Imatinib mesylate radiosensitizes human glioblastoma cells through inhibition of platelet-derived growth factor receptor

Cytotoxic and molecular chemotherapy for high-grade glioma: an emerging strategy for the future

Maximal surgical debulking and radiotherapy have been the cornerstone of therapy for high-grade gliomas. The impact of chemotherapy on outcome has been marginal and, until recently, its usage has been debatable. The development of new drugs and an improved understanding of chemoresistance have reinvigorated interest in this treatment modality. Furthermore, increasing knowledge of gliomagenesis has also led to novel non-cytotoxic approaches to targeting the molecular machinery that is responsible for tumour development and progression. These new strategies, which are currently being evaluated in clinical trials, provide new hope for the future.

Platelet-derived growth factor receptor independent proliferation of human glioblastoma cells: selective tyrosine kinase inhibitors lack antiproliferative activity

PURPOSE

The aim of this study was to investigate the role of platelet-derived growth factor (PDGF) and PDGF receptors (PDGFRs) in the proliferation of human glioblastoma cells as a prerequisite for a new therapeutic approach to the treatment of malignant brain tumors with selective tyrosine kinase inhibitors such as imatinib.

METHODS AND RESULTS

In the human glioblastoma cell lines U-87 MG, U-118 MG and U-373 MG different PDGF and PDGFR mRNAs were detected by RT-PCR, and the expression of the receptor proteins was demonstrated by immunostaining and flow cytometry. Moreover, functional activity of PDGFRs was demonstrated in PDGFRbeta expressing glioblastoma cell variants by measuring the mobilization of intracellular Ca(2+) upon PDGF-BB stimulation. However, addition of PDGF-BB to the serum-free culture medium had no stimulatory effect on cell proliferation. Furthermore, cell growth in serum-supplemented and serum-free medium was not affected by imatinib, leflunomide and AG-1296 at therapeutically relevant concentrations.

CONCLUSION

Our results suggest that clinical antitumor effects of imatinib on glioblastoma, if any, are not mediated by the PDGFR.

Immunohistochemical evaluation of KIT expression in sarcomas of the gynecologic region

KIT is expressed in most gastrointestinal stromal tumors, and they usually show c-kit aberrations (most frequently deletions or deletions coexisting with a single or multiple point mutations). Recently, several studies regarding KIT expression in gynecologic tumors have been reported; however, their outcomes were not consistent. In this study, we immunohistochemically examined KIT expression in sarcomas of the female genital tract and studied the existence of c-kit aberrations to elucidate the characteristics of KIT-positive tumors in the gynecologic region. Formalin-fixed, paraffin-embedded tissues from 25 surgically resected and 1 biopsy specimen from 26 patients were used. Histological diagnoses included 14 uterine leiomyosarcomas, 6 carcinosarcomas, 5 endometrial stromal sarcomas, and 1 vaginal epithelioid sarcoma. Immunohistochemical studies were performed using anti-KIT polyclonal antibody. Only four of the above tumors (15%) were positive for KIT, all of which were carcinosarcomas. Specific KIT immunoreactivity was observed in the only carcinomatous components in one case, in the only sarcomatous component in two cases, and in the both components in one case. However, none of the cases showed c-kit aberrations in exons 9, 11, 13, and 17. Judicious decision is mandatory before applying Imatinib therapy to KIT-positive gynecologic tumors.

Imatinib and hydroxyurea in pretreated progressive glioblastoma multiforme: a patient series

BACKGROUND

Grade IV malignancies of the brain, such as glioblastoma multiforme (GBM), are associated with a dismal prognosis. Autocrine and paracrine loops of platelet-derived growth factor (PDGF) signaling, as well as other signal transduction pathways, have been postulated to play a role in glioblastoma transformation, and molecules involved in these pathways can potentially serve as targets for therapeutic inhibitory agents. Imatinib, an inhibitor of PDGF receptors alpha and beta, as well as other selected tyrosine kinases, is indicated for treatment of chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor (GIST). Unfortunately, imatinib, as with many conventional chemotherapeutic agents, has limited efficacy as monotherapy in GBM. In preclinical studies, the chemotherapeutic agent hydroxyurea is demonstrated to have cytotoxic effects additive with imatinib.

PATIENTS AND METHODS

We tested the combination of hydroxyurea and imatinib in 30 grade IV progressive GBM patients refractory to chemo- and radiotherapy. All 30 patients were evaluable after a median 19 weeks observation time.

RESULTS

Combination therapy with imatinib and hydroxyurea resulted in a 20% response rate, including complete and partial responses. Patients experiencing response or stable disease yielded a combined clinical benefit rate of 57%. Median time to progression was 10 weeks and median overall survival was 19 weeks. Three patients continue to survive on combination therapy, with the shortest duration being 106 weeks. Six-month and 2-year progression-free survival rates were 32% and 16%, respectively.

CONCLUSION

The efficacy results, combined with findings that imatinib and hydroxyurea were well tolerated, suggest that this combination shows promise as therapy for GBM.