NEO212, temozolomide conjugated to NEO100, exerts superior therapeutic activity over temozolomide in preclinical chemoradiation models of glioblastoma

Abstract

Purpose The chemotherapeutic standard of care for patients with glioblastoma (GB) is radiation therapy (RT) combined with temozolomide (TMZ). However, during the twenty years since its introduction, this so-called Stupp protocol has revealed major drawbacks, because nearly half of all GBs harbor intrinsic treatment resistance mechanisms. Prime among these are the increased expression of the DNA repair protein O6-guanine-DNA methyltransferase (MGMT) and cellular deficiency in DNA mismatch repair (MMR). Patients with such tumors receive very little, if any, benefit from TMZ. We are developing a novel molecule, NEO212 (TMZ conjugated to NEO100), that harbors potential to overcome these limitations. Methods We used mouse models that were orthotopically implanted with GB cell lines or primary, radioresistant human GB stem cells, representing different treatment resistance mechanisms. Animals received NEO212 (or TMZ for comparison) without or with RT. Overall survival was recorded, and histology studies quantified DNA damage, apoptosis, microvessel density, and impact on bone marrow. Results In all tumor models, replacing TMZ with NEO212 in a schedule designed to mimic the Stupp protocol achieved strikingly superior extension of survival, especially in TMZ-resistant and RT-resistant models. While NEO212 displayed pronounced radiation-sensitizing, DNA-damaging, pro-apoptotic, and anti-angiogenic effects in tumor tissue, it did not cause bone marrow toxicity. Conclusion NEO212 is a candidate drug to potentially replace TMZ within the standard Stupp protocol. It has the potential to become the first chemotherapeutic agent to significantly extend overall survival in TMZ-resistant patients when combined with radiation.