Delineating the Switch between Senescence and Apoptosis in Cervical Cancer Cells under Ciclopirox Treatment

Pyridoxamine Attenuates Doxorubicin-Induced Cardiomyopathy without Affecting Its Antitumor Effect on Rat Mammary Tumor Cells

Doxorubicin (DOX) is commonly used in cancer treatment but associated with cardiotoxicity. Pyridoxamine (PM), a vitamin B6 derivative, could be a cardioprotectant. This study investigated the effect of PM on DOX cardiotoxicity and DOX antitumor effectiveness. Sprague Dawley rats were treated intravenously with DOX (2 mg/kg/week) or saline over eight weeks. Two other groups received PM via oral intake (1 g/L in water bottles) next to DOX or saline. Echocardiography was performed after eight weeks. PM treatment significantly attenuated the DOX-induced reduction in left ventricular ejection fraction (72 ± 2% vs. 58 ± 3% in DOX; p < 0.001) and increase in left ventricular end-systolic volume (0.24 ± 0.02 µL/cm2 vs. 0.38 ± 0.03 µL/cm2 in DOX; p < 0.0001). Additionally, LA7 tumor cells were exposed to DOX, PM, or DOX and PM for 24 h, 48 h, and 72 h. Cell viability, proliferation, cytotoxicity, and apoptosis were assessed. DOX significantly reduced LA7 cell viability and proliferation (p < 0.0001) and increased cytotoxicity (p < 0.05) and cleaved caspase-3 (p < 0.001). Concomitant PM treatment did not alter the DOX effect on LA7 cells. In conclusion, PM attenuated DOX-induced cardiomyopathy in vivo without affecting the antitumor effect of DOX in vitro, highlighting PM as a promising cardioprotectant for DOX-induced cardiotoxicity.

Revisiting the role of endogenous STAT3 in HPV-positive cervical cancer cells

Novel treatment options for human papillomavirus (HPV)-induced cancers are urgently required. The oncogenic transcription factor signal transducer and activator of transcription 3 (STAT3) is considered to be constitutively active in HPV-positive cervical cancer cells and essential for their proliferation. Moreover, STAT3 was reported to undergo mutually stimulatory interactions with the HPV E6/E7 oncogenes. Thus, inhibiting STAT3 in HPV-positive cancer cells is under discussion to provide a powerful novel therapeutic strategy. We here show that the antifungal drug ciclopirox destabilizes the STAT3 protein by acting as an iron chelator. However, by exploring the functional consequences of STAT3 inhibition in HPV-positive cancer cells, we obtained several unexpected results. Chemical STAT3 inhibitors heterogeneously affect cervical cancer cell proliferation and those which act antiproliferative also block the growth of STAT3 knockout cells, indicating induction of off-target effects. In contrast to several chemical inhibitors, genetic inhibition of STAT3 expression by either RNA interference or the CRISPR/Cas9 method does not appreciably affect cervical cancer cell proliferation. Transcriptome analyses indicate that blocking STAT3 expression in HPV-positive cancer cells has very limited effects on putative STAT3 target genes. Although the targeted inhibition of specific growth-promoting signaling pathways leads to a feedback activation of STAT3 in cervical cancer cells via Janus kinase 1/2, this does not lead to treatment resistance. Moreover, we did not obtain experimental evidence for a STAT3-linked activation of HPV E6/E7 oncogene expression or, vice versa, an E6/E7-dependent activation of STAT3, at endogenous conditions in cervical cancer cells. Collectively, these findings question the essential role of STAT3 in cervical cancer cell proliferation and the strategy to inhibit STAT3 in these cells for therapeutic purposes.

High-Throughput Drug Screening Revealed That Ciclopirox Olamine Can Engender Gastric Cancer Stem-like Cells

Cancer stem cells (CSCs) are relevant therapeutic targets for cancer treatment. Still, the molecular circuits behind CSC characteristics are not fully understood. The low number of CSCs can sometimes be an obstacle to carrying out assays that explore their properties. Thus, increasing CSC numbers via small molecule-mediated cellular reprogramming appears to be a valid alternative tool. Using the SORE6-GFP reporter system embedded in gastric non-CSCs (SORE6-), we performed a high-throughput image-based drug screen with 1200 small molecules to identify compounds capable of converting SORE6- to SORE6+ (CSCs). Here, we report that the antifungal agent ciclopirox olamine (CPX), a potential candidate for drug repurposing in cancer treatment, is able to reprogram gastric non-CSCs into cancer stem-like cells via activation of SOX2 expression and increased expression of C-MYC, HIF-1α, KLF4, and HMGA1. This reprogramming depends on the CPX concentration and treatment duration. CPX can also induce cellular senescence and the metabolic shift from oxidative phosphorylation (OXPHOS) to glycolysis. We also disclose that the mechanism underlying the cellular reprogramming is similar to that of cobalt chloride (CoCl2), a hypoxia-mimetic agent.

Ciclopirox drives growth arrest and autophagic cell death through STAT3 in gastric cancer cells

Ciclopirox (CPX), an antifungal drug, has recently been identified as a promising agent for cancer treatment. However, the effects and underlying mechanism of CPX as an antitumor agent of gastric cancer (GC) remain largely unknown. Here, we found that CPX dramatically suppresses GC xenograft growth in vitro via inhibiting proliferation and stimulating autophagic cell death rather than apoptosis. Moreover, CPX (20 mg/kg, intraperitoneally) substantially inhibits GC xenograft tumor growth in vivo. Mechanistically, CPX promotes growth arrest and autophagic cell death through suppressing the phosphorylation of signal transducers and activators of transcription 3 (STAT3) at tyrosine 705 (Tyr705) and serine 727 (Ser727) sites, respectively. Additionally, CPX induces STAT3 ubiquitination, which subsequently leads to a decrease in the p-STAT3 (Ser727) level. On the other hand, CPX represses the p-STAT3 (Tyr705) level via p-Src (Tyr416) inhibition. Collectively, our findings unmask a novel mechanism by which CPX regulates growth and autophagic cell death in GC cells via regulating the phosphorylation of STAT3 both at Tyr705 and Ser727 residues, and suggest that CPX may be a potential treatment for GC.

FAM57A (Family with Sequence Similarity 57 Member A) Is a Cell-Density-Regulated Protein and Promotes the Proliferation and Migration of Cervical Cancer Cells

The FAM57A (family with sequence similarity 57 member A) gene is controversially discussed to possess pro- or anti-tumorigenic potential. Here, we analyze the regulation of cellular FAM57A protein levels and study the functional role of FAM57A in HPV-positive cervical cancer cells. We find that FAM57A protein expression strongly depends on cell density, with FAM57A being readily detectable at low cell density, but undetectable at high cell density. This regulation occurs post-transcriptionally and is not mirrored by corresponding changes at the RNA level. We further show that FAM57A protein levels are highly increased in cervical cancer cells cultivated at hypoxia compared to normoxia and provide evidence that FAM57A is a hypoxia-responsive gene under control of the α-subunit of the HIF-1 (hypoxia-inducible factor-1) transcription factor. Yet, the strong relative increase of FAM57A protein levels in hypoxic cells is predominantly cell-density-dependent and occurs post-transcriptionally. Other anti-proliferative effectors besides hypoxia, such as silencing of HPV E6/E7 oncogene expression in cervical cancer cells, also result in an increase of FAM57A levels compared to untreated cells. Functional analyses reveal that FAM57A repression leads to pronounced anti-proliferative as well as anti-migratory effects in cervical cancer cells. Taken together, these results provide insights into the regulation of FAM57A protein levels and reveal that they underlie a tight cell-density-dependent control. Moreover, they identify FAM57A as a critical determinant for the phenotype of cervical cancer cells, which promotes their proliferation and migration capacities.