Can We Identify Risk for Drug Toxicity?

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October 10, 2013 – Very recently, David Kerr, Professor of Cancer Medicine at University of Oxford, in the United Kingdom, and past President of the European Society for Medical Oncology, talked on Medscape (see the video here) about risk-benefit analyses for novel, inventive cancer treatments. See here in italics his statement:

 When we talk about precision medicine and personalized medicine, it occurs to me that most of the discussion has been about benefits and seeing what we can do to better understand the cancer and the molecular biology of the tumor. Through that understanding, we would try to come up with biomarkers that allow us to select patient populations that are likely to receive added benefit.

 As Francis Collins has said, those of us who are in the cancer field are probably standard-bearers for the whole broad field of personalized medicine because of the steps that we have made in terms of linking molecular genotypes to phenotypes and identifying the people who respond better to drugs.

 However, a risk-benefit ratio implies 2 sides of the coin. It seems to me that perhaps we have been missing out in terms of considering the toxicology, the pattern of side effects. These will be determined not by the somatic tumor mutations that we use to identify biomarkers for benefit, but within the germline. How do we metabolize the drug? How do we excrete it? The absorption, distribution, and metabolism components become important. I believe that one way of improving the risk-benefit ratio is to reduce risk. If we had tools, if we had assays, if we had biomarkers to identify patients most at risk for toxicity, most at risk perhaps even for lethal toxicity, then we as an oncology community would adapt our therapy accordingly, possibly even omitting some drugs if the hazard ratio for death or lethality were very high, but more likely modulating the dose of the drug to see if we could obviate the need for inducing life-threatening grade 4 toxicities.

 There is an interesting play here. If we look at most modern, well-designed, phase 3 cancer treatment trials, sometimes including a couple of thousand patients, we are starting to get the statistics that may allow us to do some genome-wide association studies looking for patterns of genetic change in the germline — not in the tumor, but the germline. That may give us an idea about which patients are most at risk for certain adverse effects and tell us, as practicing physicians, to adjust the dose accordingly.

 It is a new science. I am going to call it tox-nostics. There you are. You have heard it here first. I am going to trademark the term. We need to do more concerted research to see if we can improve risk-benefit, but through the portal of reducing risk rather than focusing only on benefit. I think modern, well-designed trials in which germline DNA — ie, blood — has been collected, gives us a way of doing this.

 We know that some tests out there are moderately well used for 5-FU, for irinotecan.[1] I think we can improve on these. I think we can improve test performance, utility, availability. We just need a few clinical champions, a few good tests, to really make the difference.

 Thanks for listening. As always, we will be very happy to take any comments that you may care to make or to post. Medscapers, ahoy! Thank you.

 This is a very notable statement, not only for Medscapers. I would like to comment it on two accounts. First, I am not so sure whether the world has waited for the new term “tox-nostics” and whether a “trade marking” of it will be necessary and would successfully serve its purpose, namely to promote the concepts of targeted efficacy and safety of patient’s therapies. For one, “tox-“ (or any mentioning of toxicity) in the field of drug development and marketing is very negatively looked at and basically considered a “non do”.  Extensive and start-up company terminating (TheraSTrat AG to be precise (you may still search the net for it)) past experience of the author of this Blog would indicate that neither the phamaceutical industry, nor investors and financial markets, nor regulators and patients would like to hear anything near to toxicity in connection with their product and/or therapy.  On the other hand, we (and others), in the early years of the last decade, have coined the term “theragenomics” to embrace the concept of targeted efficacy and safety of patient’s therapies by applying genomic and individualized genetic knowledge to drug therapy.

 Secondly, on a far more positive note, the recently FDA-approved anti-melanoma drug Zelboraf (Vemurafinib) would be one of several good example in case for Prof. Kerr’s proposal/statement. Zelboraf (Vemurafinib) is a kinase inhibitor indicated for the treatment of patients with unresectable or metastatic melanoma with BRAF V600E mutation as detected by an FDA-approved companion genetic test. Zelboraf (Vemurafinib) is not indicated for treatment of patients with wild-type BRAF melanoma. That means in the clear that before treatment, patients need to be tested for this mutation (i.e. allelic variant of the tumor BRAF gene) by a companion gene test. Only those patients who test positive for the BRAF V600E variant are eligible for and will profit from a  treatment with Zelboraf (Vemurafinib).

 In the “Warnings and Precautions”-section of Zelboraf’s FDA-approved drug label, the following potential serious, if not fatal, adverse effects of Zelboraf are listed: New Primary Cutaneous Malignancies; New Non-Cutaneous Squamous Cell Carcinoma; Other Malignancies; Tumor Promotion in BRAF Wild-Type Melanoma; Serious Hypersensitivity Reactions; Severe Dermatologic Reactions, including Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN); QT Prolongation; Hepatotoxicity; Photosensitivity; Serious Ophthalmologic Reactions; Embryo-Fetal Toxicity. Here (at FDA) and here (at DailyMed), you will find the drug label on Zelboraf (Vemurafinib).

 The other listed severe drug effects not withstanding, at least for “Severe Dermatologic Reactions, including Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)” we know from many other drug which are associated with this adverse effect, that there seems to exist a genetic predisposition of patients to develop SJS and TEN. For example, patients carrying the HLA-B*5701 allele have a very high risk for developing SJS and TEN when treated with Ziagen (Abacavir). Likewise, patients carrying the HLA-B*1501 allele have a very high risk for developing SJS and TEN when treated with Carbamazepine-containing medications such as Tegretol, Equetro, Carbatrol, and generics thereof. For more information on SJS and TEN, you might want to consult the link here to get started.

 Here, with Zelboraf (Vemurafinib) it might be worthwhile to see, if one the HLA-alleles already associated with SJS or TEN also dispose individuals treated with Zelboraf (Vemurafinib) to SJS or TEN or if in this case, genome wide analysis (GWA) would be necessary to identify new (HLA) alleles predisposing according patients to SJS or TEN. In any case, using such procedures, clinicians might in already today be in the position to provide highly effective targeted therapies combined with targeted avoidance of severe, treatments limiting and/or fatal drug toxicities to at least some patients, all of which would be in line with Prof. Kerr’s statement.

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About the Author
Joseph Gut - thasso Ph.D.; Professor in Pharmacology and Toxicology. Senior expert in theragenomic and personalized medicine and individualized drug safety. Senior expert in pharmaco- and toxicogenetics. Senior expert in human safety of drugs, chemicals, environmental pollutants, and dietary ingredients.

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