*8.3.1. Oncolytic HSV-1*

with resection, chemotherapy and radiotherapy, was safe and without dose-limiting toxicity

Despite the aforementioned promising results from a small number of patients, the Phase III international open-label, randomized ASPECT clinical trial, which studied the intra-operative administration of adenoviral-HSV-tk followed by GCV (n=124) as compared to resection and standard of care alone (n=126), was not positive. Unfortunately, the data revealed no difference between the groups in terms of OS; furthermore, more patients in the experimental group had one or more treatment-related adverse events than those in the control group (88 [71%] vs 51

Synthetic vectors, including nanoparticles have been applied to deliver DNA plasmids, RNA and siRNA (Jin and Ye 2007; Germano and Binello 2009; Jin, Bae et al. 2011). Liposomes are perhaps the most-researched of all nanoparticles (Tobias, Ahmed et al. 2013). Given through convection-enhanced delivery via stereotactically-placed catheters a liposome-DNA complex has been used to deliver HSV-tk in a small number of patients. The treatment was welltolerated without major side effects (Jacobs, Voges et al. 2001; Voges, Reszka et al. 2003).

Pleuripotent neural stem cells procured from the subgranular zone of the hippocampus and the areas surrounding the lateral ventricles have the ability to migrate to areas of parenchymal damage (Luskin 1993). Neural stem cell clones may migrate to areas of tumor infiltration and thus were examined as vehicles for delivery of suicide genes, cytokines, or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL); there is evidence of potential efficacy in animal models but no clinical utility data yet (Aboody, Brown et al. 2000; Marsh, Goldfarb et

A well-documented characteristic of GBM is its inherent inactivation of the p53 tumor suppressor gene. Animal trials have shown that re-introduction of the wild-type p53 gene is pro-apoptotic leading to increased sensitivity to current modalities of treatment such as chemo- and radiotherapy. A Phase 1 trial of adenoviral gene transfer of intra-tumoral wildtype p53 in recurrent malignant glioma proved to be safe, but the transfected cells were not found in a radius large enough to be therapeutically effective (Lang, Bruner et al. 2003).

The realm of oncolytic virus therapy involves the use of replication-competent viruses with the ability to selectively replicate and kill cancer cells, with or without gene transfer. This is in opposition to prodrug/suicide gene therapy which makes use of replication-incompetent modalities. In order to combat the inefficiency of suicide gene therapy, oncolytic treatment employs tumor-specific, conditionally replicating viral vectors (Tobias, Ahmed et al. 2013). The mechanism of action involves viral replication which eventually leads to lysis of the host tumor cell and subsequent release of additional copies of competent virus which may lead to

(Chiocca, Aguilar et al. 2011).

al. 2013).

[43%]) (Westphal, Yla-Herttuala et al. 2013).

204 Tumors of the Central Nervous System – Primary and Secondary

*8.2.5. Tumor suppressor gene replacement*

**8.3. Oncolytic gene therapy**

*8.2.4. Nanopartical/Neural stem cell-mediated therapy*

Herpes Simplex is an enveloped, doubled-stranded DNA virus which exhibits inherent action upon the human nervous system; it can replicate in both active and quiescent cells. Conse‐ quently, safety was an original concern with this viral vector. Approximately 8 different HSV-1 genes have been altered or deleted to promote tumor specificity and lower collateral CNS damage (Tobias, Ahmed et al. 2013). There are two strains of replication-competent HSV-1 which have been significantly studied: G207 and HSV1716. G207 is the more widely-examined of the two and possesses a mechanism of action involving alteration of the gene which produces ribonucleotide reductase. In a recent phase 1B clinical trial, patients received injections of this virus both before and after tumor resection. Although viral replication was observed, treatment efficacy was sparse (Markert, Liechty et al. 2009). Additional studies have likewise shown adequate safety but minimal efficacy (Todo, Martuza et al. 2001).

G207 overcomes host defenses mediated by protein kinase R (PKR), which normally shuts down translation in infected cells through phosphorylation of eIF-2 alpha (Barzon, Zanusso et al. 2006). In a Phase I study by Markert et al., conditionally replicating G207 virus (given by stereotactic intratumor injection) was not found to lead to the development of herpes ence‐ phalitis (Markert, Medlock et al. 2000). Additionally, replication-competent HSV1716 admin‐ istration in a Phase 1 dose-escalation study by Rampling et al. did not lead to encephalitis. Furthermore, no viral shedding was noted and no viral genome was found in tumor biopsies performed months after treatment (Rampling, Cruickshank et al. 2000).

#### *8.3.2. Oncolytic adenoviruses*

Adenoviruses carrying mutations in E1A or E1B can also act on GBM via oncolysis. Their mechanism of action involves tumor-specific binding and inactivation of apoptotic proteins like pRB family and p53. Of note, adenovirus is inherently non-neurotropic, which may lend itself to superior safety versus HSV. One adenovirus, *ONYX-015,* has been found to preferen‐ tially replicate in p53 deficient cells secondary to its deletion for p53-inactivating protein E1B-55K. In one clinical trial it was injected into the surgical cavity after resection and found to have no serious adverse effects; however; almost all patients involved in the trial had progression of their GBM (Chiocca, Abbed et al. 2004). It should also be noted that Geoerger et al found human xenografts to be responsive to ONYX-015 without correlation to their p53 status (Geoerger, Grill et al. 2003).

#### *8.3.3. Oncolytic NDV*

NDV is an avian paramyxovirus, which does not harm humans except for rare pulmonary infection in poultry farmers; certain strains harm neoplastic cells via a currently unknown mechanism (Reichard, Lorence et al. 1992). Interestingly, NDV also has pleiotropic immunemodulatory properties (Schirrmacher, Haas et al. 1999). It should be noted that treatment with NDV necessitates starting at a low dose as there have been examples of treatment-related death with *NDV PV701 and solid cancers* (Pecora, Rizvi et al. 2002). *MTH-68/H*, a live attenuated oncolytic viral strain of NDV, has shown promising results is a small number of GBM patients (Csatary, Gosztonyi et al. 2004).

for clinical utility. The consistency in obtaining negative results in GBM is remarkable. How

Anti-Angiogenesis, Gene Therapy, and Immunotherapy in Malignant Gliomas

http://dx.doi.org/10.5772/58320

207

It is becoming evident that the phenotypes of GBM are not created by few solitary molecules but rather by dynamic networks with positive and negative loops that react and respond to a therapeutic intervention. The good news is that these networks are finite dimensional. Furthermore, because of the instability of cancer genomes, random mutations are introduced in the population of rapidly dividing glioma cells; hence, a particular therapy could merely delay growth by selecting a resistant subpopulation. We suggest that we should elevate the threshold by mandating stringent criteria before proceeding to very costly phase III clinical

**1.** Phase II clinical trials must include a control arm with appropriate stratification instead

**2.** Preclinical models must include proof of feasibility in at least 8-10 different cell lines/

**3.** We ought to invest in developing a better understanding of the structure of the oncogenic molecular networks in GBM and demand laboratory data depicting the reactions of these

**4.** We need to develop mathematical models, results, and simulations of these molecular

We believe that investing in the aforementioned endeavors will increase the likelihood that a chosen therapy will have proven clinical utility against GBM. Maintaining the status quo, by forging ahead with large phase III clinical trials costing about \$50-100 million each, is not

[1] Abbas, A. K, Lichtman, A. H, et al. (2014). Basic immunology : functions and disor‐

networks and acquire the ability to test therapeutic strategies in silico.

Paula Province, Alexis Bashinski Shaefer, Benjamin McCullough and

The University of Alabama at Birmingham, Birmingham, Alabama, USA

ders of the immune system. Philadelphia, W.B. Saunders Co.

can we improve and what do we do to turn the tide in our favor?

trials, as follows.

attractive.

**Author details**

**References**

Hassan M Fathallah-Shaykh

of historical controls.

networks to a new therapeutic strategy.

animal models.

#### *8.3.2. Oncolytic reoviruses*

Reovirus is a double-stranded RNA-containing virus that replicates in GBM cells because of a hyperactive ras signaling; it distinctively does not replicate in normal brain cells. A phase I clinical trial of intrattumoral administration of genetically unmodified virus was well tolerated by patients with recurrent malignant gliomas (Forsyth, Roldan et al. 2008). Further studies involving reovirus are currently underway.

#### **8.4. Gene immunotherapy**

Treatment of gliomas with immune therapy is based on harnessing of the patient's T-Cell mediated response to tumor cells. Typically, gene-immune therapy falls into the category of priming in the brain by the transfer of cytokine genes, like IL-2, IL-4, IL-12, and interferons gamma and beta (Freeman, Abboud et al. 1993; Borden, Lindner et al. 2000; Candolfi, Xiong et al. 2010; Denbo, Williams et al. 2011; Ryu, Park et al. 2011; Markert, Cody et al. 2012). A phase I clinical trial of the injection of cationic liposomes carrying the human IFN-Beta gene into the postsurgical cavity showed low toxicity (Wakabayashi, Natsume et al. 2008). A phase 1 trial of adenovirus-mediated gene transfer of INF-Beta was also well tolerated (Chiocca, Smith et al. 2008). Furthermore, a small pilot study of liposomal-mediated IFN-Beta gene transfer into the postsurgical cavity showed promising results (Yoshida, Mizuno et al. 2004).

Another important strategy combines cytokine gene transfer (human IL-2) paired with HSV-TK/GCV treatment (Palu, Cavaggioni et al. 1999; Colombo, Barzon et al. 2005). The results are promising in a small number of patients (Colombo, Barzon et al. 2005); in particular, biopsy following treatment showed tumor necrosis at site of administration as well as significant immune response in the form of activated cytotoxic T cells, macrophages and T-Helper/inducer lymphocytes (Barzon, Zanusso et al. 2006).

### **9. Conclusion**

The aforementioned negative results of several key phase III clinical trials in GBM demonstrate that current proof of efficacy in preclinical models is a necessary but not sufficient condition for clinical utility. The consistency in obtaining negative results in GBM is remarkable. How can we improve and what do we do to turn the tide in our favor?

It is becoming evident that the phenotypes of GBM are not created by few solitary molecules but rather by dynamic networks with positive and negative loops that react and respond to a therapeutic intervention. The good news is that these networks are finite dimensional. Furthermore, because of the instability of cancer genomes, random mutations are introduced in the population of rapidly dividing glioma cells; hence, a particular therapy could merely delay growth by selecting a resistant subpopulation. We suggest that we should elevate the threshold by mandating stringent criteria before proceeding to very costly phase III clinical trials, as follows.


We believe that investing in the aforementioned endeavors will increase the likelihood that a chosen therapy will have proven clinical utility against GBM. Maintaining the status quo, by forging ahead with large phase III clinical trials costing about \$50-100 million each, is not attractive.
