Herpes simplex virus Us3(-) mutant as oncolytic strategy and synergizes with phosphatidylinositol 3-kinase-Akt targeting molecular therapeutics.
OBJECTIVE
Oncolytic herpes simplex virus (HSV) vectors have shown safety in clinical trials, but efficacy remains unsatisfactory. Novel HSV vectors that possess tumor selectivity with enhanced potency are therefore needed. The gene product of HSV Us3 protects virus-infected cells from apoptosis, a cellular pathway frequently dysfunctional in tumors. We hypothesized that Us3 mutants, whose replication would be inhibited by apoptosis in normal cells, would be selective for tumor cells.


METHODS
HSV mutants G207 (ribonucleotide reductase-/gamma34.5-), R7041 (Us3-), and R7306 (Us3 revertant) were tested in normal and tumor cells for viral replication, antitumoral potency, apoptosis induction, and Akt activation. Safety and biodistribution after systemic administration and antitumoral efficacy after intratumoral (i.t.) or i.v. administration were examined.


RESULTS
Us3 deletion results in up to 3-log replication inhibition in normal cells, which correlates with enhanced apoptosis induction. In contrast, R7041 replicates very well in tumor cells, showing 1 to 2 log greater yield than G207. In vivo, R7041 shows no signs of toxicity after systemic delivery in both immunocompetent and immunodeficient mice and shows preferential and prolonged replication in tumors compared with normal tissues. R7041 displays significant antitumoral efficacy after i.t. or i.v. administration. An additional feature of Us3 mutants is enhanced Akt activation compared with wild-type infection, which sensitizes cells to phosphatidylinositol 3-kinase-Akt inhibitors (LY294002, Akt inhibitor IV), shown by synergistic antitumoral activity in vitro and enhanced efficacy in vivo.


CONCLUSIONS
Us3 deletion confers enhanced tumor selectivity and antitumoral potency on herpes simplex virus-1 and provides for a novel mechanism of combination therapy with phosphatidylinositol 3-kinase-Akt-targeting molecular therapeutics.
Liu
Ta-Chiang
TC
Molecular Neurosurgery Laboratory, Brain Tumor Research Center, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA. tachiangliu@yahoo.com
Wakimoto
Hiroaki
H
Martuza
Robert L
RL
Rabkin
Samuel D
SD
D000818:Animals; D017209:Apoptosis; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D004789:Enzyme Activation; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000628:therapy*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018139:Simplexvirus / Q000378:metabolism*; D014018:Tissue Distribution; D014709:Vero Cells; D014779:Virus Replication
D053148:Caspase 3; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt