A parainfluenza virus 5 (PIV5) with mutations in the P/V gene (P/V-CPI⁻) is restricted for spread in normal cells but not in cancer cells in vitro and is effective at reducing tumor burdens in mouse model systems. Here we show that P/V-CPI⁻ infection of HEp-2 human laryngeal cancer cells results in the majority of the cells dying, but unexpectedly, over time, there is an emergence of a population of cells that survive as P/V-CPI⁻ persistently infected (PI) cells. P/V-CPI⁻ PI cells had elevated levels of basal caspase activation, and viability was highly dependent on the activity of cellular inhibitor-of-apoptosis proteins (IAPs) such as Survivin and XIAP. In challenge experiments with external inducers of apoptosis, PI cells were more sensitive to cisplatin-induced DNA damage and cell death. This increased cisplatin sensitivity correlated with defects in DNA damage signaling pathways such as phosphorylation of Chk1 and translocation of damage-specific DNA binding protein 1 (DDB1) to the nucleus. Cisplatin-induced killing of PI cells was sensitive to the inhibition of wild-type (WT) p53-inducible protein 1 (WIP1), a phosphatase which acts to terminate DNA damage signaling pathways. A similar sensitivity to cisplatin was seen with cells during acute infection with P/V-CPI⁻ as well as during acute infections with WT PIV5 and the related virus human parainfluenza virus type 2 (hPIV2). Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish PI as well as the potential for combining chemotherapy with oncolytic RNA virus vectors.

IMPORTANCE There is intense interest in developing oncolytic viral vectors with increased potency against cancer cells, particularly those cancer cells that have gained resistance to chemotherapies. We have found that infection with cytoplasmically replicating parainfluenza virus can result in increases in the killing of cancer cells by agents that induce DNA damage, and this is linked to alterations to DNA damage signaling pathways that balance cell survival versus death. Our results have general implications for the design of safer paramyxovirus-based vectors that cannot establish persistent infection, the repurposing of drugs that target cellular IAPs as antivirals, and the combined use of DNA-damaging chemotherapy agents in conjunction with oncolytic RNA virus vectors.

副流感病毒5（PIV5）与在P / V基因（P / V-CPI突变^- ）被限制为在正常细胞传播而不是在癌细胞在体外和在降低在小鼠模型系统中肿瘤负荷有效的。在这里，我们显示P / V-CPI ^- HEp-2人喉癌细胞的感染导致大多数细胞死亡，但出乎意料的是，随着时间的流逝，出现了一群以P / V-生存的细胞CPI ^-持续性感染（PI）细胞。P / V-CPI ^-PI细胞的基础半胱天冬酶活化水平升高，并且活力高度依赖于细胞凋亡抑制蛋白（IAP）如Survivin和XIAP的活性。在具有外部凋亡诱导物的挑战性实验中，PI细胞对顺铂诱导的DNA损伤和细胞死亡更为敏感。这种增加的顺铂敏感性与DNA损伤信号通路中的缺陷相关，例如Chk1的磷酸化和损伤特异性DNA结合蛋白1（DDB1）转运到细胞核。顺铂诱导的PI细胞杀伤对野生型（WT）p53诱导蛋白1（WIP1）的抑制很敏感，该蛋白是一种磷酸酶，可终止DNA损伤信号传导途径。在P / V-CPI急性感染期间，细胞对顺铂的敏感性相似^-以及WT PIV5和相关病毒2型人类副流感病毒（hPIV2）的急性感染期间。我们的结果对不能建立PI的更安全的基于副粘病毒的载体的设计具有一般意义，并且对于将化学疗法与溶瘤性RNA病毒载体结合起来具有潜在的意义。

重要事项开发对癌细胞特别是对化学疗法具有抗性的癌细胞的效力增强的溶瘤病毒载体引起了极大的兴趣。我们发现，细胞质复制副流感病毒的感染可导致诱导DNA损伤的药剂杀死癌细胞的现象增加，这与DNA损伤信号通路的改变有关，从而平衡了细胞存活与死亡之间的关系。我们的结果对不能建立持续感染的更安全的基于副粘病毒的载体的设计，将靶向细胞IAP的药物重新用作抗病毒药物以及将DNA破坏性化学治疗剂与溶瘤性RNA病毒载体联合使用具有普遍意义。