Glioblastoma response to blood-brain-barrier permeable, MGMT-agnostic therapeutic LP-184 and sensitization by nucleotide-excision repair deficiency.

Abstract

e14023 Background: Glioblastoma (GBM), a WHO Grade IV cancer, is the most common and most aggressive primary malignant brain tumor. Prognosis following best standard-of-care surgical resection, radiation and temozolomide (TMZ) chemotherapy is poor, with median overall survival 15-18 months. TMZ, which acts primarily by methylating DNA at O6-guanine, has marginal efficacy in ̃70% of patients due to tumor expression of O-6-methylguanine-DNA methyltransferase (MGMT) and there is no effective therapy at tumor recurrence. New treatment options are therefore desperately needed for GBM patients. LP-184 is an acylfulvene-derived prodrug that is activated by the oxidoreductase PTGR1 and primarily alkylates adenine at the N3-position. Bioinformatic analysis showed that PTGR1 is elevated in clinical GBM tumor samples compared to normal brain. LP-184 response is influenced by tumor DNA repair status, and acylfulvene-induced damage is mainly repaired by the transcription-coupled nucleotide-excision repair (TC-NER) pathway. Spironolactone, an FDA approved, blood-brain-barrier permeable diuretic, induces degradation of ERCC3 protein, a key TC-NER component. Response of NER-deficient GBM was tested through co-administration of LP-184 and spironolactone. Methods: Cell viability assays with exposure to LP-184, with and without spironolactone, were used to determine IC50 values in vitro. Subcutaneous or intracranial tumor xenograft models were used to determine tumor volume or survival differences between control and LP-184 treated mice. Results: Nanomolar concentrations of LP-184 inhibited in vitro viability of multiple GBM cell models including 4 NCI-60 GBM cell lines (mean IC50= 286 nM), the TMZ-resistant LN-18 cell line (IC50= 46 nM), M1123 GBM neurosphere line (IC50= 151 nM), and a low passage GBM neurosphere isolate (IC50= 306 nM). Co-treatment with spironolactone resulted in a 3-6 fold decrease in LP-184 IC50 values in M1123, Mayo39, and U87 cultures. Pharmacokinetic analyses in SCID mice following a single LP-184 infusion (4 mg/kg, i.v.) showed favorable CNS bioavailability with brain/plasma ratio 0.11 (Cmax= 839 nM) and brain tumor/plasma ratio 0.2 (Cmax= 2.53 µM). LP-184 (4mg/kg i.v., q.o.d X 4) induced complete regression of all pre-established s.c. U87 xenografts (N = 5) and 3 of 6 M1123 s.c. xenografts (mean tumor volumes: 1456 ± 349 mm 3 controls vs 84 ± 39 LP-184, p < 0.001) and statistically significantly prolonged survival of mice bearing pre-established orthotopic U87 and M1123 xenografts (p < 0.0001). Conclusions: These preclinical results establish LP-184 as a promising new agent for future clinical testing in patients with GBM and suggest that LP-184 may be particularly efficacious in patients with intrinsic or spironolactone-induced NER deficient tumors.