Abstract P6-16-02: Oncolytic viral therapy enhances the survival of mice in a novel model of breast cancer brain metastases
Authors: Meisen W Hans , Dubin Samuel , Sizemore Steven , Mathsyaraja Haritha , Thies Katie , Lehman Norm , Boyer Peter , Jaime-Ramirez Alena C , Elder J Bradley , Powell Kimerly , Ostrowski Michael , Kaur Balveen 
Published: May 2015

Abstract
Breast cancer [BC] is one of the leading causes of brain metastases. The 2 year survival rate of patients with breast cancer brain metastases [BM] is less than 2%. Oncolytic viruses exploit the aberrant molecular and genetic pathways found in cancer cells to selectively replicate in and destroy tumors while sparing normal tissues. Here, we demonstrate the oncolytic Herpes Simplex Virus [HSV-1], 34.5ENVE, can specifically target and destroy BC brain metastases. The 34.5ENVE virus expresses anti-angiogenic Vstat120 and its replication is transcriptionally driven by the cancer specific promoter Nestin. Vstat120 expression is reduced in brain, renal, and gastric cancers, however its expression status in BC is not known. Analysis of The Cancer Genome Atlas revealed a 52% reduction in Vstat120 expression in invasive ductal breast carcinomas [n=69] compared to normal breast tissue [n=389; P&lt;0.0001]. Reduced Vstat120 expression was also associated with decreased disease free survival in BC patients [n=324; P&lt;0.03]. An examination of Vstat120 expression in 50 breast cancer cell lines from the Neve et al dataset showed Vstat120 mRNA levels were reduced in 38% of BC cell lines compared to the MCF-10A epithelial cell line [19 of 50 cell lines]. These analyses suggested BC patients may benefit from the re-expression of anti-angiogenic Vstat120. Nestin is up-regulated in several metastatic cancers, and its expression correlates with reduced survival in BC patients. In a cohort of 166 patients stratified by median Nestin expression, we observed Nestin to be significantly associated with an increased incidence of brain and lung metastases [n=164; P&lt;0.02]. Additional analysis of the Neve et al. microarray dataset showed Nestin was upregulated in 100% of the BC cell lines examined [50 of 50]. These results suggest that Nestin expression may be a strong therapeutic target for BC. 34.5ENVE was cytotoxic to human BC cells of varying subtypes in vitro including the HER2+ and triple negative BCs known to frequently metastasize to the brain. Since 34.5ENVE replication is driven by a Nestin promoter, we compared the cytotoxicity of 34.5ENVE with a similar virus lacking Nestin driven ICP34.5 expression. We observed a 54.14% and 24.44% increase in killing in the MDA-MB-468 and MDA-MB-231 cell lines in the Nestin-driven 34.5ENVE virus as compared to a virus lacking ICP34.5, respectively [P&lt;0.001]. This is the first study to specifically use Nestin expression to target BC. To test the therapeutic efficacy of 34.5ENVE against BM in vivo, we created a novel, immune competent BC BM model using Met-1 and DB-7 murine BC cell lines. Intracranial implantation of these cells resulted in tumors which recapitulated the human BM tumor biology. Treatment of mice with established Met-1 BM tumors with a single, intratumoral dose of 34.5ENVE resulted in significant tumor regression [via MRI] and increased survival. Similarly, mice bearing intracranial DB-7 tumors treated with a single dose of 34.5ENVE showed a doubling of median survival compared to control treated mice [median survival 17 days vs 34 days, respectively; P&lt;0.0004]. The results of these studies warrant further investigation of oncolytic 34.5ENVE viral therapy to treat established BC brain metastases.
Citation Format: W Hans Meisen, Samuel Dubin, Steven Sizemore, Haritha Mathsyaraja, Katie Thies, Norm Lehman, Peter Boyer, Alena C Jaime-Ramirez, J Bradley Elder, Kimerly Powell, Michael Ostrowski, Balveen Kaur. Oncolytic viral therapy enhances the survival of mice in a novel model of breast cancer brain metastases [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-16-02.