TITLE: A Fusogenic Oncolytic Herpes Simplex Virus for Therapy of Advanced Ovarian Cancer PRINCIPAL INVESTIGATOR:

Purpose and Experimental Design: Replication-compe-tent herpes simplex virus [HSV (oncolytic HSV)] holds con-siderable promise for treating malignant solid tumors, al-though the potency of the virus needs improvement if its fullclinical potential is to be realized. Incorporation of mem-brane fusion capability into an oncolytic HSV, either byscreening for a syncytial HSV mutant after random mu-tagenesis or by inserting a hyperfusogenic glycoprotein fromgibbon ape leukemia virus into the viral genome, can signif-icantly enhance the antitumor effects of the virus (X. Fu andX. Zhang, Cancer Res., 62: 2306–2312, 2002; X. Fu et al.,Mol. Ther., in press, 2003). We reasoned that both fusogenicstrategies, incorporated into a single oncolytic HSV, mightsignificantly improve virotherapy for ovarian cancer.Results: In vitro characterization of a doubly fusogeniconcolytic HSV (Synco-2D) showed that this virus produces adistinctive syncytial phenotype, leading to a significantlyincreased tumor cell killing ability, compared with that of anonfusogenic virus. When injected directly into the abdom-inal cavity of mice bearing human ovarian cancer xe-nografts, Synco-2D eradicated all tumor masses in 75% ofthe animals, whereas no animals in the conventional onco-lytic HSV-treated group were tumor free.Conclusions: This newly generated fusogenic oncolyticHSV is a promising candidate for clinical testing againstadvanced ovarian cancer.INTRODUCTIONEOC is the leading cause of death from gynecologicalmalignancies. An estimated 23,400 new cases of EOC arediagnosed in the United States each year (1). Because of itsinconspicuous early symptoms and the lack of effective screen-ing techniques, this disease frequently presents at an advancedstage (III/IV), in which the disease has usually spread to theperitoneal cavity (2). Current therapy for advanced-stage ovar-ian cancer consists of debulking surgery followed by chemo-therapy (3). Although the clinical response rate is 60–70%, mostpatients ultimately relapse and succumb to recurrent chemore-sistant disease, leading to 14,000 deaths in the United Stateseach year (1). Hence, there is an urgent need for novel thera-peutics that can provide significant clinical benefits or cure forpatients with advanced-stage EOC.One experimental therapy that holds great promise for solidtumors such as ovarian cancer is the use of replication-compe-tent (oncolytic) HSV (4, 5). These viruses can infect, replicatein, and kill tumor cells by a direct cytopathic effect, whileshowing only restricted ability to replicate in normal cells (6–8). In early clinical trials, however, treatment with the currentgeneration of oncolytic viruses did not significantly affect tumorgrowth or improve prognosis (9, 10). This suboptimal resultmay reflect viral gene deletions, which can reduce the replica-tive potential of viruses in tumor cells. For example, deletion ofthe 34.5 gene significantly reduced viral growth even in rap-idly dividing cells (8, 11–13). Hence, improvements in thepotency of these oncolytic viruses are required to obtain clearbenefits in cancer patients.We recently reported that addition of a cell membranefusion capability to an oncolytic HSV can significantly increasethe antitumor potency of the virus (14, 15). The modified viruskills tumor cells efficiently and directly through both replicationand cell membrane fusion. These two cytolytic mechanisms mayalso produce a synergistic effect through syncytial formationthat facilitates the spread of the oncolytic virus in tumor tissue.The fusogenic activity of the virus was generated by randommutagenesis of a well-characterized oncolytic HSV (14) or byinserting a hyperfusogenic membrane glycoprotein from gibbonape leukemia virus (GALV.fus) into the viral genome (15). Ineither case, the fusogenic oncolytic HSV showed strikinglyenhanced antitumor activity, compared with that of the nonfu-sogenic virus, when tested against locally established liver can-cer (15) or lung metastases of breast cancer (14).Received 11/12/02; revised 3/11/03; accepted 3/13/03.The costs of publication of this article were defrayed in part by thepayment of page charges. This article must therefore be hereby markedadvertisement in accordance with 18 U.S.C. Section 1734 solely toindicate this fact.1 Supported by institutional start-up funds.2 Present address: The Fifth Affiliated Hospital of Zhongshan Univer-sity, Zhuhai, China.3 To whom requests for reprints should be addressed, at Center for Celland Gene Therapy, Baylor College of Medicine, One Baylor Plaza,Houston, TX 77030. Phone: (713) 798-1256; Fax: (713) 798-1230; E-mail: [email protected] The abbreviations used are: EOC, epithelial ovarian cancer; HSV,herpes simplex virus; pfu, plaque-forming unit(s); FBS, fetal bovineserum; BAC, bacterial artificial chromosome; GFP, green fluorescentprotein.2727Vol. 9, 2727–2733, July 2003Clinical Cancer Research