Abstract
Adenovirus-mediated sensitization of cancer cells to cytotoxic drugs depends on simultaneous interactions of early viral genes with cell death and survival pathways. It is unclear what cellular factors mediate these interactions in the presence of DNA-damaging drugs. We found that adenovirus prevents Chk1-mediated checkpoint activation through inactivation of Mre11 and downregulation of the pChk1 adaptor-protein, Claspin, in cells with high levels of DNA-damage induced by the cytotoxic drugs gemcitabine and irinotecan. The mechanisms for Claspin downregulation involve decreased transcription and increased degradation, further attenuating pChk1-mediated signalling. Live cell imaging demonstrated that low doses of gemcitabine caused multiple mitotic aberrations including multipolar spindles, micro- and multi-nucleation and cytokinesis failure. A mutant virus with the anti-apoptotic E1B19K-gene deleted (AdΔ19K) further enhanced cell killing, Claspin downregulation, and potentiated drug-induced DNA damage and mitotic aberrations. Decreased Claspin expression and inactivation of Mre11 contributed to the enhanced cell killing in combination with DNA-damaging drugs. These results reveal novel mechanisms that are utilised by adenovirus to ensure completion of its life cycle in the presence of cellular DNA damage. Taken together, our findings reveal novel cellular targets that may be exploited when developing improved anti-cancer therapeutics.
Highlights
Replication-selective oncolytic adenoviral mutants are promising as future cancer therapeutics because of their efficient lysis of a broad range of adenocarcinoma types, including drug-resistant cancers, with demonstrated clinical safety [1, 2]
To take advantage of the virus-mediated enhancement of cancer cell killing in combination with DNA-damaging drugs we developed mutants with the anti-apoptotic E1B19K gene deleted in addition to tumour-selective deletions including the E1ACR2-domain (e.g. Ad∆∆) [11, 24, 25]
The adenoviral mutant Ad∆19K synergises with gemcitabine and irinotecan by enhancing apoptotic death in pancreatic cancer cells
Summary
Replication-selective oncolytic adenoviral mutants are promising as future cancer therapeutics because of their efficient lysis of a broad range of adenocarcinoma types, including drug-resistant cancers, with demonstrated clinical safety [1, 2]. To avoid elimination of the infected cells by cellular defence mechanisms, the early viral E1B, E3 and E4 gene-products act to inhibit apoptosis, immune response activation and DNA-damage repair. These viral functions have been exploited to engineer oncolytic mutants that are unable to propagate in normal cells but efficiently replicate in cancer cells with deregulated cell survival and apoptosis pathways [1, 2]. The clinically most efficacious replication-selective mutants harbour a small deletion of the E1ACR2-domain (e.g. dl922947 and Ad∆24) to ablate pRb-binding that results in potent anti-tumour efficacy in various solid tumours with deregulated cell cycle and limited toxicity to normal tissue Significant clinical responses have only been reported in combination with cytotoxic drugs and/or radiation therapy [1, 5, 7,8,9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
