Cannabis und Krebs

Oft wird das Argument aufgeführt, dass getrocknete Cannabisblüten etwas mehr gesundheitsschädliche Teerstoffe beim Verbrennen freisetzten als die selbe Menge Tabak. Dies ist zwar richtig, allerdings nicht relevant, da selbst ein sehr stark cannabisrauchender Konsument nicht den Bruchteil der Menge an Rauchmaterial inhaliert wie dies der regelmässige Raucher tut (oft ein oder mehrere Päckchen Zigaretten pro Tag). Ausserdem kann Cannabis problemlos durch Verdampfen (keine Teerstoffe, siehe Studie: Vaporisierer reduziert Schadstoffe [CLN#109, 09.05.2003]) oder in Form einer Mahlzeit eingenommen werden. Deshalb wollen wir auf dieses Argument nicht weiter eingehen.

Interessanter und auch umstrittener ist die Diskussion, inwiefern der psychoaktive Hauptwirkstoff von Hanf (THC) das Wachstum bzw. die Bildung von Krebs beeinflusst. Gerade in letzter Zeit ist diese Diskussion neu entbrannt. Wir wollen hier Zusammenfassungen der wichtigsten und aktuellsten Studien zur Verfügung stellen. Lesen Sie dazu dazu auch unseren Kommentar.

1. Studie der Universität von Kalifornien, Los Angeles:

Zusammenfassung:
 

Delta-9-Tetrahydrocannabinol Inhibits Antitumor Immunity by a CB2 Receptor-Mediated, Cytokine-Dependent Pathway1

Li X. Zhu, Sherven Sharma, Marina Stolina, Brian Gardner, Michael D. Roth, Donald P. Tashkin, and Steven M. Dubinett

Pulmonary Immunology Laboratory and Division of Pulmonary and Critical Care Medicine, University of California, Los Angeles, School of Medicine, Los Angeles, CA 90095; and Veterans Affairs West Los Angeles Healthcare Center, Los Angeles, CA 90073

The Journal of Immunology, 2000, 165: 373-380.

In this study, we show that Delta-9-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, suppresses host immune reactivity against lung cancer. In two different weakly immunogenic murine lung cancer models, intermittent administration of THC (5 mg/kg, four times/wk i.p. for 4 wk) led to accelerated growth of tumor implants compared with treatment with diluent alone. In contrast to our findings in immunocompetent mice, THC did not affect tumor growth in tumor-bearing SCID mice. The immune inhibitory cytokines, IL-10 and TGF-Beta, were augmented, while IFN-Gamma was down-regulated at both the tumor site and in the spleens of THC-treated mice. Administration of either anti-IL-10- or anti-TGF-Beta-neutralizing Abs prevented the THC-induced enhancement in tumor growth. Both APC and T cells from THC-treated mice showed limited capacities to generate alloreactivity. Furthermore, lymphocytes from THC-treated mice transferred the effect to normal mice, resulting in accelerated tumor growth similar to that seen in the THC-treated mice. THC decreased tumor immunogenicity, as indicated by the limited capacity for tumor-immunized, THC-treated mice to withstand tumor rechallenge. In vivo administration of a specific antagonist of the CB2 cannabinoid receptor also blocked the effects of THC. Our findings suggest the THC promotes tumor growth by inhibiting antitumor immunity by a CB2 receptor-mediated, cytokine-dependent pathway.

Zeitungsbericht dazu:

NEW YORK (Reuters Health) - There's one more potential problem to add to those already known about marijuana: the ingredient that gives it its kick, also seems to influence tumor growth. According to researchers at the University of California, Los Angeles, tetrahydrocannabinol (THC) ``promotes tumor growth by inhibiting antitumor immunity.'' In their National Institute on Drug Abuse-supported study, Dr. Steven Dubinett and colleagues looked at how THC affects lung tumors implanted in mice. When exposed to THC, tumor growth increased in mice. U.S. and friendly nation laws prohibit fully reproducing copyrighted material. In abidance with our laws this report cannot be provided in its entirety.

Dr. Franjo Grotenhermen (IACM): "Wir wissen aus Tierversuchen, dass THC die Produktion von Th-1-Zytokinen, wie etwa IL-1, IL-2 und IFN-gamma hemmen sowie die Produktion von Th-2-Zytokinen wie IL-4, IL-10 und TGF-beta stimulieren. Dies würde eine kausale therapeutische Verwendung von THC bei bestimmten Autoimmunerkrankungen, die als Th-1-vermittelt erscheinen, begründen, wie etwa Morbus Crohn, eine Form chronischer Darmentzündung, oder rheumatoide Arthritis. Auf der anderen Seite würde es die Ansprechbarkeit für Krebs und Infektionen erhöhen. Aber diese tierexperimentellen Daten mit hohen THC-Dosen können nicht einfach auf die menschliche Situation übertragen werden."
 

Kommentar:

Was sofort ins Auge fallen sollte ist, dass diese Studie vom "National Institute on Durg Abuse" unterstützt worden ist. Gerade diese Einrichtung profitiert am meisten von der Rauschhanfprohibition, da Marihuana die am meisten verwendete illegale Droge und damit Hauptarbeitsfeld der NIDA ist. Von einer wirklich unabhängigen Studie kann also nicht gesprochen werden. Man beachte ausserdem die Verabreichung von 5 mg/kg. Bei einem 70 kg wiegenden Menschen wären das 350 mg. Bei Menschen reichen laut IOM-Bericht etwa 5 mg THC intravenös bereits als Rauschdosis (THC-Gehalt im Plasma um die 100 ng/ml wie bei einem Joint). Mit anderen Worten, hier wurde mit etwa der 70-fachen Rauschdosis gearbeitet. Täte man dies mit Alkohol wären alle Versuchsobjekte sofort gestorben!

Es gibt im uebrigen eine weitere Studie fuer die US-Regierung von 1997 die genau das Gegenteil der obigen Studie fand. Dort wurden Mäuse und Ratten mit THC behandelt um festzustellen ob THC Krebs auslöst:

Kopie der Zusammenfassung dieser Studie
Orginalquelle der Zusammenfassung dieser Studie
(als PDF)

Der Überaschungseffekt (weshalb diese Studie jahrelang unter Verschluss gehalten wurde): Die mit THC behandelten Tiere lebten länger als nichtbehandelte Tiere.

"Survival of all dosed groups was generally significantly greater than that of the controls."

Mehrere Arten von Tumoren traten weniger häufig auf als bei der Kontrollgruppe:

"The incidences of mammary gland fibroadenomas and uterine stromal polyps were decreased in dosed groups of female rats, as were the incidences of pancreatic adenomas, pituitary gland adenomas, and interstitial cell adenomas of the testis in dosed male rats and liver neoplasms in dosed mice."
 

Die Glaubwürdigkeit und Aussagekraft der Studie der Universität von Kalifornien, Los Angeles ist deshalb mehr als fragwürdig bzw. muss im richtigen Zusammenhang betrachtet werden. Vor allem wenn man die unabhängige spanische Studie (siehe unten) berücksichtigt.

2. Bericht über die spanische Studie zum Thema:

Der nun folgende Bericht handelt von einer neuen spanischen Studie, die zum selben Ergebnis wie die US Studie von 1997 kam. Krebskranke, mit THC behandelte Mäuse lebten signifikant länger als nicht mit THC behandelte Mäuse:

"The term medical marijuana took on dramatic new meaning in February when researchers in Madrid announced they had destroyed incurable brain cancer tumors in rats by injecting them with THC, the active ingredient in cannabis.

The Madrid study marks only the second time that THC has been administered to tumor-bearing animals; the first was a Virginia investigation 26 years ago. In both studies, the THC shrank or destroyed tumors in a majority of the test subjects. [Ergänzung: Die beiden neuen Studien sind in diesem Bericht anscheinend nicht berücksichtigt. Alles in allem gibt es also vier große Studien zum Thema THC und Krebs. Drei unabhängige die eine Schrumpfung oder Zerstörung der Tumore durch THC beobachteten und eine von der NIDA unterstützten Studie die bei Versuchen mit der 70 fachen Rauschdosis das Gegenteil als Ergebnis beobachtete.]

Most Americans don't know anything about the Madrid discovery. Virtually no U.S. newspapers carried the story, which ran only once on the AP and news wires, on Feb. 29.

The ominous part is that this isn't the first time scientists have discovered that THC shrinks tumors. In 1974 researchers at the Medical College of Virginia, who had been funded by the National Institute of Health to find evidence that marijuana damages the immune system, found instead that THC slowed the growth of three kinds of cancer in mice -- lung and breast cancer, and a virus-induced leukemia.

The DEA quickly shut down the Virginia study and all further cannabis/tumor research, according to Jack Herer, who reports on the events in his book, "The Emperor Wears No Clothes." In 1976 President Gerald Ford put an end to all public cannabis research and granted exclusive research rights to major pharmaceutical companies, who set out -- unsuccessfully -- to develop synthetic forms of THC that would deliver all the medical benefits without the "high."

The Madrid researchers reported in the March issue of "Nature Medicine" that they injected the brains of 45 rats with cancer cells, producing tumors whose presence they confirmed through magnetic resonance imaging (MRI). On the 12th day they injected 15 of the rats with THC and 15 with Win-55,212-2 a synthetic compound similar to THC.

"All the rats left untreated uniformly died 12-18 days after glioma (brain cancer) cell inoculation ... Cannabinoid (THC)-treated rats survived significantly longer than control rats. THC administration was ineffective in three rats, which died by days 16-18. Nine of the THC-treated rats surpassed the time of death of untreated rats, and survived up to 19-35 days. Moreover, the tumor was completely eradicated in three of the treated rats." The rats treated with Win-55,212-2 showed similar results.

The Spanish researchers, led by Dr. Manuel Guzman of Complutense University, also irrigated healthy rats' brains with large doses of THC for seven days, to test for harmful biochemical or neurological effects. They found none. "Careful MRI analysis of all those tumor-free rats showed no sign of damage related to necrosis, edema, infection or trauma ... We also examined other potential side effects of cannabinoid administration. In both tumor-free and tumor-bearing rats, cannabinoid administration induced no substantial change in behavioral parameters such as motor coordination or physical activity. Food and water intake as well as body weight gain were unaffected during and after cannabinoid delivery. Likewise, the general hematological profiles of cannabinoid-treated rats were normal. Thus, neither biochemical parameters nor markers of tissue damage changed substantially during the 7-day delivery period or for at least 2 months after cannabinoid treatment ended."

Guzman's investigation is the only time since the 1974 Virginia study that THC has been administered to live tumor-bearing animals. (The Spanish researchers cite a 1998 study in which cannabinoids inhibited breast cancer cell proliferation, but that was a "petri dish" experiment that didn't involve live subjects.)

In an email interview for this story, the Madrid researcher said he had heard of the Virginia study, but had never been able to locate literature on it. Hence, the Nature Medicine article characterizes the new study as the first on tumor-laden animals and doesn't cite the 1974 Virginia investigation. "I am aware of the existence of that research. In fact I have attempted many times to obtain the journal article on the original investigation by these people, but it has proven impossible." Guzman said. In 1983 the Reagan/Bush Administration tried to persuade American universities and researchers to destroy all 1966-76 cannabis research work, including compendiums in libraries, reports Jack Herer, who states, "We know that large amounts of information have since disappeared."

Guzman provided the title of the work -- "Antineoplastic activity of cannabinoids," an article in a 1975 Journal of the National Cancer Institute -- and this writer obtained a copy at the UC medical school library in Davis and faxed it to Madrid.

The summary of the Virginia study begins, "Lewis lung adenocarcinoma growth was retarded by the oral administration of tetrahydrocannabinol (THC) and cannabinol (CBN)" -- two types of cannabinoids, a family of active components in marijuana.

"Mice treated for 20 consecutive days with THC and CBN had reduced primary tumor size."

The 1975 journal article doesn't mention breast cancer tumors, which featured in the only newspaper story ever to appear about the 1974 study -- in the Local section of the Washington Post on August 18, 1974. Under the headline, "Cancer Curb Is Studied," it read in part:

"The active chemical agent in marijuana curbs the growth of three kinds of cancer in mice and may also suppress the immunity reaction that causes rejection of organ transplants, a Medical College of Virginia team has discovered." The researchers "found that THC slowed the growth of lung cancers, breast cancers and a virus-induced leukemia in laboratory mice, and prolonged their lives by as much as 36 percent."

Guzman, writing from Madrid, was eloquent in his response after this writer faxed him the clipping from the Washington Post of aquarter century ago. In translation, he wrote:

"It is extremely interesting to me, the hope that the project seemed to awaken at that moment, and the sad evolution (lastimosa evolucion) of events during the years following the discovery, until now we once again draw back the veil' over the anti-tumoral power of THC, twenty-five years later. Unfortunately, the world bumps along between such moments of hope and long periods of intellectual castration."

News coverage of the Madrid discovery has been virtually nonexistent in this country.

The news broke quietly on Feb. 29 with a story that ran once on the UPI wire about the Nature Medicine article. This writer stumbled on it through a link that appeared briefly on the Drudge Report web page. The New York Times, Washington Post and Los Angeles Times all ignored the story, even though its newsworthiness is indisputable: a benign substance occurring in nature destroys deadly brain tumors.

For the full story, pick up "The Emperor Wears No Clothes" by Jack Herer, or log on for excerpts from the book at www.jackherer.com.

Raymond Cushing is a regular contributor to the Sacramento News & Review and the Anderson Valley (CA) Advertiser"