Colon cancer remains the major cause of cancer-associated mortalities in both men and women globally [24, 25]. Furthermore, resistance to therapies made it more difficult to treat colon cancer [26]. Therefore, there is a need to look for novel, effective, and low-toxic alternatives that could effectively prevent and/or inhibit the progression of colon cancer. In the current work, the anticancer potential of nerolidol against the HCT-116 cells were studied and the results were demonstrated the significant beneficial activities of the nerolidol. The tumor cells have a strong ability to replicate themselves and metastasize to other body parts. The uncontrolled and excessive cell proliferation causes the development of cancerous tissues, which have a propensity to metastasize to other body parts [27]. In order to demonstrate the anticancer effects of nerolidol, we attempted to discover the inhibitory potential of nerolidol on the proliferation of colon cancer HCT-116 cells using the MTT assay. The findings reveal that nerolidol treatment substantially obstructs the HCT-116 cell viability. The current findings were supported by previous research done by Lee et al. [28], who found that podophyllatoxin effectively decreased the HCT-116 cell viability.
ROS are highly reactive substances produced by mitochondria as a metabolic byproduct, which aid in the malignant transition of normal cells into neoplastic precursors [29]. Additionally, ROS are crucial intracellular signaling mediators under normal circumstances, but an abnormal gathering causes oxidative stress in cells and encourages apoptosis [30]. In order to support their fast proliferation, cancer cells produce more ROS than normal cells do. However, excessive ROS levels can cause tumor cell death by the number of pathways [31]. Cancer cells are more susceptible to medicines that increase ROS-mediated oxidative stress. In cancer treatment, the stimulation of higher ROS accumulation in the tumor cells is an effective approach [32]. It was evident that several bioactive substances with anti-cancer potential raise ROS level, triggering oxidative stress-mediated apoptosis in tumor cells [33]. In the current work, the findings of DCFH-DA staining demonstrated that nerolidol effectively augmented ROS level in HCT-116 cells, which may facilitate the oxidative stress mediated apoptotic cell death. The previous study done by Lin et al. [34] found that ferruginol effectively increased the ROS level in HCT-116 cells, thereby facilitating oxidative stress-mediated cell injury. These outcomes are supported the results of the current research work.
In addition to uncontrolled cell proliferation, defective apoptosis is also a major contributing factor in tumor growth. Apoptosis is a crucial defense mechanism against the progression of tumors. Neoplastic cells undergo oncogenic transformation when genetic and epigenetic changes cause them to become resistant to apoptosis. In tumorigenesis, the defective apoptosis regulation causes an extended life span of tumor cells, growth under stress, tumor angiogenesis, and metastasis. It also adds to therapeutic resistance in tumor cells [35]. The pathophysiology of apoptosis is multifaceted and incorporates extrinsic and intrinsic signal transduction [36]. Tumor cells produce several mechanisms to prevent apoptotic cell death, most notably the overexpression of anti-apoptotic molecules. DNA injury in precancerous lesions can cause apoptosis, which eliminates potentially hazardous cells and prevents tumor growth. Contrarily, apoptotic dysfunction can cause uncontrolled cell proliferation, tumor growth, and tumor resistance to therapies [37]. Therefore, apoptosis stimulation in cancer cells is considered a most promising approach to obstruct tumor progression. In this study, the results of dual staining exhibited that nerolidol treatment effectively stimulated apoptosis in HCT-116 cells, which evidences that nerolidol can inhibit colon cancer growth by triggering apoptotic cell death. This observation is in agreement with the previous research done by Xiang et al. [38], who found that curcumin triggered apoptosis in HCT-116 cells, which was analyzed by dual staining.
Some apparent morphological abnormalities that occur during apoptosis can be considered indicators of the beginning of the apoptotic process. In summary, apoptosis begins with chromatin condensation in the nucleus, progresses through nuclear fragmentation, and finally results in the formation of apoptotic bodies [39, 40]. The results of DAPI staining also demonstrated increased apoptotic cell nuclear morphology, which is evident by increased damaged cell morphology, nuclear fragmentation, and apoptotic bodies in the nerolidol-exposed HCT-116 cells. Hence, it was clear that nerolidol can be useful to treat colon cancer by encouraging apoptosis. Our present results were supported by the previous research work done by the Dangroo et al. [41].
In addition to cell toxicity and apoptosis induction, the impact of nerolidol on the cell cycle arrest in the HCT-116 cells was also investigated in this study. It is crucial to understand that there are various stages in the cell cycle, including gap 1 (G 1), gap 2 (G 2), and mitosis (M) [42]. A variety of regulatory molecules are involved in the intricate process of the cell cycle, which controls the growth of cancer cells [43]. The checkpoints of cell cycle are commonly stimulated due to the DNA damage and replication stress. Each checkpoint in normal cell division is strictly controlled, and any disruption of those checkpoints causes cells to divide rapidly and uncontrollably [44]. A possible target for cancer therapies is the dysregulation of the cell cycle, which promotes the development of tumor [45]. It was reported that some naturally occurring bioactive compounds, such as hydroxy-g-sanshool, inhibit colon cancer cell growth by inducing the sub-G1 population [46]. According to the current findings, we found that, compared to control cells, HCT-116 cells exposed to nerolidol had a higher sub-G1 population. Therefore, it was clear that the nerolidol caused the inhibition of cell cycle in the G0/G1 phase and reduced HCT-116 cell growth. A recent studies done by the Zhaojun et al.[47] and Kwon et al.[48] found the inhibition of cell cycle at G0/G1 phase in the HCT-116 cells using bioactive compounds, which supports the results of the present study.