Modifying the bladder microbiome may improve responses to intravesical instillation of bacillus Calmette-Guérin (BCG) for the management of non-muscle invasive bladder cancer (NMIBC), according to new data presented at the American Urological Association’s 2023 Annual Scientific Meeting.
The findings suggest that Lactobacillus bacteria may be associated with a significant increase in the uptake of BCG.
While BCG is the gold standard for the management of NMIBC, approximately 30% to 40% of patients experience treatment failure, according to investigators.
“Recently, there’s been an increased interest in the role of the urinary microbiome in numerous urologic disease processes,” said first author Zaeem Lone, a fourth-year medical student at the Cleveland Clinic Lerner College of Medicine in Ohio. “In the bladder cancer space, no study to our knowledge has looked at how the tumor intrinsic microbiome may modulate treatment response. Therefore, this study is critical to see if we can find any associations that explain preferential response to treatment.”
NGS and Shotgun Metagenomics
The researchers performed next-generation sequencing (NGS) and shotgun metagenomics on formalin-fixed bladder tumors from patients prior to intravesical BCG therapy for NMIBC. The team examined the alpha and beta diversity in 23 responders (83 male) and 24 non-responders (88% male) and found that the overall microbiome composition differed significantly as determined by both NGS and shotgun metagenomics.
The researchers defined BCG responders as patients who had no disease recurrence 2 years after induction.
“BCG is an effective treatment option for non-muscle invasive bladder cancer; however, many patients will experience cancer recurrence requiring additional and potentially more aggressive treatment,” said study co-author Nima Almassi, MD, a urologist at Glickman Urological & Kidney Institute at the Cleveland Clinic. “Developing a better understanding of optimizing the efficacy of BCG may allow us to improve outcomes with bladder cancer treatment.”
The researchers validated the NGS data with GFP-tagged BCG co-cultured with a urothelial carcinoma (UC) cell line (SW780) and candidate bacteria based on the NGS data. In addition, fresh tumor samples were collected at the time of transurethral resection of bladder tumor (TURBT). Those samples were cultured under 5 different media conditions, confirming the viability of the tumor microbiome and quantifying the bacterial mass per sample.
Lone and colleagues found that Lactobacillus species were enriched in patients who responded to BCG.
“We saw that the presence of Lactobacillus was associated with improved response,” Lone said. “In our in vitro assays to validate our sequencing data, we also observed that co-culture of Lactobacillus, BCG, and bladder cancer cells led to increased uptake of BCG into the cancer cells, which is important as internalization of BCG is the first step in engendering an immune mediated response.”
The co-culture with increasing concentrations of Lactobacillus demonstrated a significant increase in BCG-GFP internalization in UCC (16%) compared with controls (6%). When the researchers examined 10 fresh tumor samples, they found that 4 samples produced viable bacteria through culture-based approaches. Tumor bacterial density was calculated at 1.25×106 colony forming units/gram of tissue.
“Utilizing next generation sequencing, we found that compositional differences do exist in the tumor microbiome of BCG responders and non-responders,” Lone said. “Particularly interesting is that in numerous other studies it’s been observed that the presence of Lactobacillus in urine is associated with a ‘healthier’ microbiome. Therefore, it was interesting to see this signature also observed in tumor tissue.”
Joshua J. Meeks, MD, PhD, an associate professor of urology, biochemistry and molecular genetics at the Northwestern University Feinberg School in Chicago, Illinois, said the role of the microbiome in the modulation of the immune system is intriguing, and now it is possible to dissect how the host, the tumor and bacteria interact.
‘Next Generation of Medicine’
“We all think about profiling a tumor for a personalized medicine approach, but perhaps manipulating the microbiome is the next generation of medicine,” Dr Meeks said. “I am most impressed by their data showing that greater microbiome diversity is associated with response, rather than a single bacterial strain. There are several trials using bacteria to augment the immune response, so hopefully we will have an answer soon.”
To date, no reliable clinical markers are available to predict BCG response. Dr Meeks said there are still many other hurdles to overcome as well. Studies such as that conducted by Lone and colleagues “are really what we should aim for,” he said. “They begin with a finding from the clinic, employ patient-involved samples, and go right to the bench for mechanism. We look forward to seeing the arc back from the bench, translating their findings to the bedside.”
Daniel P. Petrylak, MD, Chief of Genitourinary Oncology at Yale Cancer Center in New Haven, Connecticut, said the latest findings are intriguing because there is an urgent need for better treatments. “Something as easy and cheap as affecting the microbiome is something that could clearly help patients in this situation,” Dr Petrylak said. “It certainly could be leveraged to improve treatments.”
Lone Z, Knorr J, Wernburg G, et al. The bladder tumor microbiome may augment response to BCG in non-muscle invasive bladder cancer. Presented at: AUA 2023, Chicago, Illinois, April 28-May 1. Abstract PD25-08.