Combinatorial treatment of glioblastoma with temozolomide (TMZ) plus 5-ethynyl-2'-deoxyuridine (EdU)

Background: Glioblastoma (GBM) remains highly lethal despite surgery, radiotherapy, and temozolomide (TMZ). We identified a therapeutic role for 5-ethynyl-2′-deoxyuridine (EdU), a thymidine analog whose incorporation is recognized and excised by nucleotide excision repair (NER). We hypothesized that combining TMZ (lesions processed by mismatch repair and base excision repair) with EdU (NER-triggered) would overload complementary DNA repair pathways and improve efficacy. Methods: We tested TMZ+EdU across GBM cell lines (U87, GBM8), orthotopic mouse models (U87, GBM8), and living, passage-zero GBM patient tumor tissues on organotypic brain slice culture (OBSC). Viability was quantified by bioluminescence imaging; synergy via CompuSyn (cells) and ZIP scores (patient tissues). Short-course EdU dosing followed by histology assessed targeted localization of EdU to tumor cells. Results: In vitro, TMZ+EdU produced strong synergy in U87 and GBM8 across TMZ doses. In mice bearing U87 orthotopic xenografts, median survivals, reported in days (d), were 29 d (PBS), 37 d with 200 mg/kg EdU (+~30% vs PBS, p<0.001), 43 d with 5 mg/kg TMZ (+~50% vs PBS, p<0.001), and 67 d with 5 mg/kg TMZ + 200 mg/kg EdU (+~131% vs PBS, p<0.001). Notably, the combination yielded a +~60-80% improvement over monotherapies (p<0.001). Approximately 13% of combination-treated mice survived to the study endpoint with no detectable tumor. In mice bearing orthotopic GBM8 xenografts, median survivals were 46 d (PBS), 51 d with 1 mg/kg TMZ (+~11% vs PBS, p=0.004), 135 d with 5 mg/kg TMZ (+~193% vs PBS, p<0.001), and 167.5 d with 200 mg/kg EdU (+~264% vs PBS, p=0.001). Median survival was not reached for either TMZ+EdU regimen (1 mg/kg TMZ + 200 mg/kg EdU or 5 mg/kg TMZ + 200 mg/kg EdU); all animals were alive with no detectable tumor at Day 170, significantly outperforming each monotherapy. Short-course dosing followed by histology in U87-bearing mice showed marked tumor-cell selectivity of EdU (~70-83-fold in tumor cells vs adjacent non-tumor cells). In living, passage-zero GBM patient tumor tissues on OBSC, TMZ+EdU was synergistic in 1/4 tumors (ZIP 14) and additive in the remainder (ZIP 2-3). Conclusions: TMZ and EdU act through distinct DNA repair pathways to deliver synergistic antitumor activity across GBM cell lines, mouse models of GBM, and living, passage-zero GBM patient tumor tissues. Given EdU's brain penetration, the survival benefit observed preclinically, and the demonstration of synergy in a subset of GBM patient tumor tissues, TMZ+EdU represents a compelling strategy for translational development in GBM.