Abemaciclib induces G1 arrest and lysosomal dysfunction in canine melanoma cells: synergistic effects with
Se-Hoon Kim1, Jun-Yeol Choi1, Yoon-Ho Suh1
1Laboratory of Veterinary Internal Medicine, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Seoul National University, Seoul, Republic of Korea.
Introduction:
Abemaciclib, a CDK4/6 inhibitor, is well-established for treating hormone receptor-positive and HER2-negative (HR+/HER2-) human breast cancer by inducing G1 cell cycle arrest. However, its antitumor effects in other cancers, including canine melanoma, remain largely unexplored. Canine melanoma often harbors CDK4/6 copy number gains and cell cycle dysregulation, suggesting it may be a suitable target for abemaciclib.
Methods:
Five canine melanoma cell lines (CMeC1, KMeC, LMeC, UCDK9M4, and UCDK9M5) were used to evaluate the antitumor effects of abemaciclib. Cell viability and migration were assessed using Cell Counting Kit-8 and wound healing assays, respectively. Cell cycle distribution was analyzed by flow cytometry, and the expression of cell cycle-related genes and proteins was examined using RT-PCR and western blotting. The origin of cytoplasmic vacuoles was investigated using FITC-dextran uptake and V-ATPase inhibitor assays. Impaired autophagic flux was assessed by immunofluorescence detection of p62 accumulation. Synergistic effects with fenbendazole were evaluated using the Highest Single Agent (HSA) synergy scoring method, and in vivo efficacy was assessed in a xenograft model.
Results:
Abemaciclib induced G1 cell cycle arrest and altered the expression of cell cycle-related genes and proteins. Autophagy, but not apoptosis, was activated. Vacuolization was observed and suggested to originate from lysosomes, as evidenced by FITC-dextran uptake and V-ATPase inhibitor co-treatment. p62 accumulation indicated impaired autophagy flux. Co-treatment with fenbendazole enhanced cytotoxicity and showed synergistic effects within specific dose ranges. In vivo, abemaciclib alone or in combination with fenbendazole significantly suppressed tumor growth.
Discussion:
These findings demonstrate that abemaciclib exerts potent antitumor effects in canine melanoma by inducing cell cycle arrest and disrupting lysosomal function. Its synergistic interaction with fenbendazole suggests a potential combinatorial therapeutic approach for canine melanoma.
Insights
Abemaciclib, a CDK4/6 inhibitor, effectively treats canine melanoma by halting cell cycle progression and disrupting lysosomal function. Combination therapy with fenbendazole shows synergistic antitumor effects, offering a promising new treatment strategy for canine melanoma.
Area of Science:
- Oncology
- Veterinary Medicine
- Pharmacology
Background:
- Abemaciclib is a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor approved for human breast cancer.
- Canine melanoma exhibits CDK4/6 copy number gains and cell cycle dysregulation, suggesting potential sensitivity to CDK4/6 inhibitors.
- The efficacy of abemaciclib in canine cancers remains largely uninvestigated.
Purpose of the Study:
- To evaluate the antitumor effects of abemaciclib in canine melanoma.
- To investigate the underlying mechanisms of abemaciclib's action, including cell cycle effects and autophagy.
- To assess the potential synergistic effects of abemaciclib in combination with fenbendazole.
Main Methods:
- Abemaciclib's effects on canine melanoma cell lines were assessed using cell viability, migration, and cell cycle assays.
- Gene and protein expression related to the cell cycle was analyzed via RT-PCR and western blotting.
- Autophagy, lysosomal function, and synergistic effects with fenbendazole were evaluated using various assays, including in vivo xenograft models.
Main Results:
- Abemaciclib induced G1 cell cycle arrest and altered cell cycle-related gene/protein expression in canine melanoma cells.
- Abemaciclib activated autophagy and caused vacuolization, indicating disrupted lysosomal function.
- Combination therapy with fenbendazole demonstrated synergistic cytotoxicity and suppressed tumor growth in vivo.
Conclusions:
- Abemaciclib exhibits significant antitumor activity in canine melanoma by inducing cell cycle arrest and impairing lysosomal function.
- The combination of abemaciclib and fenbendazole presents a potential synergistic therapeutic strategy for canine melanoma.
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