tumor progression. In the hepatic group, the bile-AFP content per gram of tumor tissue was 29% of that in the intraperitoneal group. It suggests that decreased excretion of AFP, Alb and total protein in bile of rat bearing tumor in the liver be related to local obstruction of excretion by the tumor mass leading to constriction of biliary canaliculi.

The effect of hydroxycamptothecin in the activity of RNA and DNA polymerases prepared from murine hepatoma cells

Hydroxycamptothecin (HCPT) is an antitumor alkaloid isolated from Camptotheca acuminata indigenous to China. It could reduce the activity of nuclear RNA polymerase II and I(III) of hepatoma cells. HCPT at 25-100 microM caused a remarkable inhibition on DNA polymerase alpha whilst only a slight inhibition on beta. The inhibitory action on alpha was restored by increasing amounts of enzyme or DNA template, but unchanged by varying amounts of substrate. It is suggested that HCPT may exert a stronger inhibition on DNA replication process.

Cytotoxicity and sister chromatid exchanges induced in vitro by six anticancer drugs developed in the People's Republic of China

Growth inhibition in the Chinese hamster cell line V79 and in the human lymphoid cell line Raji and induction of sister chromatid exchange(s) (SCE) in V79 cells after treatment with six anticancer drugs [harringtonine (HRT), homoharringtonine (HHRT), camptothecin (CPT), hydroxycamptothecin (HCPT), lycobetaine (LBT), and oxalysine (OXL)] developed in the People's Republic of China were studied. OXL is a new antibiotic; all other drugs are plant extracts. All drugs caused a dose-dependent growth inhibition in both cell types, as evidenced by decreases in plating efficiencies of V79 cells and in viable cell counts of Raji. However, the degree of inhibition differed widely among the drugs. HRT, HHRT, CPT, and HCPT were the most potent growth inhibitors, LBT was next, and OXL was the least effective inhibitor. SCE analyses were made in V79 cells treated with a drug in the presence or absence of the metabolic activation system S9 mixture (S9 mix), except for the HRT assay in which the S9 mix was not used. CPT, HCPT, and LBT induced a dose-dependent increase in SCE frequencies, while HRT, HHRT, and OXL caused no SCE induction at any dose level used. CPT was the most powerful SCE inducer. HCPT induced SCE but at a much reduced rate when compared to that of CPT. LBT was a weak SCE inducer; SCE induction was seen only in cultures treated with 40 micrograms or more LBT/ml. Addition of the S9 mix did not alter SCE frequencies, indicating that the drugs were direct-acting agents. HRT and HHRT were highly toxic, but they induced no increases in SCE frequency, indicating that cytotoxicity of a compound does not necessarily correlate with SCE induction.