Novel drugs block TRPV6 calcium channel like a natural plug

March 25, 2021

Trained in Bioinformatics at the University of Hyderabad, Dr. Rajesh Bhardwaj, who hails from Haryana, switched gears to Biochemistry and conducted his doctoral research on physical coupling mechanisms of endoplasmic reticulum and plasma membrane at Heidelberg University, Germany. He is currently working as a senior research associate at the University of Bern, Switzerland. His work combines molecular biology and computational structural biology techniques with state-of-the-art high-throughput screening and electrophysiology. The goal is to understand different aspects of store-operated, calcium release-activated calcium (CRAC) channels and epithelial calcium channel TRPV6, such as the mechanisms that regulate their activation and inactivation, regulation by oxidative stress, and modulation by chemical compounds. Here, Dr. Rajesh talks about how novel drugs block TRPV6 calcium channel like a natural plug and discusses his first author research article titled “Inactivation-mimicking block of the epithelial calcium channel TRPV6” published in Sci Adv. (2020).

Author interview

How would you explain your paper’s key results to the non-scientific community?
When it comes to human physiology, not everyone understands the role of calcium as a “second messenger” carrying out vital functions. However, “bones” or “teeth” certainly rings a bell when one thinks of calcium. Indeed, around 99% of the body’s calcium is dedicated to building strong bones and teeth. Less than a fraction of calcium in its ionic form (Ca²⁺) flows through the cells. To prevent aggregation of proteins and nucleic acids as well as precipitation of phosphates and maintain the integrity of lipids, cells maintain very low amounts of Ca²⁺ inside themselves, which is nearly 10-20 thousand times lower than their outside environment.

Ca²⁺ cannot freely cross the dense lipid bilayer around a cell. Among various other proteins embedded in the membrane, TRPV6 is an important channel protein. Four units of TRPV6 assemble to form a pore or tunnel through which calcium ions enter the cell. In the intestine, dietary calcium is absorbed through TRPV6 channels in epithelial cells, and the process is regulated by vitamin D, which boosts TRPV6 and calbindin-D9K expression to increase calcium uptake.

To avoid calcium overload, the TRPV6 channel must be inactivated. Calmodulin (CaM), a Ca²⁺-sensing protein inside cells, acts like a traffic officer by plugging the TRPV6 pore from the inside, halting further calcium influx. Overactive or excessive TRPV6 is linked to cancer due to disrupted control over cell growth and death, making it a valuable drug target.

At the University of Bern, a drug called cis-22a was discovered to potently and specifically block Ca²⁺ entry through TRPV6. More stable analogues were later developed with improved specificity. Collaborating with labs at Columbia University and Johannes Kepler University, the researchers used techniques like site-directed mutagenesis, fluorescence assays, cryo-EM, electrophysiology, and molecular dynamics to uncover how cis-22a works.

Their study showed that cis-22a directly plugs the TRPV6 channel from the inside—just like CaM does. A specific mutation (aspartic acid at position 580 changed to lysine) blocked the drug’s effect, proving that cis-22a mimics natural inactivation. Cryo-EM structures confirmed that cis-22a family drugs occupy the channel pore, preventing calcium entry.

What are the possible consequences of these findings for your research area?
This study introduced the first known inhibitor that blocks TRPV6 by plugging its pore, mimicking natural inhibition. Because cis-22a works like calmodulin, it may have fewer side effects and better therapeutic potential. The mechanistic insights gained could help in developing more effective TRPV6 inhibitors and exploring the channel’s role in disease, especially cancer.

“The knowledge on the mechanism of action of this drug that we provide makes it a valuable tool to further pharmacologically address new roles of TRPV6 in health and disease.”

What was the exciting moment (eureka moment) during your research?
The research was a team effort involving four labs, requiring integration of diverse scientific perspectives. The eureka moment arrived when findings from chemistry, cell physiology, and structural biology fit together like puzzle pieces. For Dr. Rajesh, the key moment was discovering that mutations in TRPV6 which were predicted to interact with cis-22a indeed blocked its effect, validating their hypothesis.

What do you hope to do next?
The team also discovered another binding site of cis-22a away from the pore, which also affects TRPV6 function. Mutations in this region made the channel less sensitive to the drug, implying a remote influence on pore structure. The next step is to study this second binding site and how lipids regulate TRPV6 activity. The long-term goal is to evaluate how TRPV6-mediated calcium entry influences cancer progression using these inhibitors.

Where do you seek scientific inspiration?
Dr. Rajesh credits his PhD mentor Dr. Matthias Seedorf for inspiring and training him. He acknowledges the mentorship of Prof. Hediger during his postdoctoral years. He also finds inspiration in high-achieving colleagues in his research group and peers in the Ca²⁺ signaling field, especially those who have become independent researchers. Support from his family fuels his motivation.

How do you intend to help Indian science improve?
If given the opportunity, Dr. Rajesh is open to returning to India in a faculty position. He is interested in setting up international collaborations and looks forward to networking with Indian scientists at future calcium meetings and beyond.

References

Singh AK, McGoldrick LL, Twomey EC, Sobolevsky AI. Mechanism of calmodulin inactivation of the calcium-selective TRP channel TRPV6. Sci Adv. 2018.
Stewart JM. TRPV6 as A Target for Cancer Therapy. J Cancer. 2020.
Cunha MR, Bhardwaj R, Carrel AL, Lindinger S, Romanin C, Parise-Filho R, Hediger MA, Reymond JL. Natural product inspired optimization of a selective TRPV6 calcium channel inhibitor. RSC Med Chem. 2020.
Bhardwaj R, Lindinger S, Neuberger A, Nadezhdin KD, Singh AK, Cunha MR, Derler I, Gyimesi G, Reymond JL, Hediger MA, Romanin C, Sobolevsky AI. Inactivation-mimicking block of the epithelial calcium channel TRPV6. Sci Adv. 2020. DOI: 10.1126/sciadv.abe1508