Perspective on the carcinogenic potential of phenytoin based on rodent tumor bioassays and human epidemiological data

Danish Population Based Study of Familial Epilepsy and Childhood Cancer

Objective

Results from studies investigating the association between maternal or child epilepsy, use of anticonvulsants in pregnancy, and childhood cancer are inconsistent and at times contradictory.

Methods

Linking Danish national databases, we obtained epilepsy and childhood cancer diagnoses, and anticonvulsant use data. We estimated adjusted odds ratios of all or specific childhood cancers in relation to maternal or child epilepsy and anticonvulsant therapies using conditional logistic regression.

Results

Maternal epilepsy was positively associated with all childhood cancers in offspring, specifically, with acute lymphoblastic leukemia (Odds Ratio (OR) = 1.68, 95% Confidence Interval (CI) = 1.16, 2.43) and Wilms tumor (OR = 2.13, 95%CI = 0.97, 4.68). When considering maternal ever (lifetime) ingestion of anticonvulsants, a positive association was found with all cancers (OR = 1.15, 95%CI = 1.01, 1.31), and central nervous system tumors (OR = 1.32, 95%CI = 1.03, 1.69) as well as neuroblastoma (OR = 2.05, 95%CI = 1.29, 3.28) among offspring. Maternal anticonvulsant use before or during the index pregnancy was related to CNS tumors in offspring (OR = 1.78, 95%CI = 0.99, 3.21), however the confidence interval included the null.

Significance

Maternal use of certain anticonvulsant medications may be a risk factor for cancer in offspring. Medical providers may need to consider what type of treatments to prescribe to pregnant mothers with epilepsy.

Phenytoin - An anti-seizure drug: Overview of its chemistry, pharmacology and toxicology

Phenytoin is a long-standing, anti-seizure drug widely used in clinical practice. It has also been evaluated in the context of many other illnesses in addition to its original epilepsy indication. The narrow therapeutic index of phenytoin and its ubiquitous daily use pose a high risk of poisoning. This review article focuses on the chemistry, pharmacokinetics, and toxicology of phenytoin, with a special focus on its mutagenicity, carcinogenicity, and teratogenicity. The side effects on human health associated with phenytoin use are thoroughly described. In particular, DRESS syndrome and cerebellar atrophy are addressed. This review will help in further understanding the benefits phenytoin use in the treatment of epilepsy.

A semi-automated workflow for adverse outcome pathway hypothesis generation: The use case of non-genotoxic induced hepatocellular carcinoma

The utility of the Adverse Outcome Pathway (AOP) concept has been largely recognized by scientists, however, the AOP generation is still mainly done manually by screening through evidence and extracting probable associations. To accelerate this process and increase the reliability, we have developed an semi-automated workflow for AOP hypothesis generation. In brief, association mining methods were applied to high-throughput screening, gene expression, in vivo and disease data present in ToxCast and Comparative Toxicogenomics Database. This was supplemented by pathway mapping using Reactome to fill in gaps and identify events occurring at the cellular/tissue levels. Furthermore, in vivo data from TG-Gates was integrated to finally derive a gene, pathway, biochemical, histopathological and disease network from which specific disease sub-networks can be queried. To test the workflow, non-genotoxic-induced hepatocellular carcinoma (HCC) was selected as a case study. The implementation resulted in the identification of several non-genotoxic-specific HCC-connected genes belonging to cell proliferation, endoplasmic reticulum stress and early apoptosis. Biochemical findings revealed non-genotoxic-specific alkaline phosphatase increase. The explored non-genotoxic-specific histopathology was associated with early stages of hepatic steatosis, transforming into cirrhosis. This work illustrates the utility of computationally predicted constructs in supporting development by using pre-existing knowledge in a fast and unbiased manner.

Association between antiepileptic drugs and hepatocellular carcinoma in patients with epilepsy: a population-based case-control study

BACKGROUND

This study explored whether antiepileptic drugs (AEDs) use increases the risk of hepatocellular carcinoma (HCC).

METHODS

We conducted a case-control study using data from the National Health Insurance system of Taiwan. The case group comprised 1,454 epilepsy patients with newly diagnosed HCC, and the control group comprised 1,448 epilepsy patients without HCC. Both groups had similar distributions of sex and age, and follow-up duration. Possible associations with the AEDs in Taiwan were examined.

RESULTS

After adjusted for AEDs (phenobarbital and primidone, clonazepam, clorazepate and diazepam, and other AEDs), and for the comorbidities of diabetes, chronic liver disease and cirrhosis, hepatitis B and C virus infection, and alcoholism, the odds ratio (OR) of HCC was 1.22 (95% confidence interval [CI]: 1.01-1.47) for the group of phenytoin users compared with nonphenytoin users. An annual means of 61-120, 121-180, and >180 of defined daily doses (DDDs) of phenytoin (OR: 4.07, 95% CI: 2.03-8.18; OR: 7.51, 95% CI: 3.03-18.7, and OR: 14.6, 95% CI: 7.88-26.9, respectively) were significantly correlated with the risk of HCC but not with a DDD of ≤60. Compared with nonphenytoin users, HCC patients who had used phenytoin within 1 year of HCC diagnosis were at a greatest risk of HCC (adjusted OR: 2.29, 95% CI: 1.71-3.08), followed by who had used phenytoin within 2 years of diagnosis (adjusted OR: 1.92, 95% CI: 1.44-2.56).

CONCLUSION

The results indicate that high dose of phenytoin was associated with a statistically significant increased OR for HCC, which was not demonstrated for low-dose phenytoin.

A critical review of the effectiveness of rodent pharmaceutical carcinogenesis testing in predicting for human risk

The pharmaceutical industry and regulatory agency toxicology testing paradigms in the United States currently appear successful, in part because of the continuously increasing life expectancy and the declining age-adjusted cancer rates in the United States. Although drugs likely have a minimal impact on the population statistics for cancer rates, pharmaceutical pathologists and toxicologists must focus on the individual risk for pharmaceutical carcinogenesis. As our understanding of carcinogenesis increases exponentially, and after hundreds if not thousands of rodent cancer tests, significant improvement in the precision of human pharmaceutical carcinogenesis hazard identification should now be possible and would enable a reduction in the substantial false-negative and false positive-rates reported herein. The appropriate use of acute, subchronic, chronic, and special toxicology tests to identify the major associated cancer risk factors, specifically, hormonal modulation, immunosuppression, genetic toxicity, and chronic toxicity, can be recognized through this review of pharmaceutical carcinogens. Significant opportunities exist for improving the effectiveness and efficiency of the current cancer risk assessment paradigm.