Special Issue: "Drug Repurposing for Cancer Therapies".

Cancer is one of the primary global causes of death, thus addressing cancer therapy remains a significant challenge, especially in cases where cancers exhibit resistance to treatment [...].

The role of extracellular vesicles in the transfer of drug resistance competences to cancer cells.

Drug resistance remains a major hurdle to successful cancer treatment, being accountable for approximately 90% of cancer-related deaths. In the past years, increasing attention has been given to the role of extracellular vesicles (EVs) in the horizontal transfer of drug resistance in cancer. Indeed, many studies have described the dissemination of therapy resistance traits mediated by EVs, which may be transferred from drug resistant tumor cells to their drug sensitive counterparts. Importantly, different key players of drug resistance have been identified in the cargo of those EVs, such as drug efflux pumps, oncoproteins, antiapoptotic proteins, or microRNAs, among others. Interestingly, the EVs-mediated crosstalk between cells from the tumor microenvironment (TME) and tumor cells has emerged as another important mechanism that leads to cancer cells drug resistance. Recently, the cargo of the TME-derived EVs responsible for the transfer of drug resistance traits has also become a focus of attention. In addition, the possible mechanisms involved in drug sequestration by EVs, likely to contribute to cancer drug resistance, are also described and discussed herein. Despite the latest scientific advances in the field of EVs, this is still a challenging area of research, particularly in the clinical setting. Therefore, further investigation is needed to assess the relevance of EVs to the failure of cancer patients to drug treatment, to identify biomarkers of drug resistance in the EV's cargo, and to develop effective therapeutic strategies to surmount drug resistance. This up-to-date review summarizes relevant literature on the role of EVs in the transfer of drug resistance competences to cancer cells, and the relevance of tumor cells and of TME cells in this process. Finally, this knowledge is integrated with a discussion of possible future clinical applications of EVs as biomarkers of drug resistance.

Evaluation of the Cytotoxic and Antiviral Effects of Small Molecules Selected by In Silico Studies as Inhibitors of SARS-CoV-2 Cell Entry.

The spike protein of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) relies on host cell surface glycans to facilitate interaction with the angiotensin-converting enzyme 2 (ACE-2) receptor. This interaction between ACE2 and the spike protein is a gateway for the virus to enter host cells and may be targeted by antiviral drugs to inhibit viral infection. Therefore, targeting the interaction between these two proteins is an interesting strategy to prevent SARS-CoV-2 infection. A library of glycan mimetics and derivatives was selected for a virtual screening performed against both ACE2 and spike proteins. Subsequently, in vitro assays were performed on eleven of the most promising in silico compounds to evaluate: (i) their efficacy in inhibiting cell infection by SARS-CoV-2 (using the Vero CCL-81 cell line as a model), (ii) their impact on ACE2 expression (in the Vero CCL-81 and MDA-MB-231 cell lines), and (iii) their cytotoxicity in a human lung cell line (A549). We identified five synthetic compounds with the potential to block SARS-CoV-2 infection, three of them without relevant toxicity in human lung cells. Xanthene 1 stood out as the most promising anti-SARS-CoV-2 agent, inhibiting viral infection and viral replication in Vero CCL-81 cells, without causing cytotoxicity to human lung cells.

Impact of cancer metabolism on therapy resistance - Clinical implications.

Despite an increasing arsenal of anticancer therapies, many patients continue to have poor outcomes due to the therapeutic failures and tumor relapses. Indeed, the clinical efficacy of anticancer therapies is markedly limited by intrinsic and/or acquired resistance mechanisms that can occur in any tumor type and with any treatment. Thus, there is an urgent clinical need to implement fundamental changes in the tumor treatment paradigm by the development of new experimental strategies that can help to predict the occurrence of clinical drug resistance and to identify alternative therapeutic options. Apart from mutation-driven resistance mechanisms, tumor microenvironment (TME) conditions generate an intratumoral phenotypic heterogeneity that supports disease progression and dismal outcomes. Tumor cell metabolism is a prototypical example of dynamic, heterogeneous, and adaptive phenotypic trait, resulting from the combination of intrinsic [(epi)genetic changes, tissue of origin and differentiation dependency] and extrinsic (oxygen and nutrient availability, metabolic interactions within the TME) factors, enabling cancer cells to survive, metastasize and develop resistance to anticancer therapies. In this review, we summarize the current knowledge regarding metabolism-based mechanisms conferring adaptive resistance to chemo-, radio-and immunotherapies as well as targeted therapies. Furthermore, we report the role of TME-mediated intratumoral metabolic heterogeneity in therapy resistance and how adaptations in amino acid, glucose, and lipid metabolism support the growth of therapy-resistant cancers and/or cellular subpopulations. We also report the intricate interplay between tumor signaling and metabolic pathways in cancer cells and discuss how manipulating key metabolic enzymes and/or providing dietary changes may help to eradicate relapse-sustaining cancer cells. Finally, in the current era of personalized medicine, we describe the strategies that may be applied to implement metabolic profiling for tumor imaging, biomarker identification, selection of tailored treatments and monitoring therapy response during the clinical management of cancer patients.

Pirfenidone Sensitizes NCI-H460 Non-Small Cell Lung Cancer Cells to Paclitaxel and to a Combination of Paclitaxel with Carboplatin.

Pirfenidone, an antifibrotic drug, has antitumor potential against different types of cancers. Our work explored whether pirfenidone sensitizes non-small cell lung cancer (NSCLC) cell lines to chemotherapeutic treatments. The cytotoxic effect of paclitaxel in combination with pirfenidone against three NSCLC cell lines (A549, NCI-H322 and NCI-H460) was evaluated using the sulforhodamine B assay. The effects of this combination on cell viability (trypan blue exclusion assay), proliferation (BrdU incorporation assay), cell cycle (flow cytometry following PI staining) and cell death (Annexin V-FITC detection assay and Western blot) were analyzed on the most sensitive cell line (NCI-H460). The cytotoxic effect of this drug combination was also evaluated against two non-tumorigenic cell lines (MCF-10A and MCF-12A). Finally, the ability of pirfenidone to sensitize NCI-H460 cells to a combination of paclitaxel plus carboplatin was assessed. The results demonstrated that pirfenidone sensitized NCI-H460 cells to paclitaxel treatment, reducing cell growth, viability and proliferation, inducing alterations in the cell cycle profile and causing an increase in the % of cell death. Remarkably, this combination did not increase cytotoxicity in non-tumorigenic cells. Importantly, pirfenidone also sensitized NCI-H460 cells to paclitaxel plus carboplatin. This work highlights the possibility of repurposing pirfenidone in combination with chemotherapy for the treatment of NSCLC.

Synthesis of Novel Methyl 3-(hetero)arylthieno[3,2-b]pyridine-2-carboxylates and Antitumor Activity Evaluation: Studies In Vitro and In Ovo Grafts of Chick Chorioallantoic Membrane (CAM) with a Triple Negative Breast Cancer Cell Line.

A series of novel functionalized methyl 3-(hetero)arylthieno[3,2-b]pyridine-2-carboxylates 2a-2h were synthesized by C-C Pd-catalyzed Suzuki-Miyaura cross-coupling of methyl 3-bromothieno[3,2-b]pyridine-2-carboxylate with (hetero)aryl pinacol boranes, trifluoro potassium boronate salts or boronic acids. Their antitumoral potential was evaluated in two triple negative breast cancer (TNBC) cell lines-MDA-MB-231 and MDA-MB-468, by sulforhodamine B assay. Their effects on the non-tumorigenic MCF-12A cells were also evaluated. The results demonstrated that three compounds caused growth inhibition in both TNBC cell lines, with little or no effect against the non-tumorigenic cells. The most promising compound was further studied concerning possible effects on cell viability (by trypan blue exclusion assay), cell proliferation (by bromodeoxyuridine assay) and cell cycle profile (by flow cytometry). The results demonstrated that the GI50 concentration of compound 2e (13 µM) caused a decreased in MDA-MB-231 cell number, which was correlated with a decreased in the % of proliferating cells. Moreover, this compound increased G0/G1 phase and decreased S phases, when compared to control cells (although was not statistic significant). Interestingly, compound 2e also reduced tumor size using an in ovo CAM (chick chorioallantoic membrane) model. This work highlights the potential antitumor effect of a novel methyl 3-arylthieno[3,2-b]pyridine-2-carboxylate derivative.

Extracellular vesicles as a novel source of biomarkers in liquid biopsies for monitoring cancer progression and drug resistance.

Cancer-derived extracellular vesicles (EVs) have been detected in the bloodstream and other biofluids of cancer patients. They carry various tumor-derived molecules such as mutated DNA and RNA fragments, oncoproteins as well as miRNA and protein signatures associated with various phenotypes. The molecular cargo of EVs partially reflects the intracellular status of their cellular origin, however various sorting mechanisms lead to the enrichment or depletion of EVs in specific nucleic acids, proteins or lipids. It is becoming increasingly clear that cancer-derived EVs act in a paracrine and systemic manner to promote cancer progression by transferring aggressive phenotypic traits and drug-resistant phenotypes to other cancer cells, modulating the anti-tumor immune response, as well as contributing to remodeling the tumor microenvironment and formation of pre-metastatic niches. These findings have raised the idea that cancer-derived EVs may serve as analytes in liquid biopsies for real-time monitoring of tumor burden and drug resistance. In this review, we have summarized recent longitudinal clinical studies describing promising EV-associated biomarkers for cancer progression and tracking cancer evolution as well as pre-clinical and clinical evidence on the relevance of EVs for monitoring the emergence or progression of drug resistance. Furthermore, we outlined the state-of-the-art in the development and commercialization of EV-based biomarkers and discussed the scientific and technological challenges that need to be met in order to translate EV research into clinically applicable tools for precision medicine.

The multi-factorial nature of clinical multidrug resistance in cancer.

Curative cancer therapy remains a major challenge particularly in cancers displaying multidrug resistance (MDR). The MDR phenotype is characterized by cross-resistance to a wide array of anticancer drugs harboring distinct structures and mechanisms of action. The multiple factors involved in mediating MDR may include host factors, tumor factors as well as tumor-host interactions. Among the host factors are genetic variants and drug-drug interactions. The plethora of tumor factors involves decreased drug uptake primarily via impaired influx transporters, increased drug efflux predominantly due to the overexpression of MDR efflux transporters of the ATP-binding cassette superfamily or due to drug efflux mediated by extracellular vesicles (EVs) or drug-loaded lysosomes undergoing exocytosis, deregulation of cell death mechanisms (i.e. anti-apoptotic modalities), enhanced DNA damage repair, epigenetic alterations and/or deregulation of microRNAs. The intratumor heterogeneity and dynamics, along with cancer stem cell plasticity, are important tumor factors. Among the tumor-host interactions are the role of the tumor microenvironment, selective pressure of various stressor conditions and agents, acidic pH and the intracellular transfer of traits mediated by EVs. The involvement of these diverse factors in MDR, highlights the need for precision medicine and real-time personalized treatments of individual cancer patients. In this review, written by a group of researchers from COST Action STRATAGEM "New diagnostic and therapeutic tools against multidrug resistant tumors", we aim to bring together these multidisciplinary and interdisciplinary features of MDR cancers. Importantly, it is becoming increasingly clear that deciphering the molecular mechanisms underlying anticancer drug resistance, will pave the way towards the development of novel precision medicine treatment modalities that are able to surmount distinct and well-defined mechanisms of anticancer drug resistance.

Synthesis of New Proteomimetic Quinazolinone Alkaloids and Evaluation of Their Neuroprotective and Antitumor Effects.

New quinazolinone derivatives of the marine-derived alkaloids fiscalin B (3) and fumiquinazoline G (1), with neuroprotective and antitumor effects, were synthesized. Eleven quinazolinone-containing indole alkaloids were synthesized, proceeding the anti analogs via a one-pot method, and the syn analogs by the Mazurkiewicz-Ganesan approach. The neuroprotection capacity of these compounds on the rotenone-damage human neuroblastoma cell SH-SY5y was evaluated using the MTT assay. Compounds 1, 3, 5, and 7 showed more than 25% protection. The antitumor activity was investigated using the sulforhodamine B assay and some compounds were tested on the non-malignant MCF-12A cells. Fumiquinazoline G (1) was the most potent compound, with GI50 values lower than 20 µM. Compounds 5, 7, and 11 were more active in all tumor cell lines when compared to their enantiomers. Compounds 5, 7, 10, and 11 had very little effect in the viability of the non-malignant cells. Differences between enantiomeric pairs were also noted as being essential for these activities the S-configuration at C-4. These results reinforce the previously described activities of the fiscalin B (3) as substance P inhibitor and fumiquinazoline G (1) as antitumor agent showing potential as lead compounds for the development of drugs for treatment of neurodegenerative disorders and cancer, respectively.

Characterisation of CCT271850, a selective, oral and potent MPS1 inhibitor, used to directly measure in vivo MPS1 inhibition vs therapeutic efficacy.

BACKGROUND: The main role of the cell cycle is to enable error-free DNA replication, chromosome segregation and cytokinesis. One of the best characterised checkpoint pathways is the spindle assembly checkpoint, which prevents anaphase onset until the appropriate attachment and tension across kinetochores is achieved. MPS1 kinase activity is essential for the activation of the spindle assembly checkpoint and has been shown to be deregulated in human tumours with chromosomal instability and aneuploidy. Therefore, MPS1 inhibition represents an attractive strategy to target cancers. METHODS: To evaluate CCT271850 cellular potency, two specific antibodies that recognise the activation sites of MPS1 were used and its antiproliferative activity was determined in 91 human cancer cell lines. DLD1 cells with induced GFP-MPS1 and HCT116 cells were used in in vivo studies to directly measure MPS1 inhibition and efficacy of CCT271850 treatment. RESULTS: CCT271850 selectively and potently inhibits MPS1 kinase activity in biochemical and cellular assays and in in vivo models. Mechanistically, tumour cells treated with CCT271850 acquire aberrant numbers of chromosomes and the majority of cells divide their chromosomes without proper alignment because of abrogation of the mitotic checkpoint, leading to cell death. We demonstrated a moderate level of efficacy of CCT271850 as a single agent in a human colorectal carcinoma xenograft model. CONCLUSIONS: CCT271850 is a potent, selective and orally bioavailable MPS1 kinase inhibitor. On the basis of in vivo pharmacodynamic vs efficacy relationships, we predict that more than 80% inhibition of MPS1 activity for at least 24 h is required to achieve tumour stasis or regression by CCT271850.

An Aqueous Extract of Tuberaria lignosa Inhibits Cell Growth, Alters the Cell Cycle Profile, and Induces Apoptosis of NCI-H460 Tumor Cells.

Tuberaria lignosa (Sweet) Samp. is found in European regions, and has antioxidant properties due to its composition in ascorbic acid and phenolic compounds. Given its traditional use and antioxidant properties, the tumor cell growth inhibitory potential of aqueous extracts from T. lignosa (prepared by infusion and decoction) was investigated in three human tumor cell lines: MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer), and HCT-15 (human colorectal adenocarcinoma). Both extracts inhibited the growth of these cell lines; the most potent one being the T. lignosa extract obtained by infusion in the NCI-H460 cells (GI50 of approximately 50 µg/mL). Further assays were carried out with this extract in NCI-H460 cells. At 100 µg/mL or 150 µg/mL it caused an increase in the percentage of cells in the G0/G1 phase and a decrease of cells in S phase of the cell cycle. Additionally, these concentrations caused an increase in the percentage of apoptotic cells. In agreement, a decrease in total poly (ADP-ribose) polymerase (PARP) and pro-caspase 3 levels was found. In conclusion, the T. lignosa extract obtained by infusion was more potent in NCI-H460 cells, altering the cell cycle progression and inducing apoptosis. This work highlights the importance of T. lignosa as a source of bioactive compounds with tumor cell growth inhibitory potential.

Chemosensitizing effect of pentoxifylline in sensitive and multidrug-resistant non-small cell lung cancer cells.

Aim: Multidrug resistance (MDR) is frequent in non-small cell lung cancer (NSCLC) patients, which can be due to its fibrotic stroma. This work explores the combination of pentoxifylline, an anti-fibrotic and chitinase 3-like-1 (CHI3L1) inhibitor drug, with conventional chemotherapy to improve NSCLC treatment. Methods: The effect of pentoxifylline in the expression levels of P-glycoprotein (P-gp), CHI3L1 and its main downstream proteins, as well as on cell death, cell cycle profile, and P-gp activity was studied in two pairs of sensitive and MDR counterpart NSCLC cell lines (NCI-H460/NCI-H460/R and A549/A549-CDR2). Association studies between CHI3L1 gene expression and NSCLC patients' survival were performed using The Cancer Genome Atlas (TCGA) analysis. The sensitizing effect of pentoxifylline to different drug regimens was evaluated in both sensitive and MDR NSCLC cell lines. The cytotoxicity of the drug combinations was assessed in MCF10A non-tumorigenic cells. Results: Pentoxifylline slightly decreased the expression levels of CHI3L1, ß-catenin and signal transducer and activator of transcription 3 (STAT3), and caused a significant increase in the G1 phase of the cell cycle in both pairs of NSCLC cell lines. A significant increase in the % of cell death was observed in the sensitive NCI-H460 cell line. TCGA analysis revealed that high levels of CHI3L1 are associated with low overall survival (OS) in NSCLC patients treated with vinorelbine. Moreover, pentoxifylline sensitized both pairs of sensitive and MDR NSCLC cell lines to the different drug regimens, without causing significant toxicity to non-tumorigenic cells. Conclusion: This study suggests the possibility of combining pentoxifylline with chemotherapy to increase NSCLC therapeutic response, even in cases of MDR.

Discovery of Potent Isoquinolinequinone N-Oxides to Overcome Cancer Multidrug Resistance.

Multidrug resistance (MDR) of human tumors has resulted in an immediate need to develop appropriate new drugs. This work outlines the development of 20 potent IQQ N-oxide derivatives in two isomeric families, both exhibiting nanomolar GI50 against human tumor cell lines. Preliminary NCI-60 tumor screening sees the C(6) isomers achieve a mean GI50 > 2 times lower than the corresponding C(7) isomers. MDR evaluation of nine selected compounds reveals that each presents lower GI50 concentrations in two MDR tumor cell lines. Four of the series display nanomolar GI50 values against MDR cells, having selectivity ratios up to 2.7 versus the sensitive (parental) cells. The most potent compound 25 inhibits the activity of drug efflux pumps in MDR cells, causes significant ROS accumulation, and potently inhibits cell proliferation, causing alterations in the cell cycle profile. Our findings are confirmed by 3D spheroid models, providing new candidates for studies against MDR cancers.

Fibroblasts in pancreatic cancer: molecular and clinical perspectives.

Pancreatic stellate cells (PSCs) and cancer-associated fibroblasts (CAFs) are highly abundant cells in the pancreatic tumor microenvironment (TME) that modulate desmoplasia. The formation of a dense stroma leads to immunosuppression and therapy resistance that are major causes of treatment failure in pancreatic ductal adenocarcinoma (PDAC). Recent evidence suggests that several subpopulations of CAFs in the TME can interconvert, explaining the dual roles (antitumorigenic and protumorigenic) of CAFs in PDAC and the contradictory results of CAF-targeted therapies in clinical trials. This highlights the need to clarify CAF heterogeneity and their interactions with PDAC cells. This review focuses on the communication between activated PSCs/CAFs and PDAC cells, as well as on the mechanisms underlying this crosstalk. CAF-focused therapies and emerging biomarkers are also outlined.

Establishing and characterizing a novel doxorubicin-resistant acute myeloid leukaemia cell line.

Drug resistance is a major setback in cancer treatment, thus models to study its mechanisms are needed. Our work aimed to establish and characterize a resistant cell line from a sensitive acute myeloid leukaemia (AML) cell line - HL60 - by treating the sensitive cells with increasing concentrations of doxorubicin. We confirmed (cell viability assays) that the established subline, HL60-CDR, was resistant to doxorubicin for at least 30 days without drug treatment. The HL60-CDR cells were also resistant to three other drugs (cisplatin, etoposide and daunorubicin), exhibiting a multidrug resistant (MDR) profile. We verified (Western Blotting) that the MDR cells do not express drug efflux pumps, nor present altered expression of apoptotic proteins, when compared with the parental cell line. HL60-CDR cells presented alterations in the cell cycle profile, and in the expression levels of proteins involved in DNA repair mechanisms and drug metabolism, when compared with their drug sensitive counterpart. Proteomic analysis revealed that HL60-CDR cells presented an upregulation of proteins involved in oncogenic pathways, such as TSC2, PDPK1, Annexin A2, among others. Overall, we established an AML MDR subline - HL60-CDR - which presents several resistance mechanisms, providing an in vitro model to test new compounds to circumvent MDR in AML.

The role of Extracellular Vesicles in glycolytic and lipid metabolic reprogramming of cancer cells: Consequences for drug resistance.

In order to adapt to a higher proliferative rate and an increased demand for energy sources, cancer cells rewire their metabolic pathways, a process currently recognized as a hallmark of cancer. Even though the metabolism of glucose is perhaps the most discussed metabolic shift in cancer, lipid metabolic alterations have been recently recognized as relevant players in the growth and proliferation of cancer cells. Importantly, some of these metabolic alterations are reported to induce a drug resistant phenotype in cancer cells. The acquisition of drug resistance traits severely hinders cancer treatment, being currently considered one of the major challenges of the oncological field. Evidence suggests that Extracellular Vesicles (EVs), which play a crucial role in intercellular communication, may act as facilitators of tumour progression, survival and drug resistance by modulating several aspects involved in the metabolism of cancer cells. This review aims to gather and discuss relevant data regarding metabolic reprograming in cancer, particularly involving the glycolytic and lipid alterations, focusing on its influence on drug resistance and highlighting the relevance of EVs as intercellular mediators of this process.

Novel family of [RuCp(N,N)(P)]+ compounds with simultaneous anticancer and antibacterial activity: Biological evaluation and solution chemistry studies.

A family of ten novel ruthenium(II)-cyclopentadienyl organometallics of general formula [Ru(η5-C5H5)(N,N)(PPh2(C6H4COOR)][CF3SO3] (1-10) in which (N,N) = 4,4'-R'-2,2'-bipyridyl (R = -H or -CH2CH2OH; R' = -H, -CH3, -OCH3, -CH2OH, and -CH2-biotin) was prepared from [Ru(η5-C5H5)(PPh2(C6H4COOH))2Cl]. All compounds were fully characterized by means of several spectroscopic and analytical techniques, and the molecular structures of [Ru(η5-C5H5)(PPh2(C6H4COOH))2Cl], 1, 3 and 4 have been additionally studied by single-crystal X-ray diffraction. The anticancer activity of all compounds was evaluated in sensitive and multidrug-resistant counterpart cell lines from human colorectal cancer (Colo 205 and Colo 320) and non-small cell lung cancer NSCLC (A549, NCI-H460 versus NCI-H460/R) as well. Notably, compounds 6 and 7 (R CH2CH2OH and (N,N) = bipy or Me2bipy, respectively) showed antiproliferative effect against both cell lines with high intrinsic selectivity towards cancer cells. The antibacterial activity of all compounds was also evaluated against both Gram negative and Gram positive strains, and some compounds in the series showed potent antibacterial activity against Staphylococcus aureus strains, including the methicillin-resistant MRSA strains. Solution speciation studies revealed that the complexes bearing the PPh2(C6H4COO-) ligand are neutral at physiological pH (7.4) in contrast with their ethylene glycol derivatives that have a permanent positive charge. While all compounds are lipophilic, the difference in the distribution coefficient for neutral and charged complexes is around one order of magnitude. Complexes 6 and 7 exhibited excellent biological activity and were selected for further studies. Spectrofluorometric methods were used to investigate their interaction with biomolecules such as human serum albumin (HSA) and calf thymus DNA (ct-DNA). For these complexes, binding site II of HSA is a possible binding pocket through non-covalent interactions. The release of ethidium from the DNA adduct by the charged complexes proves their interaction with DNA in contrast to the neutral ones. In conclusion, Ru(II)-cyclopentadienyl complexes with 2,2'-bipyridyl-derivatives and an ethylene glycol moiety tethered to the phenylphosphane co-ligand are very promising from a therapeutic perspective, in particular complexes 6 and 7 that display remarkable antibacterial activity with a high anti-proliferative effect against colon and non-small cell lung cancers, both clinically challenging neoplasias in need of effective solutions.

Ursolic Acid Impairs Cellular Lipid Homeostasis and Lysosomal Membrane Integrity in Breast Carcinoma Cells.

Cancer is one of the leading causes of death worldwide, thus the search for new cancer therapies is of utmost importance. Ursolic acid is a naturally occurring pentacyclic triterpene with a wide range of pharmacological activities including anti-inflammatory and anti-neoplastic effects. The latter has been assigned to its ability to promote apoptosis and inhibit cancer cell proliferation by poorly defined mechanisms. In this report, we identify lysosomes as the essential targets of the anti-cancer activity of ursolic acid. The treatment of MCF7 breast cancer cells with ursolic acid elevates lysosomal pH, alters the cellular lipid profile, and causes lysosomal membrane permeabilization and leakage of lysosomal enzymes into the cytosol. Lysosomal membrane permeabilization precedes the essential hallmarks of apoptosis placing it as an initial event in the cascade of effects induced by ursolic acid. The disruption of the lysosomal function impairs the autophagic pathway and likely partakes in the mechanism by which ursolic acid kills cancer cells. Furthermore, we find that combining treatment with ursolic acid and cationic amphiphilic drugs can significantly enhance the degree of lysosomal membrane permeabilization and cell death in breast cancer cells.

Drug Repurposing Opportunities in Pancreatic Ductal Adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is considered one of the deadliest tumors worldwide. The diagnosis is often possible only in the latter stages of the disease, with patients already presenting an advanced or metastatic tumor. It is also one of the cancers with poorest prognosis, presenting a five-year survival rate of around 5%. Treatment of PDAC is still a major challenge, with cytotoxic chemotherapy remaining the basis of systemic therapy. However, no major advances have been made recently, and therapeutic options are limited and highly toxic. Thus, novel therapeutic options are urgently needed. Drug repurposing is a strategy for the development of novel treatments using approved or investigational drugs outside the scope of the original clinical indication. Since repurposed drugs have already completed several stages of the drug development process, a broad range of data is already available. Thus, when compared with de novo drug development, drug repurposing is time-efficient, inexpensive and has less risk of failure in future clinical trials. Several repurposing candidates have been investigated in the past years for the treatment of PDAC, as single agents or in combination with conventional chemotherapy. This review gives an overview of the main drugs that have been investigated as repurposing candidates, for the potential treatment of PDAC, in preclinical studies and clinical trials.

3D Cell Culture Models as Recapitulators of the Tumor Microenvironment for the Screening of Anti-Cancer Drugs.

Today, innovative three-dimensional (3D) cell culture models have been proposed as viable and biomimetic alternatives for initial drug screening, allowing the improvement of the efficiency of drug development. These models are gaining popularity, given their ability to reproduce key aspects of the tumor microenvironment, concerning the 3D tumor architecture as well as the interactions of tumor cells with the extracellular matrix and surrounding non-tumor cells. The development of accurate 3D models may become beneficial to decrease the use of laboratory animals in scientific research, in accordance with the European Union's regulation on the 3R rule (Replacement, Reduction, Refinement). This review focuses on the impact of 3D cell culture models on cancer research, discussing their advantages, limitations, and compatibility with high-throughput screenings and automated systems. An insight is also given on the adequacy of the available readouts for the interpretation of the data obtained from the 3D cell culture models. Importantly, we also emphasize the need for the incorporation of additional and complementary microenvironment elements on the design of 3D cell culture models, towards improved predictive value of drug efficacy.