DPYD genotyping and predicting fluoropyrimidine toxicity: where do we stand?

Fluoropyrimidines (FPs) are antineoplastic drugs widely used in the treatment of various solid tumors. Nearly 30% of patients treated with FP chemotherapy experience severe FP-related toxicity, and in some cases, toxicity can be fatal. Patients with reduced activity of DPD, the main enzyme responsible for the breakdown of FP, are at an increased risk of experiencing severe FP-related toxicity. While European regulatory agencies and clinical societies recommend pre-treatment DPD deficiency screening for patients starting treatment with FPs, this is not the case with American ones. Pharmacogenomic guidelines issued by several pharmacogenetic organizations worldwide recommend testing four DPD gene (DPYD) risk variants, but these can predict only a proportion of toxicity cases. New evidence on additional common DPYD polymorphisms, as well as identification and functional characterization of rare DPYD variants, could partially address the missing heritability of DPD deficiency and FP-related toxicity.

Amyloid-ß plaque formation and BACE1 accumulation in the brains of a 5xFAD Alzheimer's disease mouse model is associated with altered distribution and not proteolysis of BACE1 substrates Sez6 and Sez6L.

The formation of amyloid-ß peptides (Aß), that accumulate in Alzheimer's disease (AD) brains, involves proteolytic processing of the amyloid precursor protein (APP) firstly by ß-secretase (BACE1). Since BACE1 cleaves a plethora of other substrates, in this work we investigated whether the proteolysis and/or distribution of other BACE1 substrates, such as seizure protein 6 (Sez6) and seizure 6-like protein (Sez6L), is altered in AD. To test this we used 5xFAD mouse model brains that show an early accumulation of Aß plaques already at 2-months of age. Here we show for the first time that accumulation of BACE1 in peri-plaque regions and its enhanced levels in AD brains does not affect proteolysis of BACE1 substrates other than APP, such as Sez6 and Sez6L. We observed altered distribution of Sez6 and Sez6L in the area of Aß plaques in 5xFAD brains which is distinct to that of APP, BACE1 and/or LAMP1, suggesting different localization and/or function of these BACE1 substrates. While it is necessary to further elucidate the potential role that this may play in the course of AD, it is likely that Aß-targeted therapies may have beneficial effects against accumulation and/or altered distribution of BACE1 and its substrates, in addition to APP.

DPYD polymorphisms c.496A>G, c.2194G>A and c.85T>C and risk of severe adverse drug reactions in patients treated with fluoropyrimidine-based protocols.

AIMS: Cancer patients with reduced dihydropyrimidine dehydrogenase (DPD) activity are at increased risk of severe fluoropyrimidine (FP)-related adverse events (AE). Guidelines recommend FP dosing adjusted to genotype-predicted DPD activity based on four DPYD variants (rs3918290, rs55886062, rs67376798 and rs56038477). We evaluated the relationship between three further DPYD polymorphisms: c.496A>G (rs2297595), *6 c.2194G>A (rs1801160) and *9A c.85T>C (rs1801265) and the risk of severe AEs. METHODS: Consecutive FP-treated adult patients were genotyped for "standard" and tested DPYD variants, and for UGT1A1*28 if irinotecan was included, and were monitored for the occurrence of grade ≥3 (National Cancer Institute Common Terminology Criteria) vs. grade 0-2 AEs. For each of the tested polymorphisms, variant allele carriers were matched to respective wild type controls (optimal full matching combined with exact matching, in respect to: age, sex, type of cancer, type of FP, DPYD activity score, use of irinotecan/UGT1A1, adjuvant therapy, radiotherapy, biological therapy and genotype on the remaining two tested polymorphisms). RESULTS: Of the 503 included patients (82.3% colorectal cancer), 283 (56.3%) developed grade ≥3 AEs, mostly diarrhoea and neutropenia. Odds of grade ≥3 AEs were higher in c.496A>G variant carriers (n = 127) than in controls (n = 376) [OR = 5.20 (95% CI 1.88-14.3), Bayesian OR = 5.24 (95% CrI 3.06-9.12)]. Odds tended to be higher in c.2194G>A variant carriers (n = 58) than in controls (n = 432) [OR = 1.88 (0.95-3.73), Bayesian OR = 1.90 (1.03-3.56)]. c.85T>C did not appear associated with grade ≥3 AEs (206 variant carriers vs. 284 controls). CONCLUSION: DPYD c.496A>G and possibly c.2194G>A variants might need to be considered for inclusion in the DPYD genotyping panel.