Motivation: Can we reach a close marriage of diagnosis and therapeutics?

Dynamic monitoring of medical conditions is very meaningful for a disease’s management, especially for chronic diseases such as malignant cancer, which is heterogeneous and is constantly changing. As students of a medical university, we are especially interested in cell therapy which is a very promising approach in cancer treatment and has received a lot of success. However, dynamic monitoring of response of cell therapy as well as traditional remedies has remained a challenge. Disease monitoring using CT imaging is the current clinical practice for assessing response to targeted therapy, yet this approach does not fully represent the molecular and pathologic changes occurring in tumors during therapy. Repeat tissue biopsies of accessible cancer lesions have been used to provide insights into therapeutic decision-making but rarely capture the complexity of tumor heterogeneity and are invasive procedures with potential complications^[1]. Current liquid biopsies are sometimes not accurate and sensitive enough because of the low concentrations of the biomarkers. And the acknowledged biomarkers in blood are limited to this date.

So, it comes to us that whether we can combine diagnostic and therapeutic capabilities into a single device. We hope that a close marriage of diagnosis and therapeutics could provide therapies that are more specific to individuals and, therefore, more likely to offer improved prognoses.

Our inspiration: What other people have done?

Synthetic Biology in disease diagnosis

Inspired by Synthetic Biology, a lot of innovative diagnostic approaches have emerged in recent years. One strategy is to engineer cells with customized receptors as well as rewired signaling pathways, so that these cells could implement long-term monitoring of disease-related metabolites and biomarkers in bloodstream. Aizhan Tastanova et al. developed a Synthetic biology-based cellular biomedical tattoo for detection of hypercalcemia associated with cancer^[2]. They engineered HEK293 cells to ectopically express calcium sensing receptor (CaSR) rewired to a synthetic signaling cascade, leading to expression of tyrosinase, which synthesizes the black pigment melanin. These designer cells were microencapsulated and implanted subcutaneously. Thus, an elevation of hypercalcemia would produce a visible tattoo, enabling detection of asymptomatic cancer. In 2018, the iGEM team NTHU_Formosa also proposed a non-invasiveness and real-time tracking device, BioWatcher, to enable detection and autonomous report of biomarkers in the bloodstream. However, these detecting strategies can only detect soluble biomarkers in bloodstream but cannot discover lesions which are immobilized and are deep inside the body.

An alternative diagnostic strategy is the systemic delivery of probes that are selectively activated and generate signals in the presence of disease^[3-5]. A cell-based in vivo sensor for highly sensitive early cancer was reported by Amin Aalipour et al.^[5]. After adoptive transfer in colorectal and breast mouse tumor models, the engineered macrophages successfully migrated to the tumors and activated arginase-1 so that they could be detected by bioluminescence imaging and luciferase measured in the blood. In another study, bacteria were engineered to function in the mammalian gut as long term live diagnostics of inflammation, and performance was proved to be robust and durable^[4].

Development of synthetic receptors

Synthetic receptors that respond to extracellular inputs in a predictable manner is very important for disease detection. Indeed, the field of programmable receptor engineering has evolved rapidly^[6]. Chimeric antigen receptors (CARs), G-protein coupled receptors (GPCRs)^[7], synNotch^[8-10], MESA^[11], and GEMS^[12] are just some of the examples. The most well-known receptor among them perhaps is CAR, which is used in CAR-T and CAR-NK therapies^[13]. The synNotch receptors are more generalized than CARs since their intracellular domain can be customized as well as their extracellular scFV domain. However, it can only detect immobilized targets whereas MESA and GEMS can respond to soluble cues.

Our goal

This year, our aim is to develop a cell-based Theranostic system which is able to monitor cancer as well as combat it. The system has a core device and a monitoring device. The core device is a population of engineered NK cells, which can respond rapidly to transformed and stressed cells and have the intrinsic potential to extravasate and reach their targets in almost all body tissues^[13]. Just as the strategy that has been mentioned above, cells of the core device work like guards that patrol a patient’s body. Once they discover their enemies—cancer cells, they will attack the enemies and send out alarm signals. Thus, the biomarkers that are immobilized and deep inside a patient’s body will be transformed into a soluble form in bloodstream and will be received by the monitoring device.

The monitoring device is a group of designer cells that will be microencapsulated and implanted subcutaneously. Just like the biomedical tattoo cells^[2], the monitoring device will form a small pattern and visualize the disease conditions.

With our Theranostic system—Wukong, we hope we could provide patients with more individualized and specific therapies in the fight of cancer, and ultimately improve patient outcomes.

References

1. Phallen, J., et al., Early Noninvasive Detection of Response to Targeted Therapy in Non-Small Cell Lung Cancer. Cancer Res, 2019. 79(6): p. 1204-1213.
2. Tastanova, A., et al., Synthetic biology-based cellular biomedical tattoo for detection of hypercalcemia associated with cancer. Sci Transl Med, 2018. 10(437).
3. Kwong, G.A., et al., Mass-encoded synthetic biomarkers for multiplexed urinary monitoring of disease. Nat Biotechnol, 2013. 31(1): p. 63-70.
4. Riglar, D.T., et al., Engineered bacteria can function in the mammalian gut long-term as live diagnostics of inflammation. Nat Biotechnol, 2017. 35(7): p. 653-658.
5. Aalipour, A., et al., Engineered immune cells as highly sensitive cancer diagnostics. Nat Biotechnol, 2019.
6. Brenner, M., J.H. Cho, and W.W. Wong, Synthetic biology: Sensing with modular receptors. Nat. Chem. Biol., 2017. 13(2): p. 131-132.
7. Adeniran, A., et al., Detection of a Peptide Biomarker by Engineered Yeast Receptors. ACS Synth Biol, 2018. 7(2): p. 696-705.
8. Irvine, Darrell J., A Receptor for All Occasions. Cell, 2016. 164(4): p. 599-600.
9. Morsut, L., et al., Engineering Customized Cell Sensing and Response Behaviors Using Synthetic Notch Receptors. Cell, 2016. 164(4): p. 780-91.
10. Roybal, K.T., et al., Engineering T Cells with Customized Therapeutic Response Programs Using Synthetic Notch Receptors. Cell, 2016. 167(2): p. 419-432 e16.
11. Daringer, N.M., et al., Modular extracellular sensor architecture for engineering mammalian cell-based devices. ACS Synth Biol, 2014. 3(12): p. 892-902.
12. Scheller, L., et al., Generalized extracellular molecule sensor platform for programming cellular behavior. Nat Chem Biol, 2018. 14(7): p. 723-729.
13. Zhang, C., et al., Chimeric Antigen Receptor-Engineered NK-92 Cells: An Off-the-Shelf Cellular Therapeutic for Targeted Elimination of Cancer Cells and Induction of Protective Antitumor Immunity. Front Immunol, 2017. 8: p. 533.