P10.24.B SCREENING NON-ONCOLOGICAL DRUGS IN A PATIENT-DERIVED GLIOBLASTOMA MODEL IDENTIFIES PITAVASTATIN WITH POTENTIAL ANTITUMOR ACTIVITY
Authors: Zekanovic S , Achaiber Sing P , Basuki A , Koolen S L W , Ntafoulis I , den Hollander C W J , Chien M P , Li Y , Mustafa D A M , Dirven C M F , Leenstra S , Lamfers M L M 
Published: September 2023

Abstract

BACKGROUND
Glioblastoma (GBM) is a malignancy which is in dire need of novel treatment options. Repurposing non-oncological drugs has become of great interest in GBM research. Non-oncological drugs have many advantages over their oncological counterparts including a well-established safety and toxicity profile, possibilities to perform dose escalation studies, and combinations with oncological drugs (e.g. temozolomide, TMZ). Making use of our patient-derived in vitro model which has been shown to recapitulate GBM in terms of genetic make-up and heterogeneity, we aim at identifying non-oncological drugs that exhibit potent antitumor activity.

MATERIAL AND METHODS
Drug screening was performed using an NIH clinical compound selection consisting of 446 non-oncological drugs on 2 patient-derived GBM cell lines. Viability 5 days post treatment was assessed using the ATP-based Cell Titer Glo assay. Validation studies were performed on a panel of 25 GBM cultures. Nanostring analysis using the Pan Cancer gene panel, flow cytometry, Western Blotting and immunofluorescence were employed to gain insight into drug mechanism of action. The zero-interaction potential method was used to quantify synergy with TMZ. Dose-modifying factors (DMF) were calculated to quantify synergy with irradiation.

RESULTS
Screening of 446 non-oncological drugs yielded a top 10 list of candidates which were evaluated on an additional cell panel. Based on safety and efficacy, pitavastatin, an HMG-CoA reductase inhibitor, was selected for further analysis. Compared to 8 other registered statins, pitavastatin revealed the most potent anti-tumor activity, with IC50 values in the low micromolar range. Pitavastatin efficacy was validated in a panel of 25 GBM cultures derived from various GBM subtypes in terms of primary/recurrence, MGMT and IDH status (IC50 ranging from 0.1 - 5.0 µM). GBM cultures derived from patients using statins for cholesterol management did not reveal resistance to pitavastatin. Combination treatment of pitavastatin with either TMZ or irradiation showed synergy with TMZ in 5/8 cultures and radiosensitizing effects in 3/5 cultures (DMF &gt;2.0). Importantly, no antagonism was observed with TMZ or irradiation. Mechanistic studies demonstrated that pitavastatin treatment led to induction of autophagy, perturbations in GBM cell cycle and attenuation of GSC stemness through downregulation of SOX2 and CD133.

CONCLUSION
Drug screening on patient derived GBM cultures identified pitavastatin as a potent inhibitor of GBM cell viability and revealed its chemo- and radiosensitizing effects. Mechanistic studies suggest that its antitumor effects could be a consequence of autophagy induction, cell cycle arrest and loss of GBM cell stemness. Currently we are exploring strategies to ensure optimal intratumoral delivery in vivo.