INNOVATION IN DNA REPAIR
INNOVATION IN DNA REPAIR
CLINUVEL’S FOCUS ON DNA REGENERATION
The backbone of human life is created by two structures forming our genetic material: pyrimidines and purines, which in turn consist of four nucleotides adenine (A), thymine (T), guanine (G), and cytosine (C). These form the DNA-helix which carries our present and future make-up, our genetic codes. Human physiology tries to keep DNA strands intact at all costs. As we are exposed to daily oxidative stress, skin cells work hard to preserve our genetic program.
At CLINUVEL, we have focussed for two decades on the interaction of light and human biology, whereby our scientific teams have worked on replicating the deleterious effects of solar radiation through standardised conditions in our laboratories. We have used broadband ultraviolet B (UVB), narrowband UVB, ultraviolet A 1 and 2 and High Energy Visible (HEV) light to irradiate human skin and observe the instantaneous reactions and damage to the epidermis and dermis. Both in healthy and diseased individuals, skin reactions can be predicted and mapped out. In most of CLINUVEL’s clinical trials, skin surfaces of various patient groups were exposed to light sources to provoke typical sun-related symptoms. In testing the lead drug afamelanotide, we collected this data and assessed its potency for systemic photoprotection.
Going a step further, CLINUVEL evaluated its drug afamelanotide in various photodermatoses and lightinduced disorders such as polymorphic light eruption (PLE), solar urticaria (SU), acne, and Hailey-Hailey Disease, and in genodermatoses erythropoietic protoporphyria (EPP), congenital erythropoietic porphyria (CEP) and xeroderma pigmentosum (XP), all diseases where radiation at certain wavelengths play a part in the triggering of severe symptoms.
In optics and physics precision is key, and in some disorders, one specifies action spectra and the inhibition spectra at particular wavelengths causing the start of symptoms in patients. Mapping out each monochromatic wavelength along the electromagnetic spectrum is part of the disciplines of photobiology, photodermatology and radiation biology, deriving scientific knowledge from optics and physics. This knowledge has become part of our in-house strength, expertise and starting point to transgress into the area of UV-provoked DNA damage.
As genetics and cellular biology took a flight the past decennia, the knowledge of the effects of ultraviolet radiation (UVR) on human cells (skin, eyes, and organs) has increased. Most are aware of the beneficial effects of 15-30 minutes of UVR per day to stimulate the synthesis of vitamin D in our skin. However, we are also made aware of how longer periods of exposure to UVR and HEV light may lead to sunburns, photodamage, actinic damage (elastosis) and an increased risk of skin cancers as skin damage becomes chronic and permanent.
The progression from healthy human volunteers to genetic disorders has been logical for CLINUVEL, whereby the most severe diseases have deserved treatment first, not least as these stand the greatest chance of regulatory approval in global pharmaceutical markets, such as Europe, the United States, Australia and Asia. That is not to say that other disorders would not benefit from afamelanotide or melanocortins, but the development route is best justified when regulatory support is given early on in a program.
HISTORY OF DNA RESEARCH
Damage to DNA provoked by UV radiation received first attention in 1893, when Robert Bowles published an article in the British Journal of Dermatology suggesting that sunlight may be responsible for skin cancers: “If the sun’s rays will produce sunburn, erythema, eczema solare, inflammation, and blistering, it is clearly capable of producing deep and intractable ulcerations of a low and chronic nature.” This finding was corroborated one year later by Paul Gerson Unna, who associated the severe degenerative changes on exposed areas of sailors’ skin with the development of skin cancer and rapid aging. In the last three decades, various renowned research institutions have focussed on the acute and chronic damage of UV and HEV radiation to human skin. Latitudinal predispositions, localisation, skin type, family history of skin damage and skin cancers were among the variables studied. As cellular biology attracted attention the cellular signalling, expressions of genes and proteins, became a focus. As the human genome project gathered momentum at the start of the millennium, the importance of MAP kinases, endothelin, WNT, cKIT, MITF and MC1R pathways in providing skin cells with the right input, directions and stimulus became widely known.
DNA REPAIR
The double-page figure to this article explains the DNA Damage Response (DDR). Starting on the left-hand side, one sees the DDR by skin cells which leads to a human defence reaction. The activation of MC1R leads to a cascade of reactions seen within the cell. Human biology is fascinating in that many reactions take place simultaneously at the speed of nanoseconds. The signalling of a skin cell – there are many different types – occurs from top to bottom, starting with a particular receptor.
The PKA-ATM-ATR axis, or the communication between these intracellular proteins, causes multiple reactions further down the cell. Following solar (UV-HEV) exposure, human reactions are needed to protect cellular structures: organelles and proteins, but specifically the nucleus which may also require reinforcement. In many ways, all the process and activity taking place above the nucleus aim to protect the genomic information, DNA, within the core of each skin cell.
UV radiation can lead to double or single strand DNA breaks, although the scientific experts tend to focus on single strand breaks. UV causes typical mutations to DNA, known as UVsignature mutations, connotated as C→T or CC→TT substitutions of nucleotides within a DNA strand. Thus, we can detect and recognise the kind of DNA damage caused by solar exposure. UV also causes some of the protein expressions to be downgraded, suppressed, and dysfunctional, making the cell work at a suboptimal level, in turn causing an inferior output by the skin cell. Together, the cellular dysfunction and substitutions of nucleotides are a cause of great concern since human biology is forced to restore the balance immediately by repairing the cellular structures. Sun exposure makes skin cells work overtime. In the doublepage figure, one sees the result of this UV cascade, the formation of Cyclobutane Pyrimidine Dimers (CPDs) and 6-4 Pyrimidine Pyrimidone Dimers (6-4PPs), or photoproducts within the nucleus caused by the sun/UVR/HEV light.
Our task after each sun exposure and sunburn is to eliminate these photoproducts by replacing a piece of DNA. Under normal circumstances, the human body is quite effective at doing so, although fair-skinned individuals (skin type I, II and III) are less efficient than darker skin types (IV, V, VI). In the first group the risk of permanent mutations is increased and in these individuals the incidence of skin cancers is much higher.
While we are interested in one pathway, the breakthrough in knowledge gained the last 15 years is that various pathways and genes within a cell communicate with each other; “horizontal discussions” occur between pathways. Therefore, the dysfunction along one pathway is sought to be compensated along another, all with the aim to restore function and UV damage.
On the right-hand side of the double-page figure one reads the properties of alpha-melanocyte stimulating hormone and its reinforced analogue – afamelanotide – in its role restoring UV damage. There are more than 30 cellular domains where the protein and DNA function are aided by alpha-melanocyte stimulating hormone, and here the 17 most important ones are listed. From CLINUVEL’s data and specific scientific work performed, one expects that afamelanotide will be a determinant in the DNA reparative processes within the cell, specifically needed for those individuals at higher risk of developing skin cancers due to genetic receptors, and their ability to respond to the UV signal.
AN EXCITING FUTURE IN PROSPECT
The coming year, CLINUVEL will be furthering this field of research in human subjects (XP patients and healthy volunteers) to confirm the efficiency of afamelanotide in these cellular and DNA reparative processes.
Fitzpatrick Types l-Vl
|
Skin Type |
l |
ll |
lll |
lV |
V-Vl |
|
Sunburn and Tan Tendency |
Always burns; Seldom tans |
Usually burns; Sometimes tans |
Sometimes burns: Usually tans |
Seldom burns; Always Tans |
Never burns; Always Tans |
|
Skin, Hair and Eye Color |
White skin, freckles; blond or red hair; blue or green eyes |
White skin; blond hair; blue or green eyes |
White skin; Usually dark hair; brown eyes |
Darker skin; usually dark hair; brown eyes |
Naturally brown to dark skin; brown or black hair; brown eyes |
Having taken more than a decade of clinical and scientific research, it is exciting to ‘close the loop’ in using afamelanotide from:
(i) assessing UV-induced skin damage in healthy volunteers, to
(ii) systemic photoprotection in diseases patients (photodermatoses), and finally, to
(iii) reducing the risk of cellular and DNA damage caused by sun/UVR/HEV light in higher risk populations (both healthy and diseased individuals), and therefore reducing the risk of skin cancer(s).
Skin cancer comes in many forms, but the three most frequently seen in the clinic are basal cell carcinoma, squamous cell carcinoma and melanoma (various types). Common to all three forms is that UV and sun exposure play a part in the development, whereby other genetic and epigenetic factors play a role. However, the ability to eliminate or reduce the UV-inducing factor in the genesis of skin cancer is a big step forward. Hormonal therapy with a melanocortin may well be the future answer, since the use of the hormone simulates the biological function of the peptide in our body, protecting us against the insult of solar radiation. Within seconds of sun exposure, alpha-melanocyte stimulating hormone is detected as being released by our skin cells as a protective measure.
A reinforced version of alpha-melanocyte stimulating hormone was developed and formulated as afamelanotide, and the vision is to use the drug as a DNA-protectant in many formulations. The requisite is and remains the safety of afamelanotide in patients and healthy volunteers, but each day that goes by is one extra day towards the 100,000 plus patient exposure days providing evidence of safe use.
Biomimicry is the phenomenon found in biology capturing and replicating nature’s ability to provide function and protection. In afamelanotide, CLINUVEL has developed a long used potent hormone to prevent sun and light damage in those who need this most, namely, those who are at risk and those who suffer from genetic disorders affecting their ability to go outdoors. Over the next 12 months, the CLINUVEL story will unfold and the significance of our progress in DNA repair in XP and healthy individuals to the general population at risk of UV-HEV damage will become apparent.