Preclinical Combination Studies of an FGFR2 Targeted Thorium-227 Conjugate and the ATR Inhibitor BAY 1895344

Abstract

We report the preclinical evaluation of a combination treatment comprising a fibroblast growth factor receptor 2-targeted thorium-227 conjugate and an ATR kinase inhibitor. In vitro we observed increased potency, elevated levels of gH2AX, and inhibition of fibroblast growth factor receptor 2 etargeted thorium-227 conjugate mediated cell cycle arrest as a result of the combination. In vivo efficacy Purpose: Fibroblast growth factor receptor 2 (FGFR2) has been previously reported to be overexpressed in several types of cancer, whereas the expression in normal tissue is considered to be moderate to low. Thus, FGFR2 is regarded as an attractive tumor antigen for targeted alpha therapy. This study reports the evaluation of an FGFR2-targeted thorium-227 conjugate (FGFR2-TTC, BAY 2304058) comprising an anti-FGFR2 antibody, a chelator moiety covalently conjugated to the antibody, and the alpha particle eemitting radionuclide thorium-227. FGFR2-TTC was assessed as a monotherapy and in combination with the DNA damage response inhibitor ATRi BAY 1895344. Methods and Materials: The in vitro cytotoxicity and mechanism of action were evaluated by determining cell viability, the DNA damage response marker gH2A.X, and cell cycle analyses. The in vivo efficacy was determined using human tumor xenograft models in nude mice. Results:In vitro mechanistic assays demonstrated upregulation of gH2A.X and induction of cell cycle arrest in several FGFR2-expressing cancer cell lines after treatment with FGFR2-TTC. In vivo, FGFR2-TTC significantly inhibited tumor growth at a dose of 500 kBq/kg in the xenograft models NCI-H716,

Advances in Precision Oncology: Targeted Thorium-227 Conjugates As a New Modality in Targeted Alpha Therapy

“…To test this hypothesis, several preclinical studies have been performed where TTCs were combined with DDR inhibitors. [84][85][86] A humanized HER2-targeting IgG1 antibody derived from trastuzumab was conjugated to the 3,2-HOPO chela-tor and subsequently radiolabeled with 227 Th resulting in HER2-TTC. 25 Robust tumor growth inhibition was achieved when HER2-TTC was combined at a subefficacious monotherapy dose of 125 kBq/kg with the poly-ADP ribose polymerase 1/2 (PARP1/2) inhibitor olaparib in the DLD-1 BRCA2 -/xenograft model established from the DLD-1 colorectal cancer cell line with inactivated BRCA2 gene, while no significant tumor inhibition occurred in the xenograft model established from the DLD-1 parental isogenic cell line (Table 2).…”

“…However, the potency of the combination was further enhanced in the DLD-1 BRCA -/model due to DNA DSB repair deficiency FGFR2-TTC ATRi 85 MSLN-TTC FGFR2-TTC demonstrated increased potency in combination with ATRi when both agents were administered at subefficacious doses in mice bearing MFM-223 tumors (TNBC) Respective monotherapies did not show tumor growth inhibition at the same doses MSLN-TTC demonstrated synergistic activity when combined with ATRi at subefficacious doses in mice bearing OVCAR-3 tumors (ovarian cancer) ATRi and olaparib 86 Similarly, MSLN-TTC demonstrated additive activity when combined with olaparib at subefficacious doses in mice bearing OVCAR-3 tumors (ovarian cancer) Respective monotherapies did not show tumor growth inhibition at the same doses ATRi, inhibitor of ataxia telangiectasia and Rad3-related; DSB, double-strand break; FGFR2, fibroblast growth factor receptor 2; HER2, human epidermal growth factor receptor 2; MSLN, mesothelin; TNBC, triple-negative breast cancer; TTC, targeted thorium-227 conjugate. treatment.…”

“…treatment. 85 In vivo, increased antitumor efficacy in the FGFR2-overexpressing human TNBC MFM-223 xenograft model was observed when the combination of FGFR2-TTC and ATRi were administered at subefficacious doses, while the respective monotherapy demonstrated only partial tumor growth inhibition (Table 2). 85 Synergistic activity between MSLN-TTC and inhibitors of ataxia telangiectasia mutated, ATR (BAY 1895344), DNA-dependent protein kinase, and PARP1/2 has been investigated in vitro and in vivo using human ovarian cancer xenograft mouse models.…”

“…85 In vivo, increased antitumor efficacy in the FGFR2-overexpressing human TNBC MFM-223 xenograft model was observed when the combination of FGFR2-TTC and ATRi were administered at subefficacious doses, while the respective monotherapy demonstrated only partial tumor growth inhibition (Table 2). 85 Synergistic activity between MSLN-TTC and inhibitors of ataxia telangiectasia mutated, ATR (BAY 1895344), DNA-dependent protein kinase, and PARP1/2 has been investigated in vitro and in vivo using human ovarian cancer xenograft mouse models. 86 The treatment of mice bearing OVCAR-3 tumors with the combination of MSLN-TTC and either ATRi (BAY 1895344) or PARP1/2 inhibitor olaparib has shown the strongest increase in potency at doses which were nonefficacious when administered as monotherapy ( Table 2).…”

Targeted α-Therapy in Cancer Management: Synopsis of Preclinical and Clinical Studies

“…108 The same group of investigators have also reported on the potential utility of 227 Th conjugates targeting the fibroblast growth factor receptor 2 (FGFR2), which is overexpressed in many cancers, and in acute myeloid leukemia targeting CD33. 109,110 212 Pb…”