Antioxidants and Cancer Therapy Part II:
Quick Reference Guide

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

FROM:   Alternative Medicine Review 2000 (Apr); 5 (2): 152–163 ~ FULL TEXT

Davis W. Lamson, MS, ND and Matthew S. Brignall, ND

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Abstract

Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7

The previous lengthy review concerning the effects of antioxidant compounds used concurrently with radiotherapy and chemotherapy has been reduced to a reference guide. There are only three presently known examples in which any agent classifiable as an antioxidant has been shown to decrease effectiveness of radiation or chemotherapy in vivo. The vast majority of both in vivo and in vitro studies have shown enhanced effectiveness of standard cancer therapies or a neutral effect on drug action.

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Introduction

This guide is meant to be a companion to the previous review on effects of antioxidant supplementation during cancer therapy. [1] Widespread use of antioxidant compounds makes this an area of increasing interest to oncologists as well as other physicians; hence, the attempt to reduce the findings of a lengthy report to a manageable guide.

Reducing complicated interactions to a single sentence can be an oversimplification. In many instances the effect of an antioxidant compound with a certain therapeutic agent may be specific to a particular tumor type, or may vary with dosage of both antioxidant and chemotherapy. This guide is best used as a means of quickly identifying which antioxidants are likely to be indicated or contraindicated with a particular therapeutic agent. Please refer either to the earlier review (Altern Med Rev 1999; 4 (5); 304-329) or the original research reports for more information on these interactions.

Many of these interactions have been studied only in vitro. While an in vitro result is often a predictor of in vivo response, this is not always the case. The interaction between the bioflavonoid tangeretin and tamoxifen is a good example of the risk in placing too much emphasis on in vitro evidence. Tangeretin was found in vitro to act synergistically with tamoxifen; but in vivo tangeretin completely reversed the inhibitory action of the drug on experimental mammary tumors. [2] The authors wish to emphasize that combinations not studied in vivo risk potential adverse reactions and should be monitored closely or avoided altogether. Similarly, it must be assumed that any antioxidant found to reduce in vivo toxicity of cancer therapy on healthy tissue has the potential to decrease effectiveness of the chemotherapy unless this was specifically studied. The studies reporting reduced toxicity to healthy tissue of a therapeutic agent with unknown effects on treatment outcomes are only reported if the reduction was noted in human studies. The following tables summarize the effect of various antioxidants when combined with specific chemotherapeutic agents or radiation. Refer to Tables 1-7.

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Conclusion

There are only three presently known examples in which an agent classifiable as an antioxidant has been shown to decrease effectiveness of radiation or chemotherapy in vivo. The vast majority of both in vivo and in vitro studies have shown enhanced effectiveness of standard cancer therapies or a neutral effect on drug action. The authors wish to thank Richard Russell and the Smiling Dog Foundation for financial support of this project and Bastyr University for its administration.

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