Noninvasive imaging and radiovirotherapy of prostate cancer using an oncolytic measles virus expressing the sodium iodide symporter

Abstract

Prostate cancer cells overexpress the measles virus (MV) receptor CD46. Herein, we evaluated the antitumor activity of an oncolytic derivative of the MV Edmonston (MV-Edm) vaccine strain engineered to express the human sodium iodide symporter (NIS; MV-NIS virus). MV-NIS showed significant cytopathic effect (CPE) against prostate cancer cell lines in vitro. Infected cells effectively concentrated radioiodide isotopes as measured in vitro by Iodide-125 ((125)I) uptake assays. Virus localization and spread in vivo could be effectively followed by imaging of (123)I uptake. In vivo administration of MV-NIS either locally or systemically (total dose of 9 x 10(6) TCID(50)) resulted in significant tumor regression (P < 0.05) and prolongation of survival (P < 0.01). Administration of (131)I further enhanced the antitumor effect of MV-NIS virotherapy (P < 0.05). In conclusion, MV-NIS is an oncolytic vector with significant antitumor activity against prostate cancer, which can be further enhanced by (131)I administration. The NIS transgene allows viral localization and monitoring by noninvasive imaging which can facilitate dose optimization in a clinical setting.

Figure 1

Replication and cytopathic effect of MV-NIS on prostate cancer cell lines and in vitro Iodide-125 (¹²⁵I) uptake of cells infected with MV-NIS. (a) Schematic representation of measles virus–sodium iodide symporter (MV-NIS). The complementary DNA encoding for the human thyroidal NIS was inserted downstream of the hemagglutinin (H) gene (N, nucleoprotein gene; P, phosphoprotein gene; M, matrix protein gene; F, fusion protein gene; L, large protein gene). (b) MV-NIS efficiently replicates in PC-3, DU-145, and LNCaP prostate cancer cells as demonstrated by one-step growth curves for cell-associated virus. (c) Cytopathic effect of MV-NIS on PC-3, DU-145, and LNCaP cells at multiplicity of infection (MOI) = 1.0. Cell viability was determined by the cell proliferation kit I (MTT) colorimetric assay. Monolayer cell cultures were completely eradicated by day 7. (d) In vitro Iodide-125 (¹²⁵I) uptake of prostate cancer cells infected with MV-NIS with or without potassium perchlorate (KClO₄). Prostate cancer cell lines were infected with MV-NIS at a MOI of 1.0. Infected cells cocultured with KClO₄, a competitive inhibitor of iodide uptake by NIS, were used as controls. Significantly more radioiodide uptake was observed in MV-NIS-infected cells as compared to controls in all prostate cancer cell lines tested (P < 0.05 for all comparisons). Results are presented as the means of three independent experiments ± SEM.

Figure 2

In vivo MV-NIS infection of prostate cancer xenografts. Histological sections reveal persistent infection and extensive syncytia formation in LNCaP xenografts 14 days after a single intravenous (IV) administration of 1.5 × 10⁶ TCID₅₀ of measles virus–sodium iodide symporter (MV-NIS). (a) Hematoxylin and eosin (H&E) staining of LNCaP tumor 14 days after IV MV-NIS injection. Extensive syncytia formation within the tumor is shown (arrow) (original magnification ×200). (b) in situ hybridization for MV-NIS N mRNA confirms viral replication in these tumors (original magnification ×200).

Figure 3

In vivo imaging of prostate cancer tumors infected with MV-NIS. Mice bearing subcutaneous LNCaP tumor xenografts on their right flank received a single intratumoral (IT) or intravenous (IV) dose of 1.5 × 10⁶ TCID₅₀ of measles virus–sodium iodide symporter (MV-NIS). MV-NIS infection led to strong, localized, functional NIS expression on the prostate cancer cells resulting in significant ¹²³I uptake. Representative radioiodide images are shown. Strong positive tumor ¹²³I uptake is seen 4 days after IT administration of MV-NIS (a) or 14 days after IV administration of MV-NIS (b). Quantification of radioiodide uptake showed significant uptake and retention of the isotope in the tumor 4 days after IT injection (c). Similarly, significant ¹²³I uptake and retention were observed 14 days after IV administration of MV-NIS (d). Error bars in c,d indicate the SD from the mean.

Figure 4

In vivo monitoring of MV-NIS infection over time. Two mice harboring LNCaP xenografts received a single IV injection of 1.5 × 10⁶ TCID₅₀ measles virus–sodium iodide symporter (MV-NIS) and viral biodistribution and kinetics were monitored by ¹²³I imaging. Initially, MV-NIS carried by the blood supply into the xenograft could be detected in small, localized sites inside the tumor. By day 14, the replicating virus had spread extensively throughout the tumor mass and strong, persistent infection could be detected for as long as 36 days. MV-NIS replication inside the tumor of mouse A resulted in significant partial regression of the growth that relapsed when the virus was cleared (negative uptake signal). Mouse B exhibited tumor growth arrest (stable disease) due to persistent MV-NIS infection. The virus was ultimately cleared from the mouse and tumor growth was reinstated.

Figure 5

Oncolytic activity of MV-NIS administered IT or IV in a subcutaneous LNCaP prostate cancer model. Mice (n = 5 per group) received a single intratumoral (IT) or intravenous (IV) dose of 1.5 × 10⁶ TCID₅₀ measles virus–sodium iodide symporter (MV-NIS) or six injections (IT or IV) of the virus at a total dose of 9 × 10⁶ TCID₅₀ or equivalent control regimens of UV-inactivated MV-NIS. All mice treated with six MV-NIS doses injected either IT or IV were alive by day 120 post-treatment initiation (these two curves completely overlap in a straight line) and survived longer as compared to animals treated with a single viral dose. Mice treated with a single IT or IV dose of MV-NIS still had significantly longer survival compared to the UV-inactivated controls (P < 0.05).

Figure 6

Radiovirotherapy of prostate cancer tumors. Mice (n = 5 per group) bearing subcutaneous LNCaP xenografts received a single intratumoral (IT) or intravenous (IV) dose of 1.5 × 10⁶ TCID₅₀ measles virus–sodium iodide symporter (MV-NIS) or UV-inactivated MV-NIS with or without subsequent ¹³¹I administration (1 mCi/mouse injected intraperitoneally 4 days after virus administration). There was significant suppression (P < 0.05) of tumor growth in the combined IT radiovirotherapy group (a) at day 25 and in the combined IV radiovirotherapy group (b) at day 27 when the plots were censored because of deaths occurring in the control and single-agent treatment groups. Tumor volumes are expressed as the percentage relative to the values on the day of ¹³¹I injection in each group and plotted against days after MV-NIS treatment. Points indicate mean; bars, SEM. (c) Mice in the IT radiovirotherapy group had significantly longer survival compared to the single-agent MV-NIS group (P < 0.05). (d) Similarly, combined IV radiovirotherapy significantly increased survival compared to single-agent MV-NIS (P < 0.05).