Behind The Medical Headlines

HAMLET, BREAST MILK AND VIRAL WARTS

• Dr EC Benton, Consultant Dermatologist, Edinburgh Royal Infirmary, Edinburgh, Scotland

Summary

Results of a study suggesting that a compound based on breast milk could be used to treat viral warts have attracted media interest. How effective is this intriguing treatment and could it be developed to treat more serious, related, conditions? Dr Claire Benton reviews the evidence.

Declaration of interests: No conflict of interests declared

Thirty years ago, prior to becoming a dermatologist, I spent a year in General Practice. Before leaving this post in 1975, I was presented with a copy of Dr Ronald Illingworth’s sixth edition of The Normal Child, a book that became a constant companion when raising my own family. I reckoned this would be a good starting point on which to base a commentary on Gustafsson’s paper in the June issue of the New England Journal of Medicine on the Treatment of skin papillomas with topical alpha lactalbumin-oleic acid, a human breast milk extract.¹ Indeed, the first two chapters of Illingworth’s book extol the virtues of breast feeding which include conferring on the infant a lower risk of respiratory or gastro-intestinal infections, these benefits being attributed to the high levels of immunoglobulins, lactoferrin and lactoperoxidase in breast milk.

Twenty years later Hakansson et al.² observed by chance while researching the effect of human milk on bacterial adherence in a human lung cancer cell line, that in the course of those experiments, both transformed and immature non-transformed cells demonstrated morphological changes consistent with programmed cell death or apoptosis. This effect was also seen with peripheral blood lymphocytes but not in normal mature cells, nor did it occur with bovine milk. They identified an active component in the casein fraction as a multimeric alpha-lactalbumin (MAL) in a partially unfolded configuration. This novel molecular entity was found to activate several aspects of a cell’s self-destruction mechanism, crossing the cell membrane and passing into the nucleus where it accumulated and disrupted the chromatin. The reaction was calcium dependent and did not occur in a calcium-free environment.

It is known that native alpha lactalbumin from breast milk does not cause apoptosis. However in 2000, Svensson et al.³ demonstrated that they could, under certain conditions, alter the native alpha lactalbumin from breast milk, producing folding of the molecule, which was then stabilised by complexing it with a lipid cofactor, oleic acid in a stereo specific fit. By acquiring the ability to cause cell death by virtue of its altered configuration, human alpha lactalbumin was made lethal to tumour cells and thus it acquired the name HAMLET. The authors also speculated that the environment in a nursing infant’s stomach resembled the conditions under which they had produced the altered molecule, with a low pH encouraging release of calcium ions required for the reaction. Thus they suggest that in addition to its well-recognised anti-microbial activities, breast milk might also contribute to mucosal immunity by a process of immune surveillance of the infant’s immature epithelium protecting it against both infection and cancer.

Subsequent work by Svanborg et al.⁴ found that cell death in vitro did not appear to be regulated by the classic pathways of apoptosis, as the effect was independent of whether cells were of wild type, null or mutant p53 genotype. This may be of relevance in cells transformed by oncogenic human papillomavirus genes such as HPV16 E6 that binds to and inactivates p53. In addition, by causing intracellular flux of calcium ions, alpha lactalbumin-oleic acid might also switch on the differentiation of keratinocytes, a process arrested in the transformed HPV infected cells.

At this point the humble viral wart enters the picture. The human papillomavirus (HPV) induces warts, both cutaneous and mucosal, by transformation of the infected keratinocytes. Cutaneous warts are common, often very persistent and therefore a readily accessible target for study of novel agents. However, over the years credence has been given to many treatments – from bacon fat to banana skin, keratolytics to cryotherapy, and immunotherapy with interferon or imiquimod – all have their proponents.⁴ But it is important when assessing any new treatment to remember that given time, the vast majority of HPV induced warts undergo spontaneous remission, up to 95% within a five-year period. Therefore to confirm the efficacy of any novel treatment a randomised placebo-controlled study is essential: a recent Cochrane review indicated that very few treatments had been assessed according to these strict criteria.⁵

The results of the study reported by Gustafsson¹ involving 40 patients with a total of 166 warts are, however, encouraging. An initial blinded comparison made between the topical application of alpha lactalbumin-oleic acid versus saline placebo over a three-week period demonstrated a median reduction in volume of the individual warts of 75% in the active group versus 15% in the placebo group (p< 0.001). The response was irrespective of gender, site of warts or presence of immunosuppression. In a subsequent open label study three months later, 33 from the 40 original patients received a further three-week course of topical alpha-lactalbumin. Follow-up at two years found an overall cure rate of 83%, but significantly more rapid resolution in those who had originally received the active product. Further validation of this treatment is required in particular a comparison of HAMLET with what is currently a rather cheaper and more readily available product, salicylic acid where cure rates of around 80% are expected. It would also be useful to assess whether in cutaneous warts, the active product actually penetrates the thick keratin layer: this was found to be a limiting factor with the topically applied immunostimulant, imiquimod which has a better success rate in non keratinised anogenital warts.⁶ A further study of potential interest would be a trial of oleic acid alone versus the alpha lactalbumin-oleic acid combination for patients with persistent or recurrent anogenital HPV infection.

Where there may be the greatest need for this targeted therapy which so far seems to possess few side-effects, is in the increasingly common problems of HPV associated genital tract neoplasia. It may also have a role in immunosuppressed patients such as organ allograft recipients in whom viral warts may not only be extensive and recalcitrant, but may be one of the cofactors in the aetiology of cutaneous squamous cancers which so many of these patients develop. Already some in vivo xenograft work has demonstrated the efficacy of this agent in the treatment of glioblastoma.⁷

Optimum mode of in vivo delivery to tumours may still pose challenges, as might the supply of sufficient quantities of human breast milk, but there seems little doubt that HAMLET promises to be a major player on the stage of cancer therapeutics.

References

1. Gustaffson L, Leijinhufvud I, Aronsson A et al. Treatment of skin papillomas with topical alpha lactalbumin-oleic acid. N Engl J Med 2004; 350:2663–72.
2. Hakansson A, Zhivotovsky B, Orrenius S et al. Apoptosis induced by a human milk protein. PNAS 1995; 92:8064–8.
3. Svensson M, Håkansson A, Mossberg A-K et al. Conversion of alpha lactalbumin to a protein inducing apoptosis. PNAS 2000; 97:4221-6
4. Svanborg C, Agerstam H, Aronson A et al. HAMLET kills tumour cells by an apoptosis-like mechanism – cellular, molecular and therapeutic aspects. Adv Cancer Res 2003; 88:1–29.
5. Leman JA, Benton EC. Verrucas – guidelines for management. Am J Clin Dermatol 2000; *1:*145–9.
6. Gibbs S, Harvey I, Sterling J et al. Local treatments for cutaneous warts: systematic review. BMJ 2002; 325:461.
7. Fischer W, Gustafsson L, Mossberg A-K et al. Human alpha-lactalbumin made lethal to tumor cells (HAMLET) kills human glioblastoma cells in brain xenografts by an apoptosis-like mechanism and prolongs survival. Cancer Res 2004; 64:2105–12.