The early clinical symptoms of RCC patients are atypical, but the late-stage symptoms may be painless hematuria, low back pain, and abdominal mass. Because the location of RCC in kidney is not obvious and early symptoms are not apparent, 30–40% of RCC patients have already developed metastasis at the first diagnosis. However, nearly 30% of RCC patients who undergo surgical treatment have recurrence and metastatic renal cell carcinoma (mRCC)[24]. For mRCC patients, the prognosis is poor, the five-year survival rate is less than 10%, and the average survival duration is less than one year[3, 12, 25]. Currently, radical nephrectomy is still the main clinical treatment for RCC[26, 27]. The prognosis of early-stage RCC patients who undergo surgical treatment is good, but for advanced renal cell carcinoma (aRCC) patients who are insensitive to radiotherapy and chemotherapy[11], surgical treatment can only reduce the tumor burden or improve symptoms; therefore, surgical treatment can only be used as a palliative treatment[28–30]. As such, it is important to explore effective treatments for RCC. TCM, in terms of antitumor efficacy, has high economic benefits, significant clinical efficacy, and fewer side effects and toxicity[31, 32]. Lathyrol is the dry mature seed of Euphorbia lathyris L. and is a TCM with a variety of active antitumor and anti-drug resistance components. Lathyrol can not only directly kill cancer cells and inhibit the proliferation of tumor tissues but also regulate the tumor microenvironment (TME) to inhibit the drug resistance of tumor cells, thereby increasing the efficacy of anticancer drugs[33–35].
From the results, we found that Lathyrol may generate the effect to the expression of CYP17A1 and PARP1, thereby affecting the synthesis and phosphorylation of AR, which has never been showed before. Studies have shown that AR activation and expression promote the occurrence and development of tumors in the advanced stage and promote malignant behaviors, such as invasion, spread and proliferation, and tumor drug resistance through different mechanisms, such as inhibiting the secretion of relevant immune factors to promote tumor immune escape, inducing angiogenesis, and activating EMT[36–42]. AR is expressed in both physiological tissues and pathological tissues and plays important roles in various physiological activities of different tissues[43] and in the development of selective androgen receptor modulators (SARMs), which also take advantage of this mechanism[44]. CYP17A1 is one of the key enzymes that affect AR synthesis, and its inhibitor, abiraterone, has been one of the targeted drugs recently implemented by international medical institutions for the treatment of metastatic castration-resistant prostate cancer (mCRPC)[45–47]. Liu et al. [48] found that CYP17A1 is expressed in rat testis and other reproductive organs and that the upregulation of CYP17A1 expression promotes AR expression in testis tissue. Giatromanolaki et al. [49] found that CYP17A1 was overexpressed in the cytoplasm of PCa cells and was directly related to AR expression in cancer cell nuclei and that the application of abiraterone, in addition to inhibiting CYP17A1 expression, could also block the secretion of AR and thus block the nuclear accumulation of AR. Sakai et al.[50] found that CYP17A1 is expressed in PCa patients and is involved in the synthesis of AR. Poly ADP-ribose polymerase-1 (PARP-1) plays an important role in the DNA damage repair process and functions as a specific regulator of the upstream and downstream targets of transcription factors. However, PARP-1 also plays a role in promoting tumor progression in several tumor models[51–53]. Clinical anticancer drugs developed against PARP, i.e., PARP inhibitors such as olaparib, are also the targeted drugs currently used for the diagnosis and treatment of PCa patients[54, 55]. Xie et al. [56] found that metformin induced the cleavage and degradation of PARP1, inhibited the expression levels of AR and its splice variant AR-V7, and thus induced the death of PCa cells. Therefore, as one of the important targets of AR synthesis and a participant in AR signal transduction, PARP1 has potential in tumor treatment and may provide an effective treatment strategy for mCRPC and mRCC patients. At present, through research on each key target associated with AR (as shown in Fig. 7), the corresponding drugs for each site of action have been developed and applied in the treatment of patients with PCa at each stage[57]. Although the research on AR in PCa is relatively mature, studies on AR in RCC are rare. In recent years, AR, as a classic immune target, has been studied with regard to the treatment of RCC. Bialek et al. [58] found that compared with normal physiological tissues, in tumor tissues, AR and its splice variant AR-V7RCC were more frequently expressed. Lee et al. [59] found that the inhibition of lysine-specific histone demethylase 1 (LSD1) expression inhibited the binding of AR to downstream target genes, thereby inhibiting the growth state and migration ability of RCC. Therefore, AR is an important target that affects the activity and function of RCC cells. The results of this study showed that while the expression of the key enzymes CYP17A1 and PARP1 was inhibited, the synthesis and phosphorylation of AR were also inhibited. Therefore, these two enzymes may be related to the synthesis and phosphorylation of AR to some extent. It is possible that Lathyrol may influence the expression of CYP17A1 and PARP1, thereby affecting the synthesis and phosphorylation of AR, then produce negative results to the function and activity of neoplasm cells.
The function of sphingosine kinase is to phosphorylate sphingosine to sphingosine 1-phosphate (S1P) to maintain the balance of sphingolipid metabolites[60]. There are two isoforms of sphingosine kinase: sphingosine kinase 2 (SPHK1) and SPHK2. Although SPHK1 and SPHK2 share high sequence similarity, the distribution, regulation and functions of SPHK2 are different from those of SPHK2 [60, 61], and SPHK-2 can be located in the nucleus and organelles of physiological cells. In the nucleus, SPHK-2 regulates gene expression and maintains telomere integrity; in organelles, such as the endoplasmic reticulum and mitochondria, SPHK-2 regulates the apoptosis pathway[10, 60]. The overexpression of SPHK2 has a tumor-promoting effect; that is, it can promote the proliferation, migration and invasion of tumor cells[62]. Lan et al.[63] found that the overexpression of SphK2 promoted the proliferation of adipocyte-induced epithelial ovarian cancer (EOC) cells. Huo et al. [64] found that methylated SPHK2 promoted the proliferation, migration and invasion of gastric cancer (GC) cells through the inhibition of KLF2 expression. Shi et al. [65] found that advanced hepatocellular carcinoma (HCC) overexpressed SPHK-2 and developed resistance to the anticancer drug regorafenib and that silencing SPHK-2 expression restored the sensitivity of HCC to regorafenib. The results of this study showed that Lathyrol may affect the invasion and EMT activity of RCC xenografts by affecting the secretion of SPHK-2.
MMPs and uPA promote tumor infiltration and invasion in the TME. MMP degrades extracellular matrix (ECM) components and releases matrix factors, cell surface-bound cytokines, and growth factors or their receptors to affect tissue integrity, immune cell recruitment and tissue turnover and promote tumor cell migration and invasion[66–68]. Masucci et al. [69] found that increased levels of uPA and uPAR in tumor tissues, stroma and biological fluids were correlated with unfavorable clinicopathological features and poor patient prognosis. After uPA binds to uPAR, it activates plasminogen to plasmin. Plasmin is a broad-spectrum matrix and fibrin-degrading enzyme that promotes tumor cell invasion and spread to distant sites. Chien et al. [70] found that timosaponin AIII suppressed the migration and invasion ability of cervical cancer cells by inhibiting the expression of uPA. This study determined the invasiveness of RCC xenografts by assessing the expression of xenograft-associated invasion proteins. The results showed that Lathyrol may affect the invasiveness of RCC xenografts by affecting the expression of AR and SPHK2.
The trans-differentiation process of epithelial cells into mesenchymal cells is called EMT, which is an important part of normal physiological functions, such as embryonic development and wound healing[71, 72]. In the process of EMT, there are two types of molecular markers: epithelial biomarkers and mesenchymal biomarkers. The ratio changes in these two indicators reflect the EMT process of cells and tissues. Common epithelial biomarkers include E-cadherin, β-catenin, and ZO-1, and common mesenchymal biomarkers include N-cadherin, vimentin, and α-SMA[71, 72]. However, in the TME, EMT plays an important role in tumor progression, metastasis and drug resistance. EMT of tumor cells could lead to the loss of cell polarity, promote tumor migration, invasion and infiltration, cause tumor cells to develop immune evasion, and promote progression into advanced and metastatic diseases[73, 74]. Therefore, the analysis of EMT in tumor cells and tumor tissues is an important means to determine cancer progression. In this study, the EMT ability of RCC xenografts was analyzed by assessing the expression of xenograft-associated EMT marker proteins. The results showed that Lathyrol can affect the EMT of RCC xenografts, an effect that may be associated with the inhibition of the expression of AR and SPHK2.
We have been committed to conducting research on the mechanism of action of the TCM Lathyrol in human RCC 786-O cells and Renca cells. In recent years, Lathyrol has been found to act through various pathways, such as the inhibition of the NF-κB pathway and related proteins in cancer tissues, promote the apoptosis of RCC cells and inhibit the proliferation and invasion of Renca cells to a certain extent by inhibiting the expression and activation of proteins in the TGF-β/Smad pathway [75–77]. In summary, based on previous studies by our group, in this study, Lathyrol inhibited the expression of invasive proteins and the incidence of EMT in RCC xenografts through the inhibition of the expression of AR and SPHK-2, key proteins in RCC xenografts, thus significantly inhibiting the invasion and EMT ability of RCC xenografts in mice; notably, Lathyrol had a small effect on the body weight of the mice. However, due to the lack of a specific gene level analysis and the analyses of other possible targets of Lathyrol, other pathways and related molecular mechanisms were not explored in depth. Therefore, the mechanism of action and specific targets associated with the development of RCC still need to be explored further to provide new ideas for the clinical diagnosis and treatment of patients with RCC.