Oncolytic adenovirus programmed by synthetic gene circuit for cancer immunotherapy

For the first time, we improve the specificity and controllability of oncolytic adenovirus with synthetic gene circuit switch and mathematical simulation for liver cancer therapy.
Oncolytic adenovirus programmed by synthetic gene circuit for cancer immunotherapy

Oncolytic virus is a natural or engineered virus that can cause specific cancer cell lysis due to selective replication. Oncolytic adenovirus kills tumor cells through multiple mechanisms: lyse tumor cells directly; virus itself can active immune responses, turning the “cold”tumor to “hot”tumor; express immune effectors and therapeutic drugs which can activate anti-tumor immune responses or kill tumor cells. To achieve selective replication of oncolytic adenovirus, two general strategies have been adopted: 1) tumor mutation compensates viral genome deletion; 2) cancer specific promotor controls adenoviral E1 gene transcription.However, the existing regulatory mechanisms are relatively simple and unable to effectively deal with issues such as lack of appropriate tumor markers or mutations, immunosuppression in tumor microenvironment and off-target effect. Although promising clinical results have been reported by using oncolytic viral therapy, how to improve the specificity and controllability of oncolytic adenovirus is still a great challenge.

Synthetic biology can integrate multiple genetic elements into one gene circuit to perform precise biological functions in live cells. With the aim to solve the current problems of oncolytic adenoviral therapy, we designed a controllable and effective gene switch circuit to regulate selective replication of oncolytic adenovirus in specific type of cancer cells. As a proof of concept, we focus on targeting hepatocellular carcinoma cells in this study. Firstly, we screened and optimized HCC specific promoter and microRNA sensors. We constructed the gene switch circuit with these artificial genetic components to control the selective expression of adenoviral E1A gene in tumor cell. We found that the gene switch circuit operates robustly to potential leaky expression in cultured human cells as well as in mouse models. Then we developed a hierarchical cloning method to quickly assemble the synthetic oncolytic adenoviruses (synOV). 

Next, we demonstrated that the synOV can selectively kill HCC in cell culture and the intratumor injection of the synOV can efficiently inhibit tumor growth in xenografted mouse model. To further improve the therapeutic efficacy of synOV, we cloned different immune effector genes into synOV. By testing in the immunocompetent mouse model, we showed that the synOV treatment can trigger a long-standing tumor inhibition, which is likely due to a synergistic effect on promoting local lymphocyte cytotoxicity and systematic vaccination. Indeed, we found that the treatment of synOV that encodes immune effectors can result in the accumulation of cytotoxicity T cells in the immunocompetent mouse model. 

Furthermore, we developed a mathematic model and analyzed the key factors affecting the therapeutic efficacy of the combination of oncolytic adenovirus and immune effector in silico. These findings provide a general guideline for further optimization of the synOV therapeutic efficacy either alone or in combinations.

In summary, by taking a synthetic-biology approach, we design and construct a programable oncolytic adenovirus for liver cancer treatment. This study provides an effective strategy to improve the specificity and efficacy of oncolytic adenovirus, which may lead to an innovative immunotherapy for a variety of cancers.

By Huiya Huang, Weixi Liao and Zhen Xie