OS1.6 Tumor Microtubes contribute to resistance against surgical lesions, and chemotherapy in malignant glioma

Abstract

AbstractBackground:The current standard for the treatment of astrocytomas, including glioblastomas, consists of tumor resection, followed by radio- and chemotherapy. As we could recently demonstrate, a dense multicellular tumor network formed by intercellular tumor microtubes (TMs) greatly contributes to radioresistance. The neuronal growth-associated protein 43 (GAP-43) is involved in this mechanism. Here we asked whether similar resistance mechanisms can be found with respect to surgical lesions, and chemotherapy.Methods:Cranial windows were implanted into 8–10 weeks old male NMRI nude mice. Human glioblastoma stem-like cells (GBMSCs; stably transduced with GFP, RFP, YFP, shRNA for GAP-43, control vector, and/or H2B-GFP to label tumor cell nuclei) were stereotactically injected into the mouse’s brain. In established tumors, 100mg/kg temozolomide (TMZ) was applied to mice p.o. for three consecutive days (day 0,1,2). For surgical lesion experiments, a regional injury was set to the brain by a 26 gauge Hamilton syringe.Results:Similar to radiotherapy, GBMSCs that were not part of the TM-connected tumor cell network died in relevant numbers 7 days after chemotherapy, while TM-connected tumor cells survived. The number of TM-connected tumor cells even increased twofold after chemotherapy, which speaks for an adapative resistance mechanism. It is currently under investigation whether knock down of GAP-43 increases overall efficacy of TMZ therapy. After surgical resection, the lesioned area was rapidly re-colonized with TM-extending tumor cells, with a striking increase in tumor cells at the site of lesion that by far extended the tumor cell densitiy in unlesioned tumor areas. Qantification revealed that the tumor cell nuclear density increased to numbers five-fold above values before surfical intervention in this area, evident as early as five days (488.3%; P=0.033; 95% CI, 50.3–726.4), and extending to 14 days (523.9%; P=0.03; 95% CI, 66.7–781.1) after surgical procedure. This apparent,,repair response” gradually diminished with increasing distance to the surgical lesion site. Finally, while dexamethasone did not relevantly change these reponses, GAP-43 knock down reduced them significantly.Conclusion:TMs convey primary and adaptive resistance to TMZ chemotherapy, in accordance to what we have shown before for radiotherapy. They are also involved in a strong repair response at the very site of a surgical lesion. Reducing the ability of gliomas to repair themselves, and to resist genotoxic stress by interfering with TM formation and function appears as a promising avenue to improve treatment efficacies in these callenging diseases.