Genomics
dsDNA and rAAV Homologous Recombination Vectors
ITR |
LH arm |
Mut
WT |
loxP |
Marker |
loxP |
RH arm
ITR |
Conventional HR vectors: dsDNA Contemporary AAV HR vectors: ssDNA virus
LH : Left Homology arm RH : Right Homology arm Marker : Selection Marker e.g. Neo Mut : Point mutation being knocked-in ITR : AAV Inverted Terminal Repeat loxP : Cre-recombinase sites to remove selection markers after gene editing
1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02
Homologous Recombination Efficiency Measured as neo-resistance correction rate
fail to do so in the present generation unless some hard decisions are made. Another issue is that an entirely new industry and service needs to be devel- oped to provide early, routine and accurate diag- nostic tests to support the development and tailor- ing of any future novel therapies, which has its own harsh economic models to deal with if per- formed outside of the established pharma industry. Finally, regulatory and healthcare agencies will need to foster these endeavours and ultimately be convinced of why this isn’t going to cost them a lot more money. Wisdom would predict this will be true, given that it will enable us to move away from blanket or over-prescription of expensive new drugs, where we are again only at the tip of the ice- berg right now.
AAV Plasmid Data from Russell et al., W09848005 Figure 1
predictive disease modelling and ultimately the design of rational clinical trials, scientists will need to be able to alter the DNA-sequence of a human cellular genome in a manner that is now routine and facile in mice and other lower organisms.
Why are we moving towards ‘personalised’ medicine? Very few diseases are simple. They are either high- ly multi-factorial like cancer, and so require many different treatments tailored to the right patient; or they can be caused by a single agent, such as HIV or a bacterial infection, but it mutates over time; and thus requires doctors to keep rapid pace with a moving target. In the case of cancer it is both these things, which makes it such a challenge to manage. In the future, however, we will have the ability to rationally prescribe and adapt the right drug, drug combination, or drug dose, to each patient based on having a detailed understanding of their disease genetics, to far more effectively manage their disease.
This is, in essence, the concept of personalised medicine; a phenomenon that is already happen- ing, but has a long way to go to realise its full potential. The principle issue is that there are cur- rently nowhere near enough drugs in the person- alised medicine toolbox to tailor to the right patients. The reality is we have only scratched the surface of ‘drugging’ the cancer genome and will
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The stark facts are that for every drug devel- oped, approximately nine fail and the cost of these failures are ultimately passed on to the consumer. Combined with the approximate 10 years and $1 billion spent per drug to reach Phase III and then fail, this is clearly an unsustainable situation mov- ing forward into a more personalised, or segment- ed, therapy world. There will be many reasons why drugs fail, but one that in principle can be fixed is to better understand which patients are more or less likely to respond. With the advent of clinical diagnostics and accurate models of human disease, new drugs in development or even already approved treatments, can increasingly be targeted to the ‘right’ patient populations who possess unambiguous ‘biomarker’ signatures of response. A clear example of the impact of such predictive models and biomarkers on directing patient thera- py will be given in a later section, as will their ben- efits to accelerating earlier stages of drug discov- ery. First, a review of the state-of-the-art in genome editing, which will underpin both the gen- eration of genetically-defined human disease mod- els and the growing needs of performing precision functional genomics.
Human genome editing
The routine and accurate editing of human cellu- lar genomes to permit disease modelling, func- tional genomics and possibly even corrective gene therapy, will represent the next important break- through in science. Given the ‘hardware’ in this case is a live human cell, one will always be restricted to working with cells’ natural biology. Historically, altering the sequence of endogenous genes within differentiated human cell types has proven to be orders of magnitude less efficient compared to lower organisms. Only recently has it become technically feasible to perform the
Drug Discovery World Spring 2011
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