Humans have a healthy appetite for miracles, be they wonders of fiction or faith, which may explain why any science that promises a new, more potent cure for disease is grasped with fervour.
Take the ‘miracle’ of genes and the discovery that human characteristics are controlled by these tiny molecules. From this, science has been attempting to build a new kind of medicine based on the role DNA plays. In 2000, as part of this and at a cost of $3 billion, every human gene was catalogued in a searchable database.
Francis Collins, then head of the International Human Genome Sequencing Consortium, predicted that by 2010 genomics would change the face of medicine.
That milestone, however, passed and the anticipated new way of treating disease mostly failed to materialise. Harold Varmus, the 1989 Nobel Laureate in Medicine, observed that genomics had proved to be more a way to do science than medicine.
Molecular biologists now concede that life at the molecular level is far more complex than anticipated. However, the beauty of science is that the search for answers never ceases. Professor Stephen Jane who heads the Central Clinical School at Monash University in Melbourne, Australia, is part of the global effort to find the missing link between genomics’ theoretical potential and a step-change in molecular therapies.
A medical doctor, and a late recruit to molecular research, Professor Jane says Harold Varmus makes an accurate but perhaps unfair point.
“For me, molecules like genes form pieces of a jigsaw puzzle and you just can’t make progress until you understand how they fit together,” he says. “So I think it is actually too early for genome-wide molecular approaches to meet their full therapeutic potential.”
For Professor Jane, those hopes for genomics to deliver a step-change in medicine will happen; just not as quickly as initially anticipated.
Over the past decade he has discovered a whole network of cellular cues – genes, biochemical signalling pathways, and growth regulators – that are essential to the health of our skin.
Fitted together, this ‘jigsaw puzzle’ has revealed new paths to drug development for a cluster of diseases. Among these are embryonic neural tube defects (such as spina bifida), wound healing, and a common form of skin cancer. With drug testing already under way in mice, sunscreen lotion that prevent this cancer is just one of the therapies now under development.
Fruit fly help
In his work, Professor Jane has drawn on a remarkable piece of evolution, manifest in one of medical science’s most unlikely of allies, the fruit fly.
Well before science could reliably clone and sequence genes, geneticists in Heidelberg, Germany, randomly mutated the fruit fly (Drosophila) genome before mapping the location of each chromosomal lesion. They then linked this altered DNA (the genotype) to specific abnormalities (the phenotype). This work, begun in the 1970s, earned three collaborating scientists, Edward Lewis, Christiane Nüsslein-Volhard and Eric Wieschaus, the 1995 Nobel Prize for Medicine.
Their work with the fruit fly identified genes that control an organism’s development from a single cell, including the actual body plan and features such as the number and type of limbs that are formed. So fundamental are these genes, researchers could manipulate and mutate them to cause an extra set of wings to form or to change antennae into legs.
It was assumed that these genes are the grist of evolution – that they vary within a population and undergo natural selection to produce new types of bodies and eventually species.
Then, to the surprise of many scientists, the same genes discovered in fruit fly were found in organisms with very different kinds of bodies – in mice and then in humans. So similar were these genes that they were interchangeable between species. And mutations in these genes often caused similar abnormalities, such as eyes failing to form in all three species.
It appeared that natural selection protected the body-plan genes, ensuring they survived unchanged through 750 million years of evolution.
It was a controversial premise, but led to a major re-appraisal of the relationship between genes and an organism’s characteristics. Gone was the idea that genes blueprint any one species. Instead, genes came to be viewed more like the music instruments that make up an orchestra. What matters is how those instruments are played relative to each other. And genes too need to be ‘expressed’ to have an impact. So science now argues that the same genes can be made to play the fly, mouse, or human symphony depending on how they are expressed.
Among the genes identified in this way is a fruit fly gene called grainy head, named after the deformed appearance of the fly’s head upon mutating the native gene. It had attracted little attention until Professor Jane discovered counterparts in mice and humans and he linked them to a cluster of diseases.
“This was about the time of the genomic revolution,” he says. “It took my colleague, Dr Tomasz Wilanowski, just 30 minutes querying the gene database to discover that there are three copies of grainy head in mammals, now called Grainy head-like (Grhl) 1, 2 and 3. Together they perform the same function as the Drosophila gene but the multiple copies allow for additional functional complexities.”
It is something like an orchestra having three violins rather than one.
Studies in mice and humans subsequently revealed that Grhl3 is a master regulator of skin, promoting wound healing and protecting us from dehydration, infection and skin cancer. It also plays a role in preventing neural tube defects by helping to guide the folding of the neural plate in embryos.
The skin we live in
Professor Jane describes Grhl3 as so fascinating that it has attracted the bulk of his research efforts – and it is the genomic ‘door opener’ to future advances such as the potential anti-skin cancer sunscreen lotion.
When its sequence was analysed, Grhl3 was found to encode a protein that binds to DNA. Once bound, it controls the expression of many other genes and in the process, it orchestrates a network of interrelated biochemical activity that is specific to skin.
And without a functioning Grhl3 gene, Professor Jane discovered that the entire biochemical network within the skin is disrupted. In adults, this leaves skin vulnerable to a type of skin cancer called squamous cell carcinoma (SCC). The finding that Grhl3 serves to prevent cancer is a hugely significant discovery, but one that medicine struggles to capitalise on.
“Drug development would involve screening millions of small molecules for those capable of increasing Grhl3 levels in skin,” he says. “But Grhl3 is a DNA binding factor and drug companies have found, through trial and error, that this class of molecules is notoriously difficult to screen.”
And thus the classic example of a gene discovery with enormous therapeutic potential failing to live up to expectations … until Professor Jane decided to see if the actual complexity of ‘jigsaw genomics’ could be turned to advantage.
In biology, ‘complexity’ occurs when molecules participating in any one network – such as the Grhl3network in skin – regroup in other cellular networks. In this way they play a variety of roles in different organs, stages of development (from embryo to adult) or even in the manifestation of different diseases.
As such, information about a molecule gleaned in one context and species can provide insights into seemingly unrelated research. That said, it is exceptionally difficult to crack the identity of the molecules that make up any one network.
This is the problem Professor Jane solved by once again drawing on the gene conservation that occurs within fruit flies and mammals.
From a handful of Drosophila genes known to come under the control of the grainy head gene, he was able to deduce the DNA sequence that a gene must contain to similarly come under the control of Grhl3 in mammals. He then used that sequence to query the gene database.
Professor Jane found that falling under Grhl3’s control are genes identified by science as among the most common cancer-promoting molecules if they mutate. (The reasons for cellular mutation are varied and complex and still being researched). For skin and SCC, the critical factor is whether or notGrhl3 is functioning normally, or has mutated and lost control of its molecular network.
So while the Grhl3 gene is beyond having a direct therapeutic role, the genes it controls are; and because of existing cancer research, drug companies are already targeting them for drug development.
“For skin cancer, that meant drugs already in clinical trials for other cancers may also be effective in treating SCC,” Professor Jane says.
It is an unexpected finding, but shows that the gap between the great hope for genomics and new therapies might yet be closed through such lateral approaches.
“It also means that several of the usual hurdles in getting therapies to trial have already been cleared (in other research) so SCC patients could be reaping the benefits of this research in under five years.
“Further, we now have something long needed by drug development companies – the genetic signature (the absence of the Grhl3 expression) needed to identify those patients most likely to benefit from this kind of treatment.”
The finding is especially relevant for Australia that yearly posts the world’s highest incidence of skin cancer. This includes nearly half-a-million new cases of SCC a year, with surgery currently the only treatment option.
But beyond the specifics of any one disease – and there is ongoing work that exploits Grhl3’s role in other disorders – there are broader lessons.
Put simply, it highlights the therapeutic value of understanding the initial gene discovery within its broader evolutionary, genetic and biochemical context.
“I think maybe people’s expectations about individual gene discoveries is that the information would be immediately applicable in medicine,” Professor Jane says. “It is much more complex than that. Genomics helped point us in the right direction but an enormous amount of work is needed to really understand the molecular interactions that underlie different diseases.”
Written by Dr Gio Braidotti