Murine double minute 2 (MDM2) E3 ligase.
Cereblon (CRBN) E3 ligase. DC50 = 0.4 nM [1]

Seldegamadlin (KT-253) is a heterobifunctional molecule consisting of a potent MDM2 ligand connected through a linker to a high-affinity ligand for CRBN. [1]
In HEK293T-HiBiT assays, KT-253 degraded MDM2 with subnanomolar potency (half maximal degradation concentration, DC50 = 0.4 nmol/L). In contrast, the small-molecule inhibitor DS-3032 treatment upregulated MDM2. [1]
In RS4;11 acute lymphoblastic leukemia (ALL) cells, KT-253 showed potent growth inhibition (IC50 = 0.3 nmol/L), which was superior to several MDM2 small-molecule inhibitors (DS-3032 IC50 = 67 nmol/L; SAR405838 IC50 = 620 nmol/L). [1]
Growth inhibition by KT-253 was dependent on CRBN recruitment, as a CRBN-dead analog (Compound 1) and the MDM2 ligand-only warhead (Compound 2) showed significantly right-shifted IC50 values. [1]
In RS4;11 cells, 4 hours of treatment with KT-253 led to potent and sustained MDM2 degradation to undetectable levels by Western blot, whereas DS-3032 treatment resulted in increased MDM2 protein levels. [1]
Targeted proteomic analysis showed that treatment of RS4;11 cells with 150 nmol/L KT-253 for 15 minutes led to an 84% knockdown of MDM2 protein levels, and 91% degradation after 1 hour. DS-3032 treatment (1 μmol/L) led to an 18% increase after 15 minutes and a 155% increase after 1 hour. [1]
A 4-hour treatment with KT-253 followed by washout was sufficient to induce caspase 3/7-mediated apoptosis over a 48-hour timeframe in RS4;11 cells. The apoptotic effect was observed across a concentration range of 1 nmol/L to 1 μmol/L. Minimal cell death was observed with DS-3032 after 48 hours. [1]
Within 2 hours post-treatment, KT-253 achieved potent p53 stabilization in RS4;11 cells at subnanomolar concentrations (EC50 = 0.05 nmol/L), which was >1,500-fold more potent than DS-3032 (EC50 = 81.4 nmol/L). [1]
An 8-hour treatment with KT-253 in RS4;11 cells showed potent, dose-dependent induction of p53 transcriptional gene targets, including MDM2, GDF15, CDKN1A, GADD45A, TNFRSF10B, FAS, and BBC3, with a fourfold or higher increase at 10 nmol/L. DS-3032 showed only modest (twofold) induction at the highest concentration (1 μmol/L). [1]
KT-253 showed potent growth inhibition in a panel of p53 wild-type hematologic cell lines (AML, ALL, DLBCL) with subnanomolar IC50 in multiple lines. It also showed potent growth inhibition and caspase activation in a range of p53 wild-type solid tumor cell lines (prostate, brain, ovarian, soft tissue sarcoma, neuroblastoma, lung, colorectal). Cell lines with mutated p53 (p53 MUT) did not respond to KT-253 at concentrations as high as 10,000 nmol/L. [1]
In RS4;11 and MV4;11 cells, flow cytometry analysis showed that treatment with 1000 nmol/L KT-253 resulted in depletion of S-phase cells (0.97% and 0.45%, respectively) and a high percentage of late apoptotic cells (75.8% and 62.1%, respectively). In contrast, treatment with 1000 nmol/L DS-3032 resulted in a higher percentage of S-phase cells (30.6% and 12.0%) and a lower percentage of late apoptotic cells (6.9% and 9.3%). [1]
In MOLM-13 AML cells in vitro, combination of KT-253 (1 or 10 nmol/L) with venetoclax (1.6 μmol/L) resulted in a significantly higher percentage of cells in early or late apoptotic stage (>50% higher) and maximal cell growth inhibition compared to either agent alone. [1]

In an RS4;11 ALL xenograft model, a single intravenous (i.v.) dose of KT-253 at 1 or 3 mg/kg induced tumor regressions. A lower exposure-matched weekly dosing regimen (0.3 mg/kg once weekly for 3 weeks) induced transient stable disease. DS-3032 (30 mg/kg and 100 mg/kg, oral, 3 days on/11 days off) had no effect or modest tumor growth inhibition, respectively. [1]
The median survival after a single dose of KT-253 at 3 mg/kg was 50 days versus 12 days for the clinically equivalent dosing regimen of DS-3032 in RS4;11 tumor-bearing mice. [1]
Targeted proteomic analysis of RS4;11 tumors 1 hour post-dosing with a single dose of KT-253 (1 or 3 mg/kg) showed robust MDM2 degradation (94% and 92%, respectively), which was associated with upregulation of p53, p21, and PHLDA3. No MDM2 degradation was observed with DS-3032. [1]
Immunohistochemical analysis of RS4;11 tumors revealed robust upregulation of p53 and induction of cleaved caspase-3 (CC-3) following a single dose of KT-253 (1 or 3 mg/kg), but not with weekly KT-253 (0.3 mg/kg) or DS-3032 treatment. [1]
In an MV4;11 AML xenograft model, a single i.v. dose of KT-253 at 3 mg/kg led to sustained tumor regressions. Complete responses were achieved in five of six animals, and four remained tumor-free for 6 months. Median survival was >180 days for the 3 mg/kg single dose group vs. 31 days for DS-3032 (100 mg/kg) and 16 days for DS-3032 (30 mg/kg). A weekly regimen of KT-253 resulted in transient stable disease. [1]
Immunohistochemical analysis of MV4;11 tumors showed robust p53 upregulation and CC-3 induction following a single dose of KT-253 (3 mg/kg), but not with weekly KT-253 or DS-3032 regimens. [1]
In four systemic AML patient-derived xenograft models, a single i.v. dose of KT-253 (1 mg/kg) led to a reduction of human CD45+ tumor burden in peripheral blood and bone marrow. In the CTG-2227 model, a complete response was observed (P = 0.009 unpaired t-test) at day 41. Partial responses were observed in CTG-2700 and CTG-2240 models. [1]
In a MOLM-13 AML xenograft model (venetoclax-resistant), a single dose of KT-253 (3 mg/kg) combined with a clinically relevant dose of venetoclax (100 mg/kg, oral daily for 1 week) or a subclinical dose (50 mg/kg, oral daily for 3 weeks) induced durable complete responses in all animals, whereas either agent alone did not. [1]
KT-253 was highly active against the p53 wild-type ABC-subtype DLBCL xenograft model (OCI-LY10), with responses similar to R-CHOP, but was not active against the p53 mutant ABC-subtype model (TMD8). [1]

The potency of MDM2 degradation was investigated in a HEK293T-HiBiT assay. HEK293T cells stably expressing C-terminal HiBiT-tagged MDM2 were used. Degradation was evaluated as the loss of luciferase signal post-treatment using a Nano-Glo HiBiT lytic detection system. Cells were treated with indicated concentrations of KT-253 or DS-3032 for 4 hours. The half maximal degradation concentration (DC50) was obtained by fitting the data with a four-parameter nonlinear-regression model. [1]
A Meso Scale Discovery (MSD) total p53 assay kit was used to quantify p53 levels. RS4;11 cells were lysed 2 hours post-treatment with 1 to 10,000 nmol/L KT-253 or DS-3032. The MSD signal was measured using a SECTOR imager. p53 levels in treated samples were calculated relative to DMSO control. Dose-response data were fitted using a four-parameter nonlinear-regression model. [1]

Cell growth inhibition and apoptosis were tested using CellTiter-Glo (CTG) and Caspase-Glo 3/7 assays according to the manufacturer's instructions. Cell line screening CTG and Caspase-Glo data were analyzed using R and the R drc package to fit growth curves and calculate absolute IC50. [1]
For Western blotting, cells treated per treatment condition were lysed using a mammalian protein extraction reagent supplemented with a protease/phosphatase inhibitor cocktail. Equal quantities of lysates were electrophoresed, transferred onto PVDF membrane, and protein levels were detected using anti-MDM2 and anti-β-actin antibodies. [1]
For qRT-PCR, cells were treated for indicated timepoints followed by a washout and allowed to grow in drug-free growth media for a total of 24 hours. RNA was extracted using an RNA Mini Kit. Reverse transcription and quantitative PCR were performed. Relative change in mRNA levels was calculated using the ΔΔCt method. [1]
Flow cytometry for cell cycle distribution was assessed using a Click-iT EdU Alexa Fluor 647 Flow Cytometry Assay Kit. Cellular apoptosis was assessed using a fluorescein isothiocyanate (FITC) Annexin V/PI kit. Cells were treated with the indicated compounds or combinations for 4 hours followed by washouts and allowed to grow in complete media for an additional 20 hours. Data were acquired using a flow cytometer. [1]
For discovery proteomics, cells were lysed using an iST sample preparation kit. After tryptic digestion, peptides were desalted and labeled using tandem mass tag pro reagents. Pooled samples were fractioned using basic reversed-phase chromatography. Each peptide fraction was analyzed by LC-MS/MS. Raw data were processed with MaxQuant. A paired statistical analysis was performed using the limma R package. [1]
For targeted proteomics (LC-PRM-MS), tumor samples were homogenized and denatured. Samples were reduced, alkylated, and digested with trypsin. Purification was carried out using an Oasis HLB plate. Peptide concentrations were measured. Stable isotope-labeled reference peptides were spiked into final samples. For each sample, 1 μg of peptides was injected onto a custom-packed reversed-phase column and analyzed by LC-PRM-MS. Data extraction and quantification were performed using SpectroDive software. [1]

For xenograft models, female Balb/c nude, CB-17 SCID, or NOD-SCID mice were used. Tumor cells were implanted subcutaneously in the hind flank. When tumors reached a specified volume (e.g., ~100 mm3 for MOLM-13; 250-500 mm3 for RS4;11, MV4;11), mice were sorted into treatment groups. For patient-derived xenograft studies, cells were inoculated intravenously. [1]
KT-253 was formulated in 20% (w/v) 2-hydroxypropyl-β-cyclodextrin (HPβCD), 0.025 mol/L hydrochloric acid (HCl), and 0.025 mol/L acetate, pH 4, to the appropriate concentration for each dose level before dosing at 5 mL/kg intravenously (i.v.). [1]
DS-3032 was dissolved in 0.5% methylcellulose at the appropriate concentration prior to each oral dose. [1]
For combination studies in the MOLM-13 model, mice were dosed with either KT-253 (3 mg/kg, i.v., single dose) or cytarabine (25 mg/kg, intraperitoneal (IP), 5 days on/2 days off) alone or in combination with venetoclax (100 mg/kg, oral daily dose, formulated in 10% ethanol, 30% PEG 400, 60% Phosal 50 PG). [1]
Body weights and tumor volumes were recorded twice per week. Endpoint was reached when tumor volumes reached 10% of the mouse's weight or when body weight loss reached 20% of initial weight. A complete response was defined as no measurable tumor for at least any 10 days during the experiment. [1]
For PK/PD experiments, mice bearing RS4;11 tumors were dosed intravenously with KT-253 at the indicated doses and euthanized at 1, 8, and 24 hours post-dosing. Blood and tumors were collected for analysis. [1]
For systemic patient-derived xenograft studies, female NOG mice were sublethally irradiated. AML blasts derived from patients were injected intravenously. Mice were monitored for clinical signs and body weight. AML burden was determined by flow cytometric analysis of whole blood and bone marrow. Mice were dosed with KT-253 at 1 mg/kg i.v., at 10 mL/kg. The vehicle control was 20% HPβCD, 0.025 mol/L HCl, and 0.025 mol/L acetate, pH 4. On day 42, a second dose was given. Sixteen hours later, animals were euthanized, and whole blood and bone marrow were collected for flow cytometry analysis. [1]

Dose fractionation data from the RS4;11 xenograft model demonstrated that tumor regressions are driven by a single dose of KT-253 (1 or 3 mg/kg) that achieved plasma concentrations ≥10 nmol/L for 12 to 22 hours. A lower exposure-matched weekly dosing regimen (0.3 mg/kg) resulted in tumor stasis, indicating that the time-over-threshold concentration exposure profile is critical for achieving rapid induction of the apoptotic pathway. [1]

The literature did not report specific quantitative data on toxicity/toxicokinetics such as LD50, organ toxicity, or plasma protein binding for KT-253. However, it was noted that dose-limiting toxicities (e.g., neutropenia, thrombocytopenia) have been observed in clinical trials with MDM2 small-molecule inhibitors, which require multiday dosing regimens. The intermittent dosing schedule of KT-253 is hypothesized to allow for the recovery of non-malignant/normal cells, potentially offering an improved therapeutic index. [1]

[1]. KT-253, A Novel MDM2 Degrader and p53 Stabilizer, Has Superior Potency and Efficacy Than MDM2 Small Molecule Inhibitors. Mol Cancer Ther. 2025 Apr 2;24(4):497-510.

Seldegamadlin (KT-253) is a first-in-clinic highly potent and selective MDM2 degrader for the treatment of solid and liquid tumors with wild-type p53 (p53 WT). It catalyzes the degradation of MDM2 and disrupts the acute autoregulatory feedback loop inherent to MDM2 small-molecule inhibitors. [1]
KT-253 has advanced into a Phase 1 clinical study to evaluate its safety, tolerability, pharmacokinetics (PK)/pharmacodynamics (PD), and clinical activity in adult patients with relapsed or refractory high-grade myeloid malignancies, acute lymphoblastic leukemia (ALL), lymphoma, and solid tumors (NCT05775406). [1]

C48H52CL2FN7O6

912.87

911.334016

C, 63.15; H, 5.74; Cl, 7.77; F, 2.08; N, 10.74; O, 10.52

2713618-08-5

166753033

White to off-white solids at room temperature

5.3

4

8

6

64

1860

3

ClC1C=CC2=C(C=1)NC([C@@]12[C@@H](C2C=CC=C(C=2F)Cl)[C@H](C(NC2CCC(C(N3CCC(C4=CC=C5C(=C4)N(C)C(N5C4C(NC(CC4)=O)=O)=O)CC3)=O)CC2)=O)NC21CCCCC2)=O

CQFHGOWYJXQICA-FKDNKQOESA-N

InChI=1S/C48H52Cl2FN7O6/c1-56-37-24-28(10-15-35(37)58(46(56)64)36-16-17-38(59)54-42(36)60)26-18-22-57(23-19-26)44(62)27-8-12-30(13-9-27)52-43(61)41-39(31-6-5-7-33(50)40(31)51)48(47(55-41)20-3-2-4-21-47)32-14-11-29(49)25-34(32)53-45(48)63/h5-7,10-11,14-15,24-27,30,36,39,41,55H,2-4,8-9,12-13,16-23H2,1H3,(H,52,61)(H,53,63)(H,54,59,60)/t27?,30?,36?,39-,41+,48+/m0/s1

(3'R,4'S,5'R)-6''-chloro-4'-(3-chloro-2-fluorophenyl)-N-((1R,4R)-4-(4-(1-((R)-2,6-dioxopiperidin-3-yl)-3-methyl-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)piperidine-1-carbonyl)cyclohexyl)-2''-oxodispiro[cyclohexane-1,2'-pyrrolidine-3',3''-indoline]-5'-carboxamide

Seldegamadlin; KT-253; 2713618-08-5; KT253; (3'R,4'S,5'R)-6'-chloro-4'-(3-chloro-2-fluorophenyl)-N-((1r,4R)-4-(4-(1-(2,6-dioxopiperidin-3-yl)-3-methyl-2-oxo-2,3-dihydro-1H-benzo[d]imidazol-5-yl)piperidine-1-carbonyl)cyclohexyl)-2''-oxodispiro[cyclohexane-1,2'-pyrrolidine-3',3'-indoline]-5'-carboxamide; Seldegamadlinum; Seldegamadlin; seldegamadlin [INN]; VNP2BV6KGL;

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)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

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.)