1. Introduction

Cancer remains a major global health challenge, with nearly 20 million new cases and 10 million deaths reported in 2022 and projections suggest annual cases could reach 35 million by 2050 (Bray et al., 2024). Natural products have historically been a cornerstone in oncology, with approximately 60% of FDA-approved anticancer drugs derived from natural sources, particularly plants (Newman and Cragg, 2020). Notable examples include vinblastine and vincristine from Catharanthus roseus (Apocynaceae), taxol and docetaxel from Taxus species (Taxaceae), and camptothecin (CPT) from Camptotheca acuminata (Nyssaceae) and Nothapodytes (Icacinaceae) (Cragg and Pezzuto, 2016). However, the high demand for taxol has resulted in the overharvesting of slow-growing Taxus trees, all of which are classified as endangered by the IUCN (Thakur and Kanwal, 2024).

Camptothecin, commonly known as CPT, is a monoterpene pentacyclic quinoline alkaloid and one of the most valuable compounds in the pharmaceutical industry, following taxol and vinca alkaloids. It was first discovered in Camptotheca acuminata (Wall et al., 1966) and has since been identified in several other plants, including Nothapodytes nimmoniana (Govindachari and Viswanathan, 1972), Pyrenacantha klaineana (Zhou et al., 2000), Ophiorrhiza rugosa var. prostata (Gharpure et al., 2010), Chonemorpha grandiflora (Kulkarni et al., 2010), and Dysoxylum binectariferum (Jain et al., 2014), as well as in many unrelated taxa (Ramesha et al., 2013). Among these sources, Nothapodytes species, particularly the roots of N. nimmoniana, are known to have the highest concentration of CPT (Namdeo and Sharma, 2012). By inhibiting DNA topoisomerase Ⅰ, an enzyme essential for DNA replication and repair, CPT disrupts crucial cellular functions, thereby enhancing its anticancer potential (Hsiang et al., 1985).

The high pharmaceutical demand for CPT, particularly from Nothapodytes nimmoniana, has led to extensive harvesting of wild populations, raising significant conservation concerns. This situation reflects a broader trend where various plant species essential for food, medicine, and materials face increasing threats. Factors such as rapid human population growth, urbanization, climate change, invasive species, and habitat degradation, along with unregulated wild plant harvesting, have placed immense pressure on natural ecosystems (Keck et al., 2025).

Traditionally, conservation efforts have focused on endemic, economically important, and endangered species or Plant Species with Extremely Small Populations (PSESP), which receive strong attention due to their urgent conservation needs and success stories in preventing extinction (Ma et al., 2013; Yang et al., 2020; Sun et al., 2024). Species listed on the IUCN Red List, the Threatened Species List of China's Higher Plants, the Endangered Species Act of the USA, and the CITES List are carefully monitored because they face a high risk of extinction (Spielman et al., 2004; Harris et al., 2012; Wang et al., 2015; Qin et al., 2017). However, much less attention is given to widespread species that are still threatened. The concept of Threatened Plant Species with Widespread Distribution (TPSWD) has emerged as a crucial yet underexplored conservation challenge, calling for new strategies to balance sustainable use with long-term ecological preservation (Gaston and Fuller, 2008; Redford et al., 2013; Thakur et al., 2018; Chen et al., 2019).

Many medicinal plants decline rapidly at a local level even when they are widely distributed. For example, Nothapodytes, a key source of camptothecin, is overharvested to meet the high demand for anticancer drugs, leading to severe population losses (Chen et al., 2024a). Similarly, slow-growing Taxus trees that provide taxol and docetaxel have been reduced heavily in exploited areas (Thakur and Kanwal, 2024). Chen et al. (2019) found that overharvesting the tuberous roots of Stemona tuberosa, a species distributed in more than ten Asian countries, is the main threat to its survival. This is worsened by pollination limits, loss of seed dispersers, habitat fragmentation, and scattered populations. Similar patterns are seen in other genera such as Aconitum and Ephedra (González-Juárez et al., 2020; Kakkar et al., 2023), where intense, localized collection pressures cause rapid declines. These cases show that a wide geographic distribution does not guarantee species survival.

This case study highlights how TPSWD can be exploited to the brink of endangerment, despite their broad distribution. In this review, we explore the paradox of TPSWD conservation by focusing on: (1) The plant resources of Nothapodytes and their significance. (2) The active ingredients of Nothapodytes with a focus on CPT. (3) Natural drugs derived from Nothapodytes and their pharmaceutical relevance. (4) Strategies for rescuing and utilizing anticancer Nothapodytes species to address conservation and industrial needs. In addition, we propose future directions to address the conservation challenges associated with Nothapodytes and achieve a sustainable balance between biodiversity preservation and pharmaceutical demands.

2. Methods 2.1. Study area, species list and conservation status

The geographic scope of this review encompasses the natural distribution range of Nothapodytes species across tropical and subtropical Asia, extending from India to Japan. A systematic literature review was conducted to examine the taxonomic placement of the genus Nothapodytes within the broader phylogenetic framework. In addition, we retrieved species occurrence records from the Global Biodiversity Information Facility (GBIF) and relevant literature to compile a validated list of Nothapodytes species. Their formal conservation status was checked against several sources, including the IUCN Red List, the CITES Appendices, and the Threatened Species List of China’s Higher Plants (Qin et al., 2017), to make sure their threat levels were thoroughly assessed.

2.2. Geographic range and threat category assessment

To assess the geographic distribution and conservation status of Nothapodytes species, we compiled 2428 occurrence records representing ten Nothapodytes species. Data were retrieved from the Global Biodiversity Information Facility (GBIF, 2025) using the rgbif package (Chamberlain and Boettiger, 2017) in R 4.2.3, which included 1660 records for nine species, and from the Chinese Virtual Herbarium (CVH; http://www.cvh.ac.cn), which contained 765 records for seven species. Additional records for Nothapodytes amamianus and N. burmanica were obtained from published literature (Ito et al., 2022; Shen et al., 2024).

We thoroughly examined and cleaned all occurrence records to ensure data reliability. Records not identified to the species level or unrelated to the genus Nothapodytes were excluded. Species names were standardized and validated using the Plants of the World Online database (POWO; https://powo.science.kew.org), and discrepancies were corrected through specimen-based verification when necessary. Only records with precise geographic coordinates were retained, with all coordinates converted from degree–minute–second to decimal degree format for consistency. Duplicate entries with identical species names and coordinates were removed. To further refine the dataset, records originating from urban areas such as botanical gardens, parks, and museums were excluded using the R package CoordinateCleaner package (Zizka et al., 2019). After all filtering and verification steps, 360 occurrence records representing ten Nothapodytes species were retained for subsequent analyses (appsec1).

Since not all Nothapodytes species have been assessed by the IUCN Red List, we conducted a preliminary conservation assessment based on the cleaned occurrence data. The extent of occurrence (EOO)—defined as the smallest polygon encompassing all valid occurrence points, where no internal angle exceeds 180°—was calculated using the convex hull method (Fig. 1c). The area of occupancy (AOO) was estimated using the default 2 × 2 km grid cells (Fig. 1d). Both EOO and AOO were computed in R v.4.2.3 using the ConR package v.2.1 (Dauby et al., 2017) with the functions EOO.computing and AOO.computing, respectively. We note that AOO values can vary depending on the chosen grid size, which is a routine methodological effect. Species were categorized according to the IUCN criteria B1 and/or B2 using the cat_criterion_b function (appsec1).

2.3. Literature survey

A comprehensive literature search was conducted using Web of Science (WoS) and cross-checked with other electronic databases, including ResearchGate, PubMed, and Google Scholar, using the keyword “Nothapodytes” to retrieve relevant articles (n = 291). These records were further screened based on their relevance to our review theme, focusing on taxonomy and distribution, phytochemistry, pharmacology, microbiology, biotechnology, conservation, and genome biology.

We compiled data on CPT content across different tissues of Nothapodytes collected from various geographic locations, along with details of the extraction techniques used. A systematic listing of phytochemicals reported from different plant parts was created, and studies on endophytes isolated from Nothapodytes were reviewed, particularly those investigating their cytotoxic potential against cancer cell lines. In addition, we studied the market value of CPT and its derivatives, tracking the timeline of FDA-approved drugs derived from this compound to contextualize its economic significance and conservation challenges.

3. Results and discussion 3.1. The paradox of TPSWD conservation

There is a common belief that widespread species are safe from extinction. However, even plants with broad distribution, while they may appear abundant, are not immune to overexploitation (Figs. 1a and 2b). TPSWD face multiple threats, including habitat loss, climate change, and targeted exploitation for medicinal, timber, and food (Pironon et al., 2024; Keck et al., 2025). Among these, the demand for medicinal products poses a particularly significant risk, especially for species targeted by the pharmaceutical industry. The global demand for natural compounds in anticancer drugs has intensified the harvesting pressure on many such species, creating a paradox in which widespread availability does not equate to a secure conservation status. Nothapodytes species, known as primary sources of camptothecin (CPT), exemplify this challenge, as their growing use in cancer therapeutics has led to severe population declines that threaten their long-term survival. Addressing this issue requires a comprehensive conservation strategy that considers both ecological sustainability and the socioeconomic drivers of exploitation.

Before formal IUCN assessments, Nothapodytes insularis was classified as Endangered (EN) in a 2018 evaluation, while N. pittosporoides (assessed in 2018) and N. montana (assessed in 2023) were listed as Least Concern (LC). According to the Threatened Species List of China's Higher Plants (Qin et al., 2017), N. collina and N. obtusifolia are classified as Endangered (EN), and N. obscura as Vulnerable (VU).

However, a preliminary conservation assessment based on IUCN B1 and/or B2 criteria indicates that although several species (Nothapodytes collina, N. montana, N. nimmoniana, N. obscura, N. pittosporoides, and N. tomentosa) have broad distributions, many are currently under threat (Fig. 1e). For instance, N. nimmoniana and N. pittosporoides initially met the criteria for LC or Near Threatened (NT) based on their vast EOO (5,370,667 km² and 2,761,368 km², respectively) (Fig. 1c). However, due to extensive exploitation (Fig. 2b), these species should be categorized as threatened. This highlights the limitations of using distribution range alone as a proxy for conservation status, as large-scale habitat fragmentation and intensive harvesting can drive population declines even in widely distributed species. This paradoxical situation underscores the urgent need for conservation measures and a re-evaluation of existing strategies.

3.2. Plant resources of Nothapodytes

The genus Nothapodytes Blume (Icacinaceae) comprises ca. 11 species and is distributed across tropical and subtropical Asia, from India to Japan (Fig. 1b) (Peng and Howard, 2008; Ito et al., 2022). It was originally described by Blume in 1851, based on N. montana Blume from Indonesia. Subsequently, the genus was reclassified by Miers (1852), transferring N. montana to Mappia Jacq. within Mappia sect. Trichocrator, grouping it with seven species found in India and Sri Lanka. Sleumer (1940) restored Nothapodytes as a distinct genus, including five previously described species, although their distributions were not specified. This classification was supported by Howard, who also recognized five species, including one species distributed from India to Taiwan, China (Howard, 1942). Sleumer (1969) further expanded the genus, adding three additional species, which were accepted by both his earlier treatment (Sleumer, 1940) and Howard's treatment (Howard, 1942). In their taxonomic treatment for the Flora of China, Peng and Howard (2008) listed six species, including five endemic to China. A new combination, N. insularis, was proposed following the reassessment of N. nimmoniana sensu lato (Ito et al., 2022). More recently, N. burmanica, a new species, was described from Kachin State, Myanmar (Shen et al., 2024). Among the genus, N. nimmoniana (previously referred to as N. foetida) is the most widely distributed, occurring across South Asia, Southeast Asia, and the southwestern islands of Japan.

In the phylogenetic context, the genus Nothapodytes remains poorly understood. Limited studies have included Nothapodytes species in attempts to resolve phylogenetic relationships within either the Icacinaceae or the lamiid clade (Kårehed, 2001; Byng et al., 2014; Stull et al., 2015). Indian samples of N. nimmoniana were included in phylogenetic analyses of Icacinaceae (Kårehed, 2001; Byng et al., 2014), while a single sample of N. montana was included in the analysis of higher-level relationships within the Lamiidae (Stull et al., 2015). Population-level analyses of N. nimmoniana have revealed genetic diversity among samples collected from different geographical locations in India (Abdul Kareem et al., 2011; Shivaprakash et al., 2014). However, a species-wide genetic analysis of this widespread species remains unexplored. The current understanding of the genus is skewed towards its western range, particularly the Western Ghats, highlighting the need for comparative analyses across its entire distribution (Fig. 3a). Darshetkar et al. (2023) developed SSR markers for N. nimmoniana which could theoretically aid in distinguishing genetically diverse populations, and prioritizing those requiring immediate conservation efforts, while SSR technology faces critical limitations and is supplanting by Next-Generation Sequencing techniques.

A comprehensive understanding of the spatial and temporal distribution of Nothapodytes species is crucial for effective conservation planning. Such knowledge requires biogeographic studies to map the current range of the genus, identify critical habitats, and evaluate the impacts of environmental change on population dynamics. In addition, systematic analyses, including taxonomic clarification and genetic diversity assessments, are essential to ensure that conservation efforts are directed toward the most vulnerable populations. Reproductive ecology further shapes species distribution, as pollination is mediated by diverse insects such as flies and bees (Fig. 2c and d), while sexual dimorphism, with distinct female and male flowers (Fig. 2e) influences reproductive success. Seed dispersal by birds (Fig. 2f and g) contributes to population connectivity across landscapes, whereas biotic pressures, including herbivory by leaf beetles (Fig. 2h), may limit regeneration. Studies on seed biology (Fig. 2i) provide insights into germination dynamics, which are critical for both natural recruitment and ex situ propagation. Collectively, these ecological and genetic studies form the foundation for region-specific conservation strategies that recognize both the ecological role and pharmaceutical significance of these plants.

3.3. Active ingredients of Nothapodytes

Nothapodytes is a genus known for producing camptothecin. Camptothecin is a pentacyclic alkaloid with a quinoline-based structure and a lactone ring, essential for its activity as a topoisomerase Ⅰ inhibitor used in cancer treatment (Hsiang et al., 1985). Camptothecin concentration in the genus Nothapodytes shows asymmetric distribution (Table 1). Studies have shown that CPT levels differ across different geographical regions such as India, Sri Lanka, and China, influenced by local climatic conditions (Namdeo et al., 2010; Pai et al., 2013; Ankad et al., 2015; Degambada et al., 2023). Nothapodytes nimmoniana from Amboli, India, yielded the highest CPT content (1.337 g/100 g dry bark) during the monsoon (August), as compared to other localities (Amba, Chandoli, Naikwadi, and Panhala) and the summer (May) (Pai et al., 2013).

The concentration of CPT also varies among different plant tissues (Fig. 3b). The highest reported CPT content, 2.67% dry weight, was obtained from Nothapodytes nimmoniana collected in India using a microwave extraction technique (Fulzele and Satdive, 2005a). The roots collected in February accumulated the highest CPT levels (2.62%), followed by fruits (1.22%), stems (0.81%), and leaves (0.70%) (Namdeo and Sharma, 2012). Temporal variations were also noted, with roots consistently yielding the highest CPT concentrations, three times higher than in leaves or stems (Table 1). Although roots show a wide range of CPT concentrations and are considered the richest source, harvesting them requires uprooting the entire tree, which can negatively impact the plant population and sustainability. Consequently, stem bark is often recommended as a more sustainable alternative (Patil et al., 2024). However, excessive bark harvesting can still pose a significant risk to tree health, particularly when done repeatedly or indiscriminately. Furthermore, seasonal differences in CPT production were studied, with the monsoon showing higher concentrations of camptothecin in the bark of N. nimmoniana compared to the summer (Pai et al., 2013). In the case of N. pittosporoides, only one study has reported the CPT content, with roots showing a concentration of 0.944% dry weight (Bai and Song, 2014). Similarly, a single study on N. tomentosa (Fig. 2a) found that CPT concentration was highest in the roots (0.096%), followed by the stems (0.069%) and leaves (0.012%) (Li et al., 2023).

Studies have shown that plants harvested from different sites, during varying seasons, and from various plant parts accumulate diverse levels and forms of CPT derivatives (Fulzele and Satdive, 2005b; Namdeo et al., 2010; Ao et al., 2011; Pai et al., 2013; Ankad et al., 2015; Li et al., 2023). This variation significantly impacts both extraction efficiency and pharmacological quality. However, no comprehensive study has been conducted across the full distribution range of these plants, underscoring the need for spatial and temporal investigations. Such studies are crucial for conservation efforts and pharmaceutical applications, as they could help identify the most productive environments and optimize harvesting strategies. Understanding how environmental factors, including soil type, climate, and altitude, affect CPT biosynthesis would provide valuable insights.

Camptothecin is a key bioactive compound that has been extensively studied within the genus Nothapodytes. Phytochemical profiling across different species, including N. nimmoniana, N. pittosporoides, and N. tomentosa, has reported a variety of bioactive compounds extracted from various plant tissues, such as stems, roots, trunk bark, fruits, and seeds (Table 2). Notably, the majority of these compounds have been isolated from stems, which are often prioritized due to their relatively higher yield of CPT derivatives. Despite the genus comprising approximately 11 species, research has predominantly focused on only three. This limited scope may be attributed to factors such as restricted distribution, lesser-known phytochemical potential, or limited accessibility to other species. Expanding phytochemical investigations to include lesser-studied species could provide a broader understanding of the diversity and distribution of CPT derivatives, offering new insights for conservation strategies and optimizing pharmaceutical applications.

Endophytes are recognized as a significant source of novel bioactive molecules. Several endophytes have been identified in Nothapodytes, and their cytotoxicity has been assessed using various cell lines (Table 3). For example, endophytic fungi such as Entrophospora infrequens, Neurospora sp. (ZP5SE), Nodulisporium sp., Fusarium sp., Diaporthe sp., Irpex sp., Botryosphaeria sp., Galactomyces sp., and Alternaria sp. have been isolated from N. nimmoniana. Similarly, endophytes, including Fusarium solani HB1-J1, Diaporthe sp., Botryosphaeria sp., Phoma sp., Mycosphaerella sp., and Colletotrichum sp., have been reported from N. pittosporoides. However, the yields reported for these endophytes have been low and inconsistent (Table 3). Co-cultivation of two endophytic fungi, Colletotrichum fructicola SUK1 (F1) and Corynespora cassiicola SUK2 (F2), isolated from N. nimmoniana, has been employed to enhance CPT production (146 mg/l) (Bhalkar et al., 2016).

Entrophospora infrequens isolated from Nothapodytes nimmoniana exhibited CPT contents ranging from 4.96 mg/100 g to 503 μg/100 g, with strong cytotoxic effects against various cancer cell lines (Amna et al., 2006, 2012; Puri et al., 2005). Likewise, Neurospora sp. (ZP5SE) and Nodulisporium sp. showed CPT yields of 5.5 μg/g and 45 μg/g, respectively, and both demonstrated notable cytotoxic activities comparable to standard camptothecin against lung (A-549), ovarian (OVCAR-5), and other cancer cell lines (Rehman et al. 2008, 2009a, 2009b). These findings underscore the remarkable potential of fungal endophytes as alternative or supplementary sources of CPT, especially given the challenges of sustainable plant-based harvesting and the often-low yields in native hosts.

Despite these promising results, several issues remain. First, CPT yields in endophytic fungi are frequently low and can vary significantly depending on factors such as culture conditions, fungal strain stability, and the symbiotic state with the host plant. Second, reliable and scalable production methods have yet to be fully established. Here, synthetic biology approaches present a promising solution. By leveraging metabolic engineering tools, researchers can (1) identify and optimize the CPT biosynthetic genes within fungal endophytes, (2) construct heterologous expression systems to enhance yields, and (3) develop stable production platforms that can be scaled up for industrial applications (Harvey et al., 2018; Kaur et al., 2020).

Studies on soil microbial communities in the root zone of Nothapodytes nimmoniana have shown that the application of organic fertilizers significantly mitigates the adverse effects of cultivation on soil microbial activities (Chung and Chang, 2012). Despite these findings, investigations into the functional roles and biotechnological potential of these endophytes remain limited. Notably, there is no evidence of horizontal gene transfer (HGT) from the host plant to the endophytes, although HGT among endophytes themselves may still be a possibility (Natarajan et al., 2023).

A critical gap in current research is the lack of a dedicated database for endophytes and their metabolites, making it challenging to fully understand the physiological and biochemical interactions between host plants and associated endophytic fungi. To enhance the production of specific metabolites and develop new analogs of active secondary metabolites, various techniques can be employed. These include physicochemical and genetic modification strategies such as the One Strain Many Compounds (OSMAC) approach (Zhang et al., 2024), co-cultivation (Bertrand et al., 2014), and epigenetic modifications (Keller, 2019). However, large-scale industrial production of bioactive compounds from fungal endophytes remains a labor-intensive process. Effective methods, such as CRISPR-Cas9 gene editing and the use of epigenetic modifiers, are necessary to optimize the biosynthesis of these compounds. Bioprospecting efforts have increasingly focused on medicinal plants to identify endophytic microorganisms capable of producing camptothecin and its structural analogs. Nevertheless, achieving cost-effective and commercially viable production of CPT from endophytic fungi remains a significant challenge.

Nothapodytes species have evolved effective chemical defenses, including the production of CPT, which is toxic to many herbivores. In CPT-producing plants, mutations in topoisomerase 1 (Top1) confer resistance, suggesting convergent evolution of this defense mechanism (Sirikantaramas et al., 2008, 2015). Certain insects, such as the chrysomelid beetle Kanarella unicolor (Ramesha et al., 2011) and the lepidopteran larva Lymantria sp. (Sajitha et al., 2018) (family Lymantriidae), have developed mechanisms to detoxify CPT, allowing them to feed exclusively on Nothapodytes leaves without adverse effects. This interaction highlights the “defense and detoxification” dynamics between Nothapodytes and its herbivores. Investigating how these herbivores detoxify CPT could provide novel insights into the development of new pharmacological compounds or the enhancement of existing therapies.

3.4. Natural drugs related to Nothapodytes

Plant-derived anticancer drugs, particularly CPT derivatives such as irinotecan and topotecan, are crucial in oncology (Fig. 4b). Irinotecan, introduced in 1994, has achieved significant commercial success, generating over $600 million in revenue by 2018, with liposomal irinotecan (Nal-IRI) contributing 20% of this value (Bailly, 2019). The biosynthesis of camptothecin (CPT) begins with the condensation of tryptamine, derived from the shikimate pathway, and secologanin, a monoterpenoid synthesized via the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. This reaction, catalyzed by secologanic acid synthase (STRAS), produces strictosidinic acid as the key central intermediate (Sadre et al., 2016). Subsequent enzymatic steps, including oxidative rearrangements, hydroxylations, reductions, and dehydration reactions, lead to the formation of characteristic pentacyclic quinoline of CPT (Sadre et al., 2016; Pu et al., 2020; Chen et al., 2024b).

The roles of the MVA and MEP pathways in CPT biosynthesis in N. nimmoniana were elucidated using fosmidomycin and lovastatin as pathway-specific inhibitors (Rather et al., 2019). Fosmidomycin significantly reduced secologanin (40–57%) and CPT (64–71.5%) levels, whereas lovastatin caused moderate reductions in secologanin (7.5%) and CPT (7–11%) levels (Rather et al., 2019). These findings suggest that the MEP pathway is the primary contributor to CPT biosynthesis, with the MVA pathway playing a supplementary role. Transcriptional analyses further supported these findings by showing altered expression of key biosynthetic genes, including deoxy-xylulose-5-phosphate reductoisomerase (DXR), 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR), secologanin synthase (SLS), and STR (Rather et al., 2019).

Further transcriptomic and metabolomic studies from N. nimmoniana have supported secologanin as a central intermediate. The identification of key enzymes, including geraniol 10-hydroxylase (NnCYP76B6), further underscores the role of secologanin and related intermediates in the biosynthesis of CPT (Rather et al., 2018). In addition, three NADPH cytochrome P450 reductase (CPR) isoforms—NfCPR1, NfCPR2, and NfCPR3—were characterized, where NfCPR2 was shown to enhance geraniol 10-hydroxylase (G10H) activity in insect cells, significantly boosting eriodictyol production (Huang et al., 2012).

Transient overexpression of SLS (NnCYP72A1) increased secologanin and CPT levels by 1.13–1.43-fold and 2.02–2.86-fold, respectively, with elicitor treatments further enhancing CPT accumulation, underscoring its potential for metabolic engineering (Rather et al., 2020). Moreover, transcriptomic studies of Nothapodytes nimmoniana stem wood have identified 13 genes associated with CPT biosynthesis, highlighting the roles of NnPG10H, NnPSLS, and NnPSTR in CPT production, which suggest that CPT is likely synthesized in the leaves and stored in the stem wood (Manjunatha et al., 2016). In addition, transcriptionally active AP2/ERF and bHLH transcription factors (TFs) were identified, revealing their roles in CPT biosynthesis through root-enriched expression, phylogenetic clustering with alkaloid-regulating TFs, and promoter cis-element analyses, suggesting regulation via jasmonic acid (Godbole et al., 2023).

Similarly, the overexpression of VeA in endophytic Fusarium solani isolated from Nothapodytes pittosporoides significantly enhanced antitumor activity, reducing the IC₅₀ value from 369.22 to 285.89 μg/mL and increasing apoptosis by 4.86-fold. Transcriptomic and metabolomic analyses revealed altered expression of 48 antitumor-related genes, including those encoding glycosyl hydrolases, the Zn(2)-Cys(6) transcription factors, cytochrome P450 monooxygenases, 3-isopropylmalate dehydratases, and polyketide synthases (Cai et al., 2022).

Structural modifications play a pivotal role in fine-tuning pharmacological activity and enhancing drug-like properties. The clinical success of two C-10 modified camptothecin derivatives, topotecan and irinotecan, as potent anticancer agents underscores the need to develop methods for accessing other functionalized congeners, such as those modified at the C-9 and C-10 positions (Fig. 4). These sites are critical for synthetic and semi-synthetic strategies, enabling the creation of tailored CPT analogs with improved therapeutic indices while retaining their potent topoisomerase Ⅰ inhibitory activity.

C-9 functionalized CPT derivatives, such as 9-hydroxycamptothecin (9-HCPT) and 9-methoxycamptothecin (9-MCPT), have emerged as potent anticancer agents with remarkable efficacy against various tumor cell lines. Notably, 9-HCPT has shown superior cytotoxicity compared to the widely used anticancer drug topotecan, being nearly an order of magnitude more effective in pancreatic cancer cells (SW1990) (Liu et al., 2022). Similarly, 9-MCPT has shown selective inhibition of ovarian (A2780) and cervical (HeLa) cancer cells, exceeding the potency of C-10 hydroxylated CPT derivatives (Wang et al., 2013). Despite their therapeutic promise, the chemical synthesis of C-9 functionalized derivatives remains challenging due to low yields and harsh reaction conditions (Gao et al., 2005). Natural sources of these derivatives have been identified in species such as Nothapodytes nimmoniana and Ophiorrhiza pumila, with studies reporting the first isolation of 9-HCPT from N. tomentosa (Li et al., 2023). Although the raw abundance of these derivatives in plants is low, the identification of biosynthetic genes holds significant potential for scalable production through synthetic biology approaches.

Recently, metabolomic and transcriptomic analyses have unveiled four key tailoring enzymes, including camptothecin 9-hydroxylase (NtCPT9H), 9-hydroxycamptothecin O-methyltransferases (NtOMT1/2), and 9-hydroxycamptothecin UDP-glycosyltransferase (NtUGT5), responsible for C-9 functionalization of CPT in Nothapodytes tomentosa (Chen et al., 2024). These enzymes facilitate the biosynthesis of derivatives such as 9-HCPT and 9-MCPT, advancing the understanding of CPT tailoring mechanisms. Comparable enzymes have been identified in other CPT-producing species, including C. acuminata and O. pumila, where cytochrome P450 enzymes, such as camptothecin 10-hydroxylase (CaCPT10H) and 11-hydroxylase (CaCPT11H), are involved in C-10 and C-11 functionalization, respectively (Nguyen et al., 2021). In addition, a 10-hydroxycamptothecin O-methyltransferase (Ca10OMT) has been reported to further modify the C-10 hydroxyl group (Fig. 4a) (Salim et al., 2018). The biosynthetic machinery specific to C-9 modifications paves the way for leveraging synthetic biology to enhance the production of C-9 functionalized CPT derivatives, enabling the development of next-generation anticancer therapeutics.

CPT derivatives have become pivotal in the development of antibody-drug conjugates (ADCs), which employ the selective targeting capabilities of monoclonal antibodies to deliver cytotoxic drugs directly to tumor cells. In particular, sacituzumab govitecan, a monoclonal antibody with a cytotoxic payload derived from the CPT metabolite SN-38, was granted approval by the US Food and Drug Administration (FDA) for the treatment of breast cancer (Wahby et al., 2021). The combination of CPT derivatives with innovative linker technologies in ADCs is revolutionizing precision oncology, offering greater efficacy and safety profiles compared to conventional chemotherapeutics (Akram et al., 2025).

In parallel, advancements in chemical synthesis have led to more efficient methods for the total and semi-synthesis of camptothecin. The total synthesis of camptothecin, though challenging due to its complex pentacyclic structure, may provide a deeper understanding of its chemical properties and synthetic feasibility. Synthetic methodologies, including total and combinatorial synthesis, are crucial for creating structurally diverse molecules with potent pharmacological effects. Advanced synthetic strategies such as Function-Oriented Synthesis (FOS) (Wender et al., 2008), Biology-Oriented Synthesis (BIOS) (Hattum and Waldmann, 2014), Diversity-Oriented Synthesis (DOS) (Zhang et al., 2022), and Pharmacophore-Oriented SemiSynthesis (POSS) (Zhou et al., 2022) should be prioritized in future research. These approaches not only increase the availability of the compound but also reduce the ecological impact of its production, offering a viable path forward for conserving Nothapodytes populations.

3.5. Rescuing and utilizing anticancer Nothapodytes species

The rescue and sustainable utilization of Nothapodytes species are critical to balancing conservation efforts with pharmaceutical demands, particularly for CPT production. Optimizing in vitro culture conditions is crucial, which is influenced by factors such as medium composition, plant growth regulator (PGR) concentrations, and environmental conditions. 2,4-dichlorophenoxyacetic acid (2,4-D) was found to be effective for callus initiation, while NAA has been shown to yield higher CPT content (Fulzele et al., 2001; Thengane et al., 2003). Callogenesis was effectively induced using Thidiazuron (TDZ) in combination with 2,4-D, with hypocotyl explants showing the highest response and calli grown on 2 mg/L TDZ + 0.5 mg/L 2,4-D exhibiting a two-fold increase in CPT content (Kadam et al., 2023). Semi-solid and liquid media have been compared, with liquid media allowing enhanced nutrient diffusion but causing CPT leaching, mitigated by XAD-7 addition to prevent degradation (Jisha, 2006; Dandin and Murthy, 2012; Karwasara and Dixit, 2013). The use of sucrose as a carbon source and selective nitrogen feeding further enhances CPT yield, but challenges remain in stabilizing high-producing cell lines and understanding regulatory biochemical pathways for industrial-scale production (Karwasara and Dixit, 2013).

Similarly, in vitro organogenesis through both direct and indirect regeneration has been studied, with BAP being the most effective PGR for shoot induction, while TDZ, despite its efficiency, requires BAP or glutamine supplementation to prevent shoot stunting (Satheeshkumar and Seeni, 2000; Dandin and Murthy, 2012). Genetic fidelity assessments using ISSR markers showed 97% homology to the mother plant (Chandrika et al., 2010), while high-performance liquid chromatography (HPLC) analysis showed consistent CPT content, ensuring chemical uniformity with the elite mother plant (Prakash et al., 2016). Somatic embryogenesis (SE) supplemented with 2,4-D, 6-benzyladenine (BA), and kinetin offers a promising avenue for large-scale propagation, with proteomics studies revealing key molecular pathways involved in embryogenic competence (Isah and Umar, 2019). Furthermore, reproductive ecology studies indicate that Nothapodytes nimmoniana, primarily pollinated by Apis dorsata and Trigona iridipennis, faces pollen limitation and reduced fruit set under exploitative conditions, highlighting the need for conservation efforts (Sharma et al., 2011).

To ensure a sustainable supply of CPT and protect Nothapodytes species, Peng et al. (2024) propose a comprehensive conservation strategy that integrates biogeographic assessments, genetic and metabolic studies, and pharmacological innovations. Balancing conservation efforts with pharmaceutical advancements requires policy-driven initiatives that reinforce sustainable resource management and enhance drug development pipelines. Integrating plant resource management with modern synthetic and biotechnological approaches will facilitate the preservation of Nothapodytes while maximizing its medicinal potential for anticancer drug development.

4. Future directions: harmonizing conservation and pharmaceutical needs

The conservation of TPSWD, such as Nothapodytes, requires a multi-faceted approach that harmonizes biodiversity protection with the pharmaceutical demand for bioactive compounds like camptothecin (Peng et al., 2024). Given the absence of comprehensive taxonomic and phylogenetic studies on Nothapodytes—and recognizing that robust taxonomy underpins effective conservation biology—an integrative taxonomic approach for this genus is urgently needed. To ensure the sustainability of these species, conservation efforts should focus on four key strategies:

(1) Reassessing the threat levels of regional populations: Accurate threat assessment is crucial for the effective conservation of Nothapodytes. While the species may be widespread, the ecological status of regional populations varies due to habitat degradation, overharvesting, and fragmented distributions. Implementing long-term population monitoring using remote sensing and GIS technologies can provide real-time data on species distribution and vulnerability. Additionally, population modeling can help predict declines and assess the impact of current harvesting practices. Incorporating these insights into IUCN Red List assessments will ensure that conservation priorities are based on up-to-date scientific data, enabling more targeted interventions.

(2) Strengthening flexible adaptive local management and conservation: Conservation strategies must be adaptable to local socio-economic conditions. In situ conservation, such as the establishment of protected areas and community-managed reserves, is critical for preserving Nothapodytes in its natural habitat. Simultaneously, ex situ conservation, including seed banks, germplasm collections, and botanical gardens, can safeguard genetic diversity and facilitate species recovery. According to the BGCI PlantSearch database, several Nothapodytes species are currently maintained in ex situ collections, primarily in Chinese botanical gardens. Nothapodytes nimmoniana is held in two institutions: the Botanischer Garten der Johannes Gutenberg Universität Mainz (Germany) and the Dr. Cecilia Koo Botanic Conservation Center (Taiwan, China). Nothapodytes pittosporoides is the most widely represented, occurring in four Chinese botanical gardens (Hunan, Kunming, Wuhan, and Xishuangbanna). Nothapodytes collina, N. obscura, and N. obtusifolia are each maintained in one or two institutions, all located in China, while N. tomentosa is represented in two collections (Kunming and Xishuangbanna). Although all six species are represented in at least one collection, their coverage remains limited, highlighting the need for broader ex situ conservation efforts, particularly seed banking, to ensure their long-term survival. In addition, sustainable conservation requires active engagement of local communities (Fig. 2j) (Chen et al., 2019). Providing training on sustainable harvesting techniques and the integration of modern propagation methods will empower residents to cultivate Nothapodytes effectively, reducing pressure on wild populations while fostering economic opportunities through the development of a sustainable medicinal plant industry.

(3) Reducing trade under certain conditions: Regulating trade in Nothapodytes-derived camptothecin requires a balanced approach that minimizes wild population depletion while supporting sustainable production. Instead of imposing strict trade restrictions, efforts should focus on shifting supply toward large-scale artificial plantations, particularly in tropical regions, where controlled cultivation can meet market demand. Expanding plantations to thousands of acres will provide a reliable, sustainable source of camptothecin while alleviating pressure on natural populations. Simultaneously, strengthening international trade monitoring through CITES regulations is essential to prevent illegal harvesting and ensure compliance with sustainable sourcing standards. Implementing certification systems, such as FairWild, can further promote traceability and ethical trade, while national policies should establish scientifically backed quotas and harvesting guidelines to regulate wild collection.

(4) Seeking alternative resources overall: To reduce pressure on wild populations, alternative camptothecin production methods must be explored. Lessons from Taxus spp. conservation, where paclitaxel production shifted from wild harvesting to semi-synthesis, cell culture, and fungal fermentation, should be applied to Nothapodytes (Yukimune et al., 1996; Xiong et al., 2021). Advances in synthetic biology, microbial fermentation, and chemical synthesis could provide scalable production methods for camptothecin, reducing dependency on natural sources. Research on endophytic microorganisms that enhance metabolite production may also open new biotechnological avenues for sustainable drug development.

(5) Enhancing camptothecin production through metabolic engineering and synthetic biology: To address resource constraints in camptothecin (CPT) production from Nothapodytes, future efforts should focus on deciphering the CPT biosynthetic pathway. This understanding will facilitate two key advancements: first, increasing CPT yields through metabolic engineering to reduce dependence on natural resources; and second, synthetic biology to optimize enzymatic steps by leveraging genetic diversity across Nothapodytes species, enabling more efficient and targeted synthesis of CPT and its active derivatives.

The conservation of TPSWD, including Nothapodytes, presents a complex challenge requiring an integrated approach that combines scientific innovation, conservation strategies, and policy interventions. By reassessing threat levels, implementing adaptive management, regulating trade, and developing alternative resources, it is possible to achieve long-term sustainability. Multidisciplinary collaboration among ecologists, pharmacologists, conservation biologists, and policymakers is essential to harmonizing biodiversity conservation with pharmaceutical advancements, ensuring that these species remain available for both ecological and medicinal purposes.

Acknowledgements

The authors thank Jianping Huang, Kunming Institute of Botany, Chinese Academy of Sciences (KIB), and the anonymous reviewers for their valuable suggestions and constructive comments. We also extend our appreciation to Zeting Zhao (KIB) for providing the photo (Fig. 2i). This work was equally supported by the National Key R&D Program of China (2024YFF1306700), the Key Project of Basic Research of Yunnan Province, China (202301AS070001), and the Regional Innovative Development Joint Fund of NSFC (U23A20149).

CRediT authorship contribution statement

Bishal Gurung: Writing – original draft, Writing – review & editing, Methodology, Visualization, Formal analysis, Data curation. Yan Zeng: Conceptualization, Writing – review & editing, Methodology. Jia Tang: Writing – review & editing, Visualization. Xing-Rong Peng: Writing – review & editing. Yu-Lin Xu: Writing – review & editing, Visualization. Feng-Mao Yang: Methodology, Visualization. Xiang-Hai Cai: Writing – review & editing. Jia Ge: Supervision, Writing – original draft, Writing – review & editing, Resources, Funding acquisition. Gao Chen: Conceptualization, Writing – original draft, Writing – review & editing, Resources, Funding acquisition.

Data availability

The datasets generated and analysed during the current review are available from the corresponding author on reasonable request.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.pld.2025.10.005.