Isoform-selective targeting of PI3K: time to consider new opportunities?

Targeting PI3K in cancer treatment: A comprehensive review with insights from clinical outcomes

The phosphoinositide 3-kinase (PI3K) pathway plays a crucial role in cancer, including cell growth, survival, metabolism, and metastasis. Its major role in tumor growth makes it a key target for cancer therapeutics, offering significant potential to slow tumor progression and enhance patient outcomes. Gain-of-function mutations, gene amplifications, and the loss of regulatory proteins like PTEN are frequently observed in malignancies, contributing to tumor development and resistance to conventional treatments such as chemotherapy and hormone therapy. As a result, PI3K inhibitors have received a lot of interest in cancer research. Several kinds of small-molecule PI3K inhibitors have been developed, including pan-PI3K inhibitors, isoform-specific inhibitors, and dual PI3K/mTOR inhibitors, each targeting a distinct component of the pathway. Some PI3K inhibitors such as idelalisib, copanlisib, duvelisib, alpelisib, and umbralisib have received FDA-approval, and are effective in the treatment of breast cancer and hematologic malignancies. Despite promising results in preclinical and clinical trials, the overall clinical success of PI3K inhibitors has been mixed. While some patients may get substantial advantages, a considerable number of them acquire resistance as a result of feedback activation of alternative pathways, adaptive tumor responses, and treatment-emergent mutations. The resistance mechanisms provide barriers to the sustained efficacy of PI3K-targeted treatments. This study reviews recent advancements in PI3K inhibitors, covering their clinical status, mechanism of action, resistance mechanisms, and strategies to overcome resistance.

Lysine-Targeted Covalent Strategy Leading to the Discovery of Novel Potent PROTAC-Based PI3Kδ Degraders

Proteolysis-targeting chimera (PROTAC) technology was employed to achieve the degradation of PI3Kδ in this study, and a series of PROTAC-based PI3Kδ degraders were first developed. Lysine-targeted covalent strategy led to the discovery of novel potent PROTAC-based PI3Kδ degraders. After screening and structure-activity relationship study, B14 was optimal and exhibited strong antiproliferation and selective PI3Kδ inhibition, with a high degradation value (DC50 = 3.98 nM). B14 induced cell cycle arrest in the premitotic phase and prompted cell apoptosis. B14 displayed effective suppression of the tumor growth in the xenograft model and significantly promoted the PI3Kδ degradation in vivo. Most importantly, B14 bound to the Lys779 of PI3Kδ to selectively degrade PI3Kδ by covalent-bonding. Mechanistic studies indicated that the ubiquitin-proteasome pathway was involved in the degradation process. This study provided an effective approach for developing PROTAC-based PI3Kδ degraders, and the lysine-targeted covalent strategy laid the foundation for the further design of potent PI3Kδ-targeting PROTACs.

Evaluating the Anti-inflammatory Potential of JN-KI3: The Therapeutic Role of PI3Kγ-Selective Inhibitors in Asthma Treatment

Asthma is a chronic airway inflammatory disease of the airways characterized by the involvement of numerous inflammatory cells and factors. Therefore, targeting airway inflammation is one of the crucial strategies for developing novel drugs in the treatment of asthma. Phosphoinositide 3-kinase gamma (PI3Kγ) has been demonstrated to have a significant impact on inflammation and immune responses, thus emerging as a promising therapeutic target for airway inflammatory disease, including asthma. There are few studies reporting on the therapeutic effects of PI3Kγ-selective inhibitors in asthma disease. In this study, we investigated the anti-inflammatory and therapeutic effects of PI3Kγ-selective inhibitor JN-KI3 for treating asthma by utilizing both in vivo and in vitro approaches, thereby proving that PI3Kγ-selective inhibitors could be valuable in the treatment of asthma. In RAW264.7 macrophages, JN-KI3 effectively suppressed C5a-induced Akt phosphorylation in a concentration-dependent manner, with no discernible toxicity observed in RAW264.7 cells. Furthermore, JN-KI3 can inhibit the PI3K/Akt signaling pathway in lipopolysaccharide-induced RAW264.7 cells, leading to the suppression of transcription and expression of the classical inflammatory cytokines in a concentration-dependent manner. Finally, an ovalbumin-induced murine asthma model was constructed to evaluate the initial therapeutic effect of JN-KI3 for treating asthma. Oral administration of JN-KI3 inhibited the infiltration of inflammatory cells and the expression of T-helper type 2 cytokines in bronchoalveolar lavage fluid, which was associated with the suppression of the PI3K signaling pathway. Lung tissue and immunohistochemical studies demonstrated that JN-KI3 inhibited the accumulation of inflammatory cells around the bronchus and blood vessels, as well as the secretion of mucus and excessive deposition of collagen around the airway. In addition, it reduced the infiltration of white blood cells into the lungs. In summary, JN-KI3 shows promise as a candidate for the treatment of asthma. Our study also suggests that the inhibitory effects of PI3Kγ on inflammation could offer an additional therapeutic strategy for pulmonary inflammatory diseases.

Isoflavone Derivatives as Potential Anticancer Agents: Synthesis and Bioactivity Studies

Isoflavones are phenolic natural compounds with a C6C3C6 framework. They possess a plethora of biological activities that are associated with putative benefits to human health. In particular, the cancer chemopreventive and chemotherapeutic potential of isoflavones has attracted the interest of researchers. Several isoflavone derivatives have been synthesised and probed for their anticancer activities. The isoflavone analogues are mainly synthesised by molecular hybridisation and other strategies that enable diversification through early or late-stage functionalisation of A-, B- and C-rings of the isoflavones. This has resulted in the discovery of isoflavone analogues with improved antiproliferative activities against several cancer cells and different mechanisms of action. In this review, the synthesis of isoflavone derivatives and their anticancer activity studies are discussed.

Important Roles of PI3K/AKT Signaling Pathway and Relevant Inhibitors in Prostate Cancer Progression

Prostate cancer (PCa) is an extremely common malignant tumor of the male genitourinary system, originating from the prostate gland epithelium. Male patients are prone to relapse after treatment, which seriously threatens their health. Phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB, also known as Akt) plays an important role in the growth, invasion, and metastasis of PCa. This review aimed to present an overview of the mechanism of action of the PI3K/AKT signaling pathway in PCa and discuss the application prospects of inhibitors of this pathway in treating PCa, providing a theoretical basis and reference for its clinical treatment targets.

An Analysis of PIK3CA Hotspot Mutations and Response to Neoadjuvant Therapy in Patients with Breast Cancer from Four Prospective Clinical Trials

PURPOSE

The PI3K signaling pathway is frequently dysregulated in breast cancer, and mutations in PIK3CA are relevant for therapy resistance in HER2-positive (HER2pos) breast cancer. Mutations in exons 9 or 20 may have different impacts on response to neoadjuvant chemotherapy-based treatment regimens.

EXPERIMENTAL DESIGN

We investigated PIK3CA mutations in 1,691 patients with early breast cancer who were randomized into four neoadjuvant multicenter trials: GeparQuattro (NCT00288002), GeparQuinto (NCT00567554), GeparSixto (NCT01426880), and GeparSepto (NCT01583426). The role of different PIK3CA exons and hotspots for pathologic complete response (pCR) following neoadjuvant chemotherapy (NACT) and patient survival were evaluated for distinct molecular subgroups and anti-HER2 treatment procedures.

RESULTS

A total of 302 patients (17.9%) of the full cohort of 1,691 patients had a tumor with a PIK3CA mutation, with a different prevalence in molecular subgroups: luminal/HER2-negative (HER2neg) 95 of 404 (23.5%), HER2pos 170 of 819 (20.8%), and triple-negative breast cancer 37 of 468 patients (7.9%). We identified the mutations in PIK3CA exon 20 to be linked with worse response to anti-HER2 treatment (OR = 0.507; 95% confidence interval, 0.320-0.802; P = 0.004), especially in hormone receptor-positive HER2-positive breast cancer (OR = 0.445; 95% confidence interval, 0.237-0.837; P = 0.012). In contrast, exon 9 hotspot mutations p.E452K and p.E545K revealed no noteworthy differences in response therapy. Luminal/HER2neg patients show a trend to have worse treatment response when PIK3CA was mutated. Interestingly, patients with residual disease following neoadjuvant treatment had better survival rates when PIK3CA was mutated.

CONCLUSIONS

The PIK3CA hotspot mutation p.H1047R is associated with worse pCR rates following NACT in HER2pos breast cancer, whereas hotspot mutations in exon 9 seem to have less impact.

Structural Basis for Highly Selective Class II Alpha Phosphoinositide-3-Kinase Inhibition

Class II phosphoinositide-3-kinases (PI3Ks) play central roles in cell signaling, division, migration, and survival. Despite evidence that all PI3K class II isoforms serve unique cellular functions, the lack of isoform-selective inhibitors severely hampers the systematic investigation of their potential relevance as pharmacological targets. Here, we report the structural evaluation and molecular determinants for selective PI3K-C2α inhibition by a structure-activity relationship study based on a pteridinone scaffold, leading to the discovery of selective PI3K-C2α inhibitors called PITCOINs. Cocrystal structures and docking experiments supported the rationalization of the structural determinants essential for inhibitor activity and high selectivity. Profiling of PITCOINs in a panel of more than 118 diverse kinases showed no off-target kinase inhibition. Notably, by addressing a selectivity pocket, PITCOIN4 showed nanomolar inhibition of PI3K-C2α and >100-fold selectivity in a general kinase panel. Our study paves the way for the development of novel therapies for diseases related to PI3K-C2α function.