Histopathological biomarkers for predicting the tumour accumulation of nanomedicines

The clinical prospects of cancer nanomedicines depend on effective patient stratification. Here we report the identification of predictive biomarkers of the accumulation of nanomedicines in tumour tissue. By using supervised machine learning on data of the accumulation of nanomedicines in tumour models in mice, we identified the densities of blood vessels and of tumour-associated macrophages as key predictive features. On the basis of these two features, we derived a biomarker score correlating with the concentration of liposomal doxorubicin in tumours and validated it in three syngeneic tumour models in immunocompetent mice and in four cell-line-derived and six patient-derived tumour xenografts in mice. The score effectively discriminated tumours according to the accumulation of nanomedicines (high versus low), with an area under the receiver operating characteristic curve of 0.91. Histopathological assessment of 30 tumour specimens from patients and of 28 corresponding primary tumour biopsies confirmed the score's effectiveness in predicting the tumour accumulation of liposomal doxorubicin. Biomarkers of the tumour accumulation of nanomedicines may aid the stratification of patients in clinical trials of cancer nanomedicines.

Free drug and ROS-responsive nanoparticle delivery of synergistic doxorubicin and olaparib combinations to triple negative breast cancer models

Combinations of the topoisomerase II inhibitor doxorubicin and the poly (ADP-ribose) polymerase inhibitor olaparib offer potential drug-drug synergy for the treatment of triple negative breast cancers (TNBC). In this study we performed in vitro screening of combinations of these drugs, administered directly or encapsulated within polymer nanoparticles, in both 2D and in 3D spheroid models of breast cancer. A variety of assays were used to evaluate drug potency, and calculations of combination index (CI) values indicated that synergistic effects of drug combinations occurred in a molar-ratio dependent manner. It is suggested that the mechanisms of synergy were related to enhancement of DNA damage as shown by the level of double-strand DNA breaks, and mechanisms of antagonism associated with mitochondrial mediated cell survival, as indicated by reactive oxygen species (ROS) generation. Enhanced drug delivery and potency was observed with nanoparticle formulations, with a greater extent of doxorubicin localised to cell nuclei as evidenced by microscopy, and higher cytotoxicity at the same time points compared to free drugs. Together, the work presented identifies specific combinations of doxorubicin and olaparib which were most effective in a panel of TNBC cell lines, explores the mechanisms by which these combined agents might act, and shows that formulation of these drug combinations into polymeric nanoparticles at specific ratios conserves synergistic action and enhanced potency in vitro compared to the free drugs.

Precise and systematic end group chemistry modifications on PAMAM and poly(l-lysine) dendrimers to improve cytosolic delivery of mRNA

Here, we aimed to chemically modify PAMAM dendrimers using lysine as a site-selective anchor for successfully delivering mRNA while maintaining a low toxicity profile. PAMAM dendrimers were multi-functionalised by amidation reactions in a regioselective, quantitative and stepwise manner with carefully selected property-modifying surface groups. Alternatively, novel lysine-based dendrimers were prepared in the same manner with the aim to unlock their potential in gene delivery. The modified dendrimers were then formulated with Cy5-EGFP mRNA by bulk mixing via liquid handling robotics across different nitrogen to phosphate ratios. The resulting dendriplexes were characterised by size, charge, mRNA encapsulation, and mRNA binding affinity. Finally, their in-vitro delivery activity was systematically investigated across key cellular trafficking stages to relate chemical design to cellular effect. We demonstrate our findings in different cell lines and benchmarked relative to a commercially available transfection agent, jetPEI®. We demonstrate that specific surface modifications are required to generate small, reliable and well-encapsulated positively charged dendriplex complexes. Furthermore, we show that introduction of fusogenic groups is essential for driving endosomal escape and achieving cellular delivery and translation of mRNA in these cell lines.

The Global Characterisation of a Drug-Dendrimer Conjugate - PEGylated poly-lysine Dendrimer

The recent emergence of drug-dendrimer conjugates within pharmaceutical industry research and development introduces a range of challenges for analytical and measurement science. These molecules are very high molecular weight (100-200kDa) with a significant degree of structural complexity. The characteristics and quality attributes that require understanding and definition, and impact efficacy and safety, are diverse. They relate to the intact conjugate, the various building blocks of these complex systems and the level of the free and bound active pharmaceutical ingredient (API). From an analytical and measurement science perspective, this necessitates the measurement of the molecular weight, impurity characterisation, the quantitation of the number of conjugated versus free API molecules, the determination of the impurity profiles of the building blocks, primary structure and both particle size and morphology. Here we report the first example of a global characterisation of a drug-dendrimer conjugate - PEGylated poly-lysine dendrimer currently under development (AZD0466). The impact of the wide variety of analytical and measurement techniques on the overall understanding of this complex molecular entity is discussed, with the relative capabilities of the various approaches compared. The results of this study are an essential platform for the research and development of the future generations of related dendrimer-based medicines.

Subcutaneous delivery of a dendrimer-BH3 mimetic improves lymphatic uptake and survival in lymphoma

As a malignant tumour of lymphatic origin, B-cell lymphoma represents a significant challenge for drug delivery, where effective therapies must access malignant cells in the blood, organs and lymphatics while avoiding off-target toxicity. Subcutaneous (SC) administration of nanomedicines allows preferential access to both the lymphatic and blood systems and may therefore provide a route to enhanced drug exposure to lymphomas. Here we examine the impact of SC dosing on lymphatic exposure, pharmacokinetics (PK), and efficacy of AZD0466, a small molecule dual Bcl-2/Bcl-xL inhibitor conjugated to a 'DEP®' G5 poly-l-lysine dendrimer. PK studies reveal that the plasma half-life of the dendrimer-drug conjugate is 8-times longer than that of drug alone, providing evidence of slow release from the circulating dendrimer nanocarrier. The SC dosed construct also shows preferential lymphatic transport, with over 50% of the bioavailable dose recovered in thoracic lymph. Increases in dose (up to 400 mg/kg) are well tolerated after SC administration and studies in a model of disseminated lymphoma in mice show that high dose SC treatment outperforms IV administration using doses that lead to similar total plasma exposure (lower peak concentrations but extended exposure after SC). These data show that the DEP® dendrimer can act as a circulating drug depot accessing both the lymphatic and blood circulatory systems. SC administration improves lymphatic exposure and facilitates higher dose administration due to improved tolerability. Higher dose SC administration also results in improved efficacy, suggesting that drug delivery systems that access both plasma and lymph hold significant potential for the treatment of haematological cancers where lymphatic and extranodal dissemination are poor prognostic factors.

Synthesis, characterisation and evaluation of hyperbranched N-(2-hydroxypropyl) methacrylamides for transport and delivery in pancreatic cell lines in vitro and in vivo

Hyperbranched polymers have many promising features for drug delivery, owing to their ease of synthesis, multiple functional group content, and potential for high drug loading with retention of solubility. Here we prepared hyperbranched N-(2-hydroxypropyl)methacrylamide (HPMA) polymers with a range of molar masses and particle sizes, and with attached dyes, radiolabel or the anticancer drug gemcitabine. Reversible addition-fragmentation chain transfer (RAFT) polymerisation enabled the synthesis of pHPMA polymers and a gemcitabine-comonomer functionalised pHPMA polymer pro-drug, with diameters of the polymer particles ranging from 7-40 nm. The non-drug loaded polymers were well-tolerated in cancer cell lines and macrophages, and were rapidly internalised in 2D cell culture and transported efficiently to the centre of dense pancreatic cancer 3D spheroids. The gemcitabine-loaded polymer pro-drug was found to be toxic both to 2D cultures of MIA PaCa-2 cells and also in reducing the volume of MIA PaCa-2 spheroids. The non-drug loaded polymers caused no short-term adverse effects in healthy mice following systemic injection, and derivatives of these polymers labelled with ⁸⁹Zr-were tracked for their distribution in the organs of healthy and MIA PaCa-2 xenograft bearing Balb/c nude mice. Tumour accumulation, although variable across the samples, was highest in individual animals for the pHPMA polymer of ∼20 nm size, and accordingly a gemcitabine pHPMA polymer pro-drug of ∼18 nm diameter was evaluated for efficacy in the tumour-bearing animals. The efficacy of the pHPMA polymer pro-drug was very similar to that of free gemcitabine in terms of tumour growth retardation, and although there was a survival benefit after 70 days for the polymer pro-drug, there was no difference at day 80. These data suggest that while polymer pro-drugs of this type can be effective, better tumour targeting and enhanced in situ release remain as key obstacles to clinical translation even for relatively simple polymers such as pHPMA.

Multi-modal molecular imaging maps the correlation between tumor microenvironments and nanomedicine distribution

Gaining insight into the heterogeneity of nanoparticle drug distribution within tumors would improve both design and clinical translation of nanomedicines. There is little data showing the spatio-temporal behavior of nanomedicines in tissues as current methods are not able to provide a comprehensive view of the nanomedicine distribution, released drug or its effects in the context of a complex tissue microenvironment. Methods: A new experimental approach which integrates the molecular imaging and bioanalytical technologies MSI and IMC was developed to determine the biodistribution of total drug and drug metabolite delivered via PLA-PEG nanoparticles and to overlay this with imaging of the nanomedicine in the context of detailed tumor microenvironment markers. This was used to assess the nanomedicine AZD2811 in animals bearing three different pre-clinical PDX tumors. Results: This new approach delivered new insights into the nanoparticle/drug biodistribution. Mass spectrometry imaging was able to differentiate the tumor distribution of co-dosed deuterated non-nanoparticle-formulated free drug alongside the nanoparticle-formulated drug by directly visualizing both delivery approaches within the same animal or tissue. While the IV delivered free drug was uniformly distributed, the nanomedicine delivered drug was heterogeneous. By staining for multiple biomarkers of the tumor microenvironment on the same tumor sections using imaging mass cytometry, co-registering and integrating data from both imaging modalities it was possible to determine the features in regions with highest nanomedicine distribution. Nanomedicine delivered drug was associated with regions higher in macrophages, as well as more stromal regions of the tumor. Such a comparison of complementary molecular data allows delineation of drug abundance in individual cell types and in stroma. Conclusions: This multi-modal imaging solution offers researchers a better understanding of drug and nanocarrier distribution in complex tissues and enables data-driven drug carrier design.

Method to Investigate the Distribution of Water-Soluble Drug-Delivery Systems in Fresh Frozen Tissues Using Imaging Mass Cytometry

Imaging mass cytometry (IMC) offers the opportunity to image metal- and heavy halogen-containing xenobiotics in a highly multiplexed experiment with other immunochemistry-based reagents to distinguish uptake into different tissue structures or cell types. However, in practice, many xenobiotics are not amenable to this analysis, as any compound which is not bound to the tissue matrix will delocalize during aqueous sample-processing steps required for IMC analysis. Here, we present a strategy to perform IMC experiments on a water-soluble polysarcosine-modified dendrimer drug-delivery system (S-Dends). This strategy involves two consecutive imaging acquisitions on the same tissue section using the same instrumental platform, an initial laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MSI) experiment followed by tissue staining and a standard IMC experiment. We demonstrated that settings can be found for the initial ablation step that leave sufficient residual tissue for subsequent antibody staining and visualization. This workflow results in lateral resolution for the S-Dends of 2 μm followed by imaging of metal-tagged antibodies at 1 μm.

Abstract 1718: Design and optimization of a dendrimer-conjugated dual Bcl-2/Bcl-xL inhibitor, AZD0466, with improved therapeutic index

Dual Bcl-2/Bcl-xL inhibitors are expected to deliver therapeutic benefit in many hematological and solid tumors, but their clinical application has been limited by tolerability issues, including thrombocytopenia. AZD4320, a potent dual Bcl-2/Bcl-xL inhibitor, showed good efficacy but encountered dose limiting cardiovascular toxicity in preclinical species, and had challenging physicochemical properties which prevented its clinical development. Nanocarriers can provide prolonged circulation time, controlled release, tumor accumulation and retention. Consequently, they have been explored to improve the therapeutic index of small molecules in oncology. This work describes the design and development of AZD0466, a novel drug-dendrimer conjugate, where AZD4320 is chemically conjugated to Starpharma's DEP® dendrimer platform, a 5-generation PEGylated poly-lysine dendrimer via a hydrolytically labile linker. Release of AZD4320 is through hydrolytic cleavage of the linker, which is characterized by a “release half-life”, defined as the time to release 50% of the active moiety. This release half-life can be modified through linker design.

Initially, three drug-dendrimer conjugates with a range of AZD4320 release half-lives (from 1.7 h to 217 h) were synthesized and efficacy was investigated in C.B-17 SCID mice bearing RS4;11 tumors while cardiovascular parameters and tolerance were assessed in a telemetered rat model. A mathematical model was developed and used to optimize the desired release rate of the active moiety, AZD4320, from the dendrimer conjugate for maximal therapeutic index in terms of preclinical anti-tumor efficacy and cardiovascular profile. Based on this modeling, AZD0466, with a release half-life of 25.5 h, was synthesized and selected for further in vivo efficacy and tolerability assessment.

Efficacy studies in the RS4;11 xenograft model showed similar efficacy to AZD4320, while cardiovascular studies in rat and dog demonstrated that AZD0466 was tolerated at doses of active-moiety that are more than ten-fold higher. In addition, it can be easily formulated for intravenous administration due to significantly enhanced solubility.

The AZD4320-dendrimer conjugate, AZD0466, identified in this study has resulted in an improved therapeutic index and enabled progression of this promising Bcl-2/Bcl-xL inhibitor into clinical development.

Citation Format: Marianne B. Ashford, Srividya B. Balachander, Lorraine Graham, Iain Grant, Francis D. Gibbons, Kathryn J. Hill, Alexander R. Harmer, Sonya Gales, Sean Redmond, Brian Kelly, William McCoull, Shenghua Wen, Martin Wild, Eric Gangl, David J. Owen, Barry R. Davies. Design and optimization of a dendrimer-conjugated dual Bcl-2/Bcl-xL inhibitor, AZD0466, with improved therapeutic index [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1718.

Abstract 1727: Challenging resistance to temozolomide in glioblastoma by drug encapsulation in apoferritin

Background: Temozolomide (TMZ) is a DNA alkylating prodrug used for the treatment of malignant, glioblastoma multiforme (GBM) tumors. Yet, TMZ therapy is blighted by resistance systems in GBM that thwart eradication of all cancer cells remaining after surgery and radiotherapy. Resistance mechanisms include drug efflux by P-glycoprotein 1 (Pgp), present on the blood brain barrier (BBB) and on GBM cells, overexpression of O6-methylguanine DNA-methyltransferase (MGMT), which removes cytotoxic O6-methylated guanine (O6-MeG) lesions caused by TMZ, and deficiency in mismatch repair (MMR), which leads to tolerance of O6-MeG lesions. Nanoscale delivery systems are proposed as a strategy to enhance drug targeting and accumulation under systemically tolerable conditions. Apoferritin (AFt), a hollow protein capsule, has been used to deliver anticancer agents. Transferrin receptor 1 (TfR1) binding sites on the AFt cage has reportedly been shown to allow AFt to cross the BBB and accumulate in GBM cells, as both BBB endothelial and GBM (but not glial) cells express TfR1. Thus, we use AFt for targeted delivery, specific uptake and controlled release of TMZ in GBM.

Methods: TMZ was encapsulated into AFt via molecular diffusion through the channels in the AFt cage. Encapsulation efficiency and stability for this formulation were assessed by dynamic light scattering (DLS) and UV-vis spectroscopy. In vitro assays were conducted (MTT, live cell count, clonogenic, flow cytometry and ELISA) against isogenic GBM cell lines, U373V (vector control) and U373M (MGMT overexpressing), as well as MMR deficient and Pgp overexpressing HCT116 (colorectal carcinoma) and healthy MRC-5 (lung fibroblasts) cells. Environmental scanning electron microscopy (ESEM) and confocal microscopy were further employed to assess morphological changes to the cells after treatment.

Results: Encapsulation of > 500 molecules of TMZ per AFt cage was achieved, with encapsulation efficiency > 70%. MTT assays demonstrated significantly increased activity of AFt-TMZ compared to TMZ alone in all cancer cell lines, with 50% growth inhibition (GI50) in resistant cancer cell lines at < 15 μM, compared to > 200 μM for TMZ alone. Clonogenic and flow cytometric cell cycle and DNA damage analyses further corroborate these findings. Additionally, ELISA quantification demonstrated significantly (P < 0.001) elevated O6-MeG levels following treatment of U373V and U373M cells with AFt-TMZ compared to naked TMZ, correlating with enhanced γ-H2AX burden in cells following exposure to AFt-TMZ. Against MRC-5, lower activity was observed, with GI50 for AFt-TMZ > 70 μM. Furthermore, cell shrinkage and blebbing were observed in GBM cells following 24 h treatment with AFt-TMZ.

Conclusions: TMZ delivered by AFt demonstrated enhanced potency. Overcoming resistance by enhancing TMZ intracellular accumulation, may prove to be a turning point in enhancing drug efficacy in GBM.

Citation Format: Kaouthar Bouzinab, Neil R. Thomas, Lyudmila Turyanska, Pavel Gershkovich, Nicola Weston, Marianne B. Ashford, Tracey D. Bradshaw. Challenging resistance to temozolomide in glioblastoma by drug encapsulation in apoferritin [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1727.

Synthesis and Characterization of Dendrimer-Based Polysarcosine Star Polymers: Well-Defined, Versatile Platforms Designed for Drug-Delivery Applications

This paper describes the synthesis of star polymers designed for future drug-delivery applications. A generation-5 lysine dendrimer was used as a macroinitiator for the ring-opening polymerization of the sarcosine N-carboxyanhydride monomer to produce 32-arm star polymers with narrow molar mass distributions and desirable hydrodynamic size control. Fluorescent dye-labeled polymers were dosed in mice to measure plasma pharmacokinetics. Long circulation times were observed, representing ideal properties for biophysical targeting of tumors. In vivo efficacy of one of these star polymers conjugated to the therapeutic molecule SN-38 was evaluated in mice bearing SW620 xenografted tumors to demonstrate high antitumor activity and low body weight loss compared to the SN-38 prodrug irinotecan and this shows the potential of these delivery systems. As a further build, we demonstrated that these star polymers can be easily chain-end-functionalized with useful chemical moieties, giving opportunities for future receptor-targeting strategies. Finally, we describe the synthetic advantages of these star polymers that make them attractive from a pharmaceutical manufacturing perspective and report characterization of the polymers with a variety of techniques.

Delivery of Temozolomide and N3-Propargyl Analog to Brain Tumors Using an Apoferritin Nanocage

Glioblastoma multiforme (GBM) is a grade IV astrocytoma, which is the most aggressive form of brain tumor. The standard of care for this disease includes surgery, radiotherapy and temozolomide (TMZ) chemotherapy. Poor accumulation of TMZ at the tumor site, tumor resistance to drug, and dose-limiting bone marrow toxicity eventually reduce the success of this treatment. Herein, we have encapsulated >500 drug molecules of TMZ into the biocompatible protein nanocage, apoferritin (AFt), using a "nanoreactor" method (AFt-TMZ). AFt is internalized by transferrin receptor 1-mediated endocytosis and is therefore able to facilitate cancer cell uptake and enhance drug efficacy. Following encapsulation, the protein cage retained its morphological integrity and surface charge; hence, its cellular recognition and uptake are not affected by the presence of this cargo. Additional benefits of AFt include maintenance of TMZ stability at pH 5.5 and drug release under acidic pH conditions, encountered in lysosomal compartments. MTT assays revealed that the encapsulated agents displayed significantly increased antitumor activity in U373V (vector control) and, remarkably, the isogenic U373M (MGMT expressing TMZ-resistant) GBM cell lines, with GI₅₀ values <1.5 μM for AFt-TMZ, compared to 35 and 376 μM for unencapsulated TMZ against U373V and U373M, respectively. The enhanced potency of AFt-TMZ was further substantiated by clonogenic assays. Potentiated G2/M cell cycle arrest following exposure of cells to AFt-TMZ indicated an enhanced DNA damage burden. Indeed, increased O6-methylguanine (O6-MeG) adducts in cells exposed to AFt-TMZ and subsequent generation of γH2AX foci support the hypothesis that AFt significantly enhances the delivery of TMZ to cancer cells in vitro, overwhelming the direct O6-MeG repair conferred by MGMT. We have additionally encapsulated >500 molecules of the N3-propargyl imidazotetrazine analog (N3P), developed to combat TMZ resistance, and demonstrated significantly enhanced activity of AFt-N3P against GBM and colorectal carcinoma cell lines. These studies support the use of AFt as a promising nanodelivery system for targeted delivery, lysosomal drug release, and enhanced imidazotetrazine potency for treatment of GBM and wider-spectrum malignancies.

Critical considerations for targeting colorectal liver metastases with nanotechnology

Colorectal cancer remains a significant cause of morbidity and mortality worldwide. Half of all patients develop liver metastases, presenting unique challenges for their treatment. The shortcomings of conventional chemotherapy has encouraged the use of nanomedicines; the application of nanotechnology in the diagnosis and treatment of disease. In spite of technological improvements in nanotechnology, the complexity of biological systems hinders the prospect of nanomedicines being applied in cancer therapy at the present time. This review highlights current biological barriers and discusses aspects of tumor biology together with the physicochemical features of the nanocarrier, that need to be considered in order to develop effective nanotherapeutics for colorectal cancer patients with liver metastases. It becomes clear that incorporating an interdisciplinary approach when developing nanomedicines should assure appropriate disease-driven design and that this will form a critical step in improving their clinical translation. This article is characterized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

High-resolution 3D visualization of nanomedicine distribution in tumors

To improve the clinical translation of anti-cancer nanomedicines, it is necessary to begin building specific insights into the broad concept of the Enhanced Permeability and Retention (EPR) effect, using detailed investigations of the accumulation, distribution and retention of nanomedicines in solid tumors. Nanomedicine accumulation in preclinical tumors has been extensively studied; however, treatment efficacy will be heavily influenced by both the quantity of drug-loaded nanomedicines reaching the tumor as well as their spatial distribution throughout the tumor. It remains a challenge to image the heterogeneity of nanomedicine distribution in 3 dimensions within solid tumors with a high degree of spatial resolution using standard imaging approaches.

Methods: To achieve this, an ex vivo micro computed tomography (µCT) imaging approach was developed to visualize the intratumoral distribution of contrast agent-loaded PEGylated liposomes. Using this semi-quantitative method, whole 3-dimensional (3D) tumor liposome distribution was determined with 17 µm resolution in a phenotypically diverse panel of four preclinical xenograft and patient-derived explant (PDX) tumor models.

Results: High-resolution ex vivo μCT imaging revealed striking differences in liposome distribution within tumors in four models with different vascular patterns and densities, stromal contents, and microenvironment morphologies. Following intravenous dosing, the model with the highest density of pericyte-supported vessels showed the greatest liposome accumulation, while the model with vessels present in regions of high α-smooth muscle actin (αSMA) content presented with a large proportion of the liposomes at depths beyond the tumor periphery. The two models with an unsupported vascular network demonstrated a more restricted pattern of liposome distribution.

Conclusion: Taken together, vessel distribution and support (the latter indicative of functionality) appear to be key factors determining the accumulation and distribution pattern of liposomes in tumors. Our findings demonstrate that high-resolution 3D visualization of nanomedicine distribution is a useful tool for preclinical nanomedicine research, providing valuable insights into the influence of the tumor vasculature and microenvironment on nanomedicine localization.

Targeting brain tumours: apoferritin nanocage for delivery of novel analogues of temozolomide

Treatment for glioblastoma multiforme (GBM) consists of surgery, radiotherapy and temozolomide (TMZ) chemotherapy. Nevertheless, patient prognosis remains poor; in England 5-year survival is < 10%. Resistance to TMZ is a major obstacle thwarting successful treatment, due to overexpression of the O6-methylguanine DNA-methyltransferase (MGMT) and deficiency in mismatch repair (MMR). To overcome resistance, novel N3-substituted analogues of TMZ have been developed. An N3-propargyl analogue, T3, has promising activity irrespective of MGMT or MMR status. However, poor brain drug bioavailability and systemic toxicity remain to be resolved. We use apoferritin (AFt) as a biocompatible nano-delivery system for encapsulation of therapeutic agents via molecular diffusion, through channels in the AFt cage. Around 520 molecules of TMZ and T3 per AFt cage were encapsulated. AFt`s small size (diameter: 12 nm) and numerous transferrin receptor recognition sites on its surface; alongside enhanced expression of transferrin receptors (TfR1; which sequester AFt) on the membranes of cancer cells, offer a dual targeting approach towards greater cancer-selectivity. The encapsulated agents have demonstrated significantly increased anti-tumour activity in brain cancer GBM cell lines, U373V (vector control) and U373M (MGMT over-expressing), with growth inhibition GI50 values < 1 μM, compared to > 30 μM for naked drugs. Clonogenic and cell cycle analyses further corroborate these findings. Hence, the AFt nano-delivery system offers a promising route for enhanced specificity, selectivity and potency of TMZ analogues.

Endocytic Profiling of Cancer Cell Models Reveals Critical Factors Influencing LNP-Mediated mRNA Delivery and Protein Expression

Lipid nanoparticles have great potential for delivering nucleic-acid-based therapeutics, but low efficiency limits their broad clinical translation. Differences in transfection capacity between in vitro models used for nanoparticle pre-clinical testing are poorly understood. To address this, using a clinically relevant lipid nanoparticle (LNP) delivering mRNA, we highlight specific endosomal characteristics in in vitro tumor models that impact protein expression. A 30-cell line LNP-mRNA transfection screen identified three cell lines having low, medium, and high transfection that correlated with protein expression when they were analyzed in tumor models. Endocytic profiling of these cell lines identified major differences in endolysosomal morphology, localization, endocytic uptake, trafficking, recycling, and endolysosomal pH, identified using a novel pH probe. High-transfecting cells showed rapid LNP uptake and trafficking through an organized endocytic pathway to lysosomes or rapid exocytosis. Low-transfecting cells demonstrated slower endosomal LNP trafficking to lysosomes and defective endocytic organization and acidification. Our data establish that efficient LNP-mRNA transfection relies on an early and narrow endosomal escape window prior to lysosomal sequestration and/or exocytosis. Endocytic profiling should form an important pre-clinical evaluation step for nucleic acid delivery systems to inform model selection and guide delivery-system design for improved clinical translation.

Evaluating the Efficiency of Hyaluronic Acid for Tumor Targeting via CD44

The development of delivery systems capable of tumor targeting represents a promising strategy to overcome issues related to nonspecific effects of conventional anticancer therapies. Currently, one of the most investigated agents for cancer targeting is hyaluronic acid (HA), since its receptor, CD44, is overexpressed in many cancers. However, most of the studies on CD44/HA interaction have been so far performed in cell-free or genetically modified systems, thus leaving some uncertainty regarding which cell-related factors influence HA binding and internalization (collectively called "uptake") into CD44-expressing cells. To address this, the expression of CD44 (both standard and variants, designated CD44s and CD44v, respectively) was evaluated in human dermal fibroblasts (HDFs) and a large panel of cancer cell lines, including breast, prostate, head and neck, pancreatic, ovarian, colorectal, thyroid, and endometrial cancers. Results showed that CD44 isoform profiles and expression levels vary across the cancer cell lines and HDF and are not consistent within the cell origin. Using composite information of CD44 expression, HA binding, and internalization, we found that the expression of CD44v can negatively influence the uptake of HA, and, instead, when cells primarily expressed CD44s, a positive correlation was observed between expression and uptake. In other words, CD44shigh cells bound and internalized more HA compared to CD44slow cells. Moreover, CD44shigh HDFs were less efficient in uptaking HA compared to CD44shigh cancer cells. The experiments described here are the first step toward understanding the interplay between CD44 expression, its functionality, and the underlying mechanism(s) for HA uptake. The results show that factors other than the amount of CD44 receptor can play a role in the interaction with HA, and this represents an important advance with respect to the design of HA-based carriers and the selection of tumors to treat according to their CD44 expression profile.

In search of effective therapies to overcome resistance to Temozolomide in brain tumours

Glioblastoma multiforme is the most common and lethal brain tumour-type. The current standard of care includes Temozolomide (TMZ) chemotherapy. However, inherent and acquired resistance to TMZ thwart successful treatment. The direct repair protein methylguanine DNA methyltransferase (MGMT) removes the cytotoxic O6-methylguanine (O6-MeG) lesion delivered by TMZ and so its expression by tumours confers TMZ-resistance. DNA mismatch repair (MMR) is essential to process O6-MeG adducts and MMR-deficiency leads to tolerance of lesions, resistance to TMZ and further DNA mutations. In this article, two strategies to overcome TMZ resistance are discussed: (1) synthesis of imidazotetrazine analogues - designed to retain activity in the presence of MGMT or loss of MMR; (2) preparation of imidazotetrazine-nanoparticles to deliver TMZ preferably to the brain and tumour site. Our promising results encourage belief in a future where better prognoses exist for patients diagnosed with this devastating disease.

Evaluating liver uptake and distribution of different poly(2-methyl-2-oxazoline) modified lysine dendrimers following intravenous administration

Residual charge and drug modification determine the cellular distribution in the liver for poly(2-methyl-2-oxazoline) modified lysine dendrimers.

Control of aggregation temperatures in mixed and blended cytocompatible thermoresponsive block co-polymer nanoparticles

A small library of thermoresponsive amphiphilic copolymers based on polylactide-block-poly((2-(2-methoxyethoxy)ethyl methacrylate)-co-(oligoethylene glycol methacrylate)) (PLA-b-P(DEGMA)-co-(OEGMA)), was synthesised by copper-mediated controlled radical polymerisation (CRP) with increasing ratios of OEGMA : DEGMA. These polymers were combined in two ways to form nanoparticles with controllable thermal transition temperatures as measured by particle aggregation. The first technique involved the blending of two (PLA-b-P(DEGMA)-co-(OEGMA)) polymers together prior to assembling nanoparticles (NPs). The second method involved mixing pre-formed nanoparticles of single (PLA-b-P(DEGMA)-co-(OEGMA)) polymers. The observed critical aggregation temperature T_t did not change in a linear relationship with the ratios of each copolymer either in the nanoparticles blended from different copolymers or in the mixtures of pre-formed nanoparticles. However, where co-polymer mixtures were based on (OEG)₉MA ratios within 5-10 mole%, a linear relationship between (OEG)₉MA composition in the blends and T_t was obtained. The data suggest that OEGMA-based copolymers are tunable over a wide temperature range given suitable co-monomer content in the linear polymers or nanoparticles. Moreover, the thermal transitions of the nanoparticles were reversible and repeatable, with the cloud point curves being essentially invariant across at least three heating and cooling cycles, and a selected nanoparticle formulation was found to be readily endocytosed in representative cancer cells and fibroblasts.

Challenges and strategies in anti-cancer nanomedicine development: An industry perspective

Successfully translating anti-cancer nanomedicines from pre-clinical proof of concept to demonstration of therapeutic value in the clinic is challenging. Having made significant advances with drug delivery technologies, we must learn from other areas of oncology drug development, where patient stratification and target-driven design have improved patient outcomes. We should evolve our nanomedicine development strategies to build the patient and disease into the line of sight from the outset. The success of small molecule targeted therapies has been significantly improved by employing a specific decision-making framework, such as AstraZeneca's 5R principle: right target/efficacy, right tissue/exposure, right safety, right patient, and right commercial potential. With appropriate investment and collaboration to generate a platform of evidence supporting the end clinical application, a similar framework can be established for enhancing nanomedicine translation and performance. Building informative data packages to answer these questions requires the following: (I) an improved understanding of the heterogeneity of clinical cancers and of the biological factors influencing the behaviour of nanomedicines in patient tumours; (II) a transition from formulation-driven research to disease-driven development; (III) the implementation of more relevant animal models and testing protocols; and (IV) the pre-selection of the patients most likely to respond to nanomedicine therapies. These challenges must be overcome to improve (the cost-effectiveness of) nanomedicine development and translation, and they are key to establishing superior therapies for patients.

In vitro co-culture model of medulloblastoma and human neural stem cells for drug delivery assessment

Physiologically relevant in vitro models can serve as biological analytical platforms for testing novel treatments and drug delivery systems. We describe the first steps in the development of a 3D human brain tumour co-culture model that includes the interplay between normal and tumour tissue along with nutrient gradients, cell-cell and cell-matrix interactions. The human medulloblastoma cell line UW228-3 and human foetal brain tissue were marked with two supravital fluorescent dyes (CDCFDASE, Celltrace Violet) and cultured together in ultra-low attachment 96-well plates to form reproducible single co-culture spheroids (d = 600 μm, CV% = 10%). Spheroids were treated with model cytotoxic drug etoposide (0.3-100 μM) and the viability of normal and tumour tissue quantified separately using flow cytometry and multiphoton microscopy. Etoposide levels of 10 μM were found to maximise toxicity to tumours (6.5% viability) while stem cells maintained a surviving fraction of 40%. The flexible cell marking procedure and high-throughput compatible protocol make this platform highly transferable to other cell types, primary tissues and personalised screening programs. The model's key anticipated use is for screening and assessment of drug delivery strategies to target brain tumours, and is ready for further developments, e.g. differentiation of stem cells to a range of cell types and more extensive biological validation.

Multiplexing spheroid volume, resazurin and acid phosphatase viability assays for high-throughput screening of tumour spheroids and stem cell neurospheres

Three-dimensional cell culture has many advantages over monolayer cultures, and spheroids have been hailed as the best current representation of small avascular tumours in vitro. However their adoption in regular screening programs has been hindered by uneven culture growth, poor reproducibility and lack of high-throughput analysis methods for 3D. The objective of this study was to develop a method for a quick and reliable anticancer drug screen in 3D for tumour and human foetal brain tissue in order to investigate drug effectiveness and selective cytotoxic effects. Commercially available ultra-low attachment 96-well round-bottom plates were employed to culture spheroids in a rapid, reproducible manner amenable to automation. A set of three mechanistically different methods for spheroid health assessment (Spheroid volume, metabolic activity and acid phosphatase enzyme activity) were validated against cell numbers in healthy and drug-treated spheroids. An automated open-source ImageJ macro was developed to enable high-throughput volume measurements. Although spheroid volume determination was superior to the other assays, multiplexing it with resazurin reduction and phosphatase activity produced a richer picture of spheroid condition. The ability to distinguish between effects on malignant and the proliferating component of normal brain was tested using etoposide on UW228-3 medulloblastoma cell line and human neural stem cells. At levels below 10 µM etoposide exhibited higher toxicity towards proliferating stem cells, whereas at concentrations above 10 µM the tumour spheroids were affected to a greater extent. The high-throughput assay procedures use ready-made plates, open-source software and are compatible with standard plate readers, therefore offering high predictive power with substantial savings in time and money.

Stimulation of Triglyceride-Rich Lipoprotein Secretion by Polysorbate 80: In Vitro and in Vivo Correlation Using Caco-2 Cells and a Cannulated Rat Intestinal Lymphatic Model

PURPOSE

To assess the effects of polysorbates 80 and 60 on intestinal lipoprotein processing in vitro, using Caco-2 cells, and to compare the results with those obtained using an in vivo intestinal lymphatic cannulated rat model.

METHODS

Caco-2 monolayers were used to monitor changes in lipoprotein secretion following exposure to excipients. In vivo data was obtained by monitoring intestinal lymphatic triglyceride levels following intraduodenal administration of the excipient to an anesthetised mesenteric lymph cannulated rat.

RESULTS

Caco-2 cells digested the polysorbate 80 to liberate oleic acid, which was used by the cells to enhance basolateral secretion of triglyceride-rich lipoproteins including chylomicrons. This response was not seen with polysorbate 60. Polysorbate 80 elicited a similar response in vivo in the rat model, stimulating enhanced triglyceride secretion in mesenteric lymph. Inhibition of lipoprotein secretion by Cremophor EL in Caco-2 cells was reversed by co-administration with polysorbate 80.

CONCLUSIONS

Polysorbate 80 promoted chylomicron secretion in Caco-2 cells and counteracted the inhibitory effects of other surfactants. These properties, in tandem with its P-gp inhibitory activity, make polysorbate 80 an ideal excipient for lymphotrophic vehicles. The ability to predict the in vivo response to Polysorbate 80 implies that the Caco-2 model is useful for studying absorption mechanisms from oral lipid-based formulations.

The effects of pluronics block copolymers and Cremophor EL on intestinal lipoprotein processing and the potential link with P-glycoprotein in Caco-2 cells

PURPOSE

This investigation was performed to study the effects of Pluronic block copolymers and Cremophor EL on intestinal lipoprotein processing and to investigate a potential link between lipoprotein processing and P-glycoprotein.

METHODS

Caco-2 cells were used to monitor changes in lipoprotein production and secretion following exposure to excipients. Effects on P-glycoprotein were monitored using cyclosporin A as a model substrate.

RESULTS

A range of surfactants commonly used as pharmaceutical excipients in lipid-based oral drug delivery systems, including Pluronics block copolymers L81, P85, and F68 and Cremophor EL, inhibited intestinal lipoprotein secretion. The effects were concentration dependent and reversible. The mechanism of inhibition appears to be related to the assembly and secretion of lipoproteins rather than to initial intracellular triglyceride synthesis. A strong correlation was found between excipient-mediated inhibition of lipoprotein secretion and inhibition of P-glycoprotein efflux, implying a link between the two biochemical processes.

CONCLUSION

The ability of such bioactive excipients to simultaneously manipulate different cellular processes must be considered in selecting excipients for oral drug delivery systems. Such information is particularly relevant when the drug is lipophilic, a candidate for P-glycoprotein efflux, and where intestinal lymphatic targeting via chylomicron stimulation is desirable.