Antitumor Effect of NK012, a 7-Ethyl-10-Hydroxycamptothecin–Incorporating Polymeric Micelle, on U87MG Orthotopic Glioblastoma in Mice Compared with Irinotecan Hydrochloride in Combination with Bevacizumab

Polymeric micelles paving the Way: Recent breakthroughs in camptothecin delivery for enhanced chemotherapy

Camptothecin, a natural alkaloid, was first isolated from the bark and stem of the Camptotheca acuminate tree in China. It, along with its analogs, has demonstrated potent anti-cancer activity in preclinical studies, particularly against solid tumors such as lung, breast, ovarian, and colon cancer. Despite its promising anti-cancer activity, the application of camptothecin is limited due to its poor solubility, toxicity, and limited biodistribution. Nanotechnology-based drug delivery systems have been used to overcome limited bioavailability and ensure greater biodistribution after administration. Additionally, various drug delivery systems, particularly polymeric micelles, have been investigated to enhance the solubility, stability, and efficacy of camptothecin. Polymeric micelles offer a promising approach for the delivery of camptothecin. Polymeric micelles possess a core-shell structure, with a typical hydrophobic core, which exhibits a high capacity to incorporate hydrophobic drugs. The structure of polymeric micelles can be engineered to have a high drug loading capacity, thereby enabling them to carry a large amount of hydrophobic drug within their core. The shell portion of polymeric micelles is composed of hydrophilic polymers Furthermore, the hydrophilic segment of polymeric micelles plays an important role in protecting against the reticuloendothelial system (RES). This review provides a discussion on recent research and developments in the delivery of camptothecin using polymeric micelles for the treatment of cancers.

Bevacizumab: A new take on therapy of muscle phase of Trichinella spiralis infection

Trichinellosis is a zoonosis that causes health and economic problems worldwide. The available therapy is far from perfect as the conventional drugs used against Trichinella spiralis (T. spiralis) are active against the intestinal adult parasites but much less active against encapsulated larvae in muscles. Therefore, this work aimed to evaluate the effect of the anti-angiogenic agent, bevacizumab, on the muscle larvae of T. spiralis. For this aim, T. spiralis-infected mice were treated by two different doses of bevacizumab, thereafter larval counts as well as biochemical and pathological changes were evaluated in the muscles. The larval burden was reduced in the muscles of treated mice, denoting a detrimental effect of bevacizumab against encapsulated Trichinella larvae. Moreover, there was marked improvement of muscle inflammation with the treatment, evidenced by reduction of the proinflammatory cytokines (IL-6 and TNF-α) and regression of the inflammatory infiltrates in histological sections. Amelioration of oxidative stress in the muscle was also observed in treated animals with reduction of malondialdehyde and carbonic anhydrase III and increase in superoxide dismutase levels. Finally, the treatment induced downregulation of the expression of VEGF and CD31, denoting suppressed angiogenesis. All these beneficial effects were found to be dose dependent. In conclusion, bevacizumab exhibited anthelmintic, anti-inflammatory, antioxidant, and anti-angiogenic activities against Trichinella during the muscular phase of infection. Therefore, bevacizumab could be considered as a useful adjuvant treatment in the late stages of trichinellosis.

Targeted Delivery of DNA Topoisomerase Inhibitor SN38 to Intracranial Tumors of Glioblastoma Using Sub-5 Ultrafine Iron Oxide Nanoparticles

Effectively delivering therapeutics for treating brain tumors is hindered by the physical and biological barriers in the brain. Even with the compromised blood-brain barrier and highly angiogenic blood-tumor barrier seen in glioblastoma (GBM), most drugs, including nanomaterial-based formulations, hardly reach intracranial tumors. This work investigates sub-5 nm ultrafine iron oxide nanoparticles (uIONP) with 3.5 nm core diameter as a carrier for delivering DNA topoisomerase inhibitor 7-ethyl-10-hydroxyl camptothecin (SN38) to treat GBM. Given a higher surface-to-volume ratio, uIONP shows one- or three-folds higher SN38 loading efficiency (48.3 ± 6.1%, mg/mg Fe) than those with core sizes of 10 or 20 nm. SN38 encapsulated in the coating polymer exhibits pH sensitive release with <10% over 48 h at pH 7.4, but 86% at pH 5, thus being protected from converting to inactive glucuronide by UDP-glucuronosyltransferase 1A1. Conjugating α_v β₃ -integrin-targeted cyclo(Arg-Gly-Asp-D-Phe-Cys) (RGD) as ligands, RGD-uIONP/SN38 demonstrates targeted cytotoxicity to α_v β₃ -integrin-overexpressed U87MG GBM cells with a half-maximal inhibitory concentration (IC₅₀ ) of 30.9 ± 2.2 nm. The efficacy study using an orthotopic mouse model of GBM reveals tumor-specific delivery of 11.5% injected RGD-uIONP/SN38 (10 mg Fe kg^-1 ), significantly prolonging the survival in mice by 41%, comparing to those treated with SN38 alone (p < 0.001).

A phase II study of NK012, a polymeric micelle formulation of SN-38, in unresectable, metastatic or recurrent colorectal cancer patients

Purpose

NK012 is a polymeric micelle formulation of SN-38, the active metabolite of irinotecan. We evaluated the efficacy and safety of NK012 in Japanese patients with unresectable metastatic colorectal cancer.

Methods

We conducted a multicenter open-label phase II trial of NK012 monotherapy in 58 patients who had been treated with an oxaliplatin-based chemotherapy regimen (group A: 53 patients with UGT1A1 genotype –/–, *6/–, or *28/–; group B: 5 patients with UGT1A1 genotype *6/*28 or *6/*6). The primary endpoint was the response rate (RR). Initial doses of 28 and 18 mg/m² for group A and group B, respectively, were administered intravenously over 30 min, and these doses were subsequently administered every 3 weeks. Group A was evaluated as the primary efficacy population, while group B was evaluated for reference.

Results

In group A, the RR was 3.8%, and the median progression-free survival and overall survival were 3.30 months and 15.03 months, respectively. In both groups, the most common grade ≥ 3 adverse drug reaction (ADR) was neutropenia and the incidence of grade ≥ 3 diarrhea was low or zero. In group A, 17 serious ADRs were observed in 10 patients (17%); all improved or recovered. In group B, no serious ADRs were observed. No treatment-related deaths were reported in either group.

Conclusions

NK012 monotherapy yielded an RR similar to the RR of irinotecan monotherapy that was reported in the phase III EPIC trial (4.2%), and the incidence of grade ≥ 3 diarrhea was low. Based on the incidence and severity of febrile neutropenia and grade ≥ 3 neutropenia, the initial dose of NK012 28 mg/m² may be too high for colorectal cancer patients who have previously been treated with an oxaliplatin-based chemotherapy regimen.

Brain- and brain tumor-penetrating disulfiram nanoparticles: Sequence of cytotoxic events and efficacy in human glioma cell lines and intracranial xenografts

There is great interest in repurposing disulfiram (DSF), a rapidly metabolizing nontoxic drug, for brain cancers and other cancers. To overcome the instability and low therapeutic efficacy, we engineered passively-targeted DSF-nanoparticles (DSFNPs) using biodegradable monomethoxy (polyethylene glycol) d,l-lactic-co-glycolic acid (mPEG-PLGA) matrix. The physicochemical properties, cellular uptake and the blood brain-barrier permeability of DSFNPs were investigated. The DSFNPs were highly stable with a size of ∼70 nm with a >90% entrapment. Injection of the nanoparticles labeled with HITC, a near-infrared dye into normal mice and tumor-bearing nude mice followed by in vivo imaging showed a selective accumulation of the formulation within the brain and subcutaneous tumors for >24 h, indicating an increased plasma half-life and entry of DSF into desired sites. The DSFNPs induced a potent and preferential killing of many brain tumor cell lines in cytotoxicity assays. Confocal microscopy showed a quick internalization of the nanoparticles in tumor cells followed by initial accumulation in lysosomes and subsequently in mitochondria. DSFNPs induced high levels of ROS and led to a marked loss of mitochondrial membrane potential. Activation of the MAP-kinase pathway leading to a nuclear translocation of apoptosis-inducing factor and altered expression of apoptotic and anti-apoptotic proteins were also observed. DSFNPs induced a powerful and significant regression of intracranial medulloblastoma xenografts compared to the marginal efficacy of unencapsulated DSF. Together, we show that passively targeted DSFNPs can affect multiple targets, trigger potent anticancer effects, and can offer a sustained drug supply for brain cancer treatment through an enhanced permeability retention (EPR).

Molecular imaging using an anti-human tissue factor monoclonal antibody in an orthotopic glioma xenograft model

Nuclear medicine examinations for imaging gliomas have been introduced into clinical practice to evaluate the grade of malignancy and determine sampling locations for biopsies. However, these modalities have some limitations. Tissue factor (TF) is overexpressed in various types of cancers, including gliomas. We thus generated an anti-human TF monoclonal antibody (mAb) clone 1849. In the present study, immunohistochemistry performed on glioma specimens using anti-TF 1849 mAb showed that TF expression in gliomas increased in proportion to the grade of malignancy based on the World Health Organization (WHO) classification, and TF was remarkably expressed in necrosis and pseudopalisading cells, the histopathological hallmarks of glioblastoma multiforme (GBM). Furthermore, in both fluorescence and single-photon emission computed tomography/computed tomography (SPECT/CT) imaging studies, anti-TF 1849 IgG efficiently accumulated in TF-overexpressing intracranial tumours in mice. Although further investigation is required for a future clinical use of immuno-SPECT with ¹¹¹In-labelled anti-TF 1849 IgG, the immuno-SPECT may represent a unique imaging modality that can visualize the biological characteristics of gliomas differently from those obtained using the existing imaging modalities and may be useful to evaluate the grade of malignancy and determine sampling locations for biopsies in patients with glioma, particularly GBM.

The brain-penetrating CXCR4 antagonist, PRX177561, increases the antitumor effects of bevacizumab and sunitinib in preclinical models of human glioblastoma

Background

Glioblastoma recurrence after treatment with the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab is characterized by a highly infiltrative and malignant behavior that renders surgical excision and chemotherapy ineffective. It has been demonstrated that anti-VEGF/VEGFR therapies control the invasive phenotype and that relapse occurs through the increased activity of CXCR4. We therefore hypothesized that combining bevacizumab or sunitinib with the novel CXCR4 antagonist, PRX177561, would have superior antitumor activity.

Methods

The effects of bevacizumab, sunitinib, and PRX177561 were tested alone or in combination in subcutaneous xenografts of U87MG, U251, and T98G cells as well as on intracranial xenografts of luciferase tagged U87MG cells injected in CD1-nu/nu mice. Animals were randomized to receive vehicle, bevacizumab (4 mg/kg iv every 4 days), sunitinib (40 mg/kg po qd), or PRX177561 (50 mg/kg po qd).

Results

The in vivo experiments demonstrated that bevacizumab and sunitinib increase the in vivo expression of CXCR4, SDF-1α, and TGFβ1. In addition, we demonstrate that the co-administration of the novel brain-penetrating CXCR4 antagonist, PRX177561, with bevacizumab or sunitinib inhibited tumor growth and reduced the inflammation. The combination of PRX177561 with bevacizumab resulted in a synergistic reduction of tumor growth with an increase of disease-free survival (DSF) and overall survival (OS), whereas the combination of PRX177561 with sunitinib showed a mild additive effect.

Conclusions

The CXC4 antagonist PRX177561 may be a valid therapeutic complement to anti-angiogenic therapy, particularly when used in combination with VEGF/VEGFR inhibitors. Therefore, this compound deserves to be considered for future clinical evaluation.

Molecular Imaging of Brain Tumors Using Liposomal Contrast Agents and Nanoparticles

The first generation of cross-sectional brain imaging using computed tomography (CT), ultrasonography, and eventually MR imaging focused on determining structural or anatomic changes associated with brain disorders. The current state-of-the-art imaging, functional imaging, uses techniques such as CT and MR perfusion that allow determination of physiologic parameters in vivo. In parallel, tissue-based genomic, transcriptomic, and proteomic profiling of brain tumors has created several novel and exciting possibilities for molecular targeting of brain tumors. The next generation of imaging translates these molecular in vitro techniques to in vivo, noninvasive, targeted reconstruction of tumors and their microenvironments.

Convection-enhanced delivery of SN-38-loaded polymeric micelles (NK012) enables consistent distribution of SN-38 and is effective against rodent intracranial brain tumor models

Convection-enhanced delivery (CED) of therapeutic agents is a promising local delivery technique that has been extensively studied as a treatment for CNS diseases over the last two decades. One continuing challenge of CED is accurate and consistent delivery of the agents to the target. The present study focused on a new type of therapeutic agent, NK012, a novel SN-38-loaded polymeric micelle. Local delivery profiles of NK012 and SN-38 were studied using rodent brain and intracranial rodent brain tumor models. First, the cytotoxicity of NK012 against glioma cell lines was determined in vitro. Proliferations of glioma cells were significantly reduced after exposure to NK012. Then, the distribution and local toxicity after CED delivery of NK012 and SN-38 were evaluated in vivo. Volume of distribution of NK012 after CED was much larger than that of SN-38. Histological examination revealed minimum brain tissue damage in rat brains after delivery of 40 µg NK012 but severe damage with SN-38 at the same dose. Subsequently, the efficacy of NK012 delivered via CED was tested in 9L and U87MG rodent orthotopic brain tumor models. CED of NK012 displayed excellent efficacy in the 9L and U87MG orthotopic brain tumor models. Furthermore, NK012 and gadolinium diamide were co-delivered via CED to monitor the NK012 distribution using MRI. Volume of NK012 distribution evaluated by histology and MRI showed excellent agreement. CED of NK012 represents an effective treatment option for malignant gliomas. MRI-guided CED of NK012 has potential for clinical application.

Localized RNAi therapeutics of chemoresistant grade IV glioma using hyaluronan-grafted lipid-based nanoparticles

Glioblastoma multiforme (GBM) is one of the most infiltrating, aggressive, and poorly treated brain tumors. Progress in genomics and proteomics has paved the way for identifying potential therapeutic targets for treating GBM, yet the vast majority of these leading drug candidates for the treatment of GBM are ineffective, mainly due to restricted passages across the blood-brain barrier. Nanoparticles have been emerged as a promising platform to treat different types of tumors due to their ability to transport drugs to target sites while minimizing adverse effects. Herein, we devised a localized strategy to deliver RNA interference (RNAi) directly to the GBM site using hyaluronan (HA)-grafted lipid-based nanoparticles (LNPs). These LNPs having an ionized lipid were previously shown to be highly effective in delivering small interfering RNAs (siRNAs) into various cell types. LNP's surface was functionalized with hyaluronan (HA), a naturally occurring glycosaminoglycan that specifically binds the CD44 receptor expressed on GBM cells. We found that HA-LNPs can successfully bind to GBM cell lines and primary neurosphers of GBM patients. HA-LNPs loaded with Polo-Like Kinase 1 (PLK1) siRNAs (siPLK1) dramatically reduced the expression of PLK1 mRNA and cumulated in cell death even under shear flow that simulate the flow of the cerebrospinal fluid compared with control groups. Next, a human GBM U87MG orthotopic xenograft model was established by intracranial injection of U87MG cells into nude mice. Convection of Cy3-siRNA entrapped in HA-LNPs was performed, and specific Cy3 uptake was observed in U87MG cells. Moreover, convection of siPLK1 entrapped in HA-LNPs reduced mRNA levels by more than 80% and significantly prolonged survival of treated mice in the orthotopic model. Taken together, our results suggest that RNAi therapeutics could effectively be delivered in a localized manner with HA-coated LNPs and ultimately may become a therapeutic modality for GBM.

Enhancement of the photocytotoxic efficiency of sub-12 nm therapeutic polymeric micelles with increased co-localisation in mitochondria

We engineered phototherapeutic sub-12 nm-sized polymeric micelles to treat malignant brain tumours (MBTs). The engineered nanoparticles in MBT cells enhanced the photocytotoxic efficiency more than 2.5-fold compared with parental and PEGylated photosensitisers (PSs). Increased subcellular co-localisation of PSs in mitochondria was observed.

The use of longitudinal 18F-FET MicroPET imaging to evaluate response to irinotecan in orthotopic human glioblastoma multiforme xenografts

Objectives

Brain tumor imaging is challenging. Although ¹⁸F-FET PET is widely used in the clinic, the value of ¹⁸F-FET MicroPET to evaluate brain tumors in xenograft has not been assessed to date. The aim of this study therefore was to evaluate the performance of in vivo¹⁸F-FET MicroPET in detecting a treatment response in xenografts. In addition, the correlations between the ¹⁸F-FET tumor accumulation and the gene expression of Ki67 and the amino acid transporters LAT1 and LAT2 were investigated. Furthermore, Ki67, LAT1 and LAT2 gene expression in xenograft and archival patient tumors was compared.

Methods

Human GBM cells were injected orthotopically in nude mice and ¹⁸F-FET uptake was followed by weekly MicroPET/CT. When tumor take was observed, mice were treated with CPT-11 or saline weekly. After two weeks of treatment the brain tumors were isolated and quantitative polymerase chain reaction were performed on the xenograft tumors and in parallel on archival patient tumor specimens.

Results

The relative tumor-to-brain (T/B) ratio of SUV_max was significantly lower after one week (123±6%, n = 7 vs. 147±6%, n = 7; p = 0.018) and after two weeks (142±8%, n = 5 vs. 204±27%, n = 4; p = 0.047) in the CPT-11 group compared with the control group. Strong negative correlations between SUV_max T/B ratio and LAT1 (r = −0.62, p = 0.04) and LAT2 (r = −0.67, p = 0.02) were observed. In addition, a strong positive correlation between LAT1 and Ki67 was detected in xenografts. Furthermore, a 1.6 fold higher expression of LAT1 and a 23 fold higher expression of LAT2 were observed in patient specimens compared to xenografts.

Conclusions

¹⁸F-FET MicroPET can be used to detect a treatment response to CPT-11 in GBM xenografts. The strong negative correlation between SUV_max T/B ratio and LAT1/LAT2 indicates an export transport function. We suggest that ¹⁸F-FET PET may be used for detection of early treatment response in patients.

Irinotecan and temozolomide brain distribution: a focus on ABCB1

Glioblastoma (GBM), the most common primary brain tumor in adults, is usually rapidly fatal with median survival duration of only 15 months and a 3-year survival rate of <7 %. Temozolomide (TMZ) is the only anticancer drug that has improved survival in GBM when administered with concomitant radiotherapy. Irinotecan (CPT-11) has also shown efficacy in recurrent gliomas monotherapy with moderate response. As the efficacy of GBM treatments relies on their brain distribution through the blood-brain barrier (BBB), the aim of the present work was to study, on an in vivo model, the brain distribution of TMZ, CPT-11 and its active metabolite, SN-38. We have focussed on the role of ABCB1, the main efflux transporter at the BBB level, through pharmacokinetics studies in CF1 mdr1a(+/+) and mdr1a(-/-) mice. Our results show that TMZ, CPT-11 and SN-38 are transported by ABCB1 at the BBB level with brain/plasma ratios of 1.1, 2.1 and 2.3, respectively.

Marked antitumor effect of NK012, a SN-38-incorporating micelle formulation, in a newly developed mouse model of liver metastasis resulting from gastric cancer

BACKGROUND

Gastric cancer with liver metastasis (LM) is associated with poor prognosis due to rapid progression. It is, therefore, important to develop a quantitative and highly reproducible animal model of LM using human gastric cancer cells.

METHODS

Cells of a human gastric cancer cell line, HSC-57, were injected into the portal vein to produce LMs. Cells from some of these metastatic foci were expanded in vitro and subsequently implanted into the portal veins of mice. This procedure was repeated nine times. The antitumor effects of CPT-11 and NK012 were compared using the LM model.

RESULTS

The potent metastatic clone 57L9 was obtained. NK012 exerted a stronger antitumor effect than CPT-11 against 57L9 cells integrated with the luciferase gene (57L9Luc). The survival rates on day 131 in the 57L9Luc mouse model were 100% and 0% for the NK012 and CPT-11 groups, respectively.

CONCLUSION

This 57L9Luc LM model was found to be useful for monitoring the responses to NK012 and CPT-11.

The potential of polymeric micelles in the context of glioblastoma therapy

Glioblastoma multiforme (GBM), a type of malignant glioma, is the most common form of brain cancer found in adults. The current standard of care for GBM involves adjuvant temozolomide-based chemotherapy in conjunction with radiotherapy, yet patients still suffer from poor outcomes with a median survival of 14.6 months. Many novel therapeutic agents that are toxic to GBM cells in vitro cannot sufficiently accumulate at the site of an intracranial tumor after systemic administration. Thus, new delivery strategies must be developed to allow for adequate intratumoral accumulation of such therapeutic agents. Polymeric micelles offer the potential to improve delivery to brain tumors as they have demonstrated the capacity to be effective carriers of chemotherapy drugs, genes, and proteins in various preclinical GBM studies. In addition to this, targeting moieties and trigger-dependent release mechanisms incorporated into the design of these particles can promote more specific delivery of a therapeutic agent to a tumor site. However, despite these advantages, there are currently no micelle formulations targeting brain cancer in clinical trials. Here, we highlight key aspects of the design of polymeric micelles as therapeutic delivery systems with a review of their clinical applications in several non-brain tumor cancer types. We also discuss their potential to serve as nanocarriers targeting GBM, the major barriers preventing their clinical implementation in this disease context, as well as current approaches to overcome these limitations.

Understanding and modulating mammalian-microbial communication for improved human health

The fact that the bacteria in the human gastrointestinal (GI) tract play a symbiotic role was noted as early as 1885, well before we began to manage microbial infections using antibiotics. However, even with the first antimicrobial compounds used in humans, the sulfa drugs, microbes were recognized to be critically involved in the biotransformation of these therapeutics. Thus, the roles played by the microbiota in physiology and in the management of human health have long been appreciated. Detailed examinations of GI symbiotic bacteria that started in the early 2000s and the first phases of the Human Microbiome Project that were completed in 2012 have ushered in an exciting period of granularity with respect to the ecology, genetics, and chemistry of the mammalian-microbial axes of communication. Here we review aspects of the biochemical pathways at play between commensal GI bacteria and several mammalian systems, including both local-epithelia and nonlocal responses impacting inflammation, immunology, metabolism, and neurobiology. Finally, we discuss how the microbial biotransformation of therapeutic compounds, such as anticancer or nonsteroidal anti-inflammatory drugs, can be modulated to reduce toxicity and potentially improve therapeutic efficacy.

Understanding and modulating mammalian-microbial communication for improved human health

The molecular basis for the regulation of the intestinal barrier is a very fertile research area. A growing body of knowledge supports the targeting of various components of intestinal barrier function as means to treat a variety of diseases, including the inflammatory bowel diseases. Herein, we will summarize the current state of knowledge of key xenobiotic receptor regulators of barrier function, highlighting recent advances, such that the field and its future are succinctly reviewed. We posit that these receptors confer an additional dimension of host-microbe interaction in the gut, by sensing and responding to metabolites released from the symbiotic microbiota, in innate immunity and also in host drug metabolism. The scientific evidence for involvement of the receptors and its molecular basis for the control of barrier function and innate immunity regulation would serve as a rationale towards development of non-toxic probes and ligands as drugs.

Glioblastoma: therapeutic challenges, what lies ahead

Glioblastoma (GBM) is one of the most aggressive human cancers. Despite current advances in multimodality therapies, such as surgery, radiotherapy and chemotherapy, the outcome for patients with high grade glioma remains fatal. The knowledge of how glioma cells develop and depend on the tumor environment might open opportunities for new therapies. There is now a growing awareness that the main limitations in understanding and successfully treating GBM might be bypassed by the identification of a distinct cell type that has defining properties of somatic stem cells, as well as cancer-initiating capacity - brain tumor stem cells, which could represent a therapeutic target. In addition, experimental studies have demonstrated that the combination of antiangiogenic therapy, based on the disruption of tumor blood vessels, with conventional chemotherapy generates encouraging results. Emerging reports have also shown that microglial cells can be used as therapeutic vectors to transport genes and/or substances to the tumor site, which opens up new perspectives for the development of GBM therapies targeting microglial cells. Finally, recent studies have shown that natural toxins can be conjugated to drugs that bind to overexpressed receptors in cancer cells, generating targeted-toxins to selectively kill cancer cells. These targeted-toxins are highly effective against radiation- and chemotherapy-resistant cancer cells, making them good candidates for clinical trials in GBM patients. In this review, we discuss recent studies that reveal new possibilities of GBM treatment taking into account cancer stem cells, angiogenesis, microglial cells and drug delivery in the development of new targeted-therapies.

Preclinical and clinical studies of NK012, an SN-38-incorporating polymeric micelles, which is designed based on EPR effect

Polymeric micelles are ideally suited to exploit the EPR effect, and they have been used for the delivery of a range of anticancer drugs in preclinical and clinical studies. NK012 is an SN-38-loaded polymeric micelle constructed in an aqueous milieu by the self-assembly of an amphiphilic block copolymer, PEG-PGlu(SN-38). The antitumor activity was evaluated in several orthotopic tumor models including glioma, renal cancer, stomach cancer, and pancreatic cancer. Two independent phase I clinical trials were conducted in Japan and the USA. In the preclinical studies, it was demonstrated that NK012 exerted significantly more potent antitumor activity with no intestinal toxicity against various orthotopic human tumor xenografts than CPT-11. In clinical trials, predominant toxicity was neutropenia. Non-hematologic toxicity, especially diarrhea, was mostly Grade 1 or 2 during study treatments. Total 8 partial responses were obtained. According to data of preclinical studies, NK012 showing enhanced distribution with prolonged SN-38 release may be ideal for cancer treatment because the antitumor activity of SN-38 is time dependent. Clinical studies showed that NK012 was well tolerated and had antitumor activity including partial responses and several occurrences of prolonged stable disease across a variety of advanced refractory cancers. Phase II studies are ongoing in patients with colorectal cancer in Japan and in patients with triple negative breast cancer and small cell lung cancer in the USA.

Detailed distribution of NK012, an SN-38-incorporating micelle, in the liver and its potent antitumor effects in mice bearing liver metastases

PURPOSE

To clarify and compare the antitumor effects and specific biodistribution of NK012, an SN-38-incorporating polymeric micelle, in mice bearing multiple liver metastases of human colon cancer HT-29 cells with irinotecan hydrochloride (CPT-11).

EXPERIMENTAL DESIGN

The maximum tolerable dose of NK012 (30 mg/kg) or CPT-11 (66.7 mg/kg) was i.v. administered three times every 4 days to mice bearing metastases to the liver colonized 7 days after the portal administration of HT-29 cells (n = 6). In vivo antitumor effects were evaluated by bioluminescence imaging and histopathologic examination. Drug biodistribution was analyzed by high-performance liquid chromatography and fluorescence microscopy (n = 3).

RESULTS

NK012 eradicated the liver metastases and produced a significant longer survival rate than CPT-11 (P = 0.0006). High-performance liquid chromatography showed the prolonged distribution of NK012 and free SN-38 released from NK012 in the tumors, liver, and spleen for weeks after NK012 administration. On the other hand, the accumulation levels of CPT-11 and free SN-38 converted from CPT-11 rapidly decreased within 1 day after CPT-11 administration. In the liver metastases, fluorescence microscopy and immunohistochemistry showed that administered NK012 was distributed mainly adjacent to tumor vessels after 1 day. As for the normal liver, NK012 was distributed in Kupffer cells instead of hepatocytes for at least 7 days after administration.

CONCLUSION

This study suggests that NK012 is strongly effective against liver metastases and does not damage the liver despite the long retention time of NK012 in Kupffer cells.