Fiber knob modifications overcome low, heterogeneous expression of the coxsackievirus-adenovirus receptor that limits adenovirus gene transfer and oncolysis for human rhabdomyosarcoma cells

Exploiting the lytic life cycle of viruses has gained recent attention as a n anticancer strategy (oncolysis), To explore the utility of adenovirus (Ad )mediated oncolysis for rhabdomyosarcoma (RMS), we tested RMS cell lines fo r Ad gene transduction and infection. RMS cells were variably transduced by Ad. Compared with control cells, RMS cells were less sensitive or even res istant to oncolysis by wild-type virus. RMS cells expressed the Ad internal ization receptors, or, integrins, but had low or undetectable expression of the major attachment receptor, coxsackievirus-Ad receptor (CAR), Mutant Ad s with ablated CAR binding exhibited only 5-20% of transgene expression in RMS cells seen with a wildtype vector, suggesting that residual or heteroge neous CAR expression mediated the little transduction that was detectable. Immunohistochemical analysis of archived clinical specimens showed little d etectable CAR expression in five embryonal and eight alveolar RMS tumors. S table transduction of the cDNA for CAR enabled both efficient Ad gene trans fer and oncolysis for otherwise resistant RMS cells, suggesting that poor C AR expression is the limiting feature. Gene transfer to RMS cells was incre ased >2 logs using Ads engineered with modified fiber knobs containing eith er an integrin-binding RGD peptide or a polylysine peptide in the exposed H I loop. The RGD modification enabled increased oncolysis for RMS cells by a conditionally replicative Ad, Ad Delta 24RGD, harboring a retinoblastoma-b inding mutation in the E1A gene. Thus, the development of replication-compe tent vectors targeted to cell surface receptors other than CAR is critical to advance the use of Ad for treating RMS.