Metronomic Doses of Temozolomide Enhance the Efficacy of Carbon Nanotube CpG Immunotherapy in an Invasive Glioma Model

Abstract

Even when treated with aggressive current therapies, most patients with glioblastoma survive less than two years. Rapid tumor growth, an invasive nature, and the blood-brain barrier, which limits the penetration of large molecules into the brain, all contribute to the poor tumor response associated with conventional therapies. Immunotherapy has emerged as a therapeutic approach that may overcome these challenges. We recently reported that single-walled carbon nanotubes (SWCNTs) can be used to dramatically increase the immunotherapeutic efficacy of CpG oligonucleotides in a mouse model of glioma. Following implantation in the mouse brain, the tumor cell line used in these previous studies (GL261) tends to form a spherical tumor with limited invasion into healthy brain. In order to evaluate SWCNT/CpG therapy under more clinically-relevant conditions, here we report the treatment of a more invasive mouse glioma model (K-Luc) that better recapitulates human disease. In addition, a CpG sequence previously tested in humans was used to formulate the SWCNT/CpG which was combined with temozolomide, the standard of care chemotherapy for glioblastoma patients. We found that, following two intracranial administrations, SWCNT/CpG is well-tolerated and improves the survival of mice bearing invasive gliomas. Interestingly, the efficacy of SWCNT/CpG was enhanced when combined with temozolomide. This enhanced anti-tumor efficacy was correlated to an increase of tumor-specific cytotoxic activity in splenocytes. These results reinforce the emerging understanding that immunotherapy can be enhanced by combining it with chemotherapy and support the continued development of SWCNT/CpG.

Cytotoxicity induced by carbon nanotubes in experimental malignant glioma

“…Similar results have been reported in the study by Ouyang et al, in which SWCNTs were administered in combination with TMZ; the authors attributed this effect to immune modulation, potentiation of TMZ and the covering of nanotubes with oligodeoxynucleotides CpG. 42 It is important to consider that the effect of CNTs is dependent on intrinsic factors such as formulation, production and endocytosis capacity. 38 This investigation evaluated the effect of the MWCNTs plus TMZ in malignant glial cells and MWCNTs bioavailability in RG2 glioma cells: functionalized MWCNTs were more efficiently endocytosed by RG2 cells than nonfunctionalized MWCNTs.…”

Decreased non-specific adhesivity, receptor targeted (DART) nanoparticles exhibit improved dispersion, cellular uptake, and tumor retention in invasive gliomas

“…While the KR158 malignant glioma model used here is highly invasive [37], numerous clinical trials testing delivery strategies to improve distribution of therapeutics in the brain [33, 38] have highlighted the difficulty with translating results from smaller pre-clinical models to humans. In the future, we plan to test this therapeutic formulation strategy in larger mammals (pigs and tumor-bearing dogs) in order to better understand critical limitations to human translation.…”

Carbon nanotubes as cancer therapeutic carriers and mediators

“…These findings demonstrated that CNTs could improve CpG uptake into tumor-associated inflammatory cells without toxicity and lead to a robust antitumor response. Recently, Ouyang et al 115 proposed an SWCNT complex that increased the immunotherapeutic efficacy of CpG ODNs. SWCNT-CpG was combined with temozolomide and evaluated in an invasive mouse glioma model (K-Luc) that better recapitulates human disease.…”