Mechanism of action of DNA topoisomerase inhibitors

Ocular adverse events associated with antibody-drug conjugates used in cancer: Focus on pathophysiology and management strategies

Antibody-drug conjugates (ADCs) are designed to maximize cancer cell death with lower cytotoxicity toward noncancerous cells and are an increasingly valuable option for targeted cancer therapies. However, anticancer treatment with ADCs may be associated with ocular adverse events (AEs) such as dry eye, conjunctivitis, photophobia, blurred vision, and corneal abnormalities. While the pathophysiology of ADC-related ocular AEs has not been fully elucidated, most ocular AEs are attributed to off-target effects. Product labelling for approved ADCs includes drug-specific guidance for dose modification and management of ocular AEs; however, limited data are available regarding effective strategies to minimize and mitigate ocular AEs. Overall, the majority of ocular AEs are reversible through dose modification or supportive care. Eye care providers play key roles in monitoring patients receiving ADC therapy for ocular signs and symptoms to allow for the early detection of ADC-related ocular AEs and to ensure the timely administration of appropriate treatment. Therefore, awareness is needed to help ophthalmologists to identify treatment-related ocular AEs and provide effective management in collaboration with oncologists as part of the patient's cancer care team. This review provides an overview of ocular AEs that may occur with approved and investigational ADC anticancer treatments, including potential underlying mechanisms for ADC-related ocular AEs. It also discusses clinical management practices relevant to ophthalmologists for prevention, monitoring, and management of ADC-related ocular AEs. In collaboration with oncologists, ophthalmologists play a vital role in caring for patients with cancer by assisting with the prompt recognition, mitigation, and management of treatment-related ocular AEs.

Multiplexed live-cell imaging for drug responses in patient-derived organoid models of cancer

Patient-derived organoid (PDO) models of cancer are a multifunctional research system that better recapitulates human disease as compared to cancer cell lines. PDO models can be generated by culturing patient tumor cells in extracellular basement membrane extracts (BME) and plating as three-dimensional domes. However, commercially available reagents that have been optimized for phenotypic assays in monolayer cultures often are not compatible with BME. Herein we describe a method to plate PDO models and assess drug effects using an automated live-cell imaging system. In addition, we apply fluorescent dyes that are compatible with kinetic measurements to simultaneously quantitate cell health and apoptosis. Image capture can be customized to occur at regular time intervals over several days. Users can analyze drug effects in individual Z-plane images or a Z Projection of serial images from multiple focal planes. Using masking, specific parameters of interest are calculated, such as PDO number, area, and fluorescence intensity. We provide proof-of-concept data demonstrating the effect of cytotoxic agents on cell health, apoptosis and viability. This automated kinetic imaging platform can be expanded to other phenotypic readouts to understand diverse therapeutic effects in PDO models of cancer.

Curcumin as a hepatoprotective agent against chemotherapy-induced liver injury

Despite significant advances in cancer therapeutics, chemotherapy remains the cornerstone of treatment for many tumors. Importantly, however, chemotherapy-induced toxicity, including hepatotoxicity, can lead to the interruption or discontinuation of potentially effective therapy. In recent years, special attention has been paid to the search for complementary therapies to mitigate chemotherapy-induced toxicity. Although there is currently a lack of specific interventions to mitigate or prevent hepatotoxicity in chemotherapy-treated patients, the polyphenol compound curcumin has emerged as a potential strategy to overcome this adverse effect. Here we review, firstly, the molecular and physiological mechanisms and major risk factors of chemotherapy-induced hepatotoxicity. We then present an overview of how curcumin has the potential to mitigate hepatotoxicity by targeting specific molecular mechanisms. Hepatotoxicity is a well-described side effect of cytotoxic drugs that can limit their clinical application. Inflammation and oxidative stress are the most common mechanisms involved in hepatotoxicity. Several studies have shown that curcumin could prevent and/or palliate chemotherapy-induced liver injury, mainly due to its anti-inflammatory, antioxidant, antifibrotic and hypolipidemic properties. Further clinical investigation using bioavailable curcumin formulations is warranted to demonstrate its efficacy as an hepatoprotective agent in cancer patients.

Revisiting treatment-related cardiotoxicity in patients with malignant lymphoma-a review and prospects for the future

Treatment of malignant lymphoma has for years been represented by many cardiotoxic agents especially anthracyclines, cyclophosphamide, and thoracic irradiation. Although they are in clinical practice for decades, the precise mechanism of cardiotoxicity and effective prevention is still part of the research. At this article we discuss most routinely used anti-cancer drugs in chemotherapeutic regiments for malignant lymphoma with the focus on novel insight on molecular mechanisms of cardiotoxicity. Understanding toxicity at molecular levels may unveil possible targets of cardioprotective supportive therapy or optimization of current therapeutic protocols. Additionally, we review novel specific targeted therapy and its challenges in cardio-oncology.

Single Inhibitors versus Dual Inhibitors: Role of HDAC in Cancer

Due to the multimodal character of cancer, inhibition of two targets simultaneously by a single molecule is a beneficial and effective approach against cancer. Histone deacetylase (HDAC) was widely investigated as a novel category of anticancer drug targets due to its crucial role in various biological processes like cell-proliferation, metastasis, and apoptosis. Numerous HDAC inhibitors such as vorinostat and panobinostat are clinically approved but have limited usage due to their low efficacy, nonselectivity, drug resistance, and toxicity. Therefore, HDACs with a dual targeting ability have attracted great attention. The strategy of combining a HDAC inhibitor with other antitumor agents has been proved advantageous for combating the nonselectivity and drug resistivity problems associated with single-target drugs. Henceforth, we have highlighted dual-targeting inhibitors to target HDAC along with topoisomerase, receptor tyrosine kinase inhibitors, and the zeste homolog 2 enzyme. Our Review mainly focuses on the impact of the substituent effect along with the linker variation of well-known HDAC-inhibitor-conjugated anticancer drugs.

Tailoring carrier-free nanocombo of small-molecule prodrug for combinational cancer therapy

The outcomes of monotherapy could not satisfy clinical cancer treatment owing to the challenges of tumor heterogeneity, multi-drug resistance, tumor metastasis and relapse. In response, the significance of combinational cancer therapy has been highlighted. Traditional combinational schemes usually utilize "free" drug for multi drug administration, independently. The diverse pharmacokinetics and biodistribution greatly hinder the antitumor effects and cause systematic toxicity. To tackle the hinderance, various nanoparticulate drug delivery systems (Nano-DDSs) have been developed. However, conventional Nano-DDSs encapsulate drugs into carrier materials through noncovalent interactions, resulting in low drug loading, fixed multi drug encapsulation ratio, chemical instability and carrier-associated toxicity. Recently, carrier-free nanocombos based on self-assembling small-molecule prodrugs (SPNCs) have emerged as a versatile Nano-DDSs for multiple drug delivery. Benefited by the self-assembly capability, SPNCs could be facilely fabricated with distinct merits of ultra-high drug loading, adjustable drug ratio and negligible carrier-associated toxicity. Herein, we summarize the latest trends of SPNCs. First, a basic review on self-assembling small-molecule prodrugs is presented. Additionally, facile techniques to prepare SPNCs are introduced. Furthermore, advanced combinational therapies based on SPNCs are spotlighted with special emphasis on synergistic mechanisms. Finally, future prospects and challenges are discussed.

Recent Advances Regarding the Molecular Mechanisms of Triterpenic Acids: A Review (Part II)

Triterpenic acids are a widespread class of phytocompounds which have been found to possess valuable therapeutic properties such as anticancer, anti-inflammatory, hepatoprotective, cardioprotective, antidiabetic, neuroprotective, lipolytic, antiviral, and antiparasitic effects. They are a subclass of triterpenes bearing a characteristic lipophilic structure that imprints unfavorable in vivo properties which subsequently limit their applications. The early investigation of the mechanism of action (MOA) of a drug candidate can provide valuable information regarding the possible side effects and drug interactions that may occur after administration. The current paper aimed to summarize the most recent (last 5 years) studies regarding the MOA of betulinic acid, boswellic acid, glycyrrhetinic acid, madecassic acid, moronic acid, and pomolic acid in order to provide scientists with updated and accessible material on the topic that could contribute to the development of future studies; the paper stands as the sequel of our previously published paper regarding the MOA of triterpenic acids with therapeutic value. The recent literature published on the topic has highlighted the role of triterpenic acids in several signaling pathways including PI3/AKT/mTOR, TNF-alpha/NF-kappa B, JNK-p38, HIF-α/AMPK, and Grb2/Sos/Ras/MAPK, which trigger their various biological activities.

Recent Advances Regarding the Molecular Mechanisms of Triterpenic Acids: A Review (Part I)

Triterpenic acids are phytocompounds with a widespread range of biological activities that have been the subject of numerous in vitro and in vivo studies. However, their underlying mechanisms of action in various pathologies are not completely elucidated. The current review aims to summarize the most recent literature, published in the last five years, regarding the mechanism of action of three triterpenic acids (asiatic acid, oleanolic acid, and ursolic acid), corelated with different biological activities such as anticancer, anti-inflammatory, antidiabetic, cardioprotective, neuroprotective, hepatoprotective, and antimicrobial. All three discussed compounds share several mechanisms of action, such as the targeted modulation of the PI3K/AKT, Nrf2, NF-kB, EMT, and JAK/STAT3 signaling pathways, while other mechanisms that proved to only be specific for a part of the triterpenic acids discussed, such as the modulation of Notch, Hippo, and MALAT1/miR-206/PTGS1 signaling pathway, were highlighted as well. This paper stands as the first part in our literature study on the topic, which will be followed by a second part focusing on other triterpenic acids of therapeutic value.

DFF40 deficiency in cancerous T cells is implicated in chemotherapy drug sensitivity and resistance through the regulation of the apoptotic pathway

The regulation of the apoptotic pathway is one of the most studied mechanisms regarding cancer cell resistance. Many mutations have been linked to drug resistance. The DNA fragmentation factor 40 (DFF40) has been gaining interest regarding cancer cell response to chemotherapy and patient outcomes. Glioblastomas and uterine leiomyosarcomas have been shown to have a downregulation of DFF40 expression, conferring a poor patient prognosis. In concordance with these observations, in this study, we showed that DFF40 gene is also downregulated in breast, endocervical, ovarian, lung, pancreas and glioblastomas. DFF40 is the endonuclease responsible of DNA fragmentation during apoptosis. In this study, we sought to determine if a DFF40 deficiency in Jurkat T cells could impact the sensitivity to conventional chemotherapy drugs. CRISPR-cas9 generated DFF40 knockout (DFF40 KO) stable Jurkat cells and wild-type (DFF40 WT) cells were treated with different antimetabolites and topoisomerase II (TOP2) inhibitors, and cell viability was subsequently assessed. DFF40 deficient cells show chemoresistance to antimetabolites (e.g. methotrexate, 6-mercaptopurine and cytarabine) and surprisingly, they are more sensitive to TOP2 inhibitors (e.g. etoposide and teniposide). DFF40 deficient cells exposed to cytarabine present lower phosphatidylserine translocation levels to the outer cell membrane layer. Etoposide exposure in DFF40 deficient cells induces higher mortality levels and downregulation of Bcl-xL cells compared to DFF40 expressing T cells. The abolition of DFF40 expression in Jurkat cells significantly impairs histone H2AX phosphorylation following etoposide and cytarabine treatments. Our findings suggest that DFF40 is a novel key target in cancer cell resistance that potentially regulates genomic stability.

Comprehensive review for anticancer hybridized multitargeting HDAC inhibitors

Despite the encouraging clinical progress of chemotherapeutic agents in cancer treatment, innovation and development of new effective anticancer candidates still represents a challenging endeavor. With 15 million death every year in 2030 according to the estimates, cancer has increased rising of an alarm as a real crisis for public health and health systems worldwide. Therefore, scientist began to introduce innovative solutions to control the cancer global health problem. One of the promising strategies in this issue is the multitarget or smart hybrids having two or more pharmacophores targeting cancer. These rationalized hybrid molecules have gained great interests in cancer treatment as they are capable to simultaneously inhibit more than cancer pathway or target without drug-drug interactions and with less side effects. A prime important example of these hybrids, the HDAC hybrid inhibitors or referred as multitargeting HDAC inhibitors. The ability of HDAC inhibitors to synergistically improve the efficacy of other anti-cancer drugs and moreover, the ease of HDAC inhibitors cap group modification prompt many medicinal chemists to innovate and develop new generation of HDAC hybrid inhibitors. Notably, and during this short period, there are four HDAC inhibitor hybrids have entered different phases of clinical trials for treatment of different types of blood and solid tumors, namely; CUDC-101, CUDC-907, Tinostamustine, and Domatinostat. This review shed light on the most recent hybrids of HDACIs with one or more other cancer target pharmacophore. The designed multitarget hybrids include topoisomerase inhibitors, kinase inhibitors, nitric oxide releasers, antiandrogens, FLT3 and JAC-2 inhibitors, PDE5-inhibitors, NAMPT-inhibitors, Protease inhibitors, BRD4-inhibitors and other targets. This review may help researchers in development and discovery of new horizons in cancer treatment.

The powerful world of antisense oligonucleotides: From bench to bedside

Antisense oligonucleotides (ASOs) represent a new and highly promising class of drugs for personalized medicine. In the last decade, major chemical developments and improvements of the backbone structure of ASOs have transformed them into true approved and commercialized drugs. ASOs target both DNA and RNA, including pre‐mRNA, mRNA, and ncRDA, based on sequence complementary. They are designed to be specific for each identified molecular and genetic alteration to restore a normal, physiological situation. Thus, the characterization of the underpinning mechanisms and alterations that sustain pathology is critical for accurate ASO‐design. ASOs can be used to cure both rare and common diseases, such as orphan genetic alterations and cancer. Through pioneering examples, this review shows the versatility of the mechanisms of action that provide ASOs with the potential capacity to achieve custom treatment, revolutionizing personalized medicine.

This article is categorized under:

RNA in Disease and Development > RNA in Disease

RNA Interactions with Proteins and Other Molecules > Small Molecule–RNA Interactions

Highlights in Resistance Mechanism Pathways for Combination Therapy

Combination chemotherapy has been a mainstay in cancer treatment for the last 60 years. Although the mechanisms of action and signaling pathways affected by most treatments with single antineoplastic agents might be relatively well understood, most combinations remain poorly understood. This review presents the most common alterations of signaling pathways in response to cytotoxic and targeted anticancer drug treatments, with a discussion of how the knowledge of signaling pathways might support and orient the development of innovative strategies for anticancer combination therapy. The ultimate goal is to highlight possible strategies of chemotherapy combinations based on the signaling pathways associated with the resistance mechanisms against anticancer drugs to maximize the selective induction of cancer cell death. We consider this review an extensive compilation of updated known information on chemotherapy resistance mechanisms to promote new combination therapies to be to discussed and tested.

DNA Double Strand Break Repair - Related Synthetic Lethality

Cancer is a heterogeneous disease with a high degree of diversity between and within tumors. Our limited knowledge of their biology results in ineffective treatment. However, personalized approach may represent a milestone in the field of anticancer therapy. It can increase specificity of treatment against tumor initiating cancer stem cells (CSCs) and cancer progenitor cells (CPCs) with minimal effect on normal cells and tissues. Cancerous cells carry multiple genetic and epigenetic aberrations which may disrupt pathways essential for cell survival. Discovery of synthetic lethality has led a new hope of creating effective and personalized antitumor treatment. Synthetic lethality occurs when simultaneous inactivation of two genes or their products causes cell death whereas individual inactivation of either gene is not lethal. The effectiveness of numerous anti-tumor therapies depends on induction of DNA damage therefore tumor cells expressing abnormalities in genes whose products are crucial for DNA repair pathways are promising targets for synthetic lethality. Here, we discuss mechanistic aspects of synthetic lethality in the context of deficiencies in DNA double strand break repair pathways. In addition, we review clinical trials utilizing synthetic lethality interactions and discuss the mechanisms of resistance.

Revealing quinquennial anticancer journey of morpholine: A SAR based review

Morpholine, a six-membered heterocycle containing one nitrogen and one oxygen atom, is a moiety of great significance. It forms an important intermediate in many industrial and organic syntheses. Morpholine containing drugs are of high therapeutic value. Its wide array of pharmacological activity includes anti-diabetic, anti-emetic, growth stimulant, anti-depressant, bronchodilator and anticancer. Multi-drug resistance in cancer cases have emerged in the last few years and have led to the failure of many chemotherapeutic drugs. Newer treatment methods and drugs are being developed to overcome this problem. Target based drug discovery is an effective method to develop novel anticancer drugs. To develop newer drugs, previously reported work needs to be studied. Keeping this in mind, last five year's literature on morpholine used as anticancer agents has been reviewed and summarized in the paper herein.

Approved Anti-cancer Drugs Target Oncogenic Non-coding RNAs

Potential RNA drug targets for small molecules are found throughout the human transcriptome, yet small molecules known to elicit a pharmacological response by directly targeting RNA are limited to antibacterials. Herein, we describe AbsorbArray, a small molecule microarray-based approach that allows for unmodified compounds, including FDA-approved drugs, to be probed for binding to RNA motif libraries in a massively parallel format. Several drug classes bind RNA including kinase and topoisomerase inhibitors. The latter avidly bound the motif found in the Dicer site of oncogenic microRNA (miR)-21 and inhibited its processing both in vitro and in cells. The most potent compound de-repressed a downstream protein target and inhibited a miR-21-mediated invasive phenotype. The compound's activity was ablated upon overexpression of pre-miR-21. Target validation via chemical crosslinking and isolation by pull-down showed direct engagement of pre-miR-21 by the small molecule in cells, demonstrating that RNAs should indeed be considered druggable.

The effects of nitidine chloride and camptothecin on the growth of Babesia and Theileria parasites

The treatment of bovine and equine piroplasmosis is limited to diminazene aceturate (DA) and imidocarb dipropionate. To address this challenge, we need to explore novel drug compounds and targets. Topoisomerases are potential drug targets because they play a vital role in solving topological errors of DNA strands during replication. This study documented the effectiveness of topoisomerase inhibitors, nitidine chloride (NC) and camptothecin (Cpt), on the growth of Babesia and Theileria parasites. The half maximal inhibitory concentrations (IC₅₀s) against B. bovis, B. bigemina, B. caballi, and T. equi were 1.01 ± 0.2, 5.34 ± 1.0, 0.11 ± 0.03, and 2.05 ± 0.4 μM for NC and 11.67 ± 1.6, 4.00 ± 1.0, 2.07 ± 0.6, and 0.33 ± 0.02 μM for Cpt, respectively. The viability experiment revealed that 4, 10, and 4 μM treatments of NC or 48, 8, and 8 μM treatments of Cpt were sufficient to stop the in vitro regrowth of B. bovis, B. bigemina, and B. caballi, respectively. However, T. equi regrew in all of the concentrations used. Moreover, increasing the concentration of NC and Cpt to 16 μM and 1.2 μM (8 × IC₅₀) did not eliminate T. equi. The micrographs of B. bigemina and B. caballi taken at 24 h and 72 h showed deformed merozoites and remnants of parasites within the red blood cell (RBC), respectively. The treatments of 25 mg/kg DA and 20 mg/kg NC administered intraperitoneally and 20 mg/kg NC given orally showed 93.7, 90.7, and 83.6% inhibition against Babesia microti (B. microti), respectively, compared to the untreated group on day 8. In summary, NC and Cpt were effective against Babesia and Theileria parasites in vitro. Moreover, 20 mg/kg NC administered intraperitoneally was as effective as 25 mg/kg DA against B. microti in mice and showed no toxic symptoms in mice. The results indicate that NC may, after further evaluations, prove to be an alternative drug against bovine and equine piroplasmoses.

Computational modeling of methionine cycle-based metabolism and DNA methylation and the implications for anti-cancer drug response prediction

The relationship between metabolism and methylation is considered to be an important aspect of cancer development and drug efficacy. However, it remains poorly defined how to apply this aspect to improve preclinical disease characterization and clinical treatment outcome. Using available molecular information from Kyoto Encyclopedia of Genes and Genomes (KEGG) and literature, we constructed a large-scale knowledge-based metabolic in silico model. For the purpose of model validation, we applied data from the Cancer Cell Line Encyclopedia (CCLE) to investigate computationally the impact of metabolism on chemotherapy efficacy. In our model, different metabolic components such as MAT2A, ATP6V0E1, NNMT involved in methionine cycle correlate with biologically measured chemotherapy outcome (IC50) that are in agreement with findings of independent studies. These proteins are potentially also involved in cellular methylation processes. In addition, several components such as 3,4-dihydoxymandelate, PAPSS2, UPP1 from metabolic pathways involved in the production of purine and pyrimidine correlate with IC50. This study clearly demonstrates that complex computational approaches can reflect findings of biological experiments. This demonstrates their high potential to grasp complex issues within systems medicine such as response prediction, biomarker identification using available data resources.

Dynamics of tobacco DNA topoisomerases II in cell cycle regulation: to manage topological constrains during replication, transcription and mitotic chromosome condensation and segregation

KEY MESSAGE

The topoisomerase II expression varies as a function of cell proliferation. Maximal topoisomerase II expression was tightly coupled to S phase and G2/M phase via both transcriptional and post-transcriptional regulation. Investigation in meiosis using pollen mother cells also revealed that it is not the major component of meiotic chromosomes, it seems to diffuse out once meiotic chromosomal condensation is completed. Synchronized tobacco BY-2 cell cultures were used to study the role of topoisomerase II in various stages of the cell cycle. Topoisomerase II transcript accumulation was observed during the S- and G2/M- phase of cell cycle. This biphasic expression pattern indicates the active requirement of topoisomerase II during these stages of the cell cycle. Through immuno-localization of topoisomerase II was observed diffusely throughout the nucleoplasm in interphase nuclei, whereas, the nucleolus region exhibited a more prominent immuno-positive staining that correlated with rRNA transcription, as shown by propidium iodide staining and BrUTP incorporation. The immuno-staining analysis also showed that topoisomerase II is the major component of mitotic chromosomes and remain attached to the chromosomes during cell division. The inhibition of topoisomerase II activity using specific inhibitors revealed quite dramatic effect on condensation of chromatin and chromosome individualization from prophase to metaphase transition. Partially condensed chromosomes were not arranged on metaphase plate and chromosomal perturbations were observed when advance to anaphase, suggesting the importance of topoisomerase II activity for proper chromosome condensation and segregation during mitosis. Contrary, topoisomerase II is not the major component of meiotic chromosomes, even though mitosis and meiosis share many processes, including the DNA replication, chromosome condensation and precisely regulated partitioning of chromosomes into daughter cells. Even if topoisomerase II is required for individualization and condensation of meiotic chromosomes, it seems to diffuse out once meiotic chromosomal condensation is completed.

Polymeric prodrugs conjugated with reduction-sensitive dextran–camptothecin and pH-responsive dextran–doxorubicin: an effective combinatorial drug delivery platform for cancer therapy

Two types of stimuli-sensitive polymeric prodrugs for combinatorial cancer therapy have been prepared and found to exhibit favorable anticancer activity in vitro and in vivo.

Polymeric nanomedicine for tumor-targeted combination therapy to elicit synergistic genotoxicity against prostate cancer

To improve the therapeutic efficacy of anticancer combination therapy, we designed a nanoplatform based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers that allows covalent bonding of two chemotherapeutics acting via different anticancer mechanisms and that can enter target cells by receptor-mediated endocytosis. Doxorubicin (DOX) was covalently conjugated to a nanosized HPMA copolymer using a pH-sensitive hydrazone bond and 5-fluorouracil (5-Fu) was conjugated to the same backbone using an enzymatically degradable oligopeptide Gly-Phe-Leu-Gly sequence. Then, the conjugate was decorated with galectin-3 targeting peptide G3-C12 [P-(G3-C12)-DOX-Fu]. The two drugs showed similar in vitro release profiles, suggesting that they may be able to work synergistically in the codelivery system. In galectin-3 overexpressed PC-3 human prostate carcinoma cells, P-(G3-C12)-DOX-Fu surprisingly exhibited comparable cytotoxicity to free DOX at high concentration by increasing cell internalization and exerting synergistic genotoxic effects of cell cycle arrest, caspase-3 activation, and DNA damage. In mice bearing PC-3 tumor xenografts, the use of tumor-targeting ligand substantially enhanced the intracellular delivery of P-(G3-C12)-DOX-Fu in tumors. The targeted dual drug-loaded conjugate inhibited tumor growth to a greater extent (tumor inhibition of 81.6%) than did nontargeted P-DOX-Fu (71.2%), P-DOX (63%), DOX·HCl (40.5%), P-Fu (32.0%), or 5-Fu (14.6%), without inducing any obvious side effects. These results demonstrate the potential of synergistic combination therapy using targeted nanocarriers for efficient treatment of prostate cancer.

Functional differentiation of cytotoxic cancer drugs and targeted cancer therapeutics

There is no nationally or internationally binding definition of the term "cytotoxic drug" although this term is used in a variety of regulations for pharmaceutical development and manufacturing of drugs as well as in regulations for protecting medical personnel from occupational exposure in pharmacy, hospital, and other healthcare settings. The term "cytotoxic drug" is frequently used as a synonym for any and all oncology or antineoplastic drugs. Pharmaceutical companies generate and receive requests for assessments of the potential hazards of drugs regularly - including cytotoxicity. This publication is intended to provide functional definitions that help to differentiate between generically-cytotoxic cancer drugs of significant risk to normal human tissues, and targeted cancer therapeutics that pose much lesser risks. Together with specific assessments, it provides comprehensible guidance on how to assess the relevant properties of cancer drugs, and how targeted therapeutics discriminate between cancer and normal cells. The position of several regulatory agencies in the long-term is clearly to regulate all drugs regardless of classification, according to scientific risk based data. Despite ongoing discussions on how to replace the term "cytotoxic drugs" in current regulations, it is expected that its use will continue for the near future.

Folding graft copolymer with pendant drug segments for co-delivery of anticancer drugs

A graft copolymer with pendant drug segments can fold into nanostructures in a protein folding-like manner. The graft copolymer is constructed by directly polymerizing γ-camptothecin-glutamate N-carboxyanhydride (Glu(CPT)-NCA) on multiple sites of poly(ethylene glycol) (PEG)-based main chain via the ring open polymerization (ROP). The "purely" conjugated anticancer agent camptothecin (CPT) is hydrophobic and serves as the principal driving force during the folding process. When exposed to water, the obtained copolymer, together with doxorubicin (Dox), another anticancer agent, can fold into monodispersed nanocarriers (with a diameter of around 50 nm) for dual-drug delivery. Equipped with a PEG shell, the nanocarriers displayed good stability and can be internalized by a variety of cancer cell lines via the lipid raft and clathrin-mediated endocytotic pathway without premature leakage, which showed a high synergetic activity of CPT and Dox toward various cancer cells. In vivo study validated that the nanocarriers exhibited strong accumulation in tumor sites and showed a prominent anticancer activity against the lung cancer xenograft mice model compared with free drugs.

PARP inhibition potentiates the cytotoxic activity of C-1305, a selective inhibitor of topoisomerase II, in human BRCA1-positive breast cancer cells

Two cellular proteins encoded by the breast and ovarian cancer type 1 susceptibility (BRCA1 and BRCA2) tumor suppressor genes are essential for DNA integrity and the maintenance of genomic stability. Approximately 5–10% of breast and ovarian cancers result from inherited alterations or mutations in these genes.

Remarkably, BRCA1/BRCA2-deficient cells are hypersensitive to selective inhibition of poly(ADP-ribose)polymerase 1 (PARP-1), whose primary functions are related to DNA base excision repair; PARP-1 inhibition significantly potentiates the cytotoxicity of various anti-cancer drugs, including inhibitors of topoisomerase I and II.

In the present study, we examined the anti-proliferative and pro-apoptotic effects of C-1305, a selective inhibitor of topoisomerase II, on human breast cancer cell lines with different BRCA1 and p53 statuses. BRCA1-competent breast cancer cell lines exhibited different responses to topoisomerase II inhibition. BT-20 cells that express high levels of BRCA1 levels were most resistant to C-1305 than other tested cells. Surprisingly, pharmacological interference with PARP-1 activity strongly inhibited their proliferation and potentiated the efficacy of C-1305 treatment. In contrast, PARP-1 inhibition only weakly affected the proliferation of BRCA1-deficient SKBr-3 cells and was not synergistic with the effects of C-1305. Further experiments revealed that the inhibition of PARP-1 in BT-20 cells caused the accumulation of DNA strand breaks and induced caspase-3 dependent apoptosis. These results seem to indicate that PARP-1 inhibition can potentiate the cytotoxicity of anti-cancer drugs in cancer cells with functional BRCA1 and suggest that mutations in other DNA repair proteins may render cancer cells more sensitive to interference with PARP-1 activity.

Therapeutic resistance in lung cancer

Despite considerable progress over the last 25 years in the systemic therapy of lung cancer, intrinsic and acquired resistance to chemotherapeutic agents and radiation remains a vexing problem. The number of mechanisms of therapeutic resistance in lung cancer has expanded considerably over the past three decades, and the crucial role of stress resistance pathways is increasingly recognised as a cause of intrinsic and acquired chemo- and radiotherapy resistance. This paper reviews recent evidence for stress defence proteins, particularly RALBP1/RLIP76, in mediating intrinsic and acquired chemotherapy and radiation resistance in human lung cancer.

Detection of topoisomerase inhibitor-induced DNA strand breaks and apoptosis by the alkaline comet assay

The alkaline comet assay is able to identify in individual cells DNA strand breaks associated with different processes. Topoisomerase inhibitors, some of which are used as chemotherapeutic agents, stabilise topoisomerase-DNA cleavable complexes by stimulating DNA strand cleavage and inhibiting religation. This can result in the activation of stress-associated signalling pathways, inducing cell cycle arrest and activation of the biochemical cascade of apoptosis. The aim of our study was to assess the ability of the comet assay to detect stabilisation of cleavable complexes and induction of apoptosis by two topoisomerase II inhibitors, etoposide and ellipticine, and two topoisomerase I inhibitors, camptothecin and topotecan. The study was carried out on Chinese hamster ovary (CHO) cells, DC3F cells and DC3F/C-10, its camptothecin-resistant counterpart. The comet assay was able to identify stabilised cleavable complexes through the presence of DNA strand breaks after 1h treatment that disappeared within 24h after drug removal. Kinetics studies allowed to discriminate between these early DNA damages and DNA fragmentation related to apoptosis characterised by reappearance of DNA strand breaks 48h after treatment.

Reduced DNA ligase activity in etoposide resistant human lymphatic leukaemia CEM cells

Drug resistance is an obstacle preventing success of cancer chemotherapy. Resistance of vaccinia virus towards the topoisomerase II (topo II) targeting anti-cancer drug etoposide has been mapped to the viral DNA ligase gene. The present study was performed to elucidate if the DNA ligase activity, besides topo II levels, was altered in human lymphatic leukaemia cell strains with different levels of etoposide resistance. At measurements of DNA ligase activity with specific substrates, to distinguish between different DNA ligases, a reduced DNA ligase activity was observed in the resistant substrains. In contrast, the initial step of the ligation process, formation of DNA ligase--AMP complex, did not decrease in the resistant cell strains, suggesting an alteration in a later reaction leading to a deteriorated DNA ligation. The results suggest that decreased DNA ligase activity, besides topo II alterations, may contribute to etoposide resistance of the investigated CEM cells. The relevance of this finding will be further investigated.

Cell cycle disturbances and apoptosis induced by topotecan and gemcitabine on human lung cancer cell lines

Apoptosis is a major mode of cell death in response to cytotoxic drug treatment. A correlation between induction of apoptosis and chemosensitivity has been documented in some preclinical models. Topotecan (a topoisomerase I inhibitor) and gemcitabine (a deoxycytidine analogue), two active new drugs for the treatment of lung cancer, were evaluated for their growth inhibitory effect on human lung cancer cell lines and their effect on cell cycle perturbation, apoptosis and apoptosis-related genes. The cytotoxicities of topotecan and gemcitabine on the human lung cancer cell lines H460 (wild-type-p53) and H322 (mutant p53 were determined after 72 h drug exposure employing the MTT assay. The apoptotic index (AI) was assessed by three methods: analysis of morphological changes using May-Grünwald-Giemsa (MGG) staining, the TUNEL assay and FACS analysis. Cell cycle disturbances were studied by FACS and the number of cells expressing p53 and p21 were determined by immunohistochemistry. Both gemcitabine and topotecan had potent growth inhibitory effects in human lung cancer cell lines; combination treatment with these two drugs showed some additivity but no synergism. Induction of apoptosis after treatment was concentration- and time-dependent with both drugs and IC80 concentrations induced the highest values. The DNA histograms at 4, 24, 48 and 72 h indicate that topotecan at IC80 concentrations causes accumulation of cells in S and G2/M phases, whereas gemcitabine at IC80 concentrations causes, accumulation of cells in G1 phase. Both compounds induced p53 and p21 expression in the H460 cell line but not in the H322 cell line; the percentage of cells expressing p53 was highest at IC80 values, whereas the highest percentage of p21 positive cells could be induced with IC50 values. This could suggest that p53 induces cell cycle arrest at low drug concentrations, whereas p53 induces apoptosis at higher concentrations. In conclusion, p53-dependent and independent pathways of apoptosis exist in lung cancer cell lines. Activation of the p53 pathway depends on the induced cellular damage. Understanding the cell cycle disturbances induced by these drugs may help in the design of more rational treatment schedules.

Are topoisomerase II inhibitor-induced micronuclei in vitro a predictive marker for the compounds' ability to cause secondary leukemias after treatment?

The inhibition of topoisomerase II (topo II) is a very powerful principle of chemotherapy and topo II inhibiting drugs are the backbone of most chemotherapeutic strategies. However, secondary malignomas can occur after treatment. Typically, secondary acute myeloid leukemia (t-AML) after treatment with topo II inhibitors has a shorter latency period than t-AML following alkylator therapy. Fragments originating from chromosome breakage as well as whole chromosomes which are not correctly distributed during mitosis give rise to micronuclei in the next interphase. Micronucleus formation has become an important endpoint in genotoxicity testing. In an effort to test the suitability of the micronucleus assay for predictive purposes, we have analyzed three human tumor cell lines for cell growth as well as micronucleus induction after treatment with four clinically used topo II inhibitors. Micronuclei were induced at levels of low toxicity by etoposide, mitoxantrone, daunorubicin and idarubicin. The induction of micronuclei was a more sensitive indicator of drug effects than reduction in cell growth. Thus, micronucleus induction may assist in the prediction of the potency of a chemotherapeutic agent for induction of secondary malignomas.

Apoptosis may be either suppressed or enhanced with strategic combinations of antineoplastic drugs or anti-IgM

A variety of drugs have been used to treat B-lymphocyte neoplasms, including both cell cycle-specific (CCS) and non-cell-cycle-specific drugs. Although the therapy for such cancers is complex and can include both types of drugs, the efficacy of these drugs in inducing cell death remains unclear. In this paper we have concentrated on specific CCS drugs and have examined their ability to induce programmed cell death (apoptosis) in Burkitt's lymphoma cell lines derived from patients. The CCS drugs chosen were hydroxyurea and aphidicolin (active in late G1, early S phase), the topoisomerase poisons camptothecin and etoposide (S, early G2 phase) and vincristine and Taxol (late G2, M phase). These choices allow comparison of two drugs with differing modes of action for each of the various phases of the cell cycle. Our results indicate that the variation in apoptosis between drugs that act at the same phase of the cell cycle is negligible. Both S/G2 and G2/M blockers are very potent at inducing apoptosis whereas G1/S blockers are ineffective in the induction of apoptosis. In addition, marked kinetic variations in the rate of apoptosis induction were observed, etoposide and camptothecin being more rapid in their action than the other agents. The order of effectiveness in inducing apoptosis on a kinetic basis was S/G2 agents >> G2/M agents >> G1/S agents. In this study we have also found that growth inhibition was induced by all the CCS agents chosen and by anti-IgM in various Burkitt's lymphoma lines. Furthermore c-myc was down-regulated under similar conditions. Since apoptosis was only selectively induced by some of the CCS agents, it implies c-myc expression is associated with growth regulation and c-myc down-regulation is an insufficient condition for the induction of apoptosis. In addition, cotreatments using the CCS and other agents revealed the following: Cotreatment using two CCS drugs which act at the same stage in the cell cycle showed either no change or only additivity to the effects seen with either agent alone. However, cotreatment with CCS drugs showed that an inhibitory effect is found between G1/S and G2/M drugs or S/G2 and G2/M drugs. No effect was found between G1/S and S/G2 drugs. Anti-IgM, which by itself was capable of inducing apoptosis, was observed to augment apoptosis induced by very low concentrations of G2/M-acting drugs but it has little effect on G1/S or the S/G2 drugs. The inhibitory effect of anti-CD40 or TNF-alpha on anti-IgM-induced apoptosis did not carry over to an effect on apoptosis induction by the CCS agents. Thus specific combinations of agents may lead to either enhancement, inhibition, or no interactive effect on apoptosis.

Catalytic inhibitors of DNA topoisomerase II

Catalytic inhibitors of mammalian DNA topoisomerase II have been found recently in natural and synthetic compounds. These compounds target the enzyme within the cell and inhibit various genetic processes involving the enzyme, such as DNA replication and chromosome dynamics, and thus proved to be good probes for the functional analyses of the enzyme in a variety of eukaryotes from yeast to mammals. Catalytic inhibitors were shown to be antagonists against topoisomerase II poisons. Thus bis(2,6-dioxopiperazines) have a potential to overcome cardiac toxicity caused by potent antitumor anthracycline antibiotics such as doxorubicin and daunorubicin. ICRF-187, a (+)-enantiomer of racemic ICRF-159, has been used in clinics in European countries as cardioprotector. Furthermore, bis(2,6-dioxopiperazines) enhance the efficacy of topoisomerase II poisons by reducing their side effects in preclinical and clinical settings. Bis(2,6-dioxopiperazines) per se among others have antitumor activity, and one of their derivatives, MST-16 or Sobuzoxane, bis(N1-isobutyloxycarbonyloxymethyl-2, 6-dioxopiperazine), has been developed in Japan as an anticancer drug used for malignant lymphomas and adult T-cell leukemia in clinics.

DNA sequence selectivity of topoisomerases and topoisomerase poisons

Chemical agents able to interfere with DNA topoisomerases are widespread in nature, and some of them have clinical efficacy as antitumor or antibacterial drugs. Drugs which have as a target DNA topoisomerases could be divided into two categories: poisons and catalytic inhibitors. Classical topoisomerase poisons stimulate cleavage in a sequence-selective manner, yielding drug-specific cleavage intensity pattern. The mechanisms of drug interaction with DNA topoisomerases, the DNA sequence selectivity of the action of topoisomerase II poisons and the identification of structural determinants of their activity have suggested that topoisomerase II poisons may fit into a specific pharmacophore, constituted by a planar ring system with DNA intercalation or intercalation-like properties, and protruding side chains interfering with the protein side of the covalent enzyme-DNA complex. The complete definition of the diverse pharmacophores of topoisomerase II poisons will certainly be of value for the design of new agents directed to specific genomic sites, and more effective in the treatment of human cancer.

Physicochemical properties, cytotoxic activity and topoisomerase II inhibition of 2,3-diaza-anthracenediones

The physicochemical, cytotoxic and pharmacological properties of 2,3-diaza-anthracenedione derivatives were examined to gain insight into the structure-activity relationships in this class of compounds. Spectrophotometric, chiroptical and voltammetric measurements were performed, along with cell cytotoxicity, alkaline elution, topoisomerase II-mediated DNA cleavage and cellular drug-uptake determination. In comparison with classic anthracenediones such as mitoxantrone and ametantrone, the aza derivatives were characterized by less negative reduction potentials, lower affinity for DNA and modified geometry of intercalation. The biological effects of the new compounds were also profoundly affected by bioisosteric N for C replacement. Stimulation of topoisomerase II-mediated DNA cleavage was not observed, whereas other mechanisms of cell cytotoxicity, possibly involving oxidative DNA damage appeared to be operative. The inability to generate protein-associated strand breaks could be explained by an unfavorable orientation of the drug in the intercalation complex rather than by a reduced binding to DNA. Geometry of drug intercalation may have a critical influence on the formation of the ternary complex. In turn, the onset of a different DNA-damaging pathway is likely to be related to easy redox cycling of the 2,3-diaza-substituted anthracenedione derivatives, which could produce radical species to a remarkably greater extent than could the carbocyclic parent drugs.