Programmable Probiotics for Early Detection of Lung Cancer

Imagine being able to take a probiotic with an inhaler that can act as an early screening test for lung cancer. For a synthetic biology laboratory such as ours, we have been working on a technology to do just that. Recently, an explosion of microbiome research has revealed the widespread prevalence of beneficial microbes within the human body, including the respiratory tract, and even malignant lung tissue. In addition, several studies including our own have demonstrated that probiotics can selectively grow in tumor environments. Given their presence and preference for tumors, probiotics represent a natural platform for development as 'smart' detection systems for lung cancer. Therefore, our aim to design a simple probiotic detection system falls under the following Lung Cancer Research Program Area of Emphasis: Identify or develop noninvasive or minimally invasive tools to improve the detection of the initial stages of lung cancer.

In this proposal, we will use approaches from the rapidly growing field of synthetic biology to genetically program probiotics to sense tumor environments and depend on them for growth. Upon entry into the tumor environment, probiotics will then grow and produce methyl salicylate (wintergreen oil) from within the central core. We will accomplish this by designing gene circuits to insert into our probiotics that allow them to sense elevated levels of specific tumor metabolic byproducts (lactate) and changes in the local tumor microenvironment (pH levels) and express a gene required for bacterial growth. This triad of gene circuits will 'lock' probiotics into the proper location to avoid the risk of colonizing healthy tissue. Subsequently, we will engineer the probiotics to produce airborne wintergreen oil that can be detected with a simple breath test. In this way, the probiotic bacteria act as a detection vehicle that reaches tumor environments, senses tumor conditions, and locally produces a detectable molecule to indicate the presence of early-stage lung tumors while restricting bacterial growth outside of the tumor environment. These types of designer detection systems could be a promising new technology for detecting lung cancer.

We will assess the efficacy and safety of our probiotics in two ways. First, because the growth rate of probiotics and the speed at which gene circuits can be designed is much faster than the rate at which they can be tested in animal models, we will characterize the tumor environment detection capability of our probiotics and subsequent wintergreen oil release in tumor spheroids in the lab to allow for rapid iteration of optimized gene circuits. Second, we will engineer our probiotics to express fluorescent proteins, and then monitor them in mouse models of lung cancer via an in vivo imaging system. As naturally occurring gut microbes, probiotics elicit a low immune response and have demonstrated safety in a number of animal models. Furthermore, our gene circuits, which restrict probiotic growth only to tumors, act as an additional series of interlocked biocontainment mechanisms on top of the confirmed safety of probiotics. Therefore, our study contributes to the advancement of lung cancer research by aiming to develop safe, engineered probiotics as a novel and economic method of detecting lung cancer. Our study will also contribute insights into microbe-tumor interactions in the respiratory tract, as well as the foundation for developing probiotic therapies for lung cancer.

If lung cancer is found early enough, chances of successful treatment increase considerably, but a large percentage of cases are not caught until later, more advanced stages, resulting in the disease's high mortality rate. Current detection methods, most notably CT (computed tomography) scanners, come with the disadvantages of size and cost, both of which can be bypassed with a probiotic detection system. Likewise, a probiotic inhaler and point-of-care breath test could be easily utilized in regions inaccessible by other methods, extending the population range that could be screened. Not only would this simple and cost-effective detection system be appropriate for screening civilian populations most at risk –- including Veterans and current military personnel, who have been found to have higher rates of smoking and exposure to other lung cancer risk factors -– but would also be able to reach Service men and women deployed in remote locations. Therefore, in bypassing issues of cost, portability, and the necessity of trained specialists, our probiotic system would help ease the process of lung cancer detection across the highly varied duties and deployment regions of military personnel, as well as civilian populations.

Overall, we propose the above research strategy with the hope of inducing a fundamental change in how and when lung cancers are detected. Within 2 years, our aim is to have generated results in a preclinical animal model with our probiotics, and within 3-5 years, have ready a probiotic that can successfully diagnose early-stage lung cancer and be ready for translation into clinical trials. The development of a safe and efficacious design platform aimed at opening the door to a radically new detection paradigm may yield improved patient outcomes and wellbeing of all directly or indirectly involved in the arduous process of lung cancer diagnosis and treatment.