Dose-limiting Toxicity Period Research Articles

HOPE: Harnessing olaparib, palbociclib, and endocrine therapy for BRCA1/2-associated HR+, HER2- metastatic breast cancer.

10616 Background: Thepoly (ADP-ribose) polymerase inhibitor olaparib yields superior progression-free survival, response rates and patient-reported outcomes compared with chemotherapy in patients with BRCA1- or BRCA2- ( BRCA1/2) associated metastatic breast cancer (MBC). Fulvestrant and palbociclib improve outcomes in patients with hormone receptor-positive (HR+) MBC. HOPE (NCT03685331) is a phase I trial to evaluate combination olaparib (O), fulvestrant (F), and palbociclib (P) in patients with BRCA1/2-associated HR+, HER2 negative MBC. Methods: A 3+3 dose escalation was used to assess safety and preliminary efficacy of O, F and P. Eligible participants (pts) had HR+ MBC, a germline (g) or somatic (s) mutation in BRCA1/2, measurable/evaluable disease, any/no prior endocrine therapy, and 0-2 prior lines of chemotherapy for MBC. Prior PARPi and CDK4/6i were permitted but not in combination. Palbociclib was added after a 28-day safety run-in (Cycle 0) of O + F alone. Fulvestrant dose was 500mg IM on day 1 of each 28-day cycle. Dose level 0 (DL0, starting level) was F, O 300mg orally BID continuously, P 75mg orally daily on days 1-21; DL-1 was F, O 250mg orally BID, P 75mg orally daily on days 1-21. The primary endpoint was MTD (adverse events (AEs) based on CTCAE v5.0). Dose limiting toxicity (DLT) period included Cycles 0 and 1. A 30% DLT rate was acceptable; 6 pts had to be treated at a dose for it to be declared MTD. RECIST v1.1 was used to evaluate response. Results: Eight treated pts (s BRCA1:1 ;g BRCA2:6; s BRCA2:1 ) had median (M) age 47; M 0 (0-2) prior lines of endocrine therapy and 0 (0-1) prior chemotherapies for MBC. Three pts each had received O, F, and CDK4/6i as part of their standard of care treatment before study. At DL0, 2/2 pts had DLT with persistent grade(G) 3 neutropenia. Among 6 pts treated at DL-1, none experienced DLT, but 3 pts missed doses of study treatment due to cytopenias (G3 neutropenia, G3 leukopenia, G3 thrombocytopenia) during the DLT period. Following the DLT period, 1 pt reduced O to 200mg orally daily and 1 discontinued P based on provider discretion due to cytopenias (G3 neutropenia, G3 thrombocytopenia). Grade 3 AEs occurring in >1 pt related to study treatment were: neutrophil count decrease (G3/2, n=5/2); white blood cell decrease (G3/2/1, n=3/2/2); platelet count decrease (G3/2/1, n=2/0/1). Overall related AEs in >50% of pts were anemia (n=7), fatigue (n=6) and nausea (n=5). Best responses were CR/PR/SD/PD in 1/1/5/1 pts. Conclusions: MTDof O, F and P (DL-1) was reached and demonstrated antitumor activity. Although no AEs meeting protocol-specified DLT criteria were observed at MTD, hematologic toxicity at this dose complicated drug delivery and required close monitoring during and after the DLT period. Combinations utilizing PARP1 selective inhibitors, lower doses of therapy or sequential rather than combination therapy may improve feasibility. Clinical trial information: NCT03685331 .

Safety run-in phase of the multi-epitope HER2 peptide vaccine in combination with trastuzumab emtansine in HER2-positive breast cancer with residual disease after neoadjuvant chemotherapy.

550 Background: Residual disease after neoadjuvant chemotherapy (NAC) in HER2-positive breast cancer (BC) confers poor outcomes. Despite additional trastuzumab emtansine (T-DM1) in the adjuvant setting, a significant number of patients with residual disease still develop recurrence. H2NVAC is a multi-epitope T helper cell-activating peptide vaccine that is composed of 4 degenerate HER2-derived HLA-DR epitopes admixed with GM-CSF. Our previous phase I trial showed that this vaccine was safe and generated robust, long-lasting T and B cell immune responses. Methods: Patients with stage II-III HER2+ BC with any amount of residual disease in the breast /axilla after NAC were enrolled in a safety run-in phase of H2NVAC in combination with T-DM1. Patients were treated with H2NVAC and T-DM1 for 6 cycles, followed by 2 boosters at 3 and 12 months. Dose-limiting toxicity (DLT) was defined as any grade (G) ≥ 3 adverse events (AE) occurring within 21 days after the first vaccination. Results: A total of20 patients were enrolled with a median age of 51 years (range 27-69), 80% were White and 15% were Black. Most patients had hormone receptor-positive disease (90%). 40% were premenopausal, 40% were postmenopausal, and 20% were unknown. 14 patients had ypT1, 3 patients ypT2, 3 patients ypT3, 1 patient ypT4, 8 patients ypN0, 9 patients yp N1, 1 patient ypN1mi, and 2 patients ypN2. H2NVAC, in combination with T-DM1, was well tolerated, with no DLT being observed. Only grades 1 and 2 AEs were observed during the DLT period, with fatigue being the most common (G1 60%, G2 5%), followed by peripheral sensory neuropathy (G1 55%, G2 5%) and injection site reaction (G1 50%). Across all treatment cycles, the top 10 most common AEs that were at least possibly related to treatment include injection site reaction (G1 85%, G2 15%), AST increase (G1 65%), ALT increase (G1 45%), fatigue (G1 35%, G2 10%), peripheral sensory neuropathy (G1 35%, G-tube 10%), alk-phos increase (40% G1), nausea (G1 35%, G2 5%), arthralgia (G1 35%), myalgia (G1 25%, G2 5%), and platelet count decrease (G1 30%). There were four patients with G3 AEs at least possibly related to the vaccine observed after the DLT period, including allergic reaction, myositis/skin infection, urticaria, and pruritus/maculopapular rash. Conclusions: H2NVAC, in combination with T-DM1, was safe without DLT observed. The side effect profile was favorable, with the most common AE being the G1 injection site reaction. A multicenter, randomized, placebo-controlled, phase II trial of H2NVAC vs. placebo in combination with trastuzumab emtansine is currently ongoing through the ACCRU consortium. Clinical trial information: NCT04197687 .

Durable complete response and overall survival in patients with heavily pretreated, poor-prognosis non-Hodgkin lymphoma to immunoactivating AVM0703 with few and mild drug-related adverse effects.

7077 Background: In 2022, the majority of new cancer drugs in clinical development are aimed at targets that are already saturated with approved drugs1. This is of concern to patients, payers, sponsor/investors, and regulatory agencies. AVM0703 activates a unique immune response mobilizing an endogenous gamma delta TCR+ and invariant TCR+ bispecific Natural Killer T-like cell (γδTCR+iTCR+NKT) (PCT/US21/19773), that has demonstrated clinical anti-cancer activity against a variety of solid and blood cancers. The potential for AVM0703 to fill a gap in the “no-option” R/R NHL treatment landscape led to the launch of the AVM0703-001 clinical trial (The OPAL Study, NCT04329728). 1) Fougner C et al. Herding in the drug development pipeline. Nat Rev Drug Discov. 2023 Aug;22(8):617-618. Methods: An open-label phase 1 trial evaluating the safety and preliminary efficacy of AVM0703 was completed in patients with hematological malignancies. AVM0703 was administered as a single intravenous (IV) infusion to patients enrolled into a 3+3 dose escalation design. Consolidation therapy of investigator’s choice was allowed, preferably 28 days after AVM0703. For each cohort, 3-6 patients were treated, and dose escalation permitted only after the cohort completed a 7-day dose limiting toxicity (DLT) assessment period with no more than 1 DLT. Patients ≥12 years and >40 kg diagnosed with WHO classified lymphoid neoplasms with R/R disease ineligible for transplant or CAR-T were included. The database has not been formally locked and a cutoff date of Dec 13, 2023, is used for presentation of these Phase 1 results. Results: In summary, 17 patients, 39-86 years of age (median 64) with a median of 4 prior lines (range: 1 to 10) received AVM0703 at 6, 9, 12, 18 and 21 mg/kg. Fifteen (88%) were poor prognosis and 4 had CNS involvement. Only 13 of 17 (76.5%) experienced study-drug related adverse events (AEs) during the DLT period; 15 AEs were grade 1 (78.9%), 2 were grade 2 (10.5%), and 2 were grade 3 (10.5%). The most common AEs were insomnia (N=5), hyperglycemia (N=3), and pruritis (N=2). The total number of All-grade TEAEs recorded in 17 patients was 114 within 30 days post dose, with 98.2% of grades 1-3. Median overall survival (OS) in all dose cohorts was 13.3 months, with 8 of 17 patients alive as of 13 Dec 2023. The recommended Phase 2 dose (RP2D) was determined as 18 mg/kg. For the 18 mg/kg group (N=6), long term durable responses were obtained in 66% (3 CR, 1 PR) with an additional patient converting to late CR, nine months survival was 100%, and median OS has not been reached with follow up between 15.9 and 27.8 months (83% still alive). No safety signals have been identified. Conclusions: RP2D AVM0703, with consolidation therapy at day 28 median (range 7 to 240 days) showed no concerning safety signals and promising long-term survival. Clinical trial information: NCT04329728 .

A phase I/II open-label clinical trial of CPI-613 in combination with modified FOLFIRINOX in patients with locally advanced (LAPC) or borderline resectable pancreatic cancer (BRPC).

4172 Background: Pancreatic ductal adenocarcinoma (PDA) carries a poor prognosis with a 5-year relative survival rate of 13%. Surgical resection is the only curative treatment option, but less than 20% of patients are eligible at diagnosis. A subset of patients with locally advanced disease can become candidates for resection with neoadjuvant (NA) therapy. mFOLFIRINOX is the standard of care in the adjuvant setting, with extrapolated data supporting its use in the NA setting. CPI-613/Devimistat (D) is a small molecule that targets mitochondrial metabolism in tumor cells leading to ROS-mediated apoptosis. A phase III trial of mFOLFIRINOX + D at 500 mg/m2 in metastatic PDA did not meet primary endpoint of overall survival (OS). Here we present the results of the combination’s use at standard and escalated doses in LAPC and BRPC. Methods: In this investigator-initiated, single-center, phase I/II, open-label trial treatment-naïve patients with investigator assessed LAPC or BRPC were treated with mFOLFIRINOX in 14 day cycles + D. In the standard dosing (SD) cohort, patients received D at 500mg/m2 while in the dose escalation (DE) cohort; D at 750 mg/m2 or 1000 mg/m2 was used. Radiographic response was assessed every 8 weeks. Patients who remained unresectable after 12 cycles could receive additional standard treatments, including chemoradiotherapy. The primary endpoint was median overall survival (mOS), with the study powered to show a mOS improvement from the historical standard of 14 months to 28 months with mFOLFIRINOX + D. Secondary endpoints were median progression free survival (mPFS), percent resected, and safety outcomes. NCT03699319 Results: Between Dec 2018 and Mar 2022, 37 patients and 11 patients enrolled in the SD and DE cohorts. Median age 69 years (range 47-78), male/female (27/21), Caucasian (83%), LAPC/BRPC (34/14). One patient (2%) withdrew, 4 patients (8%) discontinued treatment due to toxicity, 9 patients (19%) had progressive disease prior to completion of 12 cycles. In all patients mOS was 16.3 months and mPFS was 10.7 months. By cohort: SD/DE mOS: 16.2/17.6 months (p=0.56). Fourteen patients (29%) had partial response by RECIST 1.1. Twenty patients (41.7%) had resection; mOS 29.7 months. In the SD cohort, 78% and 24% of patients had grade 3 and/or 4 AEs. There were no dose limiting toxicities (DLT) in the DE cohort, and eight patients received the maximum dose of 1000 mg/m2 of D. After the DLT period, 100% patients in DE cohort had grade 3 toxicity and 55% had grade 4 toxicity. For all the most common toxicities (gr3,4) were neutropenia (27%,25%), diarrhea (25%,0), anorexia wt. loss (23%,0), nausea/vomiting (23%,0). Conclusions: The combination of mFOLFIRINOX and D is feasible in the LAPC/BRPC population at increased dose levels of D; however, it did not meet the primary endpoint of doubling OS compared to historical controls. Clinical trial information: NCT03699319 .

Phase I clinical trial of peposertib plus radiation in adults with newly diagnosed MGMT-unmethylated glioblastoma.

2076 Background: DNA-dependent protein kinase (DNA-PK) is a pivotal component of DNA damage repair (DDR) pathways and is an attractive target in glioblastoma because its expression renders tumors less vulnerable to radiotherapy. Peposertib is a small molecule DNA-PK inhibitor that has been pre-clinically shown to potentiate radiotherapy and regress glioblastoma tumors. We conducted a two-stage phase I trial of peposertib plus radiation in patients with newly-diagnosed MGMT-unmethylated glioblastoma (NCT04555577). Methods: In stage 1, patients received concurrent peposertib plus standard-of-care radiotherapy to determine the maximum-tolerated dose (MTD) based on the Bayesian Optimal Interval design (maximum n=24). Stage 2 is a window-of-opportunity expansion cohort and will include 5 surgical patients to evaluate intratumoral drug concentration. Both groups receive 6 cycles of adjuvant temozolomide. Results: Eighteen patients completed the 10-week dose-limiting toxicity (DLT) period; 3@50mg, 3@100mg, 3@200mg, 9@300mg. One DLT (G3 radiation necrosis [RN] at 300mg) was observed. Enrollment of the last three patients into the 300mg dose level began in December 2023 and will complete stage 1. To date, most notable toxicity was transient G3 dermatitis of the scalp (2@200mg, 1@300mg; not a DLT per protocol). Therefore, radiation dose constraints to the skin were incorporated and subsequent patients did not experience this toxicity. After a median follow up of 14.3 months (9.3-18.4), the median OS was 22.9 months [95% CI (16-NR)] and median PFS was 12.7 months [95% CI (9-NR)]. Next-generation sequencing (NGS) was available for 16 archival tumor tissue specimens from patients treated on this trial. Two patients had pathology-proven RN (one within and one outside of the DLT period). Both tumors had baseline mutations in DDR genes (i.e. ATRX, DICER1). Recurrent tissue was available for 4 patients after treatment with peposertib, 2 of which demonstrated gain of DDR gene mutations (2 ATM mutations in one patient and gain of MAD2L2 mutation in another patient). Conclusions: The initial safety data of peposertib plus radiation in patients with newly-diagnosed MGMT unmethylated glioblastoma is favorable. The cases with RN in tumors with DDR mutations, the gain of DDR mutations in recurrent tumors, and the cases of scalp dermatitis suggest peposertib activity may correlate with DDR function, and possibly potentiates the effect of radiation. Stage I is an independent stage of the protocol that will enable MTD determination. Complete safety and survival data and correlations with genomics and spatial transcriptomics for Stage I patients will be presented at the meeting. The study was supported by EMD Serono (CrossRef Funder ID: 10.13039/100004755). Clinical trial information: NCT04555577 .

Olaparib, AZD1390, ceralasertib, saruparib and consolidation durvalumab (CONCORDE) phase Ib platform study of novel DNA damage response inhibitor (DDRi) agents in combination with radiotherapy in non-small cell lung cancer (NSCLC).

TPS8119 Background: Lung cancer is the leading cause of cancer mortality globally, with cases projected to exceed 62,000 by 2035. Outcomes remain poor despite advances in radiotherapy (RT) technologies. Combining novel mechanism-based agents with RT could improve the therapeutic index. DNA inhibition of cellular response to radiation-induced DNA damage can overcome intrinsic radio resistance and poses a promising strategy. Methods: CONCORDE is an open label, randomised, multi-arm, phase Ib, clinical trial opened to accrual in 11 UK hospitals designed to assess multiple DDRi in combination with radical thoracic RT (60Gy in 30 fractions over 6 weeks). Patients are randomised 3:1 to RT+/-DDRi. The study utilises an adaptive Bayesian model-based approach to dose escalation aiming to identify the recommended phase II dose for each treatment combination. Two arms will deliver up to 12 months consolidation durvalumab+/-DDRi following RT. Patients are eligible based on key criteria: not suitable for concurrent chemotherapy RT, inoperable, stage IIB/III NSCLC, performance status (KPS≥70). The dose limiting toxicity (DLT) period for treatment-related toxicities is 13.5 months post start of RT treatment, with most toxicities expected within the first 4.5 months (short DLT period). At least one patient must complete the short DLT period before dose escalation. A RT-alone calibration arm aids toxicity attribution. This trial is in progress: CONCORDE-A (olaparib (PARP inhibitor)), CONCORDE-B (AZD1390 (ATM inhibitor)), CONCORDE-C (ceralasertib (ATR inhibitor) followed by consolidation durvalumab+/-ceralasertib) and CONCORDE-E (AZD5305/saruparib (PARP1select inhibitor) followed by consolidation durvalumab) are open to accrual as of 24/11/2023. 57 of 74 registered participants have been randomised across 4 study arms. Of those 57 randomised: 55 started treatment: 20 received RT-alone, 12 received olaparib+RT, 14 received AZD1390+RT, 6 received ceralasertib+RT, 3 received AZD5305+RT and 2 withdrew. CONCORDE continues to recruit to the target sample size of 160 (40/arm) and welcomes further UK centres. A parallel multimodality translational program to identify biomarkers of treatment response, toxicity and the impact on the immune system are in development. Biomarkers of interest include plasma toxicity markers, immune cell profiling, radiomics and ctDNA. Clinical trial information: 10142971.

Nivolumab plus ONC201 plus in microsatellite stable (MSS) metastatic colorectal cancer (mCRC) patients: a Brown University Oncology Research Group phase Ib/II study (BrUOG379).

Immune checkpoint inhibitors alone, or in combination with chemotherapy failed to provide meaningful clinical activity for patients with microsatellite stable (MSS) colorectal cancer (CRC). ONC201 is a small molecule that inactivates AKT and ERK signaling and actives the TRAIL pathway. Preclinical studies indicated potential benefits of combining ONC201 with checkpoint inhibitors. This is a phase Ib/II trial of ONC201 plus nivolumab for patient with MSS CRC who progressed on standard treatment. Enrolled patients received ONC201 plus nivolumab in a dose de-escalation fashion to determine the maximum tolerated dose (MTD). Additional patients were enrolled in the dose-expansion cohort. ONC201 at a dose of 625 mg was given orally at day -7 of cycle 1, followed by weekly dosing. Nivolumab was given every 2 weeks at 240 mg IV starting on day 1 of every cycle (cycle =28 days). The primary end point was dose-limiting toxicity (DLT) during the observation window (run-in dose day -7, cycle 1 to assessment pre-dosing cycle 2). The plan was to enroll 28 additional patients at the MTD so that a total of 34 patients would be treated at the MTD. Pharmacokinetics (PKs) and tumor biopsies were collected at several time points per study protocol. A total of 13 patients (8 patients in the dose escalation *6 evaluable*) were enrolled between December 4, 2019 and March 2021. All patients had received ≥2 previous lines of chemotherapy and had confirmed microsatellite stability or mismatch repair-proficient tumors. No DLTs were observed with 625 mg ONC201 in the first three patients. Three additional patients were enrolled at the same dose to confirm safety. Two patients progressed during the DLT period and had to be replaced. During the dose-expansion part, five patients were enrolled and none required dose reduction or modification. No objective tumor response was observed in the 13 treated patients. Disease progression was confirmed at the time of the first imaging evaluation at 8 weeks following cycle 2. Post discussion at the Data and Safety Monitoring Board (DSMB) on May 25, 2021, the principal investigator (PI) and Committee voted to close the study to new patient enrollment prior to reaching accrual of 34 patients, secondary to lack of efficacy. In this study of patients with advanced MSS CRC, combination ONC201/nivolumab was well-tolerated; objective responses to ONC201/nivolumab were not observed.

Abstract 5005: Safety and tolerability of multi-epitope HER2 peptide vaccines in combination with trastuzumab emtansine in HER2-positive breast cancer patients with residual disease after neoadjuvant chemotherapy

Abstract Background: Residual disease after neoadjuvant chemotherapy (NAC) in breast cancer (BC) confers poor outcomes. Trastuzumab emtansine (T-DM1) is approved for HER2+ patients with residual disease after NAC. However, many patients still develop recurrence. H2NVAC is a multi-epitope CD4 helper T cell activating vaccine that includes a pool of 4 degenerate HER2-derived HLA-DR epitopes admixed with GM-CSF. Our previous phase I trial showed that this vaccine was safe and generated robust, long-lasting T and B cell immune responses. Method: We conducted a safety run-in phase of H2NVAC in combination with T-DM1 in stage II-III HER2+ BC with residual disease after NAC. Patients were treated with H2NVAC and T-DM1 for 6 cycles, followed by 2 boosters at 3 and 12 months. Dose-limiting toxicity (DLT) was defined as any grade (G) ≥ 3 toxicity occurring within 21 days after the first vaccination. Results: 20 patients were enrolled (median age 51; 27-69 years), including 80% White and 15% Black. 90% had hormone receptor-positive disease. There was no DLT observed in the safety run-in cohort. All adverse events (AEs) during the DLT period were grades 1 and 2, with fatigue being the most common (60% G1, 5% G2), followed by peripheral sensory neuropathy (55% G1, 5% G2), and injection site reaction (50% G1). Across all treatment cycles, the 10 most common AEs that were at least possibly related to treatment in all cycles are summarized in the table below. The injection site reaction was the most common AE, with 85% G1 and 15% G2. Conclusion: H2NVAC, in combination with T-DM1, was safe, with a favorable side effect profile. There was no DLT observed. The most common AE was injection site reaction, with the majority being G1. A multicenter, randomized, placebo-controlled, phase II trial of H2NVAC vs. placebo in combination with trastuzumab emtansine is currently ongoing through the ACCRU consortium (NCT04197687). Adverse Events Grades 1 2 N % N % Injection site reaction 17 85.0 3 15.0 Aspartate aminotransferase increase 13 65.0 Alanine aminotransferase increase 9 45.0 Fatigue 7 35.0 2 10.0 Peripheral sensory neuropathy 7 35.0 2 10.0 Alkaline phosphatase increase 8 40.0 Nausea 7 35.0 1 5.0 Arthralgia 7 35.0 Myalgia 5 25.0 1 5.0 Platelet count decrease 6 30.0 Citation Format: Saranya Chumsri, Sharmila Giri, Andy J. Ness, David W. Hillman, Nadine Norton, Davitte Cogen, Brian M. Necela, Aziza Nassar, Donald W. Northfelt, Pooja Advani, Rohit Rao, Kostandinos Sideras, Alvaro Moreno-Aspitia, Brenda J. Ernst, Kathryn J. Ruddy, Matthew P. Goetz, Keith L. Knutson. Safety and tolerability of multi-epitope HER2 peptide vaccines in combination with trastuzumab emtansine in HER2-positive breast cancer patients with residual disease after neoadjuvant chemotherapy [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 5005.

Abstract C027: RSO-021, a first-in-class covalent inhibitor of mitochondrial PRX3: From bench to bedside

Abstract RSO-021 is a first-in-class mitochondrial peroxiredoxin 3 (PRX3) covalent small molecule inhibitor. The safety and tolerability of RSO-021 are currently being tested in the phase 1-2 MITOPE clinical trial in patients with malignant pleural effusion (MPE) arising from malignant mesothelioma or metastatic cancer to the lungs (NCT05278975). Altered redox status, resulting in elevated cellular hydrogen peroxide (H2O2) levels, drives the growth and proliferation of mesothelioma and other solid tumors. PRX3, the primary mitochondrial H2O2 scavenging enzyme, supports tumor cell escape from oxidative stress and aggressive tumor growth. RSO-021 attacks active site cysteine residues in PRX3 covalently to inactivate the enzyme, resulting in elevated H2O2 levels in the mitochondria incompatible with tumor cell survival. RSO-021 showed potent PRX3 inactivation and anti-tumor activity in pre-clinical cell and mouse models of mesothelioma with good tolerability supporting its clinical development. The MITOPE trial (NCT05278975) is an open-label, non-randomized, multicenter, translational phase 1-2 dose-escalation and expansion study designed to determine the safety, tolerability, dose-limiting toxicity (DLT), pharmacokinetics (PK), pharmacodynamics (PD), and preliminary anti-tumor activity of RSO-021 after intrapleural administration after complete drainage in patients with MPE due to mesothelioma or other metastatic disease. RSO-021 is administered locally as a pleural infusion through an indwelling catheter as a single dose on Day 1, 8 and 15 of each 3-week cycle. Safety is assessed at the end of the 21-day DLT period and efficacy every 6 weeks. PK and PD are assessed on pleural fluid, biopsies and with systemic sampling. RSO-021 is administered until disease progression, unacceptable toxicity, withdrawal of consent or study termination. Currently, MITOPE is actively recruiting patients in 4 open UK sites, with additional 9 sites on-boarding shortly. The dose escalation phase of the trial has 13 patients dosed at either 90, 120 or 180 mg flat dose levels and is anticipated to complete recruitment by the end of 2023. The trial will then continue to recruit patients as part of the dose expansion phase of the trial, which is exploring specific indications, including newly-diagnosed and previously-treated MM with MPE, as well as combination with systemic therapy in patients with refractory solid tumors and MPE. Citation Format: Dean A. Fennell, Sean Dulloo, Peter Szlosarek, Fiona Thistlethwaite, Simon Lord, Najib M Rahman, Brian Cunniff, Joanna Dzialo, Charlotte Poile, Rakesh Panchal, Jarrett Duncan, Pip Graham, Alice Bexon, George N. Naumov, James Spicer. RSO-021, a first-in-class covalent inhibitor of mitochondrial PRX3: From bench to bedside [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr C027.

A Phase 1 Study of Adding Pitavastatin to Venetoclax-Based Therapy in AML and CLL/SLL

Statins (HMG-CoA-reductase inhibitors) are drugs used widely for the treatment of high cholesterol and are generally well-tolerated. There has been increasing interest in repurposing statins for oncology based on the recognition that many cancer cells are “addicted” to the mevalonate biosynthetic pathway (Iannelli et al, 2017; Juarez and Fruman 2021). We have shown that statins increase expression of the pro-apoptotic BCL2 family member PUMA (Lee at al, 2018). We have strong pre-clinical evidence that statins improve responses to the BCL2 inhibitor venetoclax (VEN) in cell line models and ex vivo primary patient specimens from patients with both chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) (Lee et al, 2018). Additionally, retrospective review of patients enrolled into the early clinical trials of VEN in CLL revealed improved responses to VEN (complete remission [CR] and progression-free survival) in the patients who were concurrently on a statin medication (Lee et al, 2018). These retrospective analyses may underestimate the potential of statins for leukemia therapy, as the statin drugs most commonly prescribed for hypercholesterolemia are not pharmacologically optimized for oncology (Abdullah et al., 2018). We developed a phase 1 study of adding pitavastatin (PIT) to VEN-based therapy in patients with AML and CLL/small lymphocytic lymphoma (SLL) (NCT04512105). AML patients were eligible if receiving induction therapy with azacitidine (AZA) and VEN per standard of care. CLL/SLL patients could receive either VEN with obinutuzumab (O) or rituximab. A 3+3 design was employed. Dose level 1 was PIT 2 mg daily, and dose level 2 (DL2) was 4 mg daily. These doses are consistent with the doses used for the treatment of hypercholesterolemia. Those enrolling at DL2 had a creatinine clearance of 60 mL/min or higher based on the prescribing information for pitavastatin. Patients already on statins for the treatment for hypercholesterolemia were allowed; these patients stopped their prescribed statin for 72 hours prior to initiation of PIT. PIT started after patients completed VEN ramp-up and had been on a stable VEN dose for at least 5 days. Primary objectives were assessing safety and tolerability and determining the recommended phase 2 dose of PIT in combination with VEN-based therapies. Secondary objectives included CR rates. Exploratory objectives included performing BH3 profiling on pretreatment and post-treatment blood samples to assess whether add-on treatment with PIT increases apoptotic priming, as seen in preclinical models (Lee et al, 2018). 14 patients signed informed consent. 6 were deemed ineligible. 2 withdrew consent prior to starting PIT therapy. 6 patients received PIT on study. 2 patients had AML and received AZA+VEN. 2 patients had CLL, and 2 patients had SLL. The CLL/SLL patients all received VEN+O. Grade 1 myalgia was reported in one subject on the 4mg PIT dose. 1 patient experienced a grade 1 increase in AST on the 4mg dose. Another patient had grade 1 elevation in bilirubin and alkaline phosphatase at the 4 mg dose. Grade 3-4 toxicities included leukopenia, neutropenia (1 case of febrile neutropenia, grade 3), anemia, and thrombocytopenia. Cycle 1 was defined as the dose-limiting toxicity (DLT) period, and no hematologic toxicities occurred during the DLT period. 1 patient had grade 3 pancreatitis, but this was felt to be unrelated to therapy or disease (also outside the DLT period). No grade 5 toxicities occurred while on study therapy. Toxicities were overall felt to be similar to patients receiving VEN-based therapy in standard clinical practice. All evaluable patients (n=5) achieved clinical CR. 1 patient with SLL is awaiting re-staging at the time of this abstract. Correlative studies are ongoing. In 2 patient peripheral blood samples analyzed, the % blasts (for an AML sample) and % CD5+ B-cells (for a CLL sample) were reduced 24 hours after PIT dosing compared to prior to any treatment and before PIT/after VEN ramp-up. Based on the tolerability of PIT and encouraging clinical outcomes, a phase 2 study is being planned to better assess the efficacy of adding PIT to VEN-based therapies in AML and CLL/SLL.

A Phase 1 Study of CD38-Bispecific Antibody (XmAb18968) for Patients with Relapsed/Refractory T-Cell Acute Lymphoblastic Leukemia

Background: Outcomes of adults with relapsed/refractory T-cell acute lymphoblastic leukemia (T-ALL) has remained poor. CD38 is a transmembrane glycoprotein that is highly expressed in T-ALL and is potentially targetable with CD38 blocking agents [Naik J et al. Haematologica 2019, Bride KL et al. Blood 2018, Tembhare et al. J Immunother Cancer 2020]. XmAb18968 is a novel CD38-CD3 bi-specific T-cell engager with Fc domain modified to minimize Fcγ receptor binding and non-selective T-cell activation resulting in reduced cytokine release without compromising target cell killing. We designed a phase I clinical trial to assess the safety and tolerability of XmAb18968 in patients with T-ALL. Methods: We conducted a multicenter, open label, phase I dose escalation study of XmAb18968 (NCT05038644). Patients aged ≥18 years with relapsed/refractory T-ALL or T-lymphoblastic lymphoma (T-LBL), ECOG PS 0-2 and adequate organ function were eligible. Major exclusion criteria are hematopoietic cell transplantation within 6 months of enrollment, prior therapy with daratumumab in the last 6 months and active acute graft-versus-host disease. Dose escalation was conducted using 3+3 design, and 4 separate dose levels were studied [0.8mg, 1mg, 1.3mg, 1.5mg]. XmAb18968 was administered intravenously on days 1, 8, 15, 22 on a 28-day cycle. During cycle 1 alone, day 1 dose was fractionated and administered over 2 days to minimize the risk of significant cytokine release syndrome (CRS). Treatment was continued until progression or unacceptable toxicity. The primary objective was to determine the safety and dose limiting toxicity (DLT) and secondary objective was to determine the preliminary efficacy. Correlative studies included pharmacokinetics, characterizing changes in serum cytokines and phenotypic expression of activated T-cells and leukemic cells, correlation of the phenotypic expression with changes in transcriptome at the single-cell level, proteomics evaluation of cytokine secretion at the single-cell level and correlation of response with N-glycan profiling, quantitative site-occupancy, and direct glycopeptide analysis. Results: Four patients with relapsed/refractory T-ALL have been enrolled so far at dose level 1 (0.8mg) with 3 of them being evaluable for response (one patient came off study before DLT period). Median age was 62 years (34-74), all response evaluable patients had early T-precursor ALL (ETP-ALL), and one patient (25%) was previously treated with allogeneic HCT, CD7 CAR-T therapy and daratumumab. Grade 3 or higher adverse events are summarized in Table 1. CRS grades 1 was noted in 25% of patients, no grade ≥3 CRS or neurotoxicity (any grade) was seen. Of the 3 evaluable total patients, 2 patients had achieved complete response (CR) after 1 cycle of therapy (one patient had prior allogeneic HCT, CD7 CAR-T therapy and daratumumab) (Table 2). The two responders remain on treatment. Conclusions: XmAb18968, a novel CD-38 bispecific antibody appears safe and is showing response at the starting dose level in T-ALL. The study is currently enrolling additional patients with T-ALL. Updated analysis with additional patients and details on correlative studies examining mechanisms of therapeutic efficacy will be reported at the main meeting.

TIM-3 Inhibitor Sabatolimab for Patients with Acute Myeloid Leukemia (AML) with Measurable Residual Disease (MRD) Detected after Allogeneic Stem Cell Transplantation (AlloSCT): Preliminary Findings from the Phase Ib/II Stimulus-AML2 Study

Introduction: AlloSCT is a potentially curative treatment for patients (pts) with AML. However, MRD persistence after transplantation has been identified as a risk factor for relapse. In this regard, the graft-versus-leukemia (GvL) effect is well recognized as one of the leading mechanisms of disease control after transplantation. Sabatolimab is a novel immunotherapy that targets the immuno-myeloid regulator TIM-3 on both immune cells and leukemic blasts, and may have the potential to enhance the GvL effect. STIMULUS-AML2 (NCT04623216) is a Phase Ib/II, open-label, multicenter study of sabatolimab alone or in combination with azacitidine as pre-emptive therapy in pts with AML who are in complete remission (CR) with positive MRD (MRD+) after alloSCT. Here we report preliminary data from the safety run-in of sabatolimab monotherapy at two dose levels (400 mg or 800 mg intravenous [IV] every four weeks [Q4W]). Methods: Eligible pts for the safety run-in were adults (≥18 years [y]) with de novo or secondary AML, who achieved CR post-alloSCT but were MRD+ by local assessment at any time ≥Day (D) 60 after alloSCT (protocol amended from MRD+ D100-365 post alloSCT; March 24, 2022) and ≥2 weeks after immunosuppressive medications had been tapered off. MRD was assessed locally at baseline by polymerase chain reaction (PCR; 12 pts: NPM1 and/or WT1, 8; IDH2, 2; other, 2), multiparameter flow cytometry (MFC; 6 pts), both PCR and MFC (1 pt), and CD34+ chimerism (2 pts). In this safety run-in, adult pts received sabatolimab monotherapy at 400 mg or 800 mg IV on D1 of every 28-day cycle. The primary endpoint was incidence of treatment-emergent dose-limiting toxicity (DLT), including acute graft-vs-host disease (GvHD) and chronic GvHD during the first 2 cycles. Results: A total of21 pts were enrolled in the safety run-in (10 at 400 mg; 11 at 800 mg). Median age was 59 years. At AML diagnosis, across cohorts, 8, 9 and 4 pts had favorable, intermediate, and adverse genetic risk (European LeukemiaNet 2017), respectively. At data cut-off (April 26, 2023), 3 pts were still ongoing in the 400 mg cohort and 7 had discontinued due to disease relapse. At 800 mg, 4 pts were ongoing and 7 had discontinued (5 due to relapse, 1 due to adverse event [AE], 1 due to new therapy) ( Table 1). Across cohorts, there was 1 DLT of grade (G) 3 myocarditis after the first infusion of sabatolimab 800 mg, which recovered/resolved on the same day and sabatolimab was then withdrawn. An overview of safety is shown in Table 2. Any G and G≥3 AEs occurred in 16 (76.2%) and 8 (38.1%) pts, respectively. There were no cases of GvHD or immune-related AEs, 2 cases of G≥3 neutropenia and 1 case of G≥3 thrombocytopenia. G3 neutropenia and G3 thrombocytopenia in the same pt at 400 mg were considered treatment related and the patient later relapsed. At 400 mg, 2 pts experienced serious AEs (SAEs) after the DLT observation period (>3 cycles) and 2 pts at 800 mg had SAEs during the DLT period (G3 myocarditis [1 pt] and disease relapse with central nervous system involvement [1 pt]). There were 5 deaths, all at 400 mg and due to study indication (AML). As a preliminary indicator of efficacy, 7 pts were still on treatment and in CR at data cut-off. At 400 mg, 2 pts and 1 pt had received 14 and 15 cycles of treatment (>1 y), respectively. At 800 mg, 1 pt had received 5, 1 pt 6, and 2 pts 7 cycles. At 400 mg, 7 pts relapsed: 2 pts after cycle 1, 2 pts after cycle 2, 1 pt each after cycles 3, 4 and 7. At 800 mg, 5 pts relapsed: 1 pt after cycle 1, 2 pts after cycle 2, 1 pt after cycle 3 and 1 pt after cycle 5. Conclusions: In adult pts with AML who are in hematological CR with MRD+ after alloSCT, sabatolimab 400 mg and 800 mg monotherapies were well tolerated. Cytopenias occurred at low rates, were generally G1-2 and mostly related to imminent relapse. Importantly, there were no cases of GvHD reported or any immune-related AEs commonly seen with checkpoint inhibitors. Preliminary efficacy was promising with 30% of the pts at 400 mg still in CR after more than 1 y on treatment (available longer-term follow-up >1 y), and data may suggest a delayed onset of relapse. A dose expansion cohort at 800 mg opened for enrollment June 30, 2023. Adults will be randomized to sabatolimab as monotherapy or in combination with azacitidine, and preliminary efficacy on the prevention of hematological relapse will be evaluated. Adolescents (12-17 y) will also be enrolled to evaluate the safety of sabatolimab monotherapy. This study is sponsored by Novartis.

Safety, Efficacy and T-Cell Predictive Biomarkers in a Phase I Trial of Copanlisib+Nivolumab in Patients with Richter's Transformation (RT) or Transformed Non-Hodgkin Lymphoma (tNHL)

Background. Despite advances in targeted and cellular therapy, outcomes among patients (pts) with RT and tNHL remain dismal. Copanlisib (COPA) is a selective, small molecule, PI3Kinhibitor which preferentially targets the p110αδ isoforms . COPA has shown clinical efficacy in NHL and is an approved therapy for follicular lymphoma (FL). Nivolumab (NIVO) is a PD-1 antagonist which has demonstrated activity in NHL. Furthermore, combined targeting of PI3K and PD-1 has demonstrated synergy in pre-clinical lymphoma models. Here we report results of a phase 1 study of COPA in combination with NIVO in pts with R/R RT or tNHL (NCT03884998) and correlate response to treatment and T cell functionality in RT. Methods. This ongoing multicenter, open-label, phase I, investigator-sponsored study is enrolling pts with RT or tNHL, age ≥18 years, whose disease has relapsed or was refractory to ≥1 prior line of therapy. The phase I portion of the study follows a standard 3+3 design, followed by a dose expansion of 16 evaluable pts, with two planned dose levels of COPA administered IV (dose level [DL]1 - 45 mg on days 1, 8 and 15 and DL2 - 60 mg on days 1, 8 and 15 of a 28-day cycle). NIVO 240 mg is given IV on days 1 and 15. Pts receive up to 24 cycles of therapy. Dose limiting toxicities (DLT) were defined as grade ≥4 hematologic lasting > 7 days or grade ≥3 non-hematologic toxicities. The primary study objective is to evaluate the maximum tolerated dose (MTD) of the combination; secondary objectives are preliminary efficacy by Lugano criteria. Exploratory objectives include T-cell functionality assessed by flow cytometry analysis of cell subsets as well as scRNA-Seq performed on biospecimens banked from pts pre-treatment, after cycles 1 and 5, and at the end of treatment. Results. The study enrolled 25 pts to date, 11 in dose finding (8 at DL1 and 3 at DL2) and 14 in dose expansion cohorts. Fourteen pts had RT and 11 had tNHL (10 tFL and 1 transformed lymphoplasmacytic lymphoma). Median (med) age was 65 years (32-77), 88% (22/25) had ECOG performance status 0-1. Pts had received a med of 4 prior lines of therapy (range, 1-10); 8 pts (2 RT, 6 tNHL) had CAR T cells. During dose finding, 8 pts were treated at DL1 (45 mg COPA), of which 2 pts did not complete the DLT period due to rapidly progressive disease and were replaced. No DLTs were observed in 6 evaluable pts at DL1. At DL2 (60 mg COPA), three DLTs (neutropenia, thrombocytopenia) occurred in 2 pts determining the MTD of COPA to be 45 mg. After a median follow-up of 14 months (range 1.8-20.6), the most common treatment-related adverse events (AEs, any grade) were diarrhea and anemia (Table 1). Twenty-three pts went off protocol after a med of 3 cycles (range 1-20); 2 remain on treatment. Sixteen pts discontinued therapy due to progressive disease and 6 due to AEs. Among the 23 efficacy-evaluable pts who completed at least one cycle of therapy, 10 pts achieved a response (ORR 43%). Pts with tFL had an ORR of 60% (2 CR and 4 PR) with median progression free survival (mPFS) 4.8 months (95%CI: 0.4-16.8) and median duration of response (mDOR) 10.2 months (95%CI: 2.0-13.6) (Figure 1). Pts with RT had an ORR of 33% (2 CR and 2 PR) with mPFS 2.0 months (95%CI: 0.7-4.9) and mDOR not reached (95%CI: 3.0-NA). Analysis of paired samples from pts using flow cytometry and scRNA-Seq demonstrated an increase in circulating CD8+ T cell population and a decrease in exhaustion markers (PD1, CTLA-4) after exposure to COPA/NIVO. Analysis of 2 responding RT pts by scRNA-Seq demonstrated downregulation of MYC in tumor cells and upregulation of IFN response in T cells. This pattern was not observed 3 RT non-responders (NRs). By contrast, CD8+ effector T-cells from NRs exhibited downmodulation of the IFN response after cycle 1 of treatment and concurrent activation of p53-regulated genes and apoptotic genes. Tregs sourced from RT responders showed enhanced expression of apoptosis pathways after treatment, while these pathways were downregulated in NR Tregs. Discussion. We identified COPA 45 mg IV on days 1, 8 and 15 as the MTD/RP2D in combination with NIVO in pts with R/R RT and tFL. This combination was generally well-tolerated and had activity, particularly in pts with with tFL. We observed key differences in gene expression patterns in T cell subsets between the responders and NRs. Downregulation of MYC in the tumor, activation of the apoptotic program in Tregs and enhanced CD8 T-cell IFN response were associated with treatment response in RT. Accrual is ongoing.

CTIM-05. RESULTS OF SAFETY LEAD IN OF PHASE II TRIAL OF COMBINATION OLAPARIB, TEMOZOLOMIDE, AND PEMBROLIZUMAB FOR PATIENTS WITH IDH-MUTANT GLIOMA

Abstract BACKGROUND Recurrent gliomas are universally fatal with few adequate treatment options. IDH-mutant gliomas may be susceptible to PARP inhibition, thus combination therapy using alkylating agents and checkpoint inhibition could be synergistic. METHODS This is an open label, phase II study of olaparib, temozolomide, and pembrolizumab for patients with recurrent IDH-mutant glioma, grade 2 or 3, with measurable enhancing disease per RANO. Patients received pembrolizumab 200mg IV on day 1 of each 21-day cycle. Oral olaparib 200mg twice daily and temozolomide 50mg/m2 daily were given days 1-7 of cycles 3-11. Here, we report the results of our safety lead in, consisting of the first 6 patients to complete cycle 3. RESULTS A total of seven patients were enrolled to the safety lead-in: 2 women; 5 patients with astrocytoma, 2 oligodendroglioma. Patients had a median age of 45 (range 29-63) and median KPS 90 (range 80-100). Median number of recurrences was 3.5 (range 1-5). All had received prior alkylating therapy and all but 1 patient had received prior RT. No patients were taking steroids at the time of enrollment. Six patients completed the dose-limiting toxicity (DLT) period without any DLTs. One patient experienced clinical progression on pembrolizumab monotherapy prior to the start of combination therapy and was thus replaced. No grade 3 or 4 toxicities were seen through the DLT period. The most common clinical toxicities at least possibly related to treatment were grade 1 and 2 fatigue (n = 4), nausea (n = 3) and constipation (n = 2). Hematological toxicities include grade 1 anemia (n = 2) and decreased platelet count (n = 1). CONCLUSIONS The combination of olaparib, temozolomide, and pembrolizumab was well tolerated in this cohort. Following completion of the safety lead-in, the trial was redesigned to minimize the length of pembrolizumab monotherapy and introduce combination therapy in cycle 1. Enrollment is ongoing. NCT05188508.

CTNI-42. PHASE I CLINICAL TRIAL OF PEPOSERTIB PLUS RADIATION IN NEWLY DIAGNOSED MGMT-UNMETHYLATED GLIOBLASTOMA

Abstract BACKGROUND DNA-dependent protein kinase (DNA-PK) is a pivotal component of DNA damage repair (DDR) pathways and is an attractive target in glioblastoma because its expression renders tumors less vulnerable to radiotherapy. Peposertib is a small molecule DNA-PK inhibitor that has been shown to potentiate radiotherapy and regress glioblastoma tumors pre-clinically. We conducted a two-stage phase I trial of peposertib plus radiation in newly-diagnosed MGMT-unmethylated glioblastoma (NCT04555577). Method: In stage 1, patients received peposertib plus standard-of-care radiotherapy to determine the maximum-tolerated dose (MTD) based on the Bayesian Optimal Interval design (maximum n = 24). Stage 2 is a window-of-opportunity expansion cohort and will include 5 surgical patients to evaluate tumor drug concentration. Both groups receive adjuvant temozolomide for 6-cycles. RESULTS Fifteen completed the 10-week dose-limiting toxicity (DLT) period; 3-50mg, 3-100mg, 3-200mg, 6-300mg. One DLT (G3 radiation necrosis [RN] at 300mg) was observed. Most notable toxicity was 3 patients with transient G3 dermatitis of the scalp (not DLT per protocol) (2-200mg, 1-300mg). Therefore, radiation dose constrains to the skin were incorporated and subsequent patients did not experience this toxicity. Next-generation sequencing (NGS) was available for 13 archival tissue. Two patients had pathology-proven RN (one within and one outside of the DLT period). Both tumors had mutations in DDR genes (i.e. ATRX, DICER1). Recurrent tissue was available for one patient after treatment with peposertib showed gain of two ATM mutations. CONCLUSION The initial safety data of peposertib plus radiation in newly-diagnosed MGMT unmethylated glioblastoma is favorable. The cases with RN in tumors with DDR mutations, the gain of two ATM mutations in a recurrent tumor and the cases of scalp dermatitis suggest that peposertib is active and possibly potentiates the effect of radiation. Safety and survival data and correlations with genomics will be presented. The study was supported by EMD Serono (CrossRef Funder ID: 10.13039/100004755).

CTIM-23. SAFETY RUN-IN RESULTS OF A PHASE I/II STUDY TO EVALUATE ATEZOLIZUMAB IN COMBINATION WITH CABOZANTINIB IN PATIENTS WITH RECURRENT GLIOBLASTOMA

Abstract BACKGROUND Immune checkpoint inhibitor therapy has shown limited efficacy in the treatment of glioblastoma (GBM) in both newly diagnosed and recurrent disease which underscores the need for rational combinatorial strategies. Atezolizumab is a humanized monoclonal antibody that targets PD-L1 and has been shown to enhance the magnitude of tumor-specific T cell responses. Combining PD-L1/PD-1 axis inhibition with targeted therapy like cabozantinib which has both anti-tumoral and immunomodulatory properties may result in synergistic effects. Cabozantinib may modulate the myeloid cell population to overcome resistance to anti-PD-1/PD-L1 therapy. METHODS Eligibility criteria were those with recurrent GBM, age >18 yrs with 1st or 2nd recurrence who were naïve to antiangiogenic and receptor tyrosine kinase inhibitor treatment. The primary objective of the phase I run-in was to evaluate the safety of atezolizumab in combination with cabozantinib. RESULTS 1 dose-limiting toxicity (DLT) of a grade 3 ALT elevation was observed in the first 6 DLT evaluable patients treated during the safety run-in phase. Regarding immune related adverse events, 1 of 6 patients developed atezolizumab-related grade 1 hypothyroidism. 1 of 6 patients developed study treatment-related grade 2 diarrhea. 2 patients after completion of 2 cycles of treatment had evidence of a partial radiographic response ( > 50% decrease). 1 patient had a near partial radiographic response (45% decrease). 2 patients had stable disease after completion of 2 cycles of the combinatorial treatment. 1 patient had only completed the first 28-day cycle, DLT period, and had not yet had imaging to reassess disease status. CONCLUSIONS The combination of atezolizumab with cabozantinib was tolerable, and no new safety signals were noted. In this small cohort of recurrent GBM patients, radiographic responses were observed. The phase II component of the trial is recruiting patients (n = 45) to evaluate clinical efficacy. Multi-omic correlative studies and fecal microbiome analyses are planned.

Phase I Trial of Allogeneic Donor Gamma Delta T Cell Infusion Post-Hematopoietic Cell Transplantation, an Interim Safety Report

Background Patients with 2017 European LeukemiaNet (ELN) adverse risk acute myeloid leukemia (AML) are at 40% risk of relapse leading to poor survival after allogeneic hematopoietic cell transplantation (allo-HCT) (Hansen TCT 2021, Jimenez BMT 2021). Ex vivo donor-derived gamma delta T cells (GDT) expanded with artificial antigen presented calls (aAPC) are a novel therapy with potent MHC-independent antineoplastic cytotoxicity. An ongoing phase 1/1b study is evaluating the safety and potential efficacy of ex vivo expanded donor GDT after reduced-intensity conditioning (RIC) allo-HCT in patients with ELN adverse risk AML ( NCT05015426). We report on manufacturing, safety, and correlative biology of expanded donor GDT after allo-HCT in the first 5 treated patients (Table 1). Methods The primary endpoint is the maximum-tolerated dose (MTD) of allogeneic donor GDT as a single infusion at day 60 after RIC allo-HCT. Next generation sequencing was used for measurable residual disease (MRD) assessment pre-HCT and post-GDT infusion. Donor GDT collected from the same donor of the allo-HCT were enriched from non-mobilized leukapheresis product by stimulation with zoledronic acid and IL-2 for 7 days followed by alpha beta T cell depletion using the Miltenyi CliniMACS. Enriched GDT (>90% TCRVδ2) were then co-cultured with irradiated aAPCs in Wilson Wolf G-Rex 100MCS over 10 days (Boucher J. Immunother 2023). This single center, investigator-initiated phase 1 trial is testing 3 distinct dose cohorts of infused GDT (5 x 10 6 cells/kg, 2.5 x 10 7 cells/kg, and 1 x 10 8 cells/kg) with acceptable range of 25% margin. A Bayesian optimal interval design is used to guide dose escalation/de-escalation decisions. Results First 3 patients enrolled in dose level 1 (DL1) cohort received GDT dose of 6.25 x 10 6 cells/kg, while last 2 patients enrolled in DL2 cohort received 3.13 x 10 7 cells/kg dose. Dose-limiting toxicities (DLT) were evaluated for 42 days following GDT infusion and no DLT were observed. None of the treated patients experienced cytokine release syndrome (CRS), Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS) or graft-versus-host disease (GVHD) during DLT period. Among patients treated on DL1, patient #01 had ASXL1 AML with MRD pos (VAF 43.9%) prior to RIC haploidentical (Haplo) HCT. He is in ongoing complete remission (CR) 9 months post-HCT and has had no GVHD. Patient #02 had MRD pos (VAF 61.7%) AML with TP53 mutation/complex karyotype prior to RIC matched sibling donor allo-HCT. He is in CR and has mild chronic GVHD at 7 months post-HCT. Patient #03 with pre-HCT MRD negRUNX1 AML is in ongoing CR 7 months post-RIC Haplo HCT with no GVHD. At day 28 and day 120 post-GDT, all 3 patients were MRD neg in bone marrow and had 100% bone marrow and peripheral blood leukocyte and granulocyte chimerism. In DL2 cohort, patient #04 with RUNX1 AML and patient #05 with t(9;22) AML both were MRD neg prior to RIC Haplo HCT and remain in CR with no GVHD at 5 and 4 months post-HCT, respectively. At day 28 post-GDT, both patients were MRD neg and had 100% chimerism. Patient #05 had a fall during DLT period in a setting of orthostatic hypotension requiring hospitalization for 24 hours for hydration. This was the only grade 3 adverse event observed in this trial. Serum cytokines analyzed included IL2, IL6, IL15, IFNγ, TNFα, Angiopoietin 1&2, and GM-CSF (Figure 1). We compared results prior and up to 90 days post-GDT infusion and found no significant differences, which can explain no CRS or ICANS events yet observed on this trial. Immunophenotype (TCRVδ2, TCRVδ1, PD1, CTLA4, TIGIT and CD28) of GDT was analyzed in samples of donor apheresis, pre- and post-enrichment, infused GDT product and at days 28 and 90 post-infusion. GDT (TCRVδ2) persisted at day 28 and day 90 post-infusion and expressed low levels of cell surface inhibitory receptors. Conclusion This preliminary interim report demonstrates favorable safety and tolerability of donor GDT therapy with no CRS, ICANS or GVHD in first 5 patients treated in this trial. All these patients with adverse risk AML are in ongoing MRD neg CR following RIC allo-HCT, including 2 pre-HCT MRD pos cases with TP53 AML and AXSL1 AML. Early results of this trial are promising, which provides validation for continued testing of adoptive transfer of ex vivo expanded donor GDT. Updated results of this trial will be presented at the annual conference.

A Phase 1 Study of CD38-Bispecific Antibody (XmAb18968) for Patients with CD38 Expressing Relapsed/Refractory Acute Myeloid Leukemia

Background: Outcomes of adults with relapsed/refractory acute myeloid leukemia (RR-AML) have remained poor. CD38 is a transmembrane glycoprotein that is highly expressed in AML and is potentially targetable with CD38 blocking agents [Naik J et al. Haematologica 2019, Tembhare et al. J Immunother Cancer 2020]. XmAb18968 is a novel CD38-CD3 bi-specific T-cell engager with Fc domain modified to minimize Fcγ receptor binding and non-selective T-cell activation resulting in reduced cytokine release without compromising target cell killing. We designed a phase I clinical trial to assess the safety and tolerability of XmAb18968 in patients with RR-AML. Methods: We conducted a multicenter, open label, phase I dose escalation study of XmAb18968 (NCT05038644). Patients aged ≥18 years with relapsed/refractory AML, ECOG PS 0-2 and adequate organ function were eligible. Major exclusion criteria are hematopoietic cell transplantation within 6 months of enrollment, active acute graft-versus-host disease, and acute promyelocytic leukemia. Dose escalation was conducted using 3+3 design and 4 separate dose levels were studied [0.8mg, 1mg, 1.3mg, 1.5mg]. XmAb18968 was administered intravenously on days 1, 8, 15, 22 on a 28-day cycle. During cycle 1 alone, day 1 dose was fractionated and administered over 2 days to minimize the risk of significant cytokine release syndrome (CRS). Treatment was continued until progression or unacceptable toxicity. The primary objective was to determine the safety and dose limiting toxicity (DLT) and secondary objective was to determine the preliminary efficacy. Measurable residual disease (MRD) status was assessed using multicolor flow cytometry with 0.01% sensitivity. Correlative studies included pharmacokinetics, characterizing changes in serum cytokines and phenotypic expression of activated T-cells and leukemic cells, correlation of the phenotypic expression with changes in transcriptome at the single-cell level, proteomics evaluation of cytokine secretion at the single-cell level and correlation of response with N-glycan profiling, quantitative site-occupancy, and direct glycopeptide analysis. Results: Thirteen patients with RR-AML were enrolled, 12 of whom were evaluable (1 patient came off study before DLT period). Median age was 63 years (45-77), 77% with adverse risk disease, 38% with secondary AML, and received median two (range 2-7) prior lines of therapy. Twelve of 13 patients (92%) were previously treated with venetoclax based regimen and 31% had prior allogeneic HCT. Adverse risk mutations included TP53 (31%), RUNX1 (23%), and ASXL1 (15%). Grade 3 or higher adverse events included anemia (8%), neutropenia (15%), and thrombocytopenia (23%) (Table 1). CRS grades 1-2 were noted in 62% of patients, no grade ≥3 CRS or neurotoxicity (any grade) was seen. There was no dose limiting toxicity (DLT). Of the 12 evaluable total patients, clinically meaningful response was noted in two patients who were MRD positive by flow cytometry prior to study entry and achieved MRD negative CR (Table 2). These two patients who achieved MRD negative CR subsequently proceeded to allogeneic HCT. Median time to response was 1 cycle. Median OS of the cohort was 6.2 months (1.8-NR). Conclusions: XmAb18968 is safe and well tolerated in patients with RR-AML. Dose escalation yielded MRD negative CR in RR-AML patients who were MRD positive at study entry. Details on correlative studies examining mechanisms of therapeutic efficacy and resistance will be reported in the main meeting.

Early Results Indicate Acceptable Safety and Promising Efficacy of Venetoclax in Combination with Pola-R-CHP for Untreated High-Risk BCL-2-Positive B-Cell Lymphoma Including Double/Triple Hit Lymphoma

Background: The Phase II CAVALLI study assessed the B-cell lymphoma 2 (BCL-2) inhibitor venetoclax (Ven; 800mg for 10 days [Ds]) + rituximab (R), cyclophosphamide (C), doxorubicin (H), vincristine (O) and prednisolone (P; R-CHOP), for first line treatment of diffuse large B-cell lymphoma (DLBCL). The end of treatment (EOT) complete response (CR) rate was 64% in patients (pts) with BCL-2 overexpression by immunohistochemistry (BCL-2 IHC+); there was a 2-year progression-free survival (PFS) benefit compared with R-CHOP (GOYA trial; 78% vs 62%); but a higher incidence of Grade (Gr) 3/4 adverse events (AEs; 86% vs 66%, respectively; Morschhauser et al. Blood 2021). In the Phase III POLARIX study, polatuzumab vedotin (Pola)-R-CHP had a prolonged PFS vs R-CHOP, establishing Pola-R-CHP as standard of care for untreated DLBCL (Tilly et al. N Engl J Med 2022; Morschhauser et al. EHA 2022). Thus, we explored whether adding Ven to Pola-R-CHP could further improve outcomes in BCL-2 IHC+ DLBCL. Here, we report early safety and efficacy results from a Phase Ib study (BO42203; NCT04790903), evaluating the optimal dose/schedule of Ven+Pola-R-CHP. Methods: BO42203 is an ongoing open-label, multicenter study of pts with untreated BCL-2 IHC+ DLBCL (including Grade 3b follicular lymphoma). Pts enrolled had an International Prognostic Index (IPI) of 2-5, and BCL-2 IHC+ defined as ≥50% expression (by local pathology). The primary endpoint is to determine the recommended Phase II dose (RP2D) for Ven+Pola R-CHP based on the rate of dose-limiting toxicity (DLT) during the first 2 cycles (42 Ds), with tolerability assessed by dose modifications/delays and discontinuation. Secondary endpoints include percentage of pts with AEs, and PET-based response rates/duration. Pts are enrolled in 5 cohorts (n=10 pts each). Safety data are reviewed by an internal monitoring committee (IMC) who can alter the Ven dose/schedule for the next cohort. Pts receive 6 21-D cycles of treatment. Pola-R-CHP is administered on D1 of each cycle at the following doses: Pola 1.8mg/kg, R 375mg/m 2, C 750mg/m 2, H 50mg/m 2, and P 100mg/D for 5 Ds. All pts in Cohort 1 were assigned to Ven 800mg/D for 5 Ds/cycle; doses start on D4 of Cycle 1 and D1 of subsequent cycles (Schedule A) with optional escalation to 10 Ds/cycle from Cohort 2 onwards (Schedule B), depending on IMC assessment. Results: At the time of analysis (data cutoff: May 2, 2023), 4 cohorts were enrolled (n=40). At baseline, the median age was 64.0 years, 14 (35.0%) pts were female, and 5 (12.5%) had an Eastern Cooperative Oncology Group performance status of 2. Thirty-six (90.0%) pts had Ann Arbor Stage III-IV; 30 (75.0%) had an IPI score of ≥3; and 10 (25.0%) had poor risk cytogenetics (double/triple hit lymphoma [DHL/THL]). Thirty-eight pts have completed the DLT period; 2 pts withdrew prior to this due to meningitis and a COVID-related AE. No DLTs have been observed. Gr ≥3 myelosuppression was observed in Cohort 1 after the DLT period: neutropenia (n=5 pts [50.0%]), neutrophil count decreased (n=2 [20.0%]), and febrile neutropenia (n=1 [10.0%]). Hence, after IMC review of Cohorts 1-3 it was decided that Schedule A will be maintained/received by all future pts, as the benefit-risk of increasing the Ven schedule may not be favorable. Safety and efficacy analyses were performed on Cohorts 1-3 (n=30) as they have reached the EOT. All pts had ≥1 AE; 21 (70.0%) and 11 (36.7%) pts had at least one Gr ≥3 AE ( Table) and serious AE (SAE), respectively; 2 (6.7%) pts died due to treatment-related SAEs (investigator-assessed; sudden cardiac death [related to Ven] and sepsis [related to Ven+Pola-R-CHP]). AEs leading to dose modification/delay of any drug occurred in 11 (36.7%; 23 events) pts; 21 (91.3%) AEs led to Ven modification in 10 pts (33.3%); and 3 (10.0%) pts had an AE that led to discontinuation of any study drug. Response was evaluated in 30 pts, with an EOT PET-CT based objective response rate and CR of 86.7% (n=26; including all pts with DHL/THL [n=8; CR: 100%]); 1 pt had progressive disease [PD], and 3 were not assessed due to death (n=2) and early discontinuation (n=1; Figure). Three (10.0%) pts died due to PD. Conclusions: Ven 800mg/D for 5 Ds/cycle + Pola-R-CHP has been determined as the RP2D; early results show acceptable safety and promising efficacy for untreated BCL-2 IHC+ DLBCL. High CR rates were observed across all cohorts at EOT, including pts with DHL/THL. Updated results, including circulating tumor DNA, will be presented.

A First-in-Human Phase I Study of AT101, a Novel Anti-CD19 Chimeric Antigen Receptor T Cell Product Targeting a Membrane-Proximal Domain of CD19 in Adults with Relapsed or Refractory B Cell Non-Hodgkin Lymphoma

Introduction: Anti-CD19 chimeric antigen receptor T-cell therapies (CART19) are highly efficacious against advanced B cell non-Hodgkin lymphoma (NHL) but the majority of patients (pts) ultimately fail. Several mechanisms contribute to CART19 failure, including CD19-neg escape and CART dysfunction. Notably, all four commercial CART19 products utilize the FMC63 single chain variable fragment (scFv) with high-avidity specificity to a CD19 membrane-distal epitope. Interestingly, loss of the FMC63-recognized epitope due to CD19 mutations ( Zhang Z, JITC, 2020) or epitope-masking (CAR19:CD19) ( Ruella M, Nat Med, 2018) has been described. We hypothesized that a novel anti-CD19 scFv that engages an alternative CD19 membrane-proximal epitope independent of FMC63 with low avidity could: 1. mitigate CD19 epitope loss; but also 2. enhance CART functions ( Fig. 1A) . Methods and results: We developed an autologous, CART19 product with 4-1BB co-stimulation using a novel humanized chicken antibody (h1218) specific to a membrane-proximal epitope of CD19 (amino acids T51,S53, E55,K59 and K63). We previously reported initial preclinical data ( Patel R., ASH, 2021 #2798) that demonstrated h1218-CART19 recognize and kill B-cell leukemia that aberrantly expresses the FMC63-CAR19. More recently, we demonstrated that differently than FMC63-based CART, h1218-CART19 could respond to and kill tumor cells expressing point mutations of CD19 (L174V and R163L). Of note, h1218-CART19 had enhanced control of CD19+ B-cell neoplasms as compared to FMC63-CART19 both in vitro and in vivo. Mechanistically, thanks to the lower avidity and faster on/off rate, h1218-CART19 had decreased T cell exhaustion and activation-induced cell death. Given the promising preclinical results, we tested the clinical h1218-CART19 product (AT101) in a first-in-human, multi-center, phase I/II, dose-escalation clinical trial for pts with histologically confirmed relapsed or refractory B cell NHL (NCT05338931). For the phase I study, pts were treated with a single intravenous infusion of AT101 (day 0) in three dose levels (DL) based on a standard 3+3 design: DL1 (0.2 x 10 6 cells/kg), DL2 (1.0 x 10 6 cells/kg), or DL3 (5.0 x 10 6 cells/kg). All pts received lymphodepletion with intravenous fludarabine (250 mg/m 2) and cyclophosphamide (25 mg/m 2) on days -4, -3, and -2. The primary objective was to determine the maximum tolerated dose (MTD) of AT101. The secondary objectives were to evaluate AT101 pharmacokinetics and preliminary efficacy. At the July 3, 2023 data cut, 12 pts (median age 62.5 years (range 39-84); diffuse large B cell lymphoma (DLBCL, n=7, 58.3%), follicular lymphoma (FL, n=3, 25.0%), mantle cell lymphoma (MCL, n=1, 8.3%), and marginal zone lymphoma (MZL, n=1, 8.3%)) received AT101 ( Fig. 1B). The median follow-up after AT101 was 6.5 months (1.5-13.7 months), the median number of previous lines of treatment 3 (range 1-8); no prior cellular therapies. Five pts (41.7%) had previous autologous stem cell transplantation. Two pts (16.7%) had refractory disease and two pts (16.7%) received bridging therapy. Three pts (2 pts at DL2 and 1 pt at DL3) developed a grade (G) 1 cytokine-release syndrome (CRS) and one pt at DL3 developed a G3 CRS that resolved within 24 hours. Three pts (1 pt at each DL) developed immune-cell-related neurotoxicity syndrome (ICANS), of which one G4 dose-limiting toxicity (DLT) was reported at DL1 that corrected within 6 days. One DL3 pt experienced G3 sepsis that promptly resolved; the same pt ultimately developed fatal neutropenic septic shock outside the DLT period. Four additional patients experienced ≥G3 neutropenia without evidence of infection. Complete response (CR) occurred in 8/12 pts (66.6%) and overall response (CR+partial response) in 83.3% (95%CI, 51.6-97.9) at day 28 post-AT101 infusion ( Fig. 1B). Remarkably, in DL2 and DL3, the CR rate was 100.0%. Of the 8 pts in CR none has relapsed (median follow-up 6.0 months). AT101 cells expanded (peak in DL3 113.6 ± 6.50 x10 4 CAR gene copies/ug DNA) and persisted in patients' blood. Conclusion: In this first-in-human phase I trial, AT101 was tolerable with limited and manageable toxicities. Notable preliminary efficacy was observed at the RP2D with no evidence of disease relapse after achieving a CR. These results warrant the pursuit of the planned phase II expansion cohort.