Bintrafusp Alfa: A Bifunctional Fusion Protein Targeting PD-L1 and TGF-β, in Patients with Pretreated Colorectal Cancer: Results from a Phase I Trial

Colorectal cancer (CRC) is a heterogeneous and complex disease with limited treatment options. Targeting transforming growth factor β (TGF-β) and programmed death ligand 1 pathways may enhance antitumor efficacy. Bintrafusp alfa is a first-in-class bifunctional fusion protein composed of the extracellular domain of TGF-β receptor II (a TGF-β "trap") fused to a human IgG1 monoclonal antibody blocking programmed cell death ligand 1. We report results from an expansion cohort of a phase I study (NCT02517398) in patients with heavily pretreated advanced CRC treated with bintrafusp alfa. As of May 15, 2020, 32 patients with advanced CRC had received bintrafusp alfa for a median duration of 7.1 weeks. The objective response rate was 3.1% and the disease control rate was 6.3% (1 partial response, 1 stable disease); 2 patients were not evaluable. The safety profile was consistent with previously reported data.

Identification of HMGA2 as a predictive biomarker of response to bintrafusp alfa in a phase 1 trial in patients with advanced triple-negative breast cancer

Background

We report the clinical activity, safety, and identification of a predictive biomarker for bintrafusp alfa, a first-in-class bifunctional fusion protein composed of the extracellular domain of TGFβRII (a TGF-β "trap") fused to a human IgG1 mAb blocking PD-L1, in patients with advanced triple-negative breast cancer (TNBC).

Methods

In this expansion cohort of a global phase 1 study, patients with pretreated, advanced TNBC received bintrafusp alfa 1200 mg every 2 weeks intravenously until disease progression, unacceptable toxicity, or withdrawal. The primary objective was confirmed best overall response by RECIST 1.1 assessed per independent review committee (IRC).

Results

As of May 15, 2020, a total of 33 patients had received bintrafusp alfa, for a median of 6.0 (range, 2.0-48.1) weeks. The objective response rate was 9.1% (95% CI, 1.9%-24.3%) by IRC and investigator assessment. The median progression-free survival per IRC was 1.3 (95% CI, 1.2-1.4) months, and median overall survival was 7.7 (95% CI, 2.1-10.9) months. Twenty-five patients (75.8%) experienced treatment-related adverse events (TRAEs). Grade 3 TRAEs occurred in 5 patients (15.2%); no patients had a grade 4 TRAE. There was 1 treatment-related death (dyspnea, hemolysis, and thrombocytopenia in a patient with extensive disease at trial entry). Responses occurred independently of PD-L1 expression, and tumor RNAseq data identified HMGA2 as a potential biomarker of response.

Conclusions

Bintrafusp alfa showed clinical activity and manageable safety in patients with heavily pretreated advanced TNBC. HMGA2 was identified as a potential predictive biomarker of response.

ClinicalTrialsgov identifier

NCT02517398.

Analysis of the tumor microenvironment and anti-tumor efficacy of subcutaneous vs systemic delivery of the bifunctional agent bintrafusp alfa

Most monoclonal antibodies (MAbs), including immune checkpoint inhibitor MAbs, are delivered intravenously (i.v.) to patients. Recent clinical studies have demonstrated that some anti-PD1 MAbs may also be delivered subcutaneously (s.c.), with clinical outcomes similar of those obtained with i.v.-delivered agents. Bintrafusp alfa, a first-in-class bifunctional fusion protein composed of the extracellular domain of the human transforming growth factor β receptor II (TGF-βRII or TGF-β “trap”) fused to the heavy chain of an IgG1 antibody blocking programmed death ligand 1 (anti-PDL1), was designed to target two key immunosuppressive pathways in the tumor microenvironment (TME). Bintrafusp alfa is currently being administered i.v. in clinical studies. The studies reported here demonstrate that systemic or s.c. delivery of bintrafusp alfa, each administered at five different doses, induces similar anti-tumor effects in breast and colorectal carcinoma models. An interrogation of the TME for CD8⁺ and CD4⁺ T cells, regulatory T cells (Tregs), monocytic myeloid-derived suppressor cells (M-MDSCs) and granulocytic (G) MDSCs showed similar levels and phenotype of each cell subset when bintrafusp alfa was given systemically or s.c. Subcutaneous administration of bintrafusp alfa also sequestered TGFβ in the periphery at similar levels seen with systemic delivery. To our knowledge, this is the most comprehensive preclinical evaluation of any checkpoint inhibitor MAb given s.c. vs systemically, and the first to demonstrate this phenomenon using a bifunctional agent. These studies provide preclinical rationale to explore s.c. approaches for bintrafusp alfa in the clinic.

Bintrafusp alfa (M7824), a bifunctional fusion protein targeting TGF-β and PD-L1: results from a phase I expansion cohort in patients with recurrent glioblastoma

Background

For patients with recurrent glioblastoma (rGBM), there are few options following treatment failure with radiotherapy plus temozolomide. Bintrafusp alfa is a first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII receptor (a TGF-β “trap”) fused to a human IgG1 antibody blocking PD-L1.

Methods

In this phase I, open-label expansion cohort (NCT02517398), patients with rGBM that progressed after radiotherapy plus temozolomide received bintrafusp alfa 1200 mg Q2W until disease progression, unacceptable toxicity, or trial withdrawal. Response was assessed per RANO criteria. The primary endpoint was disease control rate (DCR); secondary endpoints included safety.

Results

As of August 24, 2018, 35 patients received bintrafusp alfa for a median of 1.8 (range, 0.5–20.7) months. Eight patients (22.9%) experienced disease control as assessed by an independent review committee: 2 had a partial response, 4 had stable disease, and 2 had non-complete response/non-progressive disease. Median progression-free survival (PFS) was 1.4 (95% confidence interval [CI], 1.2–1.6) months; 6- and 12-month PFS rates were 15.1% and 11.3%, respectively. Median overall survival (OS) was 5.3 (95% CI, 2.6–9.4) months; 6- and 12-month OS rates were 44.5% and 30.8%, respectively. The DCR (95% CI) was 66.7% (22.3–95.7%) for patients with IDH-mutant GBM (n = 6) and 13.8% (3.9–31.7%) for patients with IDH–wild-type GBM (n = 29). Disease control was seen regardless of PD-L1 expression. Twenty-five patients (71.4%) experienced treatment-related adverse events (grade ≥3; 17.1% [n = 6]).

Conclusions

The percentage of patients achieving disease control and the manageable safety profile may warrant further investigation of bintrafusp alfa in GBM.

Improving the Odds in Advanced Breast Cancer With Combination Immunotherapy: Stepwise Addition of Vaccine, Immune Checkpoint Inhibitor, Chemotherapy, and HDAC Inhibitor in Advanced Stage Breast Cancer

Breast tumors commonly harbor low mutational burden, low PD-L1 expression, defective antigen processing/presentation, and an immunosuppressive tumor microenvironment (TME). In a malignancy mostly refractory to checkpoint blockade, there is an unmet clinical need for novel combination approaches that increase tumor immune infiltration and tumor control. Preclinical data have guided the development of this clinical trial combining 1) BN-Brachyury (a poxvirus vaccine platform encoding the tumor associated antigen brachyury), 2) bintrafusp alfa (a bifunctional protein composed of the extracellular domain of the TGF-βRII receptor (TGFβ "trap") fused to a human IgG1 anti-PD-L1), 3), entinostat (a class I histone deacetylase inhibitor), and 4) T-DM1 (ado-trastuzumab emtansine, a standard of care antibody-drug conjugate targeting HER2). We hypothesize that this tetratherapy will induce a robust immune response against HER2+ breast cancer with improved response rates through 1) expanding tumor antigen-specific effector T cells, natural killer cells, and immunostimulatory dendritic cells, 2) improving antigen presentation, and 3) decreasing inhibitory cytokines, regulatory T cells, and myeloid-derived suppressor cells. In an orthotopic HER2+ murine breast cancer model, tetratherapy induced high levels of antigen-specific T cell responses, tumor CD8+ T cell/Treg ratio, and augmented the presence of IFNγ- or TNFα-producing CD8+ T cells and IFNγ/TNFα bifunctional CD8+ T cells with increased cytokine production. Similar effects were observed in tumor CD4+ effector T cells. Based on this data, a phase 1b clinical trial evaluating the stepwise addition of BN-Brachyury, bintrafusp alfa, T-DM1 and entinostat in advanced breast cancer was designed. Arm 1 (TNBC) receives BN-Brachyury + bintrafusp alfa. Arm 2 (HER2+) receives T-DM1 + BN-Brachyury + bintrafusp alfa. After safety is established in Arm 2, Arm 3 (HER2+) will receive T-DM1 + BN-Brachyury + bintrafusp alfa + entinostat. Reimaging will occur every 2 cycles (1 cycle = 21 days). Arms 2 and 3 undergo research biopsies at baseline and after 2 cycles to evaluate changes within the TME. Peripheral immune responses will be evaluated. Co-primary objectives are response rate and safety. All arms employ a safety assessment in the initial six patients and a 2-stage Simon design for clinical efficacy (Arm 1 if ≥ three responses of eight then expand to 13 patients; Arms 2 and 3 if ≥ four responses of 14 then expand to 19 patients per arm). Secondary objectives include progression-free survival and changes in tumor infiltrating lymphocytes. Exploratory analyses include changes in peripheral immune cells and cytokines. To our knowledge, the combination of a vaccine, an anti-PD-L1 antibody, entinostat, and T-DM1 has not been previously evaluated in the preclinical or clinical setting. This trial (NCT04296942) is open at the National Cancer Institute (Bethesda, MD).

The Use of a Humanized NSG-β2m-/- Model for Investigation of Immune and Anti-tumor Effects Mediated by the Bifunctional Immunotherapeutic Bintrafusp Alfa

The lack of serial biopsies in patients with a range of carcinomas has been one obstacle in our understanding of the mechanism of action of immuno-oncology agents as well as the elucidation of mechanisms of resistance to these novel therapeutics. While much information can be obtained from studies conducted with syngeneic mouse models, these models have limitations, including that both tumor and immune cells being targeted are murine and that many of the immuno-oncology agents being evaluated are human proteins, and thus multiple administrations are hampered by host xenogeneic responses. Some of these limitations are being overcome by the use of humanized mouse models where human peripheral blood mononuclear cells (PBMC) are engrafted into immunosuppressed mouse strains. Bintrafusp alfa (M7824) is an innovative first-in-class bifunctional fusion protein composed of the extracellular domain of the TGF-βRII to function as a TGF-β "trap" fused to a human IgG1 antibody blocking PD-L1. A phase I clinical trial of bintrafusp alfa showed promising anti-tumor efficacy in heavily pretreated advanced solid tumors, and multiple clinical studies are currently ongoing. There is still much to learn regarding the mechanism of action of bintrafusp alfa, including its effects on both human immune cells in the periphery and in the tumor microenvironment (TME), and any temporal effects upon multiple administrations. By using the NSG-β2m-/- mouse strain humanized with PBMC, we demonstrate here for the first time: (a) the effects of bintrafusp alfa administration on human immune cells in the periphery vs. the TME using three different human xenograft models; (b) temporal effects upon multiple administrations of bintrafusp alfa; (c) phenotypic changes induced in the TME, and (d) variations observed in the use of multiple different PBMC donors. Also discussed are the similarities and differences in the data thus far obtained employing murine syngeneic models, from clinical trials, and in the use of this humanized mouse model. The results described here may guide the future use of this agent or similar immunotherapy agents as monotherapies or in combination therapy studies.

AB052. P-20. Phase 2, open-label study of second-line M7824 treatment in patients with locally advanced or metastatic biliary tract cancer

Background

Transforming growth factor β (TGF-β) signaling promotes tumor immunosuppression; its inhibition in the tumor microenvironment may enhance the response to anti-PD-L1 treatment. M7824 is an innovative first-in-class bifunctional fusion protein composed of 2 extracellular domains of TGF-βRII (a TGF-β “trap”) fused to a human IgG1 mAb against PD-L1. Building upon encouraging efficacy observed in a phase 1 study, the present study will evaluate M7824 clinical benefit in patients with pretreated biliary tract cancer (BTC).

Methods

This multicenter, international trial is evaluating M7824 monotherapy in patients with locally advanced or metastatic (LA/M) BTC unselected for tumor PD-L1 expression who had disease progression after or were intolerant to first-line platinum-based therapy. Eligible patients must have histologically or cytologically confirmed LA/M intrahepatic cholangiocarcinoma (CCA), extrahepatic CCA, or gallbladder cancer. Patients must not have received prior immunotherapy, therapy with checkpoint inhibitors, or anti-TGF-β therapy. Patients will receive M7824 1,200 mg every 2 weeks intravenously up to 24 months or until confirmed disease progression, unacceptable toxicity, or trial withdrawal. The primary endpoint is confirmed objective response; key secondary endpoints include duration of response, progression-free survival, overall survival, and safety.

Results

This is a trial in progress; results are pending.

Conclusions

BTCs are a group of cancers with poor prognosis and few treatment options. For second-line therapy, no standard of care exists, and overall response rates (ORRs) with chemotherapy are <10%. M7824 has demonstrated promising preclinical activity as well as antitumor activity and a manageable safety profile in two phase 1 studies. In an expansion cohort of study NCT02699515 of 30 patients with pretreated advanced BTC, M7824 monotherapy demonstrated a 23.3% confirmed ORR by investigator assessment, with durable responses. The present study is, therefore, supported by preclinical and clinical evidence and will provide further insight of M7824 in BTC. Previously presented at the 2019 Cholangiocarcinoma Foundation Conference, Borad et al . Reused with permission.