Wainberg, Zev A.

Abstract MT-5111 is a 55kD engineered toxin body targeting HER2 in solid tumors that binds to an epitope distinct from trastuzumab and pertuzumab, offering potential combination strategies with other HER2-targeting agents. MT-5111 works by internalizing, self-routing through intracellular compartments to the cytosol, and inducing potent cell-kill via the enzymatic and permanent inactivation of ribosomes. This is a phase 1 study in adults with advanced HER2+ solid tumors. MT-5111 is dosed weekly IV over 30 min in every 21-day cycle until disease progression, unacceptable toxicity, death, or withdrawn consent. The study has dose escalation (Part A) cohorts enrolling patients (pts) with any HER2+ cancer (CA) and expansion (Part B) cohorts for HER2+ breast cancer (BC), Gastric or Gastroesophageal junction adenocarcinoma (GEA), or other HER2+ solid CA. As of 30 June 2022, 42 total pts had enrolled (36 in Part A on 0.5-23 µg/kg/dose, 6 pts with BC in Part B1 on 10 µg/kg/dose). Median age 65 years, 28 (66.78%) pts were female, median of 4 prior systemic and 2 prior HER2-targeting treatment (tx). 17 pts with BC, 6 with biliary CA, 9 with GEA, and 10 with other solid CA have enrolled. Of the 17 BC pts, 15 received ≥ 10 µg/kg/dose. Tx emergent adverse events (TEAEs) have been reported in 40 (95%) pts, and tx-related AEs (TRAE) occurred in 23 (55%) pts. No pt experienced G4-G5 TRAE. G1 troponin elevations were noted in 5 pts without clinical signs of cardiotoxicity (1 pt 6.75 µg/kg, 2 pts 10 µg/kg, 1 pt 17 µg/kg, 1 pt 23 µg/kg). Reversible G1/G2 infusion-related reactions were reported in 2 pts. Tx-related G1-G3 rash was observed in 5 pts (4 pts ≥ 10 µg/kg/dose); maculopapular in 2 pts, acneiform in 1 pt and associated with pruritus in 3 pts. The G3 rash developed one wk after first dose of 23 µg/kg, was declared a DLT, improved with systemic steroid therapy and the pt continued tx at the same dose without recurrence. Best overall response per RECIST thus far is stable disease (SD) in 17 pts, non-CR/non-PD in 1 pt, and progressive disease (PD) in 14 pts. 1 pt had non-CR/non-PD for 30 wks (1 μg/kg, BC); 1 pt had SD for 24wks (10 μg/kg, pancreatic); 1 pt is on tx with SD through 8 cycles (10 μg/kg, BC). Of the 10 BC pts who received ≥ 10 μg/kg/dose, the best response was 5 SD. The mean serum concentration of MT-5111 has increased in a dose-proportional manner starting at 6.75µg/kg/dose (Table 1). The soluble HER2 (sHER2) levels at end of tx were higher compared to baseline in cohorts that received ≤ 4.5µg/kg/dose, but similar or lower in cohorts that received ≥ 6.75µg/kg/dose. Higher MT-5111 doses have been well tolerated and may saturate circulating sHER2, leading to more predictable serum concentrations and tumor penetration. The Cmax in humans at doses ≥6.75 µg/kg/dose is above the in vitro IC50 for high HER2+ cell lines (0.029nM) and at 17 µg/kg/dose, above the IC50 for moderate HER2+ cells (1.6nM). In conclusion, the dose proportionate increase in serum concentration with levels above the in vitro IC50 and the leveling off/reduction of sHER2 indicate exposure to MT-5111 is at clinically therapeutic levels. Skin toxicity at higher doses may indicate on-target effect as observed in other EGFR-targeted therapies where it is associated with clinical response and a better prognosis. sHER2 biomarker data is expected for all cohorts with PK correlation and 23µg/kg safety and efficacy data. PK profile of MT-5111, C1D1 values Citation Format: Meena Okera, Brian A. Van Tine, Joleen M. Hubbard, Minal Barve, Erika Hamilton, Monica M. Mita, Frances Valdes-Albini, Daniel Ahn, Admasu Mamuye, Joshua Pelham, Amy Yuet, Diana Yurewicz, Yanning Liu, Andres Machado Sandri, William J. Edenfield, Aki Morikawa, William Gradishar, Rajiv Kumar, Zev A. Wainberg. A phase 1 study of the novel immunotoxin MT-5111 in patients with HER2+ tumors: interim results [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT2-11-01.

LBA661 Background: Liposomal irinotecan administered with 5-fluorouracil/leucovorin (5-FU/LV) is approved in the USA and Europe for mPDAC following progression with gemcitabine-based therapy. A phase 1/2 study (Wainberg et al. Eur J Cancer 2021;151:14–24; NCT02551991) demonstrated promising anti-tumor activity in patients with mPDAC who received first-line liposomal irinotecan 50 mg/m2 + 5-FU 2400 mg/m2 + LV 400 mg/m2 + oxaliplatin 60 mg/m2 (NALIRIFOX). Herein, we present results from NAPOLI-3 (NCT04083235), a randomized, open-label, phase 3 study investigating the efficacy and safety of NALIRIFOX compared with nab-paclitaxel + gemcitabine as first-line therapy in patients with mPDAC. Methods: Eligible patients with histopathologically/cytologically confirmed untreated metastatic PDAC were randomized (1:1) to receive NALIRIFOX on days 1 and 15 of a 28-day cycle or nab-paclitaxel 125 mg/m2 + gemcitabine 1000 mg/m2 (Gem+NabP) on days 1, 8 and 15 of a 28-day cycle. Randomization was stratified by ECOG performance status, geographic region and presence or absence of liver metastases. The primary endpoint was overall survival (OS); secondary endpoints were progression-free survival (PFS), overall response rate (ORR) and safety. OS was evaluated when ≥ 543 events were observed using a stratified log-rank test with an overall 1-sided significance level of 0.025. Results: Overall, 770 patients (NALIRIFOX, n = 383; Gem+NabP, n = 387) were included. Baseline characteristics were well balanced between arms. At a median follow-up of 16.1 months, 544 events had occurred. The median OS was 11.1 months in the NALIFIROX arm as compared with 9.2 months in the Gem+NabP arm (HR 0.84 [95% CI 0.71–0.99]; p = 0.04); PFS was also significantly improved (7.4 months vs 5.6 months; HR 0.70 [0.59–0.84]; p = 0.0001). Grade 3/4 treatment-emergent adverse events (TEAEs) with ≥ 10% frequency in patients receiving NALIRIFOX versus Gem+NabP included diarrhea (20.3% vs 4.5%), nausea (11.9% vs 2.6%), hypokalemia (15.1% vs 4.0%), anemia (10.5% vs 17.4%) and neutropenia (14.1% vs 24.5%). Conclusions: First-line NALIRIFOX demonstrated clinically meaningful and statistically significant improvement in OS and PFS compared with Gem+NabP in treatment-naïve patients with mPDAC. The safety profile of NALIRIFOX was manageable and consistent with the profiles of the treatment components. Funding: Funded by Ipsen. Clinical trial information: NCT04083235 .[Table: see text]

2583 Background: MT-5111 is a 55kD engineered toxin body (ETB) targeting HER2 in solid tumors that binds to an epitope distinct from trastuzumab and pertuzumab, offering potential combination strategies with other HER2-targeting agents. MT-5111 may demonstrate efficacy in patients (pts) resistant to other HER2-targeting agents, as its mechanism of action induces direct cell kill via enzymatic and permanent ribosome destruction. Methods: This is a phase 1 study in adults with advanced HER2+ solid tumors. The dose-escalation portion (Part A) enrolls pts into sequential dose cohorts, followed by Part B expansion cohorts for HER2+ breast cancer (BC), gastroesophageal adenocarcinoma (GEA), and any other HER2+ cancer (CA). MT-5111 is dosed weekly IV over 30 min in each 21-day treatment (tx) cycle until disease progression, unacceptable toxicity, death or withdrawn consent. Results: As of Jan 2022, 27 pts had enrolled in Part A cohorts (0.5 to 10 µg/kg/dose) with completed DLT assessments: 9 (33%) pts were male and 18 (67%) female, median age 67 and a median of 4 prior systemic and 2 prior HER2-targeting tx. Common tissue types were BC (9/30%), biliary CA (6/22%), GEA (4/15%). The following safety data reflect 33 treated pts to date including ongoing 13 µg/kg/dose Part A and 10 µg/kg/dose BC expansion cohorts. No Grade (G) 4/5 tx-emergent adverse events (AEs) or DLTs occurred. Tx-related AEs occurred in 17 (52%) pts, most commonly G1/2 fatigue (8/24%). 3 pts had G1 troponin elevations without clinical signs or symptoms of cardiac distress: 1 at 6.75 µg/kg/dose, 2 at 10 µg/kg/dose. 2 pts (3 and 4.5 µg/kg/dose) had reversible G2 and G1, respectively, infusion-related reactions (IRR)s. A comparison of cytokines from baseline to on-treatment timepoints reveals no evidence of significant changes, even in pts with IRR. Best response per RECIST thus far was stable disease (SD) in 7 pts or non-CR/non-PD in 2 pts: 1 pt had SD for 12 weeks (wks) (4.5 μg/kg, pancreatic CA); 1 pt (1 μg/kg/dose, BC) had non-CR/non-PD for 30 wks; 1 pt (10 μg/kg/dose, GEA) has ongoing SD for 18 wks. AUClast data match PK simulations in non-human primate studies. Cmax at 10 µg/kg/dose is ≥5 times the IC50 values of high HER2 expressing gastric CA and BC cell lines while approaching the IC50 of a moderately HER2 expressing liver CA cell line. Conclusions: MT-5111 is well tolerated to-date with no clinically significant immuno/cardiotoxicity. Dose escalation is ongoing at a dose of 13µg/kg, expected to be required for efficacious exposure. Clinical trial information: NCT04029922.

Abstract Background: Engineered toxin bodies (ETBs) are composed of a de-immunized Shiga-like Toxin A subunit genetically fused to an antibody-like binding domain. ETBs can force receptor internalization, induce potent cell-kill via enzymatic and permanent inactivation of ribosomes, and may not be subject to resistance mechanisms of other therapeutics. MT-5111 is a 55 kD ETB targeting HER2 in solid tumors that binds to an epitope distinct from trastuzumab and pertuzumab, offering potential combination strategies with other HER2-targeting agents. MT-5111 may demonstrate efficacy in patients (pts) resistant to other HER2-targeting agents, as its mechanism of action does not rely on inhibition of kinase signaling or cytoskeletal or DNA damage. Methods: The primary objective is to determine the maximum tolerated dose (MTD) of MT-5111 monotherapy in adult pts with advanced HER2+ solid tumors. Secondary objectives are pharmacokinetics (PK), efficacy, and immunogenicity. Using a modified 3+3 design, the dose-escalation part of the study enrolls pts with HER2+ tumors into 7 cohorts: 0.5, 1, 2, 3, 4.5, 6.75, and 10 µg/kg/dose. Three dose-expansion cohorts will follow for HER2+ breast cancer, gastro-esophageal cancer, and other HER2+ tumors. All pts receive MT-5111 weekly as 30-min IV infusions in each 21-day treatment (tx) cycle (C) until disease progression (PD), unacceptable toxicity, death, or withdrawn consent (NCT04029922). Results: Per data cut in June 2021, 21 pts (mean age 64 years, range 34-78; 38% male) in cohorts 1-6 with breast (n=7), biliary (n=6), gastric (n=3), pancreatic (n=2), lung (n=2), and colon (n=1) cancer were treated (Table 1). Pts had a median of 4 prior lines of systemic therapies (range, 1-8) and 2 prior lines of HER2-targeting treatments (range, 0-6). No Grade (G)4 or 5 tx-emergent (TE) adverse events (AEs) occurred. Tx-related AEs occurred in 11 (52%) pts; the most common was fatigue (n=7, 33%). One pt (4.5 µg/kg) had a possibly (per PI) related G3 serious AE (SAE) of dyspnea and hypoxia, but also lymphangitic carcinomatosis and H. influenzae infection. The other related SAE occurred in a pt (6.75 µg/kg) who had a G1 transient troponin increase without concomitant cardiac symptoms or ECG/ECHO changes. All other related AEs were ≤G2. There were no clinically significant changes in cardiac biomarkers (troponin, ECG, left ventricular ejection fraction) nor were there cases of capillary leak syndrome. Two pts (3 µg/kg and 4.5 µg/kg) had reversible G2 infusion-related reactions. Best response to date has been stable disease. AUClast data matched PK simulations based on non-human primate studies, and Cmax data at 6.75 µg/kg indicated that current in-human exposure was between the IC50 values of high and medium HER2-expressing cell lines (approximately 10-89 ng/mL). Thus, a dose of at least 10 µg/kg may be required to achieve effective exposure. To date, no dose-limiting toxicities have been observed and the 10 µg/kg/dose cohort is now accruing. Conclusions: MT-5111 was well tolerated with no clinically significant immuno- or cardiotoxicity. Dose escalation is ongoing and nearing levels expected to be required for efficacious exposure. Table 1.Metastatic HER2 status and MT-5111 treatment by cohortDose0.5 µg/kg1.0 µg/kg2.0 µg/kg3.0 µg/kg4.5 µg/kg6.75 µg/kgCohort123456Number of patients treated with MT-5111433335Metastatic HER2 2+ by IHC: ALL/BC1/11/11/01/10/04/0Metastatic HER2 3+ by IHC: ALL/BC3/12/02/12/13/01/1BC, breast cancer. Citation Format: Brian A. Van Tine, Monica Mita, Minal A. Barve, Erika P. Hamilton, Andrew J. Brenner, Frances Valdes, Daniel Ahn, Joleen Hubbard, Jason Starr, Angela Georgy, Joshua Pelham, Banmeet S. Anand, Thomas Strack, Andrés Machado Sandri, Zev A. Wainberg. Interim results of a phase 1 study of the novel immunotoxin MT-5111 in patients with HER2+tumors [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-13-45.

297 Background: MT-5111 is a 55 kD engineered toxin body (ETB) targeting HER2 in solid tumors that binds to an epitope distinct from trastuzumab and pertuzumab, offering potential combination strategies with other HER2-targeting agents. MT-5111 may demonstrate efficacy in patients (pts) resistant to other HER2-targeting agents, as its mechanism of action induces direct cell kill via enzymatic and permanent ribosome destruction and does not rely on inhibition of kinase signaling or cytoskeletal or DNA damage. Methods: This is a phase 1 study in adult pts with advanced HER2+ solid tumors. The dose-escalation portion (modified 3+3 design) enrolls pts into sequential cohorts followed by expansion cohorts for HER2+ breast cancer (BC), gastric or gastroesophageal junction adenocarcinoma (GEA), and other HER2+ tumors. MT-5111 is dosed weekly IV over 30 min in each 21-day treatment (tx) cycle until disease progression, unacceptable toxicity, death, or withdrawn consent. Results: As of Sep 2021 (contains preliminary data), 24 pts (mean age 64 yrs) were treated, 13 (54%) of whom had gastrointestinal (GI) tumors (6 biliary, 3 GEA, 2 pancreatic, 2 colo/rectal) (Table). Pts with GI tumors had a median of 3 prior systemic tx and 1 prior HER2-targeting tx. No Grade (G) 4/5 tx-emergent adverse events (AEs) occurred. Tx-related AEs occurred in 13 (54%) pts, most commonly fatigue (n=7, 29%). One pt with biliary cancer and concurrent lymphangitic carcinomatosis and H. influenzae infection (4.5 µg/kg) had a possibly related G3 serious AE (SAE) of dyspnea, which resolved 9 days later. Another related SAE occurred in a pt with GEA (6.75 µg/kg) who had a G1 transient troponin increase that resolved during hospitalization, with no clinical symptoms or ECG/ECHO changes; the pt withdrew from study before further dosing. All other related AEs were ≤G2. No other clinically significant changes in cardiac biomarkers (troponin, ECG, LVEF) or cases of capillary leak syndrome occurred. Two pts (3 and 4.5 µg/kg) had reversible G2 infusion-related reactions. Best response to date has been stable disease. AUClast data matched PK simulations based on non-human primate studies. Cmax data at 10 µg/kg indicate that current in-pt exposure was between IC50 values of high and medium HER2-expressing cell lines (approx 10-89 ng/mL). Thus, at least 10 µg/kg may be required to achieve effective exposure. No dose-limiting toxicities have been observed. The 10 µg/kg cohort is now accruing. Following this cohort, an expansion cohort for pts with BC will open. Conclusions: MT-5111 was well tolerated with no clinically significant immuno/cardiotoxicity. Dose escalation is ongoing and is nearing levels expected to be required for efficacious exposure. Clinical trial information: NCT04029922. [Table: see text]

292 Background: Despite recent approval of anti-PD-1 antibodies as 1L therapy in HER2(-) advanced GEA, benefit remains modest and limited largely to PD-L1(+) patients (pts), primarily those with combined positive scores (CPS) ≥5. Thus novel therapeutic approaches are needed for this pt population. DKN-01 is a targeted anti-DKK1 mAb which has demonstrated improved clinical outcomes in pts with elevated tumoral DKK1 expression, a subset of pts with more aggressive disease and shorter overall survival. Methods: DisTinGuish (NCT04363801) is a Phase 2a single arm 2-part trial; Part A investigated DKN-01 (D) + tislelizumab (TS) + CAPOX as 1L therapy for pts with advanced HER2(-) GEA regardless of DKK1 status; Part B investigated two dosing cohorts of D (300 mg and 600 mg) + TS as 2L therapy for DKK1-high advanced GEA pts. Primary objective was to examine safety and tolerability and secondary objectives evaluated multiple efficacy endpoints including overall response rate (ORR) in a modified intent to treat (mITT) population (>1 dose D). Results: Forty-nine pts enrolled between 01 Sept 2020 and 15 Sept 2021; 25 pts in Part A and 24 pts in Part B (D-300 mg). Key clinicopathologic features and efficacy outcomes are shown in Table. The most common D-related AEs were low grade (G1/2) fatigue, nausea, and diarrhea. Nine pts had D-related ≥G3 toxicities, elevated AST/ALT, elevated alkaline phosphatase, hypophosphatemia, hyponatremia, lymphopenia, neutropenia, diarrhea, vomiting, fatigue all occurring in 1 pt and pulmonary embolism in 2 pts (one G5 event). No new safety signals were observed in Part A or B1. Duration of response (DoR), median PFS and median OS have not been reached for Part A. Last pt enrolled in Part B1 on 15 Sept 2021. Conclusions: The combination of D/TS + CAPOX represents a well-tolerated, active 1L combination, particularly for DKK1-high patients consistent with the proposed mechanism of action. Activity appears to be independent of PD-L1 status. Part B1 is aligned with biomarker enrichment and efficacy and biomarker data will be presented along with updated Part A efficacy data. Clinical trial information: NCT04363801. [Table: see text]

AbstractLiposomal irinotecan is a liposomal formulation of irinotecan, which prolongs circulation of irinotecan and its active metabolite SN‐38. A population pharmacokinetic (PK) model was developed based on data from seven studies (N = 440). Adequacy of the model was assessed using multiple methods, including visual predictive check. Associations between PK exposure and the incidence of diarrhea (grade ≥3) and neutropenia adverse events (AEs) (grade ≥3) at first event in patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) were investigated using logistic regression based on data from two studies (the phase III NAPOLI‐1 [N = 260] and phase I/II NCT02551991 [N = 56] trials). The PKs of total irinotecan was described by a two‐compartment model with first‐order elimination, with SN‐38 formed directly by a first‐order constant from the central compartment of irinotecan or after using a transit compartment. Clearance was 17.9 L/week (0.107 L/h) and 19,800 L/week (118 L/h) for total irinotecan and SN‐38, respectively. The UGT1A1*28 7/7 homozygous genotype had no significant impact on SN‐38 clearance. Model evaluation was satisfactory for both irinotecan and SN‐38. The incidence of diarrhea (grade ≥3) at first event was significantly higher with increasing average concentrations of total irinotecan and SN‐38; there was no significant association between an increased risk of neutropenia AEs (grade ≥3) at first event and average SN‐38 concentrations. In summary, the PKs of total irinotecan and SN‐38 after administration of liposomal irinotecan were well‐described by the model. The UGT1A1*28 status had no significant impact on the PKs of liposomal irinotecan.

Abstract Background: Engineered toxin bodies (ETBs), composed of an engineered Shiga-like Toxin A subunit genetically fused to an antibody-binding domain, can force receptor internalization, induce potent cell-kill via enzymatic and permanent inactivation of ribosomes, and may not be subject to resistance mechanisms of other targeted agents. MT-5111, a de-immunized 55 kD ETB targeting HER2 in solid tumors, also binds to an epitope distinct from trastuzumab and pertuzumab, which may permit combination strategies with other HER2 targeting agents. Methods: The primary objective is to determine maximum tolerated dose (MTD) of MT-5111 monotherapy in adult patients (pts) with advanced HER2+ solid tumors. Secondary objectives are PK, efficacy, and immunogenicity. Using a modified 3+3 design, the dose-escalation part of the study includes the following 7 cohorts: 0.5, 1, 2, 3, 4.5, 6.75, and 10 µg/kg. Three dose-expansion cohorts will follow for HER2+ breast cancer, gastro-esophageal cancer, and any other HER2+ tumors. All pts will receive MT-5111 weekly as a 30-min IV infusion in each 21-d treatment (tx) cycle (C) until disease progression (PD), unacceptable toxicity, death, or withdrawn consent (NCT04029922). Results: As of the data cut in December 2020, 16 pts were treated; cancer types included breast (n=6), gastric (n=1), colon (n=1), gallbladder (n=5), and other solid tumors (n=3). Mean age was 64 years (range, 34-78); 37.5% were male. Pts received a median of 4 prior lines of systemic therapies (range, 1-8). No G4 or G5 TEAEs occurred. Six pts had 11 G3 TEAEs; the most common were increased AST and dyspnea (both n=2). Three pts had tx-emergent serious adverse events (abdominal distension [n=1]; dyspnea [n=2]). Tx-related TEAEs occurred in 8 (50%) pts; the most common was fatigue (n=5, 31.3%) and all were ≤ grade 2 in nature, except for one grade 3 event of dyspnea. No cardiac TEAEs, clinically significant changes in cardiac biomarkers (troponin, electrocardiogram, left ventricular ejection fraction), or cases of capillary leak syndrome were observed. Fifteen pts discontinued with PD; 1 pt in cohort 5 (4.5 µg/kg) is on tx with stable disease. To date, no DLTs have been observed and the MTD has not been reached. One pt in cohort 2 (1 µg/kg) had resolution of all hepatic lesions (sub-centimeter lesions pre-tx) at the end of C8; however, the pt came off study due to clinical progression at the end of C10. PK data for the first 5 cohorts matched simulations based on non-human primate studies. Conclusions: MT-5111 was well tolerated with no clinically significant cardiotoxicity. Continued dose escalations are ongoing. Citation Format: Zev A. Wainberg, Monica M. Mita, Minal A. Barve, Erika P. Hamilton, Andrew J. Brenner, Frances Valdes, Daniel Ahn, Joleen Hubbard, Jason Starr, Christine Burnett, Joshua Pelham, Eric T. Williams, Banmeet S. Anand, Thomas Strack, Andrés Machado Sandri, Brian A. Van Tine. Phase 1 study of the novel immunotoxin MT-5111 in patients with HER-2+tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT130.