PI3Kδ Inhibitor Research Articles

Phase Ib study of the oral PI3Kδ inhibitor linperlisib in patients with advanced solid tumors.

Patients with advanced solid tumors have a suboptimal prognosis. This study investigated the safety and feasibility of linperlisib, a selective phosphatidylinositol 3-kinase delta isoform (PI3Kδ) inhibitor, for treating patients with advanced solid tumors. In this phase Ib, single-arm, open-label, multi-center clinical trial, patients with histologically confirmed advanced solid tumors from eight centers in China were enrolled to receive oral linperlisib (80mg/day). The primary endpoint was safety. Between August 2019 and June 2022, 94 patients were enrolled in the trial and received the study treatment. The most common (≥ 20%) treatment emergent adverse events (TEAEs) of all grades irrespective of causality were increased aspartate aminotransferase (AST) (26.6%), proteinuria (26.6%), decreased appetite (25.5%), increased alanine aminotransferase (ALT) (22.3%), weight loss (21.3%), and anemia (21.3%). The most common grade ≥ 3 TEAEs were diarrhea (4.3%), increased AST (3.2%), increased ALT (3.2%), neutropenia (3.2%), anemia (3.2%), increased blood alkaline phosphatase (3.2%). The objective response rate (ORR) was 1.1% (95% confidence interval [CI] 0.0-5.8), and the disease control rate (DCR) was 37.2% (95% CI 27.5-47.8). As of the data cutoff, the median follow-up time was 4.2months (95% CI 2.8-6.9). The median progression-free survival (PFS) was 1.85months (95% CI 1.79-1.88). The median overall survival (OS) was not reached. Linperlisib showed an acceptable safety profile and preliminary clinical benefit in patients with a range of advanced solid tumors. Further studies of linperlisib safety and efficacy are warranted.

In Silico Discovery of a Novel PI3Kδ Inhibitor Incorporating 3,5,7-Trihydroxychroman-4-one Targeting Diffuse Large B-Cell Lymphoma.

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma, and it is highly aggressive and heterogeneous. Targeted therapy is still the main treatment method used in clinic due to its lower risk of side effects and personalized medication. Excessive activation of PI3Kδ in DLBCL leads to abnormal activation of the PI3K/Akt pathway, promoting the occurrence and development of DLBCL. The side effects of existing PI3Kδ inhibitors limit their clinical application. The discovery of PI3Kδ inhibitors with novel structures and minimal side effects is urgently needed. This study constructed a PI3Kδ inhibitor screening model to screen natural product libraries. Revealing the mechanism of natural product therapy for DLBCL through network pharmacology, kinase assays, and molecular dynamics. The results of molecular docking indicated that Silibinin had a high docking score and a good binding mode with PI3Kδ. The results of network pharmacology indicated that Silibinin could exert therapeutic effects on DLBCL by inhibiting PI3Kδ activity and affecting the PI3K/Akt pathway. The kinase assays indicated that Silibinin concentration dependently inhibited the activity of PI3Kδ. The results of molecular dynamics indicated that Silibinin could stably bind to PI3Kδ. Silibinin was a structurally novel 3,5,7-trihydroxychroman-4-one PI3Kδ inhibitor, providing valuable information for the subsequent discovery of PI3Kδ inhibitors.

CHF6523 data suggest that the phosphoinositide 3-kinase delta isoform is not a suitable target for the management of COPD

BackgroundChronic obstructive pulmonary disease (COPD) is a chronic inflammatory condition. Given patients with COPD continue to experience exacerbations despite the availability of effective therapies, anti-inflammatory treatments targeting novel pathways are needed. Kinases, notably the phosphoinositide 3-kinases (PI3K), are thought to be involved in chronic airway inflammation, with this pathway proposed as a critical regulator of inflammation and oxidative stress response in COPD. CHF6523 is an inhaled PI3Kδ inhibitor that has shown positive preclinical results. This manuscript reports the results of a study of CHF6523 in patients with stable COPD (chronic bronchitis phenotype), and who had evidence of type-2 inflammation.MethodsThis randomised, double-blind, placebo-controlled, two-way crossover study comprised two 28-day treatment periods separated by a 28-day washout. Patients (N = 44) inhaled CHF6523 in one period, and placebo in the other, both twice daily. The primary objective was to assess the safety and tolerability of CHF6523; the secondary objective was to assess CHF6523 pharmacokinetics. Exploratory endpoints included target engagement (the relative reduction in phosphatidylinositol (3,4,5)-trisphosphate [PIP3]), pharmacodynamic evaluations such as airflow obstruction, and hyperinflation, and to identify biomarker(s) of drug response using proteomics and transcriptomics.ResultsCHF6523 plasma pharmacokinetics were characterised by an early maximum concentration (Cmax), reached 15 and 10 min after dosing on Days 1 and 28, respectively, followed by a rapid decline. Systemic exposure on Day 28 showed limited accumulation, with ratios < 1.6 for Cmax and area under the curve from 0 to 12 h post-dose, and with steady state achieved on Day 20. Target engagement was confirmed by a significant 29.7% reduction from baseline in induced sputum PIP3 (29.5% reduction vs. placebo; adjusted ratio 0.705 [0.580, 0.856]; p = 0.001), but this did not translate into an anti-inflammatory pharmacodynamic effect, as assessed through measures including biomarkers and multi-omics. Additionally, although CHF6523 was generally well-tolerated, 95.2% of patients reported cough as an adverse event, most mild to moderate and resolving within one-hour post-dose.ConclusionsThese data, together with those from other PI3K inhibitors, suggest that PI3Kδ is not a suitable pathway for the management of COPD, as the achieved target engagement did not translate into any pharmacodynamic anti-inflammatory effect.Trial registrationClinicalTrials.gov (NCT04032535); posted 23rd July 2019.

A novel mitochondrial pyruvate carrier inhibitor drives stem cell-like memory CAR T cell generation and enhances antitumor efficacy

Adoptive cell transfer with chimeric antigen receptor (CAR) expressing T cells can induce remarkable complete responses in cancer patients. Therapeutic success has been correlated with central and stem cell-like memory T cell subsets in the infusion product which are better able to drive efficient CAR T cell in vivo expansion and long-term persistence. We previously reported that inhibition of the mitochondrial pyruvate carrier (MPC) during mouse CAR T cell culture, induces a memory phenotype and enhances antitumor efficacy against melanoma. Here, we use a novel MPC inhibitor, MITO-66, which robustly induces a stem cell-like memory phenotype in CD19-CAR T cells generated from healthy donors and patients with relapsed/refractory B cell malignancies. MITO-66-conditioned CAR T cells were superior in controlling human pre-B cell acute lymphoblastic leukemia in mice. Following adoptive cell transfer, MITO-66-conditioned CAR T cells maintained a memory phenotype and protected cured mice against tumor rechallenge. Furthermore, in an in vivo B cell leukemia stress model, CD19-CAR T cells generated in the presence of MITO-66 largely outperformed clinical-stage AKT and PI-3Kδ inhibitors. Thus, we provide compelling preclinical evidence that MPC inhibition with MITO-66 during CAR T cell manufacturing dramatically enhances their antitumor efficacy, thereby paving the way to clinical translation.

PI3Kδ activation, IL-6 overexpression, and CD37 loss cause resistance to naratuximab emtansine in lymphomas

AbstractCD37-directed antibody and cellular-based approaches have shown preclinical and promising early clinical activity. Naratuximab emtansine (Debio 1562; IMGN529) is an antibody-drug conjugate (ADC) incorporating an anti-CD37 monoclonal antibody conjugated to the maytansinoid DM1 as payload, with activity as a single agent and in combination with rituximab in patients with lymphoma. We studied naratuximab emtansine and its free payload in 54 lymphoma models, correlated its activity with CD37 expression, characterized 2 resistance mechanisms, and identified combination partners providing synergy. The activity, primarily cytotoxic, was more potent in B- than T-cell lymphoma cell lines. After prolonged exposure to the ADC, 1 diffuse large B-cell lymphoma (DLBCL) cell line developed resistance to the ADC due to the CD37 gene biallelic loss. After CD37 loss, we also observed upregulation of interleukin-6 (IL-6) and related transcripts. Recombinant IL-6 led to resistance. Anti-IL-6 antibody tocilizumab improved the ADC’s cytotoxic activity in CD37+ cells. In a second model, resistance was sustained by a PIK3CD activating mutation, with increased sensitivity to PI3Kδ inhibition and a functional dependence switch from MCL1 to BCL2. Adding idelalisib or venetoclax overcame resistance in the resistant derivative and improved cytotoxic activity in the parental cells. In conclusion, targeting B-cell lymphoma with the naratuximab emtansine showed vigorous antitumor activity as a single agent, which was also observed in models bearing genetic lesions associated with inferior outcomes, such as Myc Proto-Oncogene (MYC) translocations and TP53 inactivation or R-CHOP (rituximab, cyclophosphamide, doxorubicin, Oncovin [vincristine], and prednisone) resistance. Resistant DLBCL models identified active combinations of naratuximab emtansine with drugs targeting IL-6, PI3Kδ, and BCL2.

33 (PB021): Loss-of-function and gain-of-function genetic screens identify potential biomarkers and combination partners for the highly selective allosteric PI3Kδ inhibitor roginolisib (IOA-244)

33 (PB021): Loss-of-function and gain-of-function genetic screens identify potential biomarkers and combination partners for the highly selective allosteric PI3Kδ inhibitor roginolisib (IOA-244)

Development of the telescoped flow Pd-catalyzed aerobic alcohol oxidation/reductive amination sequence in the synthesis of new phosphatidylinositide 3-kinase inhibitor (CPL302415).

Herein, we describe a two-step sequential flow synthesis: Pd-catalyzed aerobic oxidation to an aldehyde 2, which is then converted by reductive amination in H-Cube® PRO into CPL302415 (3). CPL302415 is our new PI3Kδ inhibitor, which is now under evaluation for the treatment of systemic lupus erythematosus. The process was optimized using the DoE approach and generalized to other biologically active derivatives of CPL302415.

Discovery of Pyrazolo[1,5-a]pyridine Derivatives as Potent and Selective PI3Kγ/δ Inhibitors.

PI3Kγ and PI3Kδ plays critical roles in exerting immunosuppression by targeting regulatory T cells and myeloid cells. Dual inhibition of PI3Kγ and PI3Kδ has emerged as a novel therapeutic strategy for cancer immunotherapy. We herein report a series of pyrazolopyridine derivatives with distinct scaffolds as potent and selective dual inhibitors of PI3Kγ and PI3Kδ. Among them, 20e (IHMT-PI3K-315) displays an IC50 value of 4.0 and 9.1 nM against PI3Kγ and PI3Kδ respectively in biochemical assays. Meanwhile, it potently inhibits PI3Kγ and PI3Kδ-mediated phosphorylation of AKT S473 with EC50 values of 0.028 and 0.013 μM in cellular assays. In addition, 20e exhibits a favorable selectivity profile in protein kinases at 1 μM. In bone marrow-derived macrophages (BMDM), 20e can repolarize the M2 phenotype to the M1 phenotype. In vivo, 20e demonstrates acceptable pharmacokinetic properties and suppresses tumor growth in a MC38 syngeneic mouse model.

The PI3Kδ inhibitor zandelisib on intermittent dosing in relapsed/refractory follicular lymphoma: Results from a global phase 2 study.

In this global phase 2 study in patients with relapsed/refractory follicular lymphoma (FL), zandelisib was administered on intermittent dosing to mitigate immune-related adverse events and infections that have been reported with oral PI3Kδ inhibitors administered daily continuously. Eligible patients with measurable disease and progression after at least twoprior therapies were administered zandelisib until disease progression or intolerability. The primary efficacy endpoint was objective response rate (ORR) and the key secondary efficacy endpoint was duration of response (DOR). We report on 121 patients with FL administered zandelisib on intermittent dosing after 8 weeks of daily dosing for tumor debulking. The median number of prior therapies was 3 (range, 2-8) and 45% of patients had refractory disease. The ORR was 73% (95% confidence interval [CI], 63.9-80.4), the complete response (CR) rate was 38% (95% CI, 29.3-47.3), and the median DOR was 16.4 months (95% CI, 9.5-not reached). With a median follow-up of 14.3 months (range, 1-30.5), the median progression-free survival was 11.6 months (95% CI, 8.3-not reached). Twenty-one patients (17%) discontinued therapy due to an adverse event. Grade 3-4 class-related toxicities included 6% diarrhea, 5% lung infections, 3% colitis (confirmed by biopsy or imaging), 3% rash, 2% AST elevation, and 1% non-infectious pneumonitis. Zandelisib achieved a high rate of durable responses in heavily pretreated patients with relapsed/refractory FL. The intermittent dosing resulted in a relatively low incidence of severe class-related toxicities, which supports the evaluation of zandelisib as a single agent and in combination with indolent B-cell malignancies.

PI3K Inhibitors in Hematology: When One Door Closes….

The PI3K signaling pathway regulates key cellular processes and is one of the most aberrantly activated pathways in cancer. The class I PI3K catalytic subunits p110γ and p110δ are highly enriched in leukocytes, providing an additional rationale for targeting these PI3Ks in hematologic malignancies. In 2014, the PI3Kδ inhibitor idelalisib was the first of four PI3K inhibitors (PI3Ki) to receive regulatory approval for relapsed B-cell malignancies. This was followed by approvals of the pan-class I inhibitor copanlisib (2017), the dual PI3Kγ/δ inhibitor duvelisib (2018), and the PI3Kδ and casein kinase 1ε inhibitor umbralisib (2021). Copanlisib and umbralisib received accelerated approvals, whereas idelalisib and duvelisib received initial accelerated approvals followed by full approvals. The accelerated approvals were based on overall response rates; however, follow-up studies showed increased risk of death and serious side effects. Furthermore, the confirmatory trial with copanlisib failed to show an improvement in progression-free survival when compared with chemoimmunotherapy. These developments led to black box warnings for idelalisib and duvelisib and withdrawal of copanlisib and umbralisib from the market by their manufacturers. Given the uncertain future of this drug class, additional manufacturers terminated ongoing phase III trials with novel PI3Kis. In this study, we review the development and current status of PI3Kis in hematology, limitations to their use, and our perspective on whether there is a future for PI3Kis in hematology.

Selective PI3Kδ inhibitor TYM-3-98 suppresses AKT/mTOR/SREBP1-mediated lipogenesis and promotes ferroptosis in KRAS-mutant colorectal cancer

Colorectal cancer (CRC) is one of the most common tumors of the digestive system worldwide. KRAS mutations limit the use of anti-EGFR antibodies in combination with chemotherapy for the treatment of CRC. Therefore, novel targeted therapies are needed to overcome the KRAS-induced oncogenesis. Recent evidence suggests that inhibition of PI3K led to ferroptosis, a nonapoptotic cell death closely related to KRAS-mutant cells. Here, we showed that a selective PI3Kδ inhibitor TYM-3–98 can suppress the AKT/mTOR signaling and activate the ferroptosis pathway in KRAS-mutant CRC cells in a concentration-dependent manner. This was evidenced by the lipid peroxidation, iron accumulation, and depletion of GSH. Moreover, the overexpression of the sterol regulatory element-binding protein 1 (SREBP1), a downstream transcription factor regulating lipid metabolism, conferred CRC cells greater resistance to ferroptosis induced by TYM-3–98. In addition, the effect of TYM-3–98 was confirmed in a xenograft mouse model, which demonstrated significant tumor suppression without obvious hepatoxicity or renal toxicity. Taken together, our work demonstrated that the induction of ferroptosis contributed to the PI3Kδ inhibitor-induced cell death via the suppression of AKT/mTOR/SREBP1-mediated lipogenesis, thus displaying a promising therapeutic effect of TYM-3–98 in CRC treatment.

Duvelisib plus romidepsin in relapsed/refractory T cell lymphomas: a phase 1b/2a trial.

PI3K-δ inhibitors have shown impressive activity in lymphoid malignancies but have been hampered by autoimmune and infectious toxicities, leading to market withdrawals. We previously demonstrated activity of the PI3K-δγ inhibitor duvelisib in T cell lymphomas (TCLs) that was associated with inflammatory adverse events. As reported here, we conducted a phase 1b/2a study of duvelisib in combination with either romidepsin (n = 66) or bortezomib (n = 32) in patients with relapsed/refractory TCL and found that the addition of romidepsin, but not bortezomib, appeared to increase efficacy while attenuating PI3K inhibitor-driven toxicity. The primary endpoint of the study was to determine the safety and maximum tolerated dose of duvelisib, which was 75 mg twice daily when combined with romidepsin versus 25 mg twice daily when combined with bortezomib. The most common adverse events were neutropenia (42%, 25/59) and fatigue (37%, 22/59) in patients treated with duvelisib and romidepsin and diarrhea (48%, 11/23) and neutropenia (30%, 7/23) in patients treated with duvelisib and bortezomib. Duvelisib and romidepsin resulted in less grade 3/4 hepatotoxicity (14%, 8/59) compared to 40% (14/35) in our previous study with duvelisib monotherapy. This was associated with reductions in circulating inflammatory mediators and myeloid cell inflammatory gene expression. Secondary endpoints of overall and complete response rates were 55% (35/64) and 34% (22/64) for patients treated with duvelisib and romidepsin and 34% (11/32) and 13% (4/32) for patients treated with duvelisib and bortezomib. Among patients with peripheral T cell lymphomas (PTCLs), overall and complete response rates of duvelisib and romidepsin were 56% (27/48) and 44% (21/48), respectively, with exploratory analyses showing increased response rates in patients with a follicular helper T cell subtype. These findings support further development of combined PI3K and histone deacetylase (HDAC) inhibition in TCLs and suggest a unique strategy to enable PI3K inhibitor-based combinations for additional patient populations. ClinicalTrials.gov identifier: NCT02783625 .

PIK3CA inhibition in models of proliferative glomerulonephritis and lupus nephritis.

Proliferative glomerulonephritis is a severe condition that often leads to kidney failure. There is a significant lack of effective treatment for these disorders. Here, following the identification of a somatic PIK3CA gain-of-function mutation in podocytes of a patient, we demonstrate using multiple genetically engineered mouse models, single-cell RNA sequencing, and spatial transcriptomics the crucial role played by this pathway for proliferative glomerulonephritis development by promoting podocyte proliferation, dedifferentiation, and inflammation. Additionally, we show that alpelisib, a PI3Kα inhibitor, improves glomerular lesions and kidney function in different mouse models of proliferative glomerulonephritis and lupus nephritis by targeting podocytes. Surprisingly, we determined that pharmacological inhibition of PI3Kα affects B and T lymphocyte populations in lupus nephritis mouse models, with a decrease in the production of proinflammatory cytokines, autoantibodies, and glomerular complement deposition, which are all characteristic features of PI3Kδ inhibition, the primary PI3K isoform expressed in lymphocytes. Importantly, PI3Kα inhibition does not impact lymphocyte function under normal conditions. These findings were then confirmed in human lymphocytes isolated from patients with active lupus nephritis. In conclusion, we demonstrate the major role played by PI3Kα in proliferative glomerulonephritis and show that in this condition, alpelisib acts on both podocytes and the immune system.

Discovery of Novel Azaindoles as Potent and Selective PI3Kδ Inhibitors for Treatment of Multiple Sclerosis.

Multiple sclerosis (MS) is a chronic autoimmune disorder of the central nervous system and the unmet need for MS treatment demands new therapeutic development. Particularly, PI3Kδ is a high-value target for autoimmune disease, while the investigation of PI3Kδ inhibitors for MS therapy is relatively scarce. Herein, we report a novel class of azaindoles as PI3Kδ inhibitors for MS treatment. Compound 31, designed via nitrogen bioisosterism, displayed excellent PI3Kδ inhibitory activity and selectivity. In vitro assay showed that 31 exhibited superior activity on T lymphocytes to inhibit the proliferation of CD4+, CD8+, and CD3+ T cells. In the experimental autoimmune encephalomyelitis (EAE) model, 31 showed a comparable therapeutical efficacy with Dexamethasone to significantly ameliorate EAE symptoms. Mechanistic studies showed that compound 31 could significantly inhibit the PI3K/AKT/mTOR signaling pathway and inhibited T-cell proliferation and differentiation. Overall, this work provides a new structural PI3Kδ inhibitor and a new vision for MS therapy.

Abstract PO5-05-08: LOSS OF SINGLEMINDED 2S RESULTS IN A PI3K SUBUNIT SWITCH WHICH DRIVES THERAPEUTIC RESISTANCE IN ESTROGEN RECEPTOR POSITIVE BREAST CANCER

Abstract Estrogen receptor (ER) + breast cancer (BC) comprises over 70% of BC cases and are targeted via ER modulated therapies. Despite this, ER+BC patients can experience recurrence within 20 years and the majority of BC related deaths can be attributed to metastatic ER+BC. These distant metastases are commonly diagnosed as endocrine therapy resistant. Thus, there is an unmet need to identify novel biomarkers for treating ER+ patients with metastases. We have identified a tumor suppressor gene, singleminded 2s (SIM2s), expressed in breast epithelial cells that inhibits epithelial to mesenchymal transition and metastasis, and is downregulated in the progression of breast disease. In ER+BC cell lines, loss of SIM2s results in upregulation of mesenchymal markers and increased PI3K/Akt signaling. Dysregulation of the PI3K/Akt signaling pathway in ER+BC is involved with tumor progression and acquired therapeutic resistance. Our study suggests loss of SIM2s confers resistance in ER+BC through a PI3K subunit switch resulting in upregulation of pro-survival signaling. MCF7 SIM2 knock out cells exhibit increased expression of mesenchymal markers and undergo a phenotypic change compared to wild type cells. Utilizing a migration/invasion assay, MCF7 SIM2 knock out cells exemplify an increase in invasion potential compared to wild type cells. Furthermore, changes in PI3K subunit expression were observed via western blot and real time qPCR analysis. Clonogenic assays revealed an acquired resistance to PI3Kα inhibition, but a susceptibility to PI3Kδ inhibition. This is a significant finding as a current standard of care for patients with ER+ breast cancer recurrence is PI3Kα inhibition. PI3Kδ is an already approved therapeutic target in chronic lymphocytic leukemia, thus PI3Kδ may present a new therapeutically targetable opportunity for ER+BC recurrence. Elucidating the mechanism for acquired therapeutic resistance is an integral avenue for understanding how breast cancer progresses and improving the prognosis of ER+BC patients. Citation Format: Garhett Wyatt, Rachel Steinmetz, Traci Lyons, Weston Porter. LOSS OF SINGLEMINDED 2S RESULTS IN A PI3K SUBUNIT SWITCH WHICH DRIVES THERAPEUTIC RESISTANCE IN ESTROGEN RECEPTOR POSITIVE BREAST CANCER [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-05-08.

Mitochondrial transcription is essential for the potent antitumor stem memory T cells

Abstract Adoptive T cell transfer (ACT) therapy is an effective approach to treat cancer patients, where expanding the patient’s T lymphocytes and redirecting them to recognize and regress solid tumors. Unfortunately, ACT can fail in some patients due to exhaustion or impaired metabolic fitness during T cell expansion. We discovered through transcriptomic analysis that the novel mitochondrial transcription regulator REXO2 induced by regulating PI3Kδ signaling in vitro - generated stem memory T cells (TSCM) - is responsible for the antitumor potency of TSCM cells. This finding is novel, as REXO2 has never been studied in immune cells and has only recently been appreciated in regulating heart muscles during embryonic development. We found that knocking out REXO2 via CRISPR in TSCM cells impaired their mitochondrial transcription and morphology in vitro. Moreover, they had reduced metabolic fitness marked by poor spare respiratory capacity, reduced mitochondrial potential and increased production of reactive oxygen species post tumor antigen recognition. Of clinical importance, REXO2 knockout in TSCM cells impaired the antitumor potency when infused into mice. This work also has translational potential, as REXO2 could be induced in human TIL or CAR T cell products by expanding them in the presence of PI3Kδ inhibitor. Our findings reveal that REXO2 is a promising target to bolster the antitumor activity of next generation TIL and CAR T cell products to treat cancer patients.

TYM-3-98, a novel selective inhibitor of PI3Kδ, demonstrates promising preclinical antitumor activity in B-cell lymphomas

AimsPI3Kδ is expressed predominately in leukocytes and is commonly found to be aberrantly activated in human B-cell lymphomas. Although PI3Kδ has been intensively targeted for discovering anti-lymphoma drugs, the application of currently approved PI3Kδ inhibitors has been limited due to unwanted systemic toxicities, thus warranting the development of novel PI3Kδ inhibitors with new scaffolds. Main methodsWe designed TYM-3-98, an indazole derivative, and evaluated its selectivity for all four PI3K isoforms, as well as its efficacy against various B-cell lymphomas both in vitro and in vivo. Key findingsWe identified TYM-3-98 as a highly selective PI3Kδ inhibitor over other PI3K isoforms at both molecular and cellular levels. It showed superior antiproliferative activity in several B-lymphoma cell lines compared with the approved first-generation PI3Kδ inhibitor idelalisib. TYM-3-98 demonstrated a concentration-dependent PI3K/AKT/mTOR signaling blockage followed by apoptosis induction. In vivo, TYM-3-98 showed good pharmaceutical properties and remarkably reduced tumor growth in a human lymphoma xenograft model and a mouse lymphoma model. SignificanceOur findings establish TYM-3-98 as a promising PI3Kδ inhibitor for the treatment of B-cell lymphoma.

115 Off-label treatment with the selective PI3Kδ inhibitor leniolisib in 2 pediatric patients with activated phosphoinositide 3-kinase delta syndrome 2 (APDS2)

115 Off-label treatment with the selective PI3Kδ inhibitor leniolisib in 2 pediatric patients with activated phosphoinositide 3-kinase delta syndrome 2 (APDS2)

Long-term treatment with selective PI3Kδ inhibitor leniolisib in adults with activated PI3Kδ syndrome

AbstractActivated phosphoinositide 3-kinase delta (PI3Kδ) syndrome (APDS) is an inborn error of immunity that manifests as immune deficiency and dysregulation; symptoms include frequent infections and lymphoproliferation. In our dose-finding and phase 3 placebo-controlled trials, treatment with the selective PI3Kδ inhibitor leniolisib reduced lymphoproliferation and normalized lymphocyte subsets. Here, we present 6 years of follow-up from the 6 adult patients in the original dose-finding trial receiving leniolisib. We used data from the ongoing open-label extension study, which was supplemented at later time points by investigators, including health-related quality of life (HRQoL) assessed through a clinician-reported questionnaire. We observed improvements in HRQoL: 5 of 6 patients experienced an increase in physical capabilities and socialization, and a decrease in prescribed medications. Immune subsets improved in all patients: mean transitional B-cell levels decreased from 38.17% to 2.47% and the CD4:CD8 T-cell ratio normalized to 1.11. Manifestations seen before and within the first year of leniolisib exposure, such as infections and gastrointestinal conditions, attenuated after year 2, with few new conditions emerging out to year 6. Thrombocytopenia or lymphopenia remained present in half of patients at year 6. Of 83 adverse events through year 5, 90.36% were grade 1; none were grade 4/5 nor deemed leniolisib related. Collectively, we saw an enhancement in HRQoL as well as durable changes in lymphocyte subsets and clinical manifestations, further supporting the use of leniolisib as a long-term therapeutic option for the treatment of APDS. This trial was registered at www.ClinicalTrials.gov as #NCT02859727.

Abstract CT189: A first-in-human, phase 1a, dose-escalation study of BGB-10188, a phosphatidylinositol 3-kinase delta (PI3Kδ) inhibitor, + tislelizumab (anti-PD-1) in patients with solid tumors

Abstract Background: PI3Kδ inhibition hampers regulatory T-cell proliferation and function, potentially optimizing CD8+ T-cell activation for antitumor immunity in solid tumors. BGB-10188, a novel PI3Kδ inhibitor, showed high selectivity, potency, and an improved safety profile vs other PI3Kδ inhibitors in preclinical studies. Here, we present the results of BGB-10188 + tislelizumab in patients with solid tumors from the phase 1a dose-escalation part (Part D) of an open-label, multicenter, 5-part phase 1/2 study (NCT04282018). Methods: Eligible patients were aged ≥18 years with ECOG PS of 0 or 1 and had previously treated unresectable locally advanced or metastatic solid tumors. BGB-10188 was given orally once daily (QD) at 6 dose levels (20, 40, 80, 160, 320, and 540 mg). Tislelizumab 200 mg IV was given on Day 8 of the 28-day Cycle 1 and Day 1 of all subsequent 21-day cycles. Primary objectives were to assess the safety and tolerability of BGB-10188 + tislelizumab. Select secondary/exploratory objectives were to evaluate preliminary antitumor activity, pharmacokinetics, and pharmacodynamics. Results: As of August 30, 2023, 44 patients were treated with BGB-10188 + tislelizumab (median follow-up: 4.65 months; 3 patients remain on treatment). The median age was 61 years. Patients had a median of 2 prior lines of therapy (range, 1-11) and 97.7% of patients had metastatic disease at study entry. 84.1% (37 of 44) of patients had ≥1 adverse event (AE) related to either study drug. 81.8% (36) of patients had ≥1 BGB-10188-related AE, of which the most common (≥10%) were nausea (22.7%, n=10), decreased appetite (18.2%, n=8), fatigue (18.2%, n=8), alanine aminotransferase (ALT) increased (13.6%, n=6), aspartate aminotransferase (AST) increased (11.4%, n=5), and rash (11.4%, n=5). Two patients discontinued study drug treatment due to BGB-10188-related AEs. Three dose-limiting toxicities for BGB-10188 + tislelizumab were observed: grade (Gr) 5 pneumonia and Gr 5 intracranial hemorrhage at 160 mg, Gr 3 ALT/AST increase at 320 mg, and Gr 3 rash at 540 mg. Maximum tolerated dose was not reached. The confirmed objective response rate was 9.1% (4 of 44) and the disease control rate was 31.8% (14 of 44). The plasma exposure to BGB-10188 exhibited a dose-dependent increase across a range of 20 mg to 540 mg. The peak concentration of BGB-10188 typically occurred ~2 hours post dose. Additionally, the mean half-life was observed to be between 8 hours and 13 hours across dosages. Peripheral p-AKT inhibition increased with dose, suggesting valid target engagement of BGB-10188, and reached a plateau at ~84%. Conclusions: BGB-10188 + tislelizumab showed preliminary antitumor activity and was generally safe and tolerable across doses in this heavily pretreated population of patients with solid tumors. BGB-10188 + tislelizumab will be further evaluated in dose expansion (Part E). Citation Format: Rasha Cosman, Elizabeth Ahern, Jie Li, Hui K. Gan, Yu Chen, Bo Gao, Yongsheng Wang, Xiyan Mu, Huan Cheng, Yanrong Qian, Heather Zhang, Ke Cao. A first-in-human, phase 1a, dose-escalation study of BGB-10188, a phosphatidylinositol 3-kinase delta (PI3Kδ) inhibitor, + tislelizumab (anti-PD-1) in patients with solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT189.