INCB050465 (Parsaclisib), a Novel Next-Generation Inhibitor of Phosphoinositide 3-Kinase Delta (PI3Kδ)

From lab to clinic: The discovery and optimization journey of PI3K inhibitors

PI3K inhibitors have emerged as promising therapeutic agents due to their critical role in various cellular processes, particularly in cancer, where the PI3K pathway is frequently dysregulated. This review explores the evolutionary path of PI3K inhibitors from laboratory discovery to clinical application. The journey begins with early laboratory investigations into PI3K signaling and inhibitor development, highlighting fundamental discoveries that laid the foundation for subsequent advancements. Optimization strategies, including medicinal chemistry approaches and structural modifications, are scrutinized for their contributions to enhancing inhibitor potency, selectivity, and pharmacokinetic properties. The translation from preclinical studies to clinical trials is examined, emphasizing pivotal trials that evaluated efficacy and safety profiles. Challenges encountered during clinical development are critically assessed. Finally, the review discusses ongoing research directions and prospects for PI3K inhibitors, underscoring these agents' continuous evolution and therapeutic potential.

A highly selective PI3Kδ inhibitor BGB-10188 shows superior preclinical anti-tumor activities and decreased on-target side effects on colon

PI3Kδ is a key signal transduction molecule in normal and malignant B cells, as well as in T-regulatory cells, making it a promising target for treatment of hematologic malignancies through both direct killing and anti-tumor immunity regulation. BGB-10188 is a highly selective inhibitor of PI3Kδ, showing more than 3000 folds selectivity over other PI3K isoforms and no significant inhibition across tested kinases. BGB-10188 potently inhibited PI3Kδ with IC50s ranging from 1.7-16 nM through various in vitro assays and showed a long-lasting and strong target inhibition in mouse B cells in vivo. BGB-10188 showed significant antitumor effects in human B cell lymphoma xenograft models as single agent or in combination with the BTK inhibitor zanubrutinib. BGB-10188 showed significant Treg inhibition in blood but not in colon, along with less drug accumulation in colon compared with idelalisib, which is an approved PI3Kdelta inhibitor with high incidence of gastrointestinal side effects in clinic. In summary, BGB-10188 is a novel PI3Kδ inhibitor with high selectivity, potency and improved safety profile shown in preclinical studies, which is showing the potential as a best-in-class PI3Kδ inhibitor.

Design, synthesis, antineoplastic activity of new pyrazolo[3,4-d]pyrimidine derivatives as dual CDK2/GSK3β kinase inhibitors; molecular docking study, and ADME prediction

In the current study, novel pyrazolo[3,4-d]pyrimidine derivatives 5a-h were designed and synthesized as targeted anti-cancer agents through dual CDK2/GSK-3β inhibition. The designed compounds demonstrated moderate to potent activity on the evaluated cancer cell lines (MCF-7 and T-47D). Compounds 5c and 5 g showed the most promising cytotoxic activity against the tested cell lines surpassing that of the used reference standard; staurosporine. On the other hand, both compounds showed good safety and tolerability on normal fibroblast cell line (MCR5). The final compounds 5c and 5 g showed a promising dual CDK2/GSK-3β inhibitory activity with IC50 of 0.244 and 0.128 μM, respectively, against CDK2, and IC50 of 0.317 and 0.160 μM, respectively, against GSK-3β. Investigating the effect of compounds 5c and 5 g on CDK2 and GSK-3β downstream cascades showed that they reduced the relative cellular content of phosphorylated RB1 and β-catenin compared to that in the untreated MCF-7 cells. Moreover, compounds 5c and 5 g showed a reasonable selective inhibition against the target kinases CDK2/GSK-3β in comparison to a set of seven off-target kinases. Furthermore, the most potent compound 5 g caused cell cycle arrest at the S phase in MCF-7 cells preventing the cells' progression to G2/M phase inducing cell apoptosis. Molecular docking studies showed that the final pyrazolo[3,4-d]pyrimidine derivatives have analogous binding modes in the target kinases interacting with the hinge region key amino acids. Molecular dynamics simulations confirmed the predicted binding mode by molecular docking. Moreover, in silico predictions indicated their favorable physicochemical and pharmacokinetic properties in addition to their promising cytotoxic activity.

Targeting PI3K family with small-molecule inhibitors in cancer therapy: current clinical status and future directions

The Phosphatidylinositol-3-kinase (PI3K) family is well-known to comprise three classes of intracellular enzymes. Class I PI3Ks primarily function in signaling by responding to cell surface receptor stimulation, while class II and III are more involved in membrane transport. Under normal physiological conditions, the PI3K signaling network orchestrates cell growth, division, migration and survival. Aberrant activation of the PI3K signaling pathway disrupts cellular activity and metabolism, often marking the onset of cancer. Currently, the Food and Drug Administration (FDA) has approved the clinical use of five class I PI3K inhibitors. These small-molecule inhibitors, which exhibit varying selectivity for different class I PI3K family members, are primarily used in the treatment of breast cancer and hematologic malignancies. Therefore, the development of novel class I PI3K inhibitors has been a prominent research focus in the field of oncology, aiming to enhance potential therapeutic selectivity and effectiveness. In this review, we summarize the specific structures of PI3Ks and their functional roles in cancer progression. Additionally, we critically evaluate small molecule inhibitors that target class I PI3K, with a particular focus on their clinical applications in cancer treatment. Moreover, we aim to analyze therapeutic approaches for different types of cancers marked by aberrant PI3K activation and to identify potential molecular targets amenable to intervention with small-molecule inhibitors. Ultimately, we propose future directions for the development of therapeutic strategies that optimize cancer treatment outcomes by modulating the PI3K family.

Discovery of Potent and Selective PI3Kδ Inhibitors for the Treatment of Acute Myeloid Leukemia

PI3Kδ is an essential target correlated to the occurrence and development of acute myeloid leukemia (AML). Herein, we investigated the pyrazolo[3,4-d]pyrimidine derivatives as potent and selective PI3Kδ inhibitors with high therapeutic efficacy toward AML. There were 44 compounds designed and prepared in a four-round optimization, and the biological evaluation showed that (S)-36 exhibited potent PI3Kδ inhibitory activity, high selectivity, and high antiproliferative activities against MV-4-11 and MOLM-13 cells, coupled with high oral bioavailability (F = 59.6%). In the MOLM-13 subcutaneous xenograft model, (S)-36 could significantly suppress the tumor progression with a TGI of 67.81% at an oral administration dosage of 10 mg/kg without exhibiting obvious toxicity. Mechanistically, (S)-36 could robustly inhibit the PI3K/AKT pathway for significant suppression of cell proliferation and remarkable induction of apoptosis both in vitro and in vivo. Thus, compound (S)-36 represents a promising PI3Kδ inhibitor for the treatment of acute myeloid leukemia with high efficacy.

Phase 2 study of add-on parsaclisib for patients with myelofibrosis and suboptimal response to ruxolitinib: final results

ABSTRACT

Ruxolitinib reduces spleen volume, improves symptoms, and increases survival in patients with intermediate- or high-risk myelofibrosis. However, suboptimal response may occur, potentially because of signaling via the phosphoinositide 3-kinase (PI3K)/protein kinase B pathway. This phase 2 study evaluated dosing, efficacy, and safety of add-on PI3Kδ inhibitor parsaclisib for patients with primary or secondary myelofibrosis with suboptimal response to ruxolitinib. Eligible patients remained on a stable ruxolitinib dose and received add-on parsaclisib 10 or 20 mg, once daily for 8 weeks, and once weekly thereafter (daily-to-weekly dosing; n = 32); or parsaclisib 5 or 20 mg, once daily for 8 weeks, then 5 mg once daily thereafter (all-daily dosing; n = 42). Proportion of patients achieving a ≥10% decrease in spleen volume at 12 weeks was 28% for daily-to-weekly dosing and 59.5% for all-daily dosing. Proportions of patients achieving ≥50% decrease at week 12 in Myelofibrosis Symptom Assessment Form and Myeloproliferative Neoplasms Symptom Assessment Form symptom scores were 14% and 18% for daily-to-weekly dosing, and 28% and 32% for all-daily dosing, respectively. Most common nonhematologic treatment-emergent adverse events were nausea (23%), diarrhea (22%), abdominal pain and fatigue (each 19%), and cough and dyspnea (each 18%). New-onset grade 3 and 4 thrombocytopenia were observed in 19% of patients, each dosed daily-to-weekly, and in 26% and 7% of patients dosed all-daily, respectively, managed with dose interruptions. Hemoglobin levels remained steady. The addition of parsaclisib to stable-dose ruxolitinib can reduce splenomegaly and improve symptoms, with manageable toxicity in patients with myelofibrosis with suboptimal response to ruxolitinib. This trial was registered at www.clinicaltrials.gov as #NCT02718300.

A phase 2 study of the PI3Kδ inhibitor parsaclisib in relapsed and refractory marginal zone lymphoma (CITADEL-204)

ABSTRACT

Parsaclisib, a potent and highly selective PI3Kδ inhibitor, has shown clinical benefit in patients with relapsed or refractory (R/R) B-cell lymphomas. The phase 2 CITADEL-204 study (NCT03144674, EudraCT 2017-000970-12) assessed efficacy and safety of parsaclisib in Bruton tyrosine kinase (BTK) inhibitor-experienced (cohort 1) or BTK inhibitor-naive (cohort 2) patients with R/R marginal zone lymphoma (MZL). Patients aged ≥18 years with histologically confirmed R/R MZL, treated with ≥1 prior systemic therapy (including ≥1 anti-CD20 antibody) received parsaclisib 20 mg once daily for 8 weeks then 20 mg once weekly (weekly dosing group [WG]) or parsaclisib 20 mg once daily for 8 weeks then 2.5 mg once daily (daily dosing group [DG]); DG was selected for further assessment. Primary end point of the study was objective response rate (ORR). Owing to slower than expected recruitment, cohort 1 was closed with 10 patients (WG, n = 4; DG, n = 6) enrolled. Based on a planned interim analysis in cohort 2, the futility boundary was not crossed, and enrollment continued to study completion. At data cutoff (15 January 2021), 100 patients were enrolled and treated in cohort 2 (WG, n = 28; DG, n = 72). In the DG, the ORR was 58.3% (95% confidence interval [CI], 46.1-69.8), with a complete response rate of 4.2% (95% CI, 0.9-11.7); the lower bound of the ORR 95% CI exceeded the protocol-defined threshold of 40%. The median duration of response was 12.2 months (95% CI, 8.1-17.5) and progression-free survival was 16.5 months (95% CI, 11.5-20.6); median overall survival was not reached. The most common treatment-emergent adverse events (TEAEs) among all patients were diarrhea (47.0%), cough (23.0%), and rash (18.0%); the most common grade ≥3 TEAEs included diarrhea (12.0%), neutropenia, and pneumonia (9.0% each). TEAEs led to dose interruptions, reductions, and discontinuations in 56.0%, 16.0%, and 29.0% of all patients, respectively. Durable responses and an overall manageable safety profile were demonstrated in patients with R/R MZL treated with parsaclisib monotherapy.

ZNL0325, a Pyrazolopyrimidine-Based Covalent Probe, Demonstrates an Alternative Binding Mode for Kinases

The pyrazolopyrimidine (PP) heterocycle is a versatile and widely deployed core scaffold for the development of kinase inhibitors. Typically, a 4-amino-substituted pyrazolopyrimidine binds in the ATP-binding pocket in a conformation analogous to the 6-aminopurine of ATP. Here, we report the discovery of ZNL0325 which exhibits a flipped binding mode where the C3 position is oriented toward the ribose binding pocket. ZNL0325 and its analogues feature an acrylamide side chain at the C3 position which is capable of forming a covalent bond with multiple kinases that possess a cysteine at the αD-1 position including BTK, EGFR, BLK, and JAK3. These findings suggest that the ability to form a covalent bond can override the preferred noncovalent binding conformation of the heterocyclic core and provides an opportunity to create structurally distinct covalent kinase inhibitors.

Safety and efficacy of parsaclisib in combination with obinutuzumab and bendamustine in patients with relapsed or refractory follicular lymphoma (CITADEL-102): A phase 1 study

Parsaclisib is a potent and highly selective PI3Kδ inhibitor that has shown clinical benefit with monotherapy in a phase 2 study in relapsed or refractory (R/R) follicular lymphoma (FL). CITADEL-102 (NCT03039114), a phase 1, multicenter study, assessed the efficacy of parsaclisib in combination with obinutuzumab and bendamustine in patients with R/R FL. Patients were ≥18 years of age with histologically confirmed and documented CD20-positive FL, and R/R to previous rituximab-containing treatment regimens. Part one (safety run-in) determined the maximum tolerated dose of parsaclisib in combination with standard dosage regimens of obinutuzumab and bendamustine. Part two (dose expansion) was an open-label, single-group design evaluating safety, tolerability (primary endpoint), and efficacy (secondary endpoint) of parsaclisib combination therapy. Twenty-six patients were enrolled in CITADEL-102 and all patients received parsaclisib 20 mg once daily for 8 weeks, followed by 20 mg once weekly thereafter, in combination with obinutuzumab and bendamustine. One patient in safety run-in experienced a dose-limiting toxicity of grade 4 QT interval prolongation that was considered related to parsaclisib. Eight patients (30.8%) discontinued treatment due to treatment-emergent adverse events (TEAEs) of colitis (2 [7.7%]), alanine aminotransferase and aspartate aminotransferase increase (both in one patient [3.8%]), neutropenia, thrombocytopenia, QT prolongation, tonsil cancer, and maculopapular rash (each 1 [3.8%]). The most common reported TEAEs were pyrexia (53.8%), neutropenia (50.0%), and diarrhea (46.2%). Twenty-three patients (88.5%) experienced grade 3 or 4 TEAEs; the most common were neutropenia (34.6%), febrile neutropenia (23.1%), and thrombocytopenia (19.2%). Seventeen patients (65.4%) had a complete response and 3 patients (11.5%) had a partial response, for an objective response rate of 76.9%. Overall, results from CITADEL-102 suggest that the combination of parsaclisib with obinutuzumab and bendamustine did not result in unexpected safety events, with little evidence of synergistic toxicity, and demonstrated preliminary efficacy in patients with R/R FL who progressed following prior rituximab-containing regimens.

Design, synthesis and bioactivity evaluation of selenium-containing PI3Kδ inhibitors

PI3Kδ inhibitors play an important role in the treatment of leukemia, lymphoma and autoimmune diseases. Herein, using our reported compounds as the lead compound, we designed and synthesized a series of selenium-containing PI3Kδ inhibitors based on quinazoline and pyrido[3,2-d]pyrimidine skeletons. Among them, compound Se15 showed sub-nanomolar inhibition against PI3Kδ and strong δ-selectivity. Moreover, Se15 showed potent anti-proliferative effect on SU-DHL-6 cells with an IC50 value of 0.16 μM. Molecular docking study showed that Se15 was able to form multiple hydrogen bonds with PI3Kδ and was close proximity and stacking with PI3Kδ selective region. In conclusion, the Se-containing compound Se15 bearing pyrido[3,2-d]pyrimidine scaffold is a novel potent and selective PI3Kδ inhibitor. The introduction of selenium can enrich the structure of PI3Kδ inhibitors and provide a new idea for design of novel PI3Kδ inhibitors.

Parsaclisib, a PI3Kδ inhibitor, in relapsed and refractory follicular lymphoma (CITADEL-203): a phase 2 study

Background

Parsaclisib, a potent and highly selective PI3Kδ inhibitor, has shown clinical benefit in patients with relapsed or refractory (R/R) B-cell malignancies. This phase 2 study (CITADEL-203; NCT03126019, EudraCT 2017-001624-22) assessed efficacy and safety of parsaclisib monotherapy in patients with R/R follicular lymphoma (FL).

Methods

Patients ≥18 years of age with histologically confirmed R/R FL (grade 1-3a) and prior treatment with ≥2 systemic therapies received parsaclisib 20 mg once daily (QD) for 8 weeks then parsaclisib 20 mg once weekly (weekly dosing group [WG]) or parsaclisib 20 mg QD for 8 weeks then parsaclisib 2.5 mg QD (daily dosing group [DG]); DG was selected for further assessment. Primary endpoint was objective response rate (ORR).

Findings

At data cut-off (January 15, 2021), 126 patients had been treated (WG: n = 23; DG: n = 103). ORR (95% confidence interval [CI]) was 77.7% (68.4-85.3) with a complete response rate (95% CI) of 19.4% (12.3-28.4) in DG; median (95% CI) duration of response was 14.7 months (10.4-not estimable [NE]), median progression-free survival was 15.8 months (11.0-NE), and median overall survival was not reached. The most common any-grade treatment-emergent adverse events (TEAEs) among all treated patients included diarrhoea (n = 48, 38.1%), nausea (n = 31, 24.6%), and cough (n = 28, 22.2%); the most common grade ≥3 TEAEs were diarrhoea (n = 15, 11.9%), neutropenia (n = 13, 10.3%), and colitis (n = 7, 5.6%). Dose interruption, reduction, and discontinuation from TEAEs occurred in 46.8% (n = 59), 17.5% (n = 22), and 23.8% (n = 30) of patients, respectively.

Interpretation

Treatment with parsaclisib demonstrated rapid and durable responses, and a manageable safety profile in patients with R/R FL.

Funding

Incyte Corporation.

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

Phosphoinositide-3-kinases (PI3Ks) are central to several cellular signaling pathways in human physiology and are potential pharmacological targets for many pathologies including cancer, thrombosis, and pulmonary diseases. Tremendous efforts to develop isoform-selective inhibitors have culminated in the approval of several drugs, validating PI3K as a tractable and therapeutically relevant target. Although successful therapeutic validation has focused on isoform-selective class I orthosteric inhibitors, recent clinical findings have indicated challenges regarding poor drug tolerance owing to sustained on-target inhibition. Hence, additional approaches are warranted to increase the clinical benefits of specific clinical treatment options, which may involve the employment of so far underexploited targeting modalities or the development of inhibitors for currently underexplored PI3K class II isoforms. We review recent key discoveries in the development of isoform-selective inhibitors, focusing particularly on PI3K class II isoforms, and highlight the emerging importance of developing a broader arsenal of pharmacological tools.

Discovery of potent and selective PI3Kδ inhibitors bearing amino acid fragments

The selective inhibition of PI3Kδ is a potential therapeutic strategy for the treatment of hematologic malignancies. Herein, we report a series of compounds bearing amino acid fragments as potent and selective PI3Kδ inhibitors. Among them, compound A10 exhibited sub-nanomolar PI3Kδ potency. In cellular assays, A10 achieved strong antiproliferation against SU-DHL-6 cells, and caused cell cycle arrest, and induced apoptosis in SU-DHL-6 cells. The docking study showed that A10 tightly bound to PI3Kδ protein with a planar-shaped conformation. Collectively, compound A10 represented a promising potent and selective PI3Kδ inhibitor bearing amino acid fragement albeit with moderate selectivity over PI3Kγ but superior selectivity against PI3Kα and β. This study suggested that using the amino acid fragments instead of the pyrrolidine ring is new strategy for design of potent PI3Kδ inhibitors.

Parsaclisib, a PI3Kδ inhibitor, in relapsed and refractory mantle cell lymphoma (CITADEL-205): a phase 2 study

Background

Parsaclisib is a potent and highly selective PI3Kδ inhibitor that has shown clinical benefit in patients with relapsed/refractory (R/R) B-cell malignancies. In this phase 2 study (CITADEL-205; NCT03235544, EudraCT 2017-003148-19), the efficacy and safety of parsaclisib was evaluated in patients with R/R mantle cell lymphoma (MCL).

Methods

Patients ≥18 years old with pathologically confirmed R/R MCL and prior treatment with 1-3 systemic therapies, with (cohort 1) or without (cohort 2) previous Bruton kinase inhibitor (BTKi) treatment, received oral parsaclisib 20 mg once-daily (QD) for 8 weeks, then either parsaclisib 20 mg once-weekly (weekly dosing group [WG]) or parsaclisib 2.5 mg QD (daily dosing group [DG]). The primary endpoint was objective response rate (ORR).

Findings

At the primary analysis data cutoff on January 15, 2021, 53 patients in cohort 1 (BTKi-experienced) (WG, n = 12; DG: n = 41) and 108 patients in cohort 2 (BTKi-naive) (WG, n = 31; DG: n = 77) had received parsaclisib monotherapy. The BTKi-experienced cohort was closed after an interim analysis demonstrated limited clinical benefit. In the BTKi-naive cohort, the ORR (95% CI) for DG (dosing selected for further study) was 70.1% (58.6%-80.0%), with a complete response rate (95% CI) of 15.6% (8.3%-25.6%) and a median duration of response (95% CI) of 12.1 (9.0-not evaluable) months. Treatment-emergent adverse events (TEAEs) occurred among 90.7% (98/108) of all treated patients in the BTKi-naive cohort. Grade ≥3 TEAEs occurred among 62.0% (67/108) of patients, including diarrhoea (13.9%, 15/108) and neutropenia (8.3%, 9/108). Parsaclisib interruption, reduction, or discontinuation due to TEAEs occurred among 47.2% (51/108), 8.3% (9/108), and 25.0% (27/108) of patients, respectively. Fatal TEAEs were experienced by six patients and determined to be treatment-related in one patient.

Interpretation

Parsaclisib, a potent, highly selective, PI3Kδ inhibitor demonstrated meaningful clinical benefits and a manageable safety profile (25.0% discontinuation rate, low incidences of individually reported grade ≥3 or serious adverse events) in R/R MCL patients with no prior BTKi therapy. Limited clinical benefit was observed with parsaclisib monotherapy in patients who had previously received BTKi treatment. Future development of PI3K inhibitors for NHL will require further investigation of dose optimisation to improve safety and long-term survival.

Funding

Incyte Corporation.

Targeted Therapy for MPNs: Going Beyond JAK Inhibitors

PURPOSE OF REVIEW

JAK inhibition is an effective means of controlling symptom burden and improving splenomegaly in patients with myeloproliferative neoplasms (MPNs). However, a majority of patients treated with JAK inhibition will have disease progression with long-term use. In In this review, we focus on the investigation of novel targeted agents beyond JAK inhibitors both in the chronic phase of disease and in the accelerated/blast phase of disease.

RECENT FINDINGS

Relevant targeted therapies in MPNs include BET inhibitors, BCL inhibitors, LSD1 inhibitors, PI3K inhibitors, IDH inhibitors, telomerase inhibitors, and MDM2 inhibitor. Agents within these classes have been investigated either as monotherapy or in combination with a JAK inhibitor. We summarize the prospective data for these agents along with detailing the ongoing phase III trials incorporating these agents. While JAK inhibition has been a mainstay of therapy in MPNs, a majority of patients will have disease of progression. JAK inhibitors also have limited anti-clonal effect and do not impact the rate of progression to the blast phase of disease. The novel therapies detailed in this review not only show promise in ameliorating the symptom burden of MPNs but may be able to alter the natural history of disease.

Role of protein phosphorylation in cell signaling, disease, and the intervention therapy

Protein phosphorylation is an important post-transcriptional modification involving an extremely wide range of intracellular signaling transduction pathways, making it an important therapeutic target for disease intervention. At present, numerous drugs targeting protein phosphorylation have been developed for the treatment of various diseases including malignant tumors, neurological diseases, infectious diseases, and immune diseases. In this review article, we analyzed 303 small-molecule protein phosphorylation kinase inhibitors (PKIs) registered and participated in clinical research obtained in a database named Protein Kinase Inhibitor Database (PKIDB), including 68 drugs approved by the Food and Drug Administration of the United States. Based on previous classifications of kinases, we divided these human protein phosphorylation kinases into eight groups and nearly 50 families, and delineated their main regulatory pathways, upstream and downstream targets. These groups include: protein kinase A, G, and C (AGC) and receptor guanylate cyclase (RGC) group, calmodulin-dependent protein kinase (CaMK) group, CMGC [Cyclin-dependent kinases (CDKs), Mitogen-activated protein kinases (MAPKs), Glycogen synthase kinases (GSKs), and Cdc2-like kinases (CLKs)] group, sterile (STE)-MAPKs group, tyrosine kinases (TK) group, tyrosine kinase-like (TKL) group, atypical group, and other groups. Different groups and families of inhibitors stimulate or inhibit others, forming an intricate molecular signaling regulatory network. This review takes newly developed new PKIs as breakthrough point, aiming to clarify the regulatory network and relationship of each pathway, as well as their roles in disease intervention, and provide a direction for future drug development.

Cutaneous kinase activity correlates with treatment outcomes following PI3K delta inhibition in mice with experimental pemphigoid diseases

Chronic blistering at the skin and/or mucous membranes, accompanied by a varying degree of inflammation, is the clinical hallmark of pemphigoid diseases that impose a major medical burden. Pemphigoid diseases are caused by autoantibodies targeting structural proteins of the epithelial basement membrane. One major pathogenic pathway of skin blistering and inflammation is activation of myeloid cells following Fc gamma receptor-dependent binding to the skin-bound immune complexes. This process requires activation of specific kinases, such as PI3Kδ, which have emerged as potential targets for the treatment of pemphigoid diseases. Yet, it is unknown if global cutaneous kinase activity present in lesional pemphigoid disease correlates with therapeutic effects following treatment with a given target-selective kinase inhibitor. To address this, we here first determined the kinase activity in three different mouse models of pemphigoid diseases: Antibody transfer-induced mucous membrane pemphigoid (MMP), antibody transfer-induced epidermolysis bullosa acquisita (EBA) and immunization-induced EBA. Interestingly, the kinome signatures were different among the three models. More specifically, PI3Kδ was within the kinome activation network of antibody transfer-induced MMP and immunization-induced EBA, but not in antibody transfer-induced EBA. Next, the therapeutic impact of the PI3Kδ-selective inhibitor parsaclisib was evaluated in the three model systems. In line with the kinome signatures, parsaclisib had therapeutic effects in antibody transfer-induced MMP and immunization-induced EBA, but not in autoantibody-induced EBA. In conclusion, kinase activation signatures of inflamed skin, herein exemplified by pemphigoid diseases, correlate with the therapeutic outcomes following kinase inhibition, demonstrated here by the PI3Kδ inhibitor parsaclisib.

An Innovation 10 Years in the Making: The Stories in the Pages of ACS Medicinal Chemistry Letters

Innovation in medicinal chemistry has been at the heart of ACS Medicinal Chemistry Letters since the journal's founding 10 years ago. In his inaugural editorial, Editor-in-Chief Dennis Liotta laid out a vision for the journal to become the "premier international journal for rapid communication of cutting-edge studies," and, after 10 years, it has become exactly that. The great hope of drug discovery scientists is that their innovations will lead to new therapeutics to treat unmet medical needs. In the spirit of innovation and in celebration of the recent 10th anniversary of ACS Med. Chem. Lett., we highlight five therapeutics that were first reported or first comprehensively characterized within ACS Med. Chem. Lett.. This overview also serves to introduce the expansion of the scope of the Innovations article type to include Topical Innovations. With this extension, the journal hopes to provide a forum to showcase concise (rather than comprehensive) reviews of topics that are both timely and of great interest to the medicinal chemistry community. Moreover, these articles will emphasize the next steps to move the field toward new areas of interest in medicinal chemistry. Appropriate topics might include case studies of clinical candidates or approved drugs, new assay technologies in drug discovery, novel target classes, and innovative new approaches towards modulation of human physiology. Since its founding 10 years ago, ACS Med. Chem. Lett. has established itself as a venue for the rapid communication of studies in medicinal chemistry and drug discovery. There have been several drugs and clinical candidates that were first reported or first comprehensively characterized in ACS Med. Chem. Lett. In celebration of the 10th anniversary of ACS Med. Chem. Lett. this Topical Innovations article highlights five of these compounds: Ivosidenib, Siponimod, Glasdegib, Parsaclisib, and Dabrafenib.

PI3K Inhibitors for the Treatment of Chronic Lymphocytic Leukemia: Current Status and Future Perspectives

Phosphoinositide 3-kinases (PI3Ks) signaling regulates key cellular processes, such as growth, survival and apoptosis. Among the three classes of PI3K, class I is the most important for the development, differentiation and activation of B and T cells. Four isoforms are distinguished within class I (PI3Kα, PI3Kβ, PI3Kδ and PI3Kγ). PI3Kδ expression is limited mainly to the B cells and their precursors, and blocking PI3K has been found to promote apoptosis of chronic lymphocytic leukemia (CLL) cells. Idelalisib, a selective PI3Kδ inhibitor, was the first-in-class PI3Ki introduced into CLL treatment. It showed efficacy in patients with del(17p)/TP53 mutation, unmutated IGHV status and refractory/relapsed disease. However, its side effects, such as autoimmune-mediated pneumonitis and colitis, infections and skin changes, limited its widespread use. The dual PI3Kδ/γ inhibitor duvelisib is approved for use in CLL patients but with similar toxicities to idelalisib. Umbralisib, a highly selective inhibitor of PI3Kδ and casein kinase-1ε (CK1ε), was found to be efficient and safe in monotherapy and in combination regimens in phase 3 trials in patients with CLL. Novel PI3Kis are under evaluation in early phase clinical trials. In this paper we present the mechanism of action, efficacy and toxicities of PI3Ki approved in the treatment of CLL and developed in clinical trials.

4-Aminopyrazolopyrimidine scaffold and its deformation in the design of tyrosine and serine/threonine kinase inhibitors in medicinal chemistry

Deformation of the 4-aminopyrazolopyrimidine scaffold in designing small-molecule inhibitors.

PI3K Isoform Immunotherapy for Solid Tumours

Improving the anti-tumour T cell response as a consequence of immunotherapy can result in eradication of tumour burden, however, the majority of patients fail with current treatment regimens and so novel immunotherapies with greater efficacy and improved tolerability are needed. The phosphoinositide-3-kinase (PI3K) family members that are directly involved in cell signalling comprise PI3Kα, PI3Kβ, PI3Kδ and PI3Kγ, with the latter two isoforms expressed primarily by leukocytes. The survival and optimal function of regulatory T cells (Treg) and myeloid-derived suppressor cells (MDSCs) is dependent on PI3Kδ, whereas tumour-associated macrophages (TAMs), use PI3Kγ. Blocking these signalling isoforms can boost development of effective anti-cancer immune responses and result in control of tumour burden. The dependence on different PI3K isoforms in immune cells makes targeting this pathway an attractive approach for tumour immunotherapy. Herein, we discuss how inhibiting specific PI3K isoforms in pro-tumoural Tregs, MDSCS and TAMs can unleash a powerful anti-tumour immune response, driven by CD8+ T cells, capable of controlling tumour burden and consider how the immune response to therapy needs careful investigation, to identify both the correlates of successful treatment and those that impede the generation of robust anti-tumour responses. Furthermore, we review how combination immunotherapy approaches with both PI3K inhibitors and subsequent immune checkpoint blockade can potentiate the efficacy of monotherapy. Finally, we discuss the recent advances in the use of PI3K isoform-specific inhibitors as an immunotherapy for solid tumours in clinical trials.

PI3Kδ Inhibitors as Immunomodulatory Agents for the Treatment of Lymphoma Patients

The development of small molecules able to block specific or multiple isoforms of phosphoinositide 3-kinases (PI3K) has already been an active field of research for many years in the cancer field. PI3Kδ inhibitors are among the targeted agents most extensively studied for the treatment of lymphoma patients and PI3Kδ inhibitors are already approved by regulatory agencies. More recently, it became clear that the anti-tumor activity of PI3K inhibitors might not be due only to a direct effect on the cancer cells but it can also be mediated via inhibition of the kinases in non-neoplastic cells present in the tumor microenvironment. T-cells represent an important component of the tumor microenvironment and they comprise different subpopulations that can have both anti- and pro-tumor effects. In this review article, we discuss the effects that PI3Kδ inhibitors exert on the immune system with a particular focus on the T-cell compartment.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

Discovery of GSK251: A Highly Potent, Highly Selective, Orally Bioavailable Inhibitor of PI3Kδ with a Novel Binding Mode

Optimization of a previously reported lead series of PI3Kδ inhibitors with a novel binding mode led to the identification of a clinical candidate compound 31 (GSK251). Removal of an embedded Ames-positive heteroaromatic amine by reversing a sulfonamide followed by locating an interaction with Trp760 led to a highly selective compound 9. Further optimization to avoid glutathione trapping, to enhance potency and selectivity, and to optimize an oral pharmacokinetic profile led to the discovery of compound 31 (GSK215) that had a low predicted daily dose (45 mg, b.i.d) and a rat toxicity profile suitable for further development.

Development of PI3K inhibitors: Advances in clinical trials and new strategies (Review)

Phosphatidylinositol 3-kinases (PI3Ks) are the family of vital lipid kinases widely distributed in mammalian cells. The overexpression of PI3Ks leads to hyperactivation of the PI3K/AKT/mTOR pathway, which is considered a pivotal pathway in the occurrence and development of tumors. Hence, PI3Ks are viewed as promising therapeutic targets for anti-cancer therapy. To date, some PI3K inhibitors have achieved desired therapeutic effect via inhibiting the activity of PI3Ks or reducing the level of PI3Ks in clinical trials, among which, Idelalisib, Alpelisib and Duvelisib have been approved by the FDA for treatment of ER⁺/HER2^- advanced metastatic breast cancer and refractory chronic lymphocytic leukemia (CLL) and small lymphocytic lymphomas (SLL). This review focuses on the latest advances of PI3K inhibitors with efficacious anticancer activity, which are classified into Pan-PI3K inhibitors, isoform-specific PI3K inhibitors and dual PI3K/mTOR inhibitors based on the isoform affinity. Their corresponding structure characteristics and structures-activity relationship (SAR), together with the progress in the clinical application are mainly discussed. Additionally, the new PI3K inhibitory strategy, such as PI3K degradation agent, for the design of potential PI3K candidates to overcome drug resistance is referred as well.

The PI3Kδ inhibitor parsaclisib ameliorates pathology and reduces autoantibody formation in preclinical models of systemic lupus erythematosus and Sjӧgren's syndrome

Dysregulation of phosphoinositide 3-kinase δ (PI3Kδ) signaling pathway has been implicated in the pathogenesis of inflammatory and autoimmune diseases. Parsaclisib (INCB050465) represents a potent and selective PI3Kδ inhibitor, which is being clinically investigated for treatment of autoimmune hemolytic anemia and hematological malignancies. We characterized the potential of parsaclisib to ameliorate autoimmune mechanisms implicated in the pathophysiology of systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS). Spontaneous mouse models of SLE and SS were utilized to elucidate the efficacy of orally administered parsaclisib on autoreactive B-cell-mediated antibody-driven disease. Parsaclisib significantly reduced disease symptoms and pathology in three distinct mouse models of SLE. Parsaclisib effectively preserved renal function as measured by glomerular filtration rate, abrogated histopathological evidence of nephritis, modulated discrete immune cell subsets, and decreased anti-dsDNA antibody level. Furthermore, parsaclisib demonstrated efficacy in two spontaneous mouse models of SS. Oral parsaclisib treatment ameliorated the severity of salivary gland inflammation and reduced circulating levels of autoantibodies. Parsaclisib mediated improvement of salivary gland inflammation coincided with reduced B-cell activating cytokine (BAFF) in saliva. Transcriptomic analysis of kidney and salivary gland tissues revealed a downregulation in inflammatory gene expression consistent with PI3Kδ pathway inhibition. Parsaclisib reduced autoreactive B-cells and autoantibody levels, and significantly improved nephritis and salivary gland inflammation. These data provide the scientific rationale for PI3Kδ inhibition as a therapeutic strategy for treatment of B-cell-mediated antibody-driven autoimmune diseases.

Projected Dose Optimization of Amino- and Hydroxypyrrolidine Purine PI3Kδ Immunomodulators

The approvals of idelalisib and duvelisib have validated PI3Kδ inhibitors for the treatment for hematological malignancies driven by the PI3K/AKT pathway. Our program led to the identification of structurally distinct heterocycloalkyl purine inhibitors with excellent isoform and kinome selectivity; however, they had high projected human doses. Improved ligand contacts gave potency enhancements, while replacement of metabolic liabilities led to extended half-lives in preclinical species, affording PI3Kδ inhibitors with low once-daily predicted human doses. Treatment of C57BL/6-Foxp3-GDL reporter mice with 30 and 100 mg/kg/day of 3c (MSD-496486311) led to a 70% reduction in Foxp3-expressing regulatory T cells as observed through bioluminescence imaging with luciferin, consistent with the role of PI3K/AKT signaling in Treg cell proliferation. As a model for allergic rhinitis and asthma, treatment of ovalbumin-challenged Brown Norway rats with 0.3 to 30 mg/kg/day of 3c gave a dose-dependent reduction in pulmonary bronchoalveolar lavage inflammation eosinophil cell count.

Optimization of Versatile Oxindoles as Selective PI3Kδ Inhibitors

The 3,3-disubstituted oxindole moiety is a versatile and rigid three-dimensionally shaped scaffold. When engineered with a purine hinge-binding core, exceptionally selective PI3Kδ kinase inhibitors were discovered by exploiting small differences in isoform selectivity pockets. Crystal structures of early lead 2f bound to PI3Kδ and PI3Kα helped rationalize the high selectivity observed with 2f. By attenuating the lypophilicity and metabolic liabilities of an oxindole moiety, we improved the preclinical species PK and solubility and reduced adenosine uptake activity. The excellent potency and kinome selectivity of 7-azaoxindole 4d and spirooxindole 5d, together with a low plasma clearance and good half-life in rat and dog, supported a low once-daily predicted human dose.

Recent developments in anticancer kinase inhibitors based on the pyrazolo[3,4-d]pyrimidine scaffold

Pyrazolo[3,4-d]pyrimidines have become of significant interest for the medicinal chemistry community as a privileged scaffold for the development of kinase inhibitors to treat a range of diseases, including cancer. This fused nitrogen-containing heterocycle is an isostere of the adenine ring of ATP, allowing the molecules to mimic hinge region binding interactions in kinase active sites. Similarities in kinase ATP sites can be exploited to direct the activity and selectivity of pyrazolo[3,4-d]pyrimidines to multiple oncogenic targets through focussed chemical modification. As a result, pharma and academic efforts have succeeded in progressing several pyrazolo[3,4-d]pyrimidines to clinical trials, including the BTK inhibitor ibrutinib, which has been approved for the treatment of several B-cell cancers. In this review, we examine the pyrazolo[3,4-d]pyrimidines currently in clinical trials for oncology patients, as well as those published in the literature during the last 5 years for different anticancer indications.

Non-BRAF Mutant Melanoma: Molecular Features and Therapeutical Implications

Melanoma is one of the most aggressive tumors of the skin, and its incidence is growing worldwide. Historically considered a drug resistant disease, since 2011 the therapeutic landscape of melanoma has radically changed. Indeed, the improved knowledge of the immune system and its interactions with the tumor, and the ever more thorough molecular characterization of the disease, has allowed the development of immunotherapy on the one hand, and molecular target therapies on the other. The increased availability of more performing technologies like Next-Generation Sequencing (NGS), and the availability of increasingly large genetic panels, allows the identification of several potential therapeutic targets. In light of this, numerous clinical and preclinical trials are ongoing, to identify new molecular targets. Here, we review the landscape of mutated non-BRAF skin melanoma, in light of recent data deriving from Whole-Exome Sequencing (WES) or Whole-Genome Sequencing (WGS) studies on melanoma cohorts for which information on the mutation rate of each gene was available, for a total of 10 NGS studies and 992 samples, focusing on available, or in experimentation, targeted therapies beyond those targeting mutated BRAF. Namely, we describe 33 established and candidate driver genes altered with frequency greater than 1.5%, and the current status of targeted therapy for each gene. Only 1.1% of the samples showed no coding mutations, whereas 30% showed at least one mutation in the RAS genes (mostly NRAS) and 70% showed mutations outside of the RAS genes, suggesting potential new roads for targeted therapy. Ongoing clinical trials are available for 33.3% of the most frequently altered genes.

Parsaclisib Is a Next-Generation Phosphoinositide 3-Kinase δ Inhibitor with Reduced Hepatotoxicity and Potent Antitumor and Immunomodulatory Activities in Models of B-Cell Malignancy

The clinical use of first-generation phosphoinositide 3-kinase (PI3K)δ inhibitors in B-cell malignancies is hampered by hepatotoxicity, requiring dose reduction, treatment interruption, and/or discontinuation of therapy. In addition, potential molecular mechanisms by which resistance to this class of drugs occurs have not been investigated. Parsaclisib (INCB050465) is a potent and selective next-generation PI3Kδ inhibitor that differs in structure from first-generation PI3Kδ inhibitors and has shown encouraging anti-B-cell tumor activity and reduced hepatotoxicity in phase 1/2 clinical studies. Here, we present preclinical data demonstrating parsaclisib as a potent inhibitor of PI3Kδ with over 1000-fold selectivity against other class 1 PI3K isozymes. Parsaclisib directly blocks PI3K signaling-mediated cell proliferation in B-cell lines in vitro and in vivo and indirectly controls tumor growth by lessening immunosuppression through regulatory T-cell inhibition in a syngeneic lymphoma model. Diffuse large B-cell lymphoma cell lines overexpressing MYC were insensitive to proliferation blockade via PI3Kδ signaling inhibition by parsaclisib, but their proliferative activities were reduced by suppression of MYC gene transcription. Molecular structure analysis of the first- and next-generation PI3Kδ inhibitors combined with clinical observation suggests that hepatotoxicity seen with the first-generation inhibitors could result from a structure-related off-target effect. Parsaclisib is currently being evaluated in multiple phase 2 clinical trials as a therapy against various hematologic malignancies of B-cell origin (NCT03126019, NCT02998476, NCT03235544, NCT03144674, and NCT02018861). SIGNIFICANCE STATEMENT: The preclinical properties described here provide the mechanism of action and support clinical investigations of parsaclisib as a therapy for B-cell malignancies. MYC overexpression was identified as a resistance mechanism to parsaclisib in DLBCL cells, which may be useful in guiding further translational studies for the selection of patients with DLBCL who might benefit from PI3Kδ inhibitor treatment in future trials. Hepatotoxicity associated with first-generation PI3Kδ inhibitors may be an off-target effect of that class of compounds.

Surgical trauma-induced immunosuppression in cancer: Recent advances and the potential therapies

Surgical resection remains the mainstay treatment for solid cancers, especially for localized disease. However, the postoperative immunosuppression provides a window for cancer cell proliferation and awakening dormant cancer cells, leading to rapid recurrences or metastases. This immunosuppressive status after surgery is associated with the severity of surgical trauma since immunosuppression induced by minimally invasive surgery is less than that of an extensive open surgery. The systemic response to tissue damages caused by surgical operations and the subsequent wound healing induced a cascade alteration in cellular immunity. After surgery, patients have a high level of circulating damage-associated molecular patterns (DAMPs), triggering a local and systemic inflammation. The inflammatory metrics in the immediate postoperative period was associated with the prognosis of cancer patients. Neutrophils provide the first response to surgical trauma, and the production of neutrophil extracellular traps (NETs) promotes cancer progression. Activated macrophage during wound healing presents a tumor-associated phenotype that cancers can exploit for their survival advantage. In addition, the amplification and activation of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) or the elevated programmed death ligand-1 and vascular endothelial growth factor expression under surgical trauma, exacerbate the immunosuppression and favor of the formation of the premetastatic niche. Therapeutic strategies to reduce the cellular immunity impairment after surgery include anti-DAMPs, anti-postoperative inflammation or inflammatory/pyroptosis signal, combined immunotherapy with surgery, antiangiogenesis and targeted therapies for neutrophils, macrophages, MDSCs, and Tregs. Further, the application of enhanced recovery after surgery also has a feasible outcome for postoperative immunity restoration. Overall, current therapies to improve the cellular immunity under the special condition after surgery are relatively lacking. Further understanding the underlying mechanisms of surgical trauma-related immunity dysfunction, phenotyping the immunosuppressive cells, and developing the related therapeutic intervention should be explored.