Design, Synthesis, and Evaluation of Pyrazolopyridine Derivatives as Novel Calreticulin (CALR) Ligands That Inhibit Triple-Negative Breast Cancer (TNBC) via Inducing Calcium Overloading

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, posing significant therapeutic challenges due to the lack of effective targets. Elevating intracellular calcium levels is a promising strategy in cancer therapy, and highly expressed calreticulin (CALR) in tumors has emerged as a potential target for inducing calcium overload. However, few studies on CALR ligands have been reported. Herein, we designed, synthesized, and evaluated pyrazolopyridine derivatives as potential CALR ligands. Among them, the leading compound 2a was identified as a high binding affinity ligand (Kd = 2.6 μM) with potent antitumor activity (IC50 = 0.1 μM). Mechanistic studies demonstrated that 2a could interact with CALR, inducing calcium overload and leading to apoptosis in TNBC cells. Further in vivo pharmacodynamic evaluations confirmed the safety and antitumor activity of 2a. In conclusion, our findings developed a novel CALR ligand and provided a new anti-TNBC strategy via inducing calcium dysregulation.