Oral cancer (OC), a disease of epithelial origin, has a multifactorial etiology—such as genetic, epigenetic, habitual (tobacco/betel quid/cigarette/alcohol consumption), and microbial factors—which often vary with geographical region or ethnic group [1]. OC progression is linked to histological alterations—such as carcinoma in situ, dysplasia, hyperplasia, and ultimately mouth cancer—in the normal mucosa [2,3]. It is the seventh most prevalent cancer globally, with an incidence and cancer-related mortality rate of approximately 2 %. The incidence of OC in South Asia exhibits unique epidemiological trends. In Taiwan and Southeast Asia, betel quid chewing and cigarette smoking are major risk factors for OC [4].

Oral squamous cell carcinoma (OSCC) comprises approximately 90 % of malignant OCs. Oral and oropharyngeal squamous cell carcinoma are emerging as public health challenges [5]. Significant improvements in overall survival or recurrence-free survival are lacking, despite tremendous developments in treatment alternatives, including surgery, radiation therapy (RT), and chemotherapy [6]. Furthermore, drug resistance is the greatest obstacle in cancer treatment. Additionally, generally, cancers have subpar responses to medications. Therefore, effective drugs targeting OC urgently need to be developed [5,6].

Apoptosis is a clearly defined process with unique morphological and biochemical characteristics [7]. It is initiated by a variety of extrinsic and intrinsic signals, including stressors such as reactive oxygen species (ROS), DNA-damaging factors (such as radiation), thermal shock, serum depletion, and hypoxia [8]. External agents such as pesticides, environmental contaminants, and chemotherapeutics can cause apoptosis (commonly mediated via ROS). Although cancer cells typically evade apoptosis, many signals may appear in cancer cells that can rapidly lead to apoptosis [9]. Cancer cells are "ready-to- die" because they are closer to starting the apoptotic process [10]. In mammals, pharmacological or genetic strategies that inhibit the activity of these caspases can at best delay apoptosis but not prevent apoptotic cell death [11].

During angiogenesis, new blood vessels are created from preexisting vessels. Angiogenesis is a complex physiological phenomenon crucial for tissue growth, repair, and development [12]. It is finely regulated by a balance of promoting and inhibitory signals, including integrins, chemokines, angiogenic factors, oxygen sensors, and endogenous inhibitors [13]. Interestingly, angiogenesis characterizes >50 disease states, and its dysfunction is associated with various diseases, including cancer [14]. It supports the invasive expansion of tumors, leading to cancer progression and metastasis [15]. Generally, passive diffusion cannot provide sufficient nutrients to tumors >2 mm in diameter, causing equilibrium between cell proliferation and death. Therefore, through a phenomenon called the angiogenic switch, tumors initiate angiogenesis by expressing angiogenic factors for continued growth [16]. Consequently, inhibiting angiogenesis is a significant strategy for preventing and rescuing tumorigenesis.

Natural products are the source of the most active compounds in drugs, and more than 70 % of small molecular drugs are initially obtained from natural sources or based on natural products [17]. Marine-derived natural products exhibit various pharmacological effects through their bioactive secondary metabolites. They modulate various cellular mechanisms in anticancer, including reactive oxygen species (ROS) production, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, autophagy, protein kinases, and apoptosis signaling, thus showcasing their diverse regulatory potential in biological activities [[18], [19], [20]] For example, marine-derived antimicrobial peptides TP3 and paxdaxin can induce ROS production and apoptosis in osteosarcoma [21] and ovarian cancer [22], respectively. Marine sponge-derived alkaloid 3,7-bis(3,5-dimethylphenyl)-aaptamine, isoaaptamine, and manoalide cause mitochondrial dysfunction and apoptosis in lymphoma [23], glioblastoma multiforme [24], and osteosarcoma [25]. A soft coral-derived membrane-based diterpenoid demonstrates anticancer effects by inducing apoptosis in melanoma and hepatoma by inhibiting the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway [26,27]. Numerous marine natural products still require further study to elucidate their anticancer effects' efficacy and cellular mechanisms.

Piscidin-1 is a naturally occurring cationic antimicrobial peptide (AMP) derived from the mast cells of hybrid striped bass (Morone saxatilis × M. chrysops) [28]. It is characteristically cysteine-rich and protects fish against ectoparasitic, bacterial, and fungal infections. Piscidin-1 inhibits the growth of osteosarcoma (MG63) [29] and fibrosarcoma (HT1080) [28] cell lines. It also inhibits the growth of cervical, breast, and lung epithelial cancers [30] also inhibited by the modification of piscidin-1 with copper ions [29,30]. We demonstrated that piscidin-1 stimulates apoptosis in inhibited human osteosarcoma cell lines [29]. However, reports on the effects of piscidin-1 on OSCC are lacking.

To test the potential of piscidin-1 as an anticancer drug, the mechanisms of piscidin-1-induced tumor cell apoptosis must be clarified. One must verify whether it utilizes pathways other than mitochondrial inhibition to inhibit the growth of various tumor cells. Therefore, here, we explored the anti-oral cancer effects and mechanisms of piscidin-1 on OSCC cell lines (OC2 and SCC4).