Modulating Wnt Signaling in Autism and Cancer

Source: LDL receptor-related proteins 5 and 6 in Wnt/β-catenin signaling: Arrows point the way

In earlier posts I have covered various signaling pathways such as Wnt, mTOR and the unusually sounding Hedgehog.

You can go into huge detail if you want to understand these pathways, or just take a more superficial view. In most cases, things only start to go wrong if you are hypo/hyper (too little/too much) in these pathways.

We saw with mTOR that most people with autism are likely to have too much activity and so might benefit from mTOR inhibition, but a minority will have the opposite status and stand to benefit from more mTOR activity.

When it comes to Wnt signaling the research suggests the same situation. Wnt signaling is likely to be aberrant, but both extremes exist.

Wnt signaling networks in autism spectrum disorder and intellectual disability

Given the large volume of genetic data, analyzing each gene on its own is not a feasible approach and will take years to complete, let alone attempt to use the information to develop novel therapeutics. To make sense of independent genomic data, one approach is to determine whether multiple risk genes function in common signaling pathways that identify signaling “hubs” where risk genes converge. This approach has led to multiple pathways being implicated, such as synaptic signaling, chromatin remodeling, alternative splicing, and protein translation, among many others. In this review, we analyze recent and historical evidence indicating that multiple risk genes, including genes denoted as high-confidence and likely causal, are part of the Wingless (Wnt signaling) pathway. In the brain, Wnt signaling is an evolutionarily conserved pathway that plays an instrumental role in developing neural circuits and adult brain function.

While the human genetic data is an important supporting factor, it is not the only one. There are a number of mouse genetic knockout (KO) models targeting Wnt signaling molecules, describing molecular, cellular, electrophysiological, and behavioral deficits that are consistent with ASD and ID. Furthermore, the genes involved in Wnt signaling are of significant clinical interest because there are a variety of approved drugs that either inhibit or stimulate this pathway.

There are many drugs developed and tested as modulators of Wnt signaling in the cancer field that could potentially be repurposed for developmental cognitive disorders. In cases where a reduction in Wnt signaling is thought to underlie the pathology of the disorder, usage of compounds that elevated canonical Wnt signaling could be applied. An example of this is GSK-3β inhibitors that have failed in cancer trials but may be effective for ASDs and ID (e.g., Tideglusig, ClinicalTrials.gov identifier: {"type":"clinical-trial","attrs":{"text":"NCT02586935","term_id":"NCT02586935"}}NCT02586935). In cases where elevated Wnt signaling is thought to contribute to disease pathology, there are many potential options to inhibit canonical Wnt signaling using chemicals (Fig. 1) that inhibit the interaction between β-catenin and its targets (e.g., inhibiting β-catenin interaction with the TCF factors), disheveled inhibitors (through targeting of the PDZ domain which generally inhibit the Frizzled–PDZ interaction), and tankyrase inhibitors (e.g., XAV939, which induces the stabilization of axin by inhibiting the poly (ADP)-ribosylating enzymes tankyrase 1 and tankyrase 2)

As autism candidates emerge, cancer pathway rises to top

In recent years, strong autism ties have cropped up for one group of genes in particular: those that make up a well-known signaling pathway called WNT, which also has strong links to cancer. This pathway is especially compelling because some people with autism carry mutations in various members of it, including one of its central players: beta-catenin¹. What’s more, studies from the past year indicate that several of the strongest autism candidate genes, including CHD8 and PTEN, interact with this pathway.

“There might be a particular subgroup of genes associated with autism that could all be feeding into or be regulating this pathway,” says Albert Basson, reader in developmental and stem cell biology at King’s College London, who studies CHD8 and WNT. “That clearly has emerged as a relatively major theme over the last few years.”

The connection between cancer and some autism is over-activated pro-growth signaling pathways. Many signaling pathways have growth at one extreme and cell death at the other. In cancer you actually want cell death to suppress tumor growth; in much autism there is also too much growth.  

Many cancers are associated with elevated signaling of mTOR, Wnt and indeed Hedgehog.  These are targets for cancer drug therapy and so there is already a great deal known.

A complication is that in a developmental neurological condition, like autism, it also matters when these signaling pathways were/are disturbed. For example Wnt signaling is known to play a role in dendritic spines and synaptic pruning, some of this is an ongoing process but other parts are competed at an early age, so it would matter when you intervene to modulate these pathways.

Historically cancer therapies involve potent drugs, often with potent side effects, however in recent years there has been growing awareness that some safe existing drugs can have equally potent anti-cancer effects. Many of these drugs are anti-parasite drugs, but even the very widely used diabetes drug Metformin has been shown to have significant anti-cancer effects, not to forget Simvastatin.

Many autism pathways/genes play a role in cancer (RAS, PTEN) and the upstream targets considered in cancer research are also autism targets.  For example many human cancers are RAS dependent and in theory could be treated by a RAS inhibitor, but after decades of looking nobody has found one. So instead scientists go upstream to find another target that will indirectly reduce RAS. This led to the development of PAK1 inhibitors that will reduce RAS.

RAS plays a role in some types of intellectual disability and indeed autism. The collective term is RASopathy.  Logically, drugs that modulate RAS to treat cancer might be helpful in modulating RAS for some autism.

Most types of cancers are complex and so there are multiple potential targets to attack them, but also the same target can have multiple possible approaches. RAS dependent cancers can be targeted via Wnt and even Hedgehog signaling.

This may sound all very complicated but does it have any relevance to autism?

It apparently does because almost all these pathways are known to be disturbed hypo/hyper in autism.  This means that clever insights developed for cancer can be repurposed for autism.

Anti-parasite drugs and Cancer

It is indeed remarkable how many anti-parasite drugs have an anticancer effect and indeed there is a much maligned theory to justify this.

Clinical Evaluation of a New Form of Cancer Therapy Based on the Principles of Atavistic Metamorphosis

Quite possibly it is just a coincidence.

There are many ways to kill parasites, one of which involves starving them of ATP. ATP is the fuel that is produced in your mitochondria.

Cancer cells and many parasites use a very inefficient way to produce ATP that does not require oxygen. In normal human cells the process followed is known as OXPHOS, by which glucose and oxygen from the blood is converted into ATP (energy) is very efficient. Only when you run low on oxygen, like a marathon runner at the end of the race, can you run into trouble because there is not enough oxygen for OXPHOS.  What happens next is anaerobic respiration, when a different process takes over to make ATP. It is much less efficient and causes lactic acidosis which makes marathon runners' muscles hurt.

A cheap anti-parasite drug Pyrvinium targets anaerobic respiration and starves the parasite of ATP and thus kills it. Another common children’s anti-parasite drug albendazole also works by starving the parasite of ATP.

Other anti-parasite drugs work in different ways.

We already know from the autism trials of Suramin, another anti-parasite drug,  that it works via P2X and P2Y purinergic channels.

Ivermectin  binds to glutamate-gated chloride channels (GluCls) in the membranes of invertebrate nerve and muscle cells, causing increased permeability to chloride ions, resulting in cellular hyper-polarization, followed by paralysis and death.  Fortunately in mammals ivermectin does not cross the BBB.

Ivermectin is also a PAK1 inhibitor and a positive allosteric modulator of P2X7.

Both PAK1 and P2X7 are relevant to many cancers and so not surprisingly research shows that Ivermectin has an anti-cancer effect.

Ivermectin appears to have a positive effect in some autism, but strangely it does not cross the BBB.

Mebendazole is another extremely cheap children’s anti-parasite drug which has remarkable potential anti-cancer properties. It inhibits hedgehog signaling and, via the inhibition of TNIK, it is a Wnt inhibitor.

Unfortunately in the US the private sector has also noticed the anticancer effects of Mebendazole and albendazole and they have recently become astronomically expensive. Mebendazole (MBZ), which costs almost nothing in many countries, now costs hundreds of dollar per dose in the US under the name Emverm. Outside of the US, Mebendazole is OTC in many developed countries. In poor countries it is donated free by big pharma.

In the cancer research they consider taking advantage of the fact that cimetidine (a cheap H2 antihistamine) interacts with Mebendazole to increase its bioavailability. Cimetidine is by chance another generic drug also being considered to be repurposed for cancer.

While some anti-parasite drugs like Suramin have side effects or cannot be taken regularly like Ivermectin, others are seen as safe for continued use even at high doses (e.g. Mebendazole and albendazole).  

Anti-parasite drugs and Autism

Just as many anti-parasite drugs seem to have a positive effect on some cancers it looks likely that the same may be true for autism.  This does not mean that parasites cause either cancer or autism.

We know from Professor Naviaux that some people respond to Suramin.

Two people who comment on this blog have found their child responds to PAK1 inhibitors, one of which is the drug Ivermectin.

There are groups of people on the internet who think parasites cause autism and you will find some of them if you google “autism mebendazole”, but there are some very valid reasons why some people’s autism may respond to mebendazole, but nothing to do with little worms.

Potency of Anticancer drugs

Failed anticancer drugs are already considered as possible drugs to treat neurological conditions.

The same pathways do seem to be involved in some cancer and some neurological conditions, but the severity by which that pathway is affected may be very different, so a new drug may lack potency to treat a type of cancer but be potent enough to benefit others.

In the case of the anti-parasite drugs Ivermectin and indeed mebendazole the dosage being used in current cancer studies are very much higher than normally used.

Very little mebendazole makes its way out of your intestines and so researchers counter this by using a dose 15 times higher and even taking advantage of the interaction with the H2 antagonist cimetidine to boost bioavailability.

The standard human dose of Ivermectin is 3mg, but in the cancer trials (IVINCA trial - IVermectin IN CAncer) in Switzerland and Spain the trial dose is 12, 30 and 60 mg.

So when it comes to autism and the possible repurposing of these drugs, the cancer studies will give valuable safety information, but the likely dose required to fine-tune these signaling pathways will likely be a tiny fraction of the cancer dose.

The newly developed cancer drugs that fail in clinical trials, may have potential in autism but it is unlikely that anyone will develop them, test them and bring them to the market.

The clever thing for autism seems to be to keep an eye on the existing generic drugs considered to benefit the overlapping cancer pathways.

Conclusion

Aberrant Wnt signaling has been identified by researchers as playing a key role in autism; the Simons Foundation is among those now funding further research.

In practical terms you can be either hypo or hyper, but hyper seems more likely. It may be a case of shutting the stable door after the horse has bolted, because the ideal time to modulate Wnt signaling is probably as a baby, or before. Nonetheless some older people may indeed benefit from modulating Wnt; the Simons Foundation must also believe so.

In the case of people with hyperactive Wnt signaling, there is a case to make for the potential use of the cheap anti-parasite drug Mebendazole.

The drug Mebendazole (MBZ) can found in three states/polymorphs called Polymorph A, B or C. This is relevant because they do not cross the blood brain barrier to the same extent.

Brain Penetration and Efficacy of Different Mebendazole Polymorphs in a Mouse Brain Tumor Model  

To treat brain tumors, or indeed potentially some autism, you need MBZ-B or MBZ-C, it looks like MBZ-A does not cross the blood brain barrier.

Fortunately, MBZ-C is  the polymorph found most commonly in generic mebendazole tablets.  

Ivermectin is known not to cross the blood brain barrier but yet has been shown to show anti-tumor activity in brain cancer. The anti-cancer effect is thought to be as a PAK1 inhibitor, but this effect must be occurring outside the brain. Some people do use Ivermectin for autism.

The people using Ivermectin for autism are told they cannot use it continuously. Perhaps as the high dose cancer trials evolve the safety advice may change.