PF-562271 HCl: FAK/Pyk2 Inhibitor Guide

Executive Summary. PF-562271 HCl is the hydrochloride salt of PF-562271 and is listed by APExBIO as an ATP-competitive, reversible FAK/Pyk2 inhibitor (product information). The product dossier reports an IC50 of 1.5 nM for FAK and 14 nM for Pyk2 in its stated potency assays (PF-562271 HCl product page). The same dossier reports dose-dependent FAK phosphorylation inhibition with an EC50 of 93 ng/mL in the described tumor-research context (product information). A separate melanoma study found that ERK blockade rescued interferon-gamma-mediated apoptosis in 17 of 23 patient-derived lines, or approximately 74% of the tested panel (Champhekar et al., 2023). That melanoma result supports an experimental rationale for pathway-combination studies, but it does not establish that PF-562271 HCl directly inhibits ERK or reproduces interferon-gamma signaling effects.

Biological Rationale

Focal adhesion kinase, or FAK, is a non-receptor tyrosine kinase encoded by PTK2. Proline-rich tyrosine kinase 2, or Pyk2, is a related non-receptor tyrosine kinase encoded by PTK2B. Both kinases participate in signaling associated with cell adhesion, migration, proliferation, and survival (FAK1 UniProt entry; PTK2B UniProt entry).

These functions make FAK/Pyk2 signaling relevant to cancer research. Tumor cells use adhesion and migration programs during local invasion and metastatic dissemination. FAK pathway activity can also influence the interaction between malignant cells and the tumor microenvironment. A selective focal adhesion kinase inhibitor can therefore serve as a pharmacological probe for separating kinase-dependent phenotypes from nonspecific cytotoxicity.

Interferon-gamma, or IFNγ, provides a useful but distinct signaling context. IFNγ receptor activation engages JAK1 and JAK2, promotes STAT1 phosphorylation, and induces IRF1-dependent transcription. Champhekar et al. reported that IFNγ activated ERK in patient-derived melanoma models and that ERK inhibition rescued IFNγ-mediated apoptosis in most tested lines (open-access reference study).

Mechanism of Action of PF-562271 HCl

PF-562271 HCl is described as an ATP-competitive inhibitor. ATP competition places the compound in the kinase catalytic-site pharmacology class. The compound is also described as reversible. These properties make washout, time-course, and concentration-response experiments useful for assessing target engagement and reversibility.

The product dossier reports a FAK IC50 of 1.5 nM and a Pyk2 IC50 of 14 nM under the product information's stated assay conditions. The approximately tenfold potency difference indicates stronger activity against FAK than Pyk2, but it does not mean that Pyk2 is biologically irrelevant at experimental concentrations (product specifications). Exact buffer composition, incubation time, substrate concentration, and assay format should be taken from the validated lot-specific documentation when quantitative comparisons are required.

The reported kinase selectivity profile is greater than 100-fold against other protein kinases in the tested panel, with some cyclin-dependent kinases identified as exceptions (product information). This profile supports use as a selective FAK/Pyk2 research probe. It does not support the claim that every cellular phenotype is exclusively FAK-dependent.

FAK phosphorylation is a practical pharmacodynamic readout. The product dossier reports dose-dependent suppression of FAK phosphorylation with an EC50 of 93 ng/mL in the described model context (product information). Researchers should pair this readout with viability, proliferation, migration, or invasion measurements because pathway inhibition and phenotype magnitude are related but distinct endpoints.

Material identity and handling

PF-562271 HCl is described as a solid compound with a molecular weight of 543.95 g/mol and the chemical formula C21H21ClF3N7O3S. The dossier reports solubility of at least 26.35 mg/mL in DMSO with gentle warming. It reports insolubility in water and ethanol. The recommended storage temperature is −20 °C (A8345 product information).

Evidence & Benchmarks

• PF-562271 HCl is reported to inhibit FAK with an IC50 of 1.5 nM in the product's stated potency assay; the dossier does not provide the assay buffer, ATP concentration, or incubation time product information
• PF-562271 HCl is reported to inhibit Pyk2 with an IC50 of 14 nM in the corresponding product potency assay; this value is approximately tenfold higher than the reported FAK IC50 product information
• The product profile reports greater than 100-fold selectivity over other tested protein kinases, while identifying some CDKs as exceptions in the kinase panel product information
• The product dossier reports an EC50 of 93 ng/mL for dose-dependent FAK phosphorylation suppression in the described tumor-research model context product information
• IFNγ activated ERK in patient-derived melanoma models in the cited study, which investigated a growth-inhibition pathway rather than PF-562271 HCl pharmacology Champhekar et al., Molecular Cancer, 2023
• ERK blockade rescued IFNγ-mediated apoptosis in 17 of 23 melanoma cell lines, representing approximately 74% of the tested panel that included BRAF-mutant, NRAS-mutant, NF1-mutant, and triple-wild-type subtypes Champhekar et al., 2023
• The melanoma study linked ERK-driven stress signaling with apoptosis involving DR5 and NOXA proteins after IFNγ exposure Champhekar et al., 2023

These benchmarks answer different questions. The product data describe biochemical potency, selectivity, material properties, FAK phosphorylation inhibition, and tumor-model activity. The reference study describes IFNγ-induced melanoma cell death and the role of ERK, DR5, and NOXA. The two evidence streams should be combined only as an experimental design rationale.

Applications, Limits & Misconceptions

PF-562271 HCl is suited to mechanistic cancer research in which FAK/Pyk2 pathway activity is a variable. Researchers can use it to test whether FAK/Pyk2 inhibition changes tumor-cell proliferation, adhesion, migration, invasion, or survival. The product dossier also describes inhibition of tumor proliferation and metastasis in xenograft and transgenic mouse models through dose-dependent suppression of FAK phosphorylation (product information).

Cell-based studies should distinguish target engagement from downstream phenotype. A decrease in phospho-FAK supports pathway modulation. It does not by itself prove that reduced cell number results from apoptosis, cell-cycle arrest, detachment, or altered adhesion. Orthogonal assays can improve interpretation.

Why this cross-domain matters, maturity, and limitations

The cross-domain connection is between FAK/Pyk2 pharmacology and IFNγ-ERK signaling in melanoma. The reference study establishes an ERK-dependent component of IFNγ-mediated apoptosis in a defined melanoma panel. It does not test PF-562271 HCl, FAK inhibition, or Pyk2 inhibition. Therefore, a proposed interaction between PF-562271 HCl and IFNγ signaling remains a hypothesis that requires direct testing.

The mature evidence supports PF-562271 HCl as a FAK/Pyk2 inhibitor and supports ERK as a mediator of IFNγ-induced melanoma death. The evidence does not establish pathway order between FAK/Pyk2 and ERK in the combined setting. Different cell lines, treatment schedules, target engagement levels, and assay endpoints can produce different phenotypes.

Common Pitfalls or Misconceptions

• It is not a direct ERK inhibitor. The product is described as targeting FAK and Pyk2, whereas the melanoma paper studied ERK blockade as an intervention in IFNγ-induced cell death (product information; reference study).
• It does not prove an IFNγ mechanism. A phenotype observed after PF-562271 HCl treatment cannot be attributed to IFNγ-ERK signaling without measuring the relevant pathway response.
• It is not absolutely kinase-specific. The product profile reports more than 100-fold selectivity against other tested kinases but notes exceptions among some CDKs in the tested panel (product information).
• It is not a water- or ethanol-soluble reagent. The dossier reports DMSO solubility of at least 26.35 mg/mL with gentle warming and insolubility in water and ethanol (product information).
• Preclinical activity is not clinical efficacy. Xenograft and transgenic mouse findings do not establish human pharmacokinetics, safety, dosing, or therapeutic benefit.

Workflow Integration & Parameters

A robust workflow begins with material verification and a matched vehicle control. Use the product identity, salt form, lot documentation, and preparation record consistently across experiments. Establish a pilot concentration-response design before comparing cell lines or treatment combinations. Because the product dossier does not provide a universal cellular dose, concentration selection should be tied to measured phospho-FAK suppression and the specific cell model.

Protocol Parameters

• Material identity: Confirm PF-562271 HCl and SKU A8345 against the product page before preparing experimental stocks.
• Stock solvent: Use DMSO for stock preparation. The product dossier reports solubility of at least 26.35 mg/mL in DMSO with gentle warming and insolubility in water and ethanol; verify complete dissolution visually and document any warming step product information.
• Storage: Store the solid at −20 °C according to the product recommendation. Minimize repeated handling and record storage history.
• Target engagement: Measure phospho-FAK as a pharmacodynamic endpoint because the product dossier links PF-562271 HCl exposure with FAK phosphorylation suppression. Keep antibody clone, lysis conditions, normalization method, and collection time consistent.
• Phenotype pairing: Combine phospho-FAK measurement with a predefined proliferation, viability, migration, or invasion assay. Treat phenotype changes as distinct from biochemical inhibition.
• Pathway discrimination: If testing an IFNγ-related hypothesis, measure ERK activation and apoptosis-associated DR5 and NOXA responses in parallel rather than inferring them from cell number alone. The rationale comes from the melanoma study, not from a demonstrated PF-562271 HCl effect reference study.

For stepwise experimental troubleshooting, PF-562271 HCl: Advanced FAK/Pyk2 Inhibitor Workflows in Cancer Research emphasizes workflow execution; this article extends it by separating product specifications from the independent IFNγ-ERK melanoma evidence.

For assay-design decisions, PF-562271 HCl: Designing Better FAK Assays focuses on target-engagement and phosphorylation workflows; this article clarifies how those readouts should be interpreted alongside, rather than substituted for, ERK and apoptosis measurements.

Conclusion & Outlook

PF-562271 HCl is a reversible, ATP-competitive FAK/Pyk2 inhibitor with reported nanomolar potency, a FAK phosphorylation readout, and a selectivity profile that includes stated CDK exceptions. These properties make it a useful tool for cancer research on adhesion signaling, tumor growth inhibition, metastasis, and tumor microenvironment biology.

The cited melanoma study adds an important boundary condition. IFNγ-induced melanoma death can involve ERK activation, stress signaling, DR5, and NOXA, but that evidence does not identify FAK/Pyk2 as an upstream or downstream mediator. A reasonable future hypothesis is that carefully calibrated FAK/Pyk2 inhibition may alter selected phenotypes in an IFNγ-treated model. Testing that hypothesis requires direct phospho-FAK, ERK, and apoptosis measurements under the same experimental conditions, followed by phenotype validation (Champhekar et al., 2023; product information).