By using data mining techniques and CMS classification, this study identified pitavastatin and atorvastatin as potential anti-CMS4 as well as anti-metastasis CRC drugs. As expected, pitavastatin and atorvastatin not only can inhibit the survival and metastatic potential of CMS4 cells but also can influence 5-FU-resistant cells and spheroid formation, particularly under high glucose conditions. Pitavastatin and atorvastatin treatment modulated autophagy and followed ER stress/UPR signaling, which may ultimately lead to apoptosis or other forms of cell death in CRC cells. Additionally, both pitavastatin and atorvastatin decreased the expression of YAP1, contributing to cell apoptosis. Consequently, we provide evidence to repurpose pitavastatin and atorvastatin, which originally served as primary lipid-lowering drugs, for treating patients with metastatic CRC, which may also benefit patients suffering from hyperglycemia.
Examining gene expression data sourced from large drug sensitivity databases can be used to provide information on drug repurposing strategies to combat specific forms of cancer. These databases have been widely used to explore how genetic alterations in cancer cells affect their response to drugs. However, varying degrees of genomic heterogeneity exist among cells, even among those of the same cancer type. It is therefore difficult to identify possible drug candidates that depend only on single mutant genes. However, by incorporating a more comprehensive classification of molecular paradigms for each cancer type in the search phase (e.g., CMS in CRC), we may be able to predict which drugs efficiently and precisely can be repurposed for target-based cancer treatment.
The CMS procedure helps to integrate gene expression-based classifications of CRC to facilitate clinical translation [12]. CMS has been proven to be a prognostic factor and has been gradually applied in numerous clinical trials [15]. In this study, we focused on CMS4 CRC since it is a common form of advanced-stage disease and exhibits the worst prognosis. In general, CMS4 CRC is resistant to the current anti-EGFR agent cetuximab in both chemo-refractory and chemo-naïve settings [46, 47]. Moreover, no benefit of oxaliplatin treatment against CMS4 CRC has yet been reported [48]. The limited affected treatment for CMS4 CRC encouraged us to identify candidate drugs that are also capable of being repurposed for treating metastatic CMS4 CRC.
In addition to genetic heterogeneity, differences in the CRC microenvironment, including hyperglycemia, also play a pivotal role in influencing responses to drug treatments. For example, Ma et al. reported that a high glucose environment attenuated 5-FU-mediated growth inhibition in CRC cells by decreasing cell death and increasing DNA replication [49]. In another study, Ikemura et al. revealed that the efficacies of 5-FU and oxaliplatin were limited in a CRC mouse model with induced hyperglycemia, the decreased overall survival was the result of chemoresistance [50]. DM also has been found to have a negative impact on CRC prognosis. Several meta-analyses have identified an association between DM and increased all-cause mortality and worse disease-free survival in patients with advanced CRC [51–56]. In Taiwan, Yang et al. further reported that high blood glucose levels could affect both overall and disease-free survival in patients with stage III CRC who were also receiving adjuvant 5-FU and oxaliplatin-based chemotherapy [37]. Similar observations can be found in the present study. For example, we found that SW480-HG cells were more resistant to 5-FU than SW480-LG cells. It is therefore critical to develop novel strategies to overcome chemoresistance in advanced CRC by considering both genetic and environmental factors.
One of the main findings of the present study is that pitavastatin and atorvastatin, but not other statins, have the potential to treat metastatic CMS4 CRC in patients with comorbid hyperglycemia. However, based on genetic heterogeneity, the results of preclinical and clinical trials have shown that treatments involving statins combined with chemotherapy drugs may not always be effective for treating CRC. Therefore, prospective studies stratified by biomarkers are required to evaluate the efficacy of statins when combined with conventional chemotherapy (Additional File 7: Table S6). Moreover, we also note that a systematic review of randomized controlled trials did not confirm the efficacy of statins in treating patients with solid malignant tumors, including CRC [57]. Our analysis also indicated that inappropriate selection of statin drugs may result in no significant efficacy in CRC patients. (Additional File 3: Figure S13). The data from this study suggest that statins were specifically effective against CMS4 cancers. Moreover, other studies have observed that statin use is associated with a lower incidence of left-sided colon cancers and rectal cancers, which are common sites of CMS4 cancers [58–61].
Although lipid-lowering effects may be similar among statins, their potential to treat cancer may differ significantly. Statins can be classified as hydrophilic or lipophilic, with each group having a different overall tissue distribution. For example, hydrophilic statins (e.g., pravastatin, rosuvastatin, and fluvastatin) are mainly located in the liver. In contrast, lipophilic statins (e.g., simvastatin, mevastatin, lovastatin, pitavastatin, and atorvastatin) readily diffuse across cell membranes and are distributed throughout many body tissues [62, 63]. Thus, another meta-analysis found that lipophilic, but not hydrophilic, statins could significantly reduce the risk of CRC [59]. Moreover, rosuvastatin, pitavastatin, and atorvastatin can be chemically synthesized to possess a fluorophenyl group that can form an additional linkage to HMG-CoA reductase, which exhibits a more potent inhibition [64, 65]. In addition to the different pharmacokinetics of different statins, their mechanisms on CRC cells may also vary significantly. For example, a subgroup analysis of the TOHO lipid intervention trial using pitavastatin (TOHO-LIP) showed that the anticancer effect of pitavastatin may be drug-specific [66].
We further categorized pitavastatin, atorvastatin, lovastatin, simvastatin, mevastatin, and pravastatin into three classes based on their sensitivity for treating CRC cells. Class I statins (i.e., pitavastatin and atorvastatin) were sensitive against metastatic CRC cells, whereas class II statins (i.e., lovastatin, simvastatin, and mevastatin) were sensitive only to primary CRC cells. The one class III statin (pravastatin) identified was not effective in treating CRC cells. By comparing the gene signatures of six different statins in the CLUE database, we found class I and II statins show some degrees of similarities of DEGs, while little similarity can be found as compared to class III statins (Data not shown). Taken together, these results show that the significant cytotoxicity of pitavastatin and atorvastatin against CRC is related not only to their specific pharmacokinetics but also that these statins generate unique changes in gene expression relative to other statins.
Since hypercholesteremia is one of the most common comorbidities in DM patients, statins are frequently prescribed for this patient population [67]. Despite the similar potency of all statins in reducing serum cholesterol levels, they may show significant differences in their ability to treat CMS4 CRC cells and overcome 5-FU drug resistance. This may be related to dosage as well as their mechanisms of action against CRC. For example, in this study, we found that the dosage of pitavastatin to inhibit SW480 was significantly lower than that of atorvastatin. However, the equivalent dosage between pitavastatin and atorvastatin when used to reduce CRC cell viability was similar to that used to generate a cholesterol-lowering effect. Although strict control of serum glucose levels in patients with CRC and DM may improve their prognosis, elevated postprandial serum glucose levels may exist even with normal fasting glucose and glycated hemoglobin (HbA1c) levels. Moreover, direct administration of the blood-glucose-lowering agent metformin is unable to kill CMS4 CRC cells [68]. Therefore, the proper selection of specific statins (i.e., pitavastatin or atorvastatin) to treat hypercholesteremia in patients with both metastatic CRC and DM may help reduce the potential resistance to chemotherapy and improve cancer-specific survival.
Next, we extracted pitavastatin and atorvastatin-treated CRC gene signatures from CLUE database and utilized CPDB analysis to predict the specific pathways involved in their triggering events. Our findings confirm that these statins impact CRC development via similar pathways (Fig. 5A-5B). Prior research indicates that statins induce cancer cell death by triggering autophagy and apoptosis [44]. Intriguingly, our results demonstrate that pitavastatin and atorvastatin indeed stimulate autophagy, as evidenced by elevated levels of p62 and LC3B II, along with increased apoptosis-related markers such as cleaved PARP, Bax, and cleaved Caspase-3 (Fig. 5C-5D). However, co-treatment with 3-MA, which affects autophagy, did not apparently inhibit pitavastatin and atorvastatin-induced apoptosis-related markers, such as cleaved PARP and cleaved caspase 3 (Fig. 6A). Since these statin drugs-induced apoptosis-related markers slightly decreased in ATG5 KO SW480 cells, indicating modulating autophagy may still partly result in statin drugs-induced apoptosis (Fig. 6B). The robust upregulation of PERK/ATF4/CHOP expression under pitavastatin or atorvastatin treatment, indicating the induction of ER stress/UPR signaling. The administration of GSK2606414 (PERKi) decreased the cleavage of PARP, especially under high glucose conditions, indicating ER stress/UPR signaling played a crucial role in pitavastatin or atorvastatin-induced apoptosis (Fig. 6C). Additionally, since YAP serves as a critical regulator promoting cell survival under endoplasmic reticulum stress [39], pitavastatin or atorvastatin-induced increase of phosphorylated YAP, which promote its cytosolic retention and degradation by ubiquitin-proteasome system, may at least, partly, confer pitavastatin or atorvastatin-induced apoptosis (Fig. 5C). Interestingly, administration of GSK2606414 reversed pitavastatin and atorvastatin-induced ATF4/CHOP signaling as well as the decrease of YAP (Fig. 6C). The increase of YAP expression under PERK inhibition may partly result from the decrease of phosphorylated YAP. Recently, YAP also has been demonstrated to degrade via ER stress-mediated ER-associated degradation (ERAD) [69], it will be of interest to investigate whether YAP or its interplay with ER stress signaling plays a crucial role in pitavastatin or atorvastatin-induced apoptosis. The upregulation of YAP has been found to possess an anti-apoptotic effect in many cells, however, it also has been found to promote apoptosis and other forms of cell death, such as ferroptosis and pyroptosis, in some cell types [70]. Other ER stress inhibitors will be included to validate the role of ER stress/UPR signaling and YAP expression in pitavastatin and atorvastatin-mediated cell death. Whether other forms of cell death mechanisms were involved in pitavastatin, and atorvastatin-induced cell death still needs further investigation.
From a clinical standpoint, it's worth noting that the doses of pitavastatin and atorvastatin utilized in our cell culture experiments greatly exceeded typical clinical standards. This could potentially impede the translation of our research findings into practical clinical applications. For instance, the minimum dose of atorvastatin employed in our cell culture experiments was 2.5 µM, equivalent to a clinical dose of 1396 µg/L. This dosage is approximately 70 times higher than the current clinical standard of 20 µg/L [71]. Similarly, we observed that the lowest dose of pitavastatin used in our cell culture experiments was 1.25 µM, translating to a clinical dose of 1101 µg/L. This is approximately 5 times higher than the current clinical dose of 200 µg/L [72]. This discriminates the utilities of pitavastatin from atorvastatin in clinical practice. To enhance the feasibility of clinical therapeutic interventions for CRC, it may be beneficial to reduce the need for administering a single high dose by extending the duration of treatment. This approach could potentially maintain efficacy while minimizing the risk of adverse effects associated with high doses.