The challenge Breast cancer is one of the most common cancers globally, threatening women's health. According to the World Health Organization (WHO) there were approximately 2.3 million new cases of breast cancer and 670,000 related deaths worldwide in 2022 alone[1]. Advancements in medical technology have introduced various treatment options for breast cancer, including chemotherapy, radiotherapy, and surgical interventions. Surgical treatment, often the most effective and commonly used option, involves the removal of tumor-affected breast tissue or the entire breast[2]. However, patients undergoing surgical treatment often face enduring both psychological and physiological challenges. Follow-up examinations are central components of cancer survivorship care to prevent recurrence. Such examinations usually require patients to go to hospital from time to time, which costs a lot of time and medical resources. In addition, regular checkups in hospital places individuals in a state of "awaiting diagnosis," blocking their psychological transition from "patient" to "ordinary person”. Bergerot et al. (2024) pointed out, breast cancer survivors frequently exhibit significant emotional fluctuations before and after follow-up appointments, often accompanied by anxiety, panic, and sleep disturbances[5]. Therefore, there is a pressing need to improve the ways of follow-up examinations so that they could be convenient and less psychologically disturbing for breast cancer patients. Inspiration Recent years, breast reconstruction surgery has become an increasingly common choice for patients after surgery. According to data released by the American Society of Plastic Surgeons (ASPS) in 2023, the number of breast reconstruction surgeries performed in the United States reached 157,740, marking a 4% increase. Meanwhile, breast augmentation, a form of cosmetic plastic surgery, has also gained widespread popularity. In 2023, there were 304,181 breast augmentation procedures conducted in the United States, representing a 2% increase over the previous year. Globally, the breast implant market is experiencing rapid growth with $19.2 billion market scale in 2023 and will reach a higher level by 2035[7]. Therefore, we came up with the idea to develop a cancer surveillance system during plastic surgery, so that breast cancer patients who undergo surgical treatment might be able to know their cancer progression without going to hospital. Adipocyte is one of the most used tissue types for breast plastic surgery. Most importantly, adipocytes in tumor microenvironment are frequently induced to transform into cancer-associated adipocytes (CAA) that secrete a variety of pro-tumorigenic cytokines to nurture cancer cells. We realized that such interactions between CAAs and breast cancer cells may be utilized as a fundamental framework to develop a breast cancer surveillance system[6].
Working principle of ABCS
Adipocyte for Breast Cancer Surveillance, ABCS is a real-time cancer warning system specifically designed for women who have previously had breast cancer or undergone breast surgery. Procedure outline Adipocytes will be obtained from individual’s autologous adipose tissue. Through recombinant adeno-associated virus (rAAV) transfection, plasmids with sensor elements and reporter genes will be delivered into these adipocytes. These engineered adipocytes will then be transplanted to breast tissue through plastic surgery, which sense and respond to cytokines secreted by cancer cells and secret reporter molecules. These reporter molecules, for example betanin or gaussia luciferase (Gluc) might be detected in urine. Such surveillance system enables individuals to be aware of potential cancer activity, without going to hospital.
Procedure outline of ABCS
Biomarker A key mechanism to transform adipocytes into CAA is the stimulation from cytokines that are secreted from cancer cells, which usually induces expression of the target genes of these cytokines in adipocytes. Therefore, we construct a sensor element in adipocytes, enabling them to detect the cytokines by responding to the induced expression of specific target genes. Through literature review, we found that breast cancer cells secrete plasminogen activator inhibitor-1 (PAI-1) and C-X-C motif chemokine ligands (CXCLs), which upregulate the expression of procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2) and leukemia inhibitory factor (LIF) in adipocytes respectively. Based on these, we engineered a sensor element within adipocytes capable of sensing the upregulated expression of PLOD2 and LIF. In other words, PLOD2 and LIF are the target biomarkers for detection by ABCS.
Interaction between cancer cell and CAA through cytokines
Sensor element——RADAR RNA sensing using adenosine deaminases acting on RNA (RADAR) is a novel RNA detection technology based on RNA editing, composed of four parts:
An infection marker coding sequence (e.g. mCherry)
A sensor sequence that is reverse complementary to the target RNA
An output reporter gene coding sequence
The core of the sensor is a central stop codon (UAG), which prevents the expression of the downstream reporter gene. When the trigger RNA is present, it binds to the sensor sequence, forming partial double-stranded RNA (dsRNA). However, due to the presence of a CCA sequence in the target RNA, an A-C mismatch occurs at UAG. This structural feature provides a substrate for ADAR enzymes, which bind and convert the adenosine (A) of the UAG stop codon into inosine (I), effectively allowing the downstream coding sequence translated. To enable simultaneous detection of 2 trigger RNAs, in our case, PLOD2 and LIF, we have designed a sensor element that connects two sensors in tandem to form an AND gate , ensuring that the reporter gene is only expressed when both PLOD2 and LIF are present[8].
Working principle of RADAR
Reporter genes Gaussia luciferase (Gluc), an enzyme which can react with coelenterazine and produce luminescence, is one of the choices for downstream output. Gluc is nontoxic and naturally secreted, cleared mainly by the renal pathway, and can finally end up in urine[12-13]. Gluc photochemically reacts with coelenterazine, producing luminescence with a peak of 480nm and a maximum of 600nm. Therefore, coelenterazine can be added into urine samples from patients implanted with ABCS and the present of luminescence in these samples indicated occurrence of cancer cells in these patients. Future view In the future, we hope to offer ABCS as an alternative or complimentary choice of follow-up examinations for individuals that have undergone breast surgery. ABCS can function stably and safely over long periods, serving as a sentinel that reports cancer progression timely. Beyond patients’ post-surgery treatment. This system is designed to help patients overcome the anxiety and burden of breast cancer follow-up examinations in hospital.
Reference
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