Regression of glioma in rat models by intranasal application of parvovirus h-1.

PURPOSE: In previous studies, we have shown that the apathogenic rat parvovirus H-1 (H-1PV) is capable to induce regression of advanced symptomatic rat and human gliomas in a rat model, when the virus was injected in the tumor (intracranially) or intravenously. Infection with H-1PV did not provoke any pathology in nontumor tissue. This study addresses the question whether also intranasal application of this oncolytic virus is suitable and sufficient for treating gliomas in this animal model. EXPERIMENTAL DESIGN: Rat (RG-2) or human (U87) glioma cells were grafted stereotactically in the brain of rats (Wistar or RNU, respectively), and after development of tumors visible by MRI, H-1PV was instilled intranasally. Tumor regression was monitored by MRI, and survival was analyzed by Kaplan-Meier analysis. Brains from sacrificed animals were analyzed for histologic alterations, presence of viral DNA and proteins and infectious virions. In addition, distribution of virus to other organs was determined. RESULTS: A single intranasal instillation of H-1PV was sufficient to induce efficient regression of rat glioma, leading to significant prolongation of survival without any toxicity for other tissues. It is shown that the virus reaches brain and other tissues, and that the viral replication-associated (and oncolysis-associated) regulatory proteins are exclusively expressed in the tumor tissue. In rats with xenografts of human glioma, oncolytic activity of H-1PV was less pronounced, however, leading to significant prolongation of survival. CONCLUSION: In view of an ongoing clinical trial on the use of H-1PV for oncolytic virotherapy of glioma, the option of applying the virus intranasally may be a valuable alternative to invasive routes of infection.

Regression of advanced rat and human gliomas by local or systemic treatment with oncolytic parvovirus H-1 in rat models.

Oncolytic virotherapy is a potential treatment modality under investigation for various malignancies including malignant brain tumors. Unlike some other natural or modified viruses that show oncolytic activity against cerebral neoplasms, the rodent parvovirus H-1 (H-1PV) is completely apathogenic in humans. H-1PV efficiently kills a number of tumor cells without harm to corresponding normal ones. In this study, the concept of H-1PV-based virotherapy of glioma was tested for rat (RG-2 cell-derived) and for human (U87 cell-derived) gliomas in immunocompetent and immunodeficient rat models, respectively. Large orthotopic rat and human glioma cell-derived tumors were treated with either single stereotactic intratumoral or multiple intravenous (iv) H-1PV injections. Oncolysis was monitored by magnetic resonance imaging and proven by histology. Virus distribution and replication were determined in brain and organs. In immunocompetent rats bearing RG-2-derived tumors, a single stereotactic intratumoral injection of H-1PV and multiple systemic (iv) applications of the virus were sufficient for remission of advanced and even symptomatic intracranial gliomas without damaging normal brain tissue or other organs. H-1PV therapy resulted in significantly improved survival (Kaplan-Meier analysis) in both the rat and human glioma models. Virus replication in tumors indicated a contribution of secondary infection by progeny virus to the efficiency of oncolysis. Virus replication was restricted to tumors, although H-1PV DNA could be detected transiently in adjacent or remote normal brain tissue and in noncerebral tissues. The results presented here and the innocuousness of H-1PV for humans argue for the use of H-1PV as a powerful means to perform oncolytic therapy of malignant gliomas.

Polyclonal evolution of multiple secondary KIT mutations in gastrointestinal stromal tumors under treatment with imatinib mesylate.

Gastrointestinal stromal tumors (GIST) are characterized by a strong KIT receptor activation most often resulting from KIT mutations. In a smaller subgroup of tumors without KIT mutations, analogous activating mutations are found in the platelet-derived growth factor receptor alpha (PDGFRalpha) gene. Both PDGFRalpha and KIT receptors are targets of the tyrosine kinase inhibitor imatinib (Glivec) which has improved the treatment of advanced GISTs significantly. However, a subgroup of tumors show a secondary progress under therapy with imatinib after initial response. One possible mechanism of secondary resistance is the development of newly acquired KIT mutations. In the present study, we evaluated the frequency of such secondary KIT mutations in a series of GIST patients in which tumor tissue was resected under treatment. We examined one to seven different tumor areas in 32 cases (total of 104 samples) and found up to four newly acquired KIT mutations in 14 patients (43.8%). These were always located in exons encoding the first or second tyrosine kinase domain (exon 13, 14, or 17). Mutations were found only in a subset of samples analyzed from each case whereas others retained the wild-type sequence in the same region. There was never more than one new mutation in the same sample. Consistent with a secondary clonal evolution, the primary mutation was always detectable in all samples from each tumor. According to our results, the identification of newly acquired KIT mutations in addition to the primary mutation is dependent on the number of tissue samples analyzed and has high implications for further therapeutic strategies.