Can We Identify Risk for Drug Toxicity?

October 10, 2013

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.


EMA: Public consultation open on concept paper on pharmacogenomics in evaluation of authorised medicines

January 26, 2012

January 26, 2012 – I am relaying the information below by the EMA to the readers of this blog. It might be interessting to dwell into this concept paper (as a scientist, a treating physician, or an informed patient) for informations only or even for commenting.

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 The European Medicines Agency (EMA) has released a concept paper on the development of a guideline on the evaluation of pharmacogenomic methodologies in the evaluation of authorised medicines for public consultation.

The concept paper on key aspects for the use of pharmacogenomic methodologies in the pharmacovigilance evaluation of medicinal products explains that a proportion of the variability in response to medicines is due to genetic differences between individuals. Identifying individuals at risk of side effects, unexpected complications or lack of efficacy may help the development of strategies to optimise the use of medicines.

The concept paper sets out a number of issues that a future guideline could cover. These include the systematic consideration of the effects of genetic variability in safety monitoring of medicines, the use of biomarkers, the timing of the monitoring of genomic data and the information that should be provided in medicines’ product information.

The concept paper is open for comments until 15 March 2012. Comments should be sent to pgwpsecretariat@ema.europa.eu using the form for submission of comments.


Patients on Vemurafenib [Zelboraf] Need Testing for RAS Mutations: Secondary Cancers a Major Concern

January 26, 2012

January 26, 2012 – A January 20, 2012 article in Medscape Medical New illustrates how personalized medicine can be tricky. The case is Vemurafenib [Zelboraf], which was introduced to the market together with an companion genetic test mid 2011 for the treatment of advanced melanoma in suitable BRAF mutation (V600E) positive patients only. In these patients, while melanoma therapy response rates are impressive, a new problem seems to arise, namely secondary tumours. Please read the article published  by Medscape Medical News on this topic.

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Patients with advanced melanoma who are treated with Vemurafenib [Zelboraf ]  should be tested for RAS mutations, according to an editorial published in the January 19 issue of the New England Journal of Medicine.

A study that accompanies the editorial reports that RAS mutations frequently occur in secondary skin tumors that develop in vemurafenib-treated patients.

The testing is necessary because there is “potential for secondary tumor development” that arises from treatment with vemurafenib and other BRAF inhibitors, writes Ashani T. Weeraratna, PhD, from the molecular and cellular oncogenesis program at The Wistar Institute in Philadelphia, Pennsylvania, in her editorial. These secondary skin tumors — namely, cutaneous squamous cell carcinomas and keratoacanthomas — are relatively benign, compared with melanoma, and are no reason to discontinue vemurafenib, said Dr. Weeraratna. However, testing will alert clinicians to which patients have RAS-driven secondary tumors.

The testing is important because patients with RAS mutations could also develop secondary cancers in organs beyond the skin, advised Dr. Weeraratna. “If patients have RAS mutations they should be monitored closely for any development of cutaneous squamous cell carcinomas in all organs,” she told Medscape Medical News.

“Although cutaneous squamous cell carcinomas are not deadly, these lesions can be life-threatening when they occur in other organs,” Dr. Weeraratna writes in her editorial. She discussed other potentially affected organs. “Squamous cell carcinomas can potentially arise in any organ with a squamous epithelium, essentially a layer of flattened epithelial cells that line the basement membranes of organs. A squamous epithelium is found most often in organs where rapid filtration and diffusion is necessary, such as the alveolar lining of the lungs and the glomerulus (kidney). Thus, squamous cell carcinomas can be found in organs such as the lungs, cervix, and esophagus, and also account for a large proportion of head and neck cancers,” Dr. Weeraratna explained.

Importantly, there is no evidence that vemurafenib triggers tumors in other organs. “It is as yet unclear whether the generation of squamous cell carcinomas in these organs, upon BRAF inhibitor therapy, occurs, but these data certainly alert us to that potential risk,” she said.

MEK Inhibitors May Help

In this study of melanoma patients, the investigators sought to characterize the molecular mechanism behind the development of secondary skin cancers in patients treated with vemurafenib.

They admit that a skin cancer drug that causes other skin cancers is unexpected. The development of cutaneous squamous cell carcinomas and keratoacanthomas “is the opposite of what would be expected from a targeted oncogene inhibitor,” write the study authors, led by Fei Su, PhD, from Hoffman-La Roche Pharmaceuticals in Nutley, New Jersey. In their search to understand this toxicity, the investigators analyzed the DNA of a sampling of these tumors and found a high rate of RAS mutations (21 of 35 tumors; 60%). “Mutations in RAS, particularly HRAS, are frequent in cutaneous squamous cell carcinomas and keratoacanthomas that develop in patients treated with vemurafenib,” write the authors.

“This study points out that BRAF inhibitors should only be used in patients who have cancers driven by BRAF mutations, and it raises the concern that cancers driven by RAS mutations (KRAS, HRAS, or NRAS) can be paradoxically activated instead of inhibited with this class of drugs,” said coauthor Antoni Ribas, MD, PhD, in email correspondence with Medscape Medical News. He is from the division of hematology–oncology at the UCLA Medical Center in Los Angeles, California.

Why patients treated with vemurafenib have such a high rate of RAS mutations in these secondary cancers is not known. However, the investigators performed animal-model studies that suggest that the development of RAS-mutation-driven secondary tumors might be prevented with a MEK inhibitor, another class of drugs. There might be “usefulness of combining a BRAF inhibitor with a MEK inhibitor to prevent this toxic effect” of secondary cancers, write the authors.

There has already been clinical investigation of this concept — a phase 2 study of the combination of the MEK inhibitor GSK1120212 and the RAF inhibitor GSK2118436 in metastatic melanoma. That study, which was presented at the 2011 annual meeting of the American Society of Clinical Oncology, and reported at that time by Medscape Medical News, showed that the toxicity of the combination seemed to be lower than that of either agent used alone.

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NEJM: Study

NEJM: Editoral

Medscape Medical News: Article


FDA Approves Crizotinib [Xalkori] with Companion Diagnostic Test for Non-Small Cell Lung Cancers (NSCLC) Positive for the Anaplastic Lymphoma Kinase (ALK) Gene

August 28, 2011

August 26, 2011 – Today, the  American Food and Drug Administration (FDA) has approved Crizotinib [Xalkori] to treat the patient subgroup with late-stage (locally advanced or metastatic), non-small cell lung cancers (NSCLC) whos cancers express (i.e., test positive for the presence of) the abnormal anaplastic lymphoma kinase (ALK) gene.

The abnormal anaplastic lymphoma kinase (ALK) gene causes cancer cell development and growth. About 1 percent to 7 percent of the patients with NSCLC have the ALK gene abnormality. Patients with this form of lung cancer are typically non-smokers. Crizotinib [Xalkori] works by blocking certain proteins called kinases, including the protein produced by the abnormal ALK gene. Xalkori is a pill taken twice a day as a single-agent treatment.

Crizotinib [Xalkori] has been approved together with a companion diagnostic test that will help determine if a patient’s tumor expresses the abnormal ALK gene. This genetic test is called the Vysis ALK Break Apart FISH Probe Kit. The application of this specific test allows the selection of only those  patients for treatment with Crizotinib [Xalkori] who are most likely to respond to the drug. Targeted therapies such as this one invoving Crizotinib [Xalkori] are considered important options for sucessfully treating patients with this disease.

Crizotinib [Xalkori]’s effectiveness was established in two multi-center, single-arm studies enrolling a total of 255 patients with late-stage ALK-positive NSCLC. A sample of a patient’s lung cancer tissue was collected and tested for the ALK gene abnormality prior to study enrollment. The studies were designed to measure objective response rate, the percentage of patients who experienced complete or partial cancer shrinkage. Most patients in the studies had received prior chemotherapy. In one study, the objective response rate was 50 percent with a median response duration of 42 weeks. In another study, the objective response rate was 61 percent with a median response duration of 48 weeks.

Based on these favorable efficacy data, Crizotinib [Xalkori] has been approved under the FDA’s accelerated approval program, which allows the agency to approve a drug to treat a serious  and life-threatening disease based on clinical data showing that the drug has an effect on an endpoint that is reasonably likely to predict a clinical benefit to patients. The program is designed to provide patients with earlier access to promising new drugs, followed by further studies to confirm the drug’s clinical benefit.

The most common side effects reported in patients receiving Crizotinib [Xalkori] included vision disorders, nausea, diarrhea, vomiting, swelling (edema), and constipation. Vision disorders included visual impairment, flashes of light, blurred vision, floaters, double vision, sensitivity to light, and visual field defects. Xalkori use has also been associated with inflammation of the lung tissue (pneumonitis), which can be life-threatening. Patients with treatment-related pneumonitis should permanently stop treatment with Crizotinib [Xalkori]. Moreover, the drug should not be used in pregnant women. In the context of the clinical safety of Crizotinib [Xalkori], we should be aware that the companion test (Vysis ALK Break Apart FISH Probe Kit) does not identify patients with either a predisposition for any of the unwanted drug side effects, or irregularities in drug disposition (e.g., poor or ultrarapid metabolizers). We will also need many more patients treated with Crizotinib [Xalkori] in order to more completely understand the clinical safety profile of Crizotinib [Xalkori].

See the FDA Press Release here.


FDA Drug Safety Communication: Reduced effectiveness of Clopidogrel [Plavix] in patients who are poor metabolizers (i.e. carriers of selected CYP2C19 allelic variants) of the drug

March 17, 2010

March 17, 2010 – The U.S. Food and Drug Administration (FDA) has added a Boxed Warning to the label for Clopidogrel [Plavix], the anti-blood clotting medication. The Boxed Warning is about patients who do not effectively metabolize the drug (i.e. “poor metabolizers”, see below) and therefore may not receive the full benefits of the drug.

The Boxed Warning in the drug label will include information to:

  • Warn about reduced effectiveness in patients who are poor metabolizers of Clopidogrel [Plavix]. Poor metabolizers do not effectively convert Clopidogrel [Plavix] to its active form in the body.
  • Inform healthcare professionals that tests are available to identify genetic differences in CYP2C19 function.
  • Advise healthcare professionals to consider use of other anti-platelet medications or alternative dosing strategies for Clopidogrel [Plavix] in patients identified as poor metabolizers.

Clopidogrel [Plavix] is given to reduce the risk of heart attack, unstable angina, stroke, and cardiovascular death in patients with cardiovascular disease. Clopidogrel [Plavix] works by decreasing the activity of blood cells called platelets, making platelets less likely to form blood clots.

For Clopidogrel [Plavix] to work, enzymes in the liver (particularly CYP2C19) must convert (metabolize) the drug to its active form. Patients who are poor metabolizers of the drug, do not effectively convert Clopidogrel [Plavix] to its active form. In these patients, Clopidogrel [Plavix] has less effect on platelets, and therefore less ability to prevent heart attack, stroke, and cardiovascular death. It is estimated that 2 to 14% of the population are poor metabolizers; the rate varies based on racial background.

Healthcare professionals should be aware that a subgroup of patients are poor metabolizers and do not metabolize Clopidogrel [Plavix] effectively; this can result in reduced effectiveness of Clopidogrel [Plavix]. Healthcare professionals should consider use of other anti-platelet medications or alternative dosing strategies for Clopidogrel [Plavix] in these patients.

Patients should not stop taking Clopidogrel [Plavix] unless told to do so by their healthcare professional. They should talk with their healthcare professional if they have any concerns about Clopidogrel [Plavix], or to find out if they should be tested for being a poor metabolizer.

In May 2009, FDA added information about poor metabolizers of Clopidogrel [Plavix] to the drug label. However, based on additional data reviewed by the agency (see Data Summary below) the Boxed Warning is now being added to highlight the reduced effectiveness of Clopidogrel [Plavix] in these patients and to recommend that healthcare professionals consider use of other anti-platelet medications or alternative dosing strategies for Clopidogrel [Plavix] in patients identified as poor metabolizers.

Additional Information for Patients and Health Care Providers Alike

Patients currently taking Plavix should:

  • Be aware that some patients do not convert Clopidogrel [Plavix] to its active form as well as other patients. These patients may not get the same benefit from Clopidogrel [Plavix]and are known as poor metabolizers.
  • Not stop taking Clopidogrel [Plavix] unless told to do so by their healthcare professional.
  • Talk with their healthcare professional if they have any concerns about Clopidogrel [Plavix].
  • Talk with their healthcare professional to see if testing to determine their metabolizer status is appropriate.

FDA recommends that healthcare professionals should:

  • Be aware that some patients may be poor metabolizers of Clopidogrel [Plavix]. They do not effectively convert Clopidogrel [Plavix] to its active form because of low CYP 2C19 activity.The effectiveness of Plavix as a preventive therapy is reduced in these patients.
  • Be aware that tests are available to determine patients’ CYP2C19 status.
  • Consider use of other anti-platelet medications or alternative dosing strategies for Clopidogrel [Plavix] in patients who have been identified as poor metabolizers.
  • Be aware that although a higher dose regimen (600 mg loading dose followed by 150 mg once daily) in poor metabolizers increases antiplatelet response, an appropriate dose regimen for poor metabolizers has not been established in a clinical outcome trial.
  • Review the newly approved Clopidogrel [Plavix] drug label for complete information on the use of Clopidogrel [Plavix].

Scientific Background and Data Summary

The liver enzyme CYP2C19 is primarily responsible for the formation of the active metabolite of Clopidogrel [Plavix]. Pharmacokinetic and antiplatelet tests of the active metabolite of Clopidogrel [Plavix] show that the drug levels and antiplatelet effects differ depending on the genotype of the CYP2C19 enzyme. The following represent the different alleles of CYP2C19 that make up a patient’s genotype:

1. The CYP2C19*1 allele has fully functional metabolism of Clopidogrel [Plavix].

2. The CYP2C19*2 and *3 alleles have no functional metabolism of Clopidogrel [Plavix]. These two alleles account for most of the reduced function alleles in patients of Caucasian (85%) and Asian (99%) descent classified as poor metabolizers.

3. The CYP2C19*4, *5, *6, *7, and *8 and other alleles may be associated with absent or reduced metabolism of Clopidogrel [Plavix], but are less frequent than the CYP2C19*2 and *3 alleles.

A patient who carries two loss-of-function alleles (as defined above) will have poor metabolizer status.

The pharmacokinetic and antiplatelet responses to Clopidogrel [Plavix] were evaluated in a crossover trial in 40 healthy subjects. Ten subjects in each of the four CYP2C19 metabolizer groups (ultrarapid, extensive, intermediate and poor) were randomized to two treatment regimens: a 300 mg loading dose followed by 75 mg per day, or a 600 mg loading dose followed by 150 mg per day, each for a total of 5 days. After a washout period, subjects were crossed over to the alternate treatment. Decreased active metabolite exposure and increased platelet aggregation were observed in the poor metabolizers compared to the other groups. When poor metabolizers received the 600 mg loading dose followed by 150 mg daily, active metabolite exposure and antiplatelet response were greater than with the 300 mg/75 mg regimen. Healthcare professionals should note that an appropriate dose regimen for patients who are poor metabolizers has not been established in clinical outcome trials.


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