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The king of cancer


Cancer remains one of today's most pressing health challenges, with pancreatic cancer notably referred to as 'the king of cancer' due to its alarmingly low five-year survival rate1^1. According to the statistics of China's National Cancer Center2^2 and GLOBOCAN 20203^3, pancreatic cancer ranks 7th in the incidence rate of malignancy in males and 11th in females, and 6th in the mortality rate in China (Fig.1). In America, pancreatic cancer is currently the fourth-leading cause of cancer-related deaths and is projected to rise to the second-leading cause within the next two to three decades5^5.


Figure 1

Figure 1 | Estimated age-standardized incidence and mortality rate of cancer at ages <85 years in China. The bold yellow box highlights the statistics of pancreatic cancer. a, Males. b, Females. Graph production: Global Cancer Observatory (http://gco.iarc.fr)3.


​Among several subtypes of pancreatic cancer, pancreatic ductal adenocarcinoma (PDAC) stands out as the most common form of this malignancy7^7. Unfortunately, conventional treatment methods have shown limited efficacy in combatting PDAC due to the complex anatomical surroundings of the pancreas and immune escape (Fig.2). Moreover, with highly aggressive nature, pancreatic cancer is characterized by its demonstrating perineural and vascular local growth, as well as early distant metastases that often prevent curative surgical resection in the majority of patients5^5. All of the factors mentioned above collectively contribute to the disheartening reality that the 5-year survival rate for pancreatic cancer has not shown significant improvement over the past few decades.


Figure 2

Figure 2 | ​Several reasons contribute to the poorly prognosis of pancreatic cancer. a, Anatomical location of pancreas8^8. The pancreas is surrounded by multiple organs, which makes many patients with occult manifestations at an early stage. b, TME of pancreatic cancer9^9. Hypoxia, dense fiber packaging, interstitial high pressure, and immunosuppressive environment prevent drugs from effectively reaching the tumour and exerting their effects.


Existing approach


​Excitingly, the application of neoadjuvant therapy has injected new vitality into the treatment of pancreatic cancer. Notably, stereotactic body radiation therapy (SBRT) is regarded as an emerging radiotherapy technique, capable of achieving high local control rates with acceptable toxicity10,11^{10,11}. However, SBRT necessitates precise spatial localization of both the tumor and potential metastatic lesions for accurate targeting, failing which, unexpected side effects may occur outside the intended area. At present, positron emission tomography (PET) is extensively employed for monitoring the situation of tumours in clinical practice, including size, infiltration, and distant metastasis. It uses specialized radioactive glucose probes (18^{18}F-fludeoxyglucose, 18^{18}F-FDG) or other probes to differentiate them from normal tissues, capitalizing on the characteristic high metabolic activity of tumours12^{12}. However, after the injection of imaging agents, some patients may experience side effects such as nausea, allergies, gastrointestinal reactions, and in very rare cases, even fatalities. Additionally, conditions like inflammation and autoimmune diseases may manifest similar heightened metabolic responses to tumours, thus complicating the differential diagnosis process. The substantial costs associated with infrastructure and examination fees present yet another noteworthy hindrance to its broad adoption.


New therapy


​On the other hand, live bacteria therapy is emerging as a promising strategy in the field of cancer treatment. Some bacteria, such as Escherichia coli, Salmonella, and Listeria, possess innate tumour-targeting capabilities13^{13}. Unlike most therapeutics, tumor-targeting bacteria maintain their effectiveness regardless of a tumor's genetic makeup14^{14}. As microscopic ‘robotic factories’, bacterial vectors can be reprogrammed to produce and deliver anticancer agents on the basis of clinical needs, serving as potent weapons for eradicating tumours. When complementing other anticancer therapies, it could achieve better clinical outcomes.

​Thus, Peking 2023 is devoted to advancing bacterial therapy and introducing innovative modifications to revolutionize pancreatic cancer treatment.


Our solution


1.Targeting module


​A pivotal aspect of our innovative project involves constructing a hybrid promotor. TME, characterized by hypoxia and elevated lactate levels, remains relatively stable despite genetic mutations9^9. Thus, we establish an AND-gate-equivalent part, driving the expression of a knock-out essential gene (asd ) on a loop vector (Fig.3). Consequently, the engineered Escherichia coli strain Nissle 1917 (or EcN, a safe probiotic strain widely used in the clinic) can only thrive and multiply in a hypoxia and lactate-abundant environment, achieving precise targeting of pancreatic cancer.


Figure 3

Figure 3 | ​Design of the AND-gate-equivalent part. We have introduced a simple and delicate component that can realize the relatively complex AND-gate function, sensing hypoxia and high lactic acid.


2.Therapeutics


​In addition, we are pioneering an innovative ultrasonic reporting system to accurately locate tumours by expressing microvesicles15^{15}. This method is expected to provide information of tumour issues for doctors and offer accurate drug delivery.


Figure 4

Figure 4 | ​Ultrasound approach tracks engineered bacteria16^{16}. Bourdeau et al.15^{15} genetically engineered bacteria to express what they term acoustic response genes (ARG), which encode the components of hollow structures called gas vesicles that scatter sound waves and generate an echo that can be detected by ultrasound. Pressure-pulse application causes gas-vesicle collapse and disappearance of the ultrasound signal, which can be used to improve signal detection when tracking the location of cells containing gas vesicles. This approach enables in vivo monitoring of a cell population that light microscopy cannot track.


3.Controllable enveloping


​To achieve controlled immunogenicity of engineered bacteria with minimal harm to the human body, we introduce a dynamic circuit17^{17} into Escherichia coli, allowing it to dynamically alter the thickness of its cell wall. Prior to ultrasound exposure, a thicker cell surface is induced through arabinose to evade host immune responses. This surface gradually degrades and becomes thinner over time, enabling rapid clearance from the body after ultrasound.


Figure 5

Figure 5 | ​The schematic diagram of dynamic circuit17^{17}. By modulating the intensity and duration of arabinose induction, we aim to replicate the 'iCAP' effect depicted in the figure, with a concerted effort to minimize potential toxic reactions within the organism.


Figure 6

Figure 6 | ​A glimpse of our design. Engineered EcN has the capability to detect hypoxic environments and high lactic acid levels. Surviving bacteria could express microvesicles, generating appreciably echogenic when sonicated. This innovative method offers comprehensive and precise spatial localization of tumours, aiding clinicians in making informed medical decisions and ensuring affordability for a wider range of patients' medical needs.


Model and hardware


​In addition to the wet lab, our dry lab members established two models and a microfluidic chip.

​When a drug, especially one based on bacteria, is administered, it doesn't remain static. It moves, interacts, and gets metabolized in various compartments of the body. To encapsulate this dynamic, a multi-compartment model that divides the body into several compartments is proposed, each representing a significant region where the drug might interact or get metabolised.

​The main goal of the second model is to filter out a promoter sequence with the best distinction under conditions with or without environmental oxygen so that the survival of E. coli differs most in the tumour and the normal home environment. The result of this model can support or complement our wet lab results.

​The microfluidic chip is designed and constructed based on Prof. Chunxiong Luo’s research. The data acquired by the chip can work as a reference.


Beyond the lab


​As an iGEM team, we not only focus on lab work but social concerns. Our HP members organize various activities and interviews. The education group launched synthetic biology education projects in middle schools, covering 10 provinces(or municipalities), Hong Kong and Macau. We also focus on the problem of life-death matters and education.


Conclusion


​In conclusion, the Peking 2023 project aims to transcend the limitations of traditional treatments and introduce groundbreaking therapeutic alternatives for pancreatic cancer patients. We hope our research and work will contribute to the battle against the formidable "king of cancer".



References


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  4. Siegel, R. L., Miller, K. D., Wagle, N. S. & Jemal, A. Cancer statistics, 2023. CA. Cancer J. Clin. 73, 17–48 (2023).
  5. Mizrahi, J. D., Surana, R., Valle, J. W. & Shroff, R. T. Pancreatic cancer. The Lancet 395, 2008–2020 (2020).
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