XMU-MP-8 specifically targets the oncoprotein S-phase kinase-associated protein 2 (SKP2), which is a substrate-recognition subunit of the SCF E3 ubiquitin ligase complex. SKP2 promotes the ubiquitination and degradation of key tumor suppressors such as p27, thereby driving cancer cell proliferation. XMU-MP-8 acts as a molecular glue degrader that simultaneously binds to two proteins: the F-box domain of SKP2 (Kd ≈ 36 microM) and the N-terminal TPR domain of the E3 ligase STUB1 (Kd ≈ 2.5 microM). This dual binding induces the formation of a stable SKP2-SKPer1-STUB1 ternary complex (Kd ≈ 8.9 nM), which is responsible for SKP2 ubiquitination and subsequent proteasomal degradation. The compound exhibits remarkable selectivity, sparing SKP2-low-expressing normal cells.

XMU-MP-8 (10 μM, 24 h) specifically produced a cell survival phenotype in the SKP2-FC cell line, while cell survival was not observed in other FC cell lines, which ruled out the possibility that it generally interfered with the activation of FC death proteins[1]. XMU-MP-8 (1-10 μM, 0-24 h) could trigger SKP2 ubiquitination and proteasome degradation, significantly shorten its half-life and consume endogenous SKP2 protein, but did not affect its mRNA level[1]. XMU-MP-8 (72 h) inhibited the proliferation of SKP2-overexpressing cancer cells, and its IC50 values against PC-3, A549, JHH-7, SW620, LoVo, RKO, Caco2 and HeLa cells were 3.7 μM, 6.7 μM, 3.7 μM, 6.2 μM, 4.5 μM, 6.9 μM, 5.6 μM and 5.3 μM, respectively[1]. XMU-MP-8 (10 μM, 72 h) completely blocked the proliferation of SKP2-overexpressing cell lines and induced massive cell death [1]. XMU-MP-8 (10 μM, 24 h) induced SKP2 protein degradation and p27 protein accumulation in SKP2-overexpressing cell lines (JHH-7 and PC-3), but did not cause significant changes in SKP2-low-expressing cell lines (IMR-90 and MCF-10A) [1]. XMU-MP-8 (2.5-10 μM, 0-5 days) had no significant effect on the growth of normal mouse intestinal organoids and human peripheral blood mononuclear cells [1]. XMU-MP-8 (10 μM, 2.5 h) recruits the E3 ligase STUB1 to the F-box domain of SKP2 to form a ternary complex, thereby enhancing the SKP2-STUB1 interaction by 122 times, ultimately leading to SKP2 ubiquitination and degradation [1].

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In vitro, XMU-MP-8 (1‑10 uM, 0‑24 h) triggers SKP2 ubiquitination and proteasomal degradation, shortening its half-life and depleting endogenous SKP2 protein without affecting SKP2 mRNA levels. At 10 uM for 72 h, it completely blocks proliferation and induces massive cell death in SKP2‑overexpressing cancer cells, including PC‑3, A549, JHH‑7, SW620, LoVo, RKO, Caco2, and HeLa, with IC₅0 values of 3.7, 6.7, 3.7, 6.2, 4.5, 6.9, 5.6, and 5.3 uM, respectively. At 10 uM for 24 h, XMU-MP-8 induces SKP2 protein degradation and p27 protein accumulation in SKP2‑high cell lines (JHH‑7 and PC‑3), while showing no significant effects on SKP2‑low normal cell lines (IMR‑90 and MCF-10A) nor affecting the growth of normal mouse intestinal organoids or human PBMCs.

XMU-MP-8 (15 and 30 mg/kg, intravenously, once daily for 14 days) demonstrated significant antitumor efficacy in A549 and PC-3 xenograft models by exacerbating SKP2 [1]. XMU-MP-8 (30 mg/kg, intravenously, once daily for 14 days) did not show adverse effects in BALB/c nude mice [1].

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In vivo, XMU-MP-8 demonstrates significant anti-tumor efficacy with a favorable safety profile. In A549 (NSCLC) and PC-3 (prostate cancer) subcutaneous xenograft models, intravenous administration at 15 or 30 mg/kg once daily for 14 days resulted in marked tumor growth inhibition. At the highest tested dose of 30 mg/kg (IV, once daily for 14 days), XMU-MP-8 exhibited no adverse effects in BALB/c nude mice, indicating good tolerability. These findings highlight the potential of XMU-MP-8 for research in SKP2-driven cancers. Detailed histological and pharmacodynamic analyses are available in the primary reference literature.

The non‑cellular enzyme binding assay for XMU-MP‑8 evaluates its binding affinity to SKP2 and STUB1 using purified recombinant proteins. To assess SKP2 degradation in a cell‑free system, purified SKP2 and STUB1 proteins are incubated with XMU-MP‑8 (1‑10 microM) along with ubiquitination reaction components including E1, E2 (e.g., UbcH5a), ubiquitin, and ATP. After incubation at 37 degC for up to 2 hours, reaction mixtures are analyzed by immunoblotting using anti‑ubiquitin or anti‑SKP2 antibodies to assess ubiquitination. Binding affinities (Kd) are determined by isothermal titration calorimetry (ITC) or surface plasmon resonance (SPR). The formation of the ternary SKP2‑XMU‑MP‑8‑STUB1 complex (Kd = 8.9 nM) can be confirmed by native PAGE or co‑immunoprecipitation assays.

Western Blot Analysis[1]
Cell Types: JHH-7 and HeLa cells
Tested Concentrations: 1, 2, 5, and 10 μM
Incubation Duration: 0, 2, 4, 6, 8, 12 and 24 h
Experimental Results: Reduced SKP2 levels in JHH-7 and HeLa cells in a dose- and time-dependent manner. Degraded SKP2 through the proteasome, but not the lysosome. Induced ubiquitination of SKP2. Significantly reduced the SKP2 half-life of SKP2 (from 10.8 h to 3.3 h in JHH-7 cells, and from 11.3 h to 6.2 h in HeLa cells).

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Western Blot Analysis[1]
Cell Types: A549 and PC-3 cells and derived genetically modified lines.
Tested Concentrations: 5 and 10 μM
Incubation Duration: 2.5 and 24 h
Experimental Results: Failed to degrade SKP2-F-C when three lysine residues (3K>R) in its F-box domain were mutated. Failed to induce ubiquitination of the SKP2 3K>R mutant protein. Was unable to exert its anti-proliferative effect in cells where endogenous SKP2 had been replaced with the degradation-resistant 3K>R mutant. Failed to induce SKP2 ubiquitination and degradation in STUB1 knockout cells. Re-gained its ability to degrade SKP2 following the reconstitution of sgRNA-resistant STUB1 in STUB1 knockout cells. Still recruited the 3K>R mutant to STUB1, even though this mutant was resistant to degradation.

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For in vitro cell‑based assays, SKP2‑overexpressing cancer cells (e.g., PC‑3, A549, JHH‑7) are cultured in appropriate media (RPMI‑1640 or DMEM with 10% FBS). Cells are seeded in 96‑well plates and treated with XMU-MP‑8 at concentrations ranging from 0.1 to 30 microM. For proliferation inhibition, cells are incubated for 72 hours and viability is assessed using CCK‑8 or MTT assays to calculate IC₅0 values. For degradation kinetics, cells are treated with 1‑10 microM XMU-MP‑8 for 0‑24 hours, then lysed and analyzed by Western blotting using anti‑SKP2 antibody. For ubiquitination studies, cells are pre‑treated with MG132 (a proteasome inhibitor) prior to XMU-MP‑8 treatment, followed by immunoprecipitation with anti‑SKP2 and immunoblotting with anti‑ubiquitin. p27 accumulation is assessed by Western blotting after compound treatment.

Animal/Disease Models: Male BALB/c nude mice (6 weeks old)[1]
Doses: 30 mg/kg
Route of Administration: i.v., daily for 14 days
Experimental Results: Exhibited no significant changes in body weight and liver function (ALT/AST levels). Showed no histopathological damage in the heart, kidney, liver, lung, or spleen.

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Animal/Disease Models: Male BALB/c nude mice (6 weeks old) subcutaneously injected with A549 or PC-3 cells[1]
Doses: 15 and 30 mg/kg
Route of Administration: i.v., daily for 14 days
Experimental Results: Completely ceased the growth of A549 tumors. Caused a 95 % reduction in tumour growth in PC-3 xenograft model. Caused depletion of SKP2 and an increase of p27 in the xenograft PC-3 tumour.

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In vivo animal studies for XMU-MP‑8 are conducted using 4‑6 week old female BALB/c nude mice bearing subcutaneous xenograft tumors. Approximately 5×10⁶ A549 or PC‑3 cells are injected subcutaneously into the flank. When tumors reach approximately 100 mm3, mice are randomized into treatment groups. XMU-MP‑8 is formulated in a suitable vehicle such as PBS containing 5% DMSO and 10% PEG300. The compound is administered intravenously at doses of 15 or 30 mg/kg once daily for 14 days. Tumor volumes are measured every 2‑3 days using calipers, and body weight is monitored daily for tolerability. At study endpoint, tumors are excised, weighed, and processed for Western blotting (SKP2, p27) or histological analysis. The compound exhibits good tolerability at 30 mg/kg with no overt toxicity observed.

Detailed pharmacokinetic parameters for XMU-MP‑8, such as half-life, Cmax, AUC, oral bioavailability, volume of distribution, clearance, and plasma protein binding, have not been fully disclosed in the public literature. However, as a compound with demonstrated in vivo efficacy at doses of 15‑30 mg/kg administered intravenously in mouse models, XMU-MP‑8 is expected to achieve sufficient systemic exposure for its pharmacological effects. Based on its molecular properties (MW 534.56, calculated logP suitable for cellular permeability), it is anticipated to have moderate to good membrane permeability. Stability studies confirm that XMU-MP‑8 is stable for up to three years as a powder at -20 degC, and for up to one year in solvent at -80 degC. The compound is stable at ambient temperature for several days during ordinary shipping.

Based on the available preclinical data, XMU-MP‑8 is generally well‑tolerated in animal models, with no adverse effects observed at an IV dose of 30 mg/kg once daily for 14 days in BALB/c nude mice. However, comprehensive toxicological characterization, including genotoxicity, cardiotoxicity, and organ-specific toxicity studies, has not been conducted or made publicly available. General safety assessments for similar molecular glue degraders suggest low cytotoxicity and negligible off-target effects at sub‑uM concentrations in normal cells. As a research‑grade compound, XMU-MP‑8 is labeled exclusively for research use only, not for human or veterinary use. The manufacturer's SDS recommends standard safety precautions: avoid inhalation, ingestion, and skin contact; wear protective gloves, clothing, and eye/face protection; store in a cool, dry, well‑ventilated area away from incompatible materials.

[1]. A rapid imaging-based screen for induced-proximity degraders identifies a potent degrader of oncoprotein SKP2. Nat Biotechnol. 2025 Sep 10.

XMU-MP‑8 is a research‑grade small molecule that has not entered clinical trials and is not approved for therapeutic use by any regulatory authority (FDA, EMA, PMDA). It was developed as a molecular glue degrader targeting SKP2 and was first reported in the primary research literature (reference DOI 10.1002/anie.202316799). Its mechanism of action involves the molecular glue-mediated formation of a ternary complex between SKP2 and STUB1, leading to SKP2 ubiquitination and proteasomal degradation, which in turn stabilizes the tumor suppressor p27 and blocks cell cycle progression. The compound is available from multiple chemical suppliers but is universally labeled “for research use only - not for human use.” It is intended for preclinical cancer research applications focusing on SKP2 biology, targeted protein degradation, and SKP2-driven malignancies including non-small cell lung adenocarcinoma and prostate adenocarcinoma.

C26H21F3N8S

534.56

534.156

2271314-01-1

146621802

White to off-white solid powder

3

6

38

788

0

CN1C2=NC(=NC(=C2C=N1)NCC3=CN=CC=C3)C4=CC(=CC=C4)NC(=S)NC5=CC=CC(=C5)C(F)(F)F

UPEIYMKISINCQK-UHFFFAOYSA-N

InChI=1S/C26H21F3N8S/c1-37-24-21(15-32-37)23(31-14-16-5-4-10-30-13-16)35-22(36-24)17-6-2-8-19(11-17)33-25(38)34-20-9-3-7-18(12-20)26(27,28)29/h2-13,15H,14H2,1H3,(H,31,35,36)(H2,33,34,38)

1-[3-[1-methyl-4-(pyridin-3-ylmethylamino)pyrazolo[3,4-d]pyrimidin-6-yl]phenyl]-3-[3-(trifluoromethyl)phenyl]thiourea

SKPer1

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~125 mg/mL (~233.84 mM; with sonication)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)