CaSR Target Overview
The calcium-sensing receptor (CaSR) functions as a biological sensor for various signaling molecules, including calcium ions (Ca2+), situated on the cell membrane, belonging to the C-type G protein-coupled receptor (GPCR) family [1]. Similar to other C-type GPCRs, CaSR comprises extracellular "Venus Flytrap" (VFT) domains and seven transmembrane (7TM) domains, with a cysteine-rich domain (CRD) linking the VFT and TMD regions, enriched in cysteine residues. Ligands such as Ca2+ in the blood bind to the extracellular VFT domain of CaSR, activating homodimers and inducing conformational changes, further triggering intracellular G protein signaling pathways and downstream cellular physiological activities. CaSR primarily couples with intracellular Gq/11 class G protein signaling pathways, inducing phosphoinositide accumulation, endoplasmic reticulum Ca2+ release, and other cellular physiological behaviors [3]. Studies indicate that CaSR can also couple with Gi/o pathways, inhibiting cyclic adenosine monophosphate (cAMP) accumulation and activating the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK1/2) pathways [4]. Additionally, besides Ca2+, CaSR can sense various endogenous amino acids, amino acid derivatives, peptides, and polyamine compounds [2, 5-7].
Figure 1: CaSR High-Resolution 3D Cryo-EM Structure Model [22]
CaSR's Physiological Activities
Calcium ions (Ca2+) play crucial roles in physiological activities such as muscle contraction, cellular secretion, and blood clotting. The concentration of Ca2+ in the blood is typically maintained at a steady state. When the blood calcium concentration deviates from this equilibrium, the body employs specific feedback mechanisms to regulate it, ensuring the normal functioning of various calcium-related physiological processes. CaSR plays a role in maintaining calcium ion homeostasis by controlling the secretion of parathyroid hormone (PTH), thereby participating in various physiological processes including bone metabolism. When the concentration of PTH increases, it activates parathyroid hormone receptors expressed in organs such as the bones, kidneys, and gastrointestinal tract, promoting the reabsorption of calcium ions and consequently raising blood calcium levels [8]. Conversely, the secretion of PTH in parathyroid cells is regulated by feedback from the concentration of Ca2+; an increase in blood calcium concentration activates CaSR on the surface of parathyroid cells, triggering cellular physiological behaviors such as the accumulation of inositol phosphates and the release of intracellular calcium ions, thereby inhibiting PTH secretion and stabilizing blood calcium concentration[9].
In addition to regulating parathyroid hormone secretion and maintaining calcium homeostasis in the parathyroid gland, the calcium-sensing receptor is widely distributed in various tissues and organs throughout the body, exerting different physiological functions. For example, in the kidneys, CaSR can be directly activated by Ca2+, regulating the excretion of urinary calcium, integrating signals from sodium ions, pH, mineral ions, and other stimuli, and modulating the response of various hormones in the kidneys [10]. In bone tissue, CaSR participates in the development of the growth plate of cartilage and the proliferation and differentiation of osteoblasts, processes necessary for the generation of bone matrix [11]. In the gastrointestinal tract, Ca2+ can directly activate CaSR expressed in intestinal epithelial cells, thereby providing feedback regulation of Ca2+ absorption[12]. In the brain, CaSR is involved in the regulation of various neurological functions, although the specific physiological mechanisms are still under investigation [13].
Figure 2: Schematic Representation of Signaling Pathways Mediated by CaSR and Regulation of PTH Secretion
CaSR Targeted Disease Models
Due to its crucial role in numerous physiological activities, dysfunction of CaSR can lead to various diseases related to Ca2+ functionality, most of which are autosomal dominant inherited disorders. CaSR has emerged as a significant pharmacological target for disorders associated with Ca2+ dysregulation. For instance, certain gain-of-function mutations may render CaSR overly sensitive to Ca2+, resulting in its hyperactivation. This condition can lead to Familial Hypocalciuric Hypercalcemia Type 1 (FHH1), characterized by slightly elevated blood calcium levels throughout life, low urine calcium concentration, and elevated parathyroid hormone levels. In severe cases, it may cause Neonatal Severe Hyperparathyroidism (NSHPT), characterized by significantly elevated blood calcium and parathyroid hormone levels. Conversely, loss-of-function mutations may render CaSR less sensitive to Ca2+, leading to Autosomal Dominant Hypocalcemia Type 1 (ADH1). Symptoms may include seizures, spasms, and convulsions. In severe cases, it may lead to Type V Bartter Syndrome, characterized by hypokalemia, hyperkalemia, and incomplete renal development. Since most CaSR-induced disorders are caused by natural receptor mutations leading to either receptor hyperactivation or attenuation, drug development targeting CaSR primarily focuses on allosteric modulation to regulate CaSR activity, thereby intervening in disease onset [14,15,16,17].
Current Status of CaSR Targeted Drug Development
Presently, there are only three drugs on the market targeting the calcium-sensing receptor (CaSR): the peptide-based positive allosteric modulator Etelcalcetide, the small molecule chemical drug Cinacalcet, and Evocalcet [18,19,20,21]. Etelcalcetide, administered via intravenous injection, is a peptide drug used to treat secondary hyperparathyroidism in patients undergoing hemodialysis [18]. This peptide drug binds to the Venus Flytrap (VFT) domain of CaSR [22]. Cinacalcet, an oral medication, is a small molecule compound that significantly reduces secondary hyperparathyroidism associated with hemodialysis or late-stage or chronic kidney disease [19]. It can also inhibit primary hyperparathyroidism [20]. Cinacalcet binds to the 7-transmembrane (7TM) domain of CaSR [22]. Evocalcet, another oral medication, is a modified and developed version of Cinacalcet [21], also binding to the 7TM domain of CaSR [22].
Currently, there are no approved antibody drugs targeting CaSR or undergoing clinical trials. This is primarily due to the limited effectiveness of traditional IgG-formatted antibody drugs in GPCR-targeted drug development. Moreover, the development and approval of nanobody drugs, a novel form of nanobody drugs, have only gained recognition and some groundwork in recent years. Hence, there are relatively few reports and developments concerning CaSR-targeting nanobody drugs.
Introduction to Anti-CaSR Nanobody Product
Due to the insufficient availability of drugs targeting the calcium-sensing receptor (CaSR) on the market to meet the demands for treating related diseases,
Nanobio Life has independently developed an Anti-CaSR nanobody product. This product effectively targets the CaSR receptor and aids researchers in further exploring the activation mechanism of CaSR and its relevance to various diseases. It provides new directions for developing treatments for diseases related to calcium ion (Ca2+) dysregulation.
Moreover, it offers pharmaceutical companies interested in CaSR targets with new ideas for antibody drug development, thereby accelerating the process of new drug development.
|
|
Introduction to Anti-CaSR Nanobody Product
Target: Calcium-sensitive receptor / CaSR Antibody Type: Recombinant single-domain antibody Reactive Species: Human/Mouse Carrying Detection Tag: 6*His tag Molecular Weight: 100 kDa Recommended Dilution: 1:500-1:1000 Storage Conditions: 4°C, 6 months; -20°C, 2 years |
 |
Target Binding Assay of Anti-CaSR Nanobody
Figure 3: ELISA Detection of Antibody Binding to Target
Figure 4: Antibody Flow Cytometry Analysis Verification