The science behind Neuren's products

Trofinetide (previously designated by Neuren as NNZ-2566) and NNZ-2591 are patented synthetic analogs of molecules which are derived from IGF-1 and occur naturally in the brain. IGF-1 is a growth factor stimulated by growth hormone. In the central nervous system, IGF-1 is produced by both of the major types of brain cells – neurons and glia. IGF-1 in the brain is critical both for normal development and for responding to injury and disease.

In the brain, IGF-1 gets broken down into two separate molecules. One, often referred to as glypromate or GPE, comprises the last three peptides of IGF-1. GPE affects glial cells (astrocytes and microglia) while IGF-1 itself mostly affects neurons. GPE is further broken down to form cyclic glycine proline (cGP).
Trofinetide and NNZ-2591 are Neuren’s chemically modified forms of GPE and cGP respectively that can mimic the natural function in the brain. The small modifications result in the drugs having an increased half-life in the circulation, better stability for easier storage and shipping, improved transport across the blood/brain barrier and suitability for use as oral medications, whereas GPE, cGP and and IGF-1 can only be administered by injection. 
In the brain, the role of IGF-1 is to facilitate the brain’s development and maintain the biological balance required for normal functioning. These processes have evolved over millions of years and are still being extensively researched by scientists.
During development, the brain and the cells that make it up change rapidly and in complex ways. IGF-1 and GPE play a significant role in regulating these changes. In the mature brain, IGF-1 and GPE both play an important role in responding to disease, stress and injury. Whereas most drugs typically exert a specific effect on a specific target, trofinetide and NNZ-2591 exert diverse effects which can help to control or normalise abnormal biological processes in the brain. 
Although different conditions – brain injury, neurodevelopmental disorders and neurodegenerative diseases – can result in very different symptoms and outcomes, many share common, underlying pathological features.
These include inflammation, over-activation of microglia, dysfunction of synapses (the connections between neurons through which information is transmitted) and reduced levels of IGF-1. In other words, diseases and conditions caused by different mechanisms often result in the same pathology at the cellular and molecular level.
1. Inflammation
Inflammation in the brain – often referred to as neuroinflammation – is perhaps the most common pathological feature of central nervous system disorders. Much of it is the result of excess production of molecules called inflammatory cytokines. These are prominent in brain injuries, neurodevelopmental disorders such as Rett and Fragile X syndromes as well as autism, neurodegenerative diseases like Alzheimer’s and Parkinson’s and even so-called “normal” aging.

Neuroinflammation places significant stress on brain cells. Stress can disrupt normal cellular processes such as information signalling, increase energy requirements beyond the ability of the cells to meet their metabolic needs, disturb electrical functions which can lead to seizures and other abnormalities and even result in premature cell death. 
In animal models ranging from brain injury and stroke to Fragile X syndrome to age-associated cognitive impairment, trofinetide has shown an ability to significantly reduce the levels of inflammatory cytokines. This has resulted in improvement in a wide range of symptoms including post-traumatic seizures, anxiety, memory impairment and hyperactivity.

2. Over-activation of microglia
Microglia are the resident immune cells in the brain. Once thought to serve primarily a sentinel function – responding to infection and damaged cells by surrounding and removing them – it is now known that they play a central role in maintaining synapses during development and in mature brains by pruning dendrites, the many small extensions of neurons that form synapses. Microglia are also a key source of IGF-1. Due to this wide-ranging maintenance function, they have appropriately been referred to as the “constant gardeners” of the brain.
Microglia are not only activated in response to infection and injury. They also are activated by inflammation that accompanies acute brain injury and chronic conditions. In this activated state, they not only lose their ability to effectively perform their normal function in synaptic maintenance but also produce more inflammatory cytokines which can further compound the damage to neurons and other brain cells.
Trofinetide has been shown to normalise microglial biology and function in both acute and chronic conditions. Restoring normal microglial activity has resulted in improved synaptic structure as well as correction of imbalance in synaptic signalling and cell-to-cell communication. This has led to reversal of symptoms such as impaired memory, anxiety, hyperactivity and compromised social behaviour.

3. Dysfunction of synapses
Neurons communicate with each other by chemical and electrical signals transmitted via synapses. Normal synaptic function is essential for healthy brain function and underlies memory, cognition, behaviour and other brain activities. Normal synaptic function requires that the dendrites (part of the neurons) which form synapses are appropriately formed as well as that excitatory and inhibitory signals are kept in balance.
When dendritic structure and synaptic signalling are abnormal, virtually all brain activities can be negatively impacted. Synaptic dysfunction has been identified as a core feature of many conditions including acute brain injury, neurodevelopmental disorders and neurodegenerative diseases.
For example, in Rett syndrome dendrites are sparse and immature while in Fragile X syndrome, dendritic branching is excessive although the dendrites are also immature. Trofinetide increases the length and branching of dendrites in a model of Rett syndrome while increasing pruning of excess branching in Fragile X syndrome. In the Fragile X animal model, aberrant synaptic signalling was normalised within 15 minutes of the first dose.


4. Reduced levels of IGF-1

As previously mentioned, IGF-1 levels in the brain have been reported to be depressed in a number of conditions, particularly in Rett and Fragile X syndromes and brain injury. In these conditions, the critical role of IGF-1 and GPE in maintaining and repairing brain cells and synapses is impaired.
In the Fragile X model, in which the IGF-1 level is depressed, trofinetide increased the amount of IGF-1 to normal levels. This was accompanied by normalised synaptic signalling and complete reversal of cognitive and behavioural abnormalities.
In a model of Rett syndrome, increasing IGF-1 levels has been reported to correct deficits in dendritic spines and, in isolated cells from human Rett syndrome patients, both IGF-1 and GPE are able to partially reverse the deficits in cellular function.
Summarising, trofinetide helps to correct four of the hallmark pathological features of many central nervous system disorders: inflammation, over-activation of microglia, dysfunction of synapses and reduced levels of IGF-1. By simultaneously targeting multiple processes, trofinetide works to restore the natural balance of brain function.