[Alternative means of drug therapy in cancer: letril]

Letril (amygdaline) is one of drugs of alternative therapy for cancer that is used over three decades and relates to cyanogenic glycosides received from kernels of various fruits (almonds, apricots, peaches, etc. The basis of suggestion of letril as antitumor agent is hypotheses about selective fermentative splitting of amygdaline in tumor cells with developing of cyanide that should cause to apoptosis as a result of aerobic glycolysis suppression. None of these assumptions found their experimental confirmation. In clinical trials there was established inefficiency of letril with a very high probability to develop severe cyanide intoxication. Despite obtained scientific data and absence of permission from the supervising institutions (FDA) letril is still advertised, produced and distributed as anti-tumor drug.

[Uniform designed research on the active ingredients assembling of Chinese medicine prescription for anti-liver fibrosis]

OBJECTIVE

To explore the method and significance for studying active anti-liver fibrosis ingredients consisted Chinese medicine compound prescription based on Chinese medicine theory.

METHODS

Optimized prescription was screened out, adopting uniform block design with 4-factor 8-level table and regression analysis, through applying the four known effective ingredients (cordyceps sinensis polysaccharide, salvianolic acid B, amygdaloside and gypenosides) of Fuzheng Huayu Capsule (FZHYC, a new Chinese medine anti-liver fibrosis drug) to two rat liver fibrosis models established separately by dimethylnitrosamine (DMN) and CCl4, and taking the liver content of hydroxyproline (Hyp) as the screen index. Then a further study for comparing and verifying the efficacy of the obtained optimized prescription was conducted on the two former models respectively by observing the changes of Hyp content in liver, serum ALT activity and fibrosis pathology after medication, controlled by the original FZHYC and the recipe assembled by all the four ingredients.

RESULTS

Two optimized prescriptions (OPA and OPB) were screened out separately in the studies conducted on the two models. Both of them were consisted of cordyceps sinensis polysaccharide, Amygdaloside and Gypenosides, but different in constituent ratio, i.e., the ratio in OPA was 60 : 80: 50, and that in OPB, 20: 160: 50. Verifying study showed both OPA and OPA were significantly effective, with the efficacy equivalent to that of FZHYC (P>0.05). However, when they were used in combining with salvianolic acid B (the cutout ingredient in the screening), the efficacy lowered surely.

CONCLUSIONS

Uniform design is a valuable method in the compatibility research of Chinese Medicine drugs' composition. To assemble a new compound recipe reasonably based on the prescription of traditional compound recipe could make its effect equivalent to that of the original prescription. Ingredients or constituents in a prescription, either presented synergistic or antagonistic effects, are not randomly stacked together, and they should be orderly assembled in intrinsic rules of qualitative and quantitative changing.

Pharmacological properties of traditional medicines. XXV. Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid

Effects of ephedrine, amygdalin, glycyrrhizin, gypsum and their combinations on body temperature and body fluid were studied in rats using the method developed in our previous reports. Ephedrine significantly increased respiratory evaporative water loss and heat loss in response to a marked elevation of body temperature. There was a small but significant increase in body temperature when amygdalin was orally given rats at a dose of 46.32 mg/kg. Glycyrrhizin and gypsum were unable to affect body temperature. However, gypsum was able to prevent the increased action of ephedrine on body temperature, amygdalin exhibited a preventive tendency to it, and glycyrrhizin did not affect it. The results are in good agreement with classical claims of Makyo-kanseki-to and the related crude drugs in traditional medicine. Moreover, a combination of the four components reproduced the effects of Makyo-kanseki-to on body temperature and body fluid. This report suggests that the co-administration of ephedrine and gypsum is physiologically more desirable than ephedrine alone for dry-type asthmatic patients with a fever. Also, it experimentally supports the clinical efficacy of Makyo-kanseki-to.

In vitro cytotoxicity following specific activation of amygdalin by beta-glucosidase conjugated to a bladder cancer-associated monoclonal antibody

We describe a novel version of antibody-directed enzyme prodrug therapy (ADEPT), with the use of amygdalin as prodrug. Amygdalin is a naturally occurring cyanogenic glycoside, which can be cleaved by sweet almond beta-glucosidase to yield free cyanide. If amygdalin could be activated specifically at the tumour site, then malignant cells would be killed without the systemic toxicity usually associated with chemotherapy. To this end, we have conjugated beta-glucosidase to a tumour-associated monoclonal antibody (MAb) (HMFG1) and the conjugate has been tested in vitro for specificity and cytotoxicity subsequent to activation of amygdalin. Amygdalin was cytotoxic to HT1376 bladder cancer cells only at high concentrations, whereas the combination of amygdalin with HMFG1-beta-glucosidase enhanced the cytotoxic effect of amygdalin by 36-fold. When 2 concentrations of HMFG1-beta-glucosidase were compared, the toxic effect was dose dependent. The cytotoxicity of amygdalin was also enhanced by the MAb-enzyme conjugate even when the unbound conjugate was removed from the medium prior to exposure to amygdalin and the cells were washed. In addition to the cytotoxic effect, we also demonstrated specificity, using a MAb-enzyme conjugate that does not recognise the HT1376 bladder cancer cells. Finally, we studied the cytotoxic effect of the conjugate in co-culture of HMFG1-positive and-negative cell lines (HT 1376 and U87MG cells). We demonstrated that the rate of surviving cells corresponds well to the percentage of U87MG (HMFG1-negative) cells in the flask. Our findings indicate that ADEPT is more effective than non-directed enzyme activation of a prodrug and can result in a non-toxic cancer therapy.

On the metabolism of amygdalin. 2. The distribution of beta-glucosidase activity and orally administered amygdalin in rats

The organs of 15-day-old rats had the highest capability to hydrolyze amygdalin and prunasin, and most of this activity is concentrated in the tissues of the small and large intestines. The activity decreased with age. In adult rats, the ability of the organs to hydrolyze prunasin is higher than that of amygdalin and is concentrated in the spleen, large intestine, and kidney (35.0, 15.0, and 8.9 micrograms prunasin hydrolyzed . h-1 . g tissue-1). Minced tissues of the liver, spleen, kidney, and stomach contain more hydrolytic capability than the homogenate of these organs, while the reverse is the case with the small and large intestines. When 30 mg amygdalin was orally administered to adult rats, its distribution after the 1st h was as follows: stomach (0.89 mg), small intestine (0.78 mg), spleen (0.36 mg), large intestine (0.30 mg), kidney (0.19 mg), liver (0.10 mg), and serum (5.6 micrograms/mL). At the end of the 2nd h, the highest amygdalin content was found in the large intestine (0.79 mg).

Studies on high-dose chemotherapy of amygdalin in murine P388 lymphocytic leukaemia and P815 mast cell leukaemia

The anti-tumor activity of amygdalin (NSC 251222), commercially known as Laetrile, was investigated using P388 lymphocytic leukaemia and P815 mast-cell leukaemia in BDF1 mice. Doses varying from 200 mg/kg to 2,000 mg/kg were used following the days 1 and 5 and days 1, 5 and 9 schedules. Despite treatment with high doses of amygdalin there was no prolongation in the life-span of mice bearing either P388 or P815 tumor.

Congenital malformations induced by laetrile

Laetrile administered orally ot pregnant hamsters caused skeletal malformations in the offspring, but intravenous laetrile filed to result in embryopathic effects. Oral laetrile significantly increased in situ cyanide concentrations, while intravenous laetrile did not. Thiosulfate administration protected embryos from the teratogenic effects of oral laetrile. The embryopathic effects of oral laetrile appear to be due to cyanide released by bacterial beta-glucosidase activity.

The pharmacokinetics of amygdalin

Amygdalin (D-mandelonitrile-beta-D-gentiobioside) is a cyanogenic glycoside claimed to show anti-cancer activity, sold under the incorrect name "Laetrile". For a sensible discussion of its alleged activity and its established toxicity it is necessary that its fate in the organism is known. The pharmacokinetics of amygdalin have been investigated in the Beagle dog after both intravenous and oral administration. The excretion of amygdalin has also been studied in the rat. Amygdalin concentrations were determined by high performance liquid chromatography in plasma ultrafiltrate and urine. The pharmacokinetics of amygdalin after intravenous administration were compared with those of diatrizoate, a model substance for extracellular volume and glomerular filtration. The amygdalin clearance is significantly larger than that of diatrizoate. The volumes of distribution of both substance are the same. After oral administration only a few percents of the amygdalin dose are systemically available. A part of the oral dose is recovered from the urine as prunasin (D-mandelonitrile-beta-D-glucoside).

A clinical trial of amygdalin (Laetrile) in the treatment of human cancer

One hundred seventy-eight patients with cancer were treated with amygdalin (Laetrile) plus a "metabolic therapy" program consisting of diet, enzymes, and vitamins. The great majority of these patients were in good general condition before treatment. None was totally disabled or in preterminal condition. One third had not received any previous chemotherapy. The pharmaceutical preparations of amygdalin, the dosage, and the schedule were representative of past and present Laetrile practice. No substantive benefit was observed in terms of cure, improvement or stabilization of cancer, improvement of symptoms related to cancer, or extension of life span. The hazards of amygdalin therapy were evidenced in several patients by symptoms of cyanide toxicity or by blood cyanide levels approaching the lethal range. Patients exposed to this agent should be instructed about the danger of cyanide poisoning, and their blood cyanide levels should be carefully monitored. Amygdalin (Laetrile) is a toxic drug that is not effective as a cancer treatment.

Pharmacology of amygdalin (laetrile) in cancer patients

Plasma and urine concentrations of amygdalin, whole-blood concentrations of cyanide, and thiocyanate concentrations in serum and urine were determined in cancer patients following intravenous (4.5 g/m2) and oral (500-mg tablet) administration of amygdalin. To measure low plasma concentrations of amygdalin following oral administration a GC/MS assay was developed. Following intravenous administration, concentrations of parent drug as high as 1,401 microgram/ml were observed, with no increase in plasma concentrations of cyanide or serum concentrations of thiocyanate. Plasma elimination of amygdalin was best described by a two-compartment open model with a mean distributive phase half-life of 6.2 min, mean elimination phase half-life of 120.3 min, and mean clearance of 99.3 ml/min. Following oral administration of amygdalin, plasma concentrations were much lower, with peak values of less than 525 ng/ml. Cyanide concentrations increased to values as high as 2.1 microgram/ml whole blood. Thiocyanate concentrations did not increase for several days, plateauing at values as high as 38 microgram/ml serum. Ingestion of almonds by two patients taking oral amygdalin increased cyanide concentrations compared with values obtained after oral amygdalin alone.

A pharmacologic and toxicological study of amygdalin

Six patients with advanced cancer were treated with amygdalin (laetrile) at dosages similar to those employed by laetrile practitioners. Amygdalin given intravenously at 4.5 g/sq m/day was largely excreted unchanged in the urine and produced no clinical or laboratory evidence of toxic reaction. Amygdalin given orally at 0.5 g three times daily produced significant blood cyanide levels to 2.1 microgram/mL. No clinical or laboratory evidence of toxic reaction was seen in the six patients taking oral amygdalin at this dosage. One patient, however, challenged with a large intake of raw almonds, had transient symptoms of cyanide toxic reaction with escalating blood cyanide levels. This small study indicates that amygdalin in the doses employed produces few clinical side effects. A definite hazard of cyanide toxic reaction must be assumed, however, and possible long-term side effects remain unknown.

Cyanide concentrations in blood after amygdalin (laetrile) administration in rats

Toxic amounts of cyanide are released into the blood of rats following the oral administration of amygdalin (laetrile); cyanide blood concentrations and toxicity are markedly less when amygdalin is given intravenously. Analysis of the time course of cyanogenesis suggests that cyanide could accumulate in blood after repeated oral doses of amygdalin.

Blood cyanide levels in mice after administration of amygdalin

Oral doses of amygdalin and intraperitoneal (i.p.) doses of potassium cyanide (KCN) in the near-lethal range were administered to CD2F1 female mice. Blood cyanide levels were then measured as a function of time. The maximum cyanide level after amygdalin administration was reached at about 11/2 to 2 h and was within the range of values seen after KCN administration. Behaviour of mice correlated with the time of maximum blood cyanide level. Acute distress was observed at times when the cyanide level was highest. There was great variability in the nature and magnitude of the response in individual mice. The ability of the contents of various regions of the gastrointestinal tract and of tumour tissue to release cyanide from amygdalin was assessed. Stomach and upper intestine had little activity while the lower end and the faeces released large amounts. Again, there was a large variation between mice. These results are interpreted to mean that enteric contents are primarily responsible for the release of cyanide from ingested amygdalin. Freshly minced tumour tissue released negligible amounts of cyanide. Ten-fold higher doses of amygdalin administered i.p. produced very small increases in blood cyanide levels and no toxic behaviour. The doses used are comparable to doses which might be ingested by patients receiving oral amygdalin or Laetrile and indicate that oral amygdalin is potentially extremely dangerous.

Studies of amygdalin (laetrile) toxicity in rodents

Amygdalin (laetrile), given to Fischer 344 rats in doses of 250, 500, and 750 mg/kg intraperitoneally daily for five days, caused mortalities of 30.8% 44.1%, and 56.8%, respectively. The mode of death and the elevated serum cyanide levels in the dying animals strongly suggested cyanide poisoning as the cause of death. These findings seriously question the use of amygdalin in clinical medicine under any circumstances.

Laetrile and pregnancy

Pregnancy in a woman who took laetrile as daily intramuscular injections during the last trimester resulted in a live, term infant. No laboratory or clinical evidence of elevated cyanide or thiocyanate, a pricipal metabolite, could be detected. Neurological evidence of chronic cyanide exposure may not be recognizable in infancy, and long-term follow-up is indicated.

A simple method for the estimation of amygdalin in the urine

A procedure for the estimation of D- and D,L-amygdalin in urine is described. Amygdalin is hydrolyzed by beta-glucosidase and base to benzaldehyde, glucose and cyanide. Benzaldehyde is extracted with methylene chloride and the ultraviolet (UV) absorbence determined at 243 nm. The response of human urine "spiked" with amygdalin was linear between 10 and 75 microgram/ml. Mice administered 100 mg/kg of amygdalin intravenously or orally excreted about 70 and 20% of the administered dose, respectively, over 96 hours. In each instance more than 96% of excreted drug equivalents were obtained within the first 24 hours.

Laetrile toxicity studies in dogs

Dogs were fed laetrile and fresh, sweet almonds under various conditions. The doses of laetrile were similar to those prescribed for patients with cancer and ranged on a basis of gram to square meter from an equivalent of the oral dose for man to five times this dose. Six of the ten dogs died of cyanide poisoning. One dog recovered, and three dogs, at the time of sacrifice, demonstrated various levels of neurologic impairment, ranging from difficulty in walking to coma. These studies demonstrate that oral laetrile is highly toxic when taken with some common table foods. We predict that there will be an increased incidence of cyanide poisoning in man as laetrile becomes more readily available.

Antitumor tests of amygdalin in spontaneous animal tumor systems

In a series of 6 experiments with CD8F1 mice with spontaneous mammary adenocarcinomas Sugiura noted by macrovisual observation with some histology an overall average of 21% of mice with lung metastases when treated with 1,000--2,000 mg/kg/day of amygdalin compared with 90% of the control mice. The significance attributed to those early observations is seriously challenged by the negative findings of 3 independent investigators, by 2 out of 3 negative cooperative experiments in which Sugiura participated, and particularly by the blind experiment in which he and others under blind readings found no anticancer activity. Treatment of Swiss albino mice showed no destructive effect upon their spontaneous mammary adenocarcinomas. Of the treated mice, 22% were found by macrovisual observation to have lung metastases while 91% were noted among the controls. The results are subject to questions raised in the discussion. Amygdalin at 2,000 mg/kg/day was ineffective both in treating and preventing the development of spontaneous leukemia in AKR mice. At 1,000 mg/kg/day it was not found effective in preventing or significantly delaying the development of spontaneous mammary tumors in CD8F1 mice. In summary, we do not have evidence to support taking amygdalin to clinical trial, although other considerations may require that one be conducted.

Antitumor tests of amygdalin in transplantable animal tumor systems

Except for oral administration, there was no grossly observed toxicity from carefully administered high doses of amygdalin in the experimental systems used. The compound in high doses was ineffective against the DMBA-induced rat mammary carcinoma and the following transplanted experimental tumors: Sarcoma 180, plasma cell tumor LPC-1, leukemia L1210, Mecca lymphosarcoma, Ridgway osteogenic sarcoma, sarcoma T241, mammary carcinoma E0771, Taper liver tumor, Ehrlich carcinoma (solid and ascites), and Walker carcinosarcoma 256. Amygdalin did not noticeably influence the toxicity or impair the efficacy of these chemotherapeutic agents in their respective systems: Cytosine arabinoside, methotrexate, cytoxan, or 5-fluorouracil in L1210; the latter two in LPC-1; 6-mercaptopurine in Ridgway osteogenic sarcoma; estradiol-17beta or 2alpha-methyldihydrotestosterone propionate in the DMBA-induced rat mammary carcinoma.