The camptothecins

Perspectives on biologically active camptothecin derivatives

Camptothecins (CPTs) are cytotoxic natural alkaloids that specifically target DNA topoisomerase I. Research on CPTs has undergone a significant evolution from the initial discovery of CPT in the late 1960s through the study of synthetic small-molecule derivatives to investigation of macromolecular constructs and formulations. Over the past years, intensive medicinal chemistry efforts have generated numerous CPT derivatives. Three derivatives, topotecan, irinotecan, and belotecan, are currently prescribed as anticancer drugs, and several related compounds are now in clinical trials. Interest in other biological effects, besides anticancer activity, of CPTs is also growing exponentially, as indicated by the large number of publications on the subject during the last decades. Therefore, the main focus of the present review is to provide an ample but condensed overview on various biological activities of CPT derivatives, in addition to continued up-to-date coverage of anticancer effects.

Compartmentalized accumulation of cAMP near complexes of multidrug resistance protein 4 (MRP4) and cystic fibrosis transmembrane conductance regulator (CFTR) contributes to drug-induced diarrhea

Diarrhea is one of the most common adverse side effects observed in ∼7% of individuals consuming Food and Drug Administration (FDA)-approved drugs. The mechanism of how these drugs alter fluid secretion in the gut and induce diarrhea is not clearly understood. Several drugs are either substrates or inhibitors of multidrug resistance protein 4 (MRP4), such as the anti-colon cancer drug irinotecan and an anti-retroviral used to treat HIV infection, 3'-azido-3'-deoxythymidine (AZT). These drugs activate cystic fibrosis transmembrane conductance regulator (CFTR)-mediated fluid secretion by inhibiting MRP4-mediated cAMP efflux. Binding of drugs to MRP4 augments the formation of MRP4-CFTR-containing macromolecular complexes that is mediated via scaffolding protein PDZK1. Importantly, HIV patients on AZT treatment demonstrate augmented MRP4-CFTR complex formation in the colon, which defines a novel paradigm of drug-induced diarrhea.

A phase II study of weekly irinotecan in patients with locally advanced or metastatic HER2- negative breast cancer and increased copy numbers of the topoisomerase 1 (TOP1) gene: a study protocol

Background

About 20% of patients with primary breast cancer develop metastatic disease during the course of the disease. At this point the disease is considered incurable and thus treatment is aimed at palliation and life prolongation. As many patients will have received both an anthracycline and a taxane in the adjuvant setting, treatment options for metastatic breast cancer are limited. Furthermore response rates for the most commonly used drugs range from around 30% to 12% . Thus new treatment options are needed and preferably coupled to biomarkers predictive of response. Irinotecan is a topoisomerase 1 inhibitor used for decades for the treatment of colorectal cancer. Four studies have investigated the efficacy of irinotecan monotherapy in breast cancer and all have included non-biomarker selected patients. In these studies response rates for irinotecan ranged from 5%-23% and are thus comparable to response rates obtained with drugs commonly used in the metastatic setting. If a predictive biomarker could be identified for irinotecan, response rates might be even higher.

Methods/Design

This multi-centre phase II single arm trial was designed to investigate if patients with metastatic breast cancer and increased expression of the topoisomerase 1 gene have a high likelihood of obtaining a clinical benefit from treatment with irinotecan. Trial recruitment is two-staged as 19 patients are planned to participate in the first part. If less than 7 patients have clinical benefit the trial stops, if more than 7 patients have clinical benefit a total of 40 patients will be included.

Discussion

This ongoing trial is the first to prospectively test copy number of the topoisomerase I gene as a predictive biomarker of response to irinotecan.

Trial registration

EudraCT number 2012-002348-26.

RECQL5 is an important determinant for camptothecin tolerance in human colorectal cancer cells

CPTs (camptothecins) are an important class of effective anticancer agents that target type I topoisomerase in humans. Irinotecan and topotecan are currently used to treat various types of cancers and many CPT derivatives are being developed. However, these drugs are only effective in a small percentage of each type of cancer and the molecular underpinning for this individualized response to the drug has remained elusive. Thus, identification of the main determinants for cell survival in response to this unique class of drug should help to improve their clinical applications. In the present study, we examined whether RECQL5 constitutes an important determinant of CPT resistance in colon cancer cells. Specifically, RECQL5-deficient derivatives of both DDL1 and HCT116 cells, two colorectal cancer cell lines were generated by adenovirus-based somatic gene-targeting experiments and the CPT sensitivity between the RECQL5-proficient parental lines and their corresponding RECQL5-deficient derivatives were examined. We found that deletion of RECQL5 from DDL1 and HCT116 cells both resulted in a significant enhancement in CPT sensitivity under in vitro culture conditions. More importantly, xenograft tumours derived from RECQL5-deficient HCT116 cells, but not those from the parental line, could be cured by a CPT-based therapy in nude mice. Thus, the present study has identified RECQL5 as a major determinant for CPT resistance in colorectal cancer cells and a potential candidate as a biomarker for irinotecan-based treatment for colon cancer.

Anti-proliferative activity of the combination of salan Ti(iv) complexes with other organic and inorganic anticancer drugs against HT-29 and NCI-H1229 cells: synergism with cisplatin

Cytotoxic salan Ti(iv) complex demonstrated synergism with cisplatin in vitro toward human colon and lung cancer cells at various ratios.

A pH-sensitive nanocarrier for co-delivery of doxorubicin and camptothecin to enhance chemotherapeutic efficacy and overcome multidrug resistance in vitro

A pH-sensitive drug delivery system of HSNPs sealed with ZnO QDs nanocarrier, where the HSNPs have the large hollow interiors for delivering hydrophobic camptothecin and the mesoporous structure for delivering hydrophilic doxorubicin.

A polyphosphoester-conjugated camptothecin prodrug with disulfide linkage for potent reduction-triggered drug delivery

A reduction-cleavable polyphosphoester-camptothecin (CPT) prodrug tailored for enhancing drug loading content and triggering drug release has been prepared and applied in tumor chemotherapy.

Tumor-targeted co-delivery of mitomycin C and 10-hydroxycamptothecin via micellar nanocarriers for enhanced anticancer efficacy

Polymer–lipid hybrid micelles co-delivered hydrophilic mitomycin C and hydrophobic 10-hydroxycamptothecin showed improved cellular uptake and cytotoxicity in vitro and enhanced tumor accumulation and antitumor activity in vivo.

The self-assembly of anticancer camptothecin-dipeptide nanotubes: a minimalistic and high drug loading approach to increased efficacy

20-(S)-Camptothecin (CPT)-conjugated dipeptides are reported that preassemble into nanotubes with diameters ranging from 80-120 nm. These nanoassemblies maintain a high (∼47 %) drug loading and exhibit greater drug stability (i.e., resistance to lactone hydrolysis), and consequently greater efficacy against several human cancer cells (HT-29, A549, H460, and H23) in vitro compared with the clinically used prodrug irinotecan. A key and defining feature of this system is the use of the CPT-conjugated dipeptide as both the drug and precursor to the nanostructured carrier, which simplifies the overall fabrication process.

α-Tocopherol mediated amelioration of camptothecin-induced free radical damage to avert cardiotoxicities

Reactive oxygen species (ROS) such as O2(-), hydrogen peroxide, and OH(-) are highly toxic to cells. Cellular antioxidant enzymes and free radical scavengers normally protect a cell from toxic effects of ROS. However, when generation of ROS overtakes the antioxidant defense of the cells, it leads to various pathological conditions. The present study investigated the protective efficacy of α-tocopherol on the peroxidative damage and abnormal antioxidant levels in the myocardial tissue of camptothecin (CPT), administered at the dosage of 6 mg/kg/day in male Wistar rats. CPT-administered rats showed significant increase (p < 0.001) in lipid peroxidation and abnormal changes in the activities/levels of antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase, glutathione S-transferase) and nonenzymic antioxidants (reduced glutathione and vitamin E). Alterations in the levels of tissue alkaline phosphatase, lactate dehydrogenase (p < 0.01), alanine transaminase (p < 0.001), and aspartate transaminase (p < 0.001) were also observed in CPT-treated rats. In contrast, rats pretreated with α-tocopherol showed significant revision of elevated levels of lipid peroxides and abnormal antioxidant enzyme activity suggesting the ameliorative property of vitamin E. Histopathological alterations in the heart tissue observed after CPT administration were also protected in animals that were pretreated with vitamin E. Based on our results, we conclude that supplementation of vitamin E may improve the efficacy of standard and experimental cancer therapies by subsiding the toxic effect of the antineoplastic agent.

Development and evaluation of magnetic microemulsion: tool for targeted delivery of camptothecin to BALB/c mice-bearing breast cancer

PURPOSE

Development and evaluation of camptothecin-loaded-microemulsion (ME) and -magnetic microemulsion (MME) for passive/active-targeted delivery to BALB/c mice-bearing breast cancer.

METHODS

Based on the pseudo-ternary phase diagrams camptothecin-loaded-MEs and -MMEs were developed using benzyl alcohol:Captex 300 (3:1), TPGS:Tween 80 (2:1) and water. Furthermore, characterized for their droplet size distribution, magnetic susceptibility and effect of droplet size in plasma and evaluated for in vitro and in vivo targeting potential, drug release, haemolytic potential, cytotoxicity, genotoxicity, in vivo biodistribution and lactone ring stability.

RESULTS

Drug-loaded MEs showed uniform droplet distribution, extended drug release (76.07 ± 4.30% at 24 h), acceptable level of haemolytic activity (<20%), significant cytotoxicity (129 ± 3.9 ng/mL) against MCF-7 cancer cells and low DNA damage in lymphocytes. Targeting potential of MMEs was documented in 4T1 breast cancer-induced BALB/c mice. MMEs were concentrated more at the target tissue on introduction of external magnetic field. In vivo biodistribution study documented the active targeting of 5067.56 ± 354.72 ng/gm and passive targeting of 1677.58 ± 134.20 ng/gm camptothecin to breast cancer from MME and ME, respectively. Lactone stability study shows around 80% of the lactone stable at 24 h.

CONCLUSIONS

Developed ME and MME may act as a promising nanocarrier for efficient targeting of breast cancer tissues.

Cancer-cell-targeted theranostic cubosomes

This work was devoted to the development of a new type of lipid-based (cubosome) theranostic nanoparticle able to simultaneously host camptothecin, a potent anticancer drug, and a squarain-based NIR-emitting fluorescent probe. Furthermore, to confer targeting abilities on these nanoparticles, they were dispersed using mixtures of Pluronic F108 and folate-conjugated Pluronic F108 in appropriate ratios. The physicochemical characterization, performed via SAXS, DLS, and cryo-TEM techniques, proved that aqueous dispersions of such cubosomes can be effectively prepared, while the photophysical characterization demonstrated that these nanoparticles may be used for in vivo imaging purposes. The superior ability of these innovative nanoparticles in targeting cancer cells was emphasized by investigating the lipid droplet alterations induced in HeLa cells upon exposure to targeted and nontargeted cubosomes.

B-ring-aryl substituted luotonin A analogues with a new binding mode to the topoisomerase 1-DNA complex show enhanced cytotoxic activity

Topoisomerase 1 inhibition is an important strategy in targeted cancer chemotherapy. The drugs currently in use acting on this enzyme belong to the family of the camptothecins, and suffer severe limitations because of their low stability, which is associated with the hydrolysis of the δ-lactone moiety in their E ring. Luotonin A is a natural camptothecin analogue that lacks this functional group and therefore shows a much-improved stability, but at the cost of a lower activity. Therefore, the development of luotonin A analogues with an increased potency is important for progress in this area. In the present paper, a small library of luotonin A analogues modified at their A and B rings was generated by cerium(IV) ammonium nitrate-catalyzed Friedländer reactions. All analogues showed an activity similar or higher than the natural luotonin A in terms of topoisomerase 1 inhibition and some compounds had an activity comparable to that of camptothecin. Furthermore, most compounds showed a better activity than luotonin A in cell cytotoxicity assays. In order to rationalize these results, the first docking studies of luotonin-topoisomerase 1-DNA ternary complexes were undertaken. Most compounds bound in a manner similar to luotonin A and to standard topoisomerase poisons such as topotecan but, interestingly, the two most promising analogues, bearing a 3,5-dimethylphenyl substituent at ring B, docked in a different orientation. This binding mode allows the hydrophobic moiety to be shielded from the aqueous environment by being buried between the deoxyribose belonging to the G(+1) guanine and Arg364 in the scissile strand and the surface of the protein and a hydrogen bond between the D-ring carbonyl and the basic amino acid. The discovery of this new binding mode and its associated higher inhibitory potency is a significant advance in the design of new topoisomerase 1 inhibitors.

A convergent synthetic platform for single-nanoparticle combination cancer therapy: ratiometric loading and controlled release of cisplatin, doxorubicin, and camptothecin

The synthesis of polymer therapeutics capable of controlled loading and synchronized release of multiple therapeutic agents remains a formidable challenge in drug delivery and synthetic polymer chemistry. Herein, we report the synthesis of polymer nanoparticles (NPs) that carry precise molar ratios of doxorubicin, camptothecin, and cisplatin. To our knowledge, this work provides the first example of orthogonally triggered release of three drugs from single NPs. The highly convergent synthetic approach opens the door to new NP-based combination therapies for cancer.

Nucleolar control of p53: a cellular Achilles' heel and a target for cancer therapy

Nucleoli perform a crucial cell function, ribosome biogenesis, and of critical relevance to the subject of this review, they are also extremely sensitive to cellular stresses, which can cause loss of function and/or associated structural disruption. In recent years, we have learned that cells take advantage of this stress sensitivity of nucleoli, using them as stress sensors. One major protein regulated by this role of nucleoli is the tumor suppressor p53, which is activated in response to diverse cellular injuries in order to exert its onco-protective effects. Here we discuss a model of nucleolar regulation of p53, which proposes that key steps in the promotion of p53 degradation by the ubiquitin ligase MDM2 occur in nucleoli, thus providing an explanation for the observed link between nucleolar disruption and p53 stability. We review current evidence for this compartmentalization in p53 homeostasis and highlight current limitations of the model. Interestingly, a number of current chemotherapeutic agents capable of inducing a p53 response are likely to do so by targeting nucleolar functions and these compounds may serve to inform further improved therapeutic targeting of nucleoli.

Phase I dosage finding and pharmacokinetic study of intravenous topotecan and oral erlotinib in adults with refractory solid tumors

PURPOSE

Topotecan is widely used for refractory solid tumors but multi-drug resistance may occur due to tumor expression of ATP-binding cassette (ABC) transporters. Since erlotinib, an inhibitor of the epidermal growth factor receptor, also inhibits several ABC transporters, we performed a phase I study to evaluate the safety, efficacy, and pharmacokinetics of intravenous topotecan given in combination with erlotinib.

METHODS

Patients received 150 mg of oral erlotinib daily and a 30 min intravenous infusion of topotecan on days 1-5 of a 21-day cycle. Dosage escalation of topotecan occurred with a starting dosage of 0.75 mg/m(2). The pharmacokinetics of topotecan was evaluated on day 1 of cycle 1 without erlotinib and on day 1 of cycle 2 or 3 with erlotinib.

RESULTS

Twenty-nine patients were enrolled. The maximum tolerated dosage was determined to be 1.0 mg/m(2). Dose-limiting toxicities included neutropenia and thrombocytopenia. The average duration of treatment was 97 days. Two partial responses were observed. Topotecan clearance and exposure were similar with and without erlotinib.

CONCLUSIONS

The combination of topotecan and erlotinib is tolerable at clinically effective doses. Erlotinib does not affect the disposition of topotecan to a clinically significant extent.

A “Ship in a Bottle” Strategy To Load a Hydrophilic Anticancer Drug in Porous Metal Organic Framework Nanoparticles: Efficient Encapsulation, Matrix Stabilization, and Photodelivery

An essential challenge in the development of nanosized metal organic framework (nanoMOF) materials in biomedicine is to develop a strategy to stabilize their supramolecular structure in biological media while being able to control drug encapsulation and release. We have developed a method to efficiently encapsulate topotecan (TPT, 1), an important cytotoxic drug, in biodegradable nanoMOFs. Once inside the pores, 1 monomers aggregate in a "ship in a bottle" fashion, thus filling practically all of the nanoMOFs' available free volume and stabilizing their crystalline supramolecular structures. Highly efficient results have been found with the human pancreatic cell line PANC1, in contrast with free 1. We also demonstrate that one- and two-photon light irradiation emerges as a highly promising strategy to promote stimuli-dependent 1 release from the nanoMOFs, hence opening new standpoints for further developments in triggered drug delivery.

The antioxidants, vitamin A and E but not vitamin C and melatonin enhance the proapoptotic effects of irinotecan in cancer cells in vitro

Irinotecan is one of the camptothecin analog which has been shown to have a broad spectrum of antitumor activities against various malignancies. The aim of this study was to evaluate the effect of vitamin A, C, E and melatonin on proapoptotic activity of irinotecan in human cancer cells in vitro. We observed that irinotecan induced apoptosis in all types of analyzed cell lines when used as a single agent. Combination of selected antioxidants with various doses of irinotecan (7.5-60μM) resulted in significant increase in apoptotic cell death in A549 and HT29 cancer cell lines. The highest killing efficiency was observed after co-incubation of the cells with irinotecan and vitamin A (10μM), or vitamin E (25μM), respectively. The addition of vitamin C and melatonin to irinotecan treatment did not promote increase in killing of cancer cells. Our results indicate that some antioxidants can enhance the proapoptoic activity (properties) of irinotecan in human cancer cells in vitro. These findings may be supportive for the optimization of therapeutic efficacy of irinotecan treatment.

Intestinal glucuronidation protects against chemotherapy-induced toxicity by irinotecan (CPT-11)

Camptothecin (CPT)-11 (irinotecan) has been used widely for cancer treatment, particularly metastatic colorectal cancer. However, up to 40% of treated patients suffer from severe late diarrhea, which prevents CPT-11 dose intensification and efficacy. CPT-11 is a prodrug that is hydrolyzed by hepatic and intestinal carboxylesterase to form SN-38, which in turn is detoxified primarily through UDP-glucuronosyltransferase 1A1 (UGT1A1)-catalyzed glucuronidation. To better understand the mechanism associated with toxicity, we generated tissue-specific Ugt1 locus conditional knockout mouse models and examined the role of glucuronidation in protecting against irinotecan-induced toxicity. We targeted the deletion of the Ugt1 locus and the Ugt1a1 gene specifically in the liver (Ugt1(ΔHep)) and the intestine (Ugt1(ΔGI)). Control (Ugt1(F/F)), Ugt1(ΔHep), and Ugt1(ΔGI) adult male mice were treated with different concentrations of CPT-11 daily for four consecutive days. Toxicities were evaluated with regard to tissue glucuronidation potential. CPT-11-treated Ugt1(ΔHep) mice showed a similar lethality rate to the CPT-11-treated Ugt1(F/F) mice. However, Ugt1(ΔGI) mice were highly susceptible to CPT-11-induced diarrhea, developing severe and lethal mucositis at much lower CPT-11 doses, a result of the proliferative cell loss and inflammation in the intestinal tract. Comparative expression levels of UGT1A1 in intestinal tumors and normal surrounding tissue are dramatically different, providing for the opportunity to improve therapy by differential gene regulation. Intestinal expression of the UGT1A proteins is critical toward the detoxification of SN-38, whereas induction of the UGT1A1 gene may serve to limit toxicity and improve the efficacy associated with CPT-11 treatment.

Neural stem cell-mediated delivery of irinotecan-activating carboxylesterases to glioma: implications for clinical use

CPT-11 (irinotecan) has been investigated as a treatment for malignant brain tumors. However, limitations of CPT-11 therapy include low levels of the drug entering brain tumor sites and systemic toxicities associated with higher doses. Neural stem cells (NSCs) offer a novel way to overcome these obstacles because of their inherent tumor tropism and ability to cross the blood-brain barrier, which enables them to selectively target brain tumor sites. Carboxylesterases (CEs) are enzymes that can convert the prodrug CPT-11 (irinotecan) to its active metabolite SN-38, a potent topoisomerase I inhibitor. We have adenovirally transduced an established clonal human NSC line (HB1.F3.CD) to express a rabbit carboxylesterase (rCE) or a modified human CE (hCE1m6), which are more effective at converting CPT-11 to SN-38 than endogenous human CE. We hypothesized that NSC-mediated CE/CPT-11 therapy would allow tumor-localized production of SN-38 and significantly increase the therapeutic efficacy of irinotecan. Here, we report that transduced NSCs transiently expressed high levels of active CE enzymes, retained their tumor-tropic properties, and mediated an increase in the cytotoxicity of CPT-11 toward glioma cells. CE-expressing NSCs (NSC.CEs), whether administered intracranially or intravenously, delivered CE to orthotopic human glioma xenografts in mice. NSC-delivered CE catalyzed conversion of CPT-11 to SN-38 locally at tumor sites. These studies demonstrate the feasibility of NSC-mediated delivery of CE to glioma and lay the foundation for translational studies of this therapeutic paradigm to improve clinical outcome and quality of life in patients with malignant brain tumors.

Selective cytotoxicity and combined effects of camptothecin or paclitaxel with sodium-R-alpha lipoate on A549 human non-small cell lung cancer cells

Nonsmall cell lung cancer (NSCLC) is the most common type of lung cancer and remains the deadliest form of cancer in the United States and worldwide. New therapies are highly sought after to improve outcome. The effect of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity was evaluated on A549 NSCLC and BEAS-2B "normal" lung epithelial cells. Combination indices (CI) and dose reduction indices (DRI) were investigated by studying the cytotoxicity of sodium-R-alpha lipoate (0-16 mM), camptothecin (0-25 nM) and paclitaxel (0-0.06 nM) alone and in combination. 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium-bromide (MTT) was used to assess cytotoxicity. The combinational cytotoxic effects of sodium-R-alpha lipoate with camptothecin or paclitaxel were analyzed using a simulation of dose effects (CompuSyn® 3.01). The effects of sodium-R-alpha lipoate on camptothecin- and paclitaxel-induced cytotoxicity varied based on concentrations and treatment times. It was found that sodium-R-alpha lipoate wasn't cytotoxic toward BEAS-2B cells at any of the concentrations tested. For A549 cells, CIs [(additive (CI = 1); synergistic (CI < 1); antagonistic (CI < 1)] were lower and DRIs were higher for the camptothecin/sodium-R-alpha-lipoate combination (CI = ∼0.17-1.5; DRI = ∼2.2-22.6) than the paclitaxel/sodium-R-alpha-lipoate combination (CI = ∼0.8-9.9; DRI = ∼0.10-5.8) suggesting that the camptothecin regimen was synergistic and that the addition of sodium-R-alpha lipoate was important for reducing the camptothecin dose and potential for adverse effects.

Suppression of camptothecin biosynthetic genes results in metabolic modification of secondary products in hairy roots of Ophiorrhiza pumila

Camptothecin is a monoterpenoid indole alkaloid that exhibits anti-tumor activity. In Ophiorrhiza pumila, production of camptothecin and its related alkaloids was high in the hairy roots, but not in the cell suspension culture derived from hairy roots. To identify the intermediates in camptothecin biosynthesis, expression of genes encoding tryptophan decarboxylase (TDC) and secologanin synthase (SLS), the two enzymes catalyzing the early steps in camptothecin biosynthesis, were suppressed in the hairy roots of O. pumila by RNA interference (RNAi), and metabolite changes were investigated. In most TDC- and SLS-suppressed lines, accumulation of camptothecin and related alkaloids, strictosidine, strictosamide, pumiloside, and deoxypumiloside was reduced. The accumulation levels of secologanin exhibited a strong negative correlation with the expression level of TDC, and that of loganin exhibited a negative correlation with the expression level of SLS. Some hairy root-specific chromatographic peaks detected by liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (LC-FTICR-MS) exhibited positive or negative correlation with TDC expression, suggesting their possible involvement in camptothecin biosynthesis.

Identification of repurposed small molecule drugs for chordoma therapy

Chordoma is a rare, slow growing malignant tumor arising from remnants of the fetal notochord. Surgery is the first choice for chordoma treatment, followed by radiotherapy, although postoperative complications remain significant. Recurrence of the disease occurs frequently due to the anatomy of the tumor location and violation of the tumor margins at the initial surgery. Currently, there are no effective drugs available for patients with chordoma. Due to the rarity of the disease, there is limited opportunity to test agents in clinical trials and no concerted effort to develop agents for chordoma in the pharmaceutical industry. To rapidly and efficiently identify small molecules that inhibit chordoma cell growth, we screened the NCGC Pharmaceutical Collection (NPC) containing approximately 2800 clinically approved and investigational drugs at 15 different concentrations in chordoma cell lines, U-CH1 and U-CH2. We identified a group of drugs including bortezomib, 17-AAG, digitoxin, staurosporine, digoxin, rubitecan, and trimetrexate that inhibited chordoma cell growth, with potencies from 10 to 370 nM in U-CH1 cells, but less potently in U-CH2 cells. Most of these drugs also induced caspase 3/7 activity with a similar rank order as the cytotoxic effect on U-CH1 cells. Cantharidin, digoxin, digitoxin, staurosporine, and bortezomib showed similar inhibitory effect on cell lines and 3 primary chordoma cell cultures. The combination treatment of bortezomib with topoisomerase I and II inhibitors increased the therapeutic potency in U-CH2 and patient-derived primary cultures. Our results provide information useful for repurposing currently approved drugs for chordoma and potential approach of combination therapy.

Reactive oxygen species responsive nanoprodrug to treat intracranial glioblastoma

Chemotherapy for intracranial gliomas is hampered by limited delivery of therapeutic agents through the blood brain barrier (BBB). An optimal therapeutic agent for brain tumors would selectively cross the BBB, accumulates in the tumor tissue and be activated from an innocuous prodrug within the tumor. Here we show brain tumor-targeted delivery and therapeutic efficacy of a nanometer-sized prodrug (nanoprodrug) of camptothecin (CPT) to treat experimental glioblastoma multiforme (GBM). The CPT nanoprodrug was prepared using spontaneous nanoemulsification of a biodegradable, antioxidant CPT prodrug and α-tocopherol. The oxidized nanoprodrug was activated more efficiently than nonoxidized nanoprodrug, suggesting enhanced therapeutic efficacy in the oxidative tumor microenvironment. The in vitro imaging of U-87 MG glioma cells revealed an efficient intracellular uptake of the nanoprodrug via direct cell membrane penetration rather than via endocytosis. The in vivo study in mice demonstrated that the CPT nanoprodrug passed through the BBB and specifically accumulated in brain tumor tissue, but not in healthy brain tissue and other organs. The accumulation preferably occurred at the periphery of the tumor where cancer cells are most actively proliferating, suggesting optimal therapeutic efficacy of the nanoprodrug. The nanoprodrug was effective in treating subcutaneous and intracranial tumors. The nanoprodrug inhibited subcutaneous tumor growth more than 80% compared with control. The median survival time of mice implanted with an intracranial tumor increased from 40.5 days for control to 72.5 days for CPT nanoprodrug. This nanoprodrug approach is a versatile method for developing therapeutic nanoparticles enabling tumor-specific targeting and treatment. The nontoxic, tumor-specific targeting properties of the nanoprodrug system make it a safe, low cost, and versatile nanocarrier for pharmaceuticals, imaging agents, and diagnostic agents.

Association of UGT1A1*28 polymorphisms with irinotecan-induced toxicities in colorectal cancer: a meta-analysis in Caucasians

A meta-analysis in Caucasians was conducted to investigate the possible association of uridine diphosphate glucuronosyltransferase (UGT) 1A1 gene polymorphisms with irinotecan (IRI)-induced neutropenia and diarrhoea in colorectal cancer (CRC). We searched PubMed and Embase until May 2012 to identify eligible studies, extracted data, assessed methodological quality, and performed statistical analysis using REVMAN 5.1 and R software. Subgroups meta-analyses were performed in groups representing different IRI combination regimens and IRI doses. Sixteen trials were included. UGT1A1*28/*28 genotype was associated with more than fourfold (odds ratio (OR)=4.79, 95% confidence intervals (CI): 3.28-7.01; P<0.00001) and threefold (OR=3.44, 95% CI: 2.45-4.82; P<0.00001) increases in the risk of neutropenia when compared with wild type and with at least one UGT1A1*1 allele, respectively. UGT1A1*1/*28 genotype had an OR of 1.90 (95% CI: 1.44-2.51; P<0.00001) for an increased risk of neutropenia. A twofold increase in risk of diarrhoea was associated with UGT1A1*28/*28 genotype (OR=1.84, 95% CI: 1.24-2.72; P=0.002). In subgroup meta-analysis, the higher incidence of diarrhoea in UGT1A1*28/*28 patients was limited to studies where when IRI was given at higher doses (OR=2.37, 95% CI: 1.39-4.04; P=0.002) or combined with 5-fluorouracil (FU or analogue) (OR=1.78, 95% CI: 1.16-2.75; P=0.009). Genotyping of UGT1A1*28 polymorphism before treatment for CRC can tailor IRI therapy and reduce the IRI-related toxicities. IRI-combined 5-FU (or analogue) and a high-dose IRI therapy enhance IRI-induced diarrhoea among patients bearing the UGT1A1*28 allele. Although the toxicity relationships were much stronger with the UGT1A1*28 homozygous variant, associations were also found with the UGT1A1*28 heterozygous variant.

Correlation between the sensitivity of tumors to treatment with CZ48 and local concentrations of the active metabolite CPT within the tumors

Crystalline camptothecin-20-O-propionate hydrate (CZ48) is an esterification product from the reaction of natural camptothecin with propionic anhydride. CZ48 has been tested against 29 human tumor lines grown in nude mice as xenografts. Of the tested tumor lines, 28 were found to be responsive to CZ48, by regression or significant inhibition. The total response rate was 97%. However, the effective dose required to achieve the positive response varied from 100 to 2000 mg/kg/day depending on the tumor type. Thus, the sensitivity of tumors to CZ48 treatment varied from tumor to tumor. The most sensitive CLO-breast carcinoma achieved regression when treated with 100 mg/kg/day, while PC3-prostate carcinoma required as high as 1000 mg/kg/day to achieve a definitive response. To determine the reason for these differences in sensitivities among the tumors, we treated 9 human xenografts grown in nude mice with 1000 mg/kg/day CZ48 until saturation and measured the local concentrations of the parental CZ48 as well as the corresponding metabolite camptothecin (CPT) in the tumors with the established high-performance liquid chromatography procedure. Results showed that the sensitivities of these tumors to CZ48 treatment were not affected by local concentrations of the active metabolite CPT in the tumors, but instead by the types of tumors.

Human cells enter mitosis with damaged DNA after treatment with pharmacological concentrations of genotoxic agents

In the present paper, we report that mitosis is a key step in the cellular response to genotoxic agents in human cells. Cells with damaged DNA recruit γH2AX (phosphorylated histone H2AX), phosphorylate Chk1 (checkpoint kinase 1) and arrest in the G2-phase of the cell cycle. Strikingly, nearly all cells escape the DNA damage checkpoint and become rounded, by a mechanism that correlates with Chk1 dephosphorylation. The rounded cells are alive and in mitosis as measured by low phospho-Tyr(15) Cdk1 (cyclin-dependent kinase 1), high Cdk activity, active Plk1 (Polo-like kinase 1) and high phospho-histone H3 signals. This phenomenon is independent of the type of DNA damage, but is dependent on pharmacologically relevant doses of genotoxicity. Entry into mitosis is likely to be caused by checkpoint adaptation, and the HT-29 cell-based model provides a powerful experimental system in which to explore its molecular basis. We propose that mitosis with damaged DNA is a biologically significant event because it may cause genomic rearrangement in cells that survive genotoxic damage.

Simple automated radiosynthesis of 10-[11C]methoxy-20(S)-camptothecin and biodistribution in normal mice

10-[(11)C]methoxy-20(S)-camptothecin was synthesized automatically. The radiochemical yield was 30%-50% (all calculated at EOB, n=20) with [(11)C]methyl triflate as a methylating agent. The radiochemical purity was greater than 96%, and the specific activity was 8.72±2.18 GBq/μmoL at EOS. Biodistribution showed that 10-[(11)C]methoxy-20(S)-camptothecin is characterized by quick clearance from the blood and by significant uptake in the liver (5.72±1.92% ID/g at 15 min), intestines (2.43±0.38% ID/g at 15 min), and kidney (1.57±0.85% ID/g at 15 min). Micro-PET imaging clearly showed high radioactivity accumulation in liver, intestines and bladder, indicating that the primary modes of excretion of the radiotracer are through the hepatobiliary system and, to a lesser extent, through the renal system.

3D superhydrophobic electrospun meshes as reinforcement materials for sustained local drug delivery against colorectal cancer cells

In this work we expand upon a recently reported local drug delivery device, where air is used as a degradable component of our material to control drug release (J. Am. Chem. Soc. 2012, 134, 2016-2019). We consider its potential use as a drug loaded strip to provide both mechanical stability to the anastomosis, and as a means to release drug locally over prolonged periods for prevention of locoregional recurrence in colorectal cancer. Specifically, we electrospun poly(ε-caprolactone) (PCL) with the hydrophobic polymer dopant poly(glycerol monostearate-co-ε-caprolactone) (PGC-C18) and used the resultant mesh to control the release of two anticancer drugs (CPT-11 and SN-38). The increase in mesh hydrophobicity with PGC-C18 addition slows drug release both by the traditional means of drug diffusion, as well as by increasing the stability of the entrapped air layer to delay drug release. We demonstrate that superhydrophobic meshes have mechanical properties appropriate for surgical buttressing of the anastomosis, permit non-invasive assessment of mesh location and documentation of drug release via ultrasound, and release chemotherapy over a prolonged period of time (>90 days) resulting in significant tumor cytotoxicity against a human colorectal cell line (HT-29).

Potential repurposing of known drugs as potent bacterial β-glucuronidase inhibitors

The active metabolite of the chemotherapeutic irinotecan, SN-38, is detoxified through glucuronidation and then excreted into the gastrointestinal tract. Intestinal bacteria convert the glucuronidated metabolite back to the toxic SN-38 using β-glucuronidase (GUS), resulting in debilitating diarrhea. Inhibiting GUS activity may relieve this side effect of irinotecan. In this study, we sought to determine whether any known drugs have GUS inhibitory activity. We screened a library of Food and Drug Administration-approved drugs with a cell-free biochemical enzyme assay using purified bacterial GUS. After triage, five drugs were confirmed to inhibit purified bacterial GUS. Three of these were the monoamine oxidase inhibitors nialamide, isocarboxazid, and phenelzine with average IC(50) values for inhibiting GUS of 71, 128, and 2300 nM, respectively. The tricyclic antidepressant amoxapine (IC(50) = 388 nM) and the antimalarial mefloquine (IC(50) = 1.2 µM) also had activity. Nialamide, isocarboxazid, and amoxapine had no significant activity against purified mammalian GUS but showed potent activity for inhibiting endogenous GUS activity in a cell-based assay using living intact Escherichia coli with average IC(50) values of 17, 336, and 119 nM, respectively. Thus, nialamide, isocarboxazid, and amoxapine have potential to be repurposed as therapeutics to reduce diarrhea associated with irinotecan chemotherapy and warrant further investigation for this use.

Effects of camptothecin and hydroxycamptothecin on insect cell lines Sf21 and IOZCAS-Spex-II

BACKGROUND

In recent years, concerns over the potential impact of synthetic pesticides on the environment have made the discovery and development of environmentally friendly pesticides a more pressing issue. Camptothecin (CPT) and its derivatives have attracted much attention owing to their unique mechanisms of action against insects. In this paper, two insect cell lines, Sf21 and IOZCAS-Spex-II, were used to conduct a preliminary investigation of the potential of CPT and hydroxycamptothecin (HCPT) as inducers of apoptosis in insect cell lines, and to illustrate the mechanism of action of CPT on insects at the cellular level.

RESULTS

The results showed that both CPT and HCPT demonstrate potent cytotoxic effects to the tested insect cell lines in a time- and dose-dependent manner. The DNA fragmentation, activation of caspases and cytochrome c release were observed in both IOZCAS-Spex-II and Sf21 treated with CPT and HCPT. There is no significant difference in cytotoxicity and caspase-3 activation (P < 0.05, except when treated for 2 h) between CPT and HCPT, although the caspase-3 activation was slightly stronger when treated with HCPT in both Sf21 and IOZCAS-Spex-II.

CONCLUSION

The results confirm the existence of the mitochondrial-dependent pathway of apoptosis induced by CPT and HCPT in Sf21 and IOZCAS-Spex-II cell lines. Further investigations are required to reveal the mitochondrial mechanisms and regulation of caspase activation during apoptosis. These studies will provide basic knowledge needed to understand the mechanisms of action of CPT and to develop CPT and its derivatives as insecticides.

The human apoptosis inhibitor NAIP induces pyroptosis in macrophages infected with Legionella pneumophila

Human nucleotide oligomerization domain-like receptor family apoptosis inhibitory protein (NAIP) prevents apoptosis by inhibiting caspase-3, -7, and -9. Four functional Naip exist in the murine genome, each of which is equally similar to human NAIP. Among them, Naip5 induces pyroptosis by promoting caspase-1 activation in response to Legionella pneumophila infection in macrophages. However, the contribution of human NAIP to this response is unclear. To investigate the role of human NAIP in macrophage survival, we stably expressed human NAIP in RAW264.7 macrophages. Human NAIP inhibited camptothecin-induced apoptosis in macrophages; however, it promoted cytotoxicity in L. pneumophila-infected cells. This cytotoxicity was associated with caspase-1. In addition, human NAIP restricted the intracellular growth of L. pneumophila. L. pneumophila flagellin was required for cytotoxicity, caspase-1 activation, and restriction of intracellular bacterial growth. Expression of murine Naip5 produced comparable results. These data indicate that human NAIP regulates the host response to L. pneumophila infection in a manner similar to that of murine Naip5 and that human NAIP and murine Naip5 regulate cell survival by inhibiting apoptosis or by promoting pyroptosis in response to specific cellular signals.

Enhancement of anticancer efficacy using modified lipophilic nanoparticle drug encapsulation

BACKGROUND

Development of anticancer drugs is challenging. Indeed, much research effort has been spent in the development of new drugs to improve clinical outcomes with minimal toxicity. We have previously reported that a formulation of lipid gold porphyrin nanoparticles reduced systemic drug toxicity when compared with free gold porphyrin. In this study, we investigated the delivery and treatment efficiency of PEG surface-modified lipid nanoparticles as a carrier platform.

METHODS

We encapsulated antitumor drugs into PEG-modified lipid nanoparticles and these were characterized by size, zeta potential, and encapsulation efficiency. The delivery efficiency into tumor tissue was evaluated using a biodistribution study. To evaluate antitumor efficacy, gold porphyrin or camptothecin (a DNA topoisomerase I inhibitor) were encapsulated and compared using an in vivo neuroblastoma (N2A) model.

RESULTS

We showed that drug encapsulation into PEG-modified lipid nanoparticles enhanced the preferential uptake in tumor tissue. Furthermore, higher tumor killing efficiency was observed in response to treatment with PEG-modified lipid nanoparticles encapsulating gold porphyrin or camptothecin when compared with free gold porphyrin or free camptothecin. The in vivo antitumor effect was further confirmed by study of tumor inhibition and positive apoptosis activity. Surface modification of lipophilic nanoparticles with PEG increased the efficiency of drug delivery into tumor tissue and subsequently more effective antitumor activity.

CONCLUSION

This specific design of a chemotherapeutic agent using nanotechnology is important in the development of a safe and effective drug in cancer therapy.

Rapid deconjugation of SN-38 glucuronide and adsorption of released free SN-38 by intestinal microorganisms in rat

One of the dose-limiting toxicities of irinotecan hydrochloride (CPT-11) is delayed-onset diarrhea. CPT-11 is converted to its active metabolite, SN-38, which is conjugated to SN-38 glucuronide (SN-38G). SN-38G excreted in the intestinal lumen is extensively deconjugated by bacterial β-glucuronidase, resulting in the regeneration of SN-38, which causes diarrhea. However, the deconjugation of SN-38G by the intestinal microflora remains to be clarified. This study aimed to investigate the microbial transformation of SN-38G by an anaerobic mixed culture of rat cecal microorganisms. Concentrations of SN-38G and SN-38 were then determined using high-performance liquid chromatography. Complete deconjugation of SN-38G to SN-38 in the mixed cultures was observed within 1 h of incubation, with 62.7% of the added SN-38G being found in the supernatant. Approximately 80.4% of the SN-38 in the supernatant was bound to protein, and the remaining 19.6% was detected as active free SN-38. In total, only 12.3% (19.6 × 62.7%) of the SN-38G added to the test tube was found in the supernatant in the ultrafiltrable free form, indicating that approximately 90% of the SN-38G added to the growth medium either remained adsorbed onto the pelleted fraction or occurred in a protein-bound form in the supernatant. The remaining 10% of the SN-38G added to the growth medium existed in the unbound form, the form capable of causing damage to the intestinal membrane. In conclusion, these results indicated that the greater part of the SN-38 produced from SN-38G by the action of bacterial β-glucuronidase is rapidly adsorbed onto intestinal bacterial cell walls or dietary fibers in pelleted fraction, and only 10% remains in the ultrafiltrable unbound form in the intestinal luminal fluid.

IT-141, a Polymer Micelle Encapsulating SN-38, Induces Tumor Regression in Multiple Colorectal Cancer Models

Polymer micelles are promising drug delivery vehicles for the delivery of anticancer agents to tumors. Often, anticancer drugs display potent cytotoxic effects towards cancer cells but are too hydrophobic to be administered in the clinic as a free drug. To address this problem, a polymer micelle was designed using a triblock copolymer (ITP-101) that enables hydrophobic drugs to be encapsulated. An SN-38 encapsulated micelle, IT-141, was prepared that exhibited potent in vitro cytotoxicity against a wide array of cancer cell lines. In a mouse model, pharmacokinetic analysis revealed that IT-141 had a much longer circulation time, plasma exposure, and tumor exposure compared to irinotecan. IT-141 was also superior to irinotecan in terms of antitumor activity, exhibiting greater tumor inhibition in HT-29 and HCT116 colorectal cancer xenograft models at half the dose of irinotecan. The antitumor effect of IT-141 was dose-dependent and caused complete growth inhibition and tumor regression at well-tolerated doses. Varying the specific concentration of SN-38 within the IT-141 micelle had no detectible effect on this antitumor activity, indicating no differences in activity between different IT-141 formulations. In summary, IT-141 is a potent micelle-based chemotherapy that holds promise for the treatment of colorectal cancer.

Loading profile of topotecan into polyvinyl alcohol microspheres (DC Bead™) over a 7-day period

Purpose: DC Bead™ is successfully used for chemoembolization of various liver cancers. The purpose of this study was todetermine the loading capacity of the semi-synthetic topoisomerase-1 inhibitor topotecan into the DC Bead™ microspheres under static or agitated conditions and to assess the physicochemical stability over a period of 7 days.

Methods: Commercially available topotecan hydrochloride powder (Hycamtin®) was reconstituted with water for injection to yield a nominal concentration of 1 mg/mL topotecan. Polyvinyl alcohol (PVA)-based microspheres (DC Bead™, 300–500 µm, 2 mL/vial) were mixed with 4 mL of the reconstituted topotecan solution. Vials were stored light protected at room temperature under static or agitated conditions for 7 days ( n = 3, for each loading condition). At different time intervals, samples were taken from the excess solution and assayed via a stability-indicating HPLC assay. Drug-loading profiles were determined by measuring the remaining topotecan concentration in the excess solution.

Results: Under agitated conditions, topotecan was loaded into the microspheres rapidly after mixing. After 5 min 86.4 ± 0.1% of topotecan was loaded. Under static conditions, drug uptake was slower. Only 65.0 ± 0% were loaded after 5 min; 86.6 ± 0.1% drug uptake was achieved not until 1 h. Over a storage period of 7 days, topotecan remained loaded in the DC Bead™ microspheres at a level of >90%.

Conclusion: Drug uptake of 4 mg topotecan (1 mg/mL solution) into DC Beads™ was faster under agitated loading conditions. Nevertheless, after 1 h, ∼90% of topotecan was loaded into the DC Bead™ microspheres independent from the type of loading condition. The loading rate remained >90% over the observation period of 7 days and light-protected storage at room temperature. Loading and stability of topotecan-loaded DC Beads™ is suitable and convenient for preparation in a pharmacy-based cytotoxic preparation unit.