To combat heart failure, we designed a targeting device Cartin to implement RyR2-specific inhibition of phosphorylation. A heart-failure-regulatory BNP promoter and heart-tissue-specific vector AAV9 were utilized to increase the device’s specificity and biosafety. The whole project could be divided into three aspects: AAV9, BNP promoter, and AR185, respectively. Here, we will make an analogy between Cartin and homing missile to explain how the device works. The propulsion part (AAV9) is responsible for transporting the missile to the corresponding position. AAV9 can deliver the target gene sequence to the failing heart. The BNP promoter is responsible for precision guidance, which is similar to a targeting system. BNP promoter will only initiate when the heart is damaged and is a controllable switch of gene expressing. The warhead (AR185) is the center of the device that combats heart failure.

Propulsion part: AAV9

Adeno-associated virus (AAV) is a non-enveloped virus that can be engineered to deliver DNA to target cells and has attracted a significant amount of attention in the field of gene therapy. It has various advantages such as high transduction efficiency, low probability of immune response, and long-term gene transfer potential in slowly dividing or non-dividing cells. So far, several AAV serotypes have been discovered, and each of them has diverse tissue specificity. For example, AAV serotype 9 has a high cardiomyocyte specificity, thus has emerged as a new and promising vector for gene therapy of heart diseases. In our experiment, we verified that AAV-9 vector has a high specificity and efficiency.

Precision guidance: BNP promoter

Brain natriuretic peptide (BNP), also known as B-type natriuretic peptide, is a hormone secreted by cardiomyocytes in the heart ventricles. It has been regarded as an important biomarker in diagnosis of heart failure (HF), for its level is highly related to the severity of HF. The activity of BNP promoter remains low in normal hearts and elevates dramatically in that of patients with HF. Based on the qualities mentioned above, it is natural to think that we can utilize BNP promoter to control gene expression in HF gene therapy.

Warhead: AR185

AR185 is a RyR2-specific VHH antibody which is designed to inhibit RyR2 phosphorylation. It was isolated from a camelid VHH antibody library via phage display screening which is a technique received the Nobel Prize in Chemistry this year (2018). VHH, also called nanobody, derives from the variable domains of camelid heavy-chain-only antibody. Compared to the conventional antibodies, VHH has a much lower molecular weight, is a qualified candidate for intracellular antibody.

The mechanism of BNP promoter driven AR185 inhibiting RyR2 phosphorylation

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