Next-Generation Anti-Angiogenic Therapies as a Future Prospect for Glioma Immunotherapy; From Bench to Bedside

Glioblastoma (grade IV glioma) is the most aggressive histopathological subtype of glial tumors with inordinate microvascular proliferation as one of its key pathological features. Extensive angiogenesis in the tumor microenvironment supplies oxygen and nutrients to tumoral cells; retains their survival under hypoxic conditions; and induces an immunosuppressive microenvironment. Anti-angiogenesis therapy for high-grade gliomas has long been studied as an adjuvant immunotherapy strategy to overcome tumor growth. In the current review, we discussed the underlying molecular mechanisms contributing to glioblastoma aberrant angiogenesis. Further, we discussed clinical applications of monoclonal antibodies, tyrosine kinase inhibitors, and aptamers as three major subgroups of anti-angiogenic immunotherapeutics and their limitations. Moreover, we reviewed clinical and preclinical applications of small interfering RNAs (siRNAs) as the next-generation anti-angiogenic therapeutics and summarized their potential advantages and limitations. siRNAs may serve as next-generation anti-angiogenic therapeutics for glioma. Additionally, application of nanoparticles as a delivery vehicle could increase their selectivity and lower their off-target effects.

Glioblastoma multiforme

Optimal management of newly diagnosed glioblastoma multiforme includes maximal surgical resection, followed by 60 Gy of external beam radiation plus concomitant daily temozolomide and at least six additional monthly cycles of maintenance temozolomide. Several large phase 3 trials are now ongoing to determine whether agents added to this regimen may confer further survival advantage. At the time of disease recurrence, bevacizumab is the most commonly used agent. Whenever feasible, patients should be encouraged to participate in clinical trials, which are currently focused on antiangiogenic and targeted therapies.

Sunitinib in solid tumors

BACKGROUND

Until recently, few treatments were available for renal cell carcinoma (RCC) and gastrointestinal stromal tumors (GIST). Several targeted agents inhibiting key pathogenetic pathways have since been developed for RCC (sunitinib, sorafenib, bevacizumab, temsirolimus, everolimus) and GIST (imatinib, sunitinib). Sunitinib is a multi-kinase inhibitor of VEGFR-2, PDGFR (alpha,beta), FLT-3, KIT, CSF-1 and RET.

OBJECTIVE

To summarize the literature regarding the structure, pharmacokinetics, pharmacodynamics, toxicity and current clinical use of sunitinib. Other potential roles for this drug in RCC, GIST and other tumor types will be discussed.

METHODS

A literature search identified relevant (pre)clinical studies of sunitinib and other relevant agents.

RESULTS/CONCLUSIONS

Sunitinib revolutionized the management of advanced RCC and GIST. With the realization that cross-resistance between targeted agents is incomplete, evolving strategies include sequential treatment, concurrent treatment, and biomarker development. Sunitinib also shows promise in several other tumor types that lack therapeutic options. What remains less clear is its role in tumors that are not heavily dependent on a central pathogenetic pathway, especially if effective cytotoxic therapies exist. Future clinical trials will clarify whether there is a role for sunitinib in these tumors, possibly in combination with cytotoxic agents.

VEGF kinase inhibitors: how do they cause hypertension?

Neoangiogenesis is a critical phenomenon enabling the growth and metastasis of tumors, and inhibitors of neoangiogenesis have been recently added to the armamentarium of anticancer therapies available for clinical use. Dysregulated signaling through the vascular endothelial growth factor (VEGF) pathway has been implicated as a key mediator of neoangiogenesis in tumors. Agents that block signaling through the VEGF pathway demonstrated tumor shrinkage in preclinical models and were therefore developed as anticancer therapies for use in humans. VEGF kinase inhibitors are being used in the treatment of a wide variety of cancers, and recent studies have shown that patients will likely require long-term treatment with these agents. Hypertension has emerged as a frequent side effect associated with agents that block signaling through the VEGF pathway. A thorough understanding of the mechanisms underlying hypertension is crucial to developing appropriate therapeutic strategies for treating hypertension associated with VEGF kinase inhibitors. Several recent studies have advanced our understanding of the pathophysiology of hypertension associated with VEGF kinase inhibitors and will be the subject of this review.

Molecular profiling in glioblastoma: prelude to personalized treatment

The purpose of this review is to provide an up-to-date summary of the current knowledge and understanding of the molecular alterations and pathways relevant to the clinical outcome of glioblastoma patients and their potential use in designing personalized treatment for these patients. This article also discusses the potential of molecular profiling as a diagnostic modality, possible therapeutic implications of MGMT promoter methylation, the targeted inhibition of angiogenesis, and assessment of the tumor's molecular background with respect to PI3K/AKT pathway activation and associated molecules (EGFR, EGFRvIII, PTEN).