Induction of apoptosis in BCL‐2‐expressing rat prostate cancer cells using the Semliki Forest virus vector

Abstract

The Semliki Forest virus (SFV) vector is a transient RNA expression vector that has an inherent p53-independent apoptosis-inducing property. It is administered as recombinant SFV particles (rSFV) that undergo 1 round of replication only and express a gene cloned into the multicloning site. In our study we have investigated the ability of the SFV vector to induce apoptosis and inhibit tumour growth in rat prostate cancer (AT3-Neo) cells expressing the Bcl-2 oncogene (AT3-Bcl-2 cells), which normally inhibits apoptosis. rSFV expressing the enhanced green fluorescent protein (EGFP) gene (rSFV-EGFP), or recombinant RNA transfected into cells by electroporation, induced delayed apoptosis in AT3-Bcl-2 cells. SFV-mediated expression of a cloned pro-apoptotic Bax gene by the vector, however, enhanced apoptosis induction both in AT3-Bcl-2 cells and standard BHK-21 cells. Such Bax-expressing particles could be produced only at low titers compared to EGFP-expressing particles under standard conditions for particle production, but lowering the incubation temperature for particle production to 33°C partially alleviated this effect. Bax-expressing particles were shown to inhibit the growth of AT3-Neo and AT3-Bcl-2 tumours in nude mice, as did high titre EGFP-expressing particles. It is concluded that SFV recombinant particles have potential as antitumour agents to treat apoptosis-resistant tumours.

Regression of mouse tumours and inhibition of metastases following administration of a Semliki Forest virus vector with enhanced expression of IL-12

“…SFV vectors have an inherent p53-independent apoptosis inducing capability, 6 which has been successfully used to treat tumours in nude mice, 7,37 and it is likely that this operates also for the vectors used in this study. However, the presence of the enhancer in rSFV10-E-IL12 is unlikely to increase this inherent apoptosis induction since all cells infected by the unenhanced vector undergo apoptosis and the vector does not spread intercellularly.…”

“…However, the presence of the enhancer in rSFV10-E-IL12 is unlikely to increase this inherent apoptosis induction since all cells infected by the unenhanced vector undergo apoptosis and the vector does not spread intercellularly. 6,7,37 The enhanced ability of this vector to destroy tumour cells must therefore result from the induction of enhanced IL-12 secretion. IL-12 has a potent proinflammatory activity that may contribute to the antitumour effect.…”

Biology and application of alphaviruses in gene therapy

“…Additionally, the expression of the proapoptotic gene Bax reduced the growth of AT3-Neo and AT3-Bcl2 tumors in nude mice. 25 A major issue of concern has been the potential spread of virus into vital organs and especially into the central nervous system after systemic delivery of alphaviruses. For this reason, several attempts have been made to target alphaviruses to specific cell types or tissue.…”

Treatment of rapidly growing K-BALB and CT26 mouse tumours using Semliki Forest virus and its derived vector

“…As these tumours are relatively fast-growing, treatment of K-BALB tumours with VLPs in nude mice was ineffective, in contrast to the results obtained previously for the more slowly growing tumours. 13,14 VLPs expressing the antigenic viral protein E2 (rSFV-p62-6k) were employed in the hope of enhancing the Figure 6 Stimulation indices of splenocytes to SFV4 antigens from mice treated with rSFV-p62-6k VLPs (a) and SFV4 (b). Splenocytes were incubated in triplicate with UV inactivated SFV4 for 72 h and levels of IFN-g secretion were determined by capture ELISA.…”

“…13,14 Immunized nu/nu mice showed a better response than naïve mice at day 15 with treated tumours at 77.7% of the controls compared with 92.7%, but over the total duration of the experiment this difference was not statistically significant (Table 1).…”