Preclinical Evidence Relating to Vitamin C in Cancer Therapy
From a mean baseline of 70micromol/L, repeated oral dosing achieves plasma vitamin C concentrations of 220micromol/L. Intravenous administration of large dosages (18+g of vitamin C) can achieve plasma vitamin C concentrations of up to 14000micromol/L. In vitro models have demonstrated that concentrations of 1,000- 5,000micromol/L of vitamin C are selectively toxic to several cancer cell lines (Padayatty 2006).
Ten cancerous cell lines and four normal cell lines were exposed to varying concentrations of vitamin C in vitro. EC50 values (concentration of vitamin C required to reduce cell survival by 50%) were calculated for each cell line. Human lymphoma cells proved to be highly sensitive to vitamin C, with an EC50 value of 0.5micromol/L. Five additional cell lines demonstrated EC50 values of less than 4.0micromol/L, a concentration easily achieved through I.V. administration of vitamin C. 20micromol/L of vitamin C was incapable of significantly reducing survival in normal cell lines, highlighting that cytotoxic effects of vitamin C appear to be confined to cancerous cells (Chen 2005).
Guinea pigs bearing intradermal L-10 hepatocarcinoma tumors received oral or subcutaneous (SC) injections of vitamin C, with tumour mass and intra-tumour vitamin C concentrations determined at necropsy. Tumour burden reached nearly 50g in untreated animals. SC injections of ascorbate (500mg/kg/day) inhibited tumour growth by as much as 65%. “Tumor growth correlated inversely with intratumour ascorbate concentration, the latter exceeding 2mM in some cases. Ascorbate concentrations sufficient to kill tumour cells can be safely achieved in solid tumours in vivo, suggesting a possible role for high dose intravenous ascorbate in treating cancer.” (Casciari 2005).
At low concentrations in cell culture (less than 500micromol/L), vitamin C appears to inhibit intra- tumour generation of oxygen radical species. Endogenous catalase appears readily able to quench ascorbate-derived radical formation. The ascorbate-derived radical, however, inhibits catalase in a doseresponse manner. Once concentrations in cell culture reach 2,000micromol/L or greater, catalase appears to be incapable of preventing the formation of ascorbate radical (Nemoto 1997, Asano 1999, Sakagami 2000). Taken in context with the evidence presented above, it appears as though 2000 micromol/L is the lowest target plasma concentration of vitamin C, which would be desirable for use of vitamin C as a chemotherapeutic agent. Such a concentration is readily achieved through intravenous administration of vitamin C.
Intravenous Vitamin C as Cancer Treatment; Controlled Human Trials
Table 1 presents 12 controlled human trials of intravenous vitamin C for the management of several cancer types. In some reports the specific cancer types are poorly defined, while in others, a clearly defined protocol of combined chemotherapy and intravenous vitamin C is described.
One paper presented (Padayatty 2006), published in the Canadian Medical Association Journal, highlights what is likely to become the future of intravenous Vitamin C therapy in cancer. The paper includes contributions from the National Cancer Institute, the National Institute of Health, Centers for Cancer Research, and McGill University. The paper presents only three cases, however each case is of advanced, incurable cancer, documented with the highest standard of objective histopathological assessment. All three cases achieved long-term remission, with intravenous vitamin C the likely basis for the observed outcomes. The authors call for a reevaluation of intravenous vitamin C as a complementary tool for cancer management. Since the publication of this paper, several leading cancer clinics across North America have begun adding intravenous vitamin C to various cocktails used for the treatment of refractory multiple myeloma (See table 1). Please refer to table 2 for a commonly implemented protocol of intravenous vitamin C in complementary cancer management.
While it may remain the generally held opinion of oncologists across the country that intravenous use of vitamin C is inappropriate for cancer treatment, leading oncology units in North America have revived interest in this safe, non-toxic and effective chemotherapeutic strategy. It will invariably take several decades for the medical masses to become aware of recent successes of I.V. vitamin C in various clinical settings. Thankfully, the Naturopathic community never lost interest in this treatment strategy, and such therapies have remained available to patients since the pioneering work of Pauling and Cameron.
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Asano K, Satoh K, Hosaka M, Arakawa H, Inagaki M, Hisamitsu T, Maeda M, Kochi M, Sakagami H. Production of hydrogen peroxide in cancerous tissue by intravenous administration of sodium 5,6-benzylidene-Lascorbate Anticancer Res. 1999 Jan-Feb;19(1A):229-36.
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