Potential sources of chemopreventive agents from Indonesian plants against colorectal cancer: A review

Colorectal cancer (CRC) is a serious health problem worldwide. The ever-increasing cases encouraged researchers to discover more effective novel drugs from plant sources. In this review, we summarized the plants contributing to the chemoprevention of CRC, as reported in in vitro animal studies and clinical trials. A literature search was conducted to collect information regarding the biological activities of plants from PubMed and Google Scholar, and also hand searching from other literature databases. 77 plants of 47 families cultivated in Indonesia were introduced as candidates for chemopreventive agents that help reduce cancer proliferation, progression, or recurrence. Phenolic compounds were revealed to have anticancer effects in most studies. Allium sativum L., Zingiber officinale Roscoe, Annona muricata L., and Camellia sinensis (L.) Kuntze, the fourth Indonesian plant only in a clinical trial, was able to reduce the risk of recurrence of colon adenoma, safe, and tolerated. Therefore, this review article could be key to conducting clinical trials on other plants to evaluate the safety and efficacy of developing new anticancer drugs against CRC.


INTRODUCTION
According to the WHO, 700,000 people die of colorectal cancer (CRC) yearly, which equals around 2,000 deaths daily (Sutrisna et al., 2018). With 34,783 cases (8.8% of all cancer cases in Indonesia), CRC is the fourth most common, following breast, cervical, and lung cancer. CRC is the second most frequent cancer in men, after lung cancer. In women, this cancer ranks fourth, following breast, cervical, and ovarian cancer. This suggests that CRC is more common in both men and women in Indonesia than in other cancers (Globocan, 2020a). Based on those data, CRC is the third most common cancer and the second leading cause of death worldwide (Globocan, 2020b).
Therapeutic approaches for human CRC include surgery, radiotherapy, chemotherapy, or a combination of those strategies (Nussbaumer et al., 2011). However, these approaches are unsatisfactory due to significant side effects (Hosseini and Ghorbani, 2015). Cancer treatment requires research for chemopreventive agents derived from plants that offer various degrees of protection against cancer with minimal adverse effects. Chemopreventive agent refers to using natural compounds, synthetics, or chemical/biological agents to reverse, inhibit, or prevent carcinogenesis (Tsao et al., 2000).
According to research, more than 50% of pharmaceutical drugs are derived from natural plant products (Chin et al., 2006). Indonesia has an abundance of flora that is utilized for food, welfare improvement, research, and traditional medicine. Traditional medicine comes from natural ingredients traditionally used for treatment based on experience. They assume that traditional or herbal medicines have fewer side effects than synthetic drugs (Haq et al., 1999).
There are numerous studies of traditional medicine as an alternative to chemotherapy for treating CRC due to its harmful side effects. However, its use is still limited, as health practitioners and physicians are still unwilling to prescribe it. This review aims to collect data on plants that have the potential as anticancer to be used as chemopreventive agents against CRC.

METHODOLOGY
This study is using literature review that collects data and information from books, the internet, and well-published journals. The literature search was carried out in 2021. Then, the data was updated in July 2022. The literature search was conducted using search engines on PubMed and Google Scholar as well as hand searching from other literature databases. The keywords ("herbal" OR "extract" OR "medicinal plants") AND ("anticancer" OR "chemopreventive") AND ("CRC" OR "colon cancer") are used to search regarding Indonesian plants that potentially have anticancer effects against CRC. All the articles obtained met the eligibility criteria after screening by inclusion and exclusion criteria.
The inclusion criteria for articles from PubMed, Google Scholar, and hand searching are as follows: 1. Articles using extracts or fractions 2. Scopus indexed journals in English of Q1-Q3 3. SINTA-accredited national journal in Indonesian or English with a rank of S1-S3 4. Full text or free full text The exclusion criteria used for articles from PubMed, Google Scholar, and hand searching are as follows: 1. Plants not cultivated in Indonesia 2. Using of isolates 3. Effects in a combination of two or several plants or cancer-related colon cancer drugs.
Articles obtained were classified based on preclinical studies and clinical trials. Figure 1 shows the flow chart of this study with the inclusion and exclusion criteria from databases.

Preclinical studies
The literature search found 96 articles related to preclinical studies of plants. Preclinical studies are classified into in vivo and in vitro research. The model and mechanism of crude drug treatment on colon tumorigenesis are presented in Table 1.

Clinical trial
There are six articles related to the clinical trial of plants.
The type of studies, subjects, and also the outcome of formulation-  In vivo (Almagrami et al., 2014) Achyranthes aspera L. In vitro (Hajiaghaalipour et al., 2015) Green tea hydroalcoholic leaves extract 50-800 µg/ml Caco-2 Inhibit of growth of cells

DISCUSSION
Lamiaceae is the most dominant compared to other families. According to a study, Lamiaceae is the largest family of flowering plants, consisting of 250 genera, and more than 7,000 species. Essential oils from the Lamiaceae family have been evaluated for their anticancer properties and can be exploited as a source for anticancer medicines. The underlying mechanisms are antiproliferative action, induction of cell cycle arrest, apoptosis, and DNA repair (Mesquita et al., 2019;Venkateshappa and Sreenath, 2013). Several classes of chemicals, including glycosides, flavonoids, and phenols, are abundant in numerous Lamiaceae that are rich in terpenoids (Özgen et al., 2006). Terpenoids are able to inhibit nuclear factor-κB (NF-κB), a key regulator in the pathogenesis of inflammation and cancer (Salminen et al., 2008).
In this study, each plant has a variety of groups of compounds that exhibit anticancer effects on CRC. This study revealed that the medicinal plants in Indonesia contain compounds targeting cancer cells that inhibit the growth and destruction of tumor cells. Most studies showed that phenolic compounds exhibit anticancer effects on various types of colon cells. Phenol compounds are able to scavenge peroxide radicals and chelate the ferrous metals that catalyze lipid peroxides (Pavarini et al., 2012). In addition, phenolic compounds exhibit anticancer effects on cell proliferation processes such as cell cycle arrest, apoptosis, angiogenesis, inhibition of topoisomerase II, and the impact on the pathways of phosphoinositide 3-kinase (PI3-K) and protein kinase B (Akt) (Asadi-Samani et al., 2016). Moreover, Wang et al. (2012) found that only the ethyl acetate extract of Euphorbia helioscopia L. (patikan kebo) reduced the viability of SW-480 cancer cells, but the petroleum ether, chloroform, and butanol extracts had no effect. The active substances of E. helioscopia L. (patikan kebo) are primarily flavonoids and diterpenoids. In vitro assay, flavonoids induce apoptosis by cell cycle arrest and prevent migration and proliferation of cancer cells (Wang et al., 2012). D-Allose, a compound of Moringa leaf (Moringa oleifera L.), inhibits the proliferation of cancer cells in the G1 phase by stimulation of specific thioredoxin interacting protein and stabilization of p27kip1 protein without affecting normal cells. Isothiocyanates (organosulfur compounds) present in the stem skin of Moringa (M. oleifera L.) have anticancer properties (Al-Asmari et al., 2015). However, in most studies, several compounds of the plants have not been reported as exactly being responsible for anticancer effects, which should be further investigated.
Various anticancer agents that have shown efficacy in vitro have failed to exhibit the same efficacy in vivo due to poor stability and bioavailability (Ruvinov et al., 2019). The xenograft model of a tumor plays an important role in testing novel anticancer drugs. This cancer model is developed by injecting human cancerderived cells into the animal (Jung, 2014). Azoxymethane (AOM) (C2H6N2O), a metabolite of 1,2-Dimethylhydrazine (DMH), is a carcinogen used to promote colonic neoplasia in rodents. DMH is metabolized in the liver to form reactive and carcinogenic methyl diazonium ions via the intermediates AOM and methylazoxymethanol. When methyl diazonium ions are formed, In vitro (Yusof et al., 2022) Ziziphus carbonium ions are produced, which are known to induce oxidative stress, DNA alkylation, DNA damage, and mutations (Perše and Cerar, 2010). In addition to AOM, dextran sulfate sodium (DSS) or a combination of those may also be utilized. In an experimental model of human-like colon cancer, AOM and DSS were developed. The formation of colon cancer by these carcinogens begins with the pathogenesis of epithelial cells into small lesions such as abnormal crypt foci (ACF). ACF is considered a precancerous condition in both animal and human colorectal models. This model has been utilized as an intermediate biomarker to rapidly assess the CRC prevention potential of chemopreventive drugs (Uyar et al., 2021). In this study, 16 plants were in vitro and in vivo exhibited in-line effects. Park et al. (2019) investigated the ethanol extract of Carthamus tinctorius L. (kesumba) seeds against RKO colon cancer cells and RKO colon cancer cell-implanted xenograft mice-bearing tumors. In both in vitro and in vivo experiments, the ethanol extract of C. tinctorius L. (kesumba) seeds reduced the viability of RKO cancer cells, inhibited growth, and decreased tumor weight.
Oxidative stress is a condition that may cause harm to physiological and biochemical processes. Overproduction of free radicals may also cause oxidative damage to biomolecules such as DNA, proteins, and lipids. This process may eventually lead to numerous chronic diseases like cancer (Baradaran et al., 2014;Madihi et al., 2013).
Carcinogens can also generate free radicals in colonic tissue, which can be neutralized by antioxidants that consist of enzymatic antioxidants such as catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) as well as nonenzymatic antioxidants as tripeptide glutathione (GSH), which are the primary defense system against free radicals in the biological system. CAT and GPx were proposed as the principal antioxidant enzymes because they eliminate reactive oxygen species (ROS). Low CAT activity in cancerous tissue will facilitate cancer growth and infiltration into adjacent tissues. Glutathione-S-transferase and GR are secondary antioxidant enzymes that aid in ROS detoxification by decreasing peroxide levels or preserving metabolic intermediates such as GSH. GSH and other enzymes collaborate to shield cells against ROS (Sreedharan et al., 2009).
Most medicinal plants with anticancer properties contain phenolic compounds with antioxidant activity. They can also decrease the toxicity of substances that generate oxidative stress. The presence of hydroxyl groups in phenolic substances is responsible for their antioxidant properties. These plants may therefore exert their anticancer effects by scavenging free radicals (Lam et al., 2007;Pahari et al., 2012).
There are several mechanisms based on the presence of compounds in plants, both cellular and molecular. Based on the data, cellular mechanisms include inhibiting cancer cell proliferation or decreasing cancer cell viability and inhibiting colonization, cancer cell migration, and invasion. The molecular mechanisms are such as induced apoptosis by inducing cell cycle arrest at G0/G1, G1, G2, S, G1/S, or G2/M phases; decreased expression of antiapoptotic (Bcl-2 and Bcl-xL) and proapoptotic proteins (Bad, Bax), cyclin D, cyclin-dependent kinase 4, cyclin-dependent kinase inhibitor 2C (p18) or 1A (p21), and survivin; increased expression of cell cycle inhibitors, such as p53, p16, p21, p27, TRAIL R1, cytochrome c, Apaf-1, caspase-3, caspase-7, caspase-8, and caspase-9 proteins; inhibited COX-2, as well as decreased levels of malondialdehyde (MDA) and enzymatic activity of antioxidants in eliminating free radicals. However, in most conducted studies, no clear mechanism of the plants' effect has been observed, which may further be investigated.
Allium sativum L., Zingiber officinale Roscoe, Annona muricata L., and Camellia sinensis (L.) Kuntze have been conducted in clinical trials. Soursop is the only plant with data for all three tests-in vitro, in vivo, and clinical trials. Four plants were able to reduce the size, frequency, and incidence or recurrence of colon adenoma. Based on the safety evaluation, the dose of the  (Zick et al., 2011) four plants was safe for consumption and tolerable, but there were