Re: Enhanced cancer growth in mice administered daily human-equivalent doses of some H1-antihistamines: predictive in vitro correlates

Repurposing old drugs in oncology: Opportunities with clinical and regulatory challenges ahead

WHAT IS KNOWN AND OBJECTIVE

In order to expedite the availability of drugs to treat cancers in a cost-effective manner, repurposing of old drugs for oncological indications is gathering momentum. Revolutionary advances in pharmacology and genomics have demonstrated many old drugs to have activity at novel antioncogenic pharmacological targets. We decided to investigate whether prospective studies support the promises of nonclinical and retrospective clinical studies on repurposing three old drugs, namely metformin, valproate and astemizole.

METHODS

We conducted an extensive literature search through PubMed to gather representative nonclinical and retrospective clinical studies that investigated the potential repurposing of these three drugs for oncological indications. We then searched for prospective studies aimed at confirming the promises of retrospective data.

RESULTS AND DISCUSSION

While evidence from nonclinical and retrospective clinical studies with these drugs appears highly promising, large scale prospective studies are either lacking or have failed to substantiate this promise. We provide a brief discussion of some of the challenges in repurposing. Principal challenges and obstacles relate to heterogeneity of cancers studied without considering their molecular signatures, trials with small sample size and short duration, failure consider issues of ethnicity of study population and effective antioncogenic doses of the drug studied.

WHAT IS NEW AND CONCLUSION

Well-designed prospective studies demonstrating efficacy are required for repurposing old drugs for oncology indications, just as they are for new chemical entities for any indication. Early and ongoing interactions with regulatory authorities are invaluable. We outline a tentative framework for a structured approach to repurposing old drugs for novel indications in oncology.

Antihistamine use and breast cancer risk

Antihistamines are structurally similar to DPPE, a tamoxifen derivative known to promote tumor growth, and to antidepressants. Animal experiments have linked certain antihistamines and antidepressants with enhanced tumor growth in mice. The few epidemiologic studies examining antihistamine use have not indicated an increased risk. In light of suggestive animal data, structural similarities between antihistamines and DPPE, the widespread use of antihistamines, and the lack of epidemiologic investigation into their use and breast cancer risk, it is important to examine this issue. Female cases aged 25-74 years, diagnosed 1996 to 1998, were identified through the Ontario Cancer Registry. Controls were a random, age-matched sample of women. Cases (n=3,133) and controls (n=3,062) completed a mailed questionnaire that included questions about antihistamines used regularly (undefined), type and duration. Age-adjusted odds ratio (OR) estimates and 95% confidence intervals (CIs) were obtained using logistic regression. Antihistamine users were at no increased risk for breast cancer (OR=0.93, 95% CI: 0.81, 1.06), and no trend in risk was observed for age starting or duration of use. Antihistamine users were at no increased risk. No confounding or effect modification was identified in multivariate modeling. Our findings do not support the hypothesis that women who use antihistamines are at a greater breast cancer risk than those who do not.