Abstract
Nasopharyngeal carcinoma (NPC) is causally linked to Epstein‐Barr virus (EBV), and the EBV oncoprotein, latent membrane protein 1 (LMP‐1), is expressed in the majority of NPCs. LMP‐1 upregulates antiapoptotic genes, including bcl‐2, and Bcl‐2 protein is overexpressed in NPC. Given the antiapoptotic and chemoprotective effects of Bcl‐2, it represents a rational therapeutic target in NPC. We have investigated the antitumor and chemosensitizing effects of the Bcl‐2 antisense oligodeoxynucleotide G3139 (oblimersen, Genasense) in NPC. For these studies, we used the C666‐1 line, a stably infected NPC‐derived line that co‐expresses LMP‐1 and Bcl‐2. We have shown that G3139 treatment of C666‐1 in vitro caused sequence‐dependent suppression of Bcl‐2 protein, inhibition of cell growth and enhanced sensitivity to cisplatin (CDDP), as measured by increased antiproliferative and apoptotic effects. In vivo, G3139 treatment (25 mg/kg every 3 days × 5 doses) delayed engraftment and significantly inhibited growth of established C666‐1 xenografts in SCID mice compared to control oligo‐treated animals. However, G3139 alone did not prevent engraftment or cure established tumors in any animals. In contrast, G3139 treatment (25 mg/kg every 3 days × 5 starting on day 7) in combination with CDDP (8 mg/kg on day 14) completely abrogated tumor engraftment in 80% of animals compared to CDDP (0%) or CDDP + control oligo (0%). When treatment was delayed until tumor was established, G3139 in combination with CDDP significantly inhibited tumor growth compared to CDDP or CDDP + control oligo, and cured 69% animals with established tumors. No animals treated with G3139, CDDP or CDDP + control oligo were cured. Tumor burden and response to treatment correlated with EBV DNA load in serum, measured by real‐time PCR. Western blots of tumor extracts obtained during oligo treatment showed that Bcl‐2 levels were significantly decreased in G3139‐treated animals. Our studies have demonstrated that the Bcl‐2 antisense oligodeoxynucleotide, G3139, has proapoptotic effects in C666‐1, and in combination with CDDP, is curative in C666‐1 NPC xenograft tumors in vivo. The sequence‐dependency of these effects is consistent with an antisense mechanism. These studies suggest that Bcl‐2 may represent a biologically relevant target for the development of novel combinatorial therapies for NPC. © 2006 Wiley‐Liss, Inc.