The term “ laetrile ” is derived from the terms laevorotatory and mandelonitrile and is used to describe a purified form of the chemical amygdalin, a cyanogenic glucoside (a plant compound that contains sugar and produces cyanide) found in the pits of many fruits and raw nuts and in other plants, such as lima beans, clover, and sorghum.[1-6] In the 1970s, laetrile gained popularity as an anticancer agent. By 1978, more than 70,000 individuals in the United States were reported to have been treated with it.[2,7,8] Laetrile has been used for cancer treatment both as a single agent and in combination with a metabolic therapy program that consists of a specialized diet, high-dose vitamin supplements, and pancreatic enzymes.[9,10]
In the United States, researchers must file an Investigational New Drug (IND) application with the U.S. Food and Drug Administration (FDA) to conduct drug research in human subjects. In 1970, an IND application to study laetrile was filed by the McNaughton Foundation (San Ysidro, California). This request was initially approved but later rejected because preclinical evidence in animals showed that laetrile was not likely to be effective as an anticancer agent,[3,11,12] and because there were questions about how the proposed study was to be conducted. Laetrile supporters viewed this reversal as an attempt by the U.S. government to block access to new and promising cancer therapies, and pressure mounted to make laetrile available to the public. Court cases in Oklahoma, Massachusetts, New Jersey, and California challenged the FDA’s role in determining which drugs should be available to cancer patients. Consequently, laetrile was legalized in more than 20 states during the 1970s. In 1980, the U.S. Supreme Court acted to uphold a federal ban on interstate shipment of laetrile.[2,14] As a result, the use of laetrile has greatly diminished, but the compound continues to be manufactured and administered as an anticancer therapy, primarily in Mexico, and in some clinics in the United States.
Although the names laetrile, Laetrile, and amygdalin are often used interchangeably, they are not the same product. The chemical composition of U.S.-patented Laetrile (mandelonitrile-beta-glucuronide), a semisynthetic derivative of amygdalin, is different from the laetrile/amygdalin produced in Mexico (mandelonitrile beta-D-gentiobioside), which is made from crushed apricot pits.[15,16] Mandelonitrile, which contains cyanide, is a structural component of both products. It has been proposed that cyanide is the active cancer-killing ingredient in laetrile, but two other breakdown products of amygdalin—prunasin (which is similar in structure to Laetrile) and benzaldehyde —may also be cancer cell inhibitors.[17-20] The studies discussed in this summary used either Mexican laetrile/amygdalin or the patented form. In most instances, the generic term “laetrile” will be used in this summary; however, a distinction will be made between the products when necessary.
Laetrile can be administered orally as a pill, or it can be given by injection (intravenous or intramuscular). It is commonly given intravenously for a period of time followed by oral maintenance therapy. The incidence of cyanide poisoning is much higher when laetrile is taken orally [21-23] because intestinal bacteria and some commonly eaten plants contain enzymes (beta-glucosidases) that activate the release of cyanide after laetrile has been ingested.[17,22] Relatively little breakdown occurs to yield the cyanide when laetrile is injected.[7,22] Administration schedules and the length of treatment in animal models and humans vary widely.
- Ellison NM, Byar DP, Newell GR: Special report on Laetrile: the NCI Laetrile Review. Results of the National Cancer Institute's retrospective Laetrile analysis. N Engl J Med 299 (10): 549-52, 1978. [PUBMED Abstract]
- Moertel CG, Fleming TR, Rubin J, et al.: A clinical trial of amygdalin (Laetrile) in the treatment of human cancer. N Engl J Med 306 (4): 201-6, 1982. [PUBMED Abstract]
- Ross WE: Unconventional cancer therapy. Compr Ther 11 (9): 37-43, 1985. [PUBMED Abstract]
- Lewis JP: Laetrile. West J Med 127 (1): 55-62, 1977. [PUBMED Abstract]
- Unproven methods of cancer management. Laetrile. CA Cancer J Clin 22 (4): 245-50, 1972 Jul-Aug. [PUBMED Abstract]
- Rosen GM, Shorr RI: Laetrile: end play around the FDA. A review of legal developments. Ann Intern Med 90 (3): 418-23, 1979. [PUBMED Abstract]
- Curran WJ: Law-medicine notes. Laetrile for the terminally ill: Supreme Court stops the nonsense. N Engl J Med 302 (11): 619-21, 1980. [PUBMED Abstract]
- Fenselau C, Pallante S, Batzinger RP, et al.: Mandelonitrile beta-glucuronide: synthesis and characterization. Science 198 (4317): 625-7, 1977. [PUBMED Abstract]
- Chandler RF, Anderson LA, Phillipson JD: Laetrile in perspective. Can Pharm J 117 (11): 517-20, 1984.
- Newmark J, Brady RO, Grimley PM, et al.: Amygdalin (Laetrile) and prunasin beta-glucosidases: distribution in germ-free rat and in human tumor tissue. Proc Natl Acad Sci U S A 78 (10): 6513-6, 1981. [PUBMED Abstract]
- Rauws AG, Olling M, Timmerman A: The pharmacokinetics of prunasin, a metabolite of amygdalin. J Toxicol Clin Toxicol 19 (8): 851-6, 1982. [PUBMED Abstract]
- Kochi M, Takeuchi S, Mizutani T, et al.: Antitumor activity of benzaldehyde. Cancer Treat Rep 64 (1): 21-3, 1980. [PUBMED Abstract]
- Kochi M, Isono N, Niwayama M, et al.: Antitumor activity of a benzaldehyde derivative. Cancer Treat Rep 69 (5): 533-7, 1985. [PUBMED Abstract]
- Gostomski FE: The effects of amygdalin on the Krebs-2 carcinoma and adult and fetal DUB(ICR) mice. [Abstract] Diss Abstr Int B 39 (5): 2075-B, 1978.
- Herbert V: Laetrile: the cult of cyanide. Promoting poison for profit. Am J Clin Nutr 32 (5): 1121-58, 1979. [PUBMED Abstract]
- Viehoever A, Mack H: Bio-chemistry of amygdalin (bitter, cyanogenetic principle from bitter almonds). Am J Pharm 107 (Oct): 397-450, 1935.