Seletalisib: Characterization of a Novel, Potent, and Selective Inhibitor of PI3Kδ

PI3Kδ Pathway Dysregulation and Unique Features of Its Inhibition by Leniolisib in Activated PI3Kδ Syndrome and Beyond

The phosphoinositide 3-kinase (PI3K) pathway regulates diverse cellular processes, with finely tuned PI3Kδ activity being crucial for immune cell development and function. Genetic hyperactivation of PI3Kδ causes the inborn error of immunity activated phosphoinositide 3-kinase δ syndrome (APDS). Several PI3Kδ inhibitors have been investigated as treatment options for APDS, but only leniolisib has shown both efficacy and tolerability. In contrast, severe immune-mediated adverse events such as colitis, neutropenia, and hepatotoxicity have been observed with other PI3Kδ inhibitors, particularly those indicated for hematological malignancies. We propose that leniolisib is distinguished from other PI3Kδ inhibitors due to its structure, specific inhibitory properties selectively targeting the δ isoform without overinhibition of the δ or γ isoforms, and the precise match between APDS mechanism of disease and drug mechanism of action.

Discovery of novel pyrido[3,2-d]pyrimidine derivatives as selective and potent PI3Kδ inhibitors

The δ isoform of class I PI3K (PI3Kδ) has been shown as a promising target for the treatment of hematologic malignancies and immune diseases. Herein, a series of pyrido[3,2-d]pyrimidine derivatives were designed, synthesized and evaluated for the preliminary bioactivity. Compared with idelalisib, compound S5 exhibited excellent enzyme activity against PI3Kδ (IC50  = 2.82 nM) and strong antiproliferation activity against SU-DHL-6 cells (IC50  = 0.035 μM). Besides, S5 inhibited the phosphorylation of Akt, which is downstream of PI3Kδ, in concentration-dependent manner. In view of the significant improvement in potency of PI3Kδ and selectivity over other PI3K isoforms, Compound S5 deserved further investigation as a promising PI3Kδ inhibitor.

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.

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.

Design, synthesis and biological evaluation of novel selective PI3Kδ inhibitors containing pyridopyrimidine scaffold

Aim: In our study compounds with pyrido[3,2-d]pyrimidine and pyrido[3,4-d]pyrimidine were designed, synthesized and evaluated for their biological activity against hematologic tumors. Methods: The biological activity of compounds was evaluated by ADP-Glo Luminescence assay, MTT [3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide] assay, western blotting and flow cytometry, respectively. Results: Compounds A1, A5 and A7 containing pyrido[3,2-d]pyrimidine inhibited phosphoinositide 3-kinase-δ (PI3Kδ) at subnanomolar levels and had good δ-isoform selectivity. A1, A5 and A7 showed significant inhibitory effects against SU-DHL-6 cells and effectively inhibited Akt phosphorylation in a good concentration-dependent manner. A7 induced apoptosis and caused cell cycle arrest in SU-DHL-6 cells. Docking studies showed that A1, A5 and A7 bound tightly to PI3Kδ through key hydrogen bonding interactions. Conclusion: This study suggests that employing pyrido[3,2-d]pyrimidine can facilitate the design of novel potent and selective PI3Kδ inhibitors.

Ru-Catalyzed Asymmetric Reductive Amination of Aryl-Trifluoromethyl Ketones for Synthesis of Primary α-(Trifluoromethyl)arylmethylamines

The ruthenium-catalyzed asymmetric reductive amination of aryl-trifluoromethyl ketones affording high value primary α-(trifluoromethyl)arylmethylamines using cheap NH₄OAc as the nitrogen source and H₂ as the reductant is reported. This user-friendly and simple catalytic method tolerates various aromatic functions with electron-withdrawing or -donating substituents at the para- or meta-positions and as well challenging heteroaromatic functions, yielding primary α-(trifluoromethyl)arylmethylamines with excellent chemoselectivities, enantioselectivities, and useful yields (80-97% ee, 51-92% isolated yields). Finally, scalable and concise synthesis of key drug intermediates using this methodology is presented.

Molecular Insight into Drug Resistance Mechanism Conferred by Aberrant PIK3CD Splice Variant in African American Prostate Cancer

Targeting PI3Kδ has emerged as a promising therapy for hematologic and non-hematologic malignancies. Previously, we identified an oncogenic splice variant, PIK3CD-S, conferring Idelalisib resistance in African American (AA) prostate cancer (PCa). In the current study, we employed a comprehensive analysis combining molecular biology, biochemistry, histology, in silico simulation, and in vitro functional assays to investigate the PIK3CD-S expression profiles in PCa samples and to elucidate the drug resistance mechanism mediated by PI3Kδ-S (encoded by PIK3CD-S). The immunohistochemistry, RT-PCR, and Western blot assays first confirmed that PI3Kδ-S is highly expressed in AA PCa. Compared with PCa expressing the full-length PI3Kδ-L, PCa expressing PI3Kδ-S exhibits enhanced drug resistance properties, including a higher cell viability, more antiapoptotic and invasive capacities, and constitutively activated PI3K/AKT signaling, in the presence of PI3Kδ/PI3K inhibitors (Idelalisib, Seletalisib, Wortmannin, and Dactolisib). Molecular docking, ATP-competitive assays, and PI3 kinase assays have further indicated a drastically reduced affinity of PI3Kδ inhibitors with PI3Kδ-S vs. PI3Kδ-L, attributed to the lack of core binding residues in the PI3Kδ-S catalytic domain. Additionally, SRSF2 has been identified as a critical splicing factor mediating exon 20 skipping in PIK3CD pre-mRNA. The inhibition of the SRSF2 activity by SRPIN340 successfully sensitizes AA PCa cells to PI3Kδ inhibitors, suggesting a novel therapeutic option for Idelalisib-resistant tumors.

Current and future treatment in primary Sjögren's syndrome - A still challenging development

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease characterized by sicca symptoms, systemic manifestations and constitutional symptoms substantially diminishing patient's quality of life. In this review, we summarize recent recommendations for management of pSS patients and current clinical studies in pSS addressing unmet medical needs. Expanding knowledge about disease pathogenesis and the introduction of validated outcome measures, such as capturing disease activity (ESSDAI) and patient-reported outcomes (ESSPRI) have shaped recent developments. In contrast, lack of evidence for current treatment options remarkably limits the management of pSS patients as reflected by the 2019 updated EULAR recommendations for management of Sjögren's syndrome. In this context, symptomatic treatment is usually appropriate for sicca symptoms, whereas systemic treatment is reserved for moderate to severe organ manifestations including care by a multidisciplinary team in centers of expertise. Most promising targets for new treatment modalities are based on immunopathological insights and include direct B cell targeting strategies, targeting co-stimulation by CD40/CD40L blocking, inhibition of key cytokine activity (BLyS/BAFF, type I interferon) and intracellular signaling pathways.

The phosphoinositide-3-kinase (PI3K)-delta inhibitor seletalisib impairs monocyte-derived dendritic cells maturation, APC function, and promotes their migration to CCR7 and CXCR4 ligands

PI3K pathway plays a crucial role in dendritic cells (DCs) functions, as it regulates different cellular processes, such as maturation and cytokines production. However, the specific role of PI3K p110δ isoform in human DCs has not been thoroughly addressed. In this study, we analyze the effects of seletalisib, a potent and specific inhibitor of PI3K p110δ, on phenotype and antigen-presenting functions of monocyte-derived DCs undergone maturation via LPS. Seletalisib treatment reduced membrane HLA-DR as well as CD83 and CD40 costimulatory molecules, whereas CD80 and CD86 expression was only partially affected. Additionally, DCs cultures showed reduced TNF-α, IL-10, and IL-12 and increased IL-23 secretion levels. This resulted in a reduced capacity of DCs to prime allogeneic T cells, with a strong decrease of Th1 differentiation. On the other hand, PI3K p110δ inhibitor seletalisib increased CXCR4 and CCR7 expression and augmented the DCs migration toward CCL19 and CXCL12 ligands. At molecular level, inhibition of PI3K p110δ isoform by seletalisib significantly down-regulated the phosphorylation of AKT and other downstream signaling molecules, such as ribosomal protein S6, 4E-BP1, and NF-κB p65. In contrast, seletalisib did not affect p38 MAP kinase phosphorylation or TLR-associated adapter molecule TIRAP in DCs. Our results indicate that PI3K p110δ can serve as an important regulatory signal for DCs, and selective inhibition of PI3K p110δ isoform by seletalisib could be used for the prevention of exaggerated and harmful immune responses occurring in pathologic conditions, such as autoimmune disorders.

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.

PI3Kδ Sustains Keratinocyte Hyperproliferation and Epithelial Inflammation: Implications for a Topically Druggable Target in Psoriasis

The phosphatidylinositol 3-kinase (PI3K)-dependent signaling pathway is aberrantly activated in psoriatic lesions and contributes to disease pathogenesis. Among PI3Ks enzymes, PI3Kα, β, and δ isoforms are known to bind the p85 regulatory subunit and mediate activation of AKT and other downstream effectors. In this study, we deepened our understanding of the expression and function of PI3Kδ in skin lesions of patients affected by psoriasis. For the first time, we found that PI3Kδ is overexpressed in psoriatic plaques, and its expression is not only confined to infiltrating immune cells but also accumulates in proliferating keratinocytes of the epidermal basal layer. We investigated the function of PI3Kδ in psoriatic skin by evaluating the impact of seletalisib, a newly developed selective PI3Kδ inhibitor, in both in vitro and in vivo experimental models of psoriasis. Of note, we found that PI3Kδ sustains keratinocyte hyperproliferation and impaired terminal differentiation induced by IL-22, as well as induces epithelial inflammation and resistance to apoptosis mediated by TNF-α in human keratinocytes. Mechanistically, PI3Kδ promotes PDK1 phosphorylation and signals through AKT-dependent or -independent pathways. It is worth mentioning that PI3Kδ inhibition by seletalisib attenuates the severity of psoriasiform phenotype induced in the Imiquimod-induced mouse model of psoriasis by restoring the physiological proliferation and differentiation programs in epidermal keratinocytes and contrasting the cutaneous inflammatory responses. Therefore, we suggest PI3Kδ as a potential topically druggable target in psoriasis and skin diseases characterized by epidermal hyperproliferation and skin inflammation.

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.

A phase 2 randomized, double-blind, placebo-controlled, proof-of-concept study of oral seletalisib in primary Sjögren's syndrome

OBJECTIVES

This phase 2 proof-of-concept study (NCT02610543) assessed efficacy, safety and effects on salivary gland inflammation of seletalisib, a potent and selective PI3Kδ inhibitor, in patients with moderate-to-severe primary Sjögren's syndrome (PSS).

METHODS

Adults with PSS were randomized 1:1 to seletalisib 45 mg/day or placebo, in addition to current PSS therapy. Primary end points were safety and tolerability and change from baseline in EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) score at week 12. Secondary end points included change from baseline at week 12 in EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI) score and histological features in salivary gland biopsies.

RESULTS

Twenty-seven patients were randomized (seletalisib n = 13, placebo n = 14); 20 completed the study. Enrolment challenges led to early study termination with loss of statistical power (36% vs 80% planned). Nonetheless, a trend for improvement in ESSDAI and ESSPRI [difference vs placebo: -2.59 (95% CI: -7.30, 2.11; P=0.266) and -1.55 (95% CI: -3.39, 0.28), respectively] was observed at week 12. No significant changes were seen in saliva and tear flow. Serious adverse events (AEs) were reported in 3/13 of patients receiving seletalisib vs 1/14 for placebo and 5/13 vs 1/14 discontinued due to AEs, respectively. Serum IgM and IgG concentrations decreased in the seletalisib group vs placebo. Seletalisib demonstrated efficacy in reducing size and organisation of salivary gland inflammatory foci and in target engagement, thus reducing PI3K-mTOR signalling compared with placebo.

CONCLUSION

Despite enrolment challenges, seletalisib demonstrated a trend towards clinical improvement in patients with PSS. Histological analyses demonstrated encouraging effects of seletalisib on salivary gland inflammation and organisation.

TRIAL REGISTRATION

https://clinicaltrials.gov, NCT02610543.

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.

Phosphatidylinositol 3-kinase (PI3K) inhibitors: a recent update on inhibitor design and clinical trials (2016-2020)

Introduction: The phosphatidylinositol 3-kinase/protein kinase-B/mammalian target of rapamycin (PI3K/AKT/mTOR) signaling pathway plays a central role in regulating cell growth and proliferation and thus has been considered as effective anticancer drug targets. Many PI3K inhibitors have been developed and progressed to various stages of clinical trials, and some have been approved as anticancer treatment. In this review, we discuss the drug design and clinical development of PI3K inhibitors over the past 4 years. We review the selectivity and potency of 47 PI3K inhibitors. Structural determinants for increasing selectivity toward PI3K subtype-selectivity or mutant selectivity are discussed. Future research direction and current clinical development in combination therapy of inhibitors involved in PI3Ks are also discussed.Area covered: This review covers clinical trial reports and patent literature on PI3K inhibitors and their selectivity published between 2016 and 2020.Expert opinion: To PI3Kα mutants (E542K, E545K, and H1047R), it is highly desirable to design and develop mutant-specific PI3K inhibitors. It is also necessary to develop subtype-selective PI3Kα inhibitors to minimize toxicity. To reduce drug resistance and to improve efficacy, future studies should include combination therapy of PI3K inhibitors with existing anticancer drugs from different pathways.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part I): Kinase inhibitors

Autoimmune and inflammatory diseases place a huge burden on the healthcare system. Small molecule (SM) therapeutics provide much needed complementary treatment options for these diseases. This digest series highlights the latest progress in the discovery and development of safe and efficacious SMs to treat autoimmune and inflammatory diseases with each part representing a class of SMs, namely: 1) protein kinases; 2) nucleic acid-sensing pathways; and 3) soluble ligands and receptors on cell surfaces. In this first part of the series, the focus is on kinase inhibitors that emerged between 2018 and 2020, and which exhibit increased target and tissue selectivity with the aim of increasing their therapeutic index.

Discovery of novel quinazoline derivatives as potent PI3Kδ inhibitors with high selectivity

Inhibition of PI3Kδ has been proved to be an efficacious strategy for the treatment of hematological malignancies where the PI3K/Akt signaling pathway is hyperactive. Herein, a series of quinazoline derivatives bearing acrylamide fragment were prepared using skeleton-deconstruction strategy. The preliminary bioactivity evaluation resulted in the discovery of lead compound 15c. Compound 15c exhibited excellent enzyme activity against PI3Kδ (IC₅₀ = 27.5 nM) compared with BEZ235 as well as the significant anti-proliferation activities. With the high selectivity over other PI3K isoforms and potent effects on PI3K/Akt pathway, 15c can be identified as a promising PI3Kδ inhibitor worthy of further profiling.

Seletalisib for Activated PI3Kδ Syndromes: Open-Label Phase 1b and Extension Studies

Mutations in two genes can result in activated PI3Kδ syndrome (APDS), a rare immunodeficiency disease with limited therapeutic options. Seletalisib, a potent, selective PI3Kδ inhibitor, was evaluated in patients with APDS1 and APDS2. In the phase 1b study (European Clinical Trials Database 2015-002900-10) patients with genetic and clinical confirmation of APDS1 or APDS2 received 15-25 mg/d seletalisib for 12 wk. Patients could enter an extension study (European Clinical Trials Database 2015-005541). Primary endpoints were safety and tolerability, with exploratory efficacy and immunology endpoints. Seven patients (median age 15 years; APDS1 n = 3; APDS2 n = 4) received seletalisib; five completed the phase 1b study. For the extension study, four patients entered, one withdrew consent (week 24), three completed ≥84 wk of treatment. In the phase 1b study, patients had improved peripheral lymphadenopathy (n = 2), lung function (n = 1), thrombocyte counts (n = 1), and chronic enteropathy (n = 1). Overall, effects were maintained in the extension. In the phase 1b study, percentages of transitional B cells decreased, naive B cells increased, and senescent CD8 T cells decreased (human cells); effects were generally maintained in the extension. Seletalisib-related adverse events occurred in four of seven patients (phase 1b study: hepatic enzyme increased, dizziness, aphthous ulcer, arthralgia, arthritis, increased appetite, increased weight, restlessness, tendon disorder, and potential drug-induced liver injury) and one of four patients had adverse events in the extension (aphthous ulcer). Serious adverse events occurred in three of seven patients (phase 1b study: hospitalization, colitis, and potential drug-induced liver injury) and one of four patients had adverse events in the extension (stomatitis). Patients with APDS receiving seletalisib had improvements in variable clinical and immunological features, and a favorable risk-benefit profile was maintained for ≤96 wk.

Research advances on selective phosphatidylinositol 3 kinase δ (PI3Kδ) inhibitors

PI3Kδ in B cells mediates antigen receptor signaling and promote neutrophil chemotaxis. The activation of PI3Kδ can cause mast cell maturation and degranulation, myeloid cell dysfunction, and cytokine release. As a key signal molecule, PI3Kδ interacts with the lipid binding domain of a variety of cellular proteins as a secondary messenger, ultimately affecting a series of significant cellular pathways in disease pathology. Therefore, many research organizations and pharmaceutical companies have studied it to develop effectively selective PI3Kδ inhibitors as therapeutics. This review summarizes research advances in varying chemical classes of selective PI3Kδ inhibitors and the structure-activity relationship, and it mainly focuses on the propeller- versus flat-type class of inhibitors.

Preclinical characterization of CPL302-253, a selective inhibitor of PI3Kδ, as the candidate for the inhalatory treatment and prevention of Asthma

Asthma is a common chronic inflammatory disease. Although effective asthma therapies are available, part of asthmatic population do not respond to these treatment options. In this work we present the result of development of CPL302-253 molecule, a selective PI3Kδ inhibitor. This molecule is intended to be a preclinical candidate for dry powder inhalation in asthma treatment. Studies we performed showed that this molecule is safe and effective PI3Kδ inhibitor that can impact many immune functions. We developed a short, 15-day HDM induced asthma mouse model, in which we showed that CPL302-253 is able to block inflammatory processes leading to asthma development in vivo.

Selective targeting of PI3Kδ suppresses human IL-17-producing T cells and innate-like lymphocytes and may be therapeutic for IL-17-mediated diseases

The delta isoform of phosphoinositide 3-kinase (PI3Kδ) regulates various lymphocyte functions. Considering the key pro-inflammatory role of IL-17A and IL-17F cytokines in psoriasis and spondyloarthritis (SpA), we investigated the potential of PI3Kδ blockade to suppress IL-17A, IL-17F and associated pro-inflammatory cytokines that could synergize with IL-17A and IL-17F. Using in vitro studies with primary human cells and ex vivo studies with inflamed target tissues, we assessed if seletalisib, a selective PI3Kδ inhibitor, suppresses cytokine production by T cells and innate-like lymphocytes, and if seletalisib modulates the inflammatory responses in stromal cell populations in psoriasis (human dermal fibroblasts (HDF)) and SpA (fibroblast-like synoviocytes (FLS)). In vitro, seletalisib inhibited the production of pro-inflammatory cytokines, including IL-17A and IL-17F, from peripheral blood mononuclear cells (PBMCs), T helper 17 (Th17) cells as well as γδ-T cells and mucosal-associated invariant T cells. This inhibition resulted in decreased inflammatory activation of HDF in co-culture systems. Seletalisib was also efficacious in inhibiting SpA PBMCs and synovial fluid mononuclear cells (SFMCs) from producing pro-inflammatory cytokines. Furthermore, supernatant derived from cultured seletalisib-treated Th17 cells showed reduced potency for activating inflammatory responses from cultured SpA FLS and decreased their osteogenic differentiation capacity. Finally, analysis of inflamed SpA synovial tissue biopsies revealed activation of the PI3K-Akt-mTOR pathway. We observed that ex vivo seletalisib treatment of inflamed synovial tissue reduced IL-17A and IL-17F expression. Collectively, inhibition of PI3Kδ reduces the production of pro-inflammatory cytokines from IL-17-producing adaptive and innate-like lymphocytes and thereby inhibits downstream inflammatory and tissue remodeling responses. PI3Kδ-targeting may therefore represent a novel therapeutic avenue for the treatment of IL-17-mediated chronic inflammatory diseases such as psoriasis and SpA.

Immunological characterization of HM5023507, an orally active PI3Kδ/γ inhibitor

Phosphoinositide 3-kinases, delta (PI3Kδ) and gamma (PI3Kγ) are enriched in immune cells and regulate the development and function of innate and adaptive immunity. Dual PI3Kδγ inhibitors are considered high value targets for their potential to treat a variety of immune-mediated diseases, but their discovery has been challenging. Here we describe the preclinical pharmacology of HM5023507, an orally active dual inhibitor of δγ isoforms in immune signaling. HM5023507 inhibited PI3Kδ and PI3Kγ isoforms with greater than 100-fold selectivity against PI3Kα and PI3Kβ in recombinant enzymatic assays and in primary human immune cells with an exquisite selectivity against other targets. HM5023507 attenuated the PI3Kδ/γ signaling in human basophils (IC50: 42/340 nmol/L; selectivity ratio ~1:8). HM5023507 attenuated the activation and function of human B and T cells, Th17 differentiation of CD4 T cells in the blood of healthy donors and rheumatoid arthritis patients, and cytokine and IgG production in human T and B cell cocultures, in vitro. Orally dosed HM5023507 attenuated PI3K δ/γ-mediated immune signaling in the rat in a dose-related manner. In addition, HM5023507 inhibited semiestablished collagen-induced arthritic inflammation in the rats (ED50 of 0.25mg/kg, p.o. BID or 0.5 mg/kg, QD, AUC: 1422 ng/mL*h), improved histopathology- and micro-computed tomography (µCT)-based indices of joint damage, bone destruction, and attenuated the levels of anti-collagen antibody, with an overall anti-inflammatory profile matching that of a TNFα neutralizing antibody. The PI3K δγ inhibitory profile of HM5023507 and its selectivity make it a useful tool to further delineate immunobiology of dual PI3K δγ targeting.

Role of P-glycoprotein in the brain disposition of seletalisib: Evaluation of the potential for drug-drug interactions

Seletalisib is an orally bioavailable selective inhibitor of phosphoinositide 3-kinase delta (PI3Kδ) in clinical development for the treatment of immune-mediated inflammatory diseases. The present study investigated the role of P-gp in seletalisib disposition, especially brain distribution, and the associated risks of interactions. Seletalisib was found to be actively transported by rodent and human P-gp in vitro (transfected LLC-PK1 cells; K_m of ca. 20 µM), with minimal or no affinity for the other tested transporters. A distribution study in knockout rats (single oral dosing at 750 mg kg^-1) showed that P-gp restricts the brain disposition of seletalisib while having minimal effect on its intestinal absorption. Restricted brain penetration was also observed in cynomolgus monkeys (single oral dosing at 30 mg kg^-1) using brain microdialysis and cerebrospinal fluid sampling (K_p,uu of 0.09 and 0.24, respectively). These findings opened the question of potential pharmacokinetic interaction between seletalisib and P-gp inhibitors. In vitro, CsA inhibited the active transport of seletalisib with an IC₅₀ of 0.13 µM. In rats, co-administration of high doses of CsA (bolus iv followed by continuous infusion) increased the brain distribution of seletalisib (single oral dosing at 5 mg kg^-1). The observed data were found aligned with those predicted by in vitro-in vivo extrapolation. Based on the same extrapolation method combined with literature data, only very few P-gp inhibitors (i.e. CsA, quinine, quinidine) were predicted to increase the brain disposition of seletalisib in the clinical setting (maximal 3-fold changes).

PI3Kδ inhibitors for the treatment of cancer: a patent review (2015-present)

Introduction: PI3Kδ is an important subtype of PI3K kinases, which is mainly expressed in leukocytes and plays an important role in the proliferation, differentiation, maturation and self-reaction of B cells. It is an effective target in the treatment of hematological malignancies and autoimmune diseases such as rheumatoid arthritis. Therefore, many pharmaceutical companies and research institutions have focused on the PI3Kδ subtype in an attempt to develop potent and selective PI3Kδ inhibitors.Areas covered: This review aims to provide an overview of the patented selective PI3Kδ inhibitors in treating cancer from 2015 to present.Expert opinion: Due to the importance of PI3Kδ, the development of selective PI3Kδ inhibitors for the treatment of hematoma and autoimmune diseases is expected. On 23 July 2014, the world's first selective PI3Kδ inhibitor, idelalisib, was approved by the FDA for the treatment of CLL, FL and SLL. Moreover, there are still many small molecule selective PI3Kδ inhibitors at different stages of development. The future research effort for development of PI3Kδ inhibitors is to manage the toxicity and lower the side-effects.

Discovery, Optimization, and Evaluation of Potent and Highly Selective PI3Kγ-PI3Kδ Dual Inhibitors

An electronic density model was developed and used to identify a novel pyrrolotriazinone replacement for a quinazolinone, a commonly used moiety to impart selectivity in inhibitors for PI3Kγ and PI3Kδ. Guided by molecular docking, this new specificity piece was then linked to the hinge-binding region of the inhibitor using a novel cyclic moiety. Further structure-activity relationship optimization around the hinge region led to the discovery of candidate 26, a highly potent and selective PI3Kγ-PI3Kδ dual inhibitor with favorable drug metabolism and pharmacokinetic properties in preclinical species.

Conformationally restricted quinazolone derivatives as PI3Kδ-selective inhibitors: the design, synthesis and biological evaluation

A series of structurally novel quinazolone-based PI3Kδ-selective inhibitors were designed and synthesized via the approach of conformational restriction. The majority of them exhibited two-digit to single-digit nanomolar IC50 values against PI3Kδ, along with low micromolar to submicromolar GI50 values against human malignant B-cell line SU-DHL-6. The representative compound, with the most potent PI3Kδ inhibitory activity (IC50 = 6.3 nM) and anti-proliferative activity (GI50 = 0.21 μM) in this series, was further evaluated for its PI3Kδ selectivity, capability to down-regulate PI3K signaling in SU-DHL-6 cells, in vitro metabolic stability, and pharmacokinetic (PK) properties. The experimental results illustrated that this compound, as a promising lead, merits extensive structural optimization for exploring novel PI3Kδ-selective inhibitors as clinical candidates.

Discovery of Potent, Efficient, and Selective Inhibitors of Phosphoinositide 3-Kinase δ through a Deconstruction and Regrowth Approach

A deconstruction of previously reported phosphoinositide 3-kinase δ (PI3Kδ) inhibitors and subsequent regrowth led to the identification of a privileged fragment for PI3Kδ, which was exploited to deliver a potent, efficient, and selective lead series with a novel binding mode observed in the PI3Kδ crystal structure.

Phosphatidylinositol 3-kinase delta pathway: a novel therapeutic target for Sjögren's syndrome

Background

The phosphatidylinositol 3-kinase delta isoform (PI3Kδ) belongs to an intracellular lipid kinase family that regulate lymphocyte metabolism, survival, proliferation, apoptosis and migration and has been successfully targeted in B-cell malignancies. Primary Sjögren’s syndrome (pSS) is a chronic immune-mediated inflammatory disease characterised by exocrine gland lymphocytic infiltration and B-cell hyperactivation which results in systemic manifestations, autoantibody production and loss of glandular function. Given the central role of B cells in pSS pathogenesis, we investigated PI3Kδ pathway activation in pSS and the functional consequences of blocking PI3Kδ in a murine model of focal sialoadenitis that mimics some features of pSS.

Methods and results

Target validation assays showed significant expression of phosphorylated ribosomal protein S6 (pS6), a downstream mediator of the phosphatidylinositol 3-kinase delta (PI3Kδ) pathway, within pSS salivary glands. pS6 distribution was found to co-localise with T/B cell markers within pSS aggregates and the CD138+ plasma cells infiltrating the glands. In vivo blockade of PI3Kδ activity with seletalisib, a PI3Kδ-selective inhibitor, in a murine model of focal sialoadenitis decreased accumulation of lymphocytes and plasma cells within the glands of treated mice in the prophylactic and therapeutic regimes. Additionally, production of lymphoid chemokines and cytokines associated with ectopic lymphoneogenesis and, remarkably, saliva flow and autoantibody production, were significantly affected by treatment with seletalisib.

Conclusion

These data demonstrate activation of PI3Kδ pathway within the glands of patients with pSS and its contribution to disease pathogenesis in a model of disease, supporting the exploration of the therapeutic potential of PI3Kδ pathway inhibition in this condition.