Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Assessment of the Efficacy of Olive Leaf (Olea europaea L.) Extracts in the Treatment of Colorectal Cancer and Prostate Cancer Using In Vitro Cell Models

Cancer is one of the most serious public health issues worldwide, ranking second only to cardiovascular diseases as a cause of death. Numerous plant extracts have extraordinary health benefits and have been used for centuries to treat a variety of ailments with few side effects. Olive leaves have a long history of medicinal and therapeutic use. In this study, the anti-cancer properties of an olive leaf extract were investigated in vitro using colorectal and prostate cancer cell lines (HT29 and PC3, respectively). A high-performance liquid chromatography analysis showed that the olive leaf extract contained a high chlorogenic acid content. Accordingly, chlorogenic acid may be related to the observed effects of the aqueous extract on cancer cells, including increased inhibition of cancer cell growth, migration, DNA fragmentation, cell cycle arrest at the S phase, reactive oxygen species (ROS) production, and altered gene expression. The effects of the extracts were greater in HT29 than in PC3 cells. These results suggest that chlorogenic acid, the main constituent in the olive extract, is a promising new anti-cancer agent. Further analyses should focus on its in vivo effects on colorectal tumor models, both alone and in combination with established agents.

Triple-negative breast cancer: A run-through of features, classification and current therapies

Breast cancer is the most prevalent cancer in women worldwide. Triple-negative breast cancer (TNBC) is characterized by the lack of expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. It is the most aggressive subtype of breast cancer and accounts for 12-20% of all breast cancer cases. TNBC is associated with younger age of onset, greater metastatic potential, higher incidence of relapse, and lower overall survival rates. Based on molecular phenotype, TNBC has been classified into six subtypes (BL1, BL2, M, MES, LAR, and IM). TNBC treatment is challenging due to its heterogeneity, highly invasive nature, and relatively poor therapeutics response. Chemotherapy and radiotherapy are conventional strategies for the treatment of TNBC. Recent research in TNBC and mechanistic understanding of disease pathogenesis using cutting-edge technologies has led to the unfolding of new lines of therapies that have been incorporated into clinical practice. Poly (ADP-ribose) polymerase and immune checkpoint inhibitors have made their way to the current TNBC treatment paradigm. This review focuses on the classification, features, and treatment progress in TNBC. Histological subtypes connected to recurrence, molecular classification of TNBC, targeted therapy for early and advanced TNBC, and advances in non-coding RNA in therapy are the key highlights in this review.

Platinum drugs and taxanes: can we overcome resistance?

Cancer therapy is aimed at the elimination of tumor cells and acts via the cessation of cell proliferation and induction of cell death. Many research publications discussing the mechanisms of anticancer drugs use the terms "cell death" and "apoptosis" interchangeably, given that apoptotic pathways are the most common components of the action of targeted and cytotoxic compounds. However, there is sound evidence suggesting that other mechanisms of drug-induced cell death, such as necroptosis, ferroptosis, autophagy, etc. may significantly contribute to the fate of cancer cells. Molecular cross-talks between apoptotic and nonapoptotic death pathways underlie the successes and the failures of therapeutic interventions. Here we discuss the nuances of the antitumor action of two groups of the widely used anticancer drugs, i.e., platinum salts and taxane derivatives. The available data suggest that intelligent interference with the choice of cell death pathways may open novel opportunities for cancer treatment.

Overcoming anti-cancer drug resistance via restoration of tumor suppressor gene function

The cytotoxic anti-cancer drugs cisplatin, paclitaxel, doxorubicin, 5-fluorouracil (5-FU), as well as targeted drugs including imatinib, erlotinib, and nivolumab, play key roles in clinical cancer treatment. However, the frequent emergence of drug resistance severely comprosises their anti-cancer efficacy. A number of studies indicated that loss of function of tumor suppressor genes (TSGs) is involved in the development of cancer drug resistance, apart from decreased drug influx, increased drug efflux, induction of anti-apoptosis mechanisms, alterations in tumor microenvironment, drug compartmentalization, enhanced DNA repair and drug inactivation. TSGs are involved in the pathogenesis of tumor formation through regulation of DNA damage repair, cell apoptosis, autophagy, proliferation, cell cycle progression, and signal transduction. Our increased understanding of TSGs in the past decades demonstrates that gene mutation is not the only reason that leads to the inactivation of TSGs. Loss of function of TSGs may be based on the ubiquitin-proteasome pathway, epigenetic and transcriptional regualtion, post-translation modifications like phosphorylation as well as cellular translocation of TSGs. As the above processes can constitute"druggable targets", these mechanisms provide novel therapeutic approaches in targeting TSGs. Some small molecule compounds targeting these approaches re-activated TSGs and reversed cancer drug resistance. Along this vein, functional restoration of TSGs is a novel and promising approach to surmount cancer drug resistance. In the current review, we draw a scenario based on the role of loss of function of TSGs in drug resistance, on mechanisms leading to inactivation of TSGs and on pharmacological agents acting on these mechanisms to overcome cancer drug resistance. This review discusses novel therapeutic strategies targeting TSGs and offers possible modalities to conquer cancer drug resistance.

Acquired resistance to third-generation EGFR-TKIs and emerging next-generation EGFR inhibitors

The discovery that mutations in the EGFR gene are detected in up to 50% of lung adenocarcinoma patients, along with the development of highly efficacious epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs), has revolutionized the treatment of this frequently occurring lung malignancy. Indeed, the clinical success of these TKIs constitutes a critical milestone in targeted cancer therapy. Three generations of EGFR-TKIs are currently approved for the treatment of EGFR mutation-positive non-small cell lung cancer (NSCLC). The first-generation TKIs include erlotinib, gefitinib, lapatinib, and icotinib; the second-generation ErbB family blockers include afatinib, neratinib, and dacomitinib; whereas osimertinib, approved by the FDA on 2015, is a third-generation TKI targeting EGFR harboring specific mutations. Compared with the first- and second-generation TKIs, third-generation EGFR inhibitors display a significant advantage in terms of patient survival. For example, the median overall survival in NSCLC patients receiving osimertinib reached 38.6 months. Unfortunately, however, like other targeted therapies, new EGFR mutations, as well as additional drug-resistance mechanisms emerge rapidly after treatment, posing formidable obstacles to cancer therapeutics aimed at surmounting this chemoresistance. In this review, we summarize the molecular mechanisms underlying resistance to third-generation EGFR inhibitors and the ongoing efforts to address and overcome this chemoresistance. We also discuss the current status of fourth-generation EGFR inhibitors, which are of great value in overcoming resistance to EGFR inhibitors that appear to have greater therapeutic benefits in the clinic.

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EGFR gene mutations are detected in about 50% of non-small cell lung cancer (NSCLC) patients worldwide

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The three generations of EGFR tyrosine kinase inhibitors (TKIs) are critical milestones for NSCLC patients

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Like other targeted therapies, new EGFR mutations and coupled drug resistances emerge rapidly after TKI treatment, posing formidable obstacles to cancer management

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The investigational fourth-generation EGFR inhibitors are of great promise, through a number of novel mechanisms, in overcoming these resistances after third-generation TKI treatment, and will bring more benefits to NSCLC patients

Discovery of Novel Benzimidazole and Indazole Analogues as Tubulin Polymerization Inhibitors with Potent Anticancer Activities

Novel indazole and benzimidazole analogues were designed and synthesized as tubulin inhibitors with potent antiproliferative activities. Among them, compound 12b exhibited the strongest inhibitory effects on the growth of cancer cells with an average IC₅₀ value of 50 nM, slightly better than colchicine. 12b exhibited nearly equal potency against both, a paclitaxel-resistant cancer cell line (A2780/T, IC₅₀ = 9.7 nM) and the corresponding parental cell line (A2780S, IC₅₀ = 6.2 nM), thus effectively overcoming paclitaxel resistance in vitro. The crystal structure of 12b in complex with tubulin was solved to 2.45 Å resolution by X-ray crystallography, and its direct binding was confirmed to the colchicine site. Furthermore, 12b displayed significant in vivo antitumor efficacy in a melanoma tumor model with tumor growth inhibition rates of 78.70% (15 mg/kg) and 84.32% (30 mg/kg). Collectively, this work shows that 12b is a promising lead compound deserving further investigation as a potential anticancer agent.

In vitro biomimetic models for glioblastoma-a promising tool for drug response studies

The poor response of glioblastoma to current treatment protocols is a consequence of its intrinsic drug resistance. Resistance to chemotherapy is primarily associated with considerable cellular heterogeneity, and plasticity of glioblastoma cells, alterations in gene expression, presence of specific tumor microenvironment conditions and blood-brain barrier. In an attempt to successfully overcome chemoresistance and better understand the biological behavior of glioblastoma, numerous tri-dimensional (3D) biomimetic models were developed in the past decade. These novel advanced models are able to better recapitulate the spatial organization of glioblastoma in a real time, therefore providing more realistic and reliable evidence to the response of glioblastoma to therapy. Moreover, these models enable the fine-tuning of different tumor microenvironment conditions and facilitate studies on the effects of the tumor microenvironment on glioblastoma chemoresistance. This review outlines current knowledge on the essence of glioblastoma chemoresistance and describes the progress achieved by 3D biomimetic models. Moreover, comprehensive literature assessment regarding the influence of 3D culturing and microenvironment mimicking on glioblastoma gene expression and biological behavior is also provided. The contribution of the blood-brain barrier as well as the blood-tumor barrier to glioblastoma chemoresistance is also reviewed from the perspective of 3D biomimetic models. Finally, the role of mathematical models in predicting 3D glioblastoma behavior and drug response is elaborated. In the future, technological innovations along with mathematical simulations should create reliable 3D biomimetic systems for glioblastoma research that should facilitate the identification and possibly application in preclinical drug testing and precision medicine.

Therapeutic strategies to overcome taxane resistance in cancer

One of the primary causes of attenuated or loss of efficacy of cancer chemotherapy is the emergence of multidrug resistance (MDR). Numerous studies have been published regarding potential approaches to reverse resistance to taxanes, including paclitaxel (PTX) and docetaxel, which represent one of the most important classes of anticancer drugs. Since 1984, following the FDA approval of paclitaxel for the treatment of advanced ovarian carcinoma, taxanes have been extensively used as drugs that target tumor microtubules. Taxanes, have been shown to affect an array of oncogenic signaling pathways and have potent cytotoxic efficacy. However, the clinical success of these drugs has been restricted by the emergence of cancer cell resistance, primarily caused by the overexpression of MDR efflux transporters or by microtubule alterations. In vitro and in vivo studies indicate that the mechanisms underlying the resistance to PTX and docetaxel are primarily due to alterations in α-tubulin and β-tubulin. Moreover, resistance to PTX and docetaxel results from: 1) alterations in microtubule-protein interactions, including microtubule-associated protein 4, stathmin, centriole, cilia, spindle-associated protein, and kinesins; 2) alterations in the expression and activity of multidrug efflux transporters of the ABC superfamily including P-glycoprotein (P-gp/ABCB1); 3) overexpression of anti-apoptotic proteins or inhibition of apoptotic proteins and tumor-suppressor proteins, as well as 4) modulation of signal transduction pathways associated with the activity of several cytokines, chemokines and transcription factors. In this review, we discuss the abovementioned molecular mechanisms and their role in mediating cancer chemoresistance to PTX and docetaxel. We provide a detailed analysis of both in vitro and in vivo experimental data and describe the application of these findings to therapeutic practice. The current review also discusses the efficacy of different pharmacological modulations to achieve reversal of PTX resistance. The therapeutic roles of several novel compounds, as well as herbal formulations, are also discussed. Among them, many structural derivatives had efficacy against the MDR phenotype by either suppressing MDR or increasing the cytotoxic efficacy compared to the parental drugs, or both. Natural products functioning as MDR chemosensitizers offer novel treatment strategies in patients with chemoresistant cancers by attenuating MDR and increasing chemotherapy efficacy. We broadly discuss the roles of inhibitors of P-gp and other efflux pumps, in the reversal of PTX and docetaxel resistance in cancer cells and the significance of using a nanomedicine delivery system in this context. Thus, a better understanding of the molecular mechanisms mediating the reversal of drug resistance, combined with drug efficacy and the application of target-based inhibition or specific drug delivery, could signal a new era in modern medicine that would limit the pathological consequences of MDR in cancer patients.

Breaking malignant nuclei as a non-mitotic mechanism of taxol/paclitaxel

Discovered in a large-scale screening of natural plant chemicals, Taxol/paclitaxel and the taxane family of compounds are surprisingly successful anti-cancer drugs, used in treatment of the majority of solid tumors, and especially suitable for metastatic and recurrent cancer. Paclitaxel is often used in combination with platinum agents and is administrated in a dose dense regimen to treat recurrent cancer. The enthusiasm and clinical development were prompted by the discovery that Taxol binds beta-tubulins specifically found within microtubules and stabilizes the filaments, and consequently inhibits mitosis. However, questions on how paclitaxel suppresses cancer persist, as other specific mitotic inhibitors are impressive in pre-clinical studies but fail to achieve significant clinical activity. Thus, additional mechanisms, such as promoting mitotic catastrophe and impacting non-mitotic targets, have been proposed and studied. A good understanding of how paclitaxel, and additional new microtubule stabilizing agents, kill cancer cells will advance the clinical application of these common chemotherapeutic agents. A recent study provides a potential non-mitotic mechanism of paclitaxel action, that paclitaxel-induced rigid microtubules act to break malleable cancer nuclei into multiple micronuclei. Previous studies have established that cancer cells have a less sturdy, more pliable nuclear envelope due to the loss or reduction of lamin A/C proteins. Such changes in nuclear structure provide a selectivity for paclitaxel to break the nuclear membrane and kill cancer cells over non-neoplastic cells that have a sturdier nuclear envelope. The formation of multiple micronuclei appears to be an important aspect of paclitaxel in the killing of cancer cells, either by a mitotic or non-mitotic mechanism. Additionally, by binding to microtubule, paclitaxel is readily sequestered and concentrated within cells. This unique pharmacokinetic property allows the impact of paclitaxel on cells to persist for several days, even though the circulating drug level is much reduced following drug administration/infusion. The retention of paclitaxel within cells likely is another factor contributing to the efficacy of the drugs. Overall, the new understanding of Taxol/paclitaxel killing mechanism-rigid microtubule-induced multiple micronucleation-will likely provide new strategies to overcome drug resistance and for rational drug combination.