WITHDRAWN: Dual targeting of mitochondrial Lon peptidase 1 and chymotrypsin-like protease by small molecule BT317, as potential therapeutics in malignant astrocytomas

Abstract

Malignant astrocytomas are aggressive glioma tumors that have poor prognosis and limited treatments available following recurrence. These tumors are characterized by extensive hypoxia-induced, mitochondria-dependent changes such as glycolytic respiration, increased chymotrypsin-like (CT-L) proteasome activity, decreased apoptosis, and increased invasiveness. Mitochondrial Lon Peptidase 1 (LonP1) is an ATP-dependent protease directly upregulated by hypoxia-inducible factor 1 alpha (HIF-1α). Both LonP1 expression and CT-L proteasome activities are increased in gliomas and are associated with a high tumor grade and poor patient survival. Recently, dual LonP1 and CT-L inhibition has been found to exhibit synergy against multiple myeloma cancer lines. We now report that dual LonP1 and CT-L inhibition has synergistic toxicity in IDH mutant astrocytoma when compared to IDH wildtype glioma, due to increased reactive oxygen species (ROS) generation and autophagy. A novel small molecule, BT317, was derived from coumarinic compound 4 (CC4) using structure-activity modeling and was found to inhibit both LonP1 and CT-L proteasome activity and subsequently induce ROS accumulation and autophagy-dependent cell death in high-grade IDH1 mutated astrocytoma lines. In vitro, BT317 also had enhanced synergy with the commonly used chemotherapeutic temozolomide (TMZ), which blocked BT317-induced autophagy. This novel dual inhibitor was selective to the tumor microenvironment and demonstrated therapeutic efficacy both as a single agent and in combination TMZ in IDH mutant astrocytoma models. We show that BT317, a dual LonP1, and CT-L proteasome inhibitor exhibited promising anti-tumor activity and could be a promising candidate for clinical translation in the space of IDH mutant malignant astrocytoma therapeutics.