protein-coupled receptors (GPCRs). Once triggered, PI3K promptly converts phos­phatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 3,4,5-trisphosphate (PIP3) via its catalytic subunit. PIP3 functions as a secondary messenger in the cel­lular context by facilitating the recruitment of a cascade of proteins that possess a homology domain similar to the pleckstrin homology (PH) domain found in the cell membrane. The unregulated activation of PI3K signaling is a prevalent occurrence in cancer, mostly attributed to the distinct functions shown by p110α and p110β, which are its catalytic subunits. The presence of genetic alterations in the PI3KA sequence, which encodes p110α, has been seen in cancerous cells originating from several organs including the brain, colon, liver, prostate, and lung [11, 13]. PI3KA plays a crucial role in promoting angiogenesis in endothelial cells. Angiogenesis is essential in creating a network of blood vessels that enables the transportation of oxygen and nutrients. Additionally, this gene is involved in cell cycle regulation and growth. Its involvement in these processes is signicant as it can potentially facilitate the metas­tasis of cancer cells from the primary lesion. During oncogenesis, particularly in tumors initiated by RTKs and oncogenes, the isoform p110α is essential. In addition to its involvement in downstream signaling of GPCR pathways, p110β also plays a crucial role in high-grade prostatic intraepithelial neoplasia (HG-PIN) development within the epithelial prostate [14]. In an animal model of prostate cancer resulting from PTEN deciency, the reduction of p110β hindered tumor formation and inhib­ited AKT phosphorylation, whereas reducing p110α did not yield such effects [15]. The available data from recent investigations consistently indicate that the inhibition of p110α has no impact on the progression of PTEN-null CRPC. However, the genetic or pharmacological interference with p110β signicantly impedes the onset and advancement of CRPC, as shown by many studies [15, 16].

the following three isoforms with similar structures described: AKT, AKT1, and AKT2. These isoforms all possess a pleckstrin homology (PH) domain, wherein despite differences in amino acid sequences, the tertiary structure is conserved and binds to PIP3. Another domain of these isoforms is the lineage genes (LIN) domain, consisting of 39 acid amine residues and exhibiting the lowest degree of conserva­tion. Remarkably, in humans, no other protein shares signicant homology with LIN (17–46% identical). This domain acts as a linker, thus bridging between the PH domain and the domain with catalytic activity. The kinase domain spans amino acids 148 to 411 and concludes with a hydrophobic regulatory motif known as the C-terminal domain (CTD), which is responsible for adenosine triphosphate (ATP) binding. The ATP-binding region, consisting of 25 acid amines, exhibits a high degree of similarity, ranging from 96% to 100%, throughout the three isoforms. The conser­vation of the C-terminal hydrophobic domain is seen in all AGC family members of kinases. The hydrophobic amino acids are of utmost importance in facilitating the full activation of AKT for the process of substrate phosphorylation. Embedded inside the structure is an additional crucial residue responsible for the activation of the enzyme, known as Ser473. Despite structural similarities among the AKT isoforms, they exhibit distinct expression patterns in different tissues. Specically, AKT1 is highly expressed in almost all organs except for the kidney, spleen, and liver, whereas AKT2 is prominently expressed in insulin- sensitive tissues, including skeletal muscles, adi­pose tissue, and the liver. Conversely, AKT3 is present in all tissues but shows lower expression levels in skeletal muscles and the liver. Thus, different AKT isoforms demonstrate diverse roles. For instance, while excessive AKT2 expression leads to cell motility and invasion, upregulation of AKT3 is associated with invasion in hor­mone-sensitive tumors [20]. Upon phosphorylation and activation, AKT identies and phosphorylates threonine and serine residues on various substrates. Some impor­tant substrates of AKT include forkhead box transcription factors (FOXO), p21-acti­vated protein kinase (Pak1), inducible nitric oxide synthase (iNOS), caspase-9, cyclin-dependent kinase inhibitor 1 (also known as p21)(p21WAF1/CIPK1), tuber­ous sclerosis complex 2 (TSC2), BCL2 associated agonist of cell death (BAD), and glycogen synthase kinase 3 (GSK3). All of these are involved in crucial cellular pro­cesses, cell life and death, angiogenesis, and metabolism. The overactivation of AKT has been documented in several types of cancers, such as lung cancer, multiple myeloma, breast cancer, glioblastoma, and prostate cancer [21]. mTOR kinase is widely recognized as the most extensively investigated downstream substrate of AKT. The AKT protein has the ability to phosphorylate and thereby activate mTOR.Additionally, AKT may indirectly activate mTOR by phosphorylation and deactivating tuberin also known as tuberous sclerosis 2 (TSC2). Tuberin typically functions to inhibit mTOR.The stimulation of mTOR leads to an augmentation in protein translation [22]. Recent investigations have shown that the activity of AKT could be effectively suppressed by the PH domain of leucine repeat sequence-rich phosphatase (PHLPP). Precisely, PHLPP has the ability to dephosphorylate the AKT’s hydrophobic motif, with Ser473in AKT1 being the particular target [23].

cell motility, cell survival, and transcription. The mTOR pathway acts as a key regulator of energy homeostasis and body weight, being responsive to many meta­bolic signals like amino acids, insulin, glucose, and other metabolic hormones. An important point based on recent studies is that mTOR, in addition to acting as a critical substrate of AKT, also serves as a signicant activator of it. Activated mTOR typically constructs a complex with the protein rapamycin-insensitive companion of mTOR (RICTOR) and, through phosphorylation at Ser473, activates the AKT protein [24]. The sequestration of recently generated mTOR proteins inside cells after long-term rapamycin therapies might potentially be elucidated by the activa­tion of TORC2. This medication has high efcacy in causing cell death through the apoptosis pathway and inhibiting the proliferation of cells with upregulated AKT due to its ability to disrupt the reassembly of the complex by binding to it over a period of time [25].

The presence of gene amplications, deletions, insertions, and missense mutations is mostly seen in the PIK3CA gene, encoding the Class IA p110α subunit [9]. According to a study, it has been shown that PIK3CA mutations exist in roughly 4% of prostate cancer cases, while PIK3CA copy number increase or amplication is seen in approximately 66% of cases [35]. There are two signicant hotspot muta­tions identied in this study, namely exon 9 E542K and E545K located in the helical region and exon 20 H1047R in the kinase domain [35]. Recent research has pro­vided evidence indicating that the induction of invasive prostate cancer in cell lines may be attributed to the presence of PIK3CA H1047, thereby establishing it as a genetic driver of prostate cancer [35]. While there is currently no documentation of PIK3CB mutations, the involvement of PI3Kβ in carcinogenesis is signicant due to the intricate cross-regulation across PI3K isoforms. While it is true that PI3Kα is the primary isoform found in prostate epithelial cells, investigations have shown that the loss of PTEN causes the activation of oncogenic pathways and promotes tumor development through PI3Kβ [36–38]. Consistent with the aforementioned data, it was shown in a mouse model with PTEN deciency that PI3Kβ has a

signicant role in the formation of prostate tumors [39]. The aforementioned inves­tigations have provided evidence supporting the presence of a therapeutic approach for targeting PI3K via isoform-specic inhibitors, including AZD8186, SAR260301, and GSK2636771 [36]. Nevertheless, the subsequent data did not meet the antici­pated standards. The suppression of PI3Kβ led to a subsequent high level of PI3Kα activity, most likely due to the upregulation of FOXO and/or p70S6K/rpS6, which caused the rebound activity of AKT and mTOR [40]. In contrast, the administration of medicines that specically target both isoforms of PI3K effectively disrupted subsequent signaling pathways and resulted in a decrease in tumor development. The effectiveness of the treatment was found to be restricted to mice models of prostate cancer that expressed the wild-type PTEN gene, as indicated by a previous study [40]. The aforementioned characteristic was recently subjected to additional analysis in mice with prostate-specic biallelic PTEN deletion and PIK3CA­H1047R, as compared to a control group consisting of animals with just PTEN loss [35]. These sophisticated research models facilitated the investigation of the poten­tial impact of PTEN expression on PI3K activity by modulating the isoform-specic upstream activators, including RAS and RAC1 for PI3Kα and PI3Kβ, respectively. The study revealed that there was a persistent activation of the RAS/pERK signaling pathway in mice that had both PTEN deletion and PIK3CA H1047R mutation, as well as in animals that only had PTEN deletion. In contrast, it was shown that a signicant increase in RAC1 activity was only evident in PTEN-null/wild-type PIK3CA.This nding suggests that the continuous RAC1/PI3Kβ activity may be responsible for the advancement of tumors in these particular animal models. Given the limited effectiveness of pharmaceuticals that inhibit PI3Kβ, the researchers of this study proposed a treatment approach for PTEN-deleted individuals by combin­ing the disabling RAC using PI3Kβ inhibitors [35].

apoptosis. Additionally, the aforementioned treatment led to the reversal of the phe­notype mentioned above. These ndings provide support for applying PI3K-targeted treatment in clinical settings. To assess the impact of PI3K and/or mTOR inhibition, the extended dephosphorylation of both rpS6 and AKT has been observed. The effectiveness of BEZ235 was further evaluated in a more advanced model of PTEN­null CRPC.Surprisingly, the sensitivity of this model to BEZ235 was found to be lower than anticipated. According to the authors, the proposed explanation is that the simultaneous overactivation of androgen receptor, MAPK, and PI3K signaling pathways resulted in resistance to treatment [43]. However, the combination of BEZ235 with AZD6224 (a MAPK inhibitor) was shown to efciently overcome resistance, suggesting that individuals with PTEN-deleted prostate cancers may get therapeutic benets from PI3K signaling inhibitors [43].