Does Benzene Exposure Influence Chromosomal Translocation Events Involved in Childhood Leukaemia?

Leukaemia accounts for nearly a third of all childhood cancers with survival rates reaching close to 90% (CwC, 2019). Many leukaemias are thought to originate from chromosomal rearrangements in utero, as various abnormalities have been retrospectively detected at birth in leukaemia cases. Chromosomal translocations occur when a chromosome breaks and reattaches to a different chromosome leading to fusion proteins and misregulation of processes. Causes of translocations are unknown. However chemotherapy drugs, such as the topoisomerase II poison, etoposide, can induce chromosome breaks and are associated with therapy related leukaemias, with translocations similar to childhood leukaemias (Cowell et al, 2012). With leukaemia incidence increasing and long-term treatment effects contributing to secondary cancers, fertility and cardiac issues, understanding the causes and prevention of translocations is important. Epidemiological studies have identified various environmental factors associated with increased risk of childhood leukaemia i.e. parental smoking, maternal nutrition, caffeine intake, air pollution, paints, solvents and pesticides (Timms et al, 2016, Filippini et al, 2019). It is plausible these exposures in utero and in early childhood could trigger the initiating translocations of childhood leukaemia.

Benzene, one of the major carcinogens of cigarette smoke has long been linked to occupational acute myeloid leukaemia (AML) in adults (Snyder, 2012). A derivative of petroleum, benzene is also found in gasoline, air pollution and solvents used in inks and paints, which have all been associated with an increased risk of childhood leukaemia. Benzene and its metabolites are able to cross the placenta during pregnancy, and as infants have an underdeveloped excretion pathway and smaller body weight than adults, exposure to benzene may be more potent. Epidemiological studies have shown an association between childhood leukaemia and markers of benzene exposure (Carlos-Wallace et al, 2014). We aim to investigate if benzene, a potentially modifiable environmental factor associated with an increased risk of childhood leukaemia, may trigger the induction of chromosomal translocations associated with childhood leukaemia, utilising the topoisomerase II poison, etoposide, to induce susceptibility to translocations.

To determine the optimum etoposide concentrations to increase susceptibility to translocations, the leukaemic cell line NALM6 was exposed to a gradient of etoposide concentrations over varying times and allowed to recover. Cell viability and translocation events were assessed. Reverse transcription PCR and qPCR assays developed to detect the most common childhood leukaemia associated and etoposide related translocations were used. This will be repeated to determine the optimum exposure levels for benzene. Cells will then be exposed to benzene with and without the presence of etoposide, to identify if benzene alone or with etoposide treatment may increase the common translocation events associated with childhood leukaemia. COMET assays following exposure and then recovery will also allow DNA damage to be assessed.

Results show that cell viability is relatively unaffected at etoposide concentrations up to 100nM but is greatly reduced at higher etoposide concentrations found during chemotherapy treatment (10µM). Preliminary indications show that common childhood leukaemia translocations can be found at etoposide concentrations as low as 10nM over a 48 hour exposure period. Short bursts of high etoposide concentrations were also seen to induce translocations, i.e. 1µM over a 1 hour exposure. Further results on benzene exposures are to follow and will be presented.

Children with Cancer UK, (28/5/19). Cowell et al, (2012) PNAS 109: 8989-8994. Timms et al, (2016) Epigenomics 8: 519-536. Filippini et al, 2019 Environmental Health Perspectives 127: 046002-1-17. Snyder, (2012) Int. J. Environ. Res. Public Health 9: 2875-2893. Carlos-Wallace et al, (2014) Am J Epidemiol. 183:1–14.