Camptothecin (CPT) is a cytotoxic alkaloid that attenuates the replication of cancer cells via blocking DNA topoisomerase 1.

In recent years, ICIs have transformed cancer treatment by harnessing the body's immune system to target and destroy cancer cells [1][2][3]. ICIs work by blocking inhibitory signals that prevent T cells from attacking tumors, thereby reactivating the immune response against cancer. The most common targets for these therapies are the PD-1/PD-L1 and CTLA-4 pathways, which are critical in regulating immune responses [4]. By inhibiting these pathways, drugs like nivolumab, pembrolizumab, and ipilimumab have shown remarkable efficacy in treating cancers such as melanoma, non-small cell lung cancer (NSCLC), and renal cell carcinomaFor example, nivolumab, a PD -1 inhibitor, has been a breakthrough in the treatment of melanoma. In a large -scale clinical trial involving patients with advanced melanoma, nivolumab treatment led to a significant improvement in overall survival, with approximately 40% of patients surviving for more than five years compared to less than 20% with traditional chemotherapy [5]. Pembrolizumab, another PD -1 inhibitor, has shown remarkable efficacy in non -small cell lung cancer (NSCLC). In a phase III trial, it demonstrated an objective response rate of around 20% -30% in previously treated patients and has since been incorporated into first -line treatment regimens, improving survival outcomes and quality of life for many patients [6]. Ipilimumab, a CTLA -4 inhibitor, has had a transformative impact on metastatic melanoma. It was the first drug to show an overall survival benefit in this difficult -to -treat cancer, increasing the median survival time by several months and providing a new treatment option for patients with limited alternatives [7,8]. While ICIs have demonstrated efficacy in a range of cancers, including melanoma and non-small cell lung cancer, their potential in treating bone tumors remains underexplored. Addressing this gap, the article also considers strategies tailored to enhance ICI efficacy specifically in bone tumor casesThese examples clearly illustrate the remarkable success of ICIs in different cancer types and their ability to revolutionize cancer treatment. While ICIs have demonstrated efficacy in a range of cancers, including melanoma and non -small cell lung cancer, their potential in treating bone tumors remains underexplored.Addressing this gap, the article also considers strategies tailored to enhance ICI efficacy specifically in bone tumor cases.These therapies have been particularly revolutionary for cancers that were previously difficult to treat, offering the potential for long-term remission in some patients. However, despite these successes, ICIs are not universally effective. Many patients do not respond to treatment, and those who do may develop resistance over time [9]. Additionally, the activation of the immune system can lead to severe immune-related adverse events (irAEs), which can affect various organs and require careful management [10]. The challenges of suboptimal efficacy and significant toxicity highlight the need for refined strategies in the use of ICIs. Personalized approaches, combination therapies, and the development of next-generation ICIs with improved specificity and safety profiles are essential to maximizing the therapeutic potential of these treatments.Despite the transformative potential of ICIs, their use is accompanied by significant challenges.One of the foremost issues is the variable response among patients. While some individuals experience dramatic and long-lasting tumor regression, many others do not respond to ICIs at all, a phenomenon known as primary resistance [10]. Even among responders, a subset may develop acquired resistance over time, leading to cancer progression after an initial period of remission [11].Another critical challenge is the occurrence of irAEs. These toxicities arise from the over activation of the immune system and can affect multiple organs, including the skin, gastrointestinal tract, liver, and endocrine system [12]. IrAEs range from mild to severe and can be life-threatening, necessitating the use of immunosuppressive treatments that might diminish the anti-tumor efficacy of ICIs [13]. Furthermore, the high cost of ICIs presents a significant barrier to access, limiting their availability to a broader patient populationAdditionally, the phenomenon of resistance is a major hurdle. Primary resistance, where patients do not respond to ICIs from the start, may be attributed to several factors. Tumors with low immunogenicity, due to a lack of tumor -specific antigens or a suppressive tumor microenvironment rich in immunosuppressive cells like regulatory T cells (Tregs) and myeloid -derived suppressor cells (MDSCs), can prevent effective T cell activation and infiltration [14]. Genetic alterations within the tumor cells, such as mutations in the interferongamma pathway genes, can also lead to primary resistance [15]. Acquired resistance, which develops over time in initially responsive patients, may involve the upregulation of alternative immune checkpoint pathways, such as TIM -3 and LAG -3, that compensate for the blocked PD -1/PD -L1 or CTLA -4 pathways [16]. Tumor cells can also adapt by losing expression of target antigens or developing mechanisms to evade immune recognition, such as through antigenpresentation machinery defects [17]. Understanding these mechanisms underlying resistance is crucial as it sets the stage for the later discussion on emerging strategies to overcome resistance. Furthermore, the high cost of ICIs presents a significant barrier to access, limiting their availability to a broader patient population [18]. These challenges underscore the urgent need for strategies to predict response, manage toxicity, and reduce costs, thereby optimizing the clinical application of ICIs in cancer therapy.ICIs targeting the PD-1/PD-L1 and CTLA-4 pathways have become integral to modern cancer therapy [19,20]. PD-1 inhibitors, such as nivolumab and pembrolizumab,...

Approved anticancer drugs typically face challenges due to their narrow therapeutic window, primarily because of high systemic toxicity and limited selectivity for tumors. Prodrugs are initially inactive drug molecules designed to undergo specific chemical modifications. These modifications render the drugs inactive until they encounter specific conditions or biomarkers in vivo, at which point they are converted into active drug molecules. This thoughtful design significantly improves the efficacy of anticancer drug delivery by enhancing tumor specificity and minimizing off-target effects. Recent advancements in prodrug design have focused on integrating these strategies with delivery systems like liposomes, micelles, and polymerosomes to further improve targeting and reduce side effects. This review outlines strategies for designing stimuli-responsive small molecule prodrugs focused on cancer treatment, emphasizing their chemical structures and the mechanisms controlling drug release. By providing a comprehensive overview, we aim to highlight the potential of these innovative approaches to revolutionize cancer therapy.