Marinopyrrole A

Biological Activity

Marinopyrrole A (Maritoclax) is a novel and specific Mcl-1 inhibitor with an IC50 value of 10.1 μM, and shows >8 fold selectivity than BCL-xl (IC50 > 80 μM). Maritoclax blocks the binding of Bim BH3 α-helix to Mcl-1 but not Bcl-XL. Maritoclax markedly inhibits the viability of Mcl-1-IRES-BimEL cells (EC50=1.6 μM) with a selectivity greater than 40-fold over Bcl-2-IRES-BimEL (EC50=65.1 μM) and Bcl-XL-IRES-BimEL (EC50=70.0 μM) cells. Maritoclax induces cell death selectively in Mcl-1-dependent but not Bcl-2- or Bcl-XL-dependent leukemia cells. Maritoclax induces proteasome-mediated Mcl-1 degradation without induction of Mcl-1 phosphorylation and Noxa expression. Maritoclax inhibits Mcl-1 interaction with Bim in intact cells and triggers cytochrome c release from isolated mitochondria. Maritoclax synergistically sensitizes lymphoma/leukemia cells to ABT-737. Marinopyrrole A (3 μM) induced-cell death is associated with MCL1 decrease and translation inhibition. Marinopyrrole A induces a dephosphorylation of EIF4EBP1 concomitant to a decrease of EIF4E phosphorylation.

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

Conversion of different model animals based on BSA (Value based on data from FDA Draft Guidelines)

Species	Mouse	Rat	Rabbit	Guinea pig	Hamster	Dog
Weight (kg)	0.02	0.15	1.8	0.4	0.08	10
Body Surface Area (m2)	0.007	0.025	0.15	0.05	0.02	0.5
Km factor	3	6	12	8	5	20

Animal A (mg/kg) = Animal B (mg/kg) multiplied by	Animal B Km
	Animal A Km

For example, to modify the dose of Compound A used for a mouse (20 mg/kg) to a dose based on the BSA for a rat, multiply 20 mg/kg by the K_m factor for a mouse and then divide by the K_m factor for a rat. This calculation results in a rat equivalent dose for Compound A of 10 mg/kg.

Chemical Information

References

[1] Doi K, et al. Cancer Biol Ther. Maritoclax induces apoptosis in acute myeloid leukemia cells with elevated Mcl-1 expression.

[2] Doi K, et al. J Biol Chem. 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.