666-15

666-15 is a selective cyclic AMP response element binding protein (CREB) inhibitor with an IC₅₀ value of 0.081±0.04μM^[1]. 666-15 also inhibits the expression of endogenous CREB target genes, namely the transcription level of nuclear receptor-related protein 1 (Nurr1/NR4A2)^[1]. CREB is a nuclear transcription factor that can be activated by a variety of extracellular signals (including growth factors and hormones)^[2]. 666-15 blocks the neuroprotective effect of necrotizing inhibitor necrotizing inhibitor necrotizing inhibitor 1 (nec-1), which is a specific and effective inhibitor of necroptosis^[3].

In vitro, treatment of newborn rat cardiomyocytes (NRCMs) with 666-15 (1µM) for 2h effectively inhibited phenylephrine-induced CREB phosphorylation, but had no significant effect on p38 phosphorylation^[4]. Treatment of aged guinea pig chondrocytes with 666-15 (0-500nM) significantly reduced the protein level of p-CREB1 and increased cell viability^[5]. 666-15 (0-10µM) treatment of HEK293T cells transfected with different transcription factors for 5-7h showed little or no inhibition of Gal4-MLL, Gal4-c-Myb, Gal4-TEAD4/YAP1, and serum response factor (SRF)-mediated gene transcription^[6].

In vivo, 666-15 (10mg/kg) was intraperitoneally injected into mice transplanted with triple-negative breast cancer (TNBC) cells and inhibited breast cancer growth. Combination with docetaxel (DOC) showed better effects and had no significant effect on mouse body weight^[7].

References:
[1] Xie F, Li B X, Kassenbrock A, et al. Identification of a potent inhibitor of CREB-mediated gene transcription with efficacious in vivo anticancer activity[J]. Journal of medicinal chemistry, 2015, 58(12): 5075-5087.
[2] Shaywitz A J, Greenberg M E. CREB: a stimulus-induced transcription factor activated by a diverse array of extracellular signals[J]. Annual review of biochemistry, 1999, 68(1): 821-861.
[3] Yang C, Li T, Xue H, et al. Inhibition of necroptosis rescues SAH-induced synaptic impairments in hippocampus via CREB-BDNF pathway[J]. Frontiers in neuroscience, 2019, 12: 990.
[4] Zhang B, Zhang P, Tan Y, et al. C1q-TNF-related protein-3 attenuates pressure overload-induced cardiac hypertrophy by suppressing the p38/CREB pathway and p38-induced ER stress[J]. Cell death & disease, 2019, 10(7): 520.
[5] Wang Y, Wu Z, Yan G, et al. The CREB1 inhibitor 666-15 maintains cartilage homeostasis and mitigates osteoarthritis progression[J]. Bone & Joint Research, 2024, 13(1): 4-18.
[6] Li B X, Gardner R, Xue C, et al. Systemic inhibition of CREB is well-tolerated in vivo[J]. Scientific Reports, 2016, 6(1): 34513.
[7] Qin Y, Chen W, Jiang G, et al. Interfering MSN-NONO complex-activated CREB signaling serves as a therapeutic strategy for triple-negative breast cancer. Sci Adv 6: eaaw9960[J]. 2020.