A phase II trial evaluating the efficacy and safety of efavirenz in metastatic castration-resistant prostate cancer

State-of-the-art in transposable element modulation affected by drugs in malignant prostatic cancer cells

Over recent years, the investigation of transposable elements (TEs) has granted researchers a deeper comprehension of their characteristics and functions, particularly regarding their significance in the mechanisms contributing to cancer development. This manuscript focuses on prostate carcinoma cell lines and offers a comprehensive review intended to scrutinize the associations and interactions between TEs and genes, as well as their response to treatment using various chemical drugs, emphasizing their involvement in cancer progression. We assembled a compendium of articles retrieved from the PubMed database to construct networks demonstrating correlations with genes and pharmaceuticals. In doing so, we linked the transposition of certain TE types to the expression of specific transcripts directly implicated in carcinogenesis. Additionally, we underline that treatment employing different drugs revealed unique patterns of TE reactivation. Our hypothesis gathers the current understanding and guides research toward evidence-based investigations, emphasizing the association between antiviral drugs, chemotherapy, and the reduced expression of TEs in patients affected by prostate cancer.

Drugs Targeting p53 Mutations with FDA Approval and in Clinical Trials

Mutations in the tumor suppressor p53 (p53) promote cancer progression. This is mainly due to loss of function (LOS) as a tumor suppressor, dominant-negative (DN) activities of missense mutant p53 (mutp53) over wild-type p53 (wtp53), and wtp53-independent oncogenic activities of missense mutp53 by interacting with other tumor suppressors or oncogenes (gain of function: GOF). Since p53 mutations occur in ~50% of human cancers and rarely occur in normal tissues, p53 mutations are cancer-specific and ideal therapeutic targets. Approaches to target p53 mutations include (1) restoration or stabilization of wtp53 conformation from missense mutp53, (2) rescue of p53 nonsense mutations, (3) depletion or degradation of mutp53 proteins, and (4) induction of p53 synthetic lethality or targeting of vulnerabilities imposed by p53 mutations (enhanced YAP/TAZ activities) or deletions (hyperactivated retrotransposons). This review article focuses on clinically available FDA-approved drugs and drugs in clinical trials that target p53 mutations and summarizes their mechanisms of action and activities to suppress cancer progression.

Efavirenz: History, Development and Future

Efavirenz (Sustiva^®) is a first-generation non-nucleoside reverse transcriptase inhibitor (NNRTI) used to treat human immunodeficiency virus (HIV) type 1 infection or to prevent the spread of HIV. In 1998, the FDA authorized efavirenz for the treatment of HIV-1 infection. Patients formerly required three 200 mg efavirenz capsules daily, which was rapidly updated to a 600 mg tablet that only required one tablet per day. However, when given 600 mg once daily, plasma efavirenz concentrations were linked not only to poor HIV suppression but also to toxicity. Clinical data suggested that the standard dose of efavirenz could be reduced without compromising its effectiveness, resulting in a reduction in side effects and making the drug more affordable. Therefore, ENCORE1 was performed to compare the efficiency and safeness of a reduced dose of efavirenz (400 mg) with the standard dose (600 mg) plus two NRTI in antiretroviral-naïve HIV-infected individuals. Nowadays, due to the emergence of integrase strand transfer inhibitors (INSTIs), some consider that it is time to stop using efavirenz as a first-line treatment on a global scale, in the parts of the world where that is possible. Efavirenz has been a primary first-line antiviral drug for more than 15 years. However, at this moment, the best use for efavirenz could be for pre-exposure prophylaxis (PrEP) and repurposing in medicine.

An Epigenetic LINE-1-Based Mechanism in Cancer

In the last fifty years, large efforts have been deployed in basic research, clinical oncology, and clinical trials, yielding an enormous amount of information regarding the molecular mechanisms of cancer and the design of effective therapies. The knowledge that has accumulated underpins the complexity, multifactoriality, and heterogeneity of cancer, disclosing novel landscapes in cancer biology with a key role of genome plasticity. Here, we propose that cancer onset and progression are determined by a stress-responsive epigenetic mechanism, resulting from the convergence of upregulation of LINE-1 (long interspersed nuclear element 1), the largest family of human retrotransposons, genome damage, nuclear lamina fragmentation, chromatin remodeling, genome reprogramming, and autophagy activation. The upregulated expression of LINE-1 retrotransposons and their protein products plays a key role in these processes, yielding an increased plasticity of the nuclear architecture with the ensuing reprogramming of global gene expression, including the reactivation of embryonic transcription profiles. Cancer phenotypes would thus emerge as a consequence of the unscheduled reactivation of embryonic gene expression patterns in an inappropriate context, triggering de-differentiation and aberrant proliferation in differentiated cells. Depending on the intensity of the stressing stimuli and the level of LINE-1 response, diverse degrees of malignity would be generated.

Combination of Antiretroviral Drugs Zidovudine and Efavirenz Impairs Tumor Growths in a Mouse Model of Cancer

LINE1 retrotransposons, which are thought to be the remnants of ancient integrations of retrovirus-like elements, are aberrantly (re)activated in many cancer cells. Due to LINE1-induced alterations in target gene expression and/or chromosomal rearrangements, they may be important drivers of tumorigenesis. Moreover, LINE1 encoded proteins, Open Reading Frame (ORF)1 and ORF2, may have pro-oncogenic potential through inductors of oncogenic transcription factors or inhibitors of cell cycle suppressors. The current study therefore aimed to investigate in vitro and in vivo anti-tumorigenic effects of two well-known antiretroviral drugs, zidovudine, a nucleoside analogue inhibitor of RT (NRTI), and efavirenz, a non-nucleoside RT inhibitor (NNRTI). Our data demonstrate that both drugs in clinically relevant doses significantly reduced the proliferation of murine and human cancer cell lines, as well as growth of tumors in a murine subcutaneous model. Intriguingly, we found that the combination of both zidovudine and efavirenz almost entirely blocked tumorigenesis in vivo. Because both drugs are FDA-approved agents and the combination was very well tolerated in mice, the combination therapy as presented in our paper might be an opportunity to treat colorectal tumors and metastasis to the liver in an inexpensive way.

Paclitaxel-induced stress granules increase LINE-1 mRNA stability to promote drug resistance in breast cancer cells

Abnormal expression of long interspersed element-1 (LINE-1) has been implicated in drug resistance, while our previous study showed that chemotherapy drug paclitaxel (PTX) increased LINE-1 level with unknown mechanism. Bioinformatics analysis suggested the regulation of LINE-1 mRNA by drug-induced stress granules (SGs). This study aimed to explore whether and how SGs are involved in drug-induced LINE-1 increase and thereby promotes drug resistance of triple negative breast cancer (TNBC) cells. We demonstrated that SGs increased LINE-1 expression by recruiting and stabilizing LINE-1 mRNA under drug stress, thereby adapting TNBC cells to chemotherapy drugs. Moreover, LINE-1 inhibitor efavirenz (EFV) could inhibit drug-induced SG to destabilize LINE-1. Our study provides the first evidence of the regulation of LINE-1 by SGs that could be an important survival mechanism for cancer cells exposed to chemotherapy drugs. The findings provide a useful clue for developing new chemotherapeutic strategies against TNBCs.

Repurposing of Antimicrobial Agents for Cancer Therapy: What Do We Know?

The substantial costs of clinical trials, the lengthy timelines of new drug discovery and development, along the high attrition rates underscore the need for alternative strategies for finding quickly suitable therapeutics agents. Given that most approved drugs possess more than one target tightly linked to other diseases, it encourages promptly testing these drugs in patients. Over the past decades, this has led to considerable attention for drug repurposing, which relies on identifying new uses for approved or investigational drugs outside the scope of the original medical indication. The known safety of approved drugs minimizes the possibility of failure for adverse toxicology, making them attractive de-risked compounds for new applications with potentially lower overall development costs and shorter development timelines. This latter case is an exciting opportunity, specifically in oncology, due to increased resistance towards the current therapies. Indeed, a large body of evidence shows that a wealth of non-cancer drugs has beneficial effects against cancer. Interestingly, 335 drugs are currently being evaluated in different clinical trials for their potential activities against various cancers (Redo database). This review aims to provide an extensive discussion about the anti-cancer activities exerted by antimicrobial agents and presents information about their mechanism(s) of action and stage of development/evaluation.

Risk of prostate cancer in men with HIV/AIDS: a systematic review and meta-analysis

BACKGROUND

Although previous studies have shown a decreased incidence of prostate cancer in men with HIV/AIDS, the consensus has not been reached. Our aim is to conduct a systematic review and meta-analysis to assess the risk of prostate cancer among people with HIV/AIDS.

METHODS

We systematically searched PubMed, Web of Science, Embase, and Cochrane Library until March 2020. Cohort studies were included if they compared the prostate cancer risk between people with HIV/AIDS and uninfected controls or the general population. The summary standardized incidence ratio (SIR) and 95% confidence interval (CI) were calculated using a random-effects model.

RESULTS

A total of 27 studies were included for analysis, with more than 2780 males with HIV/AIDS developing prostate cancer. The results showed that HIV infection was associated with a decreased risk of prostate cancer incidence (SIR, 0.76; 95% CI, 0.64-0.91; P = 0.003), with significant heterogeneity (P < 0.001; I² = 91.6%). A range of sensitivity analyzes did not significantly change the results.

CONCLUSIONS

Our study shows that people with HIV/AIDS have a lower incidence of prostate cancer compared with the general population. However, significant heterogeneity exists among the included studies. Further prospective studies with better designs are needed to elucidate the association between HIV infection and prostate cancer.

New Understanding of the Relevant Role of LINE-1 Retrotransposition in Human Disease and Immune Modulation

Long interspersed nuclear element-1 (LINE-1) retrotransposition is a major hallmark of cancer accompanied by global chromosomal instability, genomic instability, and genetic heterogeneity and has become one indicator for the occurrence, development, and poor prognosis of many diseases. LINE-1 also modulates the immune system and affects the immune microenvironment in a variety of ways. Aberrant expression of LINE-1 retrotransposon can provide strong stimuli for an innate immune response, activate the immune system, and induce autoimmunity and inflammation. Therefore, inhibition the activity of LINE-1 has become a potential treatment strategy for various diseases. In this review, we discussed the components and regulatory mechanisms involved with LINE-1, its correlations with disease and immunity, and multiple inhibitors of LINE-1, providing a new understanding of LINE-1.

The Impact of Matrix Metalloproteinase-9 on the Sequential Steps of the Metastatic Process

In industrialized countries, cancer is the second leading cause of death after cardiovascular disease. Most cancer patients die because of metastases, which consist of the self-transplantation of malignant cells in anatomical sites other than the one from where the tumor arose. Disseminated cancer cells retain the phenotypic features of the primary tumor, and display very poor differentiation indices and functional regulation. Upon arrival at the target organ, they replace preexisting, normal cells, thereby permanently compromising the patient's health; the metastasis can, in turn, metastasize. The spread of cancer cells implies the degradation of the extracellular matrix by a variety of enzymes, among which the matrix metalloproteinase (MMP)-9 is particularly effective. This article reviews the available published literature concerning the important role that MMP-9 has in the metastatic process. Additionally, information is provided on therapeutic approaches aimed at counteracting, or even preventing, the development of metastasis via the use of MMP-9 antagonists.

Efavirenz as a potential drug for the treatment of triple-negative breast cancers

PURPOSE

In contrast to hormone receptor driven breast cancer, patients presenting with triple-negative breast cancer (TNBC) often have limited drug treatment options. Efavirenz, a non-nucleoside reverse transcriptase (RT) inhibitor targets abnormally overexpressed long interspersed nuclear element 1 (LINE-1) RT and has been shown to be a promising anticancer agent for treating prostate and pancreatic cancers. However, its effectiveness in treating patients with TNBC has not been comprehensively examined.

METHODS

In this study, the effect of Efavirenz on several TNBC cell lines was investigated by examining several cellular characteristics including viability, cell division and death, changes in cell morphology as well as the expression of LINE-1.

RESULTS

The results show that in a range of TNBC cell lines, Efavirenz causes cell death, retards cell proliferation and changes cell morphology to an epithelial-like phenotype. In addition, it is the first time that a whole-genome RNA sequence analysis has identified the fatty acid metabolism pathway as a key regulator in this Efavirenz-induced anticancer process.

CONCLUSION

In summary, we propose Efavirenz is a potential anti-TNBC drug and that its mode of action can be linked to the fatty acid metabolism pathway.

The Anti-Angiogenic Effects of Anti-Human Immunodeficiency Virus Drugs

The growth and metastasis of malignant tumors benefit from the formation of blood vessels within the tumor area. There, new vessels originate from angiogenesis (the sprouting of pre-existing neighboring vessels) and/or vasculogenesis (the mobilization of bone marrow-derived endothelial cell precursors which incorporate in tumor vasculature and then differentiate into mature endothelial cells). These events are induced by soluble molecules (the angiogenic factors) and modulated by endothelial cell interactions with the perivascular matrix. Given angiogenesis/vasculogenesis relevance to tumor progression, anti-angiogenic drugs are often employed to buttress surgery, chemotherapy or radiation therapy in the treatment of a wide variety of cancers. Most of the anti-angiogenic drugs have been developed to functionally impair the angiogenic vascular endothelial growth factor: however, this leaves other angiogenic factors unaffected, hence leading to drug resistance and escape. Other anti-angiogenic strategies have exploited classical inhibitors of enzymes remodeling the perivascular matrix. Disappointingly, these inhibitors have been found toxic and/or ineffective in clinical trials, even though they block angiogenesis in pre-clinical models. These findings are stimulating the identification of other anti-angiogenic compounds. In this regard, it is noteworthy that drugs utilized for a long time to counteract human immune deficiency virus (HIV) can directly and effectively hamper molecular pathways leading to blood vessel formation. In this review the mechanisms leading to angiogenesis and vasculogenesis, and their susceptibility to anti-HIV drugs will be discussed.

HIV-1, HAART and cancer: A complex relationship

HIV infected people are at higher risk of developing cancer, although it is globally diminished in the era of highly active antiretroviral treatment (HAART). Recently, antioncogenic properties of some HAART drugs were discovered. We discuss the role of HAART in the prevention and improvement of treatment outcomes of cancers in HIV-infected people. We describe different trends in HAART-cancer relationships: cancer-predisposing as well as cancer-preventing. We cover the roles of particular drug regimens in cancer prevention. We also describe the causes of cancer treatment with HAART drugs in HIV-negative people, including ongoing clinical studies that may directly point to a possible independent anti-oncogenic activity of HAART drugs. We conclude that despite potent antioncogenic activities of every class of HAART drugs reported in preclinical models, the evidence to date indicates that their independent clinical impact in HIV-infected people is limited. Improved cancer prevention strategies besides HAART are needed to reduce HIV-cancer-related mortality.

Drug rechanneling: A novel paradigm for cancer treatment

Cancer continues to be one of the leading contributors towards global disease burden. According to NIH, cancer incidence rate per year will increase to 23.6 million by 2030. Even though cancer continues to be a major proportion of the disease burden worldwide, it has the lowest clinical trial success rate amongst other diseases. Hence, there is an unmet need for novel, affordable and effective anti-neoplastic medications. As a result, a growing interest has sparkled amongst researchers towards drug repurposing. Drug repurposing follows the principle of polypharmacology, which states, "any drug with multiple targets or off targets can present several modes of action". Drug repurposing also known as drug rechanneling, or drug repositioning is an economic and reliable approach that identifies new disease treatment of already approved drugs. Repurposing guarantees expedited access of drugs to the patients as these drugs are already FDA approved and their safety and toxicity profile is completely established. Epidemiological studies have identified the decreased occurrence of oncological or non-oncological conditions in patients undergoing treatment with FDA approved drugs. Data from multiple experimental studies and clinical observations have depicted that several non-neoplastic drugs have potential anticancer activity. In this review, we have summarized the potential anti-cancer effects of anti-psychotic, anti-malarial, anti-viral and anti-emetic drugs with a brief overview on their mechanism and pathways in different cancer types. This review highlights promising evidences for the repurposing of drugs in oncology.

Reverse transcriptase inhibitors promote the remodelling of nuclear architecture and induce autophagy in prostate cancer cells

Emerging data indicate that the reverse transcriptase (RT) protein encoded by LINE-1 transposable elements is a promising cancer target. Nonnucleoside RT inhibitors, e.g. efavirenz (EFV) and SPV122.2, reduce proliferation and promote differentiation of cancer cells, concomitant with a global reprogramming of the transcription profile. Both inhibitors have therapeutic anticancer efficacy in animal models. Here we have sought to clarify the mechanisms of RT inhibitors in cancer cells. We report that exposure of PC3 metastatic prostate carcinoma cells to both RT inhibitors results in decreased proliferation, and concomitantly induces genome damage. This is associated with rearrangements of the nuclear architecture, particularly at peripheral chromatin, disruption of the nuclear lamina, and budding of micronuclei. These changes are reversible upon discontinuation of the RT-inhibitory treatment, with reconsititution of the lamina and resumption of the cancer cell original features. The use of pharmacological autophagy inhibitors proves that autophagy is largely responsible for the antiproliferative effect of RT inhibitors. These alterations are not induced in non-cancer cell lines exposed to RT inhibitors. These data provide novel insight in the molecular pathways targeted by RT inhibitors in cancer cells.

Therapeutic implications of altered cholesterol homeostasis mediated by loss of CYP46A1 in human glioblastoma

Dysregulated cholesterol metabolism is a hallmark of many cancers, including glioblastoma (GBM), but its role in disease progression is not well understood. Here, we identified cholesterol 24-hydroxylase (CYP46A1), a brain-specific enzyme responsible for the elimination of cholesterol through the conversion of cholesterol into 24(S)-hydroxycholesterol (24OHC), as one of the most dramatically dysregulated cholesterol metabolism genes in GBM. CYP46A1 was significantly decreased in GBM samples compared with normal brain tissue. A reduction in CYP46A1 expression was associated with increasing tumour grade and poor prognosis in human gliomas. Ectopic expression of CYP46A1 suppressed cell proliferation and in vivo tumour growth by increasing 24OHC levels. RNA-seq revealed that treatment of GBM cells with 24OHC suppressed tumour growth through regulation of LXR and SREBP signalling. Efavirenz, an activator of CYP46A1 that is known to penetrate the blood-brain barrier, inhibited GBM growth in vivo. Our findings demonstrate that CYP46A1 is a critical regulator of cellular cholesterol in GBM and that the CYP46A1/24OHC axis is a potential therapeutic target.

Thapsigargin induces apoptosis of prostate cancer through cofilin-1 and paxillin

It is widely considered that endoplasmic reticulum stress may rapidly induce apoptosis. The aim of the present study was to investigate the effect of thapsigargin on the induction of apoptosis in prostate cancer cells, and to explore its possible mechanism. A Cell Counting Kit-8 was selected to determine the effect of thapsigargin (0, 1, 10 and 100 nM) on the proliferation of PC3 cells. Cell proliferation of the prostate cancer cells was effectively inhibited by treatment with thapsigargin, and thapsigargin significantly increased the rate of apoptosis and caspase-3/9 activities in prostate cancer cells. The protein expression of phosphorylated (p)-RAC-α serine threonine-protein kinase, p-mechanistic target of rapamycin, F-actin and paxillin were significantly decreased, and cofilin-1 protein expression was significantly increased by treatment with thapsigargin in prostate cancer cells. Overall, the data of the present study revealed that thapsigargin induced apoptosis in prostate cancer cells through cofilin-1 and paxillin.

Antitumor effect of combination of the inhibitors of two new oncotargets: proton pumps and reverse transcriptase

Tumor therapy needs new approaches in order to improve efficacy and reduce toxicity of the current treatments. The acidic microenvironment and the expression of high levels of endogenous non-telomerase reverse transcriptase (RT) are common features of malignant tumor cells. The anti-acidic proton pump inhibitor Lansoprazole (LAN) and the non-nucleoside RT inhibitor Efavirenz (EFV) have shown independent antitumor efficacy. LAN has shown to counteract drug tumor resistance. We tested the hypothesis that combination of LAN and EFV may improve the overall antitumor effects. We thus pretreated human metastatic melanoma cells with LAN and then with EFV, both in 2D and 3D spheroid models. We evaluated the treatment effect by proliferation and cell death/apoptosis assays in classical and in pulse administration experiments. The action of EFV was negatively affected by the tumor microenvironmental acidity, and LAN pretreatment overcame the problem. LAN potentiated the cytotoxicity of EFV to melanoma cells and, when administered during the drug interruption period, prevented the replacement of tumor cell growth.

This study supports the implementation of the current therapies with combination of Proton Pumps and Reverse Transcriptase inhibitors.

Cytotoxic effect of Efavirenz in BxPC-3 pancreatic cancer cells is based on oxidative stress and is synergistic with ionizing radiation

The non-nucleoside reverse transcriptase inhibitor (NNRTI) Efavirenz is frequently used in human immunodeficiency virus treatment, but also efficient against cancer in mouse models. Its radiosensitizing effect makes it a promising drug for combination with radiotherapy. The efficacy of Efavirenz combined with irradiation was assessed with immunostaining of DNA-damage markers and colony formation assays in BxPC-3 pancreatic cancer cells. Gene expression and protein phosphorylation of the Efavirenz-sensitive BxPC-3 cells was compared to the resistant primary fibroblasts SBL-5. Oxidative stress, mitochondrial damage and cell death were studied with live-cell microscopy and flow cytometry. Combined Efavirenz and radiation significantly increased the number of γH2AX and phospho-ataxia telangiectasia mutated foci. Efavirenz and ionizing radiation had a synergistic effect using the clonogenic survival assay. Efavirenz selectively induced cell death in the BxPC-3 cells. The differing gene expression of cell cycle and apoptotic regulator genes in both cell cultures after Efavirenz treatment match with this selective effect against cancer cells. In the phosphoprotein array, an early phosphorylation of extracellular signal-related kinase 1/2 and p38 mitogen-activated protein kinase was notably detected in the cancer cells. The phosphorylation of AKT decreased in the cancer cells whereas it increased in the fibroblasts. Oxidative stress and mitochondrial membrane depolarization appeared in the cancer cells immediately after Efavirenz treatment, but not in the fibroblasts. Efavirenz has an anti-cancer effect against pancreatic cancer mainly by the induction of oxidative stress. The antitumor potential of Efavirenz and radiotherapy are additive.

Different Cell Cycle Modulation in SKOV-3 Ovarian Cancer Cell Line by Anti-HIV Drugs

Antiretroviral drugs used for the treatment of human immunodeficiency virus (HIV) have proven to be effective even against cancer. Drawing from this background, the aim of our research project was to evaluate the effects of anti-HIV drugs that belong to the nucleoside and nucleotide reverse transcriptase inhibitor [NRTI; abacavir (ABC) and tenofovir (TDF)], nonnucleoside reverse transcriptase inhibitor [NNRTI; efavirenz (EFV) and etravirine (ETR)], and protease inhibitor [PI; darunavir (DRV)] categories on ovarian adenocarcinoma cell line SKOV-3. Using FACS analysis, we observed that treatment with NRTIs and NNRTIs showed a block in the G₀/G₁ phase. In particular, ETR displayed a relevant block in the progression of the G₀/G₁ phase of the cell cycle compared with the other examined drugs, and it also induced differentiation of SKOV-3 cells. In contrast, FACS analysis demonstrated that ABC and the PI inhibitor DRV showed no effect on the proliferation of cancer cells. DAPI (4′,6-diamidino-2-phenylindole) staining demonstrated that cells treated with NNRTIs (EFV and ETR) presented more DNA damage compared with other treatments. Immunoblotting analysis demonstrated that TDF, EFV, and ETR were able to obtain a reduction in the expression of cyclin D1 and Rb hypophosphorylation, and an increase in p21 concentration. Finally, we observed that ETR also induced differentiation, as demonstrated by Western blot, with high levels of E-cadherin expression. Therefore, our study provides additional evidence supporting the in vitro cytotoxic effects of ETR and EFV. Furthermore, it promotes the hypothesis for their potential use as therapeutic agents in ovarian cancer.

Induction of DNA damage and apoptosis in human leukemia cells by efavirenz

As part of the efforts to drug repurposing, some HIV drugs have recently been identified to exert anticancer effects. Selected nucleoside analogues of nucleosidic reverse-transcriptase inhibitors (NRTIs) have been shown to interfere with RNA transcription of HI viruses as well as with the replication of DNA in cancer cells. Non-nucleosidic reverse transcriptase inhibitors (NNRTIs) are believed to have less effects on human DNA replication and, thus, on cancer cell proliferation. Assessment of the effect of the NNRTI efavirenz in human cancer cells, however, revealed a high sensitivity of leukemia cells to this agent at pharmacologically relevant concentrations of less than 10 µg/ml. Cell death induced by efavirenz was caused by apoptosis, as shown by FACScan analysis (Annexin binding) and western blot analysis (cleavage of caspases and PARP). Western blot analyses also revealed a pronounced activation and phosphorylation of the DNA damage marker proteins p53, chk2 and H2AX, indicating DNA replication and genomic integrity as primary targets of efavirenz in leukemia cells.

Enhanced expression of LINE-1-encoded ORF2 protein in early stages of colon and prostate transformation

LINE-1 (L1) retrotransposons are a source of endogenous reverse transcriptase (RT) activity, which is expressed as part of the L1-encoded ORF2 protein (L1-ORF2p). L1 elements are highly expressed in many cancer types, while being silenced in most differentiated somatic tissues. We previously found that RT inhibition reduces cell proliferation and promotes differentiation in neoplastic cells, indicating that high endogenous RT activity promotes cancer growth. Here we investigate the expression of L1-ORF2p in several human types of cancer.

We have developed a highly specific monoclonal antibody (mAb chA1-L1) to study ORF2p expression and localization in human cancer cells and tissues.

We uncover new evidence for high levels of L1-ORF2p in transformed cell lines and staged epithelial cancer tissues (colon, prostate, lung and breast) while no or only basal ORF2p expression was detected in non-transformed cells. An in-depth analysis of colon and prostate tissues shows ORF2p expression in preneoplastic stages, namely transitional mucosa and prostate intraepithelial neoplasia (PIN), respectively.

Our results show that L1-ORF2p is overexpressed in tumor and in preneoplastic colon and prostate tissues; this latter finding suggests that ORF2p could be considered as a potential early diagnostic biomarker.

Activation of LINE-1 Retrotransposon Increases the Risk of Epithelial-Mesenchymal Transition and Metastasis in Epithelial Cancer

Epithelial cancers comprise 80-90% of human cancers. During the process of cancer progression, cells lose their epithelial characteristics and acquire stem-like mesenchymal features that are resistant to chemotherapy. This process, termed the epithelial-mesenchymal transition (EMT), plays a critical role in the development of metastases. Because of the unique migratory and invasive properties of cells undergoing the EMT, therapeutic control of the EMT offers great hope and new opportunities for treating cancer. In recent years, a plethora of genes and noncoding RNAs, including miRNAs, have been linked to the EMT and the acquisition of stem cell-like properties. Despite these advances, questions remain unanswered about the molecular processes underlying such a cellular transition. In this article, we discuss how expression of the normally repressed LINE-1 (or L1) retrotransposons activates the process of EMT and the development of metastases. L1 is rarely expressed in differentiated stem cells or adult somatic tissues. However, its expression is widespread in almost all epithelial cancers and in stem cells in their undifferentiated state, suggesting a link between L1 activity and the proliferative and metastatic behaviour of cancer cells. We present an overview of L1 activity in cancer cells including how genes involved in proliferation, invasive and metastasis are modulated by L1 expression. The role of L1 in the differential expression of the let-7 family of miRNAs (that regulate genes involved in the EMT and metastasis) is also discussed. We also summarize recent novel insights into the role of the L1-encoded reverse transcriptase enzyme in epithelial cell plasticity that suggest it might be a potential therapeutic target that could reverse the EMT and the metastasis-associated stem cell-like properties of cancer cells.

The Reverse Transcriptase Encoded by LINE-1 Retrotransposons in the Genesis, Progression, and Therapy of Cancer

In higher eukaryotic genomes, Long Interspersed Nuclear Element 1 (LINE-1) retrotransposons represent a large family of repeated genomic elements. They transpose using a reverse transcriptase (RT), which they encode as part of the ORF2p product. RT inhibition in cancer cells, either via RNA interference-dependent silencing of active LINE-1 elements, or using RT inhibitory drugs, reduces cancer cell proliferation, promotes their differentiation and antagonizes tumor progression in animal models. Indeed, the non-nucleoside RT inhibitor efavirenz has recently been tested in a phase II clinical trial with metastatic prostate cancer patients. An in-depth analysis of ORF2p in a mouse model of breast cancer showed ORF2p to be precociously expressed in precancerous lesions and highly abundant in advanced cancer stages, while being barely detectable in normal breast tissue, providing a rationale for the finding that RT-expressing tumors are therapeutically sensitive to RT inhibitors. We summarize mechanistic and gene profiling studies indicating that abundant LINE-1-derived RT can “sequester” RNA substrates for reverse transcription in tumor cells, entailing the formation of RNA:DNA hybrid molecules and impairing the overall production of regulatory miRNAs, with a global impact on the cell transcriptome. Based on these data, LINE-1-ORF2 encoded RT has a tumor-promoting potential that is exerted at an epigenetic level. We propose a model whereby LINE1-RT drives a previously unrecognized global regulatory process, the deregulation of which drives cell transformation and tumorigenesis with possible implications for cancer cell heterogeneity.

Efavirenz Has the Highest Anti-Proliferative Effect of Non-Nucleoside Reverse Transcriptase Inhibitors against Pancreatic Cancer Cells

Background

Cancer prevention and therapy in HIV-1-infected patients will play an important role in future. The non-nucleoside reverse transcriptase inhibitors (NNRTI) Efavirenz and Nevirapine are cytotoxic against cancer cells in vitro. As other NNRTIs have not been studied so far, all clinically used NNRTIs were tested and the in vitro toxic concentrations were compared to drug levels in patients to predict possible anti-cancer effects in vivo.

Methods

Cytotoxicity was studied by Annexin-V-APC/7AAD staining and flow cytometry in the pancreatic cancer cell lines BxPC-3 and Panc-1 and confirmed by colony formation assays. The 50% effective cytotoxic concentrations (EC50) were calculated and compared to the blood levels in our patients and published data.

Results

The in vitro EC50 of the different drugs in the BxPC-3 pancreatic cancer cells were: Efavirenz 31.5μmol/l (= 9944ng/ml), Nevirapine 239μmol/l (= 63786ng/ml), Etravirine 89.0μmol/l (= 38740ng/ml), Lersivirine 543μmol/l (= 168523ng/ml), Delavirdine 171μmol/l (= 78072ng/ml), Rilpivirine 24.4μmol/l (= 8941ng/ml). As Efavirenz and Rilpivirine had the highest cytotoxic potential and Nevirapine is frequently used in HIV-1 positive patients, the results of these three drugs were further studied in Panc-1 pancreatic cancer cells and confirmed with colony formation assays. 205 patient blood levels of Efavirenz, 127 of Rilpivirine and 31 of Nevirapine were analyzed. The mean blood level of Efavirenz was 3587ng/ml (range 162–15363ng/ml), of Rilpivirine 144ng/ml (range 0-572ng/ml) and of Nevirapine 4955ng/ml (range 1856–8697ng/ml). Blood levels from our patients and from published data had comparable Efavirenz levels to the in vitro toxic EC50 in about 1 to 5% of all patients.

Conclusion

All studied NNRTIs were toxic against cancer cells. A low percentage of patients taking Efavirenz reached in vitro cytotoxic blood levels. It can be speculated that in HIV-1 positive patients having high Efavirenz blood levels pancreatic cancer incidence might be reduced. Efavirenz might be a new option in the treatment of cancer.

A LINE-1-encoded reverse transcriptase-dependent regulatory mechanism is active in embryogenesis and tumorigenesis

LINE-1 (long interspersed nuclear elements) retrotransposons constitute a large family of retrotransposable elements, accounting for 17% of the human genome. They encode proteins required for their own mobilization, including a reverse transcriptase (RT) enzyme highly expressed in mouse embryos and mouse and human cancer cells and repressed in somatic differentiated healthy cells. We have found that reverse transcription takes place in early murine embryos, yielding an increase in LINE-1 copy number during preimplantation development, which also occurs in tumor progression. RT inhibition irreversibly arrests embryo development, reduces cancer cell proliferation, promotes differentiation, antagonizes tumor growth, and causes a global reprogramming of transcription profiles. These results strongly suggest that a previously unrecognized RT-dependent regulatory mechanism operates during preimplantation development, is repressed during differentiation to normal tissues, and, when erroneously reactivated in adult life, promotes cell transformation and cancer progression by "resurrecting" embryonic transcriptional pathways. The RT-dependent mechanism emerges as a major source of genetic and epigenetic changes with physiological, pathological, and evolutionary implications.