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

The iron-chelating drug ciclopirox (CPX) may possess therapeutic potential for cancer treatment, including cervical cancer. As is observed for other chemotherapeutic drugs, CPX can induce senescence or apoptosis in cervical cancer cells which could differently affect their therapy response. The present study aims to gain insights into the determinants which govern the switch between senescence and apoptosis in cervical cancer cells. We performed proteome analyses, proliferation studies by live-cell imaging and colony formation assays, senescence and apoptosis assays, and combination treatments of CPX with inhibitors of oxidative phosphorylation (OXPHOS) or glycolysis. We found that CPX downregulates OXPHOS factors and facilitates the induction of apoptosis under limited glucose availability, an effect which is shared by classical OXPHOS inhibitors. Under increased glucose availability, however, CPX-induced apoptosis is prevented and senescence is induced, an activity which is not exerted by classical OXPHOS inhibitors, but by other iron chelators. Moreover, we show that the combination of CPX with glycolysis inhibitors blocks cervical cancer proliferation in a synergistic manner. Collectively, our results reveal that the phenotypic response of cervical cancer cells towards CPX is strongly dependent on glucose availability, link the pro-apoptotic and pro-senescent activities of CPX to its bifunctionality as an OXPHOS inhibitor and iron chelator, respectively, and provide a rationale for combining CPX with glycolysis inhibitors.

Effects of Metformin on the virus/host cell crosstalk in human papillomavirus-positive cancer cells.

Oncogenic types of human papillomaviruses (HPVs) are major human carcinogens. The viral E6/E7 oncogenes maintain the malignant growth of HPV-positive cancer cells. Targeted E6/E7 inhibition results in efficient induction of cellular senescence, which could be exploited for therapeutic purposes. Here we show that viral E6/E7 expression is strongly downregulated by Metformin in HPV-positive cervical cancer and head and neck cancer cells, both at the transcript and protein level. Metformin-induced E6/E7 repression is glucose and PI3K-dependent but-other than E6/E7 repression under hypoxia-AKT-independent. Proteome analyses reveal that Metformin-induced HPV oncogene repression is linked to the downregulation of cellular factors associated with E6/E7 expression in HPV-positive cancer biopsies. Notably, despite efficient E6/E7 repression, Metformin induces only a reversible proliferative stop in HPV-positive cancer cells and enables them to evade senescence. Metformin also efficiently blocks senescence induction in HPV-positive cancer cells in response to targeted E6/E7 inhibition by RNA interference. Moreover, Metformin treatment enables HPV-positive cancer cells to escape from chemotherapy-induced senescence. These findings uncover profound effects of Metformin on the virus/host cell interactions and the phenotype of HPV-positive cancer cells with implications for therapy-induced senescence, for attempts to repurpose Metformin as an anticancer agent and for the development of E6/E7-inhibitory therapeutic strategies.

Effects of the antifungal agent ciclopirox in HPV-positive cancer cells: Repression of viral E6/E7 oncogene expression and induction of senescence and apoptosis.

The malignant growth of human papillomavirus (HPV)-positive cancer cells is dependent on the continuous expression of the viral E6/E7 oncogenes. Here, we examined the effects of iron deprivation on the phenotype of HPV-positive cervical cancer cells. We found that iron chelators, such as the topical antifungal agent ciclopirox (CPX), strongly repress HPV E6/E7 oncogene expression, both at the transcript and protein level. CPX efficiently blocks the proliferation of HPV-positive cancer cells by inducing cellular senescence. Although active mTOR signaling is considered to be critical for the cellular senescence response towards a variety of prosenescent agents, CPX-induced senescence occurs under conditions of severely impaired mTOR signaling. Prolonged CPX treatment leads to p53-independent Caspase-3/7 activation and induction of apoptosis. CPX also eliminates HPV-positive cancer cells under hypoxic conditions through induction of apoptosis. Taken together, these results show that iron deprivation exerts profound antiviral and antiproliferative effects in HPV-positive cancer cells and suggest that iron chelators, such as CPX, possess therapeutic potential as HPV-inhibitory, prosenescent and proapoptotic agents in both normoxic and hypoxic environments.

The HPV E6/E7 Oncogenes: Key Factors for Viral Carcinogenesis and Therapeutic Targets.

Human papillomavirus (HPV)-induced cancers are expected to remain a major health problem worldwide for decades. The growth of HPV-positive cancer cells depends on the sustained expression of the viral E6 and E7 oncogenes which act in concert with still poorly defined cellular alterations. E6/E7 constitute attractive therapeutic targets since E6/E7 inhibition rapidly induces senescence in HPV-positive cancer cells. This cellular response is linked to the reconstitution of the antiproliferative p53 and pRb pathways, and to prosenescent mTOR signaling. Hypoxic HPV-positive cancer cells could be a major obstacle for treatment strategies targeting E6/E7 since they downregulate E6/E7 but evade senescence through hypoxia-induced mTOR impairment. Prospective E6/E7 inhibitors may therefore benefit from a combination with treatment strategies directed against hypoxic tumor cells.