Expression of multidrug resistance proteins in retinoblastoma

ACOT7 promotes retinoblastoma resistance to vincristine by regulating fatty acid metabolism reprogramming

The rate of vincristine (VCR) resistance in the treatment of retinoblastoma (RB) is relatively high, and the exact role and mechanism of autophagy and fatty acid (FA) metabolism in RB are still unknown. The aim of this study was to elucidate the molecular mechanism by which acyl-CoA thioesterase 7 (ACOT7) regulates FA metabolism and autophagy, which may lead to potential therapeutic strategies for RB. In the present study, the relationship between FA metabolism and cellular drug sensitivity was evaluated through ACOT7 overexpression or inhibition tests in RB-resistant cells. The lipase inhibitor orlistat and the autophagy inhibitor CQ were used to determine the effects of ACOT7 on FA metabolism, autophagy, and cellular drug sensitivity, as well as the therapeutic value of ACOT7 targeting. The results showed that ACOT7 was upregulated in VCR-resistant RB cells, significantly enhancing cell resistance and indicating that ACOT7 may serve as a biomarker for VCR resistance in RB cells. Knockdown of ACOT7 inhibited FA metabolism and reduced cell viability in VCR-resistant RB cells. The effect of ACOT7 overexpression was opposite to that of ACOT7 knockdown, and ACOT7 overexpression promoted autophagy in VCR-resistant RB cells. After treatment with orlistat or CQ, FA metabolism in VCR-resistant RB cells decreased, cell viability and autophagy were inhibited, EMT was inhibited, and the sensitivity of RB cells to VCR was increased. In conclusion, ACOT7 knockdown can mediate FA metabolism to inhibit autophagy and the migration of RB cells, thereby improving the sensitivity of RB cells to VCR.

Advances in the research of plant-derived natural products against retinoblastoma

Retinoblastoma (RB) is a highly aggressive ocular tumor, and due to socioeconomic and medical constraints, many children receive treatment only in the metaphase and advanced clinical stages, resulting in high rates of blindness and disability. Although several approaches exist in the treatment of RB, some children with the disease do not have satisfactory results because of various factors. Plant-derived natural products have shown definite therapeutic effects in the treatment of various tumors and are also widely used in the study of RB. We review plant-derived natural products used in the study of anti-RB to provide ideas for the clinical application of these drugs and the development of new therapeutic drugs.

Induction of autophagy-dependent ferroptosis to eliminate drug-tolerant human retinoblastoma cells

Carboplatin is the most used first-line drug for the treatment of human retinoblastoma (RB), a rare form of cancer in infancy and childhood. However, the clinical application of carboplatin is restricted due to the emergence of acquired multi-drug resistance (MDR) after long-term treatment. Here, we report a new strategy to eliminate MDR RB cells by inducing autophagy-dependent ferroptosis. Compared with parent cells, carboplatin-resistant human RB cells have higher autophagy activity, which drives the formation of MDR to other chemotherapeutic drugs (e.g., etoposide and vincristine). In addition to confirming the traditional strategy of inhibiting autophagy to overcome MDR, we also establish an approach of inducing selective ferritinophagy to eliminate drug-resistant cells. We evaluate the effectiveness and safety of 4-octyl itaconate, a cell-permeable derivative of the metabolite itaconate, in inducing ferritinophagy-dependent ferroptosis in the treatment of MDR RB cells in vitro and in xenograft mouse models. These findings may provide essential clues for initiating clinical trials that target autophagy-dependent ferroptosis to kill drug-tolerant persistent cells during RB therapy.

RING-Finger Protein 6 promotes Drug Resistance in Retinoblastoma via JAK2/STAT3 Signaling Pathway

Chemotherapy is the first-line treatment for human retinoblastoma (RB), but the occurrence of drug resistance greatly limited its efficacy in practice. RING-finger protein 6 (RNF6) is an E3 ubiquitin ligase that is aberrantly upregulated in a range of cancers and plays important roles in cancer progression. However, the role of RNF6 in RB is largely unknown. In this study, we investigated the role of RNF6 in RB drug resistance. Two carboplatin-resistant RB cells, Y-79/CR and SO-Rb50/CR, were generated based on Y-79 and SO-Rb50 cells. RT-PCR and western blot analyses showed that RNF6 expression on both mRNA and protein levels was significantly increased in Y-79/CR and SO-Rb50/CR cells comparing to their parental cells. Knockdown of RNF6 using siRNA in Y-79/CR and SO-Rb50/CR cells resulted in cells sensitive to carboplatin on a RNF6 siRNA dose dependent manner. Similarly, RNF6 overexpression in parental Y-79 and SO-Rb50 cells could help cells gain resistance to carboplatin on a RNF6 expression dependent manner. Signaling pathway analyses revealed that JAK2/STAT3 pathway was involved in the RNF6-induced carboplatin resistance in RB cells. We further revealed that RNF6 expression in both Y-79 and SO-Rb50 cells could render cells resistant to multiple anti-cancer drugs including carboplatin, vincristine and etoposide, an implication of RNF6 as a biomarker for RB drug resistance. Taken together, our study has revealed that RNF6 is upregulated in drug-resistant RB cells and RNF6 promotes drug resistance through JAK2/STAT3 signaling pathway. The importance of RNF6 in RB cells drug resistance may represent this protein as a potential biomarker and treatment target for drug resistance in RB.

Carboplatin- and Etoposide-Loaded Lactoferrin Protein Nanoparticles for Targeting Cancer Stem Cells in Retinoblastoma In Vitro

Purpose

Cancer stem cells (CSCs) are known to contribute to tumor relapses by virtue of their chemoresistance. With the knowledge that nanoformulations can overcome drug resistance, we evaluated the efficacy and cytotoxicity of clinical-grade carboplatin (CPT)– and etoposide (ETP)–loaded lactoferrin nanoparticles (Lf-Nps) on total, CD133-enriched (non-CSC), and CD133-depleted (CSC) populations of retinoblastoma (Rb) Y79 cells.

Methods

Physicochemical properties of drug-loaded Lf-Nps were measured with transmission electron microscopy and attenuated total reflectance–Fourier transform infrared. The encapsulation efficiency, uptake, and release of drug-loaded Lf-Nps were measured using high-performance liquid chromatography and a UV-visible spectrophotometer. Cytotoxicity of the standard and drug-loaded Lf-Nps was evaluated by the MTT assay.

Results

The mean (SD) size and encapsulation efficiency of Lf-CPT and Lf-ETP were 61.2 (3.94) nm, 60% and 45.15 (5.85) nm, 38%, respectively, and the drug release efficiency was highest at pH 6. The increased drug uptake and lower release of drug-loaded Lf-Nps were observed in CSC and non-CSC populations compared to their standard forms. The relative increase of drug uptake and sustained intracellular retention of the drug-loaded Lf-Nps compared to standard drugs showed an enhanced cytotoxicity up to 50%, especially in Rb Y79 CSCs (IC₅₀: CPT, 230.3; Lf-CPT, 118.2; ETP, 198.1; and Lf-ETP, 129) compared to non-CSCs.

Conclusions

Our study documents an increase in drug uptake, retention, and cytotoxicity of Lf-CPT and Lf-ETP on Y79 CSCs and non-CSCs as compared to their standard drugs in vitro. The reversal of chemoresistance in the CSC population by nanoformulation appears promising with the potential to pave the way for improved targeted therapy and better clinical outcomes.

Islet Co-Expression of CD133 and ABCB5 in Human Retinoblastoma Specimens

BACKGROUND

The role of CD133 und ABCB5 is discussed in treatment resistance in several types of cancer. The objective of this study was to evaluate whether CD133⁺/ABCB5⁺ colocalization differs in untreated, in beam radiation treated, and in chemotherapy treated retinoblastoma specimens. Additionally, CD133, ABCB5, sphingosine kinase 1, and sphingosine kinase 2 gene expression was analyzed in WERI-RB1 (WERI RB1) and etoposide-resistant WERI RB1 subclones (WERI ETOR).

METHODS

Active human untreated retinoblastoma specimens (n = 12), active human retinoblastoma specimens pretreated with beam radiation before enucleation (n = 8), and active human retinoblastoma specimens pretreated with chemotherapy before enucleation (n = 7) were investigated for localization and expression of CD133 and ABCB5 by immunohistochemistry. Only specimens with IIRC D, but not E, were included in this study. Furthermore, WERI RB1 and WERI ETOR cell lines were analyzed for CD133, ABCB5, sphingosine kinase 1, and sphingosine kinase 2 by the real-time polymerase chain reaction (RT-PCR).

RESULTS

Immunohistochemical analysis revealed the same amount of CD133⁺/ABCB5⁺ colocalization islets in untreated and treated human retinoblastoma specimens. Quantitative RT-PCR analysis showed a statistically significant upregulation of CD133 in WERI ETOR (p = 0.002). No ABCB5 expression was detected in WERI RB1 and WERI ETOR. On the other hand, SPHK1 (p = 0.0027) and SPHK2 (p = 0.017) showed significant downregulation in WERI ETOR compared to WERI RB1.

CONCLUSIONS

CD133⁺/ABCB5⁺ co-localization islets were noted in untreated and treated human retinoblastoma specimens. Therefore, we assume that CD133⁺/ABCB5⁺ islets might play a role in retinoblastoma genesis, but not in retinoblastoma treatment resistance.

Adhesion G protein-coupled receptor, ELTD1, is a potential therapeutic target for retinoblastoma migration and invasion

BACKGROUND

Prognosis for pediatric metastatic Retinoblastoma (Rb) is poor and current therapies are limited by high systemic toxicity rates and insufficient therapeutic efficacy for metastatic Rb. Tumor dissemination to the brain is promoted by the heterogeneous adhesive and invasive properties of Rb cells within the tumor. In this study we evaluate, for the first time, the expression, and roles of the ELTD1 and GPR125 adhesion G protein-coupled receptors (GPCRs) in Rb cell migration, viability and invasion.

METHODS

We characterized the RNA expression of adhesion-GPCRs in 64 Rb tumors compared to 11 fetal retinas using the database from the Childhood Solid Tumor Network from St Jude Children's Research Hospital. The role of ELTD1 and GPR125 in Rb were investigated ex vivo by microarray analysis, in vitro by cell viability, Western blot and migration assays, in addition to imaging of the subcellular localization of the GPCRs. To elucidate their role in vivo we utilized siRNA technology in an established Rb orthotopic xenograft murine model.

RESULTS

Our investigation demonstrates, for the first time, that ELTD1 but not GPR125, is significantly increased in Rb tumors compared to fetal retinas. We utilized established the Rb cell lines Y79 and Weri-Rb-1, which represent an aggressive, metastatic, and non-metastatic phenotype, respectively, for the in vitro analyses. The studies demonstrated that ELTD1 is enriched in Weri-Rb-1 cells, while GPR125 is enriched in Y79 cells. The measured differences extended to their subcellular localization as ELTD1 labeling displayed punctate clusters in cell-to-cell adhesion sites of Weri-Rb-1 cells, while GPR125 displayed a polarized distribution in Y79 cells. Lastly, we demonstrated the lack of both adhesion receptors does not affect Rb cell viability, yet inhibition of ELTD1 decreases Y79 cell migration in vitro and invasion in vivo.

CONCLUSION

Taken together, our data suggest that ELTD1, is a potential target to prevent extraocular Rb. The results within establish ELTD1 as a potential therapeutic target for metastatic Rb.

Expression Changes and Impact of the Extracellular Matrix on Etoposide Resistant Human Retinoblastoma Cell Lines

Retinoblastoma (RB) represents the most common malignant childhood eye tumor worldwide. Several studies indicate that the extracellular matrix (ECM) plays a crucial role in tumor growth and metastasis. Moreover, recent studies indicate that the ECM composition might influence the development of resistance to chemotherapy drugs. The objective of this study was to evaluate possible expression differences in the ECM compartment of the parental human cell lines WERI-RB1 (retinoblastoma 1) and Y79 and their Etoposide resistant subclones via polymerase chain reaction (PCR). Western blot analyses were performed to analyze protein levels. To explore the influence of ECM molecules on RB cell proliferation, death, and cluster formation, WERI-RB1 and resistant WERI-ETOR cells were cultivated on Fibronectin, Laminin, Tenascin-C, and Collagen IV and analyzed via time-lapse video microscopy as well as immunocytochemistry. We revealed a significantly reduced mRNA expression of the proteoglycans Brevican, Neurocan, and Versican in resistant WERI-ETOR compared to sensitive WERI-RB1 cells. Also, for the glycoproteins α1-Laminin, Fibronectin, Tenascin-C, and Tenascin-R as well as Collagen IV, reduced expression levels were observed in WERI-ETOR. Furthermore, a downregulation was detected for the matrix metalloproteinases MMP2, MMP7, MMP9, the tissue-inhibitor of metalloproteinase TIMP2, the Integrin receptor subunits ITGA4, ITGA5 and ITGB1, and all receptor protein tyrosine phosphatase β/ζ isoforms. Downregulation of Brevican, Collagen IV, Tenascin-R, MMP2, TIMP2, and ITGA5 was also verified in Etoposide resistant Y79 cells compared to sensitive ones. Protein levels of Tenascin-C and MMP-2 were comparable in both WERI cell lines. Interestingly, Fibronectin displayed an apoptosis-inducing effect on WERI-RB1 cells, whereas an anti-apoptotic influence was observed for Tenascin-C. Conversely, proliferation of WERI-ETOR cells was enhanced on Tenascin-C, while an anti-proliferative effect was observed on Fibronectin. In WERI-ETOR, cluster formation was decreased on the substrates Collagen IV, Fibronectin, and Tenascin-C. Collectively, we noted a different ECM mRNA expression and behavior of Etoposide resistant compared to sensitive RB cells. These findings may indicate a key role of ECM components in chemotherapy resistance formation of RB.

CD24 blunts the sensitivity of retinoblastoma to vincristine by modulating autophagy

Retinoblastoma (RB) is the most common childhood malignant intraocular tumor. The clinical efficacy of vincristine (VCR) in the treatment of RB is severely limited by drug resistance. Here, we found that CD24, a GPI-anchored protein, was overexpressed in human RB tissues and RB cell lines, and was associated with the sensitivity of RB cells in response to VCR therapy. We demonstrated that CD24 plays a critical role in impairing RB sensitivity to VCR via regulating autophagy. Mechanistically, CD24 recruits PTEN to the lipid raft domain and regulates the PTEN/AKT/mTORC1 pathway to activate autophagy. Lipid raft localization was essential for CD24 recruitment function. Collectively, our findings revealed a novel role of CD24 in regulating RB sensitivity to VCR and showed that CD24 is a potential target for improving chemotherapeutic sensitivity and RB patient outcomes.