A phase II study of milataxel: a novel taxane analogue in previously treated patients with advanced colorectal cancer

Paclitaxel and its semi-synthetic derivatives: comprehensive insights into chemical structure, mechanisms of action, and anticancer properties

Cancer is a disease that can cause abnormal cell growth and can spread throughout the body. It is among the most significant causes of death worldwide, resulting in approx. 10 million deaths annually. Many synthetic anticancer drugs are available, but they often come with side effects and can interact negatively with other medications. Additionally, many chemotherapy drugs used for cancer treatment can develop resistance and harm normal cells, leading to dose-limiting side effects. As a result, finding effective cancer treatments and developing new drugs remains a significant challenge. However, plants are a potent source of natural products with the potential for cancer treatment. These biologically active compounds may be the basis for enhanced or less toxic derivatives. Herbal medicines/phytomedicines, or plant-based drugs, are becoming more popular in treating complicated diseases like cancer due to their effectiveness and are a particularly attractive option due to their affordability, availability, and lack of serious side effects. They have broad applicability and therapeutic efficacy, which has spurred scientific research into their potential as anticancer agents. This review focuses on Paclitaxel (PTX), a plant-based drug derived from Taxus sp., and its ability to treat specific tumors. PTX and its derivatives are effective against various cancer cell lines. Researchers can use this detailed information to develop effective and affordable treatments for cancer.

The intravenous to oral switch of taxanes: strategies and current clinical developments

The taxanes paclitaxel, docetaxel and cabazitaxel are important anticancer agents that are widely used as intravenous treatment for several solid tumor types. Switching from intravenous to oral treatment can be more convenient for patients, improve cost-effectiveness and reduce the demands of chemotherapy treatment on hospital care. However, oral treatment with taxanes is challenging because of pharmaceutical and pharmacological factors that lead to low oral bioavailability. This review summarizes the current clinical developments in oral taxane treatment. Intravenous parent drugs, strategies in the oral switch, individual agents in clinical trials, challenges and further perspectives on treatment with oral taxanes are subsequently discussed.

Phytochemical-Based Nanomedicine for Advanced Cancer Theranostics: Perspectives on Clinical Trials to Clinical Use

In the current chapter, a new strategic compilation of phytochemicals with potent antitumor properties has been addressed, most importantly focusing on cell cycle arrest and apoptotic signaling mechanism. A promising approach in tumor prevention is to eliminate cancer cells preferably via cell cycle arrest and programmed cell death with lesser harm to neighboring normal cells. Cancer cells have a survival advantage to escape apoptosis and relentlessly divide to proliferate, gearing up the cell cycle process. Recently, the use of phytochemical-derived conjugated chemotherapeutic agents has increased dramatically owing to its biocompatibility, low cytotoxicity, low resistance, and dynamic physiochemical properties discriminating normal cells in the treatment of various cancer types. For decades, biomedical investigations have targeted cell cycle and apoptotic cell death mechanism as an effective cancer-killing tool for systemically assessing the potential biological interactions of functional phytocompounds compared to its synthetic counterparts during their complete life cycles from entry, biodistribution, cellular/molecular interactions to excretion. Newly emerging nanotechnology application in anticancer drug formulations has revolutionized cancer therapy. Tissue-specific phyto-nanomedicine plays a vital role in advanced cancer diagnostics using liposome, micelle, and nanoparticles as a precise and effective delivery vehicle. This chapter specifically focuses on the therapeutic phytomolecules approved by the Food and Drug Administration (FDA, USA) along with phyto-chemopreventives currently on clinical trials (Phase-I/II/III/IV). Besides, detailed coverage is given to the FDA-approved nanotechnology-based formulations only in the areas of cancer theranostics via cell cycle arrest and apoptotic pathways including present challenges and future perspectives.

A systematic review of salvage therapies in refractory metastatic colorectal cancer

PURPOSE

Established that the only approved agents in previously treated metastatic colorectal cancer (CRC) are trifluoridine/tipiracil and regorafenib, we conducted a systematic review of all the published phase 2-3 trials, with the scope to evaluate the benefit of any later-line regimens in refractory metastatic CRC.

METHODS

Phase 2-3 studies that enrolled patients with stage IV disease receiving salvage therapies for refractory CRC were identified using electronic databases (Pubmed, EMBASE, and Cochrane Library). Clinical outcomes were pooled using a point estimates for the weighted values of median overall survival (OS), progression-free survival (PFS), response rate (ORR), stable disease rate (SD), and 6-month and 1-year OS.

RESULTS

Overall, 7556 patients were included from 67 studies (n = 70 arms). Overall, the pooled ORR and SD were 15.4% (95% CI 13-18%) and 36.9% (95% CI 33.5-40.6%). Median PFS, 6-month and 1-year OS, and median OS were 3.2 (95% CI 2.9-3.3) months, 65.4% (95% CI 61.9-68.8%), 36% (95% CI 32.3-39.9%) and 8.8 (95% CI 8.3-9.2) months. Overall survival was different in the monochemotherapy, polychemotherapy, chemotherapy + targeted therapy, and targeted therapy alone arms (7.6, 9.5, 10.3, and 7.9 months, respectively, P for difference = 0.01). Median PFS were respectively 2.3, 3.9, 3.8, and 2.6, respectively (P for difference < 0.01).

CONCLUSIONS

Overall, combination therapy (polychemotherapy with or without targeted agents) is associated with a higher control of disease and better outcome than approved agents. Treatment, if possible, should be personalized according to the patients' conditions, physician preference and molecular profile of disease.

Taxanes – The Backbone of Medical Oncology

Drug development in oncology has witnessed a revolutionary growth from its humble beginning with nitrogen mustard in 1940 to immunotherapy in 1986 (Interferon alpha). The arsenal of cytotoxics is ever increasing, contributing to better survival outcomes and improved quality of life. Over the years, many cytotoxics have fallen out of favor too, due to its side effects and availability of drugs with better efficacy and toxicity profile. Taxane, a microtubule stabilizing agent extracted from the poisonous Yew tree, was discovered in 1964 and came into clinical use in 1992 with its approval for ovarian cancer. This group has grown into a cornerstone of many treatment protocols, spanning multiple tumor types. This review discusses in brief the salient features of cytotoxic agents in this drug group, its history, physico-chemical properties, mechanism of action, pharmacodynamics, and pharmacokinetics. Though the benefits of taxanes are well understood, there are unique problems associated with the use of taxanes and there is an expanding literature on taxane resistance. We briefly look at the resistance mechanisms. There have been significant efforts to circumvent the problems related to conventional taxanes, with an attempt at creating newer carrier molecules and adjunct drugs with taxanes, which is slowly gaining traction in clinical practice.

Microtubule-stabilizing agents: New drug discovery and cancer therapy

Microtubule-stabilizing agents (MSAs) have been highly successful in the treatment of cancer in the past 20years. To date, three classes of MSAs have entered the clinical trial stage or have been approved for clinical anticancer chemotherapy, and more than 10 classes of novel structural MSAs have been derived from natural resources. The microtubule typically contains two MSA-binding sites: the taxoid site and the laulimalide/peloruside site. All defined MSAs are known to bind at either of these sites, with subtle but significant differences. MSAs with different binding sites may produce a synergistic effect. Although having been extensively applied in the clinical setting, paclitaxel and other approved MSAs still pose many challenges such as multidrug resistance, low bioavailability, poor solubility, high toxicity, and low passage through the blood-brain barrier. A variety of studies focus on the structure-activity relationship in order to improve the pharmaceutical properties of these agents. Here, the mechanisms of action, advancements in pharmacological research, and clinical developments of defined MSAs during the past decade are discussed. The latest discovered MSAs are also briefly introduced in this review. The increasing number of natural MSAs indicates the potential discovery of more novel, natural MSAs with different structural bases, which will further promote the development of anticancer chemotherapy.

Taxane anticancer agents: a patent perspective

INTRODUCTION

Paclitaxel and docetaxel were two epoch-making anticancer drugs and have been successfully used in chemotherapy for a variety of cancer types. In the year 2010, a new taxane, cabazitaxel, was approved by FDA for use in combination with prednisone for the treatment of metastatic hormone-refractory prostate cancer. Albumin-bound paclitaxel (nab™-paclitaxel; abraxane) nanodroplet formulation was another notable invention (FDA approval 2005 for refractory, metastatic, or relapsed breast cancer). Abraxane in combination with gemcitabine for the treatment of pancreatic cancer was approved by FDA in 2013. Accordingly, there have been a huge number of patent applications dealing with taxane anticancer agents in the last 5 years. Thus, it is a good time to review the progress in this area and find the next wave for new developments.

AREA COVERED

This review covers the patent literature from the year 2010 to early 2015 on various aspects of taxane-based chemotherapies and drug developments.

EXPERT OPINION

Three FDA-approved taxane anticancer drugs will continue to expand their therapeutic applications, especially through drug combinations and new formulations. Inspired by the success of abraxane, new nano-formulations are emerging. Highly potent new-generation taxanes will play a key role in the development of efficacious tumor-targeted drug delivery systems.

Anticancer Agents from Diverse Natural Sources

This review attempts to portray the discovery and development of anticancer agents/drugs from diverse natural sources. Natural molecules from these natural sources including plants, microbes and marine organisms have been the basis of treatment of human diseases since the ancient times. Compounds derived from nature have been important sources of new drugs and also serve as templates for synthetic modification. Many successful anti-cancer drugs currently in use are naturally derived or their analogues and many more are under clinical trials. This review aims to highlight the invaluable role that natural products have played, and continue to play, in the discovery of anticancer agents.

Tubulin: an example of targeted chemotherapy

Anticancer drugs directed against the microtubule, including taxanes and vinca alkaloids, have been the backbone of many chemotherapy regimes for decades. These drugs have, however, significant limitations, which have prompted the development of novel microtubule targeting agents (MTAs). This article will discuss MTAs for anticancer therapies and recent debates regarding their mechanisms of action. Furthermore, the limitations of taxanes, including hypersensitivity reactions, neurotoxicity, drug resistance and lack of validated biomarkers to guide therapy will be discussed, all of which have driven the development of novel agents. The mechanisms of action and drug development of new generations of MTAs will also be outlined. Agents demonstrating utility in Phase III clinical trials, including eribulin, ixabepilone, cabazitaxel and trastuzumab-DM1 will be highlighted, as well as novel agents currently in development and future directions for MTAs.

Novel oral taxane therapies: recent Phase I results

The oral taxanes are analogues of existing taxanes with a possible broad range of antitumor activity. They also have the potential advantages of ease of administration, better efficacy and lesser toxicity than currently available taxanes. These drugs have been used in several Phase I clinical trials, the methodology and results of which will be reviewed here.

Overcoming tumor multidrug resistance using drugs able to evade P-glycoprotein or to exploit its expression

Multidrug resistance (MDR) is a major obstacle to the effective treatment of cancer. Cellular overproduction of P-glycoprotein (P-gp), which acts as an efflux pump for various anticancer drugs (e.g. anthracyclines, Vinca alkaloids, taxanes, epipodophyllotoxins, and some of the newer antitumor drugs) is one of the more relevant mechanisms underlying MDR. P-gp belongs to the superfamily of ATP-binding cassette transporters and is encoded by the ABCB1 gene. Its overexpression in cancer cells has become a therapeutic target for circumventing MDR. As an alternative to the classical pharmacological strategy of the coadministration of pump inhibitors and cytotoxic substrates of P-gp and to other approaches applied in experimental tumor models (e.g. P-gp-targeting antibodies, ABCB1 gene silencing strategies, and transcriptional modulators) and in the clinical setting (e.g. incapsulation of P-gp substrate anticancer drugs into liposomes or nanoparticles), a more intriguing strategy for circumventing MDR is represented by the development of new anticancer drugs which are not substrates of P-gp (e.g. epothilones, second- and third-generation taxanes and other microtubule modulators, topoisomerase inhibitors). Some of these drugs have already been tested in clinical trials and, in most of cases, show relevant activity in patients previously treated with anticancer agents which are substrates of P-gp. Of these drugs, ixabepilone, an epothilone, was approved in the United States for the treatment of breast cancer patients pretreated with an anthracycline and a taxane. Another innovative approach is the use of molecules whose activity takes advantage of the overexpression of P-gp. The possibility of overcoming MDR using the latter two approaches is reviewed herein. 

Microtubule-binding agents: a dynamic field of cancer therapeutics

Microtubules are dynamic filamentous cytoskeletal proteins composed of tubulin and are an important therapeutic target in tumour cells. Agents that bind to microtubules have been part of the pharmacopoeia of anticancer therapy for decades and until the advent of targeted therapy, microtubules were the only alternative to DNA as a therapeutic target in cancer. The screening of a range of botanical species and marine organisms has yielded promising new antitubulin agents with novel properties. In the current search for novel microtubule-binding agents, enhanced tumour specificity, reduced neurotoxicity and insensitivity to chemoresistance mechanisms are the three main objectives.

Tubulin-interactive natural products as anticancer agents

This review provides an overview of the discovery, structures, and biological activities of anticancer natural products that act by inhibiting or promoting the assembly of tubulin to microtubules. The emphasis is on providing recent information on those compounds in clinical use or in advanced clinical trials. The vinca alkaloids, the combretastatins, NPI-2358, the halichondrin B analogue eribulin, dolastatin 10, noscapine, hemiasterlin, and rhizoxin are discussed as tubulin polymerization inhibitors, while the taxanes and the epothilones are the major classes of tubulin polymerization promoters presented, with brief treatments of discodermolide, eleutherobin, and laulimalide. The challenges and future directions of tubulin-interactive natural products-based drug discovery programs are also discussed briefly.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.