MODULATION OF mRNA - Novationís Approach

RNA is a key intermediary molecule in gene expression and determines which proteins get made, how much is produced and for how long. It is thus an ideal target for therapeutic intervention and therefore drug discovery.

mRNA levels in normal cells are highly regulated and play a major role in controlling certain cellular functions. Different mechanisms have been proposed for the regulation of mRNA turnover. Regulation of mRNA stability is complex and can involve activation of nucleases, as well as complex signal transduction pathways. One mechanism impacting the level of mRNA present in cells and its ability to "pass on the code" is through modulation of the rate at which the mRNA once produced is degraded.

mRNA modulation is a natural cellular mechanism which the cell uses to control gene expression and the production of protein. Novation's researchers are directing their efforts towards identifying those areas in the sequence code of mRNA that are responsible for regulating its activity. These areas are known as Stability Control Elements (SCEs) and it is through these that the cell is able to modulate and control the stability (or half-life) of any particular mRNA.

These SCEs are the built-in "control points" through which the cell can either signal to the degradation machinery present in the cell, that a certain mRNA should be destroyed, or, cause it to be "reinforced" such that a protein is produced.

The cell is exquisitely able to differentiate between different mRNA and naturally exercises selectivity and specificity of effect. A number of interacting factors are responsible for this, including mRNA specific SCEs or differences in numbers and spacing of SCEs between individual mRNA. A fault in the operation of this control mechanism may result in a diseased state in which inappropriate stimulation of a protein results, or, an essential protein is not produced when it should be.

Most mRNA is only produced "when required" – such as intermediates for proteins that the cell requires for "housekeeping". However, certain mRNA is constantly being produced, so that it is immediately present when needed, but it is rendered inactive (i.e. unable to stimulate protein manufacture) through a rapid process of degradation. When the protein is required, then the cell quickly stabilizes the mRNA, extending its half-life and allowing it to accumulate, thus activating the "protein manufacturing code". Typical of such "constant" mRNA is that involved in the body's immune system. Here the mRNA is constantly being produced and de-graded, but is available for rapid stabilisation and activation if needed to fight cellular attack. This stabilisation continues for as long as the production of the particular protein is required. Once protein production is complete, the stimulus of the SCE ceases and degradation of the mRNA can then resume.

In a disease situation the SCE often remains reinforced preventing the destruction of the mRNA. The result is a continuation of the production of the protein, even though it is no longer required, resulting in an excess of the protein and giving rise to a disease state. For example, this might be continuous overproduction of inflammatory cytokines that eventually become toxic to body tissue (e.g. chronic inflammation), or, of growth factors, which stimulate over production of tissue formation and give rise to malignancies (cancer).

In cases of cancer, oncogene and growth factor over expression, regulated by mRNA, is associated with abnormal cell proliferation and malignant transformation. mRNA stability is normally tightly and coordinately regulated for transiently expressed genes such as c-myc and c-fos, and cytokines such as interleukin-1b (IL-1b) and tumor necrosis factor alpha (TNFa). However, in lung cancer for example, genes of the myc family and other oncogene mRNAs are found to be frequently over expressed as a result of inappropriate stabilisation of the mRNA causing unwanted protein production.

Thus the ability to modulate, in a specific manner, the machinery that controls mRNA and protein production is a very attractive target for disease treatment.

Novation has identified the sequence control elements (SCEs) in a number of disease related mRNA. These have been incorporated into the QUEST drug discovery system and can be used to identify small molecule compounds that are able to selectively and potently impact the SCE in the desired way.

Novation scientists identify the SCE in a target mRNA and extract and clone this into a reporter gene. These are then incorporated into a relevant disease cell and stable cell lines produced. The stable cell lines are then optimized for use in high-throughput screens and are used to screen libraries of small-molecule compounds. Those compounds that are able to impact the SCE in the desired way can be readily identified and are then further optimized into new drug treatments.

The QUEST technology has already been used to identify new active compounds that can either inhibit or stimulate specific mRNA modulation in certain types of cancer and in diabetes. Other disease targets are currently being progressed.