brain tumors prevented 100% with shrna in mice

Sounds like a job for BLT's multiple-promoter expression cassettes for simultaneous delivery of RNAi.

http://pharmapage.info/2011/10/researchers-find-coupling-of-proteins-promotes-glioblastoma-development-17/

Here's a little extract from the article:-

"Blocking either FoxM1 or beta-catenin function strongly influenced whether mice injected with glioblastoma cells developed brain tumors. Most dramatically, blocking FoxM1 with short hairpin RNA completely prevented development of brain tumors in 38 mice, while all 20 with unimpeded FoxM1 developed tumors."