PI3Kδ Inhibitor Research Articles

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.

Phosphoinositide 3-Kinase δ Inhibition Improves Neutrophil Bacterial Killing in Critically Ill Patients at High Risk of Infection.

Acquired neutrophil dysfunction frequently develops during critical illness, independently increasing the risk for intensive care unit-acquired infection. PI3Kδ is implicated in driving neutrophil dysfunction and can potentially be targeted pharmacologically. The aims of this study were to determine whether PI3Kδ inhibition reverses dysfunction in neutrophils from critically ill patients and to describe potential mechanisms. Neutrophils were isolated from blood taken from critically ill patients requiring intubation and mechanical ventilation, renal support, or blood pressure support. In separate validation experiments, neutrophil dysfunction was induced pharmacologically in neutrophils from healthy volunteers. Phagocytosis and bacterial killing assays were performed, and activity of RhoA and protein kinase A (PKA) was assessed. Inhibitors of PI3Kδ, 3-phosphoinositide-dependent protein kinase-1 (PDK1), and PKA were used to determine mechanisms of neutrophil dysfunction. Sixty-six patients were recruited. In the 27 patients (40.9%) with impaired neutrophil function, PI3Kδ inhibition consistently improved function and significantly increased bacterial killing. These findings were validated in neutrophils from healthy volunteers with salbutamol-induced dysfunction and extended to demonstrate that PI3Kδ inhibition restored killing of clinical isolates of nine pathogens commonly associated with intensive care unit-acquired infection. PI3Kδ activation was associated with PDK1 activation, which in turn phosphorylated PKA, which drove phosphorylation and inhibition of the key regulator of neutrophil phagocytosis, RhoA. These data indicate that, in a significant proportion of critically ill patients, PI3Kδ inhibition can improve neutrophil function through PDK1- and PKA-dependent processes, suggesting that therapeutic use of PI3Kδ inhibitors warrants investigation in this setting.

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

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

Topical Application of the PI3Kβ-Selective Small Molecule Inhibitor TGX-221 Is an Effective Treatment Option for Experimental Epidermolysis Bullosa Acquisita.

Class I phosphoinositide 3-kinases (PI3K) have been implemented in pathogenesis of experimental epidermolysis bullosa acquisita (EBA), an autoimmune skin disease caused by type VII collagen (COL7) autoantibodies. Mechanistically, inhibition of specific PI3K isoforms, namely PI3Kβ or PI3Kδ, impaired immune complex (IC)-induced neutrophil activation, a key prerequisite for EBA pathogenesis. Data unrelated to EBA showed that neutrophil activation is also modulated by PI3Kα and γ, but their impact on the EBA has, so far, remained elusive. To address this and to identify potential therapeutic targets, we evaluated the impact of a panel of PI3K isoform-selective inhibitors (PI3Ki) on neutrophil function in vitro, and in pre-clinical EBA mouse models. We document that distinctive, and EBA pathogenesis-related activation-induced neutrophil in vitro functions depend on distinctive PI3K isoforms. When mice were treated with the different PI3Ki, selective blockade of PI3Kα (alpelisib), PI3Kγ (AS-604850), or PI3Kβ (TGX-221) impaired clinical disease manifestation. When applied topically, only TGX-221 impaired induction of experimental EBA. Ultimately, multiplex kinase activity profiling in the presence of disease-modifying PI3Ki identified unique signatures of different PI3K isoform-selective inhibitors on the kinome of IC-activated human neutrophils. Collectively, we here identify topical PI3Kβ inhibition as a potential therapeutic target for the treatment of EBA.

833O A phase Ib study result of HMPL-689, a PI3Kδ inhibitor, in Chinese patients with relapsed/refractory lymphoma

HMPL-689, a novel class I PI3Kδ inhibitor, has shown tolerable safety profile and encouraging preliminary efficacy in patients (pts) with relapsed/refractory (R/R) lymphoma in the dose-escalation stage of a phase I study (NCT03128164) in China (Junning C, et al, ASH 2020). Here we present the preliminary safety and efficacy results of the study evaluating HMPL-689 at recommended phase 2 dose (RP2D) of 30mg QD as a monotherapy in pts with R/R lymphomas.

842P Secreted factors determine resistance to idelalisib in splenic marginal zone lymphoma (MZL) models

PI3Kδ has a central role in the BCR signaling in hematological malignancies. Idelalisib was the first-in-class PI3Kδ inhibitor, and several novel compounds are undergoing clinical investigation. To identify modalities to overcome the resistance developed to these agents, we have developed idelalisib-resistant models derived from MZL cell lines.

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, PI3KδD910A 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 PI3KδD910A 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 PI3KδD910A and PI3Kδi-treated mice. To test the role of Abs, we administered serum from WT mice to PI3KδD910A mice and found that lethality was prevented by postinfection serum. Interestingly, serum from naive WT mice provided partial protection to PI3KδD910A 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.

Venetoclax-resistant CLL cells show a highly activated and proliferative phenotype.

Venetoclax treatment has demonstrated efficacy and a safety profile in chronic lymphocytic leukemia (CLL) patients, however the emergence of resistant cells is a current complication. We and others, previously reported that the activation of CLL cells by signals that mimic microenvironment stimuli favors the upregulation of anti-apoptotic proteins from B cell lymphoma-2 (BCL-2) family that are not targeted by venetoclax, reducing malignant cell sensitivity to the drug. We here studied venetoclax-resistant CLL cells generated in vitro by autologous activated T lymphocytes, and found that they showed an aggressive phenotype characterized by increased expression of activation and proliferation markers. Moreover, surviving cells expressed high levels of B cell lymphoma-extra-large (BCL-XL) and/or myeloid cell leukemia-1 (MCL-1), and a sustained resistance to a second treatment with the drug. Interestingly, the spleen tyrosine kinase (SYK) inhibitor entospletinib, and the phosphoinositide 3-kinase delta (PI3Kδ) inhibitor idelalisib, reduced T cell activation, impaired the generation of leukemic cells with this aggressive phenotype, and were able to restore CLL sensitivity to venetoclax. Our data highlight a novel combination to overcome resistance to venetoclax in CLL.

Poster: MPN-127: Add-On Parsaclisib (a PI3Kδ Inhibitor) in Patients with Myelofibrosis and Suboptimal Response to Ruxolitinib: Interim Analysis from a Phase 2 Study

Poster: MPN-127: Add-On Parsaclisib (a PI3Kδ Inhibitor) in Patients with Myelofibrosis and Suboptimal Response to Ruxolitinib: Interim Analysis from a Phase 2 Study

IBCL-203: Umbralisib, a PI3Kδ/CK1ε Dual Inhibitor Demonstrates Marked Clinical Activity in Patients with Relapsed or Refractory Indolent Non-Hodgkin Lymphoma (iNHL): Results from the Phase 2 Global UNITY-NHL Trial

Background Umbralisib is an oral, once-daily inhibitor of PI3Kδ and CK1e that is highly selective for the delta isoform. The UNITY-NHL trial (NCT02793583) is a multicenter, open-label, Phase 2b study evaluating umbralisib in previously treated NHL patients. Herein, we present results from the UNITY-NHL study. Methods 208 patients with R/R marginal zone, follicular, or small lymphocytic lymphoma (MZL, FL, SLL) unresponsive to prior treatments (≥1 MZL; ≥2 FL/SLL), including ≥1 anti-CD20–based therapy, were administered umbralisib 800mg orally once-daily until disease progression, unacceptable toxicity, or study withdrawal. The primary endpoint of the study was overall response rate (ORR) as assessed by an independent review committee, according to the revised IWG criteria. Results At a median follow up of 27.8 months, MZL patients (n=69) had an ORR of 49.3% (95% CI 37.0% - 61.6%) with 15.9% achieving a complete response (CR), and a Disease Control Rate (DCR: CR+PR+SD) of 82.6%. Median time-to-response (TTR): 2.8 months (95% CI 2.7 - 2.9). No patient who achieved CR has progressed to date. At a median follow up of 27.5 months, FL patients (n=117) had an ORR of 45.3% (95% CI 36.1% - 54.8%) with 5.1% achieving a CR, and a DCR of 79.5%. Median TTR: 4.6 months (95% CI 3.0 - 5.6). At a median follow up of 29.3 months, SLL patients (n=22) had an ORR of 50.0% (95% CI 28.2 - 71.8) with 4.5% achieving a CR, and a DCR of 86.4%. Median TTR: 2.7 months (95% CI 2.4 - 2.8). At least one grade ≥3 treatment-emergent adverse event (TEAE) was reported in 53.4% of patients. TEAEs led to umbralisib discontinuation in 32 patients (15.4%). Grade ≥3 TEAEs reported in ≥10% of patients: neutropenia (11.5%) and diarrhea (10.1%). Increased ALT/AST (grade ≥3) occurred in 6.7%/7.2% of patients. Conclusions Umbralisib achieved meaningful clinical activity in a heavily pretreated iNHL population. The safety profile was manageable, with a relatively low incidence of immune-mediated toxicities and AE-related discontinuations. These results suggest umbralisib has a favorable benefit-risk profile in this patient population and have supported the Accelerated Approval of umbralisib in previously treated MZL and FL patients.

Physiologically Based Pharmacokinetic Modelling of Inhaled Nemiralisib: Mechanistic Components for Pulmonary Absorption, Systemic Distribution, and Oral Absorption.

Background and ObjectivesPhysiologically based pharmacokinetic (PBPK) modelling has evolved to accommodate different routes of drug administration and enables prediction of drug concentrations in tissues as well as plasma. The inhalation route of administration has proven successful in treating respiratory diseases but can also be used for rapid systemic delivery, holding great promise for treatment of diseases requiring systemic exposure. The objective of this work was to develop a PBPK model that predicts plasma and tissue concentrations following inhalation administration of the PI3Kδ inhibitor nemiralisib.MethodsA PBPK model was built in GastroPlus® that includes a complete mechanistic description of pulmonary absorption, systemic distribution and oral absorption following inhalation administration of nemiralisib. The availability of clinical data obtained after intravenous, oral and inhalation administration enabled validation of the model with observed data and accurate assessment of pulmonary drug absorption. The PBPK model described in this study incorporates novel use of key parameters such as lung systemic absorption rate constants derived from human physiological lung blood flows, and implementation of the specific permeability-surface area product per millilitre of tissue cell volume (SpecPStc) to predict tissue distribution.ResultsThe inhaled PBPK model was verified using plasma and bronchoalveolar lavage fluid concentration data obtained in human subjects. Prediction of tissue concentrations using the permeability-limited systemic disposition tissue model was further validated using tissue concentration data obtained in the rat following intravenous infusion administration to steady state.ConclusionsFully mechanistic inhaled PBPK models such as the model described herein could be applied for cross molecule assessments with respect to lung retention and systemic exposure, both in terms of pharmacology and toxicology, and may facilitate clinical indication selection.

MPN-127: Add-On Parsaclisib (a PI3K5 Inhibitor) in Patients with Myelofibrosis and Suboptimal Response to Ruxolitinib: Interim Analysis from a Phase 2 Study

Context: Ruxolitinib is highly effective in myelofibrosis (MF), improving symptoms, reducing spleen size, and prolonging survival. However, suboptimal response may occur, potentially due to persistent PI3K/AKT pathway activation despite continued JAK inhibition. Objective: This phase 2 study (NCT02718300) evaluated optimal dosing, efficacy, and safety of add-on parsaclisib (INCB050465), a potent and highly selective next-generation PI3Kδ inhibitor, in patients with MF with a suboptimal response to ruxolitinib. Design: Patients had primary or secondary MF, ECOG performance status ≤2, and suboptimal response after ≥6 months of ruxolitinib (5–25 mg twice daily; stable dose ≥8 weeks). Patients remained on their stable ruxolitinib dose and were randomized to receive add-on parsaclisib 10 or 20 mg once daily (QD) for 8 weeks and the same dose once weekly (QW) thereafter (QD/QW group) or parsaclisib 5 or 20 mg QD for 8 weeks and 5 mg QD thereafter (all QD group). The primary endpoint was change in spleen volume from baseline to week 12. Results: At data cutoff (Aug 27, 2020) for this interim analysis, 32 patients had received parsaclisib QD/QW and 35 received parsaclisib all QD. Median percentage change in spleen volume at week 12 was –1.9 (n=29) in QD/QW and –13.0 (n=27) in QD and at week 24 was –3.5 (n=23) and –21.8 (n=17), respectively. Median percentage change in Myelofibrosis-Symptoms Assessment Form Total Symptom Score at week 12 was –14.0 (n=21) in QD/QW and –37.4 (n=17) in QD. Nonhematologic treatment-emergent adverse events (TEAEs) were primarily grade 1/2. New-onset grade 3 and 4 thrombocytopenia were each observed in 6/32 (19%) patients in QD/QW and in 9/35 (26%) and 1/35 (3%) patients in QD, respectively. TEAEs of special interest included grade ≥2 diarrhea (n=4) and grade ≥2 rash (n=1) (all QD/QW). No colitis was reported. TEAEs led to parsaclisib discontinuation in 7/32 patients in QD/QW and 3/35 patients in QD and ruxolitinib discontinuation in 2/32 and 1/35 patients, respectively. Conclusions: Add-on parsaclisib showed preliminary efficacy in patients with MF experiencing suboptimal response to ruxolitinib; QD dosing appeared more efficacious than QD/QW dosing. Combination therapy was generally well tolerated with limited grade 3/4 AEs and TEAE-related discontinuations. Ruxolitinib is highly effective in myelofibrosis (MF), improving symptoms, reducing spleen size, and prolonging survival. However, suboptimal response may occur, potentially due to persistent PI3K/AKT pathway activation despite continued JAK inhibition. This phase 2 study (NCT02718300) evaluated optimal dosing, efficacy, and safety of add-on parsaclisib (INCB050465), a potent and highly selective next-generation PI3Kδ inhibitor, in patients with MF with a suboptimal response to ruxolitinib. Patients had primary or secondary MF, ECOG performance status ≤2, and suboptimal response after ≥6 months of ruxolitinib (5–25 mg twice daily; stable dose ≥8 weeks). Patients remained on their stable ruxolitinib dose and were randomized to receive add-on parsaclisib 10 or 20 mg once daily (QD) for 8 weeks and the same dose once weekly (QW) thereafter (QD/QW group) or parsaclisib 5 or 20 mg QD for 8 weeks and 5 mg QD thereafter (all QD group). The primary endpoint was change in spleen volume from baseline to week 12. At data cutoff (Aug 27, 2020) for this interim analysis, 32 patients had received parsaclisib QD/QW and 35 received parsaclisib all QD. Median percentage change in spleen volume at week 12 was –1.9 (n=29) in QD/QW and –13.0 (n=27) in QD and at week 24 was –3.5 (n=23) and –21.8 (n=17), respectively. Median percentage change in Myelofibrosis-Symptoms Assessment Form Total Symptom Score at week 12 was –14.0 (n=21) in QD/QW and –37.4 (n=17) in QD. Nonhematologic treatment-emergent adverse events (TEAEs) were primarily grade 1/2. New-onset grade 3 and 4 thrombocytopenia were each observed in 6/32 (19%) patients in QD/QW and in 9/35 (26%) and 1/35 (3%) patients in QD, respectively. TEAEs of special interest included grade ≥2 diarrhea (n=4) and grade ≥2 rash (n=1) (all QD/QW). No colitis was reported. TEAEs led to parsaclisib discontinuation in 7/32 patients in QD/QW and 3/35 patients in QD and ruxolitinib discontinuation in 2/32 and 1/35 patients, respectively. Add-on parsaclisib showed preliminary efficacy in patients with MF experiencing suboptimal response to ruxolitinib; QD dosing appeared more efficacious than QD/QW dosing. Combination therapy was generally well tolerated with limited grade 3/4 AEs and TEAE-related discontinuations.

Acetylation of the Catalytic Lysine Inhibits Kinase Activity in PI3Kδ

Covalent inhibition is a powerful strategy to develop potent and selective small molecule kinase inhibitors. Targeting the conserved catalytic lysine is an attractive method for selective kinase inactivation. We have developed novel, selective inhibitors of phosphoinositide 3-kinase δ (PI3Kδ) which acylate the catalytic lysine, Lys779, using activated esters as the reactive electrophiles. The acylating agents were prepared by adding the activated ester motif to a known selective dihydroisobenzofuran PI3Kδ inhibitor. Three esters were designed, including an acetate ester which was the smallest lysine modification evaluated in this work. Covalent binding to the enzyme was characterized by intact protein mass spectrometry of the PI3Kδ-ester adducts. An enzymatic digest coupled with tandem mass spectrometry identified Lys779 as the covalent binding site, and a biochemical activity assay confirmed that PI3Kδ inhibition was a direct result of covalent lysine acylation. These results indicate that a simple chemical modification such as lysine acetylation is sufficient to inhibit kinase activity. The selectivity of the compounds was evaluated against lipid kinases in cell lysates using a chemoproteomic binding assay. Due to the conserved nature of the catalytic lysine across the kinome, we believe the covalent inhibition strategy presented here could be applicable to a broad range of clinically relevant targets.

PI3K in T Cell Adhesion and Trafficking.

PI3K signalling is required for activation, differentiation, and trafficking of T cells. PI3Kδ, the dominant PI3K isoform in T cells, has been extensively characterised using PI3Kδ mutant mouse models and PI3K inhibitors. Furthermore, characterisation of patients with Activated PI3K Delta Syndrome (APDS) and mouse models with hyperactive PI3Kδ have shed light on how increased PI3Kδ activity affects T cell functions. An important function of PI3Kδ is that it acts downstream of TCR stimulation to activate the major T cell integrin, LFA-1, which controls transendothelial migration of T cells as well as their interaction with antigen-presenting cells. PI3Kδ also suppresses the cell surface expression of CD62L and CCR7 which controls the migration of T cells across high endothelial venules in the lymph nodes and S1PR1 which controls lymph node egress. Therefore, PI3Kδ can control both entry and exit of T cells from lymph nodes as well as the recruitment to and retention of T cells within inflamed tissues. This review will focus on the regulation of adhesion receptors by PI3Kδ and how this contributes to T cell trafficking and localisation. These findings are relevant for our understanding of how PI3Kδ inhibitors may affect T cell redistribution and function.

Disorders Related to PI3Kδ Hyperactivation: Characterizing the Clinical and Immunological Features of Activated PI3-Kinase Delta Syndromes.

Phosphoinositide-3-kinase δ (PI3Kδ) is found in immune cells and is part of the PI3K/AKT/mTOR/S6K signalling pathway essential to cell survival, growth and differentiation. Hyperactivation of PI3Kδ enzyme results in Activated PI3-kinase delta syndrome (APDS). This childhood onset, autosomal dominant, combined immunodeficiency, is caused by heterozygous gain of function (GOF) mutations in PIK3CD (encodes PI3Kδ catalytic subunit p110δ), mutations in PIK3R1 (encodes PI3Kδ regulatory subunit p85α) or LOF mutations in PTEN (terminates PI3Kδ signalling) leading to APDS1, APDS2 and APDS-Like (APDS-L), respectively. APDS was initially described in 2013 and over 285 cases have now been reported. Prompt diagnosis of APDS is beneficial as targeted pharmacological therapies such as sirolimus and potentially PI3Kδ inhibitors can be administered. In this review, we provide an update on the clinical and laboratory features of this primary immunodeficiency. We discuss the common manifestations such as sinopulmonary infections, bronchiectasis, lymphoproliferation, susceptibility to herpesvirus, malignancy, as well as more rare non-immune features such as short stature and neurodevelopmental abnormalities. Laboratory characteristics, such as antibody deficiency and B cell and T cell, phenotypes are also summarised.

Synthesis and biological evaluation of novel purinyl quinazolinone derivatives as PI3Kδ-specific inhibitors for the treatment of hematologic malignancies

Phosphatidylinositol 3-kinases (PI3Ks) mediate intracellular signal transduction. Aberrant PI3K signaling is associated with oncogenesis and disease progression in solid tumors and hematologic malignancies. Idelalisib (1), a first-in-class PI3Kδ inhibitor for the treatment of hematologic malignancies, was developed, but its sales were limited by black box warnings due to unexpected adverse effects. Therefore, to overcome these adverse events, various quinazolinone derivatives were synthesized and evaluated in vitro based on their inhibitory activity against the PI3K enzyme and the viability of cell lines such as MOLT and SUDHL. Among them, 6f (IC50 = 0.39 nM) and 6m (IC50 = 0.09 nM) showed excellent enzyme activity, and 6m displayed an approximately four-fold higher selectivity for PI3Kγ/δ compared with Idelalisib (1). Furthermore, in vivo PK experiments with 6f and 6m revealed that 6f (AUClast = 81.04 h*ng/mL, Cmax = 18.34 ng/mL, Tmax = 0.5 h, t1/2 = 10.2 h in 1 mpk dose) had improved PK compared with 1. Finally, further experiments will be conducted with 6f selected as a candidate, and the potential for it to be developed as a treatment with good efficacy for hematologic malignancies will be determined.

Abstract CT162: Addition of parsaclisib (INCB050465), a PI3Kδ inhibitor, in patients with suboptimal response to ruxolitinib: A phase 2 study in patients with myelofibrosis

Abstract Background: Ruxolitinib improves outcomes in patients (pts) with myelofibrosis (MF); however, suboptimal response may occur due to persistent PI3K/AKT pathway activation despite continued JAK inhibition. This phase 2 study (NCT02718300) evaluated optimal dosing and efficacy of add-on parsaclisib, a potent, highly selective next-generation PI3Kδ inhibitor, in pts with MF and suboptimal ruxolitinib response. Methods: Patients had primary/secondary MF, ECOG ≤2, and suboptimal response (palpable spleen >10 cm below left subcostal margin [LSM]; or palpable spleen 5-10 cm below LSM and active symptoms) after ≥6 months of ruxolitinib (5-25 mg BID; stable dose, ≥8 weeks [wks]). Patients remained on their stable ruxolitinib dose and were randomized to add-on parsaclisib QD/QW (10 or 20 mg QD for 8 wks/same dose QW thereafter) or parsaclisib QD (5 or 20 mg QD for 8 wks/5 mg QD thereafter). Endpoints: baseline-to-wk-12 spleen volume (SV) change by MRI/CT (primary endpoint); spleen length and symptom changes (Myelofibrosis-Symptoms Assessment Form Total Symptom Score [MFSAF-TSS]). Results: At data cutoff (1/20/2020), 33 pts received parsaclisib QD/QW; 20 received QD (median treatment duration, 197 days; median average daily doses: parsaclisib, 4.9 mg/day; ruxolitinib, 30.0 mg/day). Baseline median (range) SV (cm3) was 2333 (327-5324) in QD/QW (n=30) and 1890 (434-3741) in QD (n=17); median MFSAF-TSS was 10.8 (n=28) and 18.7 (n=17). In QD/QW and QD, median percent SV change was −2.3 (n=30) and −15.4 (n=17) at wk 12; and −2.5 (n=24) and −25.4 (n=9) at wk 24. In QD/QW and QD, number of pts with wk 12 SV reduction ≥10% were 10/30 (33%) and 10/17 (59%); ≥25% were 1/30 (3%) and 4/17 (24%); and ≥35% were 0 and 1/17 (6%). Median percent change in MFSAF-TSS at wk 12 was −14.0 (n=21) in QD/QW; −39.6 (n=12) in QD. Nonhematologic AEs were primarily grade 1/2. Grade 3/4 treatment-related, nonhematologic AEs included disseminated tuberculosis, enteritis, fatigue, hypertension, increased alanine aminotransferase, and increased aspartate aminotransferase in QD/QW and stomatitis in QD. In QD/QW and QD, 6/33 and 6/20 pts had new-onset grade 3 thrombocytopenia; 7/33 and 0/20 pts had grade 4 thrombocytopenia; hemoglobin levels remained steady during the study in both groups. Serious treatment-related AEs were stomatitis, herpes zoster infection, varicella zoster infection, and disseminated tuberculosis (each n=1). No colitis/dose-limiting diarrhea/rash occurred. In QD/QW and QD, 18/33 and 10/20 pts interrupted parsaclisib, and 4/33 and 4/20 interrupted ruxolitinib for AEs. Conclusions: Add-on parsaclisib showed efficacy in pts with MF experiencing suboptimal ruxolitinib response; QD dosing appeared more efficacious than QD/QW dosing. Combination therapy demonstrated acceptable safety with limited grade 3/4 AEs and no dose-limiting AEs. Citation Format: Abdulraheem Yacoub, Eunice S. Wang, Raajit K. Rampal, Uma Borate, Marina Kremyanskaya, Haris Ali, Gabriela S. Hobbs, Casey O'Connell, Albert Assad, Sue Erickson-Viitanen, Feng Zhou, Timothy C. Burn, Naval G. Daver. Addition of parsaclisib (INCB050465), a PI3Kδ inhibitor, in patients with suboptimal response to ruxolitinib: A phase 2 study in patients with myelofibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT162.

Abstract 1383: A next-generation PI3Kδ/γ inhibitor, ZX-101A inhibiting solid tumor growth by enhancing anti-tumor immunity

Abstract PI3K signaling cascade plays a central role in the regulation of key cellular pathways including growth, proliferation, differentiation, migration and survival. Previous studies suggested that both PI3Kδ and γ activities exert immunosuppression by targeting regulatory T cells (Treg) and myeloid cells. ZX-101A is an inhibitor of PI3K with predominant activity against the PI3Kδ and PI3Kγ isoforms, whose expressions are largely restricted to hematopoietic cells. Dual inhibition of PI3Kδ and PI3Kγ by ZX-101A may potentially restore the immune surveillance to limit tumor growth.The inhibitory effect of ZX-101A on PI3K activity was evaluated by blocking of AKT phosphorylation at T308 and S473 in human B-cell lymphoma DOHH2 cells and stimulated THP1 monocyte cells. ZX-101A significantly decreased the phosphorylation of AKT at S473 site in comparison to DMSO treated DOHH2 cells, but no difference on p-AKT level between the two concentrations of ZX-101A and the three treatment time points. In contrast, ZX-101A blocked the p-AKT on S473 in LPS-stimulated THP-1 cell line in both dose- and time-dependent manner. In vitro cell proliferation assay demonstrated ZX-101A potently inhibited cell proliferation of B-cell and T-cell lymphoma cell lines, but without potent effect on cells (e.g. 4T1 and CT26) derived from solid tumors. In contrast, ZX-101A inhibited tumor growth in CT26 syngeneic mouse model after 21-day treatment with TGI at 76.9% (1mg/kg QD), 79.5% (3mg/kg QD) and 90.0% (12mg/kg), which was attributed to enhanced anti-tumor immunity by ZX-101A treatment. Flow cytometry study on CT 26 tumors demonstrated that ZX-101A decreased Treg and increased M1/M2 macrophage polarization in the tumor microenvironment. Ex vivo T-cell differentiation assay using mouse spleen T cells and M1/M2 polarization assay using human PBMC cells confirmed the effect of ZX-101A on decreasing Treg differentiation and enhancing M1 macrophage function. Similarly, in vivo anti-tumor growth was observed in 4T1 and A20 syngeneic models. In A20 syngeneic model, ZX-101A in combination of anti-PD1 antibody achieved 99.7% TGI after 18 days of treatment, while anti-PD1 antibody alone only had TGI at 11.7%. Safety assessment on the mouse spleen, thymus and colon organs indicated minimal side effects by the treatment of the ZX-101A alone and in combination with anti-PD1. Its absorption, distribution, metabolism, and excretion (ADME) and safety profile, through a series of preclinical in vitro and in vivo studies, supported the ZX-101A clinical development. These results suggested ZX-101A as a potential immunotherapeutic agent to appropriate solid tumor types. Citation Format: Xiaolin Hao, Zhiyuan Peng, Kun Guo, Ying-Ying Li, Deming Kong, Jinfu Yang, Xiaoli (Shelley) Qin. A next-generation PI3Kδ/γ inhibitor, ZX-101A inhibiting solid tumor growth by enhancing anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1383.

Abstract CT202: A phase 1/2a, dose-escalation and dose-expansion study of ZX-101A in patients with relapsed/resistant or refractory advanced hematologic malignancies

Abstract ZX-101A is a next-generation PI3Kδ/γ inhibitor, without the purine motif in the first generation marketed drug duvelisib. It is not an inhibitor or substrate of major CYP enzymes and potentially avoids the drug-drug interaction limitation of duvelisib in combination therapies or with concomitant medications. Preclinical studies suggested an improved therapeutic window compared to duvelisib. Its absorption, distribution, metabolism, and excretion (ADME) and safety profile, through a series of in vitro and in vivo studies, supports the clinical development of ZX-101A in hematologic malignancies. Dual inhibition of PI3Kδ and PI3Kγ by ZX-101A as treatment of hematologic malignancies may exert synergistic effects through inhibiting PI3K signaling in malignant lymphocytes and cytokine/chemokine signaling from the tumor microenvironment as well as enhancing anti-tumor immunity. In vitro cell proliferation assay demonstrated ZX-101A potently inhibited cell proliferation of B- and T-cell lymphoma cell lines, but without effect on cells derived from solid tumors. In vivo tumor growth inhibition was observed in B-cell lymphoma CDX mouse model and multiple syngeneic animal models including A20, 4T1 and CT26, supporting a multifaceted anti-tumor effect of ZX-101A. Both in vitro and in vivo studies demonstrated that ZX-101A decreases regulatory T cell differentiation from naïve CD4+ cells and optimizes M1/M2 macrophage polarization. Additionally, in A20 syngeneic mouse model, ZX-101A in combination with anti-PD1 antibody achieved 99.7% tumor growth inhibition (TGI) after 18-days of treatment, while TGI was only 11.7% with anti-PD1 antibody alone. ZX-101A-101 is an ongoing Phase 1/2a, first-in-human, open-label, multicenter, multiple-dose ascending study to investigate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of once daily oral ZX-101A in 28-day cycles in patients with relapsed/resistant/refractory advanced hematologic malignancies (ClinicalTrials.gov Identifier: NCT04504708). The study consists of 2 parts, Dose Escalation and Dose Expansion. Part 1 dose escalation is designed to determine the safety, tolerability, and recommended phase 2 dose (RP2D) of ZX-101A. Part 2 dose expansion will evaluate ZX-101A activity in up to three disease-specific cohorts (CLL/SLL, indolent NHL, and based on emerging data from Part 1, Peripheral T-cell lymphoma may be included). Inclusion of a cohort of combination therapy is planned. Citation Format: Xiaoli (Shelley) Qin, Edgar Bautista, April Teitelbaum, Xiaolin Hao, Jinfu Yang. A phase 1/2a, dose-escalation and dose-expansion study of ZX-101A in patients with relapsed/resistant or refractory advanced hematologic malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT202.

Abstract CT252: A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of Ruxolitinib Plus Parsaclisib in Patients with JAK- and PI3K-Inhibitor Treatment-Naïve Myelofibrosis

Abstract Background: Ruxolitinib (JAK1/JAK2 inhibitor) significantly improves outcomes in patients with myelofibrosis (MF); however, a subset of patients may experience a suboptimal response. Recent phase 2 data showed that addition of PI3Kδ inhibitor parsaclisib to ruxolitinib monotherapy resulted in additional alleviation of MF symptoms and splenomegaly in patients with MF (Yacoub. EHA2020. S216). This phase 3, randomized, double-blind study (INCB 50465-313; NCT04551066), evaluates the combination of ruxolitinib and parsaclisib in patients with MF who are naïve to Janus kinase (JAK) and PI3K inhibitor therapies. Methods: Eligible patients are aged ≥18 years with a diagnosis of primary MF, post-polycythemia vera MF, or post-essential thrombocythemia MF, have a Dynamic International Prognostic Scoring System (DIPSS; Passamonti. Blood. 2010;115:1703-1708) risk category of at least Intermediate (INT)-1, palpable spleen ≥5 cm below left subcostal margin, total symptom score ≥10 at screening, ECOG PS 0-2, and life expectancy ≥24 weeks. Patients will be excluded if they previously received therapy with any JAK inhibitor, any PI3K inhibitor, any experimental or standard drug therapy for MF within 3 months of first study dose and/or lack of recovery from all toxicities related to previous therapies to grade ≤1, have recent history of inadequate bone marrow reserve (eg, platelet count <50×109/L) or have inadequate liver or renal function at screening. Approximately 440 patients will be randomized (1:1) to ruxolitinib plus parsaclisib 5 mg QD or ruxolitinib plus matching placebo, with stratification at randomization by DIPSS risk category (high vs INT-2 vs INT-1) and platelet count (≥100×109/L vs 50 to <100×109/L inclusive). Treatment will begin on Day 1, with starting ruxolitinib dose level determined by baseline platelet count, and will continue as long as treatment is tolerated and discontinuation criteria are not met. When the last enrolled patient has completed 24 weeks of treatment, the study will be unblinded and patients randomized to ruxolitinib plus placebo who have adequate hematology parameters will be able to crossover to receive parsaclisib together with continued ruxolitinib. The primary objective is the evaluation and comparison of spleen volume at Week 24 for patients who received ruxolitinib plus parsaclisib versus ruxolitinib plus placebo. Secondary objectives include evaluation and comparison of patient-reported MF symptoms, overall survival, time to onset and duration of response in spleen volume, and safety and tolerability for ruxolitinib plus parsaclisib versus ruxolitinib plus placebo. Sites are opening across the US, Canada, EU, and Asia. Citation Format: Abdulraheem Yacoub, Sue Erickson-Viitanen, Feng Zhou, Albert Assad. A Phase 3, Randomized, Double-Blind, Placebo-Controlled Study of Ruxolitinib Plus Parsaclisib in Patients with JAK- and PI3K-Inhibitor Treatment-Naïve Myelofibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT252.