demonstrated tumor specificity and adequate agent distribution with adverse effects similarly limited to target tissue damage and minimal to no systemic toxicity. These trials were limited, however, by the specificity of the delivered agents, which targeted only a subpopulation of tumor cells. Prior to our clinical trial, paclitaxel was the only conventional chemotherapeutic agent delivered via CED in a Inhibitors,research,lifescience,medical clinical trial . This was mainly because paclitaxel does not cross the BBB, thus allowing the investigators to demonstrate that DW-MRI could be used to approximate the volume of distribution of CED. The trial resulted in a large incidence (40%) of chemical meningitis, a major drawback to the choice of paclitaxel [15, 16]. Though these studies highlighted initial challenges in the application of CED, they demonstrated the importance of careful and rational selection of agents for use in this method of delivery. 3. Early Experiences: CED of Integrase inhibitor Topotecan Our initial experience with
CED Inhibitors,research,lifescience,medical of antitumor agents utilized the cytotoxic agent topotecan. Topotecan is a camptothecin-class drug and acts as a topoisomerase-I inhibitor. It causes single-strand DNA breaks during DNA replication [17, 18]. This drug was selected after we demonstrated in vitro cytotoxicity Inhibitors,research,lifescience,medical against various malignant glioma cell lines . Due to its activity in cells in the S-phase of division, topotecan is ideal for the treatment of mitotically active glioma cells
in the setting of relatively quiescent brain tissue. Previous experience with topotecan demonstrated poor penetration of the blood-brain barrier and significant dose-limiting toxicities, limiting systemic administration [20–23]. However, these same properties make it an ideal drug for administration Inhibitors,research,lifescience,medical via CED. In addition, an important aspect of the choice of topotecan was its effect on a vital Inhibitors,research,lifescience,medical cellular process, namely, the role of topoisomerase I on DNA processes. This focus on conventional chemotherapeutic agents as opposed to targeted therapies allows for greater coverage of heterogeneous glioma subpopulations. While targeted therapies can be successful in eliminating a specific subpopulation of PDK4 glioma cells that express a certain antigen, this provides a selective advantage for remaining neoplastic cells. Preclinical testing of topotecan that was performed in a model of glioblastoma was developed using a PDGF-B expressing retrovirus injected stereotactically into the adult white matter of rats to infect glial progenitors . This resulted in the consistent development of tumors that closely resembled glioblastoma, with pseudopalisading necrosis, invasion, glomeruloid vascular proliferation, and survival of 14–19 days . Topotecan was delivered using an implantable osmotic pump connected to an intracerebral infusion cannula (Alzet; Cupertino, CA) that was implanted into the tumor.