Gene expression meets screening
way to rapidly screen compounds for potential therapeutic activity
in diseases where current screening methods are limited.
The scientists are working on acute myeloid leukaemia, the most common form of leukaemia in adults, but the technique is widely applicable to other diseases, according to the researchers.
AML is characterised by a blockage in development of precursor cells into mature white blood cells (neutrophils and monocytes). These immature cells accumulate in the bone marrow, inhibiting the growth of healthy cells and causing anaemia, bleeding and impaired immune function.
The technique, reported in the March issue of Nature Genetics, used RNA profiling to compare AML cells treated with more than 1,700 drug candidates to the RNA profile of a normal, health white blood cell. They discovered 8 drug candidates that seemed to convert the AML cells into normal cells.
"Chemical genomics involves generating large collections of small molecules and using them to modulate cellular states [but] despite recent progress in the systematic synthesis of structurally diverse compounds, their use in screens of cellular circuitry is still an ad hoc process," comment the researchers.
Their approach, called gene expression-based high-throughput screening (GE-HTS), uses RNA as a gene expression signature that serves as a surrogate for cellular states.
The team used microarrays to identify a set of five genes that could serve as a differentiation signature for leukaemic cells, and then screened AML cells in microplates with their compound library. All eight 'hits' reproducibly triggered the differentiation signature, and six of them induced a genome-wide pattern of gene expression characteristic of healthy white blood cells.
The beauty of the approach is that the mechanism behind the gene expression signature does not have to be understood, they note.
The need for improved treatment for AML is clear - the five-year survival rate among children is just 50 per cent and just 18.7 per cent in adults.
A recently introduced drug called Glivec (imatinib), developed by Switzerland's Novartis, has been shown to prevent the transformation of the precursor cells in chronic myeloid leukaemia, which can sometimes progress to AML, as well as some patients with the latter disease. Combining Glivec with conventional cytotoxic chemotherapies in CML has improved five-year survival rates to around 80 per cent.
The Harvard researchers hope that their screening programme could identify drugs with a similar mechanism of action that could work in other forms of leukaemia, as well as providing new tools to tease out the mechanisms underlying diseases.