The PI3K / AKT / mTOR Pathway Part 1

okay so welcome to this video in this video what we’re going to talk about is the pi3 kinase Akt mTOR pathway and cancer okay so we want to look at the involvement of this pathway in cancer cells okay right so what we’re going to do is we’re going to start off by talking about the basic carcinogenic process okay so what happens in cancer development okay then what we’re going to do is look at the pi3 kinase Akt mTOR pathway and have a look at how important this pathway is in cellular growth and cellular proliferation and we’ll understand then why it’s one of the key pathways that ends up having its components mutated in cancer okay so there are many components of this pathway there’s a tumor suppressor genes and many that are proto oncogenes and those can end up with mutations in in cancer okay so we’ll discuss which components of the pathway are the most commonly found we taste it okay then we’ll discuss is targeting this pathway in activating this pathway for cancer therapy okay now it’s fair to say that with one exception which is the a drug used to treat chronic lymphocytic leukemia okay called idle al-ahzab with that one exception the initial testing of drugs that block this pathway for the treatment of cancer has been quite sobering okay it’s had only very modest success and we’re going to discuss potential reasons as to why there’s and we think the key reason as to why targeting this pathway hasn’t been that effect in preventing the progression of cancer is that we aren’t able to give these drugs in high enough doses again the reason is that this pathway is actually incredibly important in non cancerous cells as well so blocking it can have loads of odd target side effects so remember drug side effects can be split up into on target side effects and off target side effects on target side effects are the side effects you get because even your because the drug actually binds to the target that we intended it to bind to and that but that causes those or side effects because of how important that target is in the body okay off target effects refers to the fact the drug might by two loads of things that we never even planned for it to bind to and that’s why it might cause those or side effects as well but we think in the case of these drugs their target the pi3 kinase Akt am told that when we forget the off target side effects we think the on target side effects are so large that you can’t give these drugs in high enough doses to actually have a decent stab at the cancer basically okay and we’ll discuss potential ways that we might melt it around that in the future okay alright so let’s start off with the basic cancer development pathway okay so we want to discuss the process of carcinogenesis how does cancer emerge okay so we’re going to discuss the leading theory of what happens in the development of cancer which is the cancer occurs as a micro evolutionary process okay whereby cells gradually accumulate mutations and these mutations gradually build up a more and more aggressive phenotype until we finally get to the level where you have cells that were cancerous okay right so in this theory which is the leading theory of how cancer develops you start off with a normal somatic cell anything that say here it is and it could be a sewing all sorts of different tissues that could and style of the epithelia of the lungs a cell of the amphitheater of the pancreas you name okay to be any different type of cell okay and basically this cell is going to get a mutation that is going to allow it to over proliferate okay now there are two major classes of proteins that you can get mutations in that will then lead to a cell over proliferating so let’s introduce this concept now okay so the two major class of proteins are the proteins that come from proto-oncogenes okay and these proteins are involved in promoting cellular growth and cellular division okay the other types of proteins that are involved in controlling cellular growth and cellular

proliferation are also known as tumor suppressor genes okay and the proteins are coded for by chima suppressor genes these are energy growth and anti proliferation okay so normally in a normal cell that isn’t dividing you’ve got this balance between the proto-oncogenes and the tumor suppressor genes again no one’s winning basically the proto oncogenes are all same divided by five grow grow grow and then divide the tumor suppressor genes are then saying no don’t stop doing that okay and they’re in balance normally so if you want to tip this balance and cause division there are two different ways that you can do it either you can up the activity of the proto-oncogene gene products or you can down regulate the activity of the tumor suppressor gene gene products okay so this means that this first mutation that is going to occur in cancer which is the a mutation it’s generally fought in mutation that causes over division okay it can either be a gain of function mutation which I’ll breathe it down to gos gain a function mutation in a proto-oncogene that’s going to cause that proto-oncogenes activity to now go up hugely for instance examples gain-of-function mutations would be if you amplify the number of genes that you have for this proto-oncogene so usually you would have two copies of most proto-oncogenes one on each of the homologous chromosomes if somehow you end up totally screwing up and copying a whole new one into one of your chromosomes then you have three copies of the proto-oncogene and now that’s going to hugely increase the amount of the gene product the proteins that proto-oncogene that you produce and therefore hugely increase its activity okay that would be an example of a gain of function mutation in the pro swamp itching alternatively you could have a mutation that actually affects the structure of the protein itself and results in potentially being permanently active whereas previously it might have been inhibited by something or just increases effectiveness in some other way maybe okay so those are all examples of gain-of-function mutations in a proto-oncogene that would tip the balance because now the tumor suppressor genes that you’ve got wouldn’t be adequate enough to suppress the proto-oncogenes anymore okay alternatively you could have a fool in the activity of the temperature of suppressor genes okay so you either loss-of-function mutation in a tumor suppressor gene basically and often you would need loss of function mutations in both of the tumor suppressor genes that you have because again you’ll have two copies of each tumor suppressor gene generally one on each of the homologous chromosomes okay and generally only loss function in both of those genes in order for the function of the tumor suppressor protein to actually be lost completely okay right so examples of loss of function mutations would of course in deletions of the gene if you completely lost the two genes then that will completely remove the function of that protein within the south okay alternatively you could have changes in the structures of the protein which then lead them to miss Ford and be totally useless basically okay right so those are the two main types of genes controlling cell relative vision okay so this normal cell here is now going to get a somatic mutation okay and this somatic mutation is going to just so happen to either be a gain function in the proto-oncogene or a loss of function in a tumor suppressor gene okay now what’s going to happen okay now color this cell in a different color because now it’s got this mutation okay so that’s colorless in in purple now now what’s going to happen is it’s going to divide by by because it now has this over proliferation property and therefore what’s it going to end up producing it’s going to end up producing a whole population of styles that all have this mutation that means that they over proliferate basically okay so you’re now going to get a new mass of cells which have all got this mutation that means that they over proliferate and now if this the first mutation is powerful enough that it causes a powerful enough horizon proliferation that you get a visible alone okay then we would call that a benign tumor at this stage okay so it’s not cancer yet it’s just a benign tumor okay right so it’s a new mass of cells basically that wasn’t there previously okay right so now what is going to happen is you’re going to progress onwards and that’s the first part of the

progression towards cancer now what you have to do is to actually these cells to actually become cancer cells they have to acquire a lot of other very dangerous phenotypes okay so actually these cells need a huge number of other mutations in different genes in order to actually get the phenotypes of cancerous cells okay so now what’s believed to happen is in this population of sours that have all got this first mutation that means that they are over proliferate you’re now going to wait for one of them to get a mutation in another jingyan that’s going to give them another one of the phenotypes of cancerous cells okay so in this population these cells will be undergoing mutations occasionally these many of those mutations will of course being things that don’t progress them on towards cancerous phenotypes some of them might even you know be an essential proteins such as the proteins of complex for maybe in the respiratory chain and therefore the star will die when it gets that mutation okay but a venture if you wait long enough one of them will just so happen to get a mutation in a gene but now gives us another one of the phenotypes of a cancerous cell and therefore takes it towards being a cancerous cell okay so and that’s saying that one of the cells in this population here let’s say this one here now get some other mutations I’m going to color it in a different color now in blue here and this cells mutation is now going to take it towards cancer okay so it’s going to give it a lot of one of these phenotypes that takes you closer to being a cancerous cell okay so potentially it could just be another gain-of-function mutations in a proto-oncogene or another loss-of-function mutation and the tumor suppressor gene but now causes the cell to divide even more rapidly than need purple cells and therefore what’s going to happen is this tumor is going to firstly get bigger and it’s also going to become dominated now by the blue cells okay the blue clone of cells rather than the purple clone of cells so you will still have some of the purple clone of cells but now the main cell type that’s going to dominate the tumor is now the blue clone of cells and this is why people describe the carcinogenesis process as a evolutionary process as a Darwinian life process okay because the cell population within the tumor is evolving basically it’s going away from being the purple sounds to now being this blue clone of sales being the dominant clone of cells in the tumor population okay so here now are the blue cells and now have got very few purple cells left over okay so you can see that the dominant clone within the tumor is evolving basically which is why it’s compared to a Darwinian like evolution process okay and then this will continue in this blue clone of cells now you all just have to wait for one of these cells now to get a further mutation that gives us another one of the phenotypes of cancer and takes it closer to being a cancerous cell and this process continues this evolutionary process continues whereby the dominant clone of cells in the tumor is going to gradually evolve basically okay and as it does so the clonal Sowers is going to become closer and closer to having the phenotypes of cancerous cells okay so let me just outline some of these phenotypes that your grains are gradually build up as you progress towards cancer okay so the key phenotype nevron can name as one of the key phenotypes of cancerous cells is that they have over proliferative potential okay so they over proliferate so you’re going to gradually build up more and more gain-of-function mutations and pros Blanco genes and loss of function mutations and Shimer suppressor genes and that’s going to lead to you over proliferating hugely okay another phenotype of cancer cells is genetic instability and this one’s very very important okay so what do I mean by genetic instability genetic instability means that cancer cells undergo mutations far more rapidly than normal cells okay so why is this well sellers are getting damage to their DNA all the time that could that could lead to mutations occurring okay however why does it not lead to mutations occurring usually in a cell and it doesn’t always work but usually they don’t result in actual permanent changes to the DNA sequence and the reason is that you have all sorts of mechanisms for repairing the DNA when it’s been damaged okay so you have DNA repair mechanisms okay so

basically the cancerous cells the way that they have this property of genetic instability this tendency to acquire mutations far more rapidly than normal cells it’s because they have had mutations which have resulted in loss of function in the DNA repair mechanisms okay and if the DNA repair mechanisms go down then your frequency of acquiring mutation that goes up hugely okay so at one of these stages in the clonal evolution of the tumor one of these cells so let’s say for instance in this next step we’re going to acquire a genetic instability okay so we’ve got our blue clone of cells here one of these cells in this blue clone might now get a mutation in the mechanisms for DNA repair one of the pathways for DNA repair which in activates that pathway okay it will now over proliferate because remember it’s got all of the mutations of the purple of blue cells okay or in fact it’s got all the mutations or the blue sounds which means that it over perma frames okay so it will produce a whole clone of cells that all have this genetic instability now and over proliferate okay and now in that new clone of cells that can show this new clone of cells up another clone of cells here okay in this clone of cells the process towards cancer will now be hugely accelerated because you will get mutations occurring far more rapidly in this new clone of turquoise cells okay so the next process the next step towards another clonal evolution the next step this process will occur much quicker than these processes occur okay so you have to wait ages for one of these mutations to occur you have to wait ages for this mutation to occur now it’s going to accelerate the process okay accelerate this accumulation of mutations because this clone of cells now that we’re going to use to generate the cancer now has got this genetic instability and therefore it’s going to acquire mutations more rapidly okay so that’s why genetic instability is a general phenotype of all cancerous cells because for the actual cancer development to occur in a reasonable time scale in the life time of a human being it’s for that you need this accelerating step this genetic instability which accelerates the process after it occurred okay right so that’s one of the key phenotypes of cancerous cells you also need to lose senescence okay so let me explain what I mean by this okay so lost senescence is one of the key phenotypes of cancerous cells so normally cells that can divide in a human body so for instance fibroblast will divide in the human body hepatocyte still divide in the human body smooth muscle cells can fire in the human body they cannot divide forever okay if you take them out of the human body put them into a petri dish and we let them you know give them loads of nutrients give the loads of space they will not divide forever they will eventually stop okay they will get to the point where they can’t stop anymore because they have what’s known as a hayflick limit okay there is a hayflick limit as to how many times the cell can divide and this is because every time one of these cells divides and let me show it here here’s this sound here every time the cell finds the two daughter cells that it produces have shorter telomeres okay so the telomeres are the portions on the ends of the chromosomes okay the telomeres gradually get shorter every time it divides the two daughter cells here have shorter telomeres over than the mother cell okay and then these can divide again to produce four cells and then eight cells but every time what will be happening is the progressive generations will have shorter and shorter telomeres and eventually you’ll get to a generation where they simply cannot divide again because if they did their telomeres have gone basically and they’d start to cut away their actual chromosomes with the coding DNA and then you get to the stage where you can’t divide anymore and you’ve gone into the stage which is known as senescence okay so this was a somatic cell so it would have had a hayflick limit it’s somehow needed to get to where around this hayflick limit and it needs to not reach senescence basically again the usual way that cells do this is by activating telomerase expression which extends the telomeres back up again and effectively means that the cells can continue dividing as many times as they want because they can just reexpansion Amir’s back up so that’s another one of the key properties of

cancer with cells okay and then that will be one of these mutations that progresses he won once progresses you to a new clone that’s closer to being cancerous then okay and finally a lot of susceptibility to apoptosis I’ll call this invulnerability to apoptosis okay so again cells in the human body which can divide them there are cells in the human body which can’t divide so for instance skeletal cardiomyocytes they can’t divide neurons in the brain can’t divide okay but the cells in the body which can divide such as smooth muscle cells fibroblasts have parasites these are controlled basically okay if you’ve got a tissue that is overcrowded because too much cellular division has occurred these cells will commit apoptosis okay so that we should just show us so say we’ve got a bit of the liver here where it’s now overcrowded because too many cells are divided what will now occur is some cells in this overcrowded tissue will now commit an opto since okay to reduce the population and make more space basically okay now tumors are incredibly overcrowded okay so why are they not commit apoptosis what’s some points in this progression you must have got some mutation that made you invulnerable to apoptosis so that you wouldn’t have to make the apoptosis process and wouldn’t depopulate the tumor population okay so again that’s a phenotype of cancer cells and that will have occurred at some point along this progression towards cancer okay right now what I want to talk about is the final mutation is believed to occur that takes you from being what is a length stage benign tumor to being cancer OS you you gradually go through this clonal evolution process where the clone is gradually getting closer and closer to cancer it’s acquiring more and more of these phenotypes let’s see it’s now quite as all of these phenotypes okay what is the final mutation that occurs that tips it from being a benign tumor to being a malignant tumor or being cancer basically well the final mutation that occurs is that it gains the ability to be motile okay so the final mutation is the motility and this is what takes you from being a benign tumor to being a malignant you and this is what tips you into cancerous behavior okay so what now needs to occur then is the final mutation that’s going to occur if something that allows the cells to gain motility so sellers are not usually motile cells usually stay in there position in the body and do not move around in the body basically okay but the cells in this malignant tumor have acquired very a mutation that allows them to now move around and the body basically and this gives them two key properties it allows them to invade into the surrounding tissue and set up tumors there’s all extensions of the tumor in the surrounding tissue and it also allows them to invade into the blood and then set up secondary tumors at other sites distal from the size of the primary tumor okay so let me just describe this so previously then prior to a staining this final mutation we have this great big tumor here but it was contained okay it was still benign tumor okay it was maybe pushing on the surrounding tissues as it expands but it was not invading into the healthy cells okay the cells here was static Owen now what’s going to happen is once now in this final pan autumn apone prior to malignancy is going to get a mutation that’s going to that allow it to a game motility okay right now generally cancer cancers are formed from epithelial cells okay so for instance skin cancer that’s formed from an epithelial cell okay cancers of the gastrointestinal tract those are formed from epithelial cells lung cancer those are formed from epithelial cells pancreatic cancer those a form from epithelial cells liver cancer looser form from epithelial cells renal cell cancer those are formed from epithelial cell so generally the major forms of cancer are formed from epithelial cells rather than non epithelial cells okay so what actually happens usually for these epithelial cells to gain the ability to move is a process called epithelial mesenchymal

transition again this is a process that was you in the embryo and development basically so in the development if you want to move epithelial cells around the embryo what has to firstly happen is they have to change their phenotype to become amazing kymo cells but amazing kinda sounds can then move around and then when they’ve got their final location they can then return back to being at the fetal cells okay so if I show this rather crude they here here’s our epithelial cell which is not motor it can’t move around okay and we’re assuming that our benign tumor at the moment is constructed out of epithelial cells which are not motile within now in embryology and development if an epithelial cell wants to move while it turns into is what’s there is amazing time or cell okay which looks quite different of a different phenotype it was supposed to look more different than that is first PS or spindle shape okay and this process of turning from an epithelial cell into an easing kind of style is known as EMT so I’m going to color in the epithelial and the Me’s and Kaymer cells in different colors to highlight that how different they are okay so here’s an epithelial cell in blue oops here is my musing time or cell every run it okay so I’ll just label this up this is a museum Kaymer cell okay right so the process of EMT stands for epithelial okay mazing climb or transition again it just means an epithelial cell changing into a meeting time or SAP Oh in our knees and time’ll cells are motile these can move around okay so now this can move around in the embryo it can get to a new location within the embryo and then what’s going to happen is it’s going to turn back into an epithelial cell by process of amazing Chi more epithelial transition net okay now this is usually active in the adult human okay it’s something that’s reserved for development however what we think happens is this in this final transition where some cell requires a mutation that then allows it’s become motown what we think is that somehow and this isn’t understood at all or any at the moment somehow this cell is going to acquire the ability to return this process on it’s going to return at the fever amazing climb or transition on and what that now means is that this cell here firstly it can over proliferate because now it’s you know it’s got all of those mutations that being in there taken over proliferate so I’ll make a whole population of sounds that are all capable of doing this and what’s now going to happen is some of these cells some of these yellow cells here are now going to go through the process of epithelial mesenchymal transition they’re going to become using chiral cells and then they’re capable of invading into the surrounding tissue they’re capable of moving so now here’s our knees and climb or sell for moments okay which we’ll have him read here it’s on the move okay it can go to some new location maybe in the neighboring tissue and then it can decide right I’ll return back the epithelial cell so we’ll go through the musing time or epithelial transition okay and now it’s at this distant site basically and now once it’s gone back so they have the female cell type it can now over proliferate so we’ll know else s up its own little tumor at this site further away from the benign tumor basically okay so you can now access up multiple little tumors around the major tumor here okay so that’s the property of it being invasive it’s going to now invade into the surrounding tissue and destroy the surrounding tissue okay in addition it gets worse than that okay because what can happen is some of these recent IO cells can end up getting into the blood okay and then they can get out of the blood at really distant sites notably the most important one here is can they end up in the brain okay so it can go into the brain and then of course it will go through Me’s and climb or epithelial transition return back to being an epithelial cell and then it will form a secondary tumor in peripheral tissues basically in that process of setting up technology tumors very far away from the original primary tumor here okay so this is the primary tumor that process is known as metastasis okay and it’s generally the metastases to the brain that kills you okay intense so that’s what kills most cancer patients the metastasis that go to the brain not the primary tumor is the metastasis that go to the brain that kills the patient okay right so that’s an overview of the carcinogenic process

so what we have seen here is the utter importance of the over proliferation of cancer cells okay that’s the utterly huge you know type of cancerous cells in fact it’s believed to be the first driver the first mutation that occurs to start this whole process off is that the cell gains the ability to over proliferate and produces a whole population of cells that are all capable of over proliferating and then any further mutations that you snack on top of that are now going to get amplified because you’ve already got the over proliferation mutation and therefore you’re going to produce a whole population of cells with this new mutation you’ve acquired okay so that’s the absolutely key want to set this entire process off and indeed generally what will happen is in this clonal evolution process you won’t just acquire wore mutation that causing their proliferation you’ll be required more to put them okay right so the pi3 kinase Akt mTOR pathway back it is extremely important in cellular proliferation okay so let me just explain this we’re going to give a very basic overview of what the pi3 kinase Akt mTOR pathway does and we’ll go into it in detail okay right so basically if a cell wants to go from being one cell here to being two cells okay firstly what it has to do is it has to grow okay so the first process in proliferation is firstly for the cell to grow so growth is the first thing that needs to happen and then what can happen is this larger salish cell has grown can then divide into two cells it can split okay now in order for a cell to initiate this process you need major major epigenetic changes okay so what do i mean by that epigenetics is all about what controls which genes are actually expressed okay so you know every cell in your body roughly has the same you know okay it has the same collection of genes and it’s mucus there are a few exceptions of course red blood cells don’t have a nucleus lymphocytes have that silly old somatic recombination to create their own EMV cell receptors which means that they end up with slightly slightly different genomes okay but the hard and fast rule that generally applies for office hours is that they have the same genome they all have all the same genes okay however epigenetics is different between different cell types okay they all express different collections of genes in now if you want a cell to start this proliferation process start this growth process and then proliferate into you have to get this cell to hugely change which genes it’s going to express and if they see you need to start firstly producing the lone roots of new proteins okay so that you’ve got enough proteins for both cells so for instance all of the essential enzymes of respiration are going to have to be copied all the cytoskeletal proteins are going to have to make more of those because your brains become a bigger cell you’re going to need more cytoskeletal proteins okay and other proteins as well so for such as the proteins involved in the ribosomes the proteins involved in DNA repair you’re going to have to cut make more of these essential proteins so that you’ve got enough for two sounds rather than just one okay also you’re going to have to start expressing all of the proteins that are actually involved in coordinating the division process itself okay so there’s going to have to be a huge epigenetic shift basically to make a cell divides open now epigenetics involves several lines of control within the central dogma of biology okay so the first line of control is that you need to change which genes are actually being transcribed okay so we can call that transcriptional control if you need to change which genes are going to become transcribed to cause this epigenetic shift okay the pi3 kinase Akt mTOR pathway is not going to change transcriptional control okay there are other pathways that you need to activate in order to change transcriptional control notably the rouse rat mech earth pathway is a major one which can change which genes are being transcribed for Azarath met hook okay we’re not going to discuss that pathway we just need to note that there are these other pathways which need to occur alongside the pi3 kinase Akt mTOR pathway in order first i’ll to divide oh

is it’s important to note with this pathway cannot cause the cell to divide on its own you need these pathways as well okay the cause the transcriptional changes okay right now epigenetics however involves other changes just the transcriptional control there are other means by which you can control which genes are actually going to produce proteins and therefore be expressed okay for instance there is also transit no control you can control which MRNA knees are actually going to be translated into protein okay so the transcriptional control is now said okay right transcribe all of these genes that are involved in making the cell divides if a Raz Raz Mecca before it does that it changes which genes are transcribed and hmm gets you ready for the actual division process so it’s made all of the mRNA now that can make the cell divide that say okay however there’s no point making all of that mRNA if you’re not going to then translate it okay so translational control also has a major wet role in controlling whether a cell goes into the proliferation process and it’s translational control that the pi3 kinase Akt mTOR pathway is going to be involved in so basically normally if you just activated the transcriptional control if you just made is all these new mRNA is for the proteins involved in maintenance they’ll divide these Pro proliferation proteins then it wouldn’t actually have an insect because normally there is a blockade on these proliferation mRNAs being translated normally they’re not allowed to be translated okay the pi3-kinase NKT mTOR pathway is the pathway which says okay let them go through that then be translated and therefore these two pathways the raslak Erb pathway and the pi3 kinase Akt mTOR pathway they control the two major controls of epigenetics together and they allow the initiation of the growth and then the proliferation pathway Obie’s it’s important to understand that these works together okay right and so that’s an overview of what this pathway does and hopefully you’ll now appreciate how important it’s going to be for cancer cells that want to over divide to have some overact of this pathway along with a bit of over activation of this pathway okay so that you can then divide okay if you don’t have over activation of this pathway then even if you have over activation of this pathway you can produce as much mrna as you like but if you’re blocking it from being translated then it’s not actually going to cause the cell to grow and then divide okay so this pathway is extremely important in controlling the initiation of cellular division and therefore we can understand that it would be a two thing that’s going to have mutations found in it in cancer cells and indeed it is we found a huge number of cancer cells with mutations of in components of this pathway as we’ll discuss later okay so in the next video what we’ll do is now discuss this pathway in detail so we’ll start by discussing in phosphor notes at I free Tiny’s enzymes pi3 kinase enzymes okay then we’ll discuss all of the different ways that pr3 kinase enzymes can be activated because it is not repeated is not just by receptor tyrosine kinases and then we’ll move on to the next portions of the pathway