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| Lapatinib is a tyrosine kinase inhibitor primarily used in the treatment of HER2-positive breast cancer, among other cancer types. Its mechanism of action involves binding to the intracellular ATP-binding sites of the HER1 (also known as EGFR) and HER2 receptors, thereby inhibiting their autophosphorylation and subsequent activation of downstream signaling pathways. The major pathways involved include: -PI3K/AKT/mTOR Pathway Inhibition of this pathway leads to reduced cell survival and proliferation, as it normally promotes growth and survival signals through downstream effectors. -RAS/RAF/MEK/ERK (MAPK) Pathway Blocking the activation of this cascade affects cell cycle progression, proliferation, and differentiation. In many cancers, dysregulation of this pathway contributes to uncontrolled growth. By interfering with these signaling cascades, lapatinib can reduce tumor cell proliferation, induce apoptosis (programmed cell death), and potentially increase the sensitivity of tumor cells to additional therapeutic agents. The induction of oxidative stress is one of the ways by which lapatinib can exert cytotoxic effects on cancer cells. Elevated ROS levels can damage cellular components, such as lipids, proteins, and DNA, thereby contributing to cell death. Lapatinib — an orally administered small-molecule 4-anilinoquinazoline tyrosine kinase inhibitor that reversibly inhibits the intracellular kinase domains of HER2/ErbB2 and EGFR/ErbB1. It is a dual HER2/EGFR targeted anticancer drug, commonly abbreviated LAP or lapatinib, and is marketed as Tykerb. It is used primarily in HER2-positive advanced or metastatic breast cancer in combination with capecitabine or, in hormone-receptor-positive disease, letrozole. It remains marketed in Canada and has an active U.S. prescription-drug label. Its contemporary clinical role is generally later-line or context-dependent because newer HER2-directed agents provide superior efficacy in many treatment sequences. Primary mechanisms (ranked):
Bioavailability / PK relevance: Oral absorption is incomplete and highly variable. At 1,250 mg/day, steady-state Cmax is approximately 2.43 µg/mL and AUC approximately 36.2 µg·h/mL; effective half-life is approximately 24 hours. Lapatinib is more than 99% protein bound and is extensively metabolized mainly by CYP3A4/3A5. Food markedly increases exposure, with approximately 3- to 4-fold increases in AUC depending on meal composition; consequently the approved regimen specifies administration at least one hour before or one hour after food. Strong CYP3A4 inhibitors and inducers can substantially alter exposure. Normal-brain penetration is poor because lapatinib is a P-gp/BCRP substrate, although penetration can be greater in disrupted brain metastases. In-vitro vs systemic exposure relevance: Clinically observed total plasma Cmax at 1,250 mg/day corresponds roughly to low-micromolar total lapatinib concentrations, but more than 99% protein binding means free systemic concentrations are substantially lower. Experiments using approximately 0.1–1 µM may therefore be reasonably relevant to tumor exposure depending on tissue accumulation and protein conditions, whereas mechanistic studies using 5–20 µM, particularly NRF2/hepatotoxicity studies, substantially exceed typical unbound systemic exposure and should be interpreted primarily as mechanistic or toxicity models rather than direct therapeutic-equivalent exposure. Clinical evidence status: Approved targeted therapy / Phase III RCT evidence / combination treatment. Lapatinib has demonstrated clinical benefit with capecitabine in previously treated HER2-positive advanced breast cancer and with letrozole in HR-positive/HER2-positive metastatic breast cancer. It remains marketed, including in Canada, but has largely moved to later-line or alternative use because trastuzumab deruxtecan, tucatinib-containing regimens and other newer HER2-directed therapies generally occupy preferred contemporary treatment positions. Major safety constraints include boxed-warning hepatotoxicity, diarrhea, reduced left-ventricular ejection fraction, QT prolongation, interstitial lung disease/pneumonitis, severe cutaneous reactions and clinically important CYP3A4-mediated drug interactions. Lapatinib Mechanistic Profile
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| Glutathione (GSH) is a thiol antioxidant that scavenges reactive oxygen species (ROS), resulting in the formation of oxidized glutathione (GSSG). Decreased amounts of GSH and a decreased GSH/GSSG ratio in tissues are biomarkers of oxidative stress. Glutathione is a powerful antioxidant found in every cell of the body, composed of three amino acids: cysteine, glutamine, and glycine. It plays a crucial role in protecting cells from oxidative stress, detoxifying harmful substances, and supporting the immune system. cancer cells can have elevated levels of glutathione, which may help them survive in the oxidative environment created by the immune response and chemotherapy. This can make cancer cells more resistant to treatment. While glutathione can be obtained from certain foods (like fruits, vegetables, and meats), its absorption from supplements is debated. Some people take N-acetylcysteine (NAC) or other precursors to boost glutathione levels, but the effects on cancer prevention or treatment are still being studied. Depleting glutathione (GSH) to raise reactive oxygen species (ROS) is a strategy that has been explored in cancer research and therapy. Many cancer cells have altered redox states and may rely on GSH to survive. Increasing ROS levels can induce stress in these cells, potentially leading to cell death. Certain drugs and compounds can deplete GSH levels. For example, agents like buthionine sulfoximine (BSO) inhibit the synthesis of GSH, leading to its depletion. Cancer cells tend to exhibit higher levels of intracellular GSH, possibly as an adaptive response to a higher metabolism and thus higher steady-state levels of reactive oxygen species (ROS). "...intracellular glutathione (GSH) exhibits an astounding antioxidant activity in scavenging reactive oxygen species (ROS)..." "Cancer cells have a high level of GSH compared to normal cells." "...cancer cells are affluent with high antioxidant levels, especially with GSH, whose appearance at an elevated concentration of ∼10 mM (10 times less in normal cells) detoxifies the cancer cells." "Therefore, GSH depletion can be assumed to be the key strategy to amplify the oxidative stress in cancer cells, enhancing the destruction of cancer cells by fruitful cancer therapy." The loss of GSH is broadly known to be directly related to the apoptosis progression. |
| 8169- | Lap, | Lapatinib Activates the Kelch-Like ECH-Associated Protein 1-Nuclear Factor Erythroid 2-Related Factor 2 Pathway in HepG2 Cells |
| - | in-vitro, | Liver, | HepG2 |
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