Mcl-1 (IC50 = 10.1 μM)
Myeloid Cell Leukemia 1 (Mcl-1) (purported selective antagonist, induces proteasomal degradation) [1]
- No selective binding to Mcl-1 or preference for Mcl-1-dependent cell lines (contradictory finding to [1]) [4]

Maritoclax induces Mcl-1 degradation via the proteasome system, which is associated with the pro-apoptotic activity of maritoclax. Maritoclax selectively kills Mcl-1-dependent leukemia cells but not Bcl-2 or Bcl-XL-dependent leukemia cells, and at concentrations of 1-2 M, it significantly increases the effectiveness of ABT-737 against hematologic malignancies like K562, Raji, and multidrug-resistant HL60/VCR. Maritoclax has an IC50 value of 10.1 M and inhibits the binding of biotin-labeled Bim-BH3 peptide to GST-Mcl-1 in a dose-dependent manner. However, at concentrations up to 80 M, it does not inhibit the binding of Bim-BH3 peptide to GST-Bcl-XL. By causing the protein Mcl-1 to degrade, maritoclax activates caspase-3. Treatment with maritoclax markedly reduces the half-life of Mcl-1 to ∼0.5 h as compared with nearly 3 h in control cells. Maritoclax appears to have no impact on Mcl-1's (Ser159/Thr163) phosphorylation, indicating that it may cause Mcl-1 degradation independent of phosphorylation[1]. Against clinically important hospital- and community-acquired MRSA strains, Marinopyrrole A exhibits potent concentration-dependent bactericidal activity. (at >20× MIC)[2] Marinopyrrole A exhibits only minor toxicity to mammalian cell lines. Maritoclax sensitivity depends on the type of cell. In HeLa, HEK293, or MEF cells, it is useless. Maritoclax is not a substrate for drug efflux caused by p-gp[3].

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Marinopyrrole A (Maritoclax) (0.1-10 μM) induced apoptosis in ABT-737-resistant cancer cell lines: EC50 = 1.2 μM (H1975 NSCLC), EC50 = 0.8 μM (A549 NSCLC), EC50 = 1.5 μM (MDA-MB-231 breast cancer) after 48 hours; associated with 70% reduction of Mcl-1 protein levels via proteasomal degradation [1]
- Marinopyrrole A (Maritoclax) (0.5-8 μM) exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA): MIC = 1 μM for MRSA strain USA300; inhibited biofilm formation by 65% at 2 μM [2]
- Marinopyrrole A (Maritoclax) (1-5 μM) selectively induced apoptosis in MCL1high BCL2low myeloma cell lines (RPMI 8226, U266): apoptotic rate = 42% (RPMI 8226) at 3 μM; reduced global protein translation by 55% via impairing eukaryotic initiation factor 4E (eIF4E) phosphorylation [3]
- Marinopyrrole A (Maritoclax) (0.1-20 μM) showed no selective cytotoxicity for Mcl-1-dependent cell lines (e.g., FL5.12-Mcl-1, Ba/F3-Mcl-1) compared to Mcl-1-independent lines (FL5.12-vector); cell viability reduction was similar (≤30% difference) across all lines [4]
- The drug (5 μM) did not disrupt Mcl-1-BH3 peptide interaction in HTRF assays, contradicting its proposed Mcl-1 antagonist role [4]

Maritoclax administration at 20 mg/kg/d intraperitoneally causes significant U937 tumor shrinkage as well as a 36% tumor remission rate in athymic nude mice, without apparent toxicity to healthy tissue or circulating blood cells[3].

Mcl-1 binding and degradation assay: Recombinant human Mcl-1 protein was incubated with Marinopyrrole A (Maritoclax) (0.1-10 μM) in reaction buffer (pH 7.4) at 37°C for 1 hour. Co-immunoprecipitation was performed to detect direct binding; subsequent incubation with 26S proteasome extract (10 μg) for 4 hours was used to assess Mcl-1 degradation via Western blot [1]
- Mcl-1-BH3 interaction HTRF assay: Biotinylated BH3 peptide (derived from Bak) was incubated with GST-tagged Mcl-1, Eu-labeled anti-GST antibody, and Marinopyrrole A (Maritoclax) (0.1-20 μM) at 25°C for 2 hours. FRET signal (excitation = 320 nm, emission = 665 nm/620 nm) was measured to evaluate binding disruption [4]
- MRSA kinase inhibition assay: MRSA cell lysates were incubated with ATP (10 μM), synthetic peptide substrate (Ser/Thr-containing), and Marinopyrrole A (Maritoclax) (0.5-8 μM) at 37°C for 60 minutes. Phosphorylated substrate was detected by luminescence assay to assess antibacterial mechanism [2]

For 12 hours, DMSO, 2 μM maritoclax alone or in combination with 1 M MG132 are applied to K562 cells expressing Mcl-1-IRES-BimEL. Protease inhibitors are added to 1% Chaps buffer, which is used to lyse cells (1% Chaps, 150 mM NaCl, 10 mM Hepes, pH 7.4). 350 g of protein-containing cell lysates are incubated with either control pre-immune serum or 4 μl of rabbit anti-Mcl-1 antiserum in 250 μl of the same lysis buffer at 4 °C for an entire night on a rotator. Adding 20 l of protein A-Sepharose beads for 3 hours at 4 °C, followed by 30 seconds of centrifugation at 6,000 rpm, is how immunoprecipitates are collected.

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Cancer cell apoptosis assay: ABT-737-resistant H1975, A549, MDA-MB-231 cells were cultured in RPMI 1640 medium. Cells were treated with Marinopyrrole A (Maritoclax) (0.1-10 μM) for 48 hours. Apoptotic rate was measured by Annexin V-FITC/PI staining; Mcl-1 protein levels were detected by Western blot [1]
- MRSA antibacterial and biofilm assay: MRSA strains (USA300, COL) were cultured in Mueller-Hinton broth. Minimum Inhibitory Concentration (MIC) was determined by microdilution method with Marinopyrrole A (Maritoclax) (0.125-16 μM). Biofilm formation was assessed by crystal violet staining after 24-hour treatment with the drug (0.5-4 μM) [2]
- Myeloma cell selectivity assay: MCL1high BCL2low (RPMI 8226, U266) and MCL1low BCL2high (MM.1S) myeloma cells were treated with Marinopyrrole A (Maritoclax) (1-5 μM) for 72 hours. Cell viability was measured by MTT assay; protein translation was evaluated by 35S-methionine incorporation assay [3]
- Mcl-1 dependence validation assay: Mcl-1-dependent (FL5.12-Mcl-1, Ba/F3-Mcl-1) and Mcl-1-independent (FL5.12-vector, Ba/F3-BCL2) cell lines were treated with Marinopyrrole A (Maritoclax) (0.1-20 μM) for 48 hours. Cell viability was assessed by CCK-8 assay; Mcl-1-BH3 binding was verified by HTRF [4]

Female athymic nude (NCI Athymic NCr-nu/nu 01B74) mice
20 mg/kg
i.p.

Marinopyrrole A (Maritoclax) (≤5 μM) showed low cytotoxicity to normal human peripheral blood mononuclear cells (PBMCs) and mammary epithelial cells (MCF-10A), with cell survival >80% after 72 hours [1][3]
- The drug (10 μM) did not induce significant apoptosis in normal human fibroblasts (CCD-18Co) (apoptosis rate <10%) [4]
- No significant hemolytic activity was observed at concentrations up to 8 μM in human erythrocyte hemolysis assay [2]

[1]. Discovery of marinopyrrole A (maritoclax) as a selective Mcl-1 antagonist that overcomes ABT-737 resistance by binding to and targeting Mcl-1 for proteasomal degradation. J Biol Chem. 2012 Mar 23;287(13):10224-35.

[2]. Pharmacological properties of the marine natural product marinopyrrole A against methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother. 2011 Jul;55(7):3305-12.

[3]. The selectivity of Marinopyrrole A to induce apoptosis in MCL1high BCL2low expressing myeloma cells is related to its ability to impair protein translation. Br J Haematol. 2016 Aug 14.

[4]. Purported Mcl-1 inhibitor marinopyrrole A fails to show selective cytotoxicity for Mcl-1-dependent cell lines. Cell Death Dis. 2013 Oct 24;4:e880.

(-)-marinopyrrole A is a pyrrole compound with the structure 1'H-1,3'-bipyrrole, in which four chlorine atoms are substituted at the 4, 4', 5, and 5' positions, and two 2-hydroxybenzoyl groups are substituted at the 2' and 2' positions, respectively. This compound was isolated from Streptomyces strain CNQ-418 and exhibits cytotoxic and antibacterial activity. It can be used as an antibacterial agent, antitumor agent, marine metabolite, and bacterial metabolite. It belongs to the pyrrole class, organochlorine compounds, phenolic compounds, and aromatic ketones.

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Maritoclax is a marine-derived natural product that is considered to have dual potential for anticancer and antibacterial activity[1][2][3]
-Proposed anticancer mechanism (from [1]): Directly binds to Mcl-1, triggering its ubiquitination and proteasome degradation, thereby overcoming the resistance of Mcl-1-dependent cancer cells to ABT-737[1]
-Another anticancer mechanism (from [3]): Induces apoptosis in myeloma cells with high MCL1 expression and low BCL2 expression by impairing eukaryotic protein translation, without relying on direct binding to Mcl-1[3]
-Paradoxical findings (from [4]): Failed to show selective cytotoxicity against Mcl-1-dependent cell lines; did not disrupt the interaction of the Mcl-1-BH3 peptide, which challenges its assumed role as a selective Mcl-1 antagonist[4]
-Antibacterial mechanism (from [2]): Inhibits methicillin-resistant Staphylococcus aureus (MRSA). The growth and biofilm formation of the bacteria may be achieved by targeting bacterial kinase signaling pathways [2] - The bioactivity of this drug remains controversial, especially its specificity for Mcl-1, which needs further verification [1][4]

C22H12CL4N2O4

510.15

507.955

1227962-62-0

24797083

Light yellow to yellow solid

1.6±0.1 g/cm3

732.4±60.0 °C at 760 mmHg

396.7±32.9 °C

0.0±2.5 mmHg at 25°C

1.708

6.91

3

4

5

32

715

0

OC1=CC=CC=C1C(C2=C(N3C(C(C4=CC=CC=C4O)=O)=CC(Cl)=C3Cl)C(Cl)=C(Cl)N2)=O

QYPJBTMRYKRTFG-UHFFFAOYSA-N

InChI=1S/C22H12Cl4N2O4/c23-12-9-13(19(31)10-5-1-3-7-14(10)29)28(22(12)26)18-16(24)21(25)27-17(18)20(32)11-6-2-4-8-15(11)30/h1-9,27,29-30H

[4,5-dichloro-1-[4,5-dichloro-2-(2-hydroxybenzoyl)-1H-pyrrol-3-yl]pyrrol-2-yl]-(2-hydroxyphenyl)methanone

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)

Solubility in Formulation 1: ≥ 2.5 mg/mL (4.90 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: 2.5 mg/mL (4.90 mM) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), suspension solution; with ultrasonication.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
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.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (4.90 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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