The PI3K-Akt pathway is one of the most frequently disrupted signaling networks in human cancer, and it also plays central roles in metabolism, immunity, brain function, and aging. When working normally, it relays growth signals from the cell surface to the machinery that governs whether a cell should grow, divide, take in nutrients, or survive a stressful event. When it malfunctions, the result is often unchecked cell proliferation. That combination of broad biological importance and frequent involvement in disease has made the pathway one of the most intensely studied targets in drug development, though translating that science into effective therapies has proven harder than early optimism suggested.
How the Signaling Cascade Works
The pathway starts at the cell membrane. When a growth factor, hormone, or other signal binds to a receptor on the outside of a cell, it activates a family of enzymes called class I PI3 kinases. These enzymes all do the same core job: they produce a signaling molecule called PIP3 on the inner face of the cell membrane. Four distinct versions of the enzyme exist, paired with various regulatory partners, but they all generate PIP3 and respond to overlapping sets of upstream signals.1Europe PMC. Phosphatidylinositol-3,4,5-trisphosphate: tool of choice for class I PI 3-kinases PIP3 acts as a kind of molecular beacon. Proteins carrying a lipid-binding region drift to the membrane when they detect it, kicking off the next step of signaling.
The protein Akt is the pathway’s main downstream workhorse. In breast cancer research, a detailed picture has emerged of how Akt reaches the membrane: a helper protein called calmodulin ferries it there by latching onto a specific binding region. Once Akt arrives, PIP3 nudges calmodulin away, and the resulting shape change exposes two critical sites on Akt. One site gets tagged by an enzyme called PDK1, and the second by a complex called mTORC2. Only after both events occur is Akt fully switched on.2Biophysical Journal. Molecular mechanism of calmodulin interactions with the pleckstrin homology domain of Akt and the releasing mechanism by PIP3 This two-step activation acts as a safety check: partial activation is not enough to trigger the full cascade.
What Akt Does Once It Is Turned On
Once active, Akt fans out across the cell, modifying dozens of target proteins. Two of its most consequential actions involve cell survival and cell growth. On the survival side, Akt directly disables proteins that would otherwise push the cell toward programmed death. It tags the pro-death protein BAD, neutralizing it, and it blocks a family of transcription factors called Forkhead factors that would otherwise switch on genes favoring cell death. Akt also suppresses the activity of p53-related proteins, further tilting the balance toward survival.3PubMed. PI 3-kinase, Akt and cell survival
On the growth side, Akt stimulates the mTORC1 complex, a master regulator of protein production and cell size. It does this by tagging and disabling two proteins, TSC2 and PRAS40, that normally keep mTORC1 suppressed.4PubMed Central. Akt-dependent activation of mTORC1 complex involves phosphorylation of mTOR (mammalian target of rapamycin) by IκB kinase α (IKKα) When Akt tags TSC2, the protein becomes unstable and can no longer partner with TSC1 to restrain mTOR.5PubMed. TSC2 is phosphorylated and inhibited by Akt and suppresses mTOR signalling With the brakes released, mTORC1 ramps up the translation of new proteins, and the cell grows larger and prepares to divide. This is why overactive Akt does not just keep cells alive longer; it actively pushes them to expand.
The Pathway’s Role in Metabolism
Beyond cancer, the PI3K-Akt pathway is the main signaling conduit through which insulin tells cells to absorb glucose. After you eat, rising insulin triggers PI3K-Akt signaling in muscle and fat cells. Akt then tags a protein called AS160, which triggers glucose transporter molecules to move from internal storage compartments to the cell surface, where they can pull glucose inside. Akt also inhibits an enzyme called GSK3, stimulating the liver and muscles to convert excess glucose into glycogen for storage.6IntechOpen. Role of PI3K/AKT Pathway in Insulin-Mediated Glucose Uptake
Interestingly, the relationship between Akt and glucose uptake is not perfectly straightforward. In heart muscle cells, researchers found that having PI3K and Akt permanently switched on actually impaired glucose uptake, even though the glucose transporters still moved to the cell surface correctly. The problem occurred at a step after the transporters were already in place, suggesting that chronically high Akt activity disrupts the transporter’s ability to function properly.7PubMed Central. Cardiac PI3K-Akt impairs insulin-stimulated glucose uptake independent of mTORC1 and GLUT4 translocation This finding matters clinically because it hints at why tissues constantly bombarded by growth signals can develop something resembling insulin resistance.
PTEN and the Pathway’s Built-In Brake
The single most important negative regulator of this pathway is an enzyme called PTEN. Its job is simple: it converts PIP3 back into PIP2, effectively erasing the signal that recruits Akt to the membrane.8PubMed Central. Analysis of Site-Specific Phosphorylation of PTEN by Using Enzyme-Catalyzed Expressed Protein Ligation In healthy cells, the balance between PI3K producing PIP3 and PTEN destroying it keeps signaling tightly controlled. Lose PTEN and the pathway runs unchecked.
PTEN is one of the most commonly inactivated tumor suppressors in human cancer. Its loss can happen through inherited mutations, spontaneous mutations within a tumor, or through mechanisms that silence the gene without altering its DNA sequence, including changes in how the gene is read and modifications to the PTEN protein itself.9PubMed Central. Therapeutic targeting of cancers with loss of PTEN function Because there are so many different ways to knock PTEN out, it shows up across a strikingly wide range of tumor types, making it a pervasive driver of PI3K-Akt pathway overactivity.
How the Pathway Goes Wrong in Cancer
Cancer can hijack this pathway in two broad ways: by losing the brake (PTEN) or by jamming the accelerator. On the accelerator side, mutations in the gene encoding the PI3Kα catalytic subunit, called PIK3CA, are among the most common gain-of-function mutations across all cancers. A study of HER2-positive breast cancer patients found that roughly 14% carried PIK3CA mutations, with the most frequent being a single change called H1047R, found in about 43% of those mutation-positive cases, followed by E545K in about 29%.10PubMed Central. PI3K Mutation Profiles on Exons 9 (E545K and E542K) and 20 (H1047R) in Mexican Patients With HER-2 Overexpressed Breast Cancer and Its Relevance on Clinical–Pathological and Survival Biological Effects These “hotspot” mutations lock PI3Kα into an overactive state, flooding the membrane with PIP3 even when no external growth signal is present.
Akt itself is also frequently overactive in tumors. It is considered one of the most commonly activated pathways in human cancer, and its dysregulation is linked to the growth and maintenance of many solid tumors.11PubMed Central. Clinical Development of AKT Inhibitors and Associated Predictive Biomarkers to Guide Patient Treatment in Cancer Medicine The net effect of any of these alterations, whether PTEN loss, PIK3CA mutation, or Akt amplification, is the same: a cell that resists death, grows faster, and consumes nutrients more aggressively than its neighbors.
Cross-Talk With the Ras-ERK Pathway
One reason the PI3K-Akt pathway is so difficult to target in cancer is that it does not operate in isolation. It is deeply entangled with another major signaling network, the Ras-ERK (also called the Raf-MEK-ERK or MAPK) pathway. Although the two were originally thought of as separate channels carrying different signals, it is now clear that they share multiple points of connection and can compensate for each other.12PubMed Central. The Ras-ERK and PI3K-mTOR pathways: cross-talk and compensation
This mutual compensation has major therapeutic implications. When a drug shuts down PI3K-Akt signaling, the Ras-ERK pathway can pick up the slack, keeping the tumor alive. Mutations in both pathways can also coexist within the same tumor, meaning that blocking one while ignoring the other leaves half the problem untouched.13PubMed. Targeting the PI3K/AKT/mTOR and Raf/MEK/ERK pathways in the treatment of breast cancer This understanding has driven a wave of clinical trials testing combined inhibition of both networks, though balancing efficacy against the added toxicity of dual blockade remains a challenge.
Approved PI3K and Akt Inhibitors
Despite decades of research, the path from laboratory insight to approved drug has been rocky. Several PI3K inhibitors have received regulatory approval, most prominently alpelisib, which selectively targets the PI3Kα isoform and is used in PIK3CA-mutated breast cancer. A separate group of inhibitors targets the PI3Kδ isoform, which is enriched in white blood cells, and these drugs are approved for certain B cell cancers.14PubMed Central. PI3K-Akt Pathway: Impact and Therapeutic Potential Progress has been slowed by two persistent problems: drugs that patients struggle to tolerate and tumors that develop resistance. Multiple Akt inhibitors are also in clinical trials, and researchers are working on combination strategies designed to boost the effectiveness of these agents.11PubMed Central. Clinical Development of AKT Inhibitors and Associated Predictive Biomarkers to Guide Patient Treatment in Cancer Medicine
Why Resistance Develops and How Tumors Fight Back
The Forkhead transcription factors that Akt normally keeps quiet turn out to be central to one of the most frustrating resistance mechanisms. When a PI3K or Akt inhibitor shuts down the pathway, the Forkhead factors (particularly a family member called FOXO) become active again and switch on genes encoding receptor tyrosine kinases, the very receptors that sit at the top of the signaling cascade. Receptors like IGF-1R, EGFR, HER2, and HER3 get upregulated, flooding the cell with fresh signals that reactivate both the PI3K-Akt and MAPK pathways.15PubMed Central. Mechanisms of Resistance to PI3K Inhibitors in Cancer: Adaptive Responses, Drug Tolerance and Cellular Plasticity The tumor essentially senses that its favorite growth signal has been cut and rewires itself to produce more of the raw input.
This mechanism has been demonstrated explicitly in colorectal cancer cells treated with the PI3K inhibitor pictilisib. When researchers knocked down FOXO using targeted genetic tools, the feedback reactivation of key signaling regulators was disrupted.16PubMed Central. Pictilisib-Induced Resistance Is Mediated through FOXO1-Dependent Activation of Receptor Tyrosine Kinases in Mucinous Colorectal Adenocarcinoma Cells The finding confirms that the rebound is not just a correlate of resistance but a mechanistic driver of it, and it highlights why single-agent PI3K inhibitors often lose potency over time.
Managing Hyperglycemia, the Pathway’s Signature Side Effect
Because PI3K-Akt signaling is the primary conduit for insulin-stimulated glucose uptake, blocking the pathway inevitably raises blood sugar. Hyperglycemia is one of the most common side effects of PI3K and Akt inhibitors, and it is not an off-target accident; it is a direct, predictable consequence of the drug hitting its intended target in healthy metabolic tissues.17PubMed Central. Characterization, management, and risk factors of hyperglycemia during PI3K or AKT inhibitor treatment
Managing this side effect has become its own clinical subspecialty. The preferred strategy combines a low-carbohydrate diet with glucose-lowering medications that do not themselves rely on the PI3K pathway. Metformin is typically the first choice, increasing insulin sensitivity through a separate mechanism. SGLT2 inhibitors, which force the kidneys to excrete excess glucose, are another mainstay.18PubMed Central. Management of Phosphatidylinositol-3-Kinase Inhibitor-Associated Hyperglycemia In animal studies, SGLT2 inhibitors and a ketogenic diet each reduced both hyperglycemia and insulin spikes more effectively than metformin alone, which had only a modest impact on the acute glucose surge triggered by PI3K inhibitors.19AACE Clinical Case Reports. Alpelisib-Induced Diabetic Ketoacidosis: A Case Report and Review of Literature A small case series of patients on alpelisib found that combining very low carbohydrate diets with SGLT2 inhibitors kept blood sugar manageable enough to continue cancer treatment.20PubMed Central. Treating Alpelisib-Induced Hyperglycemia with Very Low Carbohydrate Diets and Sodium-Glucose Co-Transporter 2 Inhibitors: A Case Series
When hyperglycemia is poorly controlled, however, the consequences can be severe. Cases of diabetic ketoacidosis, a potentially life-threatening metabolic emergency, have been reported in patients on alpelisib. In at least one documented case, the drug was successfully reintroduced after aggressive glucose management was established.19AACE Clinical Case Reports. Alpelisib-Induced Diabetic Ketoacidosis: A Case Report and Review of Literature The takeaway for clinicians is that proactive metabolic monitoring needs to start before PI3K inhibitor therapy begins, not after blood sugar spirals.
Emerging Therapeutic Strategies
One of the more promising experimental approaches uses a technology called PROTACs, which stands for proteolysis-targeting chimera molecules. Rather than simply blocking the PI3K enzyme’s active site the way traditional inhibitors do, a PROTAC physically tags the enzyme for destruction by the cell’s own protein-recycling machinery. In laboratory and animal models of HER2-positive breast cancer that had become resistant to the drug lapatinib, a PI3K PROTAC reduced cell growth and restored sensitivity to lapatinib, even at very low doses. Its performance outstripped alpelisib in head-to-head comparisons, both in cell lines and in patient-derived tumor organoids.21Cancer Letters. PI3K PROTAC overcomes the lapatinib resistance in PIK3CA-mutant HER2 positive breast cancer Because PROTACs eliminate the protein rather than just blocking it, they may sidestep resistance mechanisms that rely on the enzyme still being physically present in the cell.
On a different front, researchers are exploring the pathway’s role in immunotherapy. The PI3Kγ and PI3Kδ forms of the enzyme are particularly abundant in immune cells, and selectively blocking one or the other during the expansion of T cells for adoptive cell therapy can produce dramatically more potent anti-tumor responses. When human CAR T cells were grown in the presence of a PI3Kδ inhibitor, they retained a less-differentiated memory profile and killed human tumor cells more effectively in the lab than traditionally expanded cells. Blocking both isoforms simultaneously, however, backfired: the resulting T cells were less differentiated but also functionally impaired, producing fewer effector molecules and surviving poorly after transfer.22PubMed Central. Ex vivo blockade of PI3K gamma or delta signaling enhances the antitumor potency of adoptively transferred CD8(+) T cells Getting the isoform balance right appears critical.
The Pathway in the Brain and in Aging
PI3K-Akt signaling is not exclusively the province of oncologists and endocrinologists. In the brain, the pathway contributes to synaptic plasticity, the process by which connections between neurons strengthen or weaken in response to experience. Rat studies have shown that PI3K-Akt activation promotes both cell survival in neural tissue and protein synthesis through mTOR, processes that together support memory consolidation.23PubMed. Signalling mechanisms mediated by the phosphoinositide 3-kinase/Akt cascade in synaptic plasticity and memory in the rat The same survival-promoting properties that make the pathway dangerous when they go wrong in cancer are protective in the nervous system, where replacing lost neurons is extremely difficult.
In aging research, the pathway has drawn attention for a paradoxical reason. In the roundworm C. elegans, Akt homologs relay insulin-like signals that suppress a transcription factor called DAF-16, the worm equivalent of the mammalian FOXO family. Loss-of-function mutations that reduce Akt activity allow DAF-16 to become active, driving a metabolic shift that dramatically extends lifespan.24PubMed Central. Caenorhabditis elegans Akt/PKB transduces insulin receptor-like signals from AGE-1 PI3 kinase to the DAF-16 transcription factor The mammalian equivalent of this phenomenon, sometimes called the insulin/IGF-1 paradox, suggests that dialing down the pathway increases stress resistance and longevity. When insulin/IGF-1 signaling declines in worms, activation of DAF-16 (and its mammalian FoxO counterparts) enhances expression of genes involved in stress defense and lifespan extension.25PubMed. Insulin/IGF-1 paradox of aging: regulation via AKT/IKK/NF-kappaB signaling Whether this translates cleanly into human biology is far from settled, but it raises a provocative question: by therapeutically inhibiting PI3K-Akt signaling in cancer patients, might we inadvertently be activating longevity-associated programs in healthy tissues? The full implications remain murky, but the evolutionary conservation of the pathway from worms to mammals suggests its roles in growth and aging are not coincidental.
Cardiovascular Connections
The pathway also intersects with blood vessel health. In endothelial cells lining blood vessels, Akt is known to tag the enzyme that produces nitric oxide, a molecule essential for relaxing blood vessels and maintaining normal blood pressure. Loss of the Akt1 form of the enzyme in mice eliminated insulin’s ability to trigger nitric oxide production, though basal blood pressure and vascular function remained normal because other regulatory systems compensated.26PubMed Central. Contribution of insulin and Akt1 signaling to endothelial nitric oxide synthase in the regulation of endothelial function and blood pressure The finding underscores a recurring theme with this pathway: its loss seldom produces catastrophic failure in any one system, because backup mechanisms exist. But when the pathway is chronically overactive or chronically suppressed, the cumulative effects across multiple tissues, from blood vessels to the pancreas to the brain, can be profound. For patients on long-term PI3K or Akt inhibitor therapy, cardiovascular monitoring alongside metabolic surveillance may become increasingly relevant as these drugs are used for longer durations.