Preclinical toxicology of oncolytic adenovirus-mediated cytotoxic and interleukin-12 gene therapy for prostate cancer

摘要

The purpose of this study was to examine the toxicity of combining oncolytic adenovirus-mediated cytotoxic and interleukin 12 (IL-12) gene therapy in a preclinical model to support future phase 1 trials. One hundred and twenty C57BL/6 male mice received an intraprostatic injection of saline ( n = 24) or an oncolytic adenovirus (Ad5-yCD/ mut TK_SR39 rep -mIL12) expressing two suicide genes and mouse IL-12 ( n = 96). The adenovirus was administered at three dose levels (1.3 × 106, 1.3 × 107, 1.3 × 108 vp/kg) followed by 2 weeks of 5-flurocytosine (5-FC) and gancliclovir (GCV) prodrug therapy. There were no premature deaths. Daily observations of animals did not reveal any obvious clinical problems throughout the 78-day in-life phase of the study. Animals in the highest adenovirus dose group exhibited lymphopenia and transaminitis on day 3, both of which resolved by day 17. Except for mild inflammation of the prostate and seminal vesicles, histopathology of major organs was largely unremarkable. IL-12 and interferon-gamma levels in prostate and serum peaked on day 3 and were either undetectable or returned to baseline levels by day 17. No adenoviral DNA was detected in serum in any group at any time point. The results demonstrate that local administration of an oncolytic adenovirus expressing two suicide genes and IL-12 is well tolerated and support moving this investigational approach into human trials. prs.rt("abs_end"); Introduction Oncolytic viral therapy is an investigational cancer treatment that has been evaluated in multiple disease settings using a variety of viral platforms including adenovirus, herpesvirus, measles virus, poxvirus, and others. 1 Based on hundreds of patients treated to date, this investigational approach has demonstrated a good overall safety profile and some strategies have shown signs of efficacy in randomized trials. Despite these encouraging results, it is uncertain whether oncolytic viral therapy is sufficiently robust to be efficacious when applied as a monotherapy. A major limitation is that viruses are immunogenic, and the resulting immune response restricts viral persistence and spread, as well as the effectiveness of repeated administrations. Although this limitation is desirable from a safety standpoint, it may reduce treatment efficacy depending on whether the immune response contributes to, or detracts from, antitumor activity overall. Hence, it may be necessary to arm such viruses with therapeutic genes or combine them with standard cancer treatments, or both, to push this promising strategy over the therapeutic threshold. For the past 20 years, we have been developing a multimodal approach that utilizes an oncolytic adenovirus platform armed with two cytotoxic genes. 2 ; 3 ; 4 ; 5 ; 6 ; 7 ; 8 ; 9 ; 10 ; 11 ; 12 We have evaluated the safety and potential efficacy of this approach in five clinical trials of prostate cancer. The approach has proven to be safe when applied alone or in combination with radiotherapy and antitumor activity has been demonstrated in multiple disease settings. In a randomized phase 2 trial, combining oncolytic adenovirus-mediated cytotoxic gene therapy with contemporary dose radiotherapy resulted in a 42% relative improvement in local tumor control without diminishing the patient's quality of life. 10 These encouraging results, and others, 6 , 12 lead us to believe that further refinement of this approach may ultimately lead to a successful treatment strategy. Although local tumor control is important, new cancer therapies must also target metastatic disease if they are to have an impact on survival. Hence, we recently incorporated interleukin 12 (IL-12) into our therapeutic platform. 13 IL-12 is a proinflammatory cytokine produced by antigen presenting cells that stimulates the innate and adaptive immune response, inhibits angiogenesis, and reverses the immune suppressive nature of the tumor milieu. 14 ; 15 ; 16 Although IL-12 has exhibited significant antitumor activity in preclinical models, its performance in the clinic has been modest largely because of severe toxicity when administered systemically. 17 Local administration of IL-12 may circumvent systemic toxicity without diminishing its therapeutic potential. In preparation for a phase 1 trial, we examined the toxicity of administering IL-12 intraprostatically via an oncolytic, replication-competent adenovirus. Results Study design One hundred and twenty C57BL/6 male mice received an injection of saline ( n = 24) or an oncolytic adenovirus (Ad5-yCD/ mut TK_SR39 rep -mIL12) expressing two suicide genes and mouse IL-12 ( n = 96). The adenovirus was injected intraprostatically at three dose levels (1.36 × 106, 1.36 × 107, 1.36 × 108 vp/kg) mimicking, on a weight basis, those to be used in future clinical t