Abstract B029: Studies in human bone cell co-cultures reveal a potential mechanism underlying bone fractures in children treated with entrectinib and suggest a positive association with vitamin D

Abstract Introduction: Entrectinib, a NTRK, ROS1 and ALK inhibitor, approved in the US for adult patients with ROS1-positive metastatic non-small cell lung cancer and adult and pediatric patients older than 1 month of age with solid tumors that have a NTRK gene fusion, has been associated with the occurrence of bone fractures, particularly in pediatric patients. These fractures might be caused by an inhibition of signaling pathways relevant for bone development in children. Methods: To investigate the mechanism of the observed effect we used a suite of human bone cells representing both juvenile and adult bone physiology. These models were treated with Entrectinib and its major metabolite M5. Molecular as well as functional readouts were assessed to reveal the pathomechanism of the observed clinical findings. Results: Data showed, that Entrectinib induced a reduction of cellular markers of osteoblastic activity and a reduced formation of mineralized matrix. Conversely, Entrectinib had stimulating effects on osteoclast function indicative of bone resorption. 3D osteoblast-osteoclast cultures revealed decreased stiffness after Entrectinib treatment, confirming the cell signaling data. These findings were particularly pronounced in the absence of 17β-estradiol, characteristic for juvenile bone. Finally, pre-treatment with Vitamin D led to partially restored osteoblast function in vitro, while osteoclast function was suppressed. Conclusions: These experiments support the suspected on-target effect of Entrectinib underlying increased fractures in children with developing bone, offering potential mitigation strategies once these observations have been confirmed with clinical data. Citation Format: Sabrina Ehnert, Kevin A. Schulz, Alison K. Cardenas, Georgina Meneses-Lorente, Adrian Roth, Sabine Fürst-Recktenwald. Studies in human bone cell co-cultures reveal a potential mechanism underlying bone fractures in children treated with entrectinib and suggest a positive association with vitamin D [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pediatric Cancer Research; 2024 Sep 5-8; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl):Abstract nr B029.