Inhibitory Effects of Petasin on Human Colon Carcinoma Cells Mediated by Inactivation of Akt/mTOR Pathway
Colorectal cancer (CRC) is the third most common cancer worldwide, following lung and breast cancer. It accounts for nearly 10% of total cancer cases and is the fourth leading cause of cancer-related deaths. Despite advancements in screening programs, risk factor reduction, and targeted therapies, the median survival for patients with metastatic CRC remains around 20 months. The high costs of treatment and the limited efficacy of current therapies highlight the urgent need for new anticancer agents. Natural products have long been a rich source of therapeutic agents, and petasin, a natural compound found in plants of the genus Petasites, has shown potential anticancer properties. This study investigates the anticolon cancer activity of petasin both in vitro and in vivo, focusing on its molecular mechanisms.
Petasin Inhibits Proliferation of Human Colon Carcinoma Cells
The study evaluated the effects of petasin on the proliferation of four human colon carcinoma cell lines: SW-620, Caco-2, LoVo, and HT-29. Using the MTT assay, researchers found that petasin exerted dose-dependent cytotoxicity on all four cell lines. The half-maximal inhibitory concentration (IC50) values for petasin at 48 hours were 30.07 µM for SW-620, 209.67 µM for Caco-2, 228.59 µM for LoVo, and 78.08 µM for HT-29. Among these, the SW-620 cell line was the most sensitive to petasin. Treatment with 25 µM petasin for 24, 48, and 72 hours resulted in 21.16%, 38.52%, and 47.15% inhibition of SW-620 cell growth, respectively. These findings suggest that petasin significantly inhibits the proliferation of colon cancer cells, with SW-620 cells being particularly responsive.
Petasin Induces Apoptosis in SW-620 Cells
Apoptosis, or programmed cell death, is a critical target for cancer treatment. To determine whether petasin induces apoptosis in SW-620 cells, researchers used Annexin-V-FITC/propidium iodide (PI) staining and flow cytometry. Treatment with 25 µM petasin for 48 hours significantly increased the percentage of apoptotic cells from 6.01% in the control group to 31.03% in the treated group. Hoechst 33258 staining further confirmed these results, showing clear morphological changes such as nuclear condensation in petasin-treated cells, compared to the uniform, round nuclei of control cells. These findings indicate that petasin induces apoptosis in SW-620 cells, which may contribute to its anticancer effects.
Petasin Inhibits Migration and Invasion of SW-620 Cells
Cancer cell migration and invasion are key processes in tumor metastasis. To assess the effects of petasin on these processes, researchers conducted wound-healing and Transwell assays. In the wound-healing assay, SW-620 cells treated with 25 µM petasin showed a significant reduction in migration ability, with the percentage of migration decreasing from 68.1% in the control group to 21.1% in the treated group. Similarly, the Transwell assay revealed that petasin significantly reduced the number of invasive cells, from 268 in the control group to 61 in the treated group. These results suggest that petasin inhibits both migration and invasion of SW-620 cells, potentially limiting their metastatic potential.
Petasin Inactivates the Akt/mTOR Signaling Pathway
The Akt/mTOR pathway plays a crucial role in cell survival, growth, and metabolism, and its hyperactivation is implicated in various cancers. To explore the molecular mechanisms underlying petasin’s anticancer effects, researchers examined the expression of proteins in the Akt/mTOR pathway. Western blotting analysis showed that treatment with 25 µM petasin for 24 hours significantly decreased the phosphorylation of Akt, mTOR, and P70S6K, key components of the pathway. Specifically, phosphorylation levels of Akt decreased from 1.01 to 0.74, mTOR from 0.71 to 0.32, and P70S6K from 1.23 to 0.85. These changes indicate that petasin inactivates the Akt/mTOR pathway, which may contribute to its antiproliferative effects.
In addition, petasin upregulated the expression of caspase-3 and caspase-9, which are essential for apoptosis, while downregulating the anti-apoptotic protein Bcl-2. Caspase-3 expression increased from 0.41 to 0.74, and caspase-9 from 1.10 to 1.98, whereas Bcl-2 expression decreased from 2.75 to 1.51. Furthermore, petasin suppressed the expression of matrix metalloproteinases (MMPs) MMP-3 and MMP-9, which are involved in extracellular matrix degradation and tumor invasion. MMP-3 expression decreased from 1.51 to 0.82, and MMP-9 from 1.56 to 0.94. These findings suggest that petasin’s anticancer effects are mediated, at least in part, by the inactivation of the Akt/mTOR pathway, leading to apoptosis and inhibition of migration and invasion.
In Vivo Anticolon Cancer Effects of Petasin
To validate the in vitro findings, researchers evaluated the effects of petasin in a SW-620 subcutaneous tumor model established in Balb/c nude mice. Mice were treated with 10 mg/kg petasin twice daily for 28 days. Tumor volumes were measured every 7 days, and the results showed a significant reduction in tumor size in the petasin-treated group compared to the control group. By day 21, tumor volume decreased from 488.90 mm³ in the control group to 289.22 mm³ in the treated group, and by day 28, it decreased from 924.18 mm³ to 577.67 mm³. Additionally, the TUNEL assay revealed a significant increase in apoptotic cells in the petasin-treated group, from 3.6% in the control group to 36.0% in the treated group. These in vivo results confirm that petasin inhibits tumor growth and induces apoptosis in colon cancer.
Discussion
The findings of this study demonstrate that petasin exerts significant anticancer effects on human colon carcinoma cells, both in vitro and in vivo. Petasin inhibits cell proliferation, induces apoptosis, and suppresses migration and invasion in SW-620 cells. These effects are mediated, at least in part, by the inactivation of the Akt/mTOR signaling pathway, which plays a critical role in cell survival, growth, and metabolism. By decreasing the phosphorylation of Akt, mTOR, and P70S6K, petasin activates an intrinsic apoptotic program, as evidenced by the upregulation of caspase-3 and caspase-9 and the downregulation of Bcl-2. Additionally, petasin suppresses the expression of MMP-3 and MMP-9, which are involved in tumor invasion and metastasis.
The Akt/mTOR pathway is a well-established therapeutic target in cancer, and its inhibition has shown promise in various cancer types. For example, PI3K/mTOR dual inhibitors have demonstrated robust antitumor activity in non-small-cell lung cancer, and PI3K-Akt-mTOR pathway inhibitors are being developed for breast cancer treatment. In CRC, activation of the PI3K/Akt pathway is associated with poor prognosis, making its inhibition a valuable strategy for treatment. The results of this study align with previous findings that petasin induces apoptosis in prostate cancer cells and inhibits proliferation in bladder carcinoma cells, further supporting its potential as a broad-spectrum anticancer agent.
Conclusion
In conclusion, petasin exhibits significant antitumor activity against human colon carcinoma cells by inhibiting proliferation, inducing apoptosis, and suppressing migration and invasion. These effects are mediated through the inactivation of the Akt/mTOR signaling pathway, which plays a central role in cancer cell survival and growth. The in vivo results further validate petasin’s potential as a therapeutic agent for colon cancer. Future studies should explore the exact mechanisms of petasin’s effects on tumor cells and evaluate its efficacy in clinical trials. Petasin represents a promising candidate for the development of new treatments for colorectal cancer.
doi.org/10.1097/CM9.0000000000000199
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