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Glioblastoma is the most frequent brain tumor of glial origin in adults. With the best available standard-of-care, patients with this disease have a life expectancy of only approximately 15 months after diagnosis. Because the EGF receptor (HER1/EGFR) is one of the most commonly dysregulated oncogenes in glioblastoma, HER1/EGFR-targeted agents, such as erlotinib, were expected to provide a therapeutic benefit. However, their application in the clinical setting failed. Seeking an explanation for this finding, we previously identified several candidate genes for resistance of human glioblastoma cell lines toward erlotinib. On the basis of this panel of genes, we aimed at identifying drugs that synergistically enhance the antiproliferative effect of erlotinib on established and primary glioblastoma cell lines. We found that NSC23766, an inhibitor of RAC1, enhanced the antineoplastic effects of erlotinib in U87MG, T98MG, and A172MG glioblastoma cell lines for the most part in a synergistic or at least in an additive manner. In addition, the synergistic antiproliferative effect of erlotinib and NSC23766 was confirmed in primary cultured cells, indicating a common underlying cellular and molecular mechanism in glioblastoma. Therefore, agents that suppress RAC1 activation may be useful therapeutic partners for erlotinib in a combined targeted treatment of glioblastoma.

Glioblastoma represents the most common primary brain tumor in adults. Despite improvements of multimodal therapy, the prognosis of this disease remains unfavorable. Thus, great efforts have been made to identify therapeutic agents directed against those specific molecular targets whose presence was shown to be associated with worse clinical outcomes. The epidermal growth factor receptor (HER1/EGFR) has been identified as one such target, and different compounds were developed to inhibit HER1/EGFR and/ or its mutant form, EGFRvIII. However, clinical trials did not confirm the initial enthusiasm conveyed by promising results from experimental studies. Therefore, a therapeutic approach directed at inhibiting solely HER1/EGFR does not seem to translate into a clinical benefit. This review discusses the current therapeutic situation in the setting of glioblastoma while putting the spotlight on erlotinib, a HER1/EGFR-targeted small molecule tyrosine kinase inhibitor.

Glioblastoma multiforme (GBM) is the most common malignant brain tumor in adults. Especially in this disease, qualitative and quantitative aspects render the dysregulated epidermal growth factor receptor (HER1/EGFR) an outstanding therapeutic target. A variety of therapeutic compounds was developed to target HER1/EGFR among which the clinically most advanced agents are small molecule tyrosine kinase (TK) inhibitors. Unfortunately, clinical studies examining their therapeutic efficacy have so far failed to document a major therapeutic break-through in the setting of GBM. Thus, the targeted approach against HER1/EGFR likely requires a synergistic drug combination strategy to ultimately become successful in this disease. This patents review focuses on innovative therapeutic strategies combining HER1/EGFR-targeted TK inhibitors with novel agents which for the most part have not been evaluated for the treatment of GBM yet but which constitute interesting candidates for further evaluation in this setting.

Object: The authors have previously reported that erlotinib, an EGFR tyrosine kinase inhibitor, exerts widely variable antiproliferative effects on 9 human glioblastoma multiforme (GBM) cell lines in vitro and in vivo. These effects were independent of EGFR baseline expression levels, raising the possibility that more complex genetic properties form the molecular basis of the erlotinib-sensitive and erlotinib-resistant GBM phenotypes. The aim of the present study was to determine candidate genes for mediating the cellular response of human GBMs to erlotinib., Methods: Complementary RNA obtained in cell lines selected to represent the sensitive, somewhat responsive, and resistant phenotypes were hybridized to CodeLink Human Whole Genome Bioarrays., Results: Expression analysis of 814 prospectively selected genes involved in major proliferation and apoptosis signaling pathways identified 19 genes whose expression significantly correlated with phenotype. Functional annotation analysis revealed that 2 genes (DUSP4 and STAT1) were significantly associated with sensitivity to erlotinib, and 10 genes (CACNG4, FGFR4, HSPA1B, HSPB1, NFATC1, NTRK1, RAC1, SMO, TCF7L1, and TGFB3) were associated with resistance to erlotinib. Moreover, 5 genes (BDNF, CARD6, FOSL1, HSPA9B, and MYC) involved in antiapoptotic pathways were unexpectedly found to be associated with sensitivity. Gene expressions were confirmed by quantitative polymerase chain reaction., Conclusions: Based on an analysis of gene expressions in cell lines with sensitive, somewhat responsive, and resistant phenotypes, the authors propose candidate genes for GBM response to erlotinib. The 10 gene candidates for conferring GBM resistance to erlotinib may represent therapeutic targets for enhancing the efficacy of erlotinib against GBMs. Five additional genes warrant further investigation into their role as putative cotargets of erlotinib.

Background: The antiproliferative effects of erlotinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, on human glioblastoma multiforme (GBM) cell lines in vitro and in vivo are widely variable and independent of EGFR baseline expression levels, indicating that more complex genetic signatures may form the molecular basis of GBM response to erlotinib. This study sought to determine which genes within two common genetic pathways of GBM pathogenesis, i.e., the primary and secondary pathways, may be involved in mediating the cellular response of human GBM towards erlotinib., Materials and Methods: Complementary (c)RNAs from cell lines selected to represent the sensitive, intermediately responsive and resistant phenotypes, respectively, were hybridized to CodeLink Human Whole Genome Bioarrays., Results: Expression analysis of prospectively selected 104 genes pertaining to the primary and secondary pathways of GBM pathogenesis identified two genes (IGF1, PIK3C2B) the expression of which significantly correlated with cellular resistance towards erlotinib., Conclusion: Among the genes constituting two common pathways of GBM pathogenesis, two candidate genes may confer GBM resistance towards erlotinib, suggesting that resistance towards this compound may be acquired during the natural evolution of GBM.

Background: Erlotinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, exerts highly variable antiproliferative effects on human glioblastoma multiforme (GBM) cells in vitro and in vivo. As these effects are independent of EGFR baseline expression levels, more complex genetic signatures may form the molecular basis of the erlotinib-sensitive and erlotinib-resistant GBM phenotypes. The aim of the current study was to determine which genes within the EGFR signaling pathway are candidates for mediating the cellular response of human GBM towards erlotinib., Materials and Methods: Complementary (c)RNAs from cell lines selected to represent the sensitive, intermediately responsive and resistant phenotypes, respectively, were hybridized to CodeLink Human Whole Genome Bioarrays., Results: Expression analysis of the prospectively selected 244 genes whose products constitute the EGFR signaling pathway identified five genes the expression of which significantly correlated with phenotype. Functional annotation analysis revealed one (STATI) and two (FKBP14, RAC1) genes conclusively associated with sensitivity and resistance to erlotinib, respectively. Moreover, two additional genes (PTGER4, MYC) were unexpectedly found to be associated with sensitivity. The gene expressions were confirmed by quantitative polymerase chain reaction., Conclusion: Five genes within the EGFR signaling pathway may modulate GBM response to erlotinib, which further emphasizes the importance of this pathway for the biology of GBM.

Gliomas are the most common primary central nervous system tumours and about 55% are glioblastoma multiforme (GBM). Between 40% and 50% of GBM have dysregulated epidermal growth factor receptor (HER1/EGFR), and almost half of these co-express the mutant receptor subtype EGFRvIII, which may contribute to the aggressive and refractory course of GBM. Limited therapeutic options exist for GBM, and recurrence is common. Standard therapy is surgical resection, where possible, and radiotherapy. Adjuvant chemotherapy provides a modest survival benefit. New therapies are essential, and HER1/EGFR-targeted agents may provide a viable strategy. The HER1/EGFR tyrosine kinase inhibitors erlotinib and gefitinib are in advanced clinical development for glioma, and a number of trials are in progress, or have recently been completed. Preliminary results with gefitinib show no objective responses, but do provide evidence of disease control. In contrast, preliminary data with erlotinib appear more encouraging. Erlotinib inhibits wild-type HER1/EGFR and EGFRvIII, which may underlie its promising clinical activity. Other HER1/EGFR-targeted agents are also being investigated for glioma, including monoclonal antibodies, radio-immuno conjugates, ligand-toxin conjugates, antisense oligonucleotides and ribozymes. Further studies will define their clinical potential and hopefully provide new, effective treatments for GBM and other malignant brain tumours.

New drugs and combination modalities for otherwise non-responsive brain tumors are urgently required. The anti-malarial artesunate (ART) and the EGFR tyrosine kinase inhibitor OSI-774 reveal profound cytotoxic activity. The effectiveness of a combination treatment and the underlying molecular determinants of cellular response are unknown. In the present investigation, we studied ART and OSI-774 in glioblastoma multiforme (GBM) cell lines. Supra-additive inhibition of cell growth was observed in U-87MG.DeltaEGFR cells transduced with a deletion-mutant constitutively active EGFR gene, while additive effects were present in cells transduced with wild-type EGFR (U-87MG.WT-2N), kinase-deficient EGFR (U-87MG.DK-2N), mock vector controls (U-87MG.LUX), or non-transduced parental U-87MG cells. Among nine other non-transduced GBM cell lines, supra-additive effects were found in two cell lines (G-210GM, G-599GM), while ART and OSI-774 acted in an additive manner in the other seven cell lines (G-211GM, G-750GM, G-1163GM, G-1187GM, G-1265GM, G-1301GM, and G-1408GM). Sub-additive or antagonistic effects were not observed. Genomic gains and losses of genetic material in the non-transduced cell lines as assessed by comparative genomic hybridization were correlated with the IC(50) values for ART and OSI-774 and subsequently subjected to hierarchical cluster analysis and cluster image mapping. A genomic profile of imbalances was detected that predicted cellular response to ART and OSI-774. The genes located at the genomic imbalances of interest may serve as candidate resistance genes of GBM cells towards ART and OSI-774. In conclusion, the combination treatment of ART and OSI-774 resulted in an increased growth inhibition of GBM cell lines as compared to each drug alone.

Object: Quantitative and qualitative alterations in the epidermal growth factor receptor (EGFR) commonly occur in many cancers in humans, including malignant gliomas. The aim of the current study was to evaluate molecular and cellular effects of OSI-774, a novel EGFR tyrosine kinase inhibitor, on nine glioblastoma multiforme (GBM) cell lines., Methods: The effects of OSI-774 on expression of EGFR messenger (m)RNA and protein, proliferation, anchorage-independent growth, and apoptosis were examined using semiquantitative reverse transcription-polymerase chain reaction, immunocytochemical analysis, Coulter counting, soft agar cloning, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling/fluorescence-activated cell sorting, respectively. All p53 genes were completely and bidirectionally sequenced. Suppression of anchorage-independent growth by OSI-774 was inversely correlated to the induction of EGFR mRNA during relative serum starvation (r = -0.74) and was unrelated to p53 status. Overall, suppression of anchorage-independent growth was a considerably stronger effect of OSI-774 than inhibition of proliferation. The extent of OSI-774-induced apoptosis positively correlated with both proliferation and anchorage-independent growth of GBM cell lines (r = 0.75 and 0.79, respectively). In a single cell line derived from a secondary GBM, exposure to concentrations of greater than or equal to 1 micromol/L resulted in a substantial net cell loss during proliferation studies., Conclusions: The induction of EGFR mRNA may constitute a cellular mechanism to counteract the inhibitory effect of OSI-774 on the anchorage-independent growth of GBM cells. In contrast, no considerable correlation could be established between baseline expression levels of EGFR (both mRNA and protein) in GBM cell lines and their biological response to OSI-774. The OSI-774 induced greater (p53-independent) apoptosis in more malignant GBM phenotypes and may be a promising therapeutic agent against secondary GBM.