Glucocorticoids (GCs) are among the most important drugs for acute lymphoblastic leukaemia (ALL), yet despite their clinical importance, the exact mechanisms involved in GC cytotoxicity and the development of resistance remain uncertain. We examined the baseline profile of a panel of T-ALL cell lines to determine factors that contribute to GC resistance without prior drug selection. Transcriptional profiling indicated GC resistance in T-ALL is associated with a proliferative phenotype involving upregulation of glycolysis, oxidative phosphorylation, cholesterol biosynthesis and glutamate metabolism, increased growth rates and activation of PI3K/AKT/mTOR and MYC signalling pathways. Importantly, the presence of these transcriptional signatures in primary ALL specimens significantly predicted patient outcome. We conclude that in lymphocytes the activation of bioenergetic pathways required for proliferation may suppress the apoptotic potential and offset the metabolic crisis initiated by GC signalling. It is likely that the link between GC resistance and proliferation in T-ALL has not been fully appreciated to date because such effects would be masked in the context of current multiagent therapies. The data also provide the first evidence that altered expression of wild-type MLL may contribute to GC-resistant phenotypes. Our findings warrant the continued development of selective metabolic inhibitors for the treatment of ALL.

Cell lines are important models for drug resistance in acute lymphoblastic leukaemia (ALL), but are often criticised as being unrepresentative of primary disease. There are also doubts regarding the authenticity of many lines. We have characterised a panel of ALL cell lines for growth and drug resistance and compared data with that published for primary patient specimens. In contrast to the convention that cell lines are highly proliferative, those established in our laboratory grow at rates similar to estimates of leukaemic cells in vivo (doubling time 53 -442 h). Authenticity was confirmed by genetic fingerprinting, which also demonstrated the potential stability of long-term cultures. In vitro glucocorticoid resistance correlated well with that measured ex vivo, but all lines were significantly more sensitive to vincristine than primary specimens. Sensitivity to methotrexate was inversely correlated to that of glucocorticoids and L-asparaginase, indicating possible reciprocity in resistance mechanisms. A cell line identified as highly methotrexate resistant (IC 50 48000-fold higher than other lines) was derived from a patient receiving escalating doses of the drug, indicating in vivo selection of resistance as a cause of relapse. Many of these lines are suitable as models to study naturally occurring resistance phenotypes in paediatric ALL.

The neuregulins (NRGs) are a family of four structurally related growth factors that are expressed in the developing and adult brain. NRG-1 is essential for normal heart formation and has been implicated in the development and maintenance of both neurons and glia. NRG-2 was identified on the basis of its homology to NRG-1 and, like NRG-1, is expressed predominantly by neurons in the central nervous system. We have generated mice with the active domain of NRG-2 deleted in an effort to characterize the biological function of NRG-2 in vivo. In contrast to the NRG-1 knockout animals, NRG-2 knockouts have no apparent heart defects and survive embryogenesis. Mutant mice display early growth retardation and reduced reproductive capacity. No obvious histological differences were observed in the major sites of NRG-2 expression. Our results indicate that in vivo NRG-2 activity differs substantially from that of NRG-1 and that it is not essential for normal development in utero.The neuregulin (NRG) family of growth factors comprises numerous glycoproteins that arise via alternative splicing from four distinct genes (NRG-1, NRG-2, NRG-3, and NRG-4). These proteins have a similar mosaic-like structure with a number of recognizable protein domains. The prototypic member of this family, NRG-1, was independently identified as a Schwann cell mitogen (12,19), an activator of erbB2 (15,29), and an inducer of acetylcholine receptor synthesis at the neuromuscular junction (7). The NRG-1 gene gives rise to as many as 15 different splice forms, generated by alternative splicing and differential promoter usage. These variants are also known as heregulin, acetylcholine receptor-inducing activity (ARIA), sensory and motor neuron-derived differentiation factor, Neu differentiation factor, and glial growth factor. More recently, a number of genes encoding proteins related to NRG-1 have been identified. These genes, named NRG-2 (also identified as Don-1 and NTAK) (2-4, 14), NRG-3 (32), and NRG-4 (13), were discovered by using sequences from NRG-1 to either search nucleotide databases or perform low-stringency hybridization and/or PCR.Of the four NRG genes, NRG-1 and NRG-2 are the most closely related, although all members possess a 50-amino-acid region with homology to epidermal growth factor. This domain alone is sufficient for receptor binding and activation (2-4, 15, 32). The epidermal growth factor-like domains of NRGs 1 to 4 are 40 to 48% similar to each other in pairwise comparisons. Despite this low homology, all the NRG epidermal growth factor-like domains bind to either ErbB4 or ErbB3, albeit with different affinities (16). The epidermal growth factor-like domains of NRG-1 and NRG-2 each have two variants, designated ␣ and ␤, arising from alternative exon usage, which also exhibit differential receptor binding affinities (16).