Promising clinical benefit rates in advanced cancers alongside potential biomarker correlation in a phase I/II trial investigating bexmarilimab, a novel macrophage-guided immunotherapy

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Background: Clever-1 is an immunosuppressive scavenger receptor expressed on tumor associated macrophages. High levels of Clever-1 are associated with poor survival and immunotherapy resistance. Bexmarilimab (FP-1305) is a novel humanized anti-CLEVER-1 IgG4-antibody capable of inducing a phenotypic M2 to M1 immune switch of tumor-associated macrophages. Methods: MATINS (Macrophage Antibody To INhibit immune Suppression) trial is a first-in-human phase I/II study (NCT03733990) to assess safety and preliminary efficacy of Bexmarilimab in patients with refractory advanced solid tumours. Part I has been completed with initial good safety profile of the IMP, preliminary signs of efficiency, and recommended dose of 1mg/kg Q3W for part II (ESMO 2020). In Part II (ESMO 2021), 10 distinct solid tumour types were enrolled to assess preliminary efficacy (overall survival (OS), progression free survival (PFS), and clinical benefit rate (CBR). Clever-1 IHC in pre-treatment biopsies with Ventana platform using a primary antibody 4G9 (Santa Cruz) was scored by % of positive cells compared to the viable tumor cells. Results: At the Jan 2022, a total of 193 patients have been enrolled to the study. In the completed cohorts, 138 patients have received 1-21 doses (median 3) of Bexmarilimab Q3W. Bexmarilimab was well tolerated, and no new safety signals were detected. Part I and Part II fully enrolled 11 cancer cohorts, the median PFS was 2.0 months (95% CI 1.9 – 2.0) and the median OS was 5.2 months (95% CI 4.3 – 6.4). CBR for Part II was 17.3% (19/110) at cycle 4 of treatment (by RECIST v.1.1). Notably, 30-40% CBR at cycle 4 was seen in cutaneous melanoma (30%), gastric cancer (30%), cholangiocarcinoma (30%), hepatocellular cancer (40%), and ER+ breast cancer (40%). Six-month survival rates (landmark analysis) were 70.1% for CBR compared to 34.7% for non-CBR patients, with a similar duration of prior therapy in both groups. Preliminary biomarker analysis (n = 77) demonstrated positive trend (p = 0.038) between CBR and higher intratumoral Clever-1 positivity (median of 15% positivity (range 0-25) in CBR and 3% (range 0-85) in non-CBR patients) Conclusions: Bexmarilimab continues to demonstrate promising anti-tumour activity as a monotherapy in several refractory solid tumours. Furthermore, preliminary biomarker analysis suggests a possibility for patient selection based on tumour Clever-1 expression. Further expansion of the study will investigate optimal dosing and biomarkers of efficacy. Clinical trial information: NCT03733990.

Pharmacodynamic effects in blood and tumor tissue of eftozanermin alfa, a tumor necrosis factor-related apoptosis-inducing ligand receptor agonist

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Background: Eftozanermin alfa (eftoza; formerly known as ABBV-621), a 2nd-generation tumor necrosis factor-related apoptosis-inducing ligand receptor agonist, is being evaluated in previously treated solid and hematologic malignancies (NCT03082209). In a dose-expansion cohort, patients (pts) with KRAS-mutant colorectal cancer (n = 24) and pancreatic cancer (n = 24) were evaluated at 3 dose levels with 12 mandatory paired biopsies per tumor type (pretreatment [Tx] and on-Tx collection). Following eftoza dosing, RNA and protein expression including posttranslational modifications were assessed in tumor biopsies to understand the target engagement and downstream pathway activation. Plasma was evaluated for changes in somatic mutant allele frequency and M30, M65 (circulating apoptotic markers). Methods: Biopsies were collected anytime during the screening period (pre-Tx) and 24±4 h following 2nd or 3rd infusion (on-Tx). Of the requested 4–6 fresh biopsy cores, 1–2 cores were collected as formalin fixed paraffin embedded (FFPE) and the rest were frozen tissue. FFPE tissue was analyzed by multiplex immunohistochemistry (IHC) and RNAseq; reverse phase protein array was used for frozen cores. Plasma was collected at cycle 1 predose and 2, 8, 24, 48, and 168 h postdose and analyzed for M30, M65 (by ELISA) and circulating tumor DNA (64-gene PlasmaSELECT assay). Results: Twenty-five pts consented to biopsies; paired biopsies were obtained from 16 pts at a 64% success rate: FFPE (n = 15) and frozen cores (n = 12). Tumor cells were detected in 11/15 (73%) FFPE and 4/12 (33%) frozen cores. Increase in M30, activated caspases, and cleaved PARP levels was observed in on-Tx biopsy samples compared with pre-Tx, thus serving as evidence for apoptosis induction in tumors following eftoza dosing. Changes in the tumor microenvironment were observed post-Tx by RNAseq and multiplex IHC (eg, CD68 level). Downregulation of prosurvival signaling pathways (eg, AKT/MEK) was also observed following eftoza dosing. Thirteen out of 16 pts showed transient increase in mutant allele fractions post eftoza Tx that correlated with increased plasma circulating tumor markers M30 and M65 at similar time points, suggesting activation of apoptosis pathway. Increase in M30, M65 levels also preceded increase in liver enzymes (ALT/AST) at 2, 48 hr post-Tx. Conclusions: Pharmacodynamic effect of eftoza was successfully demonstrated in blood and tumor tissue, including induction of apoptosis and modulation of PI3K and MEK signaling pathways. Clinical trial information: NCT03082209.

Immune activation in first-in-human anti-macrophage antibody (anti-Clever-1 mAb; FP-1305) phase I/II MATINS trial: Part I dose-escalation, safety, and efficacy results

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Background: The scavenger receptor CLEVER-1 mediates the clearance of “unwanted” self-components and is highly expressed on tumor associated macrophages (TAMs). CLEVER-1 expression is associated with immunotherapy resistance and poor survival in several cancers. Pre-clinical studies demonstrate that CLEVER-1 inhibition increases TAM pro-inflammatory cytokine secretion and antigen presentation reactivating CD8 T cell responses with robust anti-tumor activity. Targeting CLEVER-1 could therefore overcome the immunosuppressive tumor microenvironment and has led to the development of FP-1305, a humanized anti-CLEVER-1 IgG4-antibody. Methods: The MATINS (Macrophage Antibody To INhibit immune Suppression) trial is a multicenter first-in-human phase I/II study (NCT03733990) to assess the tolerability, safety and preliminary efficacy of FP-1305 in patients (pts) with advanced cancers including immunotherapy-refractory melanoma, cholangiocarcinoma, hepatocellular carcinoma, ovarian cancer, colorectal (CRC), and pancreatic ductal adenocarcinoma. Part 1 consisted of a dose escalation phase; 30 pts (median age 65, range 30-81) were enrolled to examine 5 dose levels (0.1, 0.3, 1.0, 3.0, 10 mg/kg), to determine the optimal dose of FP-1305 for Parts 2 and 3. Two-stage time-to-event continual reassessment method (TITE-CRM) was utilized for the dose escalation in Part 1. Pts received 1-8 cycles (median 3) of FP-1305 Q3w. FP-1305 was well tolerated without dose-limiting toxicities. A consistent increase in blood NK cells, CD8/CD4 T cell ratio, B cells and a decrease in regulatory T cells was demonstrated. FP-1305 dosing led to the activation (CD25+) and Th1 skewing (CXCR3+) of T cell populations including increase in effector CD8 T-cells with downregulation of several inhibitory immune checkpoint molecules (PD-1, PD-L1, CTLA-4, and LAG3). Increased circulating IFNɣ levels were detected, with the highest levels in a heavily pretreated metastatic, microsatellite stable (MSS) colorectal cancer patient leading to a partial tumor response (-52%). FP-1305 is the first macrophage checkpoint inhibitor candidate promoting immune switch with promising tolerability and clinical anti-tumor activity. FP-1305 represents a novel treatment option to provoke immune response especially in non-inflamed tumors. Full safety, pharmacokinetic and efficacy results of MATINS trial (Part 1) will be presented for the first time in a final late breaking abstract. Clinical trial information: 2018-002732-24 .