Fluorescence-polarization-based binding assays for XIAP, cIAP-1 and cIAP-2 proteins

To determine the binding affinities of SM-164 to XIAP containing both BIR2 andBIR3 domains, an FP-based competitive binding assay was established using a bivalent fluorescently tagged tracer, named Smac-1F. The Kd value of the bivalent tagged tracer to XIAP containing BIR2 and BIR3 domains was determined to be 2.3 nM. In competitive binding experiments, a tested compound was incubated with 3 nM of XIAP protein containing both BIR2 and BIR3 domain (residues 120-356) and 1 nM of in the same assay buffer.

Cell lines

MDA-MB-231 breast cancer cell

Preparation method

Limited solubility. General tips for obtaining a higher concentration: Please warm the tube at 37 ℃ for 10 minutes and/or shake it in the ultrasonic bath for a while. Stock solution can be stored below -20℃ for several months.

Reaction Conditions

12 h-48 h

Applications

12 h 1 nmol/L SM-164 treatment induces 32%, 33%, and 37% of the MDA-MB-231, SK-OV-3 and MALME-3M cells to undergo apoptosis. SM-164 also leads to cIAP-1 degradation in resistant cancer cell line and effectively antagonizes cellular XIAP. Moreover, 3 to 10 nmol/L SM-164 induces cell death with or without TNFα in all these sensitive cancer cell lines.

Animal models

MDA-MB-231 xenograft tumor mice model

Dosage form

A single i.v. dose of SM-164 at 5 mg/kg.

Applications

At the 3-hour time point, SM-164 induces prominent apoptosis in tumor tissues, and more than 50% of tumor cells were TUNEL positive at the 6-hour time point. SM-164 reduces the tumor volume from 147 ± 54 mm3 (day 25-start of the treatment) to 54 ± 32 mm3 (day 36-end of treatment), a 65% reduction. SM-164 treatment also shows no significant weight loss or sign of toxicity.

Other notes

Please test the solubility of all compounds indoor, and the actual solubility may slightly differ with the theoretical value. This is caused by an experimental system error and it is normal.

SM-164 is a bivalent mimetic of Smac with Ki values of 0.31 nM, 1.1 nM and 0.56 nM for cIAP-1, cIAP-2 and XIAP, respectively¹.

SM-164 is developed as an anticancer agent. It plays its antitumor roles through inducing degradation of cellular inhibitor of apoptosis protein (cIAP)-1/2, antagonizing X-linked inhibitor of apoptosis protein (XIAP) and inducing TNFα–dependent apoptosis in tumor cells. SM-164 is a bivalent mimetic containing two SM-122 analogues. It binds to cIAP-1 protein containing bothBIR2 and BIR3 domains, cIAP-2 BIR3 protein and XIAP protein containing both BIR2 and BIR3 domains with Ki values of 0.31 nM, 1.1 nM and 0.56 nM, respectively. In tumor cells, treatment of SM-164 significantly reduced cIAP-1 level to undetectable levels (1nM, 60min), effectively antagonized cellular XIAP and enhanced TNFα secretion. In the MDA-MB-231 xenograft model, administration of SM-164 at dose of 5mg/kg markedly decreased cIAP-1 level within 1 hour and activated caspase-8, caspase-9 and caspase-3 at 3 hour¹.

References:
1. Lu J, Bai L, Sun H, et al. SM-164: a novel, bivalent Smac mimetic that induces apoptosis and tumor regression by concurrent removal of the blockade of cIAP-1/2 and XIAP. Cancer research, 2008, 68(22): 9384-9393.