Adenoviral E4orf3 and E4orf6 proteins, but not E1B55K, increase killing of cancer cells by radiotherapy in vivo.
OBJECTIVE
Radiotherapy is widely used for treatment of many tumor types, but it can damage normal tissues. It has been proposed that cancer cells can be selectively sensitized to radiation by adenovirus replication or by using radiosensitizing transgenes. Adenoviral proteins E1B55K, E4orf3, and E4orf6 play a role in radiosensitization, by targeting the Mre11, Rad50, and NBS1 complex (MRN) and inhibiting DNA double-strand break (DSB) repair. We hypothesize that combined with irradiation, these adenoviral proteins increase cell killing through the impairment of DSB repair.


METHODS
We assessed the radiosensitizing/additive potential of replication-deficient adenoviruses expressing E1B55K, E4orf3, and E4orf6 proteins. Combination treatments with low-dose external photon beam radiotherapy were studied in prostate cancer (PC-3MM2 and DU-145), breast cancer (M4A4-LM3), and head and neck cancer (UT-SCC8) cell lines. We further demonstrated radiosensitizing or additive effects in mice with PC-3MM2 tumors.


RESULTS
We show enhanced cell killing with adenovirus and radiation combination treatment. Co-infection with several of the viruses did not further increase cell killing, suggesting that both E4orf6 and E4orf3 are potent in MRN inhibition. Our results show that adenoviral proteins E4orf3 and E4orf6, but not E1B55K, are effective also in vivo. Enhanced cell killing was due to inhibition of DSB repair resulting in persistent double-strand DNA damage, indicated by elevated phospho-H2AX levels at 24 h after irradiation.


CONCLUSIONS
This knowledge can be applied for improving the treatment of malignant tumors, such as prostate cancer, for development of more effective combination therapies and minimizing radiation doses and reducing side effects.
Liikanen
Ilkka
I
Haartman Institute & Finnish Institute for Molecular Medicine, University of Helsinki, Helsinki, Finland.
Dias
João D
JD
Nokisalmi
Petri
P
Sloniecka
Marta
M
Kangasniemi
Lotta
L
Rajecki
Maria
M
Dobner
Thomas
T
Tenhunen
Mikko
M
Kanerva
Anna
A
Pesonen
Sari
S
Ahtiainen
Laura
L
Hemminki
Akseli
A
D017504:Adenovirus E4 Proteins / Q000378:metabolism / Q000502:physiology*; D000260:Adenoviruses, Human / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001943:Breast Neoplasms / Q000532:radiotherapy; D045744:Cell Line, Tumor; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism / Q000532:radiotherapy* / Q000821:virology; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011836:Radiation Tolerance / Q000502:physiology*; D011879:Radiotherapy Dosage; D011897:Random Allocation; D014764:Viral Proteins / Q000378:metabolism / Q000502:physiology*
D017504:Adenovirus E4 Proteins; C553319:E1B55K protein, adenovirus; C553317:E4orf3 protein, adenovirus; C553318:E4orf6 protein, adenovirus; C468783:H2AX protein, human; D006657:Histones; D014764:Viral Proteins