Irinotecan: a new antineoplastic agent for the management of colorectal cancer

A Stable Irinotecan Liposome with Enhanced Antitumor Activity in a Range of Tumor Models

PURPOSE

This study aimed to prepare a stable irinotecan liposome (CPT-11 liposome) and evaluate its antitumor efficacy in a range of tumor models.

METHODS

CPT-11 liposome was prepared with a Z-average particle size of 110 ~ 120 nm and high entrapment efficiency (> 95%) and had a good stability within 18 months. Then the antitumor efficacy was studied in human colon (Ls-174t), gastric (NCI-N87), pancreatic (BxPC-3) and small cell lung (NCI-H526) cancer xenograft models. The toxicity of high-dose CPT-11 liposome was also evaluated in Beagle dogs.

RESULTS

The results showed that the anti-tumor effects of CPT-11 liposome were markedly superior (at least 10 times higher) to those of the CPT-11 injection group in all four xenograft models. The tissue distribution test in the Ls-174t model further demonstrated that the CPT-11 liposome could alter the plasma and tissue distribution of CPT-11, increase the exposure level of its active metabolite SN-38 in tumor, and ultimately improve antitumor efficiency. Meanwhile, CPT-11 liposome showed a much less toxicity than CPT-11 injection in beagle dogs.

CONCLUSIONS

Overall, the CPT-11 liposome may be developed as a new clinical alternative for the cancer patients.

A "Trojan Horse" Strategy: The Preparation of Bile Acid-Modifying Irinotecan Hydrochloride Nanoliposomes for Liver-Targeted Anticancer Drug Delivery System Study

The bile acid transport system is a natural physiological cycling process between the liver and the small intestine, occurring approximately 6-15 times during the day. There are various bile acid transporter proteins on hepatocytes that specifically recognize bile acids for transport. Therefore, in this paper, a novel liposome, cholic acid-modified irinotecan hydrochloride liposomes (named CA-CPT-11-Lip), was prepared based on the "Trojan horse" strategy. The liposomes preparation process was optimized, and some important quality indicators were investigated. The distribution of irinotecan hydrochloride in mice was then analyzed by high-performance liquid chromatography (HPLC), and the toxicity of liposomes to hepatocellular carcinoma cells (HepG-2) was evaluated in vitro. As a result, CA-CPT-11-Lip was successfully prepared. It was spherical with a particle size of 154.16 ± 4.92 nm, and the drug loading and encapsulation efficiency were 3.72 ± 0.04% and 82.04 ± 1.38%, respectively. Compared with the conventional liposomes (without cholic acid modification, named CPT-11-Lip), CA-CPT-11-Lip had a smaller particle size and higher encapsulation efficiency, and the drug accumulation in the liver was more efficient, enhancing the anti-hepatocellular carcinoma activity of irinotecan hydrochloride. The novel nanoliposome modified by cholic acid may help to expand the application of irinotecan hydrochloride in the treatment of hepatocellular carcinoma and construct the drug delivery system mode of drug liver targeting.

Design, synthesis and molecular docking studies of thymol based 1,2,3-triazole hybrids as thymidylate synthase inhibitors and apoptosis inducers against breast cancer cells

Natural product produced by plants has been the backbone for numerous anticancer agents. In the present work, natural bioactive thymol based 1,2,3-triazole hybrids have been synthesized and evaluated for anticancer activity in MCF-7 and MDA-MB-231 cancer cells. The synthesized molecules displayed desired pharmacokinetic predictions for an orally available drug. Among the synthesized hybrids, compound 4-((2-isopropyl-5-methylphenoxy)methyl)-1-o-tolyl-1H-1,2,3-triazole (10) was the most potent (IC₅₀ 6.17 μM) showing comparable cytotoxity to tamoxifen (IC₅₀ 5.62 μM) and 3.2 fold inhibition to 5-fluorouracil (IC₅₀ 20.09 μM) against MCF-7 cancer cells. Whereas against MDA-MB-231 cancer cells, compound 10 (IC₅₀ 10.52 μM) and 3-(4-((2-isopropyl-5-methylphenoxy)methyl)-1H-1,2,3-triazol-1-yl)benzoic acid (12) (IC₅₀ 11.41 μM) displayed 1.42 and 1.3 fold inhibition, respectively to tamoxifen (IC₅₀ 15.01 μM) whereas 2.4 fold and 2.2 activity to 5-Florouracil (IC₅₀ 25.31 μM). Furthermore, 10 and 12 significantly inhibited thymidylate synthase enzyme with 2.4 and 1.26 fold activity to standard drug, Pemetrexed (IC₅₀ 5.39 μM) suggesting their mode of action as thymidylate synthase inhibitors. Cell cycle arrest and annexin V induced apoptosis study of compound 10 showed cell cycle arrest at the G2/M phase and induction of apoptosis in MCF-7 cells. The molecular docking was accomplished onto thymidylate synthase (TS) protein. The active compounds exhibited promising binding interactions and binding affinities into active sites. Finally, density functional theory (DFT) calculations including chemical reactivity and molecular electrostatic potential (MEP) have been performed to confirm the data obtained from docking and biological experiments. The results from this study inferred that compound 10 could be served as a lead molecule for the treatment of breast cancer.

Current Perspectives in the Application of Medicinal Plants Against Cancer: Novel Therapeutic Agents

Background:

Cancer is a disease characterized by uncontrolled cell growth and proliferation. It has become a major health problem in the past decades and is now the second leading cause of death globally. Although, there are different types of treatment such as chemotherapy, immune therapy, radiation, hormone therapy and targeted therapy used against cancer, they have possible side effects and significant deficiencies.

Methods:

This review aims to outline the benefits of medicinal plants and plant-derived products and highlight why they should be used as novel anti-cancer therapeutics. Electronic databases, including PubMed, Scopus, ScienceDirect, Cochrane library, and MedlinePlus were searched to summarize in vitro, in vivo and clinical studies on anticancer effects of medicinal plants and their bioactive compounds up-to-date.

Results:

In recent years, a number of medicinal plants have been administered to cancer patients in order to prevent and treat cancer as an alternative therapy. These plants were used because of their rich anticarcinogenic and chemoprotective potentials. In addition to these remarkable properties, these plants have less toxic anticancer, anti-tumor and anti-proliferation agents than traditional therapeutics. Nevertheless, only a small number of natural anti-tumor products including vinblastine, vincristine, podophyllotoxin, paclitaxel (Taxol) and camptothecin have been tested clinically, while vinflunine ditartrate, anhydrovinblastine, NK-611, tafluposide, paclitaxel poliglumex, combretastatins, salvicine, curcumin, indirubin, triptolide, homoharringtonine are still on trial.

Conclusion:

Consequently, more effective anticancer compounds are identified during the clinical trials; these natural products could be a key source of antitumor agents in modern anticancer therapy. It is expected that novel anticancer phytopharmaceuticals produced from medicinal plants could be effectively used in prevention and therapy for the cancers.

Significance of Kampo, traditional Japanese medicine, in supportive care of cancer patients

The current standard treatment for cancer is a multidisciplinary therapy whereby various types of treatment are properly combined. Chemotherapy with multiple anticancer drugs is now common, and traditional, complementary, and alternative therapies are adopted as supportive measures. Medical care in Japan is distinguished by the ability for patients to access both Western and Kampo medical cares at the same time. There is a high degree of trust in the safety of Kampo therapies because they are practiced by medical doctors who are educated with fundamental diagnosis of Western medicine. Highly reliable clinical studies are being published, demonstrating that palliative or supportive care for cancer patients using Kampo preparations alleviates adverse effects of chemotherapy or radiotherapy. This paper reports the circumstances around cancer care in Japan where traditional therapeutic Kampo formulas are used for patients undergoing cancer treatment with cutting-edge chemotherapy, specifically to alleviate adverse effects of anticancer drugs.

High antimetastatic efficacy of MEN4901/T-0128, a novel camptothecin carboxymethyldextran conjugate

The antimetastatic activity of a novel camptothecan conjugate, MEN4901/T-0128, in which 7-ethyl-10-aminopropyloxy-camptothecin (T-2513) is bound to a biodegradable carboxymethyldextran via a Gly-Gly-Gly linker, was observed in this study. High antimetastatic activity of MEN4901/T-0128 was demonstrated in a clinically-relevant orthotopic mouse model of human colon cancer. MEN4901/T-0128 and irinotecan were compared for anti-metastatic activity as well as efficacy against the primary tumor. An imageable, metastatic model was made by surgical orthotopic implantation (SOI) of the green fluorescent protein (GFP)-expressing HT-29 tumor in nude mice. MEN4901/T-0128 and irinotecan were administered intravenously at various doses and schedules. MEN4901/T-0128, with treatment beginning on d 49 after SOI, was highly effective on lymph node metastasis as well as against the primary tumor. Both GFP imaging and histology demonstrated a markedly lower metastatic incidence of lymph nodes in all MEN4901/T-0128 treated mice compared with irinotecan-treated and untreated mice. At the most efficacious dose of MEN4901/T-0128, only 1 of 12 animals had lymph node metastasis compared with 19 of 20 in the control group. The present study demonstrates the principle that when a camptothecan is conjugated to an appropriate polymer, the drug can become extremely effective with important clinical potential for antimetastatic therapy, a most urgent need.

Single nucleotide polymorphism in ABCG2 is associated with irinotecan-induced severe myelosuppression

Irinotecan is an anti-neoplastic agent that is widely used for treating colorectal and lung cancers, but often causes toxicities such as severe myelosuppression and diarrhea. In this study, we performed a two-stage case-control association study for irinotecan-induced severe myelosuppression (grades 3 and 4). In the first stage, 23 patients who developed severe myelosuppression and 58 patients who did not develop any toxicity were examined for 170 single nucleotide polymorphisms (SNPs) in 14 genes involved in the metabolism and transport of irinotecan. A total of five SNPs were identified to show the possible association with severe myelosuppression (P(Fisher)<0.01) and were further examined in 7 cases and 20 controls in the second stage of the study. An intronic SNP, rs2622604, in ABCG2 showed P(Fisher)=0.0419 in the second stage and indicated a significant association with severe myelosuppression in the combined study (P(Fisher)=0.000237; P(Corrected)=0.036). Although only limited subjects were investigated, our results suggested that a genetic polymorphism in ABCG2 might alter the transport activity for the drug and elevate the systemic circulation level of irinotecan, leading to severe myelosuppression.

Natural products as leads to anticancer drugs

Throughout history, natural products have afforded a rich source of compounds that have found many applications in the fields of medicine, pharmacy and biology. Within the sphere of cancer, a number of important new commercialised drugs have been obtained from natural sources, by structural modification of natural compounds, or by the synthesis of new compounds, designed following a natural compound as model. The search for improved cytotoxic agents continues to be an important line in the discovery of modern anticancer drugs. The huge structural diversity of natural compounds and their bioactivity potential have meant that several products isolated from plants, marine flora and microorganisms can serve as "lead" compounds for improvement of their therapeutic potential by molecular modification. Additionally, semisynthesis processes of new compounds, obtained by molecular modification of the functional groups of lead compounds, are able to generate structural analogues with greater pharmacological activity and with fewer side effects. These processes, complemented with high-throughput screening protocols, combinatorial chemistry, computational chemistry and bioinformatics are able to afford compounds that are far more efficient than those currently used in clinical practice. Combinatorial biosynthesis is also applied for the modification of natural microbial products. Likewise, advances in genomics and the advent of biotechnology have improved both the discovery and production of new natural compounds.

Camptothecin and podophyllotoxin derivatives: inhibitors of topoisomerase I and II - mechanisms of action, pharmacokinetics and toxicity profile

Camptothecins represent an established class of effective agents that selectively target topoisomerase I by trapping the catalytic intermediate of the topoisomerase I-DNA reaction, the cleavage complex. The water-soluble salt camptothecin-sodium - introduced in early trials in the 1960s - was highly toxic in animals, whereas the semisynthetic derivatives irinotecan and topotecan did not cause haemorrhagic cystitis because of their higher physicochemical stability and solubility at lower pH values. Myelosuppression, neutropenia and, to a lesser extent, thrombocytopenia are dose-limiting toxic effects of topotecan. In contrast to the structurally-related topotecan, irinotecan is a prodrug which has to be converted to SN-38, its active form. SN-38 is inactivated by conjugation, thus patients with Gilbert's syndrome and other forms of genetic glucuronidation deficiency are at an increased risk of irinotecan-induced adverse effects, such as neutropenia and diarrhoea. The cytotoxic mechanism of podophyllotoxin is the inhibition of topoisomerase II. Common adverse effects of etoposide include dose-limiting myelosuppression. Hypersensitivity reactions are more common with etoposide and teniposide than with etoposide phosphate because the formulations of the former contain sensitising solubilisers. Leukopenia and thrombocytopenia occur in 65% and 80%, respectively, of patients after administration of conventional doses of teniposide. Anorexia, vomiting and diarrhoea are generally of mild severity after administration of conventional doses of topoisomerase II inhibitors. Clinical pharmacokinetic studies have revealed substantial interindividual variabilities regarding the area under the concentration-time curve values and steady-state concentrations for all drugs reviewed in this article. Irinotecan, etoposide and teniposide are degraded via complex metabolic pathways. In contrast, topotecan primarily undergoes renal excretion. Regarding etoposide and teniposide, the extent of catechol formation over time during drug metabolism may be associated with a higher risk for secondary malignancies.

Pharmacogenetics of uridine diphosphoglucuronosyltransferase (UGT) 1A family members and its role in patient response to irinotecan

Glucuronidation, catalyzed by the glucuronosyltransferase (UGT) superfamily, is a major biotransformation pathway for several drugs, including irinotecan. Irinotecan is commonly used in colorectal cancer chemotherapy. Irinotecan undergoes metabolism in humans and is converted to its active metabolite SN-38, a topoisomerase I inhibitor. SN-38 is inactivated via glucuronidation catalyzed by various hepatic and extrahepatic UGT1A isozymes. Although the role of the UGT1A1 *28 genetic variant has received much attention in altered toxicity upon irinotecan treatment, other UGT1A enzymes also play an important role. This review summarizes pharmacokinetic, toxicologic, and pharmacogenetic studies carried out to date in irinotecan and SN-38 disposition.

Effect of pH and human serum albumin on the cytotoxicity of a glucuronide prodrug of 9-aminocamptothecin

PURPOSE

9-aminocamptothecin glucuronide (9ACG) is a prodrug of 9-aminocamptothecin (9AC) that displays potent antitumor activity against human tumor xenografts in nude mice. Camptothecins exist in a pH dependent equilibrium between active lactone and inactive carboxy forms that can be altered by binding to human serum albumin (HSA). Here we investigated the influence of pH and HSA on the lactone-carboxy equilibrium, HSA binding, and cytotoxicity of 9ACG.

METHODS

Microfiltration and HPLC were used to measure the influence of pH on lactone to carboxy conversion and HSA binding of 9ACG as compared to other camptothecins. In vitro cytotoxicity of drugs was determined against EJ human bladder carcinoma cells and CL1-5 human lung cancer cells.

RESULTS

The rate of lactone to carboxy conversion was similar for 9ACG and 9AC. Decreasing the pH from 7.6 to 6.0 increased the equilibrium levels of the lactone forms of the drugs from 20 to almost 95% of total drug. HSA moderately diminished the amount of free 9ACG lactone but did not change the ratio of 9ACG lactone to 9ACG carboxy. Consistent with the effect of pH on lactone levels, lowering the pH of EJ human bladder carcinoma cells from 7.6 to 6.8 decreased the IC(50) of 9ACG from 480 to 98 nM and 9AC from 33 to 12 nM. Activation of 9ACG by human beta-glucuronidase anchored on the surface of EJ cells further decreased its IC(50) value to 26 nM. Although HSA significantly decreased the cytotoxicity of 9AC and 9ACG, activation of 9ACG at cancer cells with an antibody-beta-glucuronidase immunoconjugate produced greater cytotoxicity than 9AC.

CONCLUSIONS

Acidification and targeted delivery of beta-glucuronidase can enhance 9ACG cytotoxicity even in the presence of HSA.

Enhanced therapeutic efficacy of a novel liposome-based formulation of SN-38 against human tumor models in SCID mice

SN-38 is an active metabolite of CPT-11. The poor solubility of SN-38 in any pharmaceutically acceptable solvent and pH-dependent activity has limited its clinical use. Our objective was to evaluate an easy-to-use liposome-based formulation of SN-38 (LE-SN38) and compare the antitumor activity with its pro-drug CPT-11 against cancer cell lines and human xenograft tumor models. The cytotoxicity of LE-SN38 and CPT-11 was determined in four human cancer cell lines using the sulforhodamine B assay. The therapeutic efficacy was tested against human colon (HT-29) and breast (MX-1) xenograft tumor models in SCID mice. LE-SN38 with greater than 95% drug entrapment was found to be highly cytotoxic against four different cell lines with GI50 values of less than 0.1 microM. In the HT-29 tumor model, LE-SN38 (q x d5) at 2, 4 or 8 mg/kg resulted in 33, 81 and 91% tumor growth inhibition, respectively, compared to the drug-free liposome group. In contrast, similar dose levels of CPT-11 treatment led to only 2, 36 and 46% growth inhibition. For the MX-1 model, LE-SN38 (q x d5) regressed tumor growth by 44 and 88% at 4 and 8 mg/kg dose, respectively, whereas no regression was observed in the CPT-11-treated group. We conclude that LE-SN38 is a novel liposome-based formulation with enhanced therapeutic efficacy against human tumor models.

Stability of the new prodrug 9-aminocamptothecin glucuronide (9ACG) in the presence of human serum albumin

9-aminocamptothecin glucuronide (9ACG) is a new water-soluble prodrug of 9-aminocamptothecin (9AC) that is a substrate for beta-glucuronidase and displays potent antitumor activity against human tumor xenografts. The lactone ring of camptothecins (CPTs) is required for antitumor activity but spontaneously opens under physiological conditions to an inactive carboxy form. The carboxy form of many CPTs, including 9AC, preferentially binds to human serum albumin (HSA), which further reduces the equilibrium amount of active lactone and greatly decreases antitumor efficacy. In this study, we examined the hypothesis that the unique structure of 9ACG might alter prodrug interaction with HSA and increase 9ACG lactone stability as compared with 9AC. HPLC analysis revealed that HSA did not affect the equilibrium level of 9ACG lactone whereas both CPT lactone and 9AC lactone were greatly reduced in the presence of HSA as compared to their equilibrium levels in PBS. Similar results were found in human serum and whole blood. The lactone ring of 9ACG also opened more slowly (t(1/2)=50 min) as compared with 9AC (t(1/2)=20 min) in the presence of HSA. Both 9ACG lactone and 9ACG carboxy bound HSA with similar affinities (K(D) approximately 4.5 x 10(-5)M(-1)). Binding of 9ACG to HSA reduced prodrug toxicity to cancer cells by about 10-fold in vitro. Injection of HSA into nude mice prolonged the half-life of 9ACG by about 3-fold, indicating that albumin-bound 9ACG lactone may act as a depot of active prodrug in vivo. Our results suggests that in contrast to CPT and 9AC, HSA does not appear to adversely affect 9ACG and may enhance the selective antitumor activity of 9ACG in tumors that contain beta-glucuronidase.

This CE is published through an unrestricted educational grant from Bristol-Myers Squibb

Credit

This lesson is good for 0.2 CE units, with a passing grade of 70%.

Goal

The goal of this program is to inform the participant about common types of malignant gliomas and to discuss new treatment modalities.

Objectives

At the completion of this program the participant will be able to: 1. Identify the standard types of treatment for primary brain tumors 2. Explain the pharmacology of temozolomide and irinotecan 3. List the most common adverse effects associated with temozolomide and irinotecan 4. Determine appropriate monitoring and provide dosing adjustments