ATPase x Proton pump

Researchers applied functional and structural analyses to investigate what structural features of proton/potassium (H+/K+) pumps and sodium/potassium (Na+/K+) pumps lead them to regulate the passage of salts across membrane barriers. In a recently published research article, Pablo Artigas, Ph.D., from the Center for Membrane Protein Research at the Texas Tech University Health Sciences Center (TTUHSC) School of Medicine’s Department of Cell Physiology and Molecular Biophysics, and a team of collaborators applied functional and structural analyses to investigate what structural features of proton/potassium (H+/K+) pumps and sodium/potassium (Na+/K+) pumps lead them to regulate the passage of salts across membrane barriers. The study, “Structure and Function of H+/K+ Pump Mutants Reveal Na+/K+ Pump Mechanisms,” was published in September by Nature Communications. The research team included Artigas and TTUHSC graduate students Victoria C. Young, Ph.D., and Dylan J. Meyer, Ph.D.; Hanayo Nakanishi, Ph.D., Atsunori Oshima, Ph.D., and Kazuhiro Abe, Ph.D., from Nagoya (Japan) University; and Tomohiro Nishizawa, Ph.D., from Yokohama (Japan) City University. The study was funded by the National Science Foundation and The CH Foundation. In every human cell, the Na+/K+ pump transports two potassium (K+) ions into the cell and brings out three sodium (Na+) ions. The concentration gradients for these ions are needed for electrical signaling in the brain, heart and muscle, and for the intake of nutrients and regulation of intracellular concentrations of calcium and protons in all cell types. The four types of Na+/K+ pumps localize to different tissues. Disease mutations within three of these Na+/K+ pumps cause neuromuscular, cognitive, endocrine or cardiovascular disorders. Two H+/K+ pumps have slightly different ion-recognition sites and are expressed on the apical side of many epithelia, where they transport one proton (H+) out of the cell and bring in one potassium (K+) ion. The gastric H+/K+ pump acidifies the stomach and is the target of omeprazole, an antacid drug. The non-gastric H+/K+ pump participates in K+ reabsorption and contributes to acidification of the airway, an important part of cystic fibrosis pathology. “The two proteins (H+/K+ and Na+/K+ pumps) are about 70% identical, so we looked at what minor differences could be responsible for the difference in the selectivity and in the number of ions that are transported,” Artigas explained.  The study determined that simultaneously replacing amino acid residues at four spots within the non-gastric H+/K+ pump with those present in the Na+/K+ pump is enough to transform a protein that normally transports one proton for one potassium into one that transports three sodium for two potassium, giving new insight into how these proteins select the ions they must transport. “To the best of our knowledge, this is the first demonstration of changing a protein that exclusively transports H+ is transformed into a protein that exclusively transports Na+,” Artigas said. “We think it could help others conducting similar types of work with other membrane proteins to design a similar change to the selectivity between Na+ and H+. We can do it one way, but we are now trying to do it the other way: come from the Na+/K+ pump to the (non-gastric) H+/K+ pump.” The importance of the non-gastric H+/K+ pump in the body remains largely unknown, but it is known that its inhibition prevents airway infections in an animal model of cystic fibrosis. “In addition to transforming one type of protein into another, thanks to our structural-biologist collaborators in Japan, we determined the structure of the non-gastric H+/K+ pump,” Artigas said. “This structure could be used to develop specific inhibitors to effectively treat cystic fibrosis patients.” Now that Artigas and his collaborators have successfully converted the non-gastric H+/K+ pump to a Na+/K+ pump, they are attempting several other conversions using the gastric H+/K+ and Na+/K+ pumps. “We still haven't been able to convert the gastric H+/K+ pump into a Na+/K+ pump or a Na+/K+ pump into a H+/K+ pump to fully understand the mechanism of selectivity,” Artigas said. “We will use the current and future structures of the non-gastric H+/K+pump to attempt generating specific inhibitors to help treat cystic fibrosis patients.” ###

There’s no time for rest in biopharma — at least not at Phathom Pharmaceuticals. Just over a month after submitting two NDAs for its lead acid-fighter vonoprazan, the biotech is already lining up a third, and collecting an extra $50 million to push things along. Vonoprazan met its primary non-inferiority endpoints in a Phase III study comparing it to standard-of-care Prevacid in a type of gastroesophageal reflux disease (GERD) called erosive esophagitis (EE). It also proved superior to the popular heartburn drug by multiple measures, including healing rate and maintenance of healing. “The results further solidify vonoprazan’s potential to be the first major innovation in the U.S. and European GERD market in more than 30 years,” CEO Terrie Curran said in a statement. Phathom Pharmaceuticals has come a long way since it was spun out of Takeda, with the help of Frazier, two years ago to handle the ex-Japan development of vonoprazan. Vonoprazan, discovered by Takeda, is a P-CAB: a class of drugs that blocks the potassium-binding site of gastric hydrogen potassium ATPase (also known as the proton pump), which is the enzyme largely responsible for acidification of the stomach. It’s already approved in Japan to treat a variety of acid-related conditions, including EE. The Phase III Phalcon-EE trial enrolled just over 1,000 EE patients in the US and Europe, who were treated with a 20 mg dose of vonoprazan in a healing phase and one of two doses (10 mg or 20 mg) in a maintenance phase. In the healing phase, vonoprazan proved non-inferior to Prevacid in terms of patients who achieved complete healing by Week 8, with a healing rate of 93% in the vonoprazan arm compared to 85% in the Prevacid arm (p<0.0001). It also passed an exploratory superiority test, with a p-value of 0.0001. Patients on vonoprazan saw significantly faster healing in this phase. However, a superiority test comparing a 20 mg dose of vonoprazan to a 30 mg dose of Prevacid for sustained resolution of heartburn by Day 3 did not turn up statistically significant (p=0.2196). Vonoprazan met the primary and all secondary endpoints in the maintenance phase, though, demonstrating superiority in maintenance of healing (79% for vonoprazan 10 mg, 81% for vonoprazan 20 mg, and 72% for Prevacid). The p-values there were less than 0.0001 for both non-inferiority comparisons, 0.0218 for the 10 mg superiority test and 0.0068 for the 20 mg superiority test. Both vonoprazan doses also achieved superiority in the percentage of patients with moderate-to-severe disease who maintained healing of EE through Week 24 (75% for vonoprazan 10 mg, 77% for vonoprazan 20 mg, and 61% for Prevacid). The frequency of serious adverse events were roughly the same in the 20 mg vonoprazan and Prevacid arms of the healing phase, but about twice as high in the 20 mg vonoprazan arm of the maintenance phase, according to Phathom. However, that does include five patients in the 20 mg arm who got Covid-19, which was unrelated to the treatment. The new data will allow Phathom to submit an NDA in the first half of next year, and triggers an extra $50 million from its term loan facility with Hercules Capital. It’s also good news for Catalent, which inked a deal to manufacture the drug just a few weeks ago.