Topoisomerase I poisons-induced autophagy: Cytoprotective, Cytotoxic or Non-protective

Preliminary Insights into the Cyto/Genoprotective Properties of Propolis and Its Constituent Galangin In Vitro

Propolis has been well known for centuries as a natural preventive and therapeutic agent. Its numerous health benefits are mainly attributed to its high content of phenolic compounds that have a remarkable antioxidant activity. Since phenolics may exert a dual nature (pro-oxidant and antioxidant) the aim of this study was to investigate the safety profile of the ethanolic extract of propolis and the related flavonoid galangin and their ability to protect lymphocytes from irinotecan-induced cyto/genotoxicity in vitro. Isolated human peripheral blood lymphocytes were exposed for 3 h to three concentrations of propolis extract and galangin corresponding to the average daily dose of 0.25 mL of extract [propolis in 70% ethanol (3:7, w/w)], as well as a five- and ten-fold higher concentration. Cyto- and genoprotective effects were tested using a cytokinesis-block micronucleus cytome assay. Treatment with propolis and galangin in the selected concentrations exerted high biocompatibility with lymphocytes and diminished the level of cytogenetic damage caused by irinotecan. Propolis at the same concentration offered a stronger protective effect than single galangin. Also, apoptosis was the prevailing mechanism of cell death in our experimental conditions. These preliminary results speak in favour of future investigations of propolis using other available cytogenetic methods and cell models.

Proteasome Inhibition Enhances Lysosome-mediated Targeted Protein Degradation

Proteasome inhibitor drugs are currently used in the clinic to treat multiple myeloma and mantle cell lymphoma. These inhibitors cause accumulation of undegraded proteins, thus inducing proteotoxic stress and consequent cell death. However, cancer cells counteract this effect by activating an adaptive response through the transcription factor Nuclear factor erythroid 2-related factor 1 (NRF1, also known as NFE2L1). NRF1 induces transcriptional upregulation of proteasome and autophagy/lysosomal genes, thereby reducing proteotoxic stress and diminishing the effectiveness of proteasome inhibition. While suppressing this protective autophagy response is one potential strategy, here we investigated whether this heightened autophagy could instead be leveraged therapeutically. To this end, we designed an autophagy-targeting chimera (AUTAC) compound to selectively degrade the anti-apoptotic protein Mcl1 via the lysosome. Our results show that this lysosome-mediated targeted degradation is significantly amplified in the presence of proteasome inhibition, in a NRF1-dependent manner. The combination of the proteasome inhibitor carfilzomib and Mcl1 AUTAC synergistically promoted cell death in both wild-type and proteasome inhibitor-resistant multiple myeloma and lung cancer cells. Thus, our work offers a novel strategy for enhancing proteasome inhibitor efficacy by exploiting the adaptive autophagy response. More broadly, our study establishes a framework for amplifying lysosome-mediated targeted protein degradation, with potential applications in cancer therapeutics and beyond.

Evidence for cytoprotective autophagy in response to HER2-targeted monoclonal antibodies

The advent of HER2-targeted monoclonal antibodies such as trastuzumab has significantly improved the clinical outcomes for patients with breast cancer overexpressing HER2 and, more recently, also for gastric cancers. However, the development of resistance, as is frequently the case for other antineoplastic modalities, constrains their clinical efficacy. Multiple molecular mechanisms and signaling pathways have been investigated for their potential involvement in the development of resistance to HER2-targeted therapies, among which is autophagy. Autophagy is an inherent cellular mechanism whereby cytoplasmic components are selectively degraded to maintain cellular homeostasis via the generation of energy and metabolic intermediates. Although the cytoprotective form of autophagy is thought to predominate, other forms of autophagy have also been identified in response to chemotherapeutic agents in various tumor models; these include cytotoxic, cytostatic, and nonprotective functional forms of autophagy. In this review, we provide an overview of the autophagic machinery induced in response to HER2-targeted monoclonal antibodies, with a focus on trastuzumab and trastuzumab-emtansine, in an effort to determine whether autophagy targeting or modulation could be translated clinically to increase their effectiveness and/or overcome the development of resistance. SIGNIFICANCE STATEMENT: This manuscript is one in a series of papers that interrogate the role(s) of the autophagy induced in response to antineoplastic agents in various cancer models. This series of papers was developed in an effort to establish whether autophagy targeting or modulation is likely to be an effective adjuvant strategy to increase the efficacy of cancer chemotherapeutic agents. This review explores the relationship between the autophagic machinery and HER2-targeted therapies.

Rationally designed catalytic nanoplatform for enhanced chemoimmunotherapy via deploying endogenous plus exogenous copper and remodeling tumor microenvironment

Chemodynamic therapy represents a novel tumor therapeutic modality via triggering catalytic reactions in tumors to yield highly toxic reactive oxygen species (ROS). Nevertheless, low efficiency catalytic ability, potential systemic toxicity and inefficient tumor targeting, have hindered the efficacy of chemodynamic therapy. Herein, a rationally designed catalytic nanoplatform, composed of folate acid conjugated liposomes loaded with copper peroxide (CP) and chloroquine (CQ; a clinical drug) (denoted as CC@LPF), could power maximal tumor cytotoxicity, mechanistically via maneuvering endogenous and exogenous copper for a highly efficient catalytic reaction. Despite a massive autophagosome accumulation elicited by CP-powered autophagic initiation and CQ-induced autolysosomal blockage, the robust ROS, but not aberrant autophagy, underlies the synergistic tumor inhibition. Otherwise, this combined mode also elicits an early onset, above all, long-term high-level existence of immunogenic cell death markers, associated with ROS and aberrant autophagy -triggered endoplasmic reticulum stress. Besides, CC@LPF, with tumor targeting capability and selective tumor cytotoxicity, could elicit intratumor dendritic cells (mainly attributed to CQ) and tumor infiltrating CD8+ T cells, upon combining with PD-L1 therapeutic antibody, further induce significant anti-tumor effect. Collectively, the rationally designed nanoplatform, CC@LPF, could enhance tumor chemoimmunotherapy via deploying endogenous plus exogenous copper and remodeling tumor microenvironment.

Is Autophagy Targeting a Valid Adjuvant Strategy in Conjunction with Tyrosine Kinase Inhibitors?

Tyrosine kinase inhibitors (TKIs) represent a relatively large class of small-molecule inhibitors that compete with ATP for the catalytic binding site of tyrosine kinase proteins. While TKIs have demonstrated effectiveness in the treatment of multiple malignancies, including chronic myelogenous leukemia, gastrointestinal tumors, non-small cell lung cancers, and HER2-overexpressing breast cancers, as is almost always the case with anti-neoplastic agents, the development of resistance often imposes a limit on drug efficacy. One common survival response utilized by tumor cells to ensure their survival in response to different stressors, including anti-neoplastic drugs, is that of autophagy. The autophagic machinery in response to TKIs in multiple tumor models has largely been shown to be cytoprotective in nature, although there are a number of cases where autophagy has demonstrated a cytotoxic function. In this review, we provide an overview of the literature examining the role that autophagy plays in response to TKIs in different preclinical tumor model systems in an effort to determine whether autophagy suppression or modulation could be an effective adjuvant strategy to increase efficiency and/or overcome resistance to TKIs.

Selagibenzophenone B and Its Derivatives: , a Dual Topoisomerase I/II Inhibitor Identified through In Vitro and In Silico Analyses

The development of multitargeted drugs represents an innovative approach to cancer treatment, aiming to enhance drug effectiveness while minimizing side effects. Herein, we sought to elucidate the inhibitory effect of selagibenzophenone B derivatives on the survival of cancer cells and dual topoisomerase I/II enzyme activity. Results demonstrated that among the compounds, SelB-1 selectively inhibited the proliferation and migration of prostate cancer cells while exhibiting minimal effects on healthy cells. Furthermore, SelB-1 showed a dual inhibitory effect on topoisomerases. Computational analyses mirrored the results from enzyme inhibition assays, demonstrating the compound's strong binding affinity to the catalytic sites of the topoisomerases. To our surprise, SelB-1 did not induce apoptosis in prostate cancer cells; instead, it induced autophagic gene expression and lipid peroxidation while reducing GSH levels, which might be associated with ferroptotic death mechanisms. To summarize, the findings suggest that SelB-1 possesses the potential to serve as a dual topoisomerase inhibitor and can be further developed as a promising candidate for prostate cancer treatment.

A Conversation with ChatGPT on Contentious Issues in Senescence and Cancer Research

Artificial intelligence (AI) platforms, such as Generative Pretrained Transformer (ChatGPT), have achieved a high degree of popularity within the scientific community due to their utility in providing evidence-based reviews of the literature. However, the accuracy and reliability of the information output and the ability to provide critical analysis of the literature, especially with respect to highly controversial issues, has generally not been evaluated. In this work, we arranged a question/answer session with ChatGPT regarding several unresolved questions in the field of cancer research relating to therapy-induced senescence (TIS), including the topics of senescence reversibility, its connection to tumor dormancy, and the pharmacology of the newly emerging drug class of senolytics. ChatGPT generally provided responses consistent with the available literature, although occasionally overlooking essential components of the current understanding of the role of TIS in cancer biology and treatment. Although ChatGPT, and similar AI platforms, have utility in providing an accurate evidence-based review of the literature, their outputs should still be considered carefully, especially with respect to unresolved issues in tumor biology. SIGNIFICANCE STATEMENT: Artificial Intelligence platforms have provided great utility for researchers to investigate biomedical literature in a prompt manner. However, several issues arise when it comes to certain unresolved biological questions, especially in the cancer field. This work provided a discussion with ChatGPT regarding some of the yet-to-be-fully-elucidated conundrums of the role of therapy-induced senescence in cancer treatment and highlights the strengths and weaknesses in utilizing such platforms for analyzing the scientific literature on this topic.

Autophagy and senescence facilitate the development of antiestrogen resistance in ER positive breast cancer

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer diagnosed annually in the US with endocrine-based therapy as standard-of-care for this breast cancer subtype. Endocrine therapy includes treatment with antiestrogens, such as selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). Despite the appreciable remission achievable with these treatments, a substantial cohort of women will experience primary tumor recurrence, subsequent metastasis, and eventual death due to their disease. In these cases, the breast cancer cells have become resistant to endocrine therapy, with endocrine resistance identified as the major obstacle to the medical oncologist and patient. To combat the development of endocrine resistance, the treatment options for ER+, HER2 negative breast cancer now include CDK4/6 inhibitors used as adjuvants to antiestrogen treatment. In addition to the dysregulated activity of CDK4/6, a plethora of genetic and biochemical mechanisms have been identified that contribute to endocrine resistance. These mechanisms, which have been identified by lab-based studies utilizing appropriate cell and animal models of breast cancer, and by clinical studies in which gene expression profiles identify candidate endocrine resistance genes, are the subject of this review. In addition, we will discuss molecular targeting strategies now utilized in conjunction with endocrine therapy to combat the development of resistance or target resistant breast cancer cells. Of approaches currently being explored to improve endocrine treatment efficacy and patient outcome, two adaptive cell survival mechanisms, autophagy, and "reversible" senescence, are considered molecular targets. Autophagy and/or senescence induction have been identified in response to most antiestrogen treatments currently being used for the treatment of ER+ breast cancer and are often induced in response to CDK4/6 inhibitors. Unfortunately, effective strategies to target these cell survival pathways have not yet been successfully developed. Thus, there is an urgent need for the continued interrogation of autophagy and "reversible" senescence in clinically relevant breast cancer models with the long-term goal of identifying new molecular targets for improved treatment of ER+ breast cancer.

Making the Case for Autophagy Inhibition as a Therapeutic Strategy in Combination with Androgen-Targeted Therapies in Prostate Cancer

Androgen receptor targeting remains the primary therapeutic strategy in prostate cancer, encompassing androgen biosynthesis inhibitors and androgen receptor antagonists. While both androgen-receptor-positive and "castration-resistant" prostate cancer are responsive to these approaches, the development of resistance is an almost inevitable outcome leading to the castration-resistant form of the disease. Given that "cytoprotective" autophagy is considered to be a predominant mechanism of resistance to various chemotherapeutic agents as well as to radiation in the cancer literature, the purpose of this review is to evaluate whether autophagy plays a central role in limiting the utility of androgen deprivation therapies in prostate cancer. Unlike most of our previous reports, where multiple functional forms of autophagy were identified, making it difficult if not impossible to propose autophagy inhibition as a therapeutic strategy, the cytoprotective form of autophagy appears to predominate in the case of androgen deprivation therapies. This opens a potential pathway for improving the outcomes for prostate cancer patients once effective and reliable pharmacological autophagy inhibitors have been developed.

Cytoprotective, Cytotoxic and Cytostatic Roles of Autophagy in Response to BET Inhibitors

The bromodomain and extra-terminal domain (BET) family inhibitors are small molecules that target the dysregulated epigenetic readers, BRD2, BRD3, BRD4 and BRDT, at various transcription-related sites, including super-enhancers. BET inhibitors are currently under investigation both in pre-clinical cell culture and tumor-bearing animal models, as well as in clinical trials. However, as is the case with other chemotherapeutic modalities, the development of resistance is likely to constrain the therapeutic benefits of this strategy. One tumor cell survival mechanism that has been studied for decades is autophagy. Although four different functions of autophagy have been identified in the literature (cytoprotective, cytotoxic, cytostatic and non-protective), primarily the cytoprotective and cytotoxic forms appear to function in different experimental models exposed to BET inhibitors (with some evidence for the cytostatic form). This review provides an overview of the cytoprotective, cytotoxic and cytostatic functions of autophagy in response to BET inhibitors in various tumor models. Our aim is to determine whether autophagy targeting or modulation could represent an effective therapeutic strategy to enhance the response to these modalities and also potentially overcome resistance to BET inhibition.

Is Autophagy Inhibition in Combination with Temozolomide a Therapeutically Viable Strategy?

Temozolomide is an oral alkylating agent that is used as the first line treatment for glioblastoma multiform, and in recurrent anaplastic astrocytoma, as well as having demonstrable activity in patients with metastatic melanoma. However, as the case with other chemotherapeutic agents, the development of resistance often limits the therapeutic benefit of temozolomide, particularly in the case of glioblastoma. A number of resistance mechanisms have been proposed including the development of cytoprotective autophagy. Cytoprotective autophagy is a survival mechanism that confers upon tumor cells the ability to survive in a nutrient deficient environment as well as under external stresses, such as cancer chemotherapeutic drugs and radiation, in part through the suppression of apoptotic cell death. In this review/commentary, we explore the available literature and provide an overview of the evidence for the promotion of protective autophagy in response to temozolomide, highlighting the possibility of targeting autophagy as an adjuvant therapy to potentially increase the effectiveness of temozolomide and to overcome the development of resistance.