Initial testing of the replication competent Seneca Valley virus (NTX-010) by the pediatric preclinical testing program

Abstract

Background: Seneca Valley virus (NTX-010) is a non-recombinant, replication competent RNA virus that is undergoing phase 1 clinical trials in adults for tumors with neuroendocrine characteristics. Here we have evaluated the antitumor activity of NTX-010 administered systemically.

Procedures: In vitro NTX-010 was tested against 23 cell lines exposed for 96 hr at 1 x 10(-4) to 10(4) viral particles (vp)/cell. In vivo NTX-010 was administered intravenously once at 3 x 10(12) vp/kg. Three measures of antitumor activity were used: (1) an objective response measure modeled after the clinical setting; (2) a treated to control (T/C) tumor volume measure; and (3) a time to event (fourfold increase in tumor volume for solid tumor models), measure based on the median event-free survival (EFS) of treated and control animals for each xenograft.

Results: In vitro NTX-010 demonstrated a marked cytotoxic effect in a subset of the cell lines from the neuroblastoma, Ewing sarcoma, and rhabdomyosarcoma panels. In vivo the most consistent activity was observed for the rhabdomyosarcoma and the neuroblastoma panels, with all four of the alveolar rhabdomyosarcoma xenografts and four of five neuroblastoma xenografts achieving CR or maintained CR. Objective responses were also observed in the rhabdoid tumor, Wilms tumor, and glioblastoma panels.

Conclusions: NTX-010 demonstrated a high level of activity both in vitro and in vivo. Further analysis of existing testing and molecular characterization data may help define the biological characteristics of cancer cells that are associated with response to NTX-010.

Figure 1

NTX-010 in vitro activity. (A) graphically represents the relative potency of NTX-010 against each cell line with each point representing the IC₅₀ of an individual line. (B) shows the cell number (% control) at the highest NTX-010 concentration tested (1×10⁴ vp/cell). Each of the 9 cell lines that show more than 90% inhibition to NTX-010 at this concentration are in either the rhabdomyosarcoma, Ewing sarcoma, or neuroblastoma panels. (C) Representative dose-response data for sensitive (Rh18) and (D) insensitive (RD) cell lines exposed to NTX-010.

Figure 2

NTX-010 in vivo objective response activity. Left: The colored ‘heat map’ depicts group response scores. A high level of activity is indicated by a score of 6 or more, intermediate activity by a score of ≥ 2 but < 6, and low activity by a score of < 2. Right: representation of tumor sensitivity based on the difference of individual tumor lines from the midpoint response (stable disease). Bars to the right of the median represent lines that are more sensitive (objective responses), and to the left are tumor models that are less sensitive (non-objective response). Red bars indicate lines with a significant difference in EFS distribution between treatment and control groups, while blue bars indicate lines for which the EFS distributions were not significantly different.

Figure 3

NTX-010 activity against neuroblastoma xenografts. Kaplan-Meier curves for EFS, median relative tumor volume graphs, and individual tumor volume graphs are shown for each line. (A) NB-SD (B) NB-1771, (C) NB-1643, (D) NB-1691, (E) NB-EBc1. Controls (gray lines); Treated (black lines).

Figure 4

NTX-010 activity against rhabdomyosarcoma xenografts. Kaplan- Kaplan-Meier curves for EFS, median relative tumor volume graphs, and individual tumor volume graphs are shown for rhabdomyosarcoma lines: (A) Rh-10 (B) Rh28, (C) Rh30, (D) Rh30R. Controls (gray lines); Treated (black lines).

Figure 5

Gene expression (Affymetrix U133 Plus 2.0) in PPTP cell lines and xenografts as visualized using GeneSifter software (VizX Labs, Seattle, WA) for selected genes that serve as markers for cells of neuroendocrine origin. Gray indicates an absent call from Affymetrix quality control. Gene expression analysis methods are as previously described [34]. NCAM = neural cell adhesion molecule 1 (NCAM1, CD56); SYP = synaptophysin; CHGA = chromogranin A; and NRCAM = neuronal cell adhesion molecule