ZD6474 induces growth arrest and apoptosis of GIST-T1 cells, which is enhanced by concomitant use of sunitinib

New targets and therapies for gastrointestinal stromal tumors

INTRODUCTION

The majority of gastrointestinal stromal tumors (GIST) are driven by an abnormal receptor tyrosine kinase (RTK) signaling, occurring mainly due to somatic mutations in KIT or platelet derived growth factor receptor alpha (PDGFRA). Although the introduction of tyrosine kinase inhibitors (TKIs) has revolutionized therapy for GIST patients, with time the vast majority of them develop TKI resistance. Advances in understanding the molecular background of GIST resistance allows for the identification of new targets and the development of novel strategies to overcome or delay its occurrence. Areas covered: The focus of this review is on novel, promising therapeutic approaches to overcome heterogeneous resistance to registered TKIs. These approaches involve new TKIs, including drugs specific for a mutated form of KIT/PDGFRA, drugs with inhibitory effect against multiple RTKs, compounds targeting dysregulated downstream signaling pathways, drugs affecting KIT expression and degradation, inhibitors of cell cycle, and immunotherapeutics. Expert commentary: As the resistance to standard TKI treatment can be heterogeneous, a combinational approach for refractory GIST could be beneficial. Moreover, the understanding of the molecular background of resistant disease would allow development of a more personalized approach for these patients and their response to targeted therapy could be monitored closely using 'liquid biopsy'.

Changes in signaling pathways induced by vandetanib in a human medullary thyroid carcinoma model, as analyzed by reverse phase protein array

BACKGROUND

Medullary thyroid carcinoma (MTC) is a rare tumor that is caused by activating mutations in the proto-oncogene RET. Vandetanib, a tyrosine-kinase inhibitor, has been recently approved to treat adult patients with metastatic MTC. The aim of this study was to investigate changes in signaling pathways induced by vandetanib treatment in preclinical MTC models, using the reverse-phase protein array method (RPPA).

METHODS

The human TT cell line was used to assess in vitro and in vivo activity of vandetanib. Protein extracts from TT cells or TT xenografted mice, treated by increasing concentrations of vandetanib for different periods of time, were probed with a set of 12 antibodies representing major signaling pathways, using RPPA. Results were validated using two distinct protein detection methods: Western immunoblotting and immunohistochemistry.

RESULTS

Vandetanib displays antiproliferative and antiangiogenic activities and inhibits RET autophosphorylation. The MAPK and AKT pathways were the two major signaling pathways inhibited by vandetanib. Interestingly, phosphorylated levels of NFκB-p65 were significantly increased by vandetanib. Comparable results were obtained in both the in vitro and in vivo approaches, as well as for the protein detection methods. However, some discrepancies were observed between RPPA and Western immunoblotting, possibly due to lack of specificity of the primary antibodies used.

CONCLUSIONS

Overall, our results confirmed the interest of RPPA for screening global changes induced in signaling pathways by kinase inhibitors. MAPK and AKT were identified as the main pathways involved in vandetanib response in MTC models. Our results also suggest alternative routes for controlling the disease, and provide a rationale for the development of therapeutic combinations based on the comprehensive identification of molecular events induced by inhibitors.

Autophagy inhibition induces enhanced proapoptotic effects of ZD6474 in glioblastoma

BACKGROUND

Autophagy is a lysosomal degradation pathway that can provide energy through its recycling mechanism to act as a cytoprotective adaptive response mediating treatment resistance in cancer cells. We investigated the autophagy-inducing effects of ZD6474, a small-molecule inhibitor that blocks activities of vascular endothelial growth factor receptor (VEGFR), epidermal growth factor receptor (EGFR), and RET tyrosine kinases.

METHODS

We investigated the effects of ZD6474 on autophagy in glioblastomas cells. The ZD6474 mechanism of action was determined by western blot. We then examined the impacts of the inhibition of autophagy in combination with ZD6474 on cell apoptosis in vitro. Furthermore, we evaluated the synergistic anticancer activity of combination treatment with an autophagy inhibitor (chloroquine) and ZD6474 in U251 glioblastoma cells xenograft model.

RESULTS

ZD6474-induced autophagy was dependent on signalling through the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway. ZD6474-induced autophagy was inhibited by both knockdown of the ATG7 and Beclin 1 gene, essential autophagy genes, and pharmacologic agents (chloroquine and 3-methyalanine) treatment. Both treatments also dramatically sensitised glioblastoma cells to ZD6474-induced apoptosis, decreasing cell viability in vitro. Furthermore, in a xenograft mouse model, combined treatment with ZD6474 and chloroquine significantly inhibited U251 tumour growth, and increased the numbers of apoptotic cells compared with treatment with either agent alone.

CONCLUSION

Autophagy protects glioblastoma cells from the proapoptotic effects of ZD6474, which might contribute to tumour resistance against ZD6474 treatment.

Changes in signaling pathways induced by vandetanib in a human medullary thyroid carcinoma model, as analyzed by reverse phase protein array

BACKGROUND

Medullary thyroid carcinoma (MTC) is a rare tumor that is due to activating mutations in the proto-oncogene RET. Vandetanib, a tyrosine-kinase inhibitor, has been recently approved to treat adult patients with metastatic MTC. The aim of this study was to investigate changes in signaling pathways induced by vandetanib treatment in preclinical MTC models, using the reverse-phase protein array method (RPPA).

METHODS

The human TT cell line was used to assess in vitro and in vivo activity of vandetanib. Protein extracts from TT cells or TT xenografted mice, treated by increasing concentrations of vandetanib for different periods of time, were probed with a set of 12 antibodies representing major signaling pathways, using RPPA. Results were validated using two distinct protein detection methods, western-immunoblotting and immunohistochemistry.

RESULTS

Vandetanib displays antiproliferative and antiangiogenic activities and inhibits RET auto-phosphorylation. MAPK and AKT pathways were the two major signaling pathways inhibited by vandetanib. Interestingly, phosphorylated levels of NFκB-p65 were significantly increased by vandetanib. Comparable results were obtained in both the in vitro and in vivo approaches as well as for the protein detection methods, although some discrepancies were observed between RPPA and western-immunoblotting.

CONCLUSIONS

Results confirmed the reliability and the utility of RPPA for screening global changes induced in signaling pathways by kinase inhibitors. MAPK and AKT were identified as the main pathways involved in vandetanib response in MTC models. Our results also suggest alternative routes for controlling the disease and provide a rationale for the development of therapeutic combinations based on the comprehensive identification of molecular events induced by inhibitors.

Analysis of anti-proliferative and chemosensitizing effects of sunitinib on human esophagogastric cancer cells: Synergistic interaction with vandetanib via inhibition of multi-receptor tyrosine kinase pathways

The receptor tyrosine kinases (RTKs), epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor 1-3 (VEGFR1-3), are frequently expressed in gastric cancer and are putative therapeutic targets in this disease. We have investigated the anti-proliferative and chemosensitizing properties of the multitargeted small-molecule RTK inhibitors sunitinib and vandetanib in a panel of 4 human gastric and esophageal cancer cell lines. In the 1st instance, the expression of potential targets of these small-molecule inhibitors was examined by reverse transcriptase-polymerase chain reaction, western blotting, and flow cytometry. EGFR mRNA and protein was detected in all cases, with VEGFR2 expression noted in all but 1 line. Both EGF and VEGF were shown to stimulate tumor cell growth, and both sunitinib and vandetanib were found to be associated with significant dose-dependent inhibition of proliferation and an enhancement of apoptosis, as determined by MTT and propidium iodide/Annexin V labeling assays, respectively. The addition of sunitinib to VEGF-stimulated NCI-N87 cells was associated with a reduction in MAPK phosphorylation (pMAPK) but not Akt phosphorylation (pAkt), whereas the addition of vandetanib was associated with reductions in both VEGF- and EGF-mediated VEGFR2 phosphorylation, pMAPK and pAkt. Co-administration of sunitinib significantly enhanced the sensitivity of MKN-45 cells to cisplatin and irinotecan. In addition, vandetanib synergistically enhanced the sunitinib-associated inhibition of gastric cancer cell growth. In conclusion, these preliminary data confirm the importance of EGFR and VEGFR signaling in gastric cancer and suggest that the simultaneous inhibition of RTK-pathways through sunitinib and vandetanib may provide therapeutic benefit in this disease.

Gastrointestinal stromal tumor in Brazil: clinicopathology, immunohistochemistry, and molecular genetics of 513 cases

The aim of the present study was to evaluate the clinicopathological, immunohistochemical, and molecular genetic features of gastrointestinal stromal tumors in Brazil and compare them with cases from other countries. Five hundred and thirteen cases were retrospectively analyzed. HE-stained sections and clinical information were reviewed and the immunohistochemical expression of CD117, CD34, smooth-muscle actin, S-100 protein, desmin, CD44v3 adhesion molecule, p53 protein, epidermal growth factor receptor, and Ki-67 antigen was studied using tissue microarrays. Mutation analysis of KIT and platelet-derived growth factor receptor-alpha genes was also performed. There was a slight female predominance (50.3%) and the median age at diagnosis was 59 years. The tumors were mainly located in the stomach (38.4%). Immunohistochemistry showed that CD117 was expressed in 95.7% of cases. Epidermal growth factor receptor expression was observed in 84.4% of tumors. p53 protein expression was found only in 2.6% of cases but all belonged to the high-risk group for aggressive behavior according to the National Institutes of Health consensus approach. No CD44v3 adhesion molecule expression was detected. KIT exon 11 mutations were the most frequent (62.2%). The present data confirm that gastrointestinal stromal tumors in Brazilian patients do not differ from tumors occurring in other countries.

EGFR and gastrointestinal stromal tumor: an immunohistochemical and FISH study of 82 cases

Gastrointestinal stromal tumor is the most common mesenchymal neoplasm of the gastrointestinal tract. Mutually exclusive KIT or platelet-derived growth factor receptor-alpha mutations are key events in gastrointestinal stromal tumor pathogenesis, and specific treatment targeting KIT/platelet-derived growth factor receptor-alpha activation is available. Epidermal growth factor receptor plays an important role in cancer biology and also constitutes a promising molecular target of therapy. Very few reports have been published in the literature about the relationship between gastrointestinal stromal tumor and epidermal growth factor receptor. The aim of this study was to investigate epidermal growth factor receptor immunohistochemical expression and epidermal growth factor receptor gene amplification in 82 consecutive gastrointestinal stromal tumor cases using tissue microarray technique. Hematoxylin- and eosin-stained sections and clinical information were reviewed, and expression of CD117 (KIT), CD34 and epidermal growth factor receptor was investigated by immunohistochemistry. Epidermal growth factor receptor gene copy number was determined using fluorescence in situ hybridization. Immunohistochemistry revealed that CD117 and CD34 were expressed in 96 and 57% of tumors, respectively. Variable epidermal growth factor receptor protein immunohistochemical overexpression was detected in 96% of gastrointestinal stromal tumor cases, but none of the 75 cases with represented tumor tissue cores and countable fluorescence signals exhibited epidermal growth factor receptor gene amplification by fluorescence in situ hybridization. These results show that there is no correlation between epidermal growth factor receptor protein overexpression by immunohistochemistry and epidermal growth factor receptor gene amplification by fluorescence in situ hybridization. Considering that the mechanisms of epidermal growth factor receptor protein overexpression are not well understood and the possibility that anti-epidermal growth factor receptor therapy may be beneficial for patients with gastrointestinal stromal tumor that overexpresses epidermal growth factor receptor, additional studies are encouraged.

Phase II, open-label study of PTK787/ZK222584 for the treatment of metastatic gastrointestinal stromal tumors resistant to imatinib mesylate

BACKGROUND

We evaluated safety and efficacy of PTK787/ZK222584 (PTK/ZK), a novel tyrosine kinase inhibitor of KIT, platelet-derived growth factor receptors and vascular endothelial cell growth factor receptors (VEGFRs), in patients with imatinib-resistant gastrointestinal stromal tumor (GIST). This is the first study of PTK/ZK in this population.

PATIENTS AND METHODS

Patients with metastatic GIST that had progressed after >/= 4-week treatment with imatinib mesylate were eligible. Prior VEGFR-2 inhibitor therapy was not permitted. PTK/ZK 1250 mg orally once-daily was administered to 15 patients (accrued as a two-stage procedure), most of whom (n = 11) had been unsuccessfully treated with imatinib 800 mg daily, until treatment failure. Patients were monitored at 4- to 8-week intervals.

RESULTS

All 15 patients enrolled were eligible; two (13%) achieved partial response (PR), eight (53%) had stable disease (SD) >/=3 months, and five (33%) progressed. The clinical benefit rate (PR + SD) was 67% (95% CI 38% to 86%). Median time to progression was 8.5 months (range 0.9-24.8+ months). Three patients had not progressed at the time of analysis, including one PR at 24.8 months and two SDs at 16.6 and 18.6 months on treatment. PTK/ZK was generally well tolerated.

CONCLUSION

PTK/ZK 1250 mg p.o. once daily is active and well tolerated in patients with imatinib-resistant GIST.