Malignant astrocytomas are aggressive glioma tumors characterized by extensive hypoxia-induced, mitochondria-dependent changes such as altered respiration, increased chymotrypsin-like (CT-L) proteasome activity, decreased apoptosis, drug resistance, stemness and increased invasiveness. Mitochondrial Lon Peptidase I (LonP1) overexpression and increased CT-L proteasome inhibitors activity are the biomarkers of aggressive high grade glioma phenotype, poor prognosis and found to be associated with recurrence and poor patient survival, and drugs targeting either LonP1 or the CT-L activity have anti-glioma activity in preclinical models. We here for the first time introduced and evaluated a novel small molecule, BT317, derived from coumarinic compound 4 (CC4) using structure-activity modeling which we found to inhibit both LonP1 and CT-L proteasome activity. Using gain-of-function and loss-of-function genetic models, we discovered that BT317 is more effective than the individual LonP1 or CT-L inhibition in increasing reactive oxygen species (ROS) generation and inducing apoptosis in high-grade astrocytoma lines. In vitro, BT317 had activity as a single agent but, more importantly, enhanced synergy with the standard of care commonly used chemotherapeutic temozolomide (TMZ). In orthotopic xenograft, patient derived glioma models, BT317 was able to cross the blood-brain barrier, to show selective activity at the tumor site and to demonstrate therapeutic efficacy both as a single agent and in combination with TMZ. BT317 defines an emerging class of dual LonP1, and CT-L proteasome inhibitors exhibited promising anti-tumor activity and could be a promising candidate for clinical translation in the space of malignant astrocytoma therapeutics.
Keywords: BT317; CT-L proteasome; Glioblastoma; LonP1; malignant astrocytoma; reactive oxygen species.