PF-477736, also known as PF-00477736, is an investigational ATP-competitive checkpoint kinase 1 (Chk1) inhibitor developed by Pfizer. Its molecular formula is C22H25N7O2, while the PF-477736 molecular weight is 419.48 g/mol. The IUPAC name is (2R)-2-amino-2-cyclohexyl-N-[2-(1-methyl-1H-pyrazol-4-yl)-6-oxo-5,6-dihydro-1H-[1,2]diazepino[4,5,6-cd]indol-8-yl]acetamide. Registered as CAS 952021-60-2, the compound represents the specified (2R) stereoisomer rather than an unspecified racemate.
Application of PF-477736
The Chk1 inhibitor PF-477736 is used to examine DNA damage checkpoint signaling and the consequences of overriding S- and G2-phase arrest after genotoxic stress. It is particularly useful in combination studies with agents such as gemcitabine or carboplatin. Reported preclinical experiments found greater chemopotentiation in several p53-deficient cancer models than in p53-competent normal cells, but this pattern should not be generalized to every cell type or treatment condition.
In Vitro
In cell-free assays, PF 477736 inhibited Chk1 with a Ki of 0.49 nM and Chk2 with a Ki of 47 nM, corresponding to approximately 96-fold selectivity. It also inhibited VEGFR2, Fms, Yes, Aurora-A, FGFR3, Flt3, and Ret at 8–39 nM, whereas the reported CDK1 value was 9.9 μM. These off-target data are important when selecting cellular concentrations.
In checkpoint-abrogation assays, PF-477736 reversed camptothecin-induced G2 arrest with EC50 values of 45 nM in CA46 cells, 38 nM in HeLa cells, and 42 nM in HT29 cells. The compound also enhanced the cytotoxicity of DNA-damaging agents in multiple preclinical cancer models.
In Vivo
In Colo205 xenografts, PF-477736 was administered at 4–60 mg/kg on a q3d × 4 schedule beginning 24 hours after gemcitabine. Doses of 15 and 30 mg/kg increased caspase-3 activation, histone H3 phosphorylation, and H2AX phosphorylation, consistent with checkpoint abrogation, DNA damage, and apoptosis. Under the reported conditions, the combination improved gemcitabine activity without additional body-weight loss. The Pfizer PF-477736 program also entered a Phase 1 combination study with gemcitabine, but that study was terminated; the compound is not an approved therapy.
Biochemical and Physiological Actions
The PF-477736 chemical structure enables binding within the ATP site of Chk1. Inhibiting Chk1 disrupts checkpoint signaling that normally delays cell-cycle progression while damaged DNA is repaired. Cells may therefore enter mitosis with unresolved lesions, increasing replication stress and apoptotic signaling.
The defined stereocenter in the PF-477736 molecular structure establishes chemical identity but does not make cellular responses specific to Chk1 at every concentration. Activity against Chk2 and several other kinases should be considered when interpreting phenotypes.
Features and Benefits of PF-477736
- Sub-nanomolar biochemical potency against Chk1.
- Quantified selectivity margins across a broad kinase panel.
- Cellular and xenograft data for combination-study design.
- A defined stereoisomer registered as 952021-60-2.
PF-477736 provides a characterized tool for DNA damage response research, including checkpoint-abrogation and chemopotentiation studies. Before use, verify the PF-477736 structure, purity, and stereochemical identity against the product-specific CoA.
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