Asparaginase (ASP) is considered as a backbone of successful treatment of acute lymphoblastic leukemia (ALL). Cell growth and division of malignant lymphoblasts are highly dependent on asparagine and glutamine. ASP depletes them from extracellular fluid which leads to apoptosis of lymphoblasts. Aside from the aimed antileukemic properties, asparaginase exposes patients to multiple adverse effects including severe hypertriglyceridemia which potentially hampers efficient leukemia therapy. Molecular background of ASP-induced hypertriglyceridemia and its regulators are not well known. We aimed to investigate constitutional genetic factors as biomarkers for hypertriglyceridemia following ASP therapy.
We analyzed clinical and laboratory data recorded in The Finnish Hematology Registry (FHR) from 52 adult ALL patients treated at the Helsinki University Hospital, Department of Hematology in 2014-2016. Study subjects were selected for further analyses if germline whole exome sequencing (WES) had been performed, patients had received ASP and data on basic chemistry and lipids before and after ASP dosing were available. Sixteen patients fulfilled these criteria.
The patients' germline DNA was extracted from a skin biopsy taken in conjunction with a bone marrow sampling. Roche MedExome kit was used to target the coding regions of the genome and sequencing was conducted using an Illumina HiSeq sequencer. The reads were processed and aligned to the GRCh37 human reference genome. SNVs and indels in the exome sequencing data were analyzed using an in-house developed analysis tool. Shared variants in patients with similar serum triglyceride level changes after ASP treatment were analyzed and variants in genes associated with lipid metabolism were selected as candidate target genes.
Three patient groups were identified based on to the maximum triglyceride changes pre- and post ASP infusion (both clinical and exome data available, n=7, 5, and 4; respectively). Mean changes in the Groups 1-3 were 1.7, 8.4, and 72,7 mmol/L, respectively. Differences in patients' BMI or corticosteroids use did not explain the distribution. Hence, a germline determinant was hypothesized and a candidate gene analysis (xx known genes affecting lipid and ASP metabolisms) performed from patients' germline WES.
Mean changes in the Groups 1-3 were 1.7, 8.4, and 72,7 mmol/L, respectively. Differences in patients' BMI or usage of corticosteroids did not explain the distribution. Hence, a germline determinant was hypothesized and candidate gene search performed on patients' germline WES.
Four of the candidate variants in ATF5, NKX1-1, THEM4, and LPCAT2 were enriched in patients with ASP-induced hyperTG. None of the variants suggested here have been previously reported to be associated with ASP-induced hypertriglyceridemia, but another SNP in ATF5 has been linked to adverse outcome in ASP-treated patients. ATF5, a transcription factor, regulates asparagine synthetase biosynthesis and is also involved in the cell cycle and apoptosis regulation, in the cellular stress response and the ceramide pathway. NKX1-1 is a transcription factor and an essential regulator of organ development, and it is also probably associated with energy homeostasis. THEM4 is an acyl-CoA thioesterase and is probably involved in mitochondrial fatty acid metabolism as well as in AKT1 signaling and apoptosis. LPCAT2 is a member of the lysophospholipid acyltransferase family involved in the synthesis of phospholipids, but also in the biosynthesis of platelet-activating factor (PAF) in inflammatory conditions.
Here, we present four candidate genes and variations in them possibly linking to ASP-induced hypertriglyceridemia in adult ALL patients. Prospective studies exploring the impact of these findings are called for.
Figure 1. Patient groups (3) identified according to the maximum triglyceride changes pre (green dot) - and post (red dot) ASP infusion.
Porkka: Pfizer: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding.
Asterisk with author names denotes non-ASH members.