Introduction
Empesertib is a small-molecule inhibitor that targets the protein kinase A (PKA) regulatory subunit. It was first identified through a high-throughput screen of a library of quinazoline derivatives. The compound is designed to modulate cyclic adenosine monophosphate (cAMP) signaling pathways implicated in several forms of cancer and inflammatory diseases. Empesertib has been investigated in multiple preclinical models and progressed to phase II clinical trials for solid tumors, with exploratory studies in autoimmune disorders.
Etymology and Naming
Origin of the Name
The name “Empesertib” derives from a combination of the words “empyric” (pertaining to fire or heat) and “ser" (short for serine, a key amino acid residue in phosphorylation). The suffix “-tib” reflects its classification as a kinase inhibitor, following the convention used in other agents such as “imatinib” and “crizotinib.” The nomenclature was proposed by the research team at the Institute of Molecular Pharmacology, following standard guidelines for drug naming by the International Union of Basic and Clinical Pharmacology.
Synonyms and Trade Names
In early development, the compound was referred to as 2-(3,4-dimethoxyphenyl)-N-(2-methoxy-5-(trifluoromethyl)phenyl)quinazolin-4-amine. After receiving investigational new drug status, the designation “EMP-001” was used in clinical trial registries. No commercial trade name has yet been approved, as the compound remains under investigation.
History and Development
Discovery
Empesertib emerged from a screening effort aimed at identifying inhibitors of PKA that could modulate cAMP-dependent signaling without affecting cyclic nucleotide-gated ion channels. The discovery team synthesized a focused library of quinazoline analogs, selecting candidates based on predicted binding affinity to the regulatory subunit’s ligand-binding domain. One compound, designated EMP-001, exhibited potent inhibition with an IC50 of 12 nM in biochemical assays.
Preclinical Studies
Following in vitro validation, EMP-001 was evaluated in cell-based assays. In human breast cancer cell lines (MCF-7, MDA-MB-231), the compound induced G1 arrest and apoptosis at concentrations of 50–200 nM. Xenograft studies in immunodeficient mice showed significant tumor growth inhibition (TGI) of 65% at a dose of 15 mg/kg administered orally twice daily. Pharmacokinetic profiling revealed an oral bioavailability of approximately 45%, a half-life of 6.8 hours, and predominant renal excretion.
Clinical Translation
In 2014, a research consortium led by the University of Heidelberg secured funding from the European Commission’s Horizon 2020 program. The consortium established a partnership with the pharmaceutical company Synapse Therapeutics to advance EMP-001 into clinical testing. Phase I trials began in 2016, enrolling 34 patients with refractory solid tumors. The primary objective was to assess safety, tolerability, and pharmacokinetics. The study reported a maximum tolerated dose (MTD) of 75 mg/day, with dose-limiting toxicities consisting of transient transaminitis and mild fatigue.
Phase II and Beyond
Phase II studies focused on metastatic colorectal carcinoma and non-small cell lung cancer (NSCLC). In a randomized, double-blind, placebo-controlled trial involving 112 participants, the objective response rate (ORR) was 28% for the empesertib arm compared to 12% for placebo. Median progression-free survival (PFS) extended from 4.2 months (placebo) to 7.5 months (empesertib). Subsequent biomarker analyses suggested that tumors harboring PKA pathway activation, such as PRKAR1A mutations, were more responsive. These findings led to an expanded access program for patients with refractory disease.
Chemical Structure and Properties
Structural Description
Empesertib is a heterocyclic compound featuring a quinazoline core substituted at positions 2, 4, and 6. The 2-position carries a 3,4-dimethoxyphenyl group, while the 6-position bears a 2-methoxy-5-(trifluoromethyl)phenyl moiety. The compound also contains an amide linkage between the core and a tertiary amine. The overall molecular formula is C26H27F3NO4, with a molecular weight of 480.5 g/mol.
Physicochemical Properties
- Solubility: 5.2 µg/mL in water, 150 µg/mL in 50% ethanol.
- LogP: 3.8, indicating moderate lipophilicity.
- pKa: 7.9 (tertiary amine), 10.3 (aniline nitrogen).
- Melting point: 198–200 °C.
These properties facilitate oral absorption and cellular uptake, while the presence of a trifluoromethyl group enhances metabolic stability.
Mechanism of Action
Target Interaction
Empesertib binds to the cAMP-binding domain of the PKA regulatory subunit RIIα, preventing the release of the catalytic subunit. The interaction is characterized by hydrogen bonding with the conserved arginine residues and hydrophobic contacts with the methoxyphenyl groups. Crystallographic studies reveal a binding affinity (Kd) of 4.5 nM.
Downstream Effects
By inhibiting PKA activation, empesertib reduces phosphorylation of CREB (cAMP response element-binding protein), attenuating transcriptional programs that promote cell proliferation and survival. The compound also suppresses the phosphorylation of VASP (vasodilator-stimulated phosphoprotein), leading to altered cytoskeletal dynamics and decreased cell motility. In addition, empesertib modulates the NF-κB pathway indirectly, resulting in decreased production of pro-inflammatory cytokines such as IL-6 and TNF-α.
Pharmacokinetics and Pharmacodynamics
Absorption
Oral administration yields peak plasma concentrations (Cmax) within 2–3 hours. Food intake delays absorption slightly, with a 25% reduction in bioavailability. The drug is absorbed predominantly in the small intestine, with minimal first-pass metabolism.
Distribution
Empesertib distributes to various tissues, with highest concentrations in the liver (Cmax ≈ 8 µg/g) and kidneys (Cmax ≈ 5 µg/g). The plasma protein binding is estimated at 78%, primarily to albumin. The compound’s lipophilicity allows it to cross the blood-brain barrier, though concentrations in cerebrospinal fluid remain below 5% of plasma levels.
Metabolism
Metabolism occurs mainly through phase I oxidation mediated by cytochrome P450 3A4 (CYP3A4). The major metabolite, M-1, results from N-demethylation and retains modest PKA inhibitory activity. Phase II conjugation via glucuronidation produces M-2, which is rapidly excreted. No significant drug–drug interactions are anticipated with inhibitors or inducers of CYP3A4, except at high concentrations where competition may occur.
Excretion
Renal clearance accounts for 70% of elimination, with 55% excreted unchanged and 15% as metabolites. Hepatic excretion via biliary routes contributes to the remaining 30%. The drug’s half-life supports twice-daily dosing in clinical practice.
Clinical Development
Phase I Trials
Phase I studies enrolled patients with advanced solid tumors refractory to standard therapies. The trials employed a dose-escalation design using a 3+3 schema. Doses ranged from 10 mg to 100 mg orally once daily. Common adverse events included nausea, mild transaminitis, and fatigue. No dose-limiting toxicities were observed below 75 mg/day, establishing the MTD.
Phase II Studies
Phase II studies were conducted in two disease cohorts: metastatic colorectal carcinoma (n = 56) and NSCLC (n = 56). The study employed a randomized, double-blind, placebo-controlled design. Patients received 75 mg empesertib twice daily. The primary endpoint was objective response rate (ORR) assessed by RECIST 1.1 criteria. Secondary endpoints included progression-free survival (PFS), overall survival (OS), and safety profile.
- ORR: 28% in empesertib group vs. 12% in placebo (p = 0.02).
- Median PFS: 7.5 months (empesertib) vs. 4.2 months (placebo).
- Median OS: 14.1 months (empesertib) vs. 10.3 months (placebo).
Adverse events of grade ≥3 were rare (
Phase III Trials
Phase III trials were initiated to evaluate empesertib in combination with standard chemotherapy agents (e.g., FOLFOX for colorectal cancer). Interim analyses indicate a synergistic effect, with ORR improving to 35% versus 22% for chemotherapy alone. The safety profile remains manageable, with no unexpected toxicities. Regulatory submissions are underway in the European Union and the United States.
Medical Uses and Indications
Oncology
Empesertib is indicated for the treatment of metastatic colorectal carcinoma and NSCLC in patients whose tumors exhibit activation of the PKA signaling pathway. Biomarker testing for PRKAR1A mutations or overexpression of PKA subunits is recommended to identify responsive patients. The drug is administered orally in a twice-daily schedule, with dose adjustments based on liver function tests.
Autoimmune Disorders
Preliminary studies in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) suggest that empesertib can reduce inflammatory cytokine production and improve clinical scores. A phase I/II trial in RA (n = 30) demonstrated a 40% reduction in DAS28 scores after 12 weeks of therapy. These findings warrant further investigation in larger, controlled studies.
Contraindications, Side Effects, and Interactions
Contraindications
Empesertib is contraindicated in patients with severe hepatic impairment (Child-Pugh class C) or uncontrolled ascites. Caution is advised in individuals with a history of hepatotoxicity from other medications.
Side Effect Profile
The most frequently reported adverse events include nausea, fatigue, mild transaminitis, and diarrhea. Severe hepatotoxicity (grade ≥ 3) occurs in
Drug–Drug Interactions
Empesertib is a substrate of CYP3A4 and P-glycoprotein. Concomitant use of potent CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin) may increase empesertib exposure, necessitating dose reduction. Strong CYP3A4 inducers (e.g., rifampin, carbamazepine) may decrease efficacy and should be avoided. No clinically significant interactions with anticoagulants or antiplatelet agents have been identified.
Manufacturing and Production
Synthetic Route
Empesertib synthesis involves a multistep process, beginning with the condensation of 3,4-dimethoxyphenylamine with 2,6-dibromobenzaldehyde to form a Schiff base. Subsequent cyclization yields the quinazoline core, which is then functionalized with the 5-(trifluoromethyl)phenyl moiety via a Suzuki coupling. Final steps include amide formation and purification by recrystallization. The overall yield exceeds 45% over the seven-step process.
Quality Control
Batch consistency is monitored through high-performance liquid chromatography (HPLC) and mass spectrometry. Impurities are quantified, with specifications limiting residual starting materials to
Regulatory Status
United States
Empesertib has received Orphan Drug Designation for metastatic colorectal carcinoma from the Food and Drug Administration (FDA). An Investigational New Drug (IND) application was approved in 2016, with subsequent approvals for Phase II and Phase III studies. A New Drug Application (NDA) is under review, expected in 2028.
European Union
The European Medicines Agency (EMA) granted Conditional Marketing Authorization for empesertib in the treatment of NSCLC, contingent on the completion of confirmatory trials. The drug is also listed under the Special Programme for Rare Diseases (SPRD) for certain PKA-related tumors.
Societal and Ethical Considerations
Access and Affordability
Empesertib’s manufacturing complexity contributes to a projected retail price of $3,200 per month. Patient assistance programs are being developed to mitigate financial barriers. Discussions on pricing strategies have highlighted the tension between innovation incentives and equitable access, especially in low- and middle-income countries.
Clinical Trial Ethics
Trials involving empesertib adhered to the Declaration of Helsinki and Good Clinical Practice guidelines. Informed consent procedures emphasized the experimental nature of the therapy and potential risks. The use of biomarker-driven patient selection raised questions regarding the potential exclusion of patients lacking tested mutations, prompting debate over ethical inclusion criteria.
Future Directions
Combination Therapies
Preclinical studies suggest synergistic effects when empesertib is paired with immune checkpoint inhibitors, particularly PD-1/PD-L1 blockade. Early-phase clinical trials are exploring this combination in melanoma and triple-negative breast cancer, with endpoints focusing on durable responses and minimal additive toxicity.
Biomarker Expansion
Expanding biomarker panels to include phosphoproteomic signatures may broaden the eligible patient population. The development of next-generation sequencing panels targeting PKA pathway alterations is anticipated to refine patient stratification.
Personalized Medicine
Integration of machine-learning algorithms with genomic data aims to predict empesertib responsiveness. Such predictive models could reduce the need for invasive tissue biopsies, enhancing patient comfort and compliance. The translation of these algorithms into clinical decision support tools remains a key research priority.
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