Retinoblastoma is a rare cancer that affects the retina in young children through the malignant proliferation of retinal cells and can be life-threatening if left untreated (Rollins, 2023). It is estimated that approximately 7 000 to 8 000 new cases of retinoblastoma are reported annually worldwide (Cahyana, 2022). Symptoms of retinoblastoma include leukocoria, a whiteness in the pupils that is present in 60% of cases, strabismus, a misalignment of the eyes that appears as crossed eyes found and is present in 20% of cases, and vision loss or blindness (Lam and Suh, 2022). Other symptoms may include eye inflammation, neovascularization of the eye, haemorrhage, glaucoma, and hypopyon (Farhat, 2022). In developing countries, proptosis, or the bulging of the eye, is the most common symptom (Marouf et al., 2022). In advanced stages of the disease, the survival rate and the likelihood of preserving the affected eye are low (Sherief et al., 2022). Retinoblastoma occurs as a result of the genetic mutation of a single cell in the retina, known as a homozygous retinoblastoma gene (RB1) mutation (Rozanska et al., 2022). This mutation takes place when both copies of the RB1 gene within the cell are impacted, leading to the uncontrolled growth of cells in the retina, which can be fatal if not treated in a timely manner (Dimaras et al., 2015). The RBb1 gene is among the most extensively studied tumour suppressors and is considered to be a key regulator of genes (Kanber et al., 2022). RBb1 is widely recognised as the main driving force behind retinoblastoma (RB) and is a well-defined genetic element and clinical target. Point mutations, deletions, and epigenetic alterations in Rb1 have also been linked to several other forms of malignancy (Padma et al., 2020).

The retinoblastoma protein (pRbb), encoded by the RB1 gene, plays a critical role in the pathophysiology of retinoblastoma (Karla et al., 2023). In addition to regulating replication, genome stability, proliferation, and apoptosis, pRbb serves as a key factor in the G1/S transition phase (Mandigo et al., 2022). When the RB1 gene is mutated, it results in the inability of the Rb1b protein to perform its functions, leading to the formation of retinoblastoma (Desvoyes and Gutierrez, 2022). A tumour-promoting process can lead to the inactivation of Rb1 through phosphorylation by CDK4/6-Cyclin D (Scheiblecker et al., 2020). The phosphorylation of Rb1 results in the release of a transcription factor called E2F, which facilitates progression through the G1 phase (Berry et al., 2019).

Cyclin-dependent kinases, Cdk4 and Cdk6, when forming complexes with D-type cyclins, promote cell proliferation (Hu and Huang, 2023). Cdk4 and Cdk6 are known to target the retinoblastoma protein (Rb1), which serves to inhibit cell-cycle progression until it is phosphorylated and inactivated by these kinases (Syahirah et al., 2022). The exact role of Rb1 phosphorylation by cyclin D-Cdk4,6 in cell cycle progression remains unclear, but it is known that other cyclin-Cdks can also phosphorylate Rb, and cyclin D-Cdk4,6 has additional targets that can play a role in cell division (Topacio et al., 2019).

In addition to surgical procedures such as enucleation and local therapies like cryotherapy and thermotherapy, patients with retinoblastoma may also receive radiotherapy and chemotherapy to treat their condition (Mollick, 2020). Chemotherapy is specifically used as an alkylating agent to slow or halt the progression of tumour cells within the body (Fabian et al., 2018). Timely initiation of treatment is crucial in reducing the risk of intraocular and extra-ocular spread of the tumour (Zhao et al., 2021). Advancements in molecular therapies are driving research and development efforts to create new treatments for cancer and other diseases. The aim is to maximise efficacy towards the target while minimising systemic side effects and toxicity, and optimising tolerability (Russo et al., 2020). At present, there is no lack of a singular therapy that is both highly effective and readily accessible to the general public for the treatment of retinoblastoma, while also having minimal adverse effects (Wanigasekara, 2023). The natural world offers a range that has been found to contain various phytochemicals with anti-proliferative and anti-cancer properties, one such example being the extract derived from milk thistle (Masi et al., 2019). The phytochemical is recognised for its diverse functions possessing multiple functions, including hepatoprotection, cardioprotection, neuroprotection, and modulation of the immune system modulation, as well as having both antidotal and antineoplastic properties (Fanoudi et al., 2020). The potent anti-cancer and chemo-preventive properties of milk thistle have been demonstrated to be effective in preventing and treating a variety of epithelial cancers, such as those including skin, colon, prostate, and lung (Emadi et al., 2022). Furthermore, the incorporation of silibinin and other therapeutic agents in the prevention of cancer has been shown to reduce toxicity and chemo-resistance caused by drugs through their synergistic interactions (Reed et al., 2020). The use of milk thistle (Silybum marianum) as a therapeutic agent has a long history, extending over two millennia, and has been employed in traditional medicine for the treatment of various ailments including liver, kidney, rheumatic, gastronomic, cardiac and gallbladder disorders such as jaundice, hepatitis and cirrhosis (Cheng et al., 2018). Despite its historical significance, this biennial herb, which has the capacity to attain a height of up to 10 feet, has been largely overlooked as a potential inhibitor of CDK4, CDK6 and pRbB proteins (Nandi et al., 2022).

Recent studies have revealed that milk thistle effectively inhibits the proliferation of malignant cells, restricts angiogenesis, prevents metastasis, induces apoptosis, and enhances the therapeutic efficacy of chemotherapy and radiotherapy, both in vitro and in vivo (Dutta et al., 2019). This potent plant-derived compound has shown promising therapeutic potential against a variety of cancers, including haematological, lymphoma, prostate, breast, cervical, ovarian, and colon cancers (Khan et al., 2021). A study has demonstrated that the milk thistle has potential to activate the p38 MAPK and JNK signalling pathways to trigger apoptosis in Y79 cells, thus potentially preventing cancer, reducing the risk of disease recurrence, and reversing drug resistance (Reed et al., 2020). This efficacy is achieved through the modulation of key signalling pathways, including transforming growth factor beta, epidermal growth factor receptor, insulin-like growth factor-1 receptor, and nuclear factor-kappa B, offering a novel therapeutic approach for human retinoblastoma (Kim et al., 2019). Although some adverse effects were observed, they were of limited occurrence, and the probability of extraocular tumour spread following intravitreal injection was found to be low. A significant proportion of treated eyes were found to retain functional vision post-vitreous seed remission, with 68% achieving complete remission (Khaqan et al., 2021). Virtual screening experiments, including molecular docking and ADMET analysis, were performed to evaluate the binding affinities and pharmacological properties of milk thistle phytochemicals as potential natural inhibitors of retinoblastoma.

These experiments aimed to assess the feasibility of using these substances as novel anticancer agents by examining their drug-like characteristics, including lead likeness, pharmacokinetics, and physiochemical properties.