Antitumor Activity Of Combination Research Articles

Phase Ib/II Study of Lacnotuzumab in Combination with Spartalizumab in Patients with Advanced Malignancies.

Blocking the colony-stimulating factor 1 (CSF-1) signal on tumor-associated macrophages can lead to an upregulation of checkpoint molecules, such as programmed cell death ligand 1 (PD-L1), thus causing resistance to this blockade. Combining spartalizumab (PDR001), a high-affinity, ligand-blocking, humanized anti-PD-1 immunoglobulin G4 antibody, with lacnotuzumab (MCS110), a high-affinity, humanized monoclonal antibody directed against human CSF-1 can potentially overcome this resistance. This was a multicenter, phase Ib/II trial using a combination of spartalizumab with lacnotuzumab in patients with advanced cancers, including anti-PD-1/PD-L1 treatment-resistant melanoma, and anti-PD-1/PD-L1 treatment-naïve triple-negative breast cancer, pancreatic cancer, and endometrial cancer (ClinicalTrials.gov identifier: NCT02807844). The primary objective of dose escalation phase Ib was to assess safety, tolerability, and recommended phase II dose. The primary objective of the phase II expansion study was to assess the combination's antitumor activity, including objective response rate and clinical benefit rate. A total of eight patients (five in phase Ib and three in phase II) were evaluable for adverse events (AEs) at our study site. All eight patients experienced at least grade 1 AE. The most common treatment-related AEs were increased serum aspartate aminotransferase (38%), fatigue (38%), anemia (25%), increased alkaline phosphatase (25%), hyperbilirubinemia (25%), hypocalcemia (25%), and hypoalbuminemia (25%). Most of these AEs were grade 1 or 2. None of the patients experienced grade 4 AEs and no drug-related fatal AEs were reported among the eight patients treated in the study. One (13%) patient had stable disease (SD) (captured as unknown by the study sponsor because the evaluation criteria set per protocol was not met) and three (38%) patients had progressive disease. Four (50%) patients developed clinical disease progression based on investigator evaluation. One patient with pancreatic cancer achieved immune-related SD for 26 months while on the study treatments. The study completed phase Ib dose escalation and phase II. However, gating criteria for efficacy were not met for expansion beyond 80 patients in phase II and the sponsor did not continue development of the combination of spartalizumab and lacnotuzumab for oncology indications. The potential signal of activity in pancreatic cancer should be further explored.

Abstract 3319: The MTA-cooperative PRMT5 inhibitor, MRTX1719, demonstrates increased anti-tumor activity in combination with KRAS mutant-selective inhibitors in MTAP del,KRAS-mutant cancers

Abstract MRTX1719 is an MTA-cooperative PRMT5 inhibitor that leverages the increased concentration of the metabolite MTA in cancer cells harboring a homozygous deletion of the MTAP gene (MTAP del) under investigation in clincial trials. MRTX1719 preferentially binds to the PRMT5•MTA complex to selectively inhibit PRMT5, an essential gene for all cells, in MTAP del cancer cells while sparing PRMT5 activity in normal MTAP-wildtype cells. MTAP del occurs in ~10% of all cancers, and these patients exhibit remarkably poor survival. Among pancreatic cancer, MTAP del occurs in ~ 25% of patients and of these ~30% have co-occurring KRAS G12D mutations. In addition, ~15% of lung adenocarcinoma patients harbor MTAP del and of these ~13% harbor KRAS G12C. While recently approved KRAS G12C mutant selective inhibitors demonstrate anti-tumor activity, strategies to address drug resistance and maximize clinical benefit are warranted. Combination of MRTX1719 with adagrasib or the KRAS G12D inhibitor MRTX1133 in CDX models harboring both a KRAS mutation (G12C or G12D) and homozygous MTAP deletion resulted in increased anti-tumor activity compared to either single agent. This includes the pancreatic KP4 model in which initial tumor regression in response to single agent MRTX1133 was observed, followed by adaptative resistance and tumor progression with monotherapy while co-administration with MRTX1719 continued to result in marked tumor regression. Mechanistically, combination treated animals demonstrated strong inhibition of both PRMT5 and RAS pathway signaling and combinatorial targeting of these pathways converged on enhanced inhibition of RB-1 phosphorylation. We also characterized this combination treatment in the context of resistance to KRAS selective inhibitors or MRTX1719 to evaluate the benefit of combination over sequential treatment. Finally, an NF1 mutant, MTAP del malignant peripheral nerve sheath tumor (MPNST) PDX model was treated with MRTX1719, the SOS1 inhibitor MRTX0902, or the combination, and a similar increase in anti-tumor activity was observed in the combination treatment compared to either monotherapy alone. These results suggest that the combination of an MTA-cooperative PRMT5 inhibitor with a KRAS mutant selective or KRAS pathway inhibitor may lead to deeper and more durable responses in MTAP del cancer patients with co-alterations in the KRAS pathway. Citation Format: Laura Waters, Ruth Aranda, Xousaen Helu, Laura Vegar, Krystal Moya, Andrew Calinisan, Allan Hebbert, Jill Hallin, Darin Vanderpool, David M. Briere, James G. Christensen, Peter A. Olson, Lars D. Engstrom. The MTA-cooperative PRMT5 inhibitor, MRTX1719, demonstrates increased anti-tumor activity in combination with KRAS mutant-selective inhibitors in MTAP del,KRAS-mutant cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3319.

Abstract 2022: E7386, a Wnt/β-catenin signaling modulator, suppresses the differentiation of regulatory T cells in combination with lenvatinib plus anti-PD-1 antibody

Abstract Background: E7386, a selective inhibitor of the interaction between β-catenin and CREB binding protein (CBP), showed antitumor activity in preclinical tumor models with aberrant activation of the Wnt/β-catenin signaling pathway. Previously, we reported the enhanced antitumor activity of a triple combination (E7386 in combination with Lenvatinib [LEN, a multiple receptor tyrosine kinase inhibitor mainly targeting VEGFRs and FGFRs] plus anti-PD-1 antibody) versus a 2-drug combination (LEN plus anti-PD-1 antibody). In this study, we further investigated the immunomodulatory functions of E7386 as a triple combination by single-cell RNA-sequencing (scRNA-Seq) analysis and subsequent functional assays. Methods: Mice bearing subcutaneous RAG (mouse renal cell carcinoma) tumors were randomized into 4 groups (n=6 in each group), including ⑴ Nontreatment, ⑵ E7386 at 25 mg/kg (PO, QD), ⑶ LEN at 10 mg/kg (PO, QD) plus anti-PD-1 antibody at 10 mg/kg (IP, BIW), and ⑷ triple combination. Tumor tissues were collected after a 2-week treatment period. CD45+ immune cells were isolated from the tumors by magnetic cell separation (MACS) and subjected to scRNA-Seq using 10x Genomics pipelines. Bioinformatics data analysis was conducted with Clarivate Analytics. To evaluate the effects of E7386 on Treg differentiation, an in vitro-induced regulatory T cells (Tregs) differentiation assay was conducted. Naïve CD4+ T cells were isolated by MACS and plated under iTreg differentiation conditions (stimulation of TGF-β and IL-2) with or without treatment of E7386. Induced Tregs and conditional culture medium were collected for evaluation of Treg differentiation, including gene expression and protein analysis. Results: CD45+ immune cells were clustered into 14 cell-type groups. Increased proportion of monocytes, NK cells, Tregs, CD4+ T cells, CD8+ T cells, eosinophils, and neutrophils were observed after LEN plus anti-PD-1 treatment. Among these subpopulations, Treg were most significantly suppressed by E7386 plus LEN plus anti-PD-1. Gene expression analysis revealed that the triple combination suppressed the activated gene expression of the Stat5/Foxp3 axis in CD4+ T cells, particularly Tregs, induced by LEN plus anti-PD-1 treatment. Consistently, the iTreg differentiation assay confirmed the suppressive function of E7386 on the Treg differentiation rate. Multiple subsequent in vitro assays also demonstrated the inhibitory effects of E7386 on TGF-β secretion and the expression levels of TGF-β downstream target genes. Conclusion: In summary, these data suggest a suppressive role of E7386 on Treg differentiation, which leads to antitumor activity of E7386 in combination with lenvatinib and anti-PD-1 antibody in a preclinical tumor model. Citation Format: Jialing Shen, Ryoga Ishida, Masahiko Kume, Takayuki Kimura, Yusuke Adachi, Yu Kato. E7386, a Wnt/β-catenin signaling modulator, suppresses the differentiation of regulatory T cells in combination with lenvatinib plus anti-PD-1 antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2022.

PRT2527, a Novel Highly Selective Cyclin-Dependent Kinase 9 (CDK9) Inhibitor, Has Potent Antitumor Activity in Combination with BTK and BCL2 Inhibition in Various Lymphoid Malignancies

CDK9 is a master regulator of transcription that modulates transcription elongation via phosphorylation of RNA polymerase II. Short-term inhibition of CDK9 depletes short-lived transcripts and labile proteins such as MCL1, BFL1 and MYC to promote cancer cell death. We previously described PRT2527, a novel, potent, highly selective CDK9 inhibitor with anti-leukemic activity in various preclinical models. PRT2527 is currently under evaluation in a Phase I clinical trial in patients with relapsed/refractory hematologic malignancies (NCT05159518). Here we demonstrate PRT2527 potently inhibits cancer growth and induces cell death in various models of Diffuse Large B Cell Lymphoma (DLBCL), Mantle Cell Lymphoma (MCL) and Chronic Lymphocytic Leukemia (CLL), through depletion of MCL1, BFL1 and MYC. We also show that combination of PRT2527 with BTK inhibitors (BTKi) or BCL2 inhibitors (BCL2i) leads to more robust and durable responses in multiple pre-clinical models. In these studies, the combination of PRT2527 with BTKi or BCL2i was well tolerated. Mechanistically, we show that in cell lines, BTK inhibition upregulates BMF, an endogenous inhibitor of BCL2 and BCL-xL, driving cells towards MCL1 and BFL1 dependency. Concurrent depletion of MCL1 and BFL1 with PRT2527 led to complete inhibition of Bcl-2- family mediated survival signaling, potently inducing cell death. In a similar fashion, Venetoclax-driven BCL2 inhibition also potentiated the anti-tumor activity of PRT2527. Consistent with our findings in vitro, we confirmed potent combinatorial inhibition of tumor growth by PRT2527, administered once weekly, and BTKi or BCL2i, administered daily, in CDX and PDX in vivo models of DLBCL and MCL. We observed reduced BFL1 and MCL1 as well as increased BMF in tumors of mice treated with BTKi and PRT2527 suggesting complete Bcl-2 family inhibition. We also demonstrated enhanced induction of apoptosis by PRT2527 in primary CLL patient samples simultaneously treated with BTKi or BCL2i. Additionally, we demonstrated that PRT2527 potently inhibits growth in Ibrutinib-resistant MCL cell lines. Further work characterizing PRT2527 as monotherapy and in combination with BTKi and BCL2i in in vivo models of BTKi-resistant MCL and CLL is currently ongoing. Altogether these data provide a rationale for evaluating PRT2527 in combination with BTK and BCL2 inhibitors for the treatment of patients with relapsed/refractory hematologic malignancies.

Preliminary Safety, Pharmacological and Efficacy Data from Patients with Relapsed or Refractory B-Cell Malignancies Treated with the ICP-248, a Next Generation BCL2 Inhibitor

Background: BCL2, a key protein regulator of the apoptotic pathway, is constitutively expressed in various malignancies, which is a hallmark of cancer cell. BCL2 inhibitors have been shown to be safe and effective and are approved for the treatment of patients with chronic lymphocytic leukemia/small cell lymphoma (CLL/SLL) or acute myeloid leukemia (AML). Venetoclax, the first and only approved BCL2 inhibitor, is associated with gastrointestinal toxicities and tumor lysis syndrome (TLS). Therefore, ICP-248 was developed as a potent and highly selective inhibitor of BCL2 and has shown antitumor activity superior to venetoclax in preclinical studies. Preclinical studies of ICP-248 have demonstrated favorable pharmacokinetics profile, broad safety window and excellent safety profile, as well as synergistic effect in anti-tumor activity in combination with Orelabrutinib, a novel and highly selective BTK inhibitor. Methods: ICP-CL-1201 is a phase I study to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary efficacy of ICP-248 in patients with relapsed or refractory B-cell malignancies ( ClinicalTrials.gov ID: NCT05728658). The study will be conducted in 2 parts. Part 1 will evaluate ICP-248 as monotherapy at the target dose of 100mg, 200mg, 300mg, 400mg, 500mg and 600mg (once daily and 28 days per cycle) and will explore different ramp-up dosing strategies. Part 2 will evaluate ICP-248 in selected and proposed indications. The dose escalation in Part 1 will follow the 3+3 design with dose-limiting toxicity (DLT) observation window with 49 days. Eligible patients include those with CLL/SLL and B-cell non-Hodgkin lymphomas (NHLs) who failed on available therapy. Key exclusion criteria include CNS involvement, prior exposure to BCL2 inhibitors and clinically significant cardiovascular disease. Adverse events (AEs) are reported per common terminology criteria for AEs (CTCAE) v5.0. Efficacy was evaluated according to the Lugano 2014 or International Workshop on Chronic Lymphocytic Leukemia (iwCLL) 2018 criteria. Minimal residual disease was evaluated with flow or next generation sequencing. Results: As of 30 th July, 2023 (data cutoff date) 3 patents (mantle cell lymphoma [MCL], SLL and CLL) had been enrolled at the dose level of 100 mg QD; age ranging from 53 to 68; follow-up ranging from 1.9 to 4.7 months); median of prior regimen numbers was 3 (range, 1-3; 2 out 3 patients failed on zanubrutinib or pirtobrutinib). ICP-248 demonstrated a favorable PK profile, approximate dose proportionality was observed across the ramp-up stage. No DLTs and SAEs were observed. All the AEs were grade 1 to 2 (mainly neutropenia) without dose interruption and modifications. No TLS including laboratory TLS was observed. Two patients with MCL and SLL were assessed as complete response (CR) at the end of cycle 2, and the CLL patient was assessed as stable disease without sign and symptom of disease and recovering hematology. Undetectable MRD was confirmed in the patient with SLL and MCL. Conclusions: Preliminary results suggest that ICP-248 is safe and well tolerated in relapsed or refractory B-cell malignancies. The favorable clinical pharmacological and safety profiles support current dose ramp up strategy. Preliminary efficacy data demonstrated good response with deep remission. Further assessment of safety and efficacy with additional dose levels and dosing strategies will be pursued in expanded patient population and in the combination with orelabrutinib.

Antitumor Activity of Dehydroxymethylepoxychinomycin (DHMEQ) and Cisplatin Combination in a Model of Disseminated Ovarian Cancer

Introduction. Ovarian cancer (OC) is recognized to be a pressing problem of modern oncology. Cytoreductive surgery and combined therapy based on platinum and taxanes play an important role in OC treatment. The response rate to first-line therapy accounts for about 80–90%. However, most patients relapse and develop resistance to therapy. Thus, the search for new effective drugs and new combinations for OC treatment is an urgent task of modern oncology.Aim. To evaluate in vivo the antitumor activity of dehydroxymethylepoxyquinomycin (DHMEQ) and cisplatin combination in an ovarian cancer model.Materials and methods. An experimental model of disseminated OC in rats was used to evaluate antitumor activity. A strain of ovarian tumor (OT) was transplanted into 200 female Wistar rats. The drugs were administered intraperitoneally. The “median life expectancy” was taken as a benchmark for the quality evaluation of experimental treatment.Results. It was found that DHMEQ and cisplatin combination increased the survival rate by 387% (p = 0.005, log-rank test) compared to the control group and by 91% compared to the group of animals treated with cisplatin (p = 0.003, log-rank test) in mono mode. More than 50% of the animals in the DHMEQ + cisplatin group remained alive on day 73 of the experiment. No animals remained alive in the cisplatin group, and only one rat remained in the DHMEQ group.Discussion. Thus, the obtained data demonstrate a potentiating antitumor effect of the DHMEQ + cisplatin combination by 387% compared to the control group.Conclusion. The results of the experiments demonstrated a potentiating antitumor effect of DHMEQ in combination with cisplatin. DHMEQ in combination with cisplatin manifests high efficacy in an in vivo model of ovarian cancer.

FF-10850, a Novel Liposomal Topotecan Achieves Superior Antitumor Activity via Macrophage- and Ammonia-Mediated Payload Release in the Tumor Microenvironment.

Topotecan, an approved treatment for refractory or recurrent ovarian cancer, has clinical limitations such as rapid clearance and hematologic toxicity. To overcome these limitations and maximize clinical benefit, we designed FF-10850, a dihydrosphingomyelin-based liposomal topotecan. FF-10850 demonstrated superior antitumor activity to topotecan in ovarian cancer cell line-based xenograft models, as well as in a clinically relevant DF181 platinum-refractory ovarian cancer patient-derived xenograft model. The safety profile was also improved with mitigation of hematologic toxicity. The improved antitumor activity and safety profile are achieved via its preferential accumulation and payload release triggered in the tumor microenvironment. Our data indicate that tumor-associated macrophages internalize FF-10850, resulting in complete payload release. The release mechanism also appears to be mediated by high ammonia concentration resulting from glutaminolysis, which is activated by tumor metabolic reprogramming. In ammonia-rich conditions, FF-10850 released payload more rapidly and to a greater extent than liposomal doxorubicin, a currently approved treatment for ovarian cancer. FF-10850 significantly enhanced antitumor activity in combination with carboplatin or PARP inhibitor without detrimental effects on body weight in murine xenograft models, and demonstrated synergistic antitumor activity combined with anti-PD-1 antibody with the development of tumor antigen-specific immunity. These results support phase I investigation of FF-10850 for the treatment of solid tumors including ovarian cancer (NCT04047251), and further evaluation in combination settings.

Selected Articles from This Issue

Highlights| June 13 2023 Selected Articles from This Issue Author & Article Information Online ISSN: 1557-3265 Print ISSN: 1078-0432 ©2023 American Association for Cancer Research2023American Association for Cancer Research Clin Cancer Res (2023) 29 (12): 2171. https://doi.org/10.1158/1078-0432.CCR-29-12-HI Related Content A commentary has been published: Proinflammatory Macrophage Activation by the Polysialic Acid-Siglec-16 Axis Is Linked to Increased Survival of Patients with Glioblastoma A commentary has been published: SALVO: Single-Arm Trial of Ipilimumab and Nivolumab as Adjuvant Therapy for Resected Mucosal Melanoma A commentary has been published: Eganelisib, a First-in-Class PI3Kγ Inhibitor, in Patients with Advanced Solid Tumors: Results of the Phase 1/1b MARIO-1 Trial View more A commentary has been published: Clinical Importance of the lncRNA NEAT1 in Cancer Patients Treated with Immune Checkpoint Inhibitors View less Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Cite Icon Cite Search Site Article Versions Icon Versions Version of Record June 13 2023 Citation Selected Articles from This Issue. Clin Cancer Res 15 June 2023; 29 (12): 2171. https://doi.org/10.1158/1078-0432.CCR-29-12-HI Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest Search Advanced Search Eganelisib (IPI-549) is a first-in-class, potent, and highly selective phosphoinositide-3-kinase (PI3K)-γ inhibitor. Based on preclinical studies, PI3K-γ blockade reprograms myeloid cells to a proinflammatory phenotype, leading to immune activation in the tumor microenvironment and synergistic antitumor activity in combination with checkpoint inhibitors. In this study, Hong and colleagues present the data from MAcrophage Reprogramming in Immuno-Oncology-1 (MARIO-1), the first-in-human study of eganelisib as monotherapy and in combination with nivolumab in patients with advanced solid tumors. The overall safety profile was manageable both as monotherapy and combination therapy. Based on safety, preliminary clinical activity, pharmacokinetic, and pharmacodynamic results of this study, eganelisib doses of 30 mg and 40 mg daily are being investigated in combination with immune checkpoint inhibitors in phase II clinical trials. Checkpoint inhibitors have made tremendous improvements in outcomes for cutaneous melanoma both in the metastatic and adjuvant settings. For mucosal melanoma, which confers a worse prognosis, small... You do not currently have access to this content.

AB-101, an allogeneic, non–genetically modified, natural killer (NK) cell therapy, evaluated as monotherapy or in combination with rituximab in R/R non-Hodgkin lymphoma.

7529 Background: AB-101 is a non-genetically modified, cord blood-derived, allogeneic, cryopreserved, NK cell therapy for use in combination with monoclonal antibody (mAb) or innate cell engager therapies. AB-101 is being developed to enhance response to mAb therapy through the antibody-dependent cellular cytotoxicity (ADCC) mechanism. Many cancer patients (pts) are unable to mount a robust ADCC response, rendering mAb therapy less effective for these pts. AB-101 has attributes that enhance NK cell activity: Consistent phenotype for tumor engagement and cytotoxicity; Selected killer immunoglobulin-like receptor B (KIR B) haplotype; V/V CD16 polymorphism at F158 for enhanced ADCC. AB-101 outpatient administration provides optimized NK cells to pts, potentially enhancing their anti-tumor activity in combination with mAb that utilize the ADCC mechanism. We have initiated a Ph 1/2 clinical trial evaluating the combination of AB-101 with rituximab (RTX) in pts with R/R NHL of B-cell origin. Methods: Two AB-101 dose levels, 1 or 4e9 cells, will be evaluated as monotherapy or combination with RTX. All enrolled pts will receive at least 1 cycle of 4 weekly AB-101 doses, with cyclophosphamide/fludarabine lymphodepletion (LD). Pts receiving the combination may receive up to 4 treatment cycles. Results: Dose escalation is ongoing with 17 pts enrolled. Pts were elderly (median of 68 yrs) and heavily pretreated (median of 4 prior lines) with 64% having had prior CD19 CAR-T. Pts had DLBCL (9), FL (5), MCL (2), and LPL/WM (1). 11 monotherapy pts and 6 RTX combination pts were treated at time of abstract. 16 pts received AB-101 at 1e9 cells/dose; 1 pt received 4e9 cells/dose. 4 of 6 combination pts have received > 1 cycle. AB-101 was generally well tolerated. The most common G3+ AEs were LD-related neutropenia and lymphopenia. All AB-101 related AEs were G1/2. ICANs and GVHD, events associated with allogeneic cell therapy, were not reported; Gr 1 CRS occurred in 2 pts and resolved within 24h. SAEs were reported in 9 pts. The most common SAEs were associated with either infections (n = 3) or PD (n = 3) and one related SAE of Gr 1 fever was reported. No pts discontinued treatment due to an AB-101-related AE. ORR for the RTX cohort was 67% (4/6) with a CR rate of 50% (3/6). 3 of 4 responses were observed in pts who failed prior CAR-T therapy. ORR for the monotherapy cohorts was 27% (3/11). Conclusions: 4 weekly doses of AB-101 given alone or with RTX appeared to be safe and well tolerated without the serious/severe toxicities associated with CAR-T therapies. Preliminary efficacy of the combination treatment is encouraging. The study is ongoing and continues to enroll the combination cohorts and the 4e9 cells/dose level. Updated safety, efficacy, and exploratory PK/PD/immunogenicity results will be provided during the presentation. Clinical trial information: NCT04673617 .

Phase 1/2 dose expansion study evaluating first-in-class eIF4A inhibitor zotatifin in patients with ER+ metastatic breast cancer.

1080 Background: Zotatifin (eFT226) is a first-in-class, potent and sequence selective inhibitor of RNA helicase eIF4A that promotes a stable mRNA:eIF4A:drug ternary complex at specific polypurine motifs within the 5’-UTR, preventing translation of select transcripts. In preclinical models zotatifin treatment simultaneously down-regulated translation of numerous oncogenes including CDK4, ERα, ERBB2, KRAS, and CCND1. Methods: Following a 3+3 dose escalation portion of the protocol (Part 1), Part 2 is a Simon’s two-stage design of cohorts of up to 18 patients (pts) with ER+ metastatic breast cancer enrolled at the recommended phase 2 dose of zotatifin (0.07 mg/kg IV two weeks on/one week off) in combination with fulvestrant (ful) (ECBF: Expansion, Combination, Breast, Ful) or in combination with ful and abemaciclib (abema) (ECBF+A: Expansion, Combination, Breast, Ful + Abema). Key eligibility criteria included at least one line of therapy for advanced/metastatic disease, progression on hormone therapy, and in addition, the ECBF cohort required prior CDK 4/6 inhibitor (CDKI). Primary endpoint was objective response rate (ORR) per RECIST v1.1. Additional endpoints included safety, other efficacy analyses, and for Parts 1 and 2, characterization of pharmacodynamic (PD) markers and pharmacokinetics. Results: As of a data cut-off of Jan 31, 2023, 18 pts were enrolled in each cohort. Median prior metastatic lines of therapy were 3 and 7 in ECBF+A and ECBF, respectively. In 16 evaluable pts in ECBF+A cohort, there were two confirmed partial responses (PR), two additional PRs awaiting confirmatory scans, and 8 pts with best overall response (OR) of stable disease (SD). All pts with PR/unconfirmed PR received prior CDKI and ful, including one pt with disease progression on combination abema and ful as the last therapy prior to enrollment. In 18 evaluable pts in ECBF, there was one confirmed PR and six SD as best OR. There were no dose-limiting toxicities or grade (Gr) 5 adverse events (AEs) in either cohort. In ECBF+A the most common AEs (all Gr 1/2) were diarrhea (44%) and nausea (31%) and 21% of pts had Gr 3/4 AEs. The most common AEs in ECBF (all Gr 1/2) were nausea (39%) and constipation (27%), and 28% of pts had Gr 3/4 AEs. Blood-based PD markers and ctDNA in Part 1 showed dose-dependent evidence of target engagement and anti-tumor activity. Conclusions: In dose expansion cohorts of heavily pre-treated metastatic breast cancer pts, eIF4A inhibitor zotatifin showed evidence of anti-tumor activity in combination with fulvestrant and abemaciclib and had a favorable safety profile consisting of primarily grade 1/2 adverse events. Clinical trial information: NCT04092673 .

Abstract CT107: Phase Ib Study of Pembrolizumab in Combination with Intratumoral Injection of Clostridium novyi-NT in Patients with Advanced Solid Tumors

Abstract BACKGROUND: Intra-tumoral Clostridium novyi-NT (non-toxic) is an attenuated strain of C. novyi lacking alpha toxin replication within hypoxic tumor regions, causing tumor cell lysis and inflammation. Immunotherapy (IO) augments anticancer activity with intratumoral agents in prior preclinical and clinical studies. This phase 1b dose escalation study assessed safety and potential synergistic effects of pembrolizumab and C. novyi-NT in advanced solid tumors. METHODS: We enrolled patients with percutaneous injectable, solid tumors to receive single intratumoral injection of C. novyi-NT administered on Day 8 across 4 dose cohorts (3 × 10^4 to 100 × 10^4 spores, 3+3 design) with pembrolizumab 200mg IV Q3weekly starting on Day 0 up to 24 months. Primary objectives: Safety, tolerability and maximum tolerated dose (MTD) of combination. Secondary objectives: anti-tumor activity of combination in the injected tumor lesion and overall response by iRECIST 1.1. RESULTS: At data cutoff on October 24, 2022, 16 patients were enrolled and evaluable for toxicity and efficacy. It was well tolerated across all cohorts without dose limiting toxicities with median number of 5 cycles administered (1-34). 10 patients (63%) experienced progression; 1 withdrew consent; 1 completed therapy; 1 came off trial due to toxicity (immune related dermatitis) and 3 patients remain on trial. Median age was 62.5 years (40-71) while all patients (100%) had performance status of 1. 8 (50%) received prior IO and 7 (44%) had > 4 lines of prior therapies. Confirmed overall objective response rate (ORR) was 25% in 4 patients [non-keratinizing undifferentiated nasopharyngeal squamous carcinoma (NPC), human papilloma virus positive squamous cell carcinoma of base of tongue, vulvar melanoma and chordoma] with 3 partial responses (PR) and 1 complete response (CR). Among responders, median duration of response was 8.18 months and 1/4 (25%) had prior IO. NPC patient completed 24 months on trial to completion with best response at PR (-87%) while vulvar melanoma patient remains on trial with best response at CR (-100%). Median injected tumor size was 2.65cm (1-11) with confirmed ORR in injected lesions at 19% with 2 PRs and 1 CR. Most prevalent grade 1 and 2 adverse events were injection site reaction (25%), pyrexia (19%), pruritus (13%), leukopenia (13%) and anemia (13%). No grade 3 or 4 treatment related adverse events noted. Signs and symptoms of C. novyi-NT germination (infection) including fever, injection site pain, erythema, swelling, tenderness, and in some cases, ulceration, spontaneous drainage, tissue sloughing, bleeding, and malodor were observed in 5 patients. CONCLUSIONS: Intratumoral C. novyi-NT with pembrolizumab demonstrates clinical activity with favorable tolerability in patients regardless of tumor histology. This study is ongoing to define the recommended phase 2 dose (NCT03435952). Citation Format: Blessie Elizabeth Nelson, Filip Janku, Siqing Fu, Ecaterina I. Dumbrava, David S. Hong, Daniel Karp, Aung Naing, Jordi Rodon, Apostolia Tsimberidou, Rodabe N. Amaria, Anthony Conley, Senthil Damodaran, Kanwal P. Raghav, Brent L. Kreider, David Tung, Mary Varterasian, Khashayarsha Khazaie, Sarina Piha-Paul. Phase Ib Study of Pembrolizumab in Combination with Intratumoral Injection of Clostridium novyi-NT in Patients with Advanced Solid Tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT107.

FAP-targeted CAR-T suppresses MDSCs recruitment to improve the antitumor efficacy of claudin18.2-targeted CAR-T against pancreatic cancer

PurposeThe claudin 18.2 (CLDN18.2) antigen is frequently expressed in malignant tumors, including pancreatic ductal adenocarcinoma (PDAC). Although CLDN18.2-targeted CAR-T cells demonstrated some therapeutic efficacy in PDAC patients, further improvement is needed. One of the major obstacles might be the abundant cancer-associated fibroblasts (CAFs) in the PDAC tumor microenvironment (TME). Targeting fibroblast activation protein (FAP), a vital characteristic of CAFs provides a potential way to overcome this obstacle. In this study, we explored the combined antitumor activity of FAP-targeted and CLDN18.2-targeted CAR-T cells against PDAC.MethodsNovel FAP-targeted CAR-T cells were developed. Sequential treatment of FAP-targeted and CLDN18.2-targeted CAR-T cells as well as the corresponding mechanism were explored in immunocompetent mouse models of PDAC.ResultsThe results indicated that the priorly FAP-targeted CAR-T cells infusion could significantly eliminate CAFs and enhance the anti-PDAC efficacy of subsequently CLDN18.2-targeted CAR-T cells in vivo. Interestingly, we observed that FAP-targeted CAR-T cells could suppress the recruitment of myeloid-derived suppressor cells (MDSCs) and promote the survival of CD8+ T cells and CAR-T cells in tumor tissue.ConclusionIn summary, our finding demonstrated that FAP-targeted CAR-T cells could increase the antitumor activities of sequential CAR-T therapy via remodeling TME, at least partially through inhibiting MDSCs recruitment. Sequential infusion of FAP-targeted and CLDN18.2-targeted CAR-T cells might be a feasible approach to enhance the clinical outcome of PDAC.

Abstract 6246: The MTA-cooperative PRMT5 inhibitor AM-9747 exhibits robust antitumor activity in combination with clinically relevant chemotherapies and targeted agents in MTAP null tumor models

Abstract Homozygous deletion of chr9p21, containing genes CDKN2A and MTAP, occurs in about 15% of cancers. MTAP loss, a key enzyme in the methionine and adenine salvage pathways, leads to the accumulation of its substrate MTA. MTA competes with the methyl donor SAM for binding to type II arginine methyltransferase PRMT5, placing PRMT5 in a hypomorphic state and vulnerable to further PRMT5 inhibition. MTA-cooperative PRMT5 inhibitors are an emerging class of therapeutics targeting MTAP null tumors. AMG 193, currently in Phase 1 trials, and its representative analog AM-9747 have broad spectrum activity in MTAP null tumor models across hematologic and solid tumor indications. Mechanistically, AM-9747 induces DNA damage, shown by increased phosphorylated H2AX, resulting in cell cycle arrest and senescence. Exploration of clinically relevant therapeutic combinations with standard of care (SOC) chemotherapies or targeted agents that could potentiate this DNA damage or target orthogonal pathways is a rational therapeutic approach. Here, we evaluated AM-9747 in combination with SOC chemotherapies and assessed synergy using the Chou-Talalay Method to generate Combination Index (CI) scores. SOC agents representing a variety of mechanisms of action (paclitaxel, carboplatin, gemcitabine, pemetrexed, irinotecan, 5-FU) were evaluated and results ranged from strongly synergistic (CI<0.3) to additive (CI=1) in a panel of non-small cell lung carcinoma (NSCLC) and pancreatic cancer cell lines. The SOC combinations augmented AM-9747 induced DNA damage resulting in increased cell cycle arrest and nuclear count assays confirmed the synergistic antiproliferative effects of the combinations. Combinations of AM-9747 and one strongly synergistic agent (carboplatin) and one moderately synergistic agent (paclitaxel) were evaluated in H292 NSCLC xenografts. Significant reductions in tumor burden compared to single agent treatments were observed with AM-9747 + paclitaxel (67% TGI) and AM-9747 + carboplatin (82% TGI). Additionally, roughly 2-3% of NSCLC tumors harbor both MTAP loss and a KRAS G12C mutation. To target both pathways we combined the FDA-approved KRAS G12C inhibitor sotorasib with AM-9747 and observed synergy (CI<0.6) in MIAPACA2 cells. Nuclear counts confirmed a greater cell growth inhibition in the combination and immunoblots confirmed on target inhibition of both pathways. Combination treatment of AM-9747 and sotorasib in LU99 NSCLC xenografts resulted in significant tumor regression compared to each single agent with 10/10 mice tumor free. This combination is being tested in additional MTAP null KRAS G12C mutant models. Overall, our data suggests that combining MTA-cooperative inhibitor AM-9747 with SOC or clinically relevant targeted agents is a compelling therapeutic strategy for the treatment of MTAP null cancers. Citation Format: Katherine Slemmons, Brian Belmontes, Siyuan Liu, Jodi Moriguchi, Antonia Policheni, Paul E. Hughes. The MTA-cooperative PRMT5 inhibitor AM-9747 exhibits robust antitumor activity in combination with clinically relevant chemotherapies and targeted agents in MTAP null tumor models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6246.

Abstract 1837: E7386, a selective inhibitor of the interaction between β-catenin and CREB-binding protein (CBP), enhances antitumor activity in combination with lenvatinib (LEN), and LEN + anti-PD-1 antibody in a preclinical tumor model

Abstract E7386, a novel orally active CBP/β-catenin modulator, shows antitumor activity in preclinical tumor models with aberrant activation of the Wnt/β-catenin-signaling pathway driven by mutations in genes such as adenomatous polyposis coli (APC). We previously reported that E7386 enhanced the antitumor activity of an anti-PD-1 antibody (Ab) by induction of T cell infiltration into tumors, and E7386 enhanced the antitumor activity of LEN (a multiple kinase inhibitor mainly targeting VEGFRs and FGFRs) by enhancement of antiangiogenic effect in preclinical tumor models. Clinical studies of E7386 in combination with LEN and with pembrolizumab are in progress. Here, we investigated the antitumor activity of E7386 in combination with LEN and with LEN + anti-PD-1 Ab (triple combination) in a mouse renal cell carcinoma RAG model. We also evaluated the mechanism of action underlying the activity of E7386 + LEN and the triple combination. Mice bearing subcutaneous RAG and HepG2 tumors were treated with E7386 at 25 mg/kg (po, qd), LEN at 10 mg/kg (po, qd), and anti-PD-1 Ab at 10 mg/kg (ip, twice weekly) for 4 weeks. Immune-cell population analyses in tumor tissues were performed by flow cytometry. Mouse syngeneic and human xenograft tumor endothelial cells were isolated as CD31-positive cells using magnetic beads and flow cytometry techniques for gene-expression analysis. E7386 + LEN showed enhanced antitumor activity compared with each monotherapy and the triple combination showed enhanced antitumor activity compared with the 2-drug combinations (LEN + anti-PD-1 or LEN + E7386) in the RAG model. Immune-cell population analysis of RAG tumors using flow cytometry revealed that LEN decreased the population of tumor-associated macrophage (TAM) and E7386 + LEN further decreased the population of TAM. E7386 combination decreased the population of immunosuppressive monocytic-myeloid-derived suppressor cells that was increased with LEN monotherapy and with LEN + anti-PD-1 Ab combination. Gene-expression analysis demonstrated that expression levels of Axin2 and Vcan (Wnt/β-catenin target genes) were upregulated in endothelial cells isolated from RAG tumors after LEN treatment. In addition, combination treatment of E7386 + LEN suppressed the upregulation of Axin2 and Vcan with LEN monotherapy in tumor endothelial cells in the HepG2 human hepatoblastoma xenograft model. E7386 suppressed the Wnt signal that was activated with LEN in tumor endothelial cells and E7386 + LEN, and the triple combination also decreased the immunosuppressive myeloid cells that were increased with LEN, and LEN + anti-PD-1 Ab. These activities of E7386 on the tumor microenvironment could provide unique mechanisms of antitumor activity for this triple combination in preclinical tumor models. Citation Format: Yusuke Adachi, Yoichi Ozawa, Mizuki Kimura, Jialing Shen, Masahiko Kume, Ryoga Ishida, Takayuki Kimura, Junji Matsui, Akira Yokoi, Yu Kato, Yasuhiro Funahashi. E7386, a selective inhibitor of the interaction between β-catenin and CREB-binding protein (CBP), enhances antitumor activity in combination with lenvatinib (LEN), and LEN + anti-PD-1 antibody in a preclinical tumor model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1837.

Abstract 3474: Identification of the selective CBL-b inhibitors which effectively prevent T cells from exhaustion and demonstrate synergistic anti-tumor activity in combination with an anti-PD1 antibody

Abstract The E3 ubiquitin ligase Casitas B-lineage lymphoma b (Cbl-b) is a member of the highly conserved family of Cbl (casitas b-lineage lymphoma) proteins. CBL-b is widely expressed in immune cells and plays as a “gate keeper” to negatively regulate the activation of immune cells. Engagement of TCR/BCR triggers the Cbl-b-mediated ubiquitination and degradation of the key components in TCR axis, such as Vav1 and PLCγ, and consequently attenuates TCR/BCR signal axis which finally results in T/B cells exhaustion. Besides, Cbl-b was reported to negatively regulate the activation of dendritic cells, NK, NKT, and mast cells. Cbl-b KO mice show resistance to tumor transplantation, and the anti-tumor activities depend on the T and NK cells. According to the above observation, Cbl-b emerges as a novel intracellular immune checkpoint target to prevent immune cells from exhaustion and improve the antitumor immunotherapy. Here we identified a series of highly potent Cbl-b inhibitors. The inhibition of Cbl-b protein was evaluated by an in vitro CBL-b/E2-ubiquitin assay. Results showed that our candidates strongly inhibited Cbl-b with IC50s at single-digital nanomolar level, and meanwhile, these compounds displayed over than 10-fold selectivity against c-CBL/E2-ubiquitin, a member of the Cbl family, which was reported to synergistically enhance toxicity caused by Cbl-b. Consistent with the Cbl-b inhibition, these compounds further enhanced activation of Jurkat T cells as well as human PBMCs with dramatical increase of IL-2 or IFNɣ secretion in presence of anti-CD3/CD28, and without any significant cytotoxicity even up to 10 µM concertation. Furthermore, these compounds exhibited the restoring function in exhausted T cells in presence with PEG2 or adenosine treatment. Favorable ADME and bioavailability supported the oral administration. In naïve mice, our inhibitors dose-dependently promoted the cytokine IL-2 and IFNɣ production in serum and spleens following the anti-CD3 challenge. In a syngeneic model, CT26, oral administration of our Cbl-b inhibitor effectively inhibited tumor growth, while completely inhibited tumor growth in combination with an anti-PD1 antibody. Further study demonstrated that the increased lymphocytes infiltration and cytokines release in tumor tissues were observed either in Cbl-b mono or in anti-PD1 combo groups, which correlated well with anti-tumor efficacy. In conclusion, our selective Cbl-b inhibitors demonstrated robust immune activation and anti-tumor activity in vitro and in vivo and showed synergistic activities with immune checkpoint inhibitors, such as anti-PD(L)1. Currently, one of our leading molecules is in IND enabling studies. Citation Format: Feng Zhou, Zhengtao Li, Yajing Liu, Guimei Yang, Wansun Mai, Wenqing Yang, Liting Xue, Ping Chen, Renhong Tang. Identification of the selective CBL-b inhibitors which effectively prevent T cells from exhaustion and demonstrate synergistic anti-tumor activity in combination with an anti-PD1 antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3474.

Abstract 4098: Chimeric antigen receptor (CAR) T cells overexpressing Bcl-xL increase proliferation and antitumor activity alone and in combination with BH3 mimetics

Abstract Background: Chimeric antigen receptor (CAR) T cells have become a well-established treatment option for patients, with six products approved for different hematologic diseases and new approvals allowing for their therapeutic use as early as second line. However, relapse rates of around 50% have been observed in all patient subsets, with one major mechanism associated with CAR T failure being cancer cell resistance to apoptosis. A form of cancer therapeutic named BH3-mimetics has been designed to inhibit members of the anti-apoptotic B cell lymphoma-2 (Bcl-2) family and, therefore, directly activate the apoptotic machinery in malignant cells. We hypothesized that integration of these anti-apoptotic molecules into CAR T cells would induce resistance towards the BH3 mimetics and allow combinational therapeutic approaches. Methods: 4-1BB and CD28 CAR constructs were designed to overexpress one of four anti-apoptotic proteins: wildtype Bcl-2, a Venetoclax-resistant Bcl-2 variant (G101V), B cell extra-large (Bcl-xL), or myeloid cell leukemia-1 (Mcl-1). CAR T cells made from these constructs were tested against leukemia (Nalm6) and lymphoma (JeKo-1) cell lines in combination with three different BH-3 mimetics: Venetoclax (ABT-199, an FDA-approved Bcl-2 inhibitor), Navitoclax (ABT-263, a Bcl-2/Bcl-xL inhibitor), and AZD5991 (an Mcl-1 inhibitor). Results: CAR T cells with a 4-1BB costimulatory domain tended to have increased killing over CARs with CD28 and were less susceptible to apoptosis; therefore, 4-1BB CARs were used for all further testing. Integration of Bcl-2 family proteins into CAR T cells didn’t impair or even increase tumor cell clearance in vitro; however, in combination with Venetoclax, Navitoclax, or AZD5991, killing capacity significantly increased compared to control CAR T cells. Even without combination with drugs, CAR T cells overexpressing Bcl-xL and Bcl-2 (both wildtype and mutant) provided higher anti-tumor activity and prolonged survival against JeKo-1 cells in vivo, whereas only Bcl-xL overexpression showed increased tumor control compared to regular 4-1BB CARs against Nalm6 cells. Conclusion: Of the tested antiapoptotic proteins, Bcl-xL overexpressing CAR T cells proved superior, having higher proliferation and increased anti-tumor activity in combination with or without BH3 mimetics, providing a new strategy to optimize CAR T cell function for the treatment of leukemia and lymphoma. Citation Format: Felix Korell, Michael Olson, Diego Salas-Benito, Mark B. Leick, Rebecca C. Larson, Harrison Silva, Alessandro Gasparetto, Trisha R. Berger, Amanda Bouffard, Michael C. Kann, Markus Mergen, Tamina Kienka, Marc Wehrli, Stefanie R. Bailey, Anthony Letai, Marcela V. Maus. Chimeric antigen receptor (CAR) T cells overexpressing Bcl-xL increase proliferation and antitumor activity alone and in combination with BH3 mimetics. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4098.

Abstract 3075: Enhanced efficacy of ARV-471, a novel PROTAC® estrogen receptor degrader, in combination with targeted agents in estrogen receptor-positive (ER+) breast cancer models

Abstract ARV-471 is a selective, orally bioavailable PROteolysis-TArgeting Chimera (PROTAC®) small molecule that induces wild-type and mutant estrogen receptor (ER) alpha degradation via the ubiquitin-proteasome system. ARV-471 demonstrates superior ER degradation and antitumor activity compared to fulvestrant in endocrine sensitive and resistant xenograft models and has shown significant ER degradation and promising clinical benefit in late-line ER+ breast cancer patients. Dual pathway inhibition combining ER targeting agents with CDK4/6 or PIK3CA/mTOR pathway inhibitors is now a central strategy for treatment of advanced ER+ breast cancer. However, resistance to aromatase inhibitors resulting from ESR1 gene mutations, suboptimal ER degradation and the intramuscular route of administration of fulvestrant underscore a need for superior orally bioavailable endocrine therapy backbones for these combinations. Here, we assessed the effects of ARV-471 in combination with CDK4/6 or PIK3CA/mTOR pathway inhibitors in preclinical models of ER+ breast cancer. In vitro studies revealed evidence of synergistic interactions between ARV-471 and the CDK4/6 inhibitors abemaciclib and ribociclib, the mTOR inhibitor everolimus, or the PIK3CA inhibitors alpelisib and inavolisib in ER+ breast cancer cells. Evidence of synergistic effects between ARV-471 and everolimus was also observed in ER+ breast cancer cells expressing ER Y537S or D538G mutations. ARV-471 in combination with CDK4/6, PIK3CA or mTOR inhibitors led to tumor regressions in MCF7 xenografts when compared to single agents alone. ARV-471 also displayed greater anti-tumor activity in combination with abemaciclib, ribociclib or inavolisib than that observed with fulvestrant in combination with these agents. Taken together, these data suggest the potential utility of ARV-471 as a combination partner for clinically relevant targeted agents for treatment of early and late-stage ER+ disease. Citation Format: Jessica Teh, Elizabeth Bortolon, Jennifer Pizzano, Melissa Pannone, Sean Landrette, Richard Gedrich, Ian Taylor. Enhanced efficacy of ARV-471, a novel PROTAC® estrogen receptor degrader, in combination with targeted agents in estrogen receptor-positive (ER+) breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3075.

Abstract 5043: Radium-223 demonstrates increased antitumor activity in combination with 177Lu-PSMA-617 in the intratibial LNCaP xenograft model of bone metastatic prostate cancer

Abstract Radium-223, a bone-specific alpha particle therapy, increased survival of patients with metastatic castration-resistant prostate cancer (mCRPC) and bone metastases (Parker et al., NEJM 2013) 177Lu-PSMA-617 is a small molecule radioligand that delivers beta-particle radiation to cancer cells expressing prostate-specific membrane antigen (PSMA). Despite improving overall survival of patients with heavily pretreated mCRPC (Sator et al., NEJM 2021), responses to 177Lu-PSMA-617 are often not durable and many patients develop progressive disease presumably due to microscopic osseous lesions. Compared to beta-particle radiation, alpha particles have a shorter range and higher linear energy transfer, making them more suitable for treating microscopic lesions. In this study, we evaluated preclinical antitumor efficacy and potential beneficial combination effects of radium-223 combined with 177Lu-PSMA-617 in the intratibial LNCaP xenograft model mimicking progressive prostate cancer micrometastases in bone. LNCaP prostate cancer cells were inoculated into the right tibiae of male NOD.scid mice. Six weeks after inoculation, the mice were randomized to treatment groups based on serum prostate-specific antigen (PSA) and treated with two injections (Q4Wx2, i.v.) of vehicle, radium-223 (330 kBq/kg), 177Lu-PSMA-617 (10 MBq) or their combination 177Lu-PSMA-617 was given 24 hours after radium-223. PSA and bone formation marker procollagen type I intact N-terminal propeptide (PINP) were measured from blood samples and tumor-induced abnormal bone growth was determined by radiography. Terminal blood samples were analyzed for hematologic status at sacrifice. The combination treatment of radium-223 and 177Lu-PSMA-617 demonstrated robust antitumor efficacy, as indicated by lower serum PSA (mean change relative to pretreatment levels: 63.9 % vs 631 % (vehicle control), p=0.026), decreased tumor-induced abnormal bone area in tumor-bearing tibiae (p<0.001) and suppression of abnormal bone metabolic activity as evidenced by a reduced level of the bone formation marker PINP (p<0.001), compared with vehicle. Tolerability of the combination treatment was evidenced by the lack of significant body weight loss and the absence of cumulative hematological toxicity. In conclusion, these preclinical results show that the combination of radium-223 and 177Lu-PSMA-617 is well-tolerated and efficacious in inhibiting osseous tumor growth and improving response. The combination of radium-223 and 177Lu-PSMA-I&T is currently being investigated in patients with mCRPC in a phase 1/2 trial (AlphaBet, NCT05383079). Citation Format: Arne Scholz, Matias Knuuttila, Justyna Zdrojewska, Mari I. Suominen, Esa Alhoniemi, Christoph A. Schatz, Sabine Zitzmann-Kolbe, Sanna-Maria Käkönen, Urs B. Hagemann. Radium-223 demonstrates increased antitumor activity in combination with 177Lu-PSMA-617 in the intratibial LNCaP xenograft model of bone metastatic prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5043.

Abstract 5075: Antitumor activity of liposomal formulation of eribulin combined with anti-human PD-1 antibody using hPBMC-humanized mouse models

Abstract Eribulin (ERI) has been reported a microtubule dynamics inhibitor with unique tumor microenvironment modulations such as vascular remodeling and reversal of epithelial-mesenchymal transition activities. In the previous meeting (AACR2022), we reported that ERI and liposomal formulation of ERI (ERI-LF) have immunomodulatory activity that induces CD8+ T cells via its vascular remodeling activity and ERI-LF has greater immunomodulatory activity than ERI. Furthermore, we also reported that these immunomodulatory activities contribute combination antitumor activity of ERI and ERI-LF with anti-PD-1 antibody (Ab) using a P-glycoprotein-knockout 4T1 mouse breast cancer syngeneic model; however, evaluation of antitumor activity of immune-checkpoint inhibitor (ICI) using mouse cancer syngeneic model has limitation because numbers and cancer types of mouse cancer cell lines are limited. In this study, we developed humanized mouse model bearing both human cancer cell lines and human peripheral blood mononuclear cells (hPBMC) to evaluate antitumor activity of ICI for various cancer types. Furthermore, we also evaluated combination antitumor activity of ERI-LF with anti-human PD-1 Ab using this hPBMC-humanized mouse models to verify generality of this combination. We first isolated hPBMC from healthy volunteers and the obtained hPBMC was intravenously injected into NOG mice. To confirm transplantation of hPBMC in the mice, we performed flow cytometric analysis of peripheral blood of mice in a time course manner. In the peripheral blood of humanized mice, chimera ratio of hCD45+ cells gradually increased until 5 weeks after hPBMC-injection and then decreased after 6 weeks after hPBMC-injection. Because tumor growth of some cancer cell lines was rejected by hPBMC transplantation, we evaluated some human cancer cell lines that are able to grow in hPBMC-humanized condition and selected MKN45 and NCI-H526 cell lines for human gastric cancer and small cell lung cancer models, respectively. Finally, we verified combination antitumor activity of ERI-LF with anti-human PD-1 Ab in hPBMC-humanized MKN45 and NCI-H526 models. In both models, combination of ERI-LF with anti-human PD-1 Ab showed significantly stronger antitumor activity compared with each monotherapy. In summary, we demonstrated that combination of ERI-LF with anti-PD-1 Ab is effective for gastric and small cell lung cancers, suggesting that this combination therapy is effective for various cancer types. Currently, Phase 1b/2 clinical trial of ERI-LF plus nivolumab in patients with selected solid cancers including gastric and small cell lung cancers (NCT04078295) is underway. Citation Format: Yuki Niwa, Taro Semba. Antitumor activity of liposomal formulation of eribulin combined with anti-human PD-1 antibody using hPBMC-humanized mouse models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5075.

Antitumor activity of the PI3K δ-sparing inhibitor MEN1611 in PIK3CA mutated, trastuzumab-resistant HER2 + breast cancer

PurposeDysregulation of the PI3K pathway is one of the most common events in breast cancer. Here we investigate the activity of the PI3K inhibitor MEN1611 at both molecular and phenotypic levels by dissecting and comparing its profile and efficacy in HER2 + breast cancer models with other PI3K inhibitors.MethodsModels with different genetic backgrounds were used to investigate the pharmacological profile of MEN1611 against other PI3K inhibitors. In vitro studies evaluated cell viability, PI3K signaling, and cell death upon treatment with MEN1611. In vivo efficacy of the compound was investigated in cell line- and patient-derived xenografts models.ResultsConsistent with its biochemical selectivity, MEN1611 demonstrated lower cytotoxic activity in a p110δ-driven cellular model when compared to taselisib, and higher cytotoxic activity in the p110β-driven cellular model when compared to alpelisib. Moreover, MEN1611 selectively decreased the p110α protein levels in PIK3CA mutated breast cancer cells in a concentration- and proteasome-dependent manner. In vivo, MEN1611 monotherapy showed significant and durable antitumor activity in several trastuzumab-resistant PIK3CA-mutant HER2 + PDX models. The combination of trastuzumab and MEN1611 significantly improved the efficacy compared to single agent treatment.ConclusionsThe profile of MEN1611 and its antitumoral activity suggest an improved profile as compared to pan-inhibitors, which are limited by a less than ideal safety profile, and isoform selective molecules, which may potentially promote development of resistance mechanisms. The compelling antitumor activity in combination with trastuzumab in HER2 + trastuzumab-resistant, PIK3CA mutated breast cancer models is at the basis of the ongoing B-Precise clinical trial (NCT03767335).