Selective inhibitors of phosphoinositide 3-kinase delta: modulators of B-cell function with potential for treating autoimmune inflammatory diseases and B-cell malignancies

PI3Kδ and mTOR dual inhibitors: Design, synthesis and anticancer evaluation of 3-substituted aminomethylquinoline analogues

Phosphatidylinositide-3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) have recently been identified as potential cancer targets. In our work, a new family of quinoline analogues was designed, developed, and evaluated as dual inhibitors of PI3Kδ/mTOR. The preliminary biological activity analysis led to the discovery of the lead compounds 5h and 5e. Compounds 5h and 5e exhibited excellent anti-tumor potency with IC50 of 0.26 µM and 0.34 µM against Ramos cells, respectively. Importantly, based on the enzymatic activity assay results, compounds 5h and 5e were identified as dual inhibitors of PI3Kδ and mTOR, with IC50 values of 0.042 µM and 0.056 µM for PI3Kδ and 0.059 µM and 0.073 µM for mTOR, respectively. Furthermore, these compounds showed superior selectivity for blocking PI3Kδ compared to other PI3K isoforms (α, β, and γ), supporting the concept of developing inhibitors that specifically target PI3Kδ/mTOR. The most effective compound 5h was chosen for additional biological testing. At a low dose of 0.5 µM, a western blot investigation confirmed the anticancer effects by inhibiting the PAM cascade, which in turn reduced downstream biomarkers pAkt (Ser473), pAkt (Thr308), and pRPS6 (Ser235/236). Furthermore, it increased apoptosis at the early (10.03 times) and late (17.95 times) stages in the Annexin-V assay as compared to the standard. In addition, the expression of p53, caspase-3, caspase-9, and the Bax/BCl-2 ratio were all significantly increased by compound 5h in the ELISA assay. Based on these results, it appears that 5h may activate the intrinsic apoptosis pathway, which in turn triggers cell death. Furthermore, the anticancer effects could be attributed to the inhibition of PI3Kδ/mTOR, as shown by docking interactions. Lastly, it demonstrated improved in vitro metabolic stability and passed the in silico ADMET/drug-likeness test. This profile recommends 5h for future in vivo PK-PD and efficacy investigations in animal cancer models.

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.

Evaluation of the cardiac safety of parsaclisib, a selective PI3Kδ inhibitor, in patients with previously treated B-cell malignancies: Results from the CITADEL-101 study

Parsaclisib, a potent and selective phosphatidylinositol 3 kinase δ inhibitor, has been investigated for the treatment of B-cell malignancies and studied in patients with autoimmune diseases and myelofibrosis. The CITADEL-101 study (NCT02018861) assessed safety, tolerability, and preliminary efficacy of parsaclisib in patients with relapsed or refractory non-Hodgkin lymphoma. This study evaluated the cardiac safety of parsaclisib as monotherapy based on data from 72 patients enrolled in the CITADEL-101 study. Time-matched pharmacokinetic and ECG measurements were collected at specified times for 69 patients receiving monotherapy in doses of 5, 10, 15, 20, 30, and 45 mg once daily. Based on the categorical outlier analysis, no dose-dependent effect was observed on the incidence of outliers in QT interval corrected for heart rate (HR) by Fridericia's method (QTcF), HR, or cardiac conduction. Based on central tendency analysis, the least square means (LSMs) (90% confidence interval [CI]) of ΔQTcF from the central tendency analysis ranged from -6.83 (-18.8 to 5.19) to 4.75 ms (0.410-9.09) across dose groups (below 20 ms, the threshold of large QT effects) and was not considered dose dependent. Moreover, the LSMs of ΔHR, ΔPR interval, and ΔQRS interval were minor. From the concentration-ΔQTcF analyses, the predicted ΔQTcF (90% CI) for all dose levels was between 0.365 (-1.75 to 2.48) and 7.87 ms (0.921-14.8), with the highest upper limit of CIs well below 20 ms, and therefore, a large QT/QTc effect was ruled out up to the highest dose level (45 mg) investigated. Overall, parsaclisib at the dose ranges studied did not reveal concentration-dependent effects on change in QTcF and did not have a significant effect on HR or cardiac conduction.

A review of prophylactic regimens to prevent invasive fungal infections in hematology patients undergoing chemotherapy or stem cell transplantation

INTRODUCTION

The recent introduction of targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors, and immunotherapies has improved the cure rate of hematologic patients. The implication of personalized treatment on primary antifungal prophylaxis will be discussed.

AREAS COVERED

We reviewed the literature for clinical trials reporting the rate of invasive fungal infections during targeted and cellular therapies and stem cell transplant, and the most recent international guidelines for primary antifungal prophylaxis.

EXPERT OPINION

As the use of personalized therapies is growing, the risk of invasive fungal infection has emerged in various clinical settings. Therefore, it is possible that the use of mold-active antifungal prophylaxis would spread in the next years and the risk of breakthrough infections would increase. The introduction of new antifungal agents in the clinical armamentarium is expected to reduce clinical unmet needs concerning the management of primary antifungal prophylaxis and improve outcome of patients.

Type 1 diabetes and inborn errors of immunity: Complete strangers or 2 sides of the same coin?

Type 1 diabetes (T1D) is a polygenic disease and does not follow a mendelian pattern. Inborn errors of immunity (IEIs), on the other hand, are caused by damaging germline variants, suggesting that T1D and IEIs have nothing in common. Some IEIs, resulting from mutations in genes regulating regulatory T-cell homeostasis, are associated with elevated incidence of T1D. The genetic spectrum of IEIs is gradually being unraveled; consequently, molecular pathways underlying human monogenic autoimmunity are being identified. There is an appreciable overlap between some of these pathways and the genetic variants that determine T1D susceptibility, suggesting that after all, IEI and T1D are 2 sides of the same coin. The study of monogenic IEIs with a variable incidence of T1D has the potential to provide crucial insights into the mechanisms leading to T1D. These insights contribute to the definition of T1D endotypes and explain disease heterogeneity. In this review, we discuss the interconnected pathogenic pathways of autoimmunity, β-cell function, and primary immunodeficiency. We also examine the role of environmental factors in disease penetrance as well as the circumstantial evidence of IEI drugs in preventing and curing T1D in individuals with IEIs, suggesting the repositioning of these drugs also for T1D therapy.

Tuning the Biological Activity of PI3Kδ Inhibitor by the Introduction of a Fluorine Atom Using the Computational Workflow

As a member of the class I PI3K family, phosphoinositide 3-kinase δ (PI3Kδ) is an important signaling biomolecule that controls immune cell differentiation, proliferation, migration, and survival. It also represents a potential and promising therapeutic approach for the management of numerous inflammatory and autoimmune diseases. We designed and assessed the biological activity of new fluorinated analogues of CPL302415, taking into account the therapeutic potential of our selective PI3K inhibitor and fluorine introduction as one of the most frequently used modifications of a lead compound to further improve its biological activity. In this paper, we compare and evaluate the accuracy of our previously described and validated in silico workflow with that of the standard (rigid) molecular docking approach. The findings demonstrated that a properly fitted catalytic (binding) pocket for our chemical cores at the induced-fit docking (IFD) and molecular dynamics (MD) stages, along with QM-derived atomic charges, can be used for activity prediction to better distinguish between active and inactive molecules. Moreover, the standard approach seems to be insufficient to score the halogenated derivatives due to the fixed atomic charges, which do not consider the response and indictive effects caused by fluorine. The proposed computational workflow provides a computational tool for the rational design of novel halogenated drugs.

In vitro and in vivo metabolic profiling of PD105, a PI3Kδ inhibitor, using UHPLC-Q-Exactive plus-MS

PD105, a PI3Kδ inhibitor, is a candidate for the treatment of rheumatoid arthritis. This study aims to identify the metabolic profiling in vitro and in vivo by UHPLC-Q-Exactive Plus-MS.The in vitro metabolism of PD105 was studied by mouse liver microsomes and hepatocytes, while the in vivo metabolic profiling was obtained from mouse plasma, urine, and faeces. A total of 20 metabolites were tentatively identified based on accurate mass, fragment pathways, and characteristic fragment ions, including 4 in vitro and 20 in vivo.The proposed metabolic pathways of PD105 showed that there were 18 phase I metabolites and 2 phase II metabolites. The phase I metabolic pathways included oxidation, hydration, desaturation and oxidative dechlorination, while the phase II metabolic reactions were mainly methylation and arginine conjugation. Among them, oxidation was the main metabolic pathway of PD105.The comprehensive metabolic profiling contributed to further elucidation of pharmacological action and mechanism of PD105.

Construction of molecular subgroups in childhood systemic lupus erythematosus using bioinformatics

BACKGROUND

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder. In patients with childhood SLE (cSLE), the onset of the disease occurs before 18 years of age and accounts for a high proportion of childhood autoimmune diseases. Adult SLE and cSLE differ in terms of clinical manifestations, gene expression profiles, and treatment. Because current diagnostic methods do not meet clinical requirements, researchers currently use transcriptome analysis to investigate the characteristics of the cSLE genome. In the present study, we used bioinformatics methods to genotype cSLE and identify potential therapeutic targets.

METHODS

The transcriptomes of 952 patients with cSLE and 94 normal controls were obtained from the Gene Expression Omnibus using unsupervised class learning to determine the genotypes in the microarray dataset, and the clinical characteristics, differentially expressed genes, and biological characteristics of the subtypes were analyzed.

RESULTS

Patients with cSLE were accordingly classified into three subgroups. Subgroup I was associated with lupus nephritis, female patients, and a high SLE disease activity index, and the disease in this subgroup was more severe than that in other subgroups. The SLE disease activity index in subgroup II was low; this subgroup may be related to lupus vasculitis. Subgroup III mostly included male patients and was associated with neuropsychiatric manifestations of lupus.

CONCLUSION

We divided patients with cSLE into three subgroups with different characteristics based on transcriptome data. Our findings provide molecular evidence for future diagnosis and individualized treatment of cSLE.

Real-life efficacy and safety of idelalisib in 55 double-refractory follicular lymphoma patients

Idelalisib, a reversible inhibitor of PI3Kδ (phosphoinositide-3 kinase delta), showed remarkable activity in the phase II DELTA trial, leading to its approval by the European Medicines Agency (EMA) in patients with relapsed/refractory (R/R) follicular lymphoma (FL). However, real-life data on idelalisib are scarce. We treated 55 double-refractory FL patients with idelalisib in a real-life setting. With a median exposure to idelalisib of 10 months (range 1-43), overall response rate was 73%, the highest ever reported. Non-haematological toxicities were mild and manageable. At 12 months, 80% of patients were alive, and 72% disease-free. The efficacy and safety of idelalisib was confirmed in a real-life setting.

Design, Synthesis, and Development of pyrazolo[1,5-a]pyrimidine Derivatives as a Novel Series of Selective PI3Kδ Inhibitors: Part I—Indole Derivatives

Phosphoinositide 3-kinase δ (PI3Kδ), a member of the class I PI3K family, is an essential signaling biomolecule that regulates the differentiation, proliferation, migration, and survival of immune cells. The overactivity of this protein causes cellular dysfunctions in many human disorders, for example, inflammatory and autoimmune diseases, including asthma or chronic obstructive pulmonary disease (COPD). In this work, we designed and synthesized a new library of small-molecule inhibitors based on indol-4-yl-pyrazolo[1,5-a]pyrimidine with IC50 values in the low nanomolar range and high selectivity against the PI3Kδ isoform. CPL302253 (54), the most potent compound of all the structures obtained, with IC50 = 2.8 nM, is a potential future candidate for clinical development as an inhaled drug to prevent asthma.

A nonneglectable stereochemical factor in drug development: Atropisomerism

Chirality is one of the key factors affecting the medicinal efficacy of compounds. In addition to central chirality, sterically hindered chiral axes commonly appear in drugs and the resulting chirality is known as atropisomerism. With developments in medicinal chemistry, atropisomerism has attracted increasing attention. This review discusses the classification, biological activity, pharmacokinetics, toxicity and side effects of atropisomers, and can serve as a reference in the research and development of potential chiral drugs.

Design, Synthesis, and Development of Pyrazolo[1,5-a]pyrimidine Derivatives as a Novel Series of Selective PI3Kδ Inhibitors: Part II—Benzimidazole Derivatives

Phosphoinositide 3-kinase (PI3K) is the family of lipid kinases participating in vital cellular processes such as cell proliferation, growth, migration, or cytokines production. Due to the high expression of these proteins in many human cells and their involvement in metabolism regulation, normal embryogenesis, or maintaining glucose homeostasis, the inhibition of PI3K (especially the first class which contains four subunits: α, β, γ, δ) is considered to be a promising therapeutic strategy for the treatment of inflammatory and autoimmune diseases such as systemic lupus erythematosus (SLE) or multiple sclerosis. In this work, we synthesized a library of benzimidazole derivatives of pyrazolo[1,5-a]pyrimidine representing a collection of new, potent, active, and selective inhibitors of PI3Kδ, displaying IC50 values ranging from 1.892 to 0.018 μM. Among all compounds obtained, CPL302415 (6) showed the highest activity (IC50 value of 18 nM for PI3Kδ), good selectivity (for PI3Kδ relative to other PI3K isoforms: PI3Kα/δ = 79; PI3Kβ/δ = 1415; PI3Kγ/δ = 939), and promising physicochemical properties. As a lead compound synthesized on a relatively large scale, this structure is considered a potential future candidate for clinical trials in SLE treatment.

Development of New Drugs for Autoimmune Hemolytic Anemia

Autoimmune hemolytic anemia (AIHA) is a rare disorder characterized by the autoantibody-mediated destruction of red blood cells, and treatments for it still remain challenging. Traditional first-line immunosuppressive therapy, which includes corticosteroids and rituximab, is associated with adverse effects as well as treatment failures, and relapses are common. Subsequent lines of therapy are associated with higher rates of toxicity, and some patients remain refractory to currently available treatments. Novel therapies have become promising for this vulnerable population. In this review, we will discuss the mechanism of action, existing data, and ongoing clinical trials of current novel therapies for AIHA, including B-cell-directed therapy, phagocytosis inhibition, plasma cell-directed therapy, and complement inhibition.

Invasive Fungal Infections and Targeted Therapies in Hematological Malignancies

The use of targeted biologic therapies for hematological malignancies has greatly expanded in recent years. These agents act upon specific molecular pathways in order to target malignant cells but frequently have broader effects involving both innate and adaptive immunity. Patients with hematological malignancies have unique risk factors for infection, including immune dysregulation related to their underlying disease and sequelae of prior treatment regimens. Determining the individual risk of infection related to any novel agent is challenging in this setting. Invasive fungal infections (IFIs) represent one of the most morbid infectious complications observed in hematological malignancy. In recent years, growing evidence suggests that certain small molecule inhibitors, such as BTK inhibitors and PI3K inhibitors, may cause an increased risk of IFI in certain patients. It is imperative to better understand the impact that novel targeted therapies might have on the development of IFIs in this high-risk patient population.

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.

Critical Roles of Phosphoinositide 3-Kinase δ in the Humoral Immune Response to Trypanosoma congolense Infection

PI3Kδ is critical in generating humoral and regulatory immune responses. In this study, we determined the impact of PI3Kδ in immunity to Trypanosoma congolense, an African trypanosome that can manipulate and evade Ab responses critical for protection. Upon infection with T. congolense, PI3Kδ^D910A mice lacking PI3Kδ activity paradoxically show a transient enhancement in early control of parasitemia, associated with impaired production of regulatory IL-10 by B cells in the peritoneum. C57BL/6 wild-type (WT) mice treated with the PI3Kδ inhibitor (PI3Kδi) Idelalisib showed a similar transient decrease in parasitemia associated with reduced IL-10. Strikingly, however, we find that PI3Kδ^D910A mice were ultimately unable to control this infection, resulting in uncontrolled parasitemia and death within 2 wk. Assessment of humoral responses revealed delayed B cell activation, impaired germinal center responses, and compromised Ab responses to differing degrees in PI3Kδ^D910A and PI3Kδi-treated mice. To test the role of Abs, we administered serum from WT mice to PI3Kδ^D910A mice and found that lethality was prevented by postinfection serum. Interestingly, serum from naive WT mice provided partial protection to PI3Kδ^D910A mutants, indicating an additional role for natural Abs. Together our findings suggest that although PI3Kδ drives immune regulatory responses that antagonize early control of parasite growth in the peritoneum, it is also required for generation of Abs that are critical for protection from systemic trypanosome infection. The essential role of PI3Kδ for host survival of African trypanosome infection contrasts with findings for other pathogens such as Leishmania, underlining the critical importance of PI3Kδ-dependent humoral immunity in this disease.

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.

Bioisosteric replacements of the indole moiety for the development of a potent and selective PI3Kδ inhibitor: Design, synthesis and biological evaluation

Based on indole scaffold, a potent and selective phosphoinositide 3-kinase delta (PI3Kδ) inhibitor, namely FD223, was developed by the bioisosteric replacement drug discovery approach and studied for the treatment of acute myeloid leukemia (AML). In vitro studies revealed that FD223 displays high potency (IC₅₀ = 1 nM) and selectivity (29-51 fold over other PI3K isoforms) against PI3Kδ, and exhibits efficient inhibition of the proliferation of AML cell lines (MOLM-16, HL-60, EOL-1 and KG-1) by suppressing p-AKT Ser473 thus causing G1 phase arrest during the cell cycle. Further given the favorable pharmacokinetic (PK) profiles of FD223, in vivo studies were evaluated using xenograft model in nude mice, confirming its significant antitumor efficacy meanwhile with no observable toxicity. All these results are comparable to the positive group of Idelalisib (CAL-101), indicating that FD223 has potential for further development as a promising PI3Kδ inhibitor for the treatment of leukemia such as AML.

The PI-3-Kinase P110α Catalytic Subunit of T Lymphocytes Modulates Collagen-Induced Arthritis

The phosphatidylinositol 3-kinase (PI3K) family of enzymes plays a determinant role in inflammation and autoimmune responses. However, the implication of the different isoforms of catalytic subunits in these processes is not clear. Rheumatoid arthritis (RA) is a chronic, systemic autoimmune inflammatory disease that entails innate and adaptive immune response elements in which PI3K is a potential hub for immune modulation. In a mouse transgenic model with T-cell-specific deletion of p110α catalytic chain (p110α-/-ΔT), we show the modulation of collagen-induced arthritis (CIA) by this isoform of PI3K. In established arthritis, p110α-/-ΔT mice show decreased prevalence of illness than their control siblings, higher IgG1 titers and lower levels of IL-6 in serum, together with decreased ex vivo Collagen II (CII)-induced proliferation, IL-17A secretion and proportion of naive T cells in the lymph nodes. In a pre-arthritis phase, at 13 days post-Ag, T-cell-specific deletion of p110α chain induced an increased, less pathogenic IgG1/IgG2a antibodies ratio; changes in the fraction of naive and effector CD4+ subpopulations; and an increased number of CXCR5+ T cells in the draining lymph nodes of the p110α-/-ΔT mice. Strikingly, T-cell blasts in vitro obtained from non-immunized p110α-/-ΔT mice showed an increased expression of CXCR5, CD44 and ICOS surface markers and defective ICOS-induced signaling towards Akt phosphorylation. These results, plus the accumulation of cells in the lymph nodes in the early phase of the process, could explain the diminished illness incidence and prevalence in the p110α-/-ΔT mice and suggests a modulation of CIA by the p110α catalytic chain of PI3K, opening new avenues of intervention in T-cell-directed therapies to autoimmune diseases.

A Case for Phosphoinositide 3-Kinase-Targeted Therapy for Infectious Disease

PI3Ks activate critical signaling cascades and have multifaceted regulatory functions in the immune system. Loss-of-function and gain-of-function mutations in the PI3Kδ isoform have revealed that this enzyme can substantially impact immune responses to infectious agents and their products. Moreover, reports garnered from decades of infectious disease studies indicate that pharmacologic inhibition of the PI3K pathway could potentially be effective in limiting the growth of certain microbes via modulation of the immune system. In this review, we briefly highlight the development and applications of PI3K inhibitors and summarize data supporting the concept that PI3Kδ inhibitors initially developed for oncology have immune regulatory potential that could be exploited to improve the control of some infectious diseases. This repurposing of existing kinase inhibitors could lay the foundation for alternative infectious disease therapy using available therapeutic agents.

Kinase inhibitors developed for treatment of hematologic malignancies: implications for immune modulation in COVID-19

Tyrosine kinase inhibitors (TKIs) are used to target dysregulated signaling pathways in virtually all hematologic malignancies. Many of the targeted signaling pathways are also essential in nonmalignant immune cells. The current coronavirus severe acute respiratory syndrome coronavirus 2 pandemic catalyzed clinical exploration of TKIs in the treatment of the various stages of COVID-19, which are characterized by distinct immune-related complications. Most of the reported effects of TKIs on immune regulation have been explored in vitro, with different class-specific drugs having nonoverlapping target affinities. Moreover, many of the reported in vivo effects are based on artificial animal models or on observations made in symptomatic patients with a hematologic malignancy who often already suffer from disturbed immune regulation. Based on in vitro and clinical observations, we attempt to decipher the impact of the main TKIs approved or in late-stage development for the treatment of hematological malignancies, including inhibitors of Bruton's tyrosine kinase, spleen tyrosine kinase, BCR-Abl, phosphatidylinositol 3-kinase/ mammalian target of rapamycin, JAK/STAT, and FMS-like tyrosine kinase 3, to provide a rationale for how such inhibitors could modify clinical courses of diseases, such as COVID-19.

BRD4 inhibition sensitizes aggressive non-Hodgkin lymphomas to PI3Kδ inhibitors by suppressing PI3K reactivation and c-MYC expression

Targeting phosphatidylinositol 3-kinase δ (PI3Kδ) is an important therapeutic strategy for indolent non-Hodgkin lymphomas (NHLs). However, we previously observed reactivation of phosphatidylinositol 3-kinase (PI3K) pathways in aggressive NHL cell lines following continuous exposure to PI3Kδ inhibitors (PI3Kδi), which limited their efficacy and suggests that more studies should be focused on this reactivation to improve current PI3Kδi-based treatments. Herein we conducted a drug synergy screening that combined a marketed PI3Kδi, idelalisib, with 14 well-characterized epigenetic drugs across several types of aggressive NHL cell lines. We identified BRD4 inhibitors (BRD4i) as potent partners that, in combination with idelalisib, were capable of synergistically exerting anti-proliferative activity and inducing cell apoptosis in a panel of aggressive NHL cell lines through continuous suppression of PI3K pathways. More importantly, the combination of BRD4i and PI3Kδi simultaneously inhibited transcription and translation of the oncogenic transcription factor c-MYC, downregulating the expression of c-MYC and continuously suppressing the proliferation of cancer cells in vitro, as well as the growth of tumors in vivo even after drug withdrawal. This study, thus, reveals the potential of simultaneously targeting PI3Kδ and BRD4 as a new therapeutic strategy for aggressive forms of NHL.

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.

Skin-Associated B Cells in the Pathogenesis of Cutaneous Autoimmune Diseases-Implications for Therapeutic Approaches

B lymphocytes are crucial mediators of systemic immune responses and are known to be substantial in the pathogenesis of autoimmune diseases with cutaneous manifestations. Amongst them are lupus erythematosus, dermatomyositis, systemic sclerosis and psoriasis, and particularly those driven by autoantibodies such as pemphigus and pemphigoid. However, the concept of autoreactive skin-associated B cells, which may reside in the skin and locally contribute to chronic inflammation, is gradually evolving. These cells are believed to differ from B cells of primary and secondary lymphoid organs and may provide additional features besides autoantibody production, including cytokine expression and crosstalk to autoreactive T cells in an antigen-presenting manner. In chronically inflamed skin, B cells may appear in tertiary lymphoid structures. Those abnormal lymph node-like structures comprise a network of immune and stromal cells possibly enriched by vascular structures and thus constitute an ideal niche for local autoimmune responses. In this review, we describe current considerations of different B cell subsets and their assumed role in skin autoimmunity. Moreover, we discuss traditional and B cell-associated approaches for the treatment of autoimmune skin diseases, including drugs targeting B cells (e.g., CD19- and CD20-antibodies), plasma cells (e.g., proteasome inhibitors, CXCR4 antagonists), activated pathways (such as BTK- and PI3K-inhibitors) and associated activator molecules (BLyS, APRIL).

Phase 2 study of parsaclisib (INCB050465), a highly selective, next-generation PI3Kδ inhibitor, in relapsed or refractory diffuse large B-cell lymphoma (CITADEL-202)

Parsaclisib, a potent, highly selective, next-generation PI3Kδ inhibitor, was evaluated as monotherapy in CITADEL-202 (NCT02998476), an open-label, multicenter, phase 2 study in patients with relapsed or refractory diffuse large B-cell lymphoma. Patients enrolled into 2 groups (A, Bruton tyrosine kinase [BTK] inhibitor naïve, n = 55; B, BTK inhibitor experienced, n = 5) received oral parsaclisib 20 mg once daily for 8 weeks, then 20 mg once weekly while deriving benefit. The futility boundary was crossed at the interim analysis of Group A, resulting in a negative study. Parsaclisib monotherapy demonstrated an objective response rate (ORR) of 25.5% (8 complete metabolic responses/6 partial metabolic responses) and a median duration of response of 6.2 months. ORR in Group B was 20.0% (1 complete metabolic response). Parsaclisib monotherapy demonstrated manageable toxicities with no new safety signals reported. Further evaluation of parsaclisib in combination with standard therapies and active investigational agents is underway.

Effects of AS2819899, a novel selective PI3Kδ inhibitor, in a NZB/W F1 mouse lupus-like nephritis model

Phosphoinositide 3-kinases generate lipid-based second messengers that control an array of intracellular signaling pathways. In particular, phosphoinositide 3-kinases delta (PI3Kδ) is expressed primarily in hematopoietic cells and plays an important role in B-cell development and function. B cells play a critical role in autoimmune diseases by producing autoantibodies. Studies have therefore increasingly focused on PI3Kδ as a therapeutic target for the treatment of inflammatory and autoimmune diseases. One such autoimmune disease is systemic lupus erythematosus (SLE). SLE is a chronic systemic autoimmune disease with repeated recurrence and remission, and autoantibodies play an important role in its pathogenesis. Here, we examined the pharmacological profile of the novel PI3Kδ selective inhibitor AS2819899 and investigated its therapeutic potential against SLE in a NZB/W F1 mouse lupus-like nephritis model, a widely-used SLE mouse model. AS2819899 prevented B and T cell activation in vitro, and inhibited antibody production in a T-cell independent de novo antibody production mouse model. In the spontaneous NZB/W F1 mouse model, AS2819899 treatment significantly reduced anti-dsDNA antibody titers and improved kidney dysfunction. Further, AS2819899 inhibited the memory recall reaction in a T-cell dependent antibody production mouse model, suggesting that AS2819899 can potentially maintain remission of SLE. Moreover, we identified a pharmacodynamics marker for AS2819899 that may be useful in clinical studies. These results indicate that AS2819899 may be an attractive therapeutic candidate for SLE, including the maintenance of remission.

Efficacy and safety of idelalisib for the treatment of indolent B-cell malignancies

INTRODUCTION

The outcome of patients with lymphoid malignancies has markedly improved in recent years due to the implementation of new therapeutic options. Chronic lymphocytic leukemia (CLL) and indolent B-cell non-Hodgkin lymphomas (NHL) are characterized by the activation of the phosphatidylinositol 3-kinase (PI3 K) pathway via B-cell receptor signaling. The PI3 K delta (PI3 Kδ) p110δ isoform inhibitor, idelalisib, showed high anti-tumor activity in this group of tumors. It was the first agent from a new class of isoform-specific inhibitors to receive regulatory approvals for the treatment of refractory/relapsed CLL, as well as small lymphocytic lymphoma and follicular lymphoma.

AREAS COVERED

In this paper, the authors provide a comprehensive overview of the activity and safety profile of idelalisib and other, newly developed PI3 K inhibitors in patients with indolent B-cell malignancies.

EXPERT OPINION

Idelalisib is a very potent anti-lymphoma agent in CLL and other NHL. However, there are some limitations of its broad clinical use according to some important side effects observed during treatment. Consequently, the development of new PI3 K inhibitors, which will be highly active and possess better safety profiles are warranted.

An Open-Label Study to Assess the Effect of Itraconazole and Rifampin on Parsaclisib Pharmacokinetics When Administered Orally in Healthy Participants

Parsaclisib, a selective, potent phosphatidylinositol 3‐kinase delta inhibitor being developed for the treatment of cancer and autoimmune diseases, is primarily metabolized by cytochrome P450 (CYP) 3A4. This study assessed the pharmacokinetics (PK) and safety of parsaclisib alone or combined with itraconazole (potent CYP3A inhibitor) or rifampin (potent CYP3A4 inducer) in healthy participants. In this open‐label, fixed‐sequence study, cohort 1 received oral parsaclisib 10 mg once daily on days 1 and 8 and oral itraconazole 200 mg once daily on days 4‐11; cohort 2 received oral parsaclisib 20 mg once daily on days 1 and 11 and oral rifampin 600 mg once daily on days 4‐12. Parsaclisib plasma concentration was tested and PK parameters calculated by noncompartmental analysis. Geometric mean ratios (GMRs) and 2‐sided 90% confidence intervals (CIs) were estimated by 2‐factor analysis of variance. Thirty‐six healthy participants were enrolled (18 per cohort). Parsaclisib maximum plasma drug concentration (C_max) and area under the concentration‐time curve extrapolated to infinity (AUC_0‐∞) were increased by 21% and 107% with concomitant itraconazole versus parsaclisib alone (GMR, 1.21; 90%CI, 1.14‐1.29; and 2.07; 90%CI, 1.97‐2.17, respectively). Parsaclisib C_max and AUC were reduced by 43% and 77%, respectively, with concomitant rifampin versus parsaclisib alone (GMR, 0.57; 90%CI, 0.53‐0.60; and 0.23; 90%CI, 0.21‐0.24, respectively). Headache was the most common adverse event, reported by 13.9% of participants (all in cohort 2). Single‐dose parsaclisib alone or combined with itraconazole or rifampin appeared safe and well tolerated in healthy participants. Parsaclisib dose adjustment may be necessary with concomitant administration of strong CYP3A4 inhibitors or inducers.

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.

PI3Kδ as a Novel Therapeutic Target in Pathological Angiogenesis

Diabetic retinopathy is the most common microvascular complication of diabetes, and in the advanced diabetic retinopathy appear vitreal fibrovascular membranes that consist of a variety of cells, including vascular endothelial cells (ECs). New therapeutic approaches for this diabetic complication are urgently needed. Here, we report that in cultured human retinal microvascular ECs, high glucose induced expression of p110δ, which was also expressed in ECs of fibrovascular membranes from patients with diabetes. This catalytic subunit of a receptor-regulated PI3K isoform δ is known to be highly enriched in leukocytes. Using genetic and pharmacological approaches, we show that p110δ activity in cultured ECs controls Akt activation, cell proliferation, migration, and tube formation induced by vascular endothelial growth factor, basic fibroblast growth factor, and epidermal growth factor. Using a mouse model of oxygen-induced retinopathy, p110δ inactivation was found to attenuate pathological retinal angiogenesis. p110δ inhibitors have been approved for use in human B-cell malignancies. Our data suggest that antagonizing p110δ constitutes a previously unappreciated therapeutic opportunity for diabetic retinopathy.

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

A medicinal chemistry effort focused on identifying a structurally diverse candidate for phosphoinositide 3-kinase delta (PI3Kδ) led to the discovery of clinical candidate INCB050465 (20, parsaclisib). The unique structure of 20 contains a pyrazolopyrimidine hinge-binder in place of a purine motif that is present in other PI3Kδ inhibitors, such as idelalisib (1), duvelisib (2), and INCB040093 (3, dezapelisib). Parsaclisib (20) is a potent and highly selective inhibitor of PI3Kδ with drug-like ADME properties that exhibited an excellent in vivo profile as demonstrated through pharmacokinetic studies in rats, dogs, and monkeys and through pharmacodynamic and efficacy studies in a mouse Pfeiffer xenograft model.

Phosphoinositide 3-kinase δ inactivation prevents vitreous-induced activation of AKT/MDM2/p53 and migration of retinal pigment epithelial cells

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that play a critical role in transmitting signals from cell-surface molecules to intracellular protein effectors. Key PI3Ks include PI3Kα, PI3Kβ, and PI3Kδ, which are regulated by receptors. The signaling pathway comprising the PI3Ks, along with a Ser/Thr kinase (AKT), a proto-oncogene product (mouse double minute (MDM)2), and a tumor suppressor protein (p53), plays an essential role in experimental proliferative vitreoretinopathy (PVR), which is a fibrotic blinding eye disorder. However, which PI3K isoforms are involved in PVR is unknown. A major characteristic of PVR is the formation of epi (or sub)-retinal membranes that consist of extracellular matrix and cells, including retinal pigment epithelium (RPE) cells, glial cells, and macrophages. RPE cells are considered key players in PVR pathogenesis. Using immunoblotting and immunofluorescence analyses, we herein provide the evidence that PI3Kδ is highly expressed in human RPEs when it is primarily expressed in leukocytes. We also found that PI3Kδ inactivation through two approaches, CRISPR/Cas9-mediated depletion and a PI3Kδ-specific inhibitor (idelalisib), not only blocks vitreous-induced activation of AKT and MDM2 but also abrogates a vitreous-stimulated decrease in p53. Furthermore, we demonstrate that PI3Kδ inactivation prevents vitreous-induced proliferation, migration, and contraction of human RPEs. These results suggest that PI3Kδ may represent a potential therapeutic target for RPE-related eye diseases, including PVR.

Invasive fungal infections in the immunocompromised host: Mechanistic insights in an era of changing immunotherapeutics

The use of cytotoxic chemotherapy in the treatment of malignant and inflammatory disorders is beset by considerable adverse effects related to nonspecific cytotoxicity. Accordingly, a mechanistic approach to therapeutics has evolved in recent times with small molecular inhibitors of intracellular signaling pathways involved in disease pathogenesis being developed for clinical use, some with unparalleled efficacy and tolerability. Nevertheless, there are emerging concerns regarding an association with certain small molecular inhibitors and opportunistic infections, including invasive fungal diseases. This is perhaps unsurprising, given that the molecular targets of such agents play fundamental and multifaceted roles in orchestrating innate and adaptive immune responses. Nevertheless, some small molecular inhibitors appear to possess intrinsic antifungal activity and may therefore represent novel therapeutic options in future. This is particularly important given that antifungal resistance is a significant, emerging concern. This paper is a comprehensive review of the state-of-the-art in the molecular immunology to fungal pathogens as applied to existing and emerging small molecular inhibitors.

Parsaclisib, a potent and highly selective PI3Kδ inhibitor, in patients with relapsed or refractory B-cell malignancies

This phase 1/2 study assessed parsaclisib (INCB050465), a next-generation, potent, and highly selective phosphatidylinositol 3-kinase δ (PI3Kδ) inhibitor, in patients with relapsed or refractory B-cell malignancies, alone or in combination with a Janus kinase 1 inhibitor (itacitinib) or chemotherapy (rituximab, ifosfamide, carboplatin, and etoposide). Seventy-two patients received parsaclisib monotherapy (5-45 mg once daily). Expansion doses were 20 and 30 mg once daily; intermittent dosing at 20 mg (once daily for 9 weeks, then once weekly) was explored. No dose-limiting toxicities were identified, and maximum tolerated dose was not reached. Most common nonhematologic treatment-emergent adverse events (TEAEs) were diarrhea/colitis (36%), nausea (36%), fatigue (31%), and rash (31%). Grade 3/4 neutropenia occurred in 19% of patients. Serious TEAEs (>2 patients) were diarrhea/colitis (n = 9), pyrexia (n = 4), hypotension (n = 3), and sepsis (n = 3). Aspartate and alanine transaminase elevations occurring before treatment discontinuation were grade 1, except 1 grade 3 event each, secondary to sepsis. Two patients experienced 3 fatal parsaclisib-unrelated TEAEs (respiratory failure; respiratory failure and sepsis). In non-Hodgkin lymphoma (NHL), objective response rates to monotherapy were 71% in follicular lymphoma, 78% in marginal zone lymphoma, 67% in mantle cell lymphoma, and 30% in diffuse large B-cell lymphoma; 93% of responses occurred at first assessment (∼9 weeks). Parsaclisib has demonstrated antitumor activity in relapsed or refractory B-cell NHL with the potential for improved long-term patient outcomes. Phase 2 studies in relapsed or refractory B-cell NHL subtypes are ongoing. This trial was registered at www.clinicaltrials.gov as #NCT02018861.

Current and emerging treatment options for autoimmune hemolytic anemia

INTRODUCTION

Autoimmune hemolytic anemia (AIHA) is a heterogeneous disease mainly due to autoantibody-mediated destruction of erythrocytes but also involves complement activation, dysregulation of cellular and innate immunity, and defective bone marrow compensatory response. Several drugs targeting these mechanisms are under development in addition to standard therapies. Areas covered: The following targeted therapies are illustrated: drugs acting on CD20 (rituximab, alone or in association with bendamustine and fludarabine) and CD52 (alemtuzumab), B cell receptor and proteasome inhibitors (ibrutinib, bortezomib), complement inhibitors (eculizumab, BIVV009, APL-2), and other drugs targeting T lymphocytes (subcutaneous IL-2, belimumab, and mTOR inhibitors), IgG driven extravascular hemolysis (fostamatinib), and bone marrow activity (luspatercept). Expert opinion: Although AIHA is considered benign and often easy to treat, chronic/refractory cases represent a challenge even for experts in the field. Bone marrow biopsy is fundamental to assess one of the main mechanisms contributing to AIHA severity, i.e. inadequate compensation, along with lymphoid infiltrate, the presence of fibrosis or dyserythropoiesis. The latter may give hints for targeted therapies (either B or T cell directed) and for new immunomodulatory drugs. Future studies on the genomic landscape in AIHA will further help in designing the best choice, sequence and/or combination of targeted therapies.

The phosphoinositide-3 kinase (PI3K)-δ,γ inhibitor, duvelisib shows preclinical synergy with multiple targeted therapies in hematologic malignancies

Duvelisib is an orally active dual inhibitor of PI3K-δ and PI3K-γ in clinical development in hematologic malignancies (HM). To identify novel pairings for duvelisib in HM, it was evaluated alone and in combination with 35 compounds comprising a diverse panel of standard-of-care agents and emerging drugs in development for HM. These compounds were tested in 20 cell lines including diffuse large B-cell, follicular, T-cell, and mantle cell lymphomas, and multiple myeloma. Single agent activity was seen in fourteen cell lines, with a median GI50 of 0.59 μM. A scalar measure of the strength of synergistic drug interactions revealed a synergy hit rate of 19.3% across the matrix of drug combinations and cell lines. Synergy with duvelisib was prominent in lymphoma lines with approved and emerging drugs used to treat HM, including dexamethasone, ibrutinib, and the BCL-2 inhibitor venetoclax. Western blotting revealed that certain duvelisib-treated cell lines showed inhibition of phosphorylated (p) AKT at serine 473 only out to 12 hours, with mTORC2 dependent re-phosphorylation of pAKT evident at 24 hours. Combination with dexamethasone or ibrutinib, however, prevented this reactivation leading to durable inhibition of pAKT. The combination treatments also inhibited downstream signaling effectors pPRAS40 and pS6. The combination of duvelisib with dexamethasone also significantly reduced p-4EBP1, which controls cap dependent translation initiation, leading to decreased levels of c-MYC 6 hours after treatment. In support of the in vitro studies, in vivo xenograft studies revealed that duvelisib in combination with the mTOR inhibitor everolimus led to greater tumor growth inhibition compared to single agent administration. These data provide a rationale for exploring multiple combinations in the clinic and suggest that suppression of mTOR-driven survival signaling may be one important mechanism for combination synergy.

Therapeutic Effect of a Novel Phosphatidylinositol-3-Kinase δ Inhibitor in Experimental Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita (EBA) is a rare, but prototypical, organ-specific autoimmune disease, characterized and caused by autoantibodies against type VII collagen (COL7). Mucocutaneous inflammation, blistering, and scarring are the clinical hallmarks of the disease. Treatment of EBA is difficult and mainly relies on general immunosuppression. Hence, novel treatment options are urgently needed. The phosphatidylinositol-3-kinase (PI3K) pathway is a putative target for the treatment of inflammatory diseases, including EBA. We recently discovered LAS191954, an orally available, selective PI3Kδ inhibitor. PI3Kδ has been shown to be involved in B cell and neutrophil cellular functions. Both cell types critically contribute to EBA pathogenesis, rendering LAS191954 a potential drug candidate for EBA treatment. We, here, demonstrate that LAS191954, when administered chronically, dose-dependently improved the clinical phenotype of mice harboring widespread skin lesions secondary to immunization-induced EBA. Direct comparison with high-dose corticosteroid treatment indicated superiority of LAS191954. Interestingly, levels of circulating autoantibodies were unaltered in all groups, indicating a mode of action independent of the inhibition of B cell function. In line with this, LAS191954 also hindered disease progression in antibody transfer-induced EBA, where disease develops dependent on myeloid, but independent of B cells. We further show that, in vitro, LAS191954 dose-dependently impaired activation of human myeloid cells by relevant disease stimuli. Specifically, immune complex-mediated and C5a-mediated ROS release were inhibited in a PI3Kδ-dependent manner. Accordingly, LAS191954 also modulated the dermal–epidermal separation induced in vitro by co-incubation of immune complexes with polymorph nuclear cells, thus pointing to an important role of PI3Kδ in EBA effector functions. Altogether, these results suggest a new potential mechanism for the treatment of EBA and potentially also other autoimmune bullous diseases.

Efficacy of Idelalisib as Bridge to Allogeneic Stem Cell Transplant in Relapsed Follicular Lymphoma: A Case Report

Purpose

A large number of new therapeutic agents have been studied for patients with relapsed/refractory follicular lymphoma (FL). Among new therapies, idelalisib, a novel PI3K inhibitor, shows promising results in the management of this disease.

Case report

We describe the case of a 39-year-old patient with a diagnosis of grade 3a FL and a Follicular Lymphoma International Prognostic Index score of 2, who underwent several lines of therapy (including autologous stem cell transplant) with transient responses or no response at all. The patient was subsequently treated with 5 courses of idelalisib monotherapy, achieving a partial response. No relevant toxicities occurred. The patient underwent allogeneic stem cell transplant (allo-SCT) from an unrelated donor and obtained a complete response, which was confirmed after 3, 6, 9, and 12 months, and is still ongoing.

Conclusions

As previously reported, the achievement of a good response is predictive for a better outcome after allo-SCT: idelalisib represents an effective treatment option for patients with relapsed/refractory FL, which can also be adopted as a bridge to allo-SCT.

Phase 1 study of the PI3Kδ inhibitor INCB040093 ± JAK1 inhibitor itacitinib in relapsed/refractory B-cell lymphoma

Because both phosphatidylinositol 3-kinase δ (PI3Kδ) and Janus kinase (JAK)-signal transducer and activator of transcription pathways contribute to tumor cell proliferation and survival in B-cell malignancies, their simultaneous inhibition may provide synergistic treatment efficacy. This phase 1 dose-escalation/expansion study assessed the safety, efficacy, pharmacokinetics, and pharmacodynamics of INCB040093, a selective PI3Kδ inhibitor, as monotherapy or combined with itacitinib (formerly INCB039110), a selective JAK1 inhibitor, in adult patients with relapsed or refractory (R/R) B-cell lymphomas. Final results are reported. Overall, 114 patients were treated (monotherapy, n = 49; combination therapy, n = 72 [7 patients crossed over from monotherapy to combination]). INCB040093 100 mg twice daily (monotherapy) and INCB040093 100 mg twice daily + itacitinib 300 mg once daily (combination) were the recommended phase 2 doses. One dose-limiting toxicity (gastrointestinal bleed secondary to gastric diffuse large B-cell lymphoma [DLBCL] regression) occurred with monotherapy. The most common serious adverse events with monotherapy were pneumonia (n = 5) and pyrexia (n = 4), and with combination Pneumocystis jiroveci pneumonia (n = 5), pneumonia (unrelated to P jiroveci; n = 5), and pyrexia (n = 4). Grade 3 or higher transaminase elevations were less common with combination. INCB040093 was active across the B-cell lymphomas; 63% of patients (5/8) with follicular lymphoma responded to monotherapy. Adding itacitinib provided promising activity in select subtypes, with responses of 67% (14/21) in classic Hodgkin lymphoma (vs 29% [5/17] with monotherapy) and 31% (4/13) in nongerminal center B-cell-like DLBCL. INCB040093 with/without itacitinib was tolerated and active in this study, and is a promising treatment strategy for patients with select R/R B-cell lymphomas. This trial was registered at www.clinicaltrials.gov as #NCT01905813.

The PI3Kδ-Selective Inhibitor Idelalisib Minimally Interferes with Immune Effector Function Mediated by Rituximab or Obinutuzumab and Significantly Augments B Cell Depletion In Vivo

Idelalisib is a highly selective oral inhibitor of PI3Kδ indicated for the treatment of patients with relapsed chronic lymphocytic leukemia in combination with rituximab. Despite additive clinical effects, previous studies have paradoxically demonstrated that targeted therapies potentially negatively affect anti-CD20 mAb effector mechanisms. To address these potential effects, we investigated the impact of PI3Kδ inhibition by idelalisib on the effector mechanisms of rituximab and obinutuzumab. At clinically relevant concentrations, idelalisib minimally influenced rituximab- and obinutuzumab-mediated Ab-dependent cellular cytotoxicity and phagocytosis on human lymphoma cell lines, while maintaining the superiority of obinutuzumab-mediated Ab-dependent cellular cytotoxicity. Consistent with this, idelalisib did not influence obinutuzumab-mediated B cell depletion in whole-blood B cell-depletion assays. Further, idelalisib significantly enhanced obinutuzumab-mediated direct cell death of chronic lymphocytic leukemia cells. In murine systems, in vivo inhibition of PI3Kδ minimally interfered with maximal rituximab- or obinutuzumab-mediated depletion of leukemic targets. In addition, the duration of rituximab- and obinutuzumab-mediated depletion of leukemia cells was extended by combination with PI3Kδ inhibition. Collectively, these data demonstrate that PI3Kδ inhibition does not significantly affect the effector mechanisms induced by rituximab or obinutuzumab and provides an effective in vivo therapeutic combination. Therefore, combinations of obinutuzumab and idelalisib are currently being assessed in clinical studies.

Pan-phosphatidylinositol 3-kinase inhibition with buparlisib in patients with relapsed or refractory non-Hodgkin lymphoma

Activation of the phosphatidylinositol 3-kinase/mechanistic target of rapamycin pathway plays a role in the pathogenesis of non-Hodgkin lymphoma. This multicenter, open-label phase 2 study evaluated buparlisib (BKM120), a pan-class I phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or refractory non-Hodgkin lymphoma. Three separate cohorts of patients (with diffuse large B-cell lymphoma, mantle cell lymphoma, or follicular lymphoma) received buparlisib 100 mg once daily until progression, intolerance, or withdrawal of consent. The primary endpoint was overall response rate based on a 6-month best overall response by cohort; secondary endpoints included progression-free survival, duration of response, overall survival, safety, and tolerability. Overall, 72 patients (26 with diffuse large B-cell lymphoma, 22 with mantle cell lymphoma, and 24 with follicular lymphoma) were treated. The overall response rates were 11.5%, 22.7%, and 25.0% in patients with diffuse large B-cell lymphoma, mantle cell lymphoma, and follicular lymphoma, respectively; two patients (one each with diffuse large B-cell lymphoma and mantle cell lymphoma) achieved a complete response. The most frequently reported (>20%) adverse events of any grade in the population in which safety was studied were hyperglycemia, fatigue, and nausea (36.1% each), depression (29.2%), diarrhea (27.8%), and anxiety (25.0%). The most common grade 3/4 adverse events included hyperglycemia (11.1%) and neutropenia (5.6%). Buparlisib showed activity in relapsed or refractory non-Hodgkin lymphoma, with disease stabilization and sustained tumor burden reduction in some patients, and acceptable toxicity. Development of mechanism-based combination regimens with buparlisib is warranted. (This study was funded by Novartis Pharmaceuticals Corporation and registered with ClinicalTrials.gov number, NCT01693614).

Discovery of CDZ173 (Leniolisib), Representing a Structurally Novel Class of PI3K Delta-Selective Inhibitors

The predominant expression of phosphoinositide 3-kinase δ (PI3Kδ) in leukocytes and its critical role in B and T cell functions led to the hypothesis that selective inhibitors of this isoform would have potential as therapeutics for the treatment of allergic and inflammatory disease. Targeting specifically PI3Kδ should avoid potential side effects associated with the ubiquitously expressed PI3Kα and β isoforms. We disclose how morphing the heterocyclic core of previously discovered 4,6-diaryl quinazolines to a significantly less lipophilic 5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine, followed by replacement of one of the phenyl groups with a pyrrolidine-3-amine, led to a compound series with an optimal on-target profile and good ADME properties. A final lipophilicity adjustment led to the discovery of CDZ173 (leniolisib), a potent PI3Kδ selective inhibitor with suitable properties and efficacy for clinical development as an anti-inflammatory therapeutic. In vitro, CDZ173 inhibits a large spectrum of immune cell functions, as demonstrated in B and T cells, neutrophils, monocytes, basophils, plasmocytoid dendritic cells, and mast cells. In vivo, CDZ173 inhibits B cell activation in rats and monkeys in a concentration- and time-dependent manner. After prophylactic or therapeutic dosing, CDZ173 potently inhibited antigen-specific antibody production and reduced disease symptoms in a rat collagen-induced arthritis model. Structurally, CDZ173 differs significantly from the first generation of PI3Kδ and PI3Kγδ-selective clinical compounds. Therefore, CDZ173 could differentiate by a more favorable safety profile. CDZ173 is currently in clinical studies in patients suffering from primary Sjögren's syndrome and in APDS/PASLI, a disease caused by gain-of-function mutations of PI3Kδ.

The Selective Phosphoinoside-3-Kinase p110δ Inhibitor IPI-3063 Potently Suppresses B Cell Survival, Proliferation, and Differentiation

The class I phosphoinoside-3-kinases (PI3Ks) are important enzymes that relay signals from cell surface receptors to downstream mediators driving cellular functions. Elevated PI3K signaling is found in B cell malignancies and lymphocytes of patients with autoimmune disease. The p110δ catalytic isoform of PI3K is a rational target since it is critical for B lymphocyte development, survival, activation, and differentiation. In addition, activating mutations in PIK3CD encoding p110δ cause a human immunodeficiency known as activated PI3K delta syndrome. Currently, idelalisib is the only selective p110δ inhibitor that has been FDA approved to treat certain B cell malignancies. p110δ inhibitors can suppress autoantibody production in mouse models, but limited clinical trials in human autoimmunity have been performed with PI3K inhibitors to date. Thus, there is a need for additional tools to understand the effect of pharmacological inhibition of PI3K isoforms in lymphocytes. In this study, we tested the effects of a potent and selective p110δ inhibitor, IPI-3063, in assays of B cell function. We found that IPI-3063 potently reduced mouse B cell proliferation, survival, and plasmablast differentiation while increasing antibody class switching to IgG1, almost to the same degree as a pan-PI3K inhibitor. Similarly, IPI-3063 potently inhibited human B cell proliferation in vitro. The p110γ isoform has partially overlapping roles with p110δ in B cell development, but little is known about its role in B cell function. We found that the p110γ inhibitor AS-252424 had no significant impact on B cell responses. A novel dual p110δ/γ inhibitor, IPI-443, had comparable effects to p110δ inhibition alone. These findings show that p110δ is the dominant isoform mediating B cell responses and establish that IPI-3063 is a highly potent molecule useful for studying p110δ function in immune cells.

Design and Synthesis of Soluble and Cell-Permeable PI3Kδ Inhibitors for Long-Acting Inhaled Administration

PI3Kδ is a lipid kinase that is believed to be important in the migration and activation of cells of the immune system. Inhibition is hypothesized to provide a powerful yet selective immunomodulatory effect that may be beneficial for the treatment of conditions such as asthma or rheumatoid arthritis. In this work, we describe the identification of inhibitors based on a thiazolopyridone core structure and their subsequent optimization for inhalation. The initially identified compound (13) had good potency and isoform selectivity but was not suitable for inhalation. Addition of basic substituents to a region of the molecule pointing to solvent was tolerated (enzyme inhibition pIC₅₀ > 9), and by careful manipulation of the pK_a and lipophilicity, we were able to discover compounds (20b, 20f) with good lung retention and cell potency that could be taken forward to in vivo studies where significant target engagement could be demonstrated.

Puquitinib, a novel orally available PI3Kδ inhibitor, exhibits potent antitumor efficacy against acute myeloid leukemia

The PI3Kδ isoform (PIK3CD), also known as P110δ, is predominately expressed in leukocytes and has been implicated as a potential target in the treatment of hematological malignancies. In this report, we detailed the pharmacologic properties of puquitinib, a novel, orally available PI3Kδ inhibitor. Puquitinib, which binds to the ATP‐binding pocket of PI3Kδ, was highly selective and potent for PI3Kδ relative to other PI3K isoforms and a panel of protein kinases, exhibiting low‐nanomolar biochemical and cellular inhibitory potencies. Additional cellular profiling demonstrated that puquitinib inhibited proliferation, induced G₁‐phase cell‐cycle arrest and apoptosis in acute myeloid leukemia (AML) cell lines, through downregulation of PI3K signaling. In in vivo AML xenografts, puquitinib alone showed stronger efficacy than the well‐known p110δ inhibitor, CAL‐101, in association with a reduction in AKT and ERK phosphorylation in tumor tissues, without causing noticeable toxicity. Furthermore, the combination of puquitinib with cytotoxic drugs, especially daunorubicin, yielded significantly stronger antitumor efficacy compared with each agent alone. Thus, puquitinib is a promising agent with pharmacologic properties that are favorable for the treatment of AML.