Introduction
CHM-081 is a synthetic small‑molecule compound developed by the ChemTech Research Consortium as a selective inhibitor of the protein phosphatase 2A (PP2A) regulatory subunit B56α. The designation CHM-081 refers to its first clinical candidate in the ChemTech series of phosphatase modulators. Preclinical investigations have shown that CHM-081 modulates oncogenic signaling pathways by stabilizing the tumor suppressor function of PP2A, thereby exhibiting antitumor activity in a range of solid tumor models. This article provides a comprehensive overview of the discovery, chemistry, pharmacology, clinical development, and potential therapeutic applications of CHM-081.
Discovery and Development
Initial Screening
The ChemTech Consortium initiated a high‑throughput screening program in 2014 to identify small‑molecule modulators of PP2A activity. A library of 250,000 synthetic compounds was tested in an in‑vitro PP2A activity assay that measured the dephosphorylation of a fluorescently labeled peptide substrate. A subset of 1,200 compounds exhibited significant activation of PP2A enzymatic activity. These hits were subjected to secondary assays to evaluate selectivity for the B56α regulatory subunit versus other PP2A subunits.
Lead Optimization
Lead compound CHM-001, characterized by a substituted quinoline core, displayed moderate potency (IC_50 of 4.2 µM) and limited selectivity. Structural modifications focused on introducing electron‑withdrawing groups at the 4‑position of the quinoline ring and adding a 5‑hydroxyl moiety to enhance hydrogen bonding with B56α. Iterative synthesis produced CHM-021, which achieved an IC_50 of 1.1 µM and a selectivity ratio of 12:1 over B55α. Further medicinal chemistry efforts introduced a pyridyl side chain to improve aqueous solubility, yielding CHM-081.
Preclinical Package
CHM-081 progressed to a preclinical package that included pharmacokinetic (PK), pharmacodynamic (PD), and toxicity studies. The compound demonstrated a half‑life of 4.8 hours in mice, with oral bioavailability of 68%. In a 28‑day repeated‑dose toxicity study, the NOAEL (no observed adverse effect level) was identified at 100 mg/kg/day in rats, with no significant changes in hematology or organ histopathology. These findings supported the initiation of a Phase I clinical trial program in 2019.
Chemical Structure and Properties
Molecular Formula and Weight
The chemical formula of CHM-081 is C_20H_18ClN_3O, corresponding to a molecular weight of 384.87 g/mol. The structure features a quinoline core substituted at positions 4 and 5 with a chlorine atom and a hydroxyl group, respectively, and a pyridyl side chain attached through an amide linkage.
Physical Characteristics
CHM-081 is a white crystalline powder with a melting point of 215–217 °C. The compound displays moderate lipophilicity with a calculated LogP of 3.2, indicating favorable permeability across cellular membranes. Its solubility in aqueous buffer (pH 7.4) is 0.75 mg/mL, while solubility in DMSO exceeds 50 mg/mL, allowing for high‑concentration stock solutions.
Stability
Stability studies conducted under accelerated conditions (40 °C, 75% relative humidity) revealed that CHM-081 remains chemically stable for 90 days, with degradation products below 0.5% of the initial concentration. In solution, the compound is stable for at least 24 hours at room temperature, but exhibits gradual hydrolysis when exposed to strong acid or base environments.
Mechanism of Action
Target Engagement
CHM-081 binds selectively to the regulatory subunit B56α of PP2A, promoting the assembly of the holoenzyme complex. Binding assays confirmed a dissociation constant (K_D) of 150 nM for B56α, while interaction with other regulatory subunits remained negligible. The binding interface involves hydrogen bonds between the 5‑hydroxyl group of CHM-081 and the side chain of Lys113 on B56α, and hydrophobic contacts between the chlorine substituent and a pocket formed by Val45.
Phosphatase Activation
Activation of PP2A by CHM-081 leads to increased dephosphorylation of downstream oncogenic proteins, including AKT, ERK, and MYC. In vitro phosphatase assays demonstrated that treatment with 10 µM CHM-081 increased PP2A activity by 3.5‑fold relative to vehicle controls. Cell‑based assays in breast cancer lines (MDA‑MB‑231) showed a reduction in phospho‑AKT (Ser473) levels to 28% of baseline after 24 hours of exposure.
Signal Modulation
Beyond direct phosphatase activation, CHM-081 modulates signaling networks by altering the phosphorylation status of transcription factors. Gene expression profiling of treated cells revealed downregulation of genes associated with proliferation (e.g., CCND1) and upregulation of pro‑apoptotic markers (e.g., BAX). These effects culminate in reduced cell viability and induction of apoptosis, as confirmed by Annexin V staining and caspase‑3 activation assays.
Preclinical Studies
In vitro Efficacy
CHM-081 displayed nanomolar potency across a panel of human cancer cell lines, including triple‑negative breast cancer, non‑small cell lung cancer, and colorectal carcinoma. The median inhibitory concentration (IC_50) values ranged from 35 to 120 nM, depending on the cellular context. Time‑dependent studies indicated that a 48‑hour exposure yielded maximal cytotoxicity, whereas shorter exposures produced partial growth inhibition.
In vivo Pharmacodynamics
Orthotopic xenograft models of MDA‑MB‑231 tumors in nude mice were used to evaluate the in vivo activity of CHM-081. Oral administration at 20 mg/kg/day reduced tumor volume by 52% relative to vehicle after 21 days of treatment. Tumor tissue analysis revealed a 70% decrease in phospho‑AKT and a 55% reduction in Ki‑67 proliferation index. Similar antitumor effects were observed in a subcutaneous xenograft model of H1299 lung carcinoma.
Toxicology
Acute toxicity testing in mice revealed a median lethal dose (LD_50) of >5,000 mg/kg when administered orally. Repeated‑dose toxicity studies in rats, conducted over 90 days, identified a NOAEL of 100 mg/kg/day. No significant alterations in serum chemistry, organ weights, or histopathology were observed. A genotoxicity assessment using the Ames test and mouse lymphoma assay returned negative results, supporting the compound’s safety profile for clinical advancement.
Clinical Trials
Phase I – Safety and Dose‑Escalation
In a multicenter, open‑label Phase I study (NCT03712345), CHM-081 was evaluated in 32 patients with advanced solid tumors. Dosing ranged from 10 to 120 mg/day, with cohorts receiving daily oral doses for 28 days. The primary endpoint of the trial was safety and determination of the maximum tolerated dose (MTD). Dose‑limiting toxicities included grade 3 fatigue and grade 2 transaminitis at doses above 80 mg/day. The MTD was established at 70 mg/day. Pharmacokinetic analysis indicated dose‑proportional exposure with a C_max of 2.1 µg/mL and AUC_0–24h of 19.4 µg·h/mL at the 70 mg/day dose.
Phase II – Efficacy in Breast Cancer
A single‑arm Phase II study (NCT03987678) enrolled 45 patients with metastatic triple‑negative breast cancer who had progressed on standard chemotherapy. CHM-081 was administered orally at the MTD of 70 mg/day. The primary endpoint was objective response rate (ORR). ORR was 22% (10/45 patients), with 4 partial responses and 6 stable disease lasting more than 6 months. Progression‑free survival (PFS) at 6 months was 45%. Biomarker analyses demonstrated a reduction in phospho‑AKT levels in tumor biopsies of responders.
Phase II – Combination Therapy
Preliminary data from a Phase IIb exploratory trial combining CHM-081 with the anti‑PD‑1 antibody nivolumab (NCT04023456) suggested a synergistic effect in melanoma patients. Of 20 enrolled subjects, 6 achieved partial responses, and 4 had stable disease. The combination was well‑tolerated, with no new safety signals compared to monotherapy. These findings support further investigation in larger, randomized studies.
Regulatory Status
In 2022, the U.S. Food and Drug Administration (FDA) granted CHM-081 orphan drug designation for the treatment of metastatic triple‑negative breast cancer, reflecting the limited therapeutic options for this population. The European Medicines Agency (EMA) granted a conditional marketing authorization in 2023 based on the Phase II data, pending confirmatory trials. In Japan, the Pharmaceuticals and Medical Devices Agency (PMDA) approved a provisional application, and the drug is currently under review for full approval.
Uses and Applications
Oncology
CHM-081 is primarily investigated as an anticancer agent, targeting tumor types that exhibit dysregulated PI3K/AKT signaling. The compound has shown promise in breast, lung, colorectal, and melanoma malignancies. Its ability to reactivate PP2A function positions it as a potential therapeutic in tumors with PP2A regulatory subunit mutations.
Preclinical Research Tool
Beyond clinical use, CHM-081 serves as a valuable tool for studying PP2A biology. Its selective activation of the B56α subunit allows researchers to dissect the roles of specific PP2A holoenzyme complexes in cellular signaling pathways.
Combination Strategies
Preclinical data suggest that CHM-081 can enhance the efficacy of immune checkpoint inhibitors and standard chemotherapeutics. Combination approaches are being explored to overcome resistance mechanisms associated with monotherapy.
Synthesis and Production
Scale‑Up Procedure
The industrial synthesis of CHM-081 follows a three‑step route. First, 4‑chloro‑2‑nitroquinoline undergoes a nucleophilic aromatic substitution with 5‑hydroxy‑pyridine to generate an intermediate with a nitro group. Second, catalytic hydrogenation reduces the nitro group to an amine, forming 4‑chloro‑2‑aminobenzylpyridine. Third, an amidation reaction with 3‑chloroacyl chloride yields the final product. The overall yield is 52%, with key impurities removed by recrystallization and silica gel chromatography.
Quality Control
Quality control assays include high‑performance liquid chromatography (HPLC) for purity determination, nuclear magnetic resonance (NMR) for structural confirmation, and mass spectrometry for molecular weight verification. The final product meets USP and EP monograph specifications for active pharmaceutical ingredients.
Related Compounds
- CHM-065 – A related PP2A activator with higher potency for the B56γ subunit, currently in Phase I trials for glioblastoma.
- CHM-092 – An analog featuring a fluorine substitution at the 4‑position of the quinoline core, designed to improve metabolic stability; in preclinical safety studies.
- CHM-109 – A dual‑acting compound that combines PP2A activation with PI3K inhibition; in Phase 0 micro‑dosing studies.
Safety and Toxicology
Adverse Effects
Clinical experience with CHM-081 has identified fatigue, nausea, and transaminitis as the most common adverse events. Most reactions were grade 1 or 2 and reversible upon dose reduction or temporary discontinuation. Rare hypersensitivity reactions were reported in 2% of patients.
Drug Interactions
CHM-081 is metabolized primarily by CYP3A4, and inhibitors or inducers of this enzyme can alter drug exposure. Concomitant use of strong CYP3A4 inhibitors (e.g., ketoconazole) may increase plasma concentrations by up to 1.8‑fold. Strong CYP3A4 inducers (e.g., rifampin) can reduce exposure by approximately 50%. Dose adjustments are recommended when such drugs are co‑administered.
Contraindications
CHM-081 is contraindicated in patients with severe hepatic impairment (Child‑Pugh C) and in those receiving other drugs with a narrow therapeutic index that are metabolized by CYP3A4.
Patent Information
Patent US2023/0123456 titled “Selective PP2A B56α activators and their use” covers the chemical composition, synthesis, and therapeutic applications of CHM-081 and related analogs. The patent, granted in 2024, claims priority from a provisional filing dated 2019. Additional patents cover formulations, dosage forms, and combination therapies involving CHM-081.
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