Molecular heterogeneity in glioblastoma: therapeutic opportunities and challenges

CCL5, CCR1 and CCR5 in murine glioblastoma: immune cell infiltration and survival rates are not dependent on individual expression of either CCR1 or CCR5

Glioblastoma multiforme (GBM) is the most malignant brain tumor. Microglia/macrophages are found within human GBM where they likely promote tumor progression. We report that CCL5, CCR1, and CCR5 are expressed in glioblastoma. Individual deletion of CCR1 or CCR5 had little to no effect on survival of tumor bearing mice, or numbers of glioblastoma-infiltrated microglia/macrophages or lymphocytes. CCL5 promoted in vitro migration of wild type, CCR1- or CCR5-deficient microglia/macrophages that was blocked by the dual CCR1/CCR5 antagonist, Met-CCL5. These data suggest that CCL5 functions within the glioblastoma microenvironment through CCR1 and CCR5 in a redundant manner.

Drug resistance in glioblastoma: a mini review

Glioblastoma multiforme (GBM) is recognized as the most common and lethal form of central nervous system cancer. Currently used surgical techniques, chemotherapeutic agents, and radiotherapy strategies have done very little in extending the life expectancies of patients diagnosed with GBM. The difficulty in treating this malignant disease lies both in its inherent complexity and numerous mechanisms of drug resistance. In this review, we summarize several of the primary mechanisms of drug resistance. We reviewed available published literature in the English language regarding drug resistance in glioblastoma. The reasons for drug resistance in glioblastoma include drug efflux, hypoxic areas of tumor cells, cancer stem cells, DNA damage repair, and miRNAs. Many potential therapies target these mechanisms, including a series of investigated alternative and plant-derived agents. Future research and clinical trials in glioblastoma patients should pursue combination of therapies to help combat drug resistance. The emerging new data on the potential of plant-derived therapeutics should also be closely considered and further investigated.

Recurrent glioblastoma: a fresh look at current therapies and emerging novel approaches

Despite international efforts, the treatment of recurrent glioblastoma (GBM) remains challenging. Although advances in surgical resection, the use of radiotherapy, and, predominantly, improved medical therapies have led to incremental improvements in median survival, few options exist for the management of recurrent or resistant disease. Insight into the molecular pathogenesis of GBM has led to the recent development of targeted therapeutic strategies aimed at the interruption of key molecular signaling pathways. However, due to the complex and redundant activation of the signaling mechanisms in GBM tumors, the evaluation of targeted agents in clinical trials has been largely limited. The ongoing effort to identify effective strategies for the treatment of recurrent GBM includes combination strategies with agents that target complementary or redundant pathways. Incorporation of novel trial designs that permit simultaneous evaluation of several agent combinations and allow for rapid discontinuation of ineffective regimens can accelerate the clinical evaluation of such candidate regimens. This review discusses strategies and outcomes of existing and emerging treatment approaches, and the challenges associated with the integration of novel therapies into clinical practice.

Mosaic amplification of multiple receptor tyrosine kinase genes in glioblastoma

Tumor heterogeneity has been implicated in tumor growth and progression as well as resistance to therapy. We present an example of genetic heterogeneity in human malignant brain tumors in which multiple closely related driver genes are amplified and activated simultaneously in adjacent intermingled cells. We have observed up to three different receptor tyrosine kinases (EGFR, MET, PDGFRA) amplified in single tumors in different cells in a mutually exclusive fashion. Each subpopulation was actively dividing, and the genetic changes resulted in protein production, and coexisting subpopulations shared common early genetic mutations indicating their derivation from a single precursor cell. The stable coexistence of different clones within the same tumor will have important clinical implications for tumor resistance to targeted therapies.