KINGSTON, RI – September 19, 2022 – A research team from the University of Rhode Island and Miriam Hospital in Providence has demonstrated a potential new weapon in the fight against bladder cancer.
Researchers showed that a cancer-seeking molecule called pHLIP, used in combination with an FDA-approved fluorescent dye called ICG, can successfully target tumors in human bladders by illuminating cancerous lesions to make them easier for surgeons to see and measure remove are. In a separate experiment reported in the same study, the researchers showed that pHLIP® Peptides combined with a powerful toxin called amanitin could penetrate and kill bladder cancer cells in a petri dish.
The researchers say the results could pave the way for a potential clinical trial to test the effectiveness of pHLIP-based treatments in patients with non-muscle-invasive bladder cancer.
“Bladder cancer can be a devastating disease, and the number of cases is increasing, especially here in Rhode Island,” said Yana Reshetnyak, physics professor at URI and co-author of the study. “Our results suggest that pHLIP peptides could potentially be used to aid in fluorescence-guided surgery or to target bladder and possibly other urinary tract cancers.”
The study is published in the journal Frontiers in urology.
A cancer-seeking peptide
Reshetnyak and Oleg Andreev, also a physics professor at URI, have been developing pHLIP technology as a potential cancer fighter since 2004 as part of an ongoing collaboration with Yale biophysicist Donald Engelman. The molecule attacks cancer cells through its acidity, which is a hallmark of malignant tumors. While the environment around healthy cells has a fairly neutral pH of around 7.4, cancer cells have a much lower pH in their environment, between 5.5 and 6.5 (lower numbers indicate higher acidity).
The pHLIP molecule (short for pH-Low Insertion Peptide) comes from bacteriorhodopsin, a membrane protein that enables some unicellular organisms to convert light into energy. Bacteriorhodopsin consists of seven peptide helices linked together in a protein complex. Engelman’s experiments showed that one of these helices – which would later become known as pHLIP – could only cross a cell membrane when the surrounding pH was low. When Reshetnyak joined Engelman’s lab as a postdoc in 2003, she came up with the idea of using this helix to find cancer cells.
“We knew that cancer cells tend to be acidic, and here we had this peptide that only crosses a cell membrane at low pH,” Reshetnyak said. “It was then that we started to think that this might be useful in cancer treatment.”
She worked with Andreev and Engelman to further study the peptide and show that it can actually target cancer cells while leaving surrounding healthy cells untouched. They also showed that they can bind other molecules to pHLIP – chemotherapy drugs, immunomodulating drugs or fluorescent molecules useful for tumor imaging. The pHLIP peptide could then deliver these molecules directly to cancer cells and either bind them to the cell surface or escort them through the cell membrane.
A new weapon against bladder cancer
To test whether pHLIP compounds could be helpful in treating bladder cancer, the pHLIP team worked with Dr. Dragan Golijanin, Director of Genitourinary Oncology at The Miriam Hospital.
Golijanin’s team selected 26 patients whose bladders needed to be removed as part of their cancer treatment. After the bubbles were removed, his team injected a pHLIP solution® Molecules combined with a fluorescent molecule ICG. Golijanin then used a cystoscope, a small camera placed inside the bladder, to examine the inside of each bladder. The experiment showed that pHLIP-ICG illuminated tumors with high specificity and sensitivity. In fact, pHLIP-ICG improved cancer detection by 17% compared to a widely used diagnostic method.
According to Golijanin, the results suggest that pHLIP-ICG has potential for fluorescence-guided surgery. Not only does it find tumors that other techniques miss, it also works faster than other methods, potentially making pHLIP-ICG more practical for use in the operating room.
“We showed that you might be able to do a cystoscopy by injecting pHLIP-ICG about 15 minutes before the procedure and you can see any malignant lesions,” Golijanin said. “This could allow us better cancer healing and better resection of tumors at the time of cystoscopy. And it’s a lot less cumbersome than other methods that take at least an hour, which isn’t a comfortable wait for the patient.”
The results extend the promise of pHLIP-ICG in fluorescence-guided surgery. A Phase 1 fluorescence-guided surgical clinical trial in breast cancer patients is ongoing at Memorial Sloan Kettering Cancer Center in New York City. These new results suggest that pHLIP-ICG could also help in bladder cancer surgery.
For the second part of the research, the team tested pHLIP in combination with amanitin, a toxin derived from mushrooms. Using different types of breast and bladder cancer cell lines, the experiments showed that pHLIP-Amanitin was able to enter and kill cancer cells when their pH was low. These results indicate that pHLIP-Amanitin can successfully target and kill malignant lesions while minimizing the impact on surrounding cells with normal pH.
A Phase 1 clinical trial led by Cybrexa Therapeutics is currently testing pHLIP in conjunction with another cytotoxic drug, exatecan. These new results suggest that pHLIP-Amanitin could be another potential therapeutic combination.
Taken together, the researchers say, the results suggest that pHLIP could be useful in the diagnosis as well as in the surgical and therapeutic management of bladder cancer.
“This approach to imaging and this approach to treatment go hand in hand because they follow the sampling principle,” Golijanin said. “I think it has the potential to revolutionize the treatment of non-muscle invasive bladder cancer.”
The research was supported by the National Institutes of Health (R01GM073857, R01CA203737) and a research grant from the Feibelman family. The Phase 1 fluorescence-guided surgery clinical trial (NCT05130801) measures the safety of escalating pHLIP-ICG doses and drug performance in the operating room for identifying cancer lesions using a Stryker Corp. provided fluorescence imaging instrument.