(SS#I) Gladiator Project Award (2023 Award Winner): Unique Tissue-based Analysis Following Convection-enhanced Delivery of Topotecan Reveals Individualized Mechanisms of Response and Resistance

Introduction: New approaches are needed to address the limitations in drug delivery and treatment response assessment contributing to the ineffectiveness of glioblastoma (GBM) therapies. In our recently completed phase 1b trial in recurrent GBM patients, topotecan was delivered chronically by convection-enhanced delivery (CED) via an implanted pump. While median survival (12 months) of patients favorably exceeded historical controls, all tumors recurred. The innovative clinical trial design permitted the collection of MRI-localized biopsies before treatment at pump implantation and after treatment at pump removal. Advanced molecular and cellular tissue analyses comparing pretreatment to post-treatment tissue provided a unique opportunity to understand individualized treatment response.

Methods: 5 patients with recurrent GBM underwent subcutaneous implantation of a pump-catheter system which delivered multiple pulses of topotecan into peritumoral brain over 30 days. Multiple MRI-localized biopsies of the tumor and peritumoral regions taken before and after treatment were analyzed with RNA sequencing (RNAseq) and immunohistochemistry analysis.

Results: RNAseq analysis revealed a significant shift from proliferating to quiescent/mesenchymal tumor cells post-treatment. Expression of CD68, a marker of inflammatory microglia and macrophages, was significantly increased in the microenvironment of post-CED biopsies. Post-CED biopsies revealed significant increases in pro-inflammatory transcriptional programs and upregulation of inflammatory cytokines.

Conclusion : While successfully eliminating proliferating glioma cells, prolonged infusion of topotecan via CED results in a significant shift towards a treatment-resistant mesenchymal tumor cell phenotype and a pro-inflammatory local immune response. Follow-up studies have identified drugs that effectively target quiescent/mesenchymal tumor cells and induce immunogenic cell death, offering new strategies to target the topotecan resistant population. This clinical trial design provides an unparalleled view into treatment response and identifies mechanisms of tumor resistance and recurrence to design new individualized therapies with a precision medicine approach.