Leaky Tumor Vessels Research Articles

Abstract LB447: Drug delivery and efficacy testing using vascularized tumor-on-a-chip

Abstract The inhibition of tumor angiogenesis is considered a promising strategy to impede cancer progression, as the vasculature associated with tumors plays a crucial role in supplying blood and facilitating metastasis. Therefore, the in vitro replication of vascularized tumors is essential for comprehending cancer pathology and discerning the mechanisms governing tumor cell proliferation, metastasis, and response to pharmaceutical interventions. In this study, we fabricated vascularized tumor-on-a-chip to recapitulate the pathological features of solid tumors. We first developed hybrid spheroids consisting of tumor and endothelial cells, resulting in self-assembled intratumoral vessels. This approach enhanced the uniformity of the spheroids and peritumoral angiogenic capacity compared to spheroids composed of only cancer cells. RNA sequencing analysis revealed that the tumor-EC hybrid spheroids exhibited expression profiles associated with aggressive behaviors, such as cancer progression, invasion and metastasis. The blood vessels sprouting around the hybrid spheroids on the chip displayed the distinctive characteristics of leaky tumor vessels. We further validated the suppressive effects of axitinib on tumor growth and angiogenesis, depending on exposure dose and time. Notably, we successfully induced both lymphangiogenesis and angiogenesis around the tumor hybrid spheroids by promoting interstitial flow. In summary, our findings demonstrated that vascularized tumor-on-a-chip reproduces various characteristics of vascularized tumors. Consequently, our model stands as a valuable platform for investigating interactions between within tumor microenvironments and exploring therapeutic strategies in cancer. Citation Format: Da-Hyun Kim. Drug delivery and efficacy testing using vascularized tumor-on-a-chip [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB447.

A Multicenter, Prospective Clinical Study of the R-CDOP Regimen in Previously Untreated Non-Hodgkin Lymphoma with High Tumor Burden

Background: The treatment of non-Hodgkin lymphoma (NHL) with high tumor burden is facing severe challenges. The response rate and survival of R-CHOP treatment still need to be further explored in these patients. Pegylated liposomal doxorubicin (PLD) is a promising alternative drug to the current regimen, with a safety and efficacy profile through the enhanced permeability and retention effect and longer circulation1-3, and especially less cardiotoxic compared with traditional anthracyclines4. We conducted this prospective study to evaluate the efficacy and safety of PLD combined with R-COP (R-CDOP) regimen in treatment for previously untreated (TN) NHL with high tumor burden. Methods: This study was a single-arm, multicenter, prospective clinical trial (NCT05040555). TN Patients with CD20+ diffuse large B-cell lymphoma or grade 3b follicular lymphoma with high tumor burden were recruited. Patients are considered to have high tumor burden if they meet at least one of the following criteria: (1) presence of at least three lymph nodes with a diameter of 3 cm or more; (2) presence of any lymph nodes or extranodal masses with a diameter of 7 cm or more; (3) presence of hepatomegaly and splenomegaly confirmed by PET-CT; Spleen: female > 15cm, male > 16cm); (4) presence of pleural and peritoneal effusions determined through cytological examination, flow cytometry, or diagnosed by PET-CT, (5) LDH levels exceeding 3 times the upper limit of normal value, and (6) PET-CT TMTV exceeding 220cm3. The patients received PLD (30-35mg/ m2, d1) plus Rituximab (375mg/m2, d0), Cyclophosphamide (750mg/ m2, d1), Vindesine (3mg/ m2, d1) / Vincristine (1.4mg/m2, d1) and Prednisone (60mg/ m2, d1-5) Q3W for 4 (Limited-stage lymphoma) or 6 (Advanced lymphoma) cycles with an additional 2 cycles of Rituximab therapy. The primary endpoints was objective response rate (ORR). The secondary endpoint were complete response rate (CRR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and safety. Results: At the data cut-off of 5 June 2023, 44 eligible pts were enrolled (Table 1). The ORR and CRR was 84.2% (32/38) [95%CI, 68.8%-94.0%] and 60.5% (23/38) [95%CI, 43.4-76.0%], respectively. The DCR was 89.5% (34/38) [95%CI, 75.2%-97.1%]. The median PFS was 14.4 months [95%CI, 4.7%-24.2%], and the median OS was not reached. The median PFS and OS will be updated after long-term follow-up. The most common grade 3/4 AEs were neutropenia (29.5%), leucopenia (25.0%) and anemia (11.4%). Left ventricular ejection fraction (LVEF) declined in 1(1/44, 2.3%) pt, but did not fall below 50%. Congestive heart failure was not occurred. Dose adjustment and treatment delay due to AE occurred in only one pt, and no treatment termination due to AE occurred except for 1 patient death. Conclusions: The preliminary results of the study indicate that the R-CDOP regimen is safe and shows promising efficacy for treating TN NHL with a high tumor burden. References： 1. Hashizume H, Baluk P, Morikawa S, et al. Openings between defective endothelial cells explain tumor vessel leakiness. Am J Pathol. 2000;156 (4):1363-1380 2. Gabizon A, Shmeeda H, Grenader T. Pharmacological basis of pegylated liposomal doxorubicin: impact on cancer therapy. Eur J Pharm Sci. 2012;45(4):388-398. 3. Sadzuka Y, Sugiyama I, Tsuruda T, et al. Characterization and cytotoxicity of mixed polyethyleneglycol modified liposomes containing doxorubicin. Int J Pharm. 2006;312(1-2):83-89. 4. Lu B, Shen L, Ma Y, et al. Cardiovascular adverse events associated with cyclophosphamide, pegylated liposomal doxorubicin, vincristine, and prednisone with or without rituximab ((R)-CDOP) in non-Hodgkin's lymphoma: A systematic review and meta-analysis. Front Pharmacol. 2022;13:1060668.

3D microengineered vascularized tumor spheroids for drug delivery and efficacy testing.

Tumor angiogenesis is regarded as a promising target for limiting cancer progression because tumor-associated vasculature supplies blood and provides a path for metastasis. Thus, in vitro recapitulation of vascularized tumors is critical to understand the pathology of cancer and identify the mechanisms by which tumor cells proliferate, metastasize, and respond to drugs. In this study, we microengineered a vascularized tumor spheroid (VTS) model to reproduce the pathological features of solid tumors. We first generated tumor-EC hybrid spheroids with self-assembled intratumoral vessels, which enhanced the uniformity of the spheroids and peritumoral angiogenic capacity compared to spheroids composed only with cancer cells. Notably, the hybrid spheroids also exhibited expression profiles associated with aggressive behavior. The blood vessels sprouting around the hybrid spheroids on the VTS chip displayed the distinctive characteristics of leaky tumor vessels. With the VTS chip showing a progressive tumor phenotype, we validated the suppressive effects of axitinib on tumor growth and angiogenesis, which depended on exposure dose and time, highlighting the significance of tumor vascularization to predict the efficacy of anticancer drugs. Ultimately, we effectively induced both lymphangiogenesis and angiogenesis around the tumor spheroid by promoting interstitial flow. Thus, our VTS model is a valuable platform with which to investigate the interactions between tumor microenvironments and explore therapeutic strategies in cancer. STATEMENT OF SIGNIFICANCE: We conducted an integrative study within a vascularized tumor spheroid (VTS) model. We first generated tumor-EC hybrid spheroids with self-assembled intratumoral vessels, which enhanced the uniformity of the spheroids and peritumoral angiogenic capacity compared to spheroids composed only with cancer cells. Through RNA sequencing, we elucidated that the tumor-EC hybrid spheroids exhibited expression profiles associated with aggressive behavior such as cancer progression, invasion and metastasis. The blood vessels sprouting around the hybrid spheroids on the VTS chip displayed the distinctive characteristics of leaky tumor vessels. We further validated the suppressive effects of axitinib on tumor growth and angiogenesis, depending on exposure dose and time. Ultimately, we effectively induced both lymphangiogenesis and angiogenesis around the tumor spheroid by promoting interstitial flow.

A microfluidic device inspired by leaky tumor vessels for hematogenous metastasis mechanism research.

Endothelial intercellular pores of tumor vessels generally lead to enhanced interstitial flow and may facilitate the migration of tumor cells. The permeability of tumor vessels causes a concentration gradient of growth factors (CGGF) from blood vessels to tumor tissues, which is opposite to the direction of interstitial flow. In this work, exogenous chemotaxis under the CGGF is demonstrated as a mechanism of hematogenous metastasis. A bionic microfluidic device inspired by endothelial intercellular pores of tumor vessels has been designed to study the mechanism. A porous membrane vertically integrated into the device using a novel compound mold is utilized to mimic the leaky vascular wall. The formation mechanism of the CGGF caused by endothelial intercellular pores is numerically analyzed and experimentally verified. The migration behavior of U-2OS cells is studied in the microfluidic device. The device is divided into three regions of interest (ROI): primary site, migration zone, and tumor vessel. The number of cells in the migration zone increases significantly under the CGGF, but decreases under no CGGF, indicating tumor cells may be guided to the vascellum by exogenous chemotaxis. Transendothelial migration is subsequently monitored, demonstrating the successful replication of the key steps in vitro in the metastatic cascade by the bionic microfluidic device.

Bacterial minicells to the rescue: cyto-Immunotherapy for the treatment of late stage cancers with minimal to no toxicity.

Bacterial minicells to the rescue: cyto-Immunotherapy for the treatment of late stage cancers with minimal to no toxicity.

P90RSK-MAGI1 Module Controls Endothelial Permeability by Post-translational Modifications of MAGI1 and Hippo Pathway.

Previously, we reported that post-translational modifications (PTMs) of MAGI1, including S741 phosphorylation and K931 de-SUMOylation, both of which are regulated by p90RSK activation, lead to endothelial cell (EC) activation. However, roles for p90RSK and MAGI1-PTMs in regulating EC permeability remain unclear despite MAGI1 being a junctional molecule. Here, we show that thrombin (Thb)-induced EC permeability, detected by the electric cell-substrate impedance sensing (ECIS) based system, was decreased by overexpression of dominant negative p90RSK or a MAGI1-S741A phosphorylation mutant, but was accelerated by overexpression of p90RSK, siRNA-mediated knockdown of magi1, or the MAGI1-K931R SUMOylation mutant. MAGI1 depletion also increased the mRNA and protein expression of the large tumor suppressor kinases 1 and 2 (LATS1/2), which inhibited YAP/TAZ activity and increased EC permeability. Because the endothelial barrier is a critical mediator of tumor hypoxia, we also evaluated the role of p90RSK activation in tumor vessel leakiness by using a relatively low dose of the p90RSK specific inhibitor, FMK-MEA. FMK-MEA significantly inhibited tumor vessel leakiness at a dose that does not affect morphology and growth of tumor vessels in vivo. These results provide novel insights into crucial roles for p90RSK-mediated MAGI1 PTMs and the Hippo pathway in EC permeability, as well as p90RSK activation in tumor vessel leakiness.

Estimating Tumor Vascular Permeability of Nanoparticles Using an Accessible Diffusive Flux Model.

Understanding the complex interplay of factors affecting nanoparticle accumulation in solid tumors is a challenge that must be surmounted to develop effective cancer nanomedicine. Among other unique microenvironment properties, tumor vascular permeability is an important feature of leaky tumor vessels which enables nanoparticles to extravasate. However, permeability has thus far been measured by intravital microscopy on optical window tumors, which has many limitations of its own. Additionally, mathematical models of particle tumor transport are often too complicated to be accessible to most researchers. Here, we present a more simplified and accessible mathematical model based on diffusive flux, which uses particle tumor accumulation and plasma pharmacokinetics to yield effective permeability, Peff. This model, called diffusive flux modeling (DFM), allows effects from multiple parameters to be decoupled and is also the first demonstration, to the best our knowledge, of extracting Peff values from bulk biodistribution results (e.g., routine positron emission tomography studies). The DFM equation was used to explain in vivo results of sub-20 nm nanocarriers called three-helix-micelles (3HM), particularly 3HM's selective accumulation in different tumor models. When DFM was applied to multiple published biodistribution data, a semiquantitative comparison of various tumor models, particle size, and active targeting strategies could be made. The analysis clearly pointed out the importance of balancing multiple characteristics of nanoparticles to ensure successful treatment outcome and highlights the usefulness of this simple model for initial particle design, selection, and subsequent optimization.

Nanoparticle Delivery and Tumor Vascular Normalization: The Chicken or The Egg?

Tumor-induced angiogenesis has been a significant focus of anti-cancer therapies for several decades. The immature and “leaky” tumor vasculature leads to significant cancer cell intravasation, increasing the metastatic potential, while the disoriented and hypo-perfused tumor vessels hamper the anti-tumor efficacy of immune cells and prevent the efficient diffusion of chemotherapeutic drugs. Therefore, tumor vascular normalization has emerged as a new treatment goal, aiming to provide a mature tumor vasculature, with higher perfusion, decreased cancer cell extravasation, and higher efficacy for anti-cancer therapies. Here we propose an overview of the nanodelivery approaches that target tumor vasculature, aiming to achieve vascular normalization. At the same time, abnormal vascular architecture and leaky tumor vessels have been the cornerstone for nanodelivery approaches through the enhanced permeability and retention (EPR) effect. Vascular normalization presents new opportunities and requirements for efficient nanoparticle delivery against the tumor cells and overall improved anti-cancer therapies.

Controlling the Phenotype of Tumor-Infiltrating Macrophages via the PHD-HIF Axis Inhibits Tumor Growth in a Mouse Model.

SummaryThe tumor microenvironment (TME) polarizes tumor-infiltrating macrophages toward tumor support. Macrophage-abundant tumors are highly malignant and are the cause of poor prognosis and therapeutic resistance. In this study, we show that the prolyl hydroxylase (PHD) inhibitor FG-4592 (FG) inhibits tumor growth of macrophage-abundant tumors and prolongs mouse survival. FG not only normalizes tumor vessels and improves tumor oxygenation but also directly affects macrophages and activates phagocytosis through the PHD-hypoxia-inducible factor (HIF) axis. Remarkably, FG can promote phagocytic ability of the Ly6Clo subset of tumor-infiltrating macrophages, leading to tumor growth inhibition. Moreover, Ly6Cneg macrophages contributed to blood vessel normalization. Using a malignant tumor mouse model, we characterized macrophage function and subsets. Altogether, our findings suggest that the PHD inhibitor can promote the anti-tumor potential of macrophages to improve cancer therapy.

Reengineering the Tumor Vasculature: Improving Drug Delivery and Efficacy

A solid tumor is like an aberrant organ - comprised of cancer cells and a variety of host cells embedded in an extracellular matrix - nourished by blood vessels and drained by lymphatic vessels. In its journey from the blood stream to cancer cells, a therapeutic agent must cross the vessel wall and the extracellular matrix that cancer cells are ensconced in. Growth of tumors in a confined space along with deposition of matrix components, including collagen (yellow) and hyaluronan (pink), increases 'solid stress', which compresses blood and lymphatic vessels and impairs their function. The leakiness of tumor vessels also impairs tumor blood flow and increases 'intratumor fluid pressure'. The abnormal blood flow not only impedes drug delivery, but the resulting hypoxia also aids tumor invasion, metastasis, immunosuppression, inflammation, fibrosis, and treatment resistance. Engineers and physical scientists have dissected the molecular, cellular, and physical mechanisms underlying these abnormalities and developed a number of strategies to reengineer the tumor microenvironment to overcome these barriers and thus improve delivery and efficacy of treatments. Finally, these strategies have been translated from bench to bedside for treatment of cancer and have the potential to improve the treatment outcome for many diseases characterized by an abnormal microenvironment.

Quantifying the effects of antiangiogenic and chemotherapy drug combinations on drug delivery and treatment efficacy.

Tumor-induced angiogenesis leads to the development of leaky tumor vessels devoid of structural and morphological integrity. Due to angiogenesis, elevated interstitial fluid pressure (IFP) and low blood perfusion emerge as common properties of the tumor microenvironment that act as barriers for drug delivery. In order to overcome these barriers, normalization of vasculature is considered to be a viable option. However, insight is needed into the phenomenon of normalization and in which conditions it can realize its promise. In order to explore the effect of microenvironmental conditions and drug scheduling on normalization benefit, we build a mathematical model that incorporates tumor growth, angiogenesis and IFP. We administer various theoretical combinations of antiangiogenic agents and cytotoxic nanoparticles through heterogeneous vasculature that displays a similar morphology to tumor vasculature. We observe differences in drug extravasation that depend on the scheduling of combined therapy; for concurrent therapy, total drug extravasation is increased but in adjuvant therapy, drugs can penetrate into deeper regions of tumor.

Investigation of Factors Determining the Enhanced Permeability and Retention Effect in Subcutaneous Xenografts.

Liposomal chemotherapy offers several advantages over conventional therapies, including high intratumoral drug delivery, reduced side effects, prolonged circulation time, and the possibility to dose higher. The efficient delivery of liposomal chemotherapeutics relies, however, on the enhanced permeability and retention (EPR) effect, which refers to the ability of macromolecules to extravasate leaky tumor vessels and accumulate in the tumor tissue. Using a panel of human xenograft tumors, we evaluated the influence of the EPR effect on liposomal distribution in vivo by injection of pegylated liposomes radiolabeled with (111)In. Liposomal accumulation in tumors and organs was followed over time by SPECT/CT imaging. We observed that fast-growing xenografts, which may be less representative of tumor development in patients, showed higher liposomal accumulation than slow-growing xenografts. Additionally, several other parameters known to influence the EPR effect were evaluated, such as blood and lymphatic vessel density, intratumoral hypoxia, and the presence of infiltrating macrophages. The investigation of various parameters showed a few correlations. Although hypoxia, proliferation, and macrophage presence were associated with tumor growth, no hard conclusions or predictions could be made regarding the EPR effect or liposomal uptake. However, liposomal uptake was significantly correlated with tumor growth, with fast-growing tumors showing a higher uptake, although no biological determinants could be elucidated to explain this correlation.

Safe and efficient local gene delivery into skeletal muscle via a combination of Pluronic L64 and modified electrotransfer

Efficient DNA electrotransfer into muscles can be achieved by combining two types of electronic pulses sequentially: short high-voltage (HV) pulse for the cell electropermeabilization and long low-voltage (LV) pulse for the DNA electrophoresis into cells. However, the voltages currently applied can still induce histological and functional damages to tissues. Pluronic L64 has been considered as a molecule possessing cell membrane-disturbing ability. For these reasons, we hope that L64 can be used as a substitute for the HV pulse in cell membrane permeabilization, and a safe LV pulse may still keep the ability to drive plasmid DNA across the permeabilized membrane. In this work, we optimized the electrotransfer parameters to establish a safe and efficient procedure using a clinically applied instrument, and found out that the critical condition for a successful combination of electrotransfer with L64 was that the injection of plasmid/L64 mixture should be applied 1 h before the electrotransfer. In addition, we revealed that the combined procedure could not efficiently transfer plasmid into solid tumor because the uncompressed plasmid may rapidly permeate the leaky tumor vessels and flow away. Altogether, the results demonstrate that the combined procedure has the potential for plasmid-based gene therapy through safe and efficient local gene delivery into skeletal muscles.

Gold nanoparticles in radiation research: potential applications for imaging and radiosensitization.

The potential of gold nanoparticles (GNPs) in therapeutic and diagnostic cancer applications is becoming increasingly recognized. These biologically compatible particles can be easily synthesized, tuned to different sizes, and functionalized by conjugation to various biologically useful materials. Efficient and specific delivery to tumor tissue can then be accomplished either by passive accumulation in leaky tumor vessels and tissue, or by directly targeting tumor-specific biomarkers. Tumor-localized GNPs can serve as both adjuvants for enhancing the efficacy of radiation therapy and also as contrast agents for various imaging modalities. In this review, we will discuss recent advancements and future potential in the application of GNP as both a radiosensitizer and an imaging contrast agent. Due to their versatility and biocompatibility, gold nanoparticles may represent a novel theranostic adjuvant for radiation applications in cancer management.

Abstract 2338: Aflibercept (VEGF Trap) impairs tumor growth and perfusion, and restrains metastasis invasion in orthotopic models

Abstract Aflibercept (VEGF Trap), a potent angiogenesis inhibitor that binds to all isoforms of circulating VEGF as well as to placental growth factor, is currently in Phase 3 clinical trials in combination with chemotherapy for several cancer indications. The VELOUR Phase 3 trial in oxaliplatin pre-treated metastatic colorectal cancer showed that aflibercept in combination with FOLFIRI significantly improved overall survival, progression-free survival and response rate (in comparison with FOLFIRI plus placebo), with some increases in adverse events. The aim of the current study was to explore the effect of aflibercept on tumor vessel function and determine the impact of a prolonged treatment regimen on the development of metastases in orthotopic preclinical models. For the functional evaluation of tumor perfusion by contrast enhanced ultrasound imaging (CE-US), SCID mice underwent renal subcapsular implantation of the human renal SK-NEP-1 Ewing sarcoma. The pattern of vascularization in these rapidly growing tumors was found to be heterogeneous: tumor areas in the proximal kidney remained highly perfused, while avascular areas appeared in the distal kidney region which is likely a consequence of spontaneous necrosis in large tumors. Aflibercept administered bi-weekly at 40mg/kg for two weeks showed a statistically significant effect on tumor growth (5% T/C). Aflibercept efficiently down-regulated tumor perfusion inducing a reduction of tumor blood volume immediately after the first injection, followed by subsequent stabilization and rebound two weeks after the end of treatment. The MDA-MB-231-D3H2LN-luc breast tumor model spontaneously induces lymph node metastasis when orthotopically implanted into the inguinal mammary fat pads of SCID mice. Aflibercept (at 25 mg/kg) or vehicle were administered bi-weekly for five weeks in mice pair-matched by bioluminescent photon emission rates into aflibercept treatment and control groups. This continuous aflibercept treatment induced antitumor activity on the primary tumors with 19% T/C based on bioluminescent signal at the end of treatment. Aflibercept also controlled metastatic dissemination to the axillary regions with a median 21-day delay for lymph node invasion in treated mice. Conclusion: In an orthotopic Ewing sarcoma model in mice, repeated administrations of aflibercept reduced tumor perfusion and stabilized tumor growth. In an orthotopic mammary carcinoma model, prolonged treatment with aflibercept inhibited tumor growth and delayed spontaneous lymph node metastasis. These outcomes are consistent with the mechanism of action postulated for aflibercept which, upon prolonged treatment is expected to reduce the density of tumor vasculature and the leakiness of tumor vessels, thereby controlling tumor growth and metastatic dissemination. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2338. doi:1538-7445.AM2012-2338

Cancer-Stroma Targeting Therapy by Cytotoxic Immunoconjugate Bound to the Collagen 4 Network in the Tumor Tissue

Some cytotoxic immunoconjugates have been approved for malignant lymphoma, a representative of hypervascular and stroma-poor tumors. However, many human solid tumors possess abundant intercellular stromata that prevent diffusion of cancer cell-specific monoclonal antibodies (mAb) and become a barrier preventing immunoconjugates from directly attacking cancer cells. Here we show the successful development of a new strategy that overcomes this drawback and achieves a highly localized concentration of a topoisomerase I inhibitor, SN 38, by conjugating it via an ester bond to a mAb targeted against collagen 4, a plentiful component of the tumor stroma. Poly(ethylene glycol) (PEG) was utilized as a spacer, close to each bond, to maintain stability in the blood. Immunoconjugates selectively extravasated from leaky tumor vessels and minimally from normal vessels because the immunoconjugates are too large to pass through normal vessel walls. Stroma-targeting immunoconjugates bound to the stroma to create a scaffold, from which sustained release of cytotoxic agent occurred and the agent subsequently diffused throughout the tumor tissue to damage both tumor cells and vessels. Cancer-stroma-targeting immunoconjugate therapy was thus validated as a new modality of oncological therapy, especially for refractory, stromal-rich cancers.

Increased Efficacy of Breast Cancer Chemotherapy in Thrombocytopenic Mice

Platelets contribute to homeostasis of the tumor vasculature by helping prevent hemorrhage. Thus, we hypothesized that inducing thrombocytopenia would increase tumor vascular leakiness and facilitate the effective delivery of chemotherapeutic agents to tumors. In a mammary carcinoma murine model, platelet depletion induced bleeding specifically at the tumor site, favoring the accumulation of fluorescently labeled microspheres only in the tumor. Moreover, induction of thrombocytopenia in tumor-bearing mice before injection of paclitaxel increased its intratumoral accumulation and reduced growth of both slow- and fast-growing tumors, compared with mice with normal platelet counts that were treated only with paclitaxel. Histologic analysis confirmed the expectation of an increase in tumor apoptosis and a reduction in tumor proliferation in thrombocytopenic mice receiving chemotherapy. No increased toxicity was seen in other organs or blood cells. Taken together, our results indicate that low platelet count selectively induces leakiness of tumor vessels and favors the delivery of chemotherapy to tumor sites, enhancing its tumoricidal effects.

Deep in vivo two-photon imaging of blood vessels with a new dye encapsulated in pluronic nanomicelles

Our purpose is to test if Pluronic® fluorescent nanomicelles can be used for in vivo two-photon imaging of both the normal and the tumor vasculature. The nanomicelles were obtained after encapsulating a hydrophobic two-photon dye: di-stryl benzene derivative, in Pluronic block copolymers. Their performance with respect to imaging depth, blood plasma staining, and diffusion across the tumor vascular endothelium is compared to a classic blood pool dye Rhodamin B dextran (70 kDa) using two-photon microscopy. Pluronic nanomicelles show, like Rhodamin B dextran, a homogeneous blood plasma staining for at least 1 h after intravenous injection. Their two-photon imaging depth is similar in normal mouse brain, using 10 times less injected mass. In contrast with Rhodamin B dextran, no extravasation is observed in leaky tumor vessels due to their large size: 20-100 nm. In conclusion, Pluronic nanomicelles can be used as a blood pool dye, even in leaky tumor vessels. The use of Pluronic block copolymers is a valuable approach for encapsulating two-photon fluorescent dyes that are hydrophobic and not suitable for intravenous injection.

Thrombocytopenia Induced-Tumor Vascular Leakiness Increases Drug Efficacy

AbstractAbstract 2105Important research goals in cancer therapy include delivering high doses of drug to tumor sites for maximum treatment efficacy while minimizing side effects to healthy organs. We have recently demonstrated that platelets contribute to tumor vascular homeostasis through prevention of severe tumor hemorrhage. In order to define a new way of increasing drug delivery to the tumor site, we hypothesized that the selective induction of tumor vascular leakiness by thrombocytopenia may facilitate the delivery of chemotherapeutic agents to tumors. Using a mammary carcinoma murine model, we showed that platelet depletion induced hemorrhage specifically at the tumor site and favored the accumulation of fluorescently-labeled microspheres in the tumor. Moreover, the induction of thrombocytopenia in tumor-bearing mice before injection of the chemotherapeutic drug paclitaxel significantly reduced tumor growth compared to mice with normal platelet count that were treated with paclitaxel. Analysis of the tumors ex vivo revealed an increase in tumor apoptosis and a reduction in tumor cell proliferation in thrombocytopenic mice that received therapy. No increased toxicity was seen on other organs and blood cells. Taken together, our results indicate that low platelet count selectively induces leakiness of tumor vessels and allows better access of a chemotherapeutic agent to the tumor, enhancing its tumoricidal effect. Disclosures:No relevant conflicts of interest to declare.

An in vitro Study of a Phase-Shift Nanoemulsion: A Potential Nucleation Agent for Bubble-Enhanced HIFU Tumor Ablation

Phase-shift nanoemulsions have the potential to nucleate bubbles and enhance high-intensity focused ultrasound (HIFU) cancer therapy. This emulsion consists of albumin-coated dodecafluoropentane (DDFP) droplets with a mean diameter of approximately 260 nm at 37°C. It is known that superheated perfluorocarbon droplets can be vaporized with microsecond long ultrasound pulses if the acoustic pressure exceeds a specific threshold. In addition, it is well documented that particles smaller than 400 nm can extravasate through leaky tumor vessels and accumulate in the tumor interstitial space. Thus, nanoemulsions may passively target solid tumors, thus localizing cavitation nuclei for bubble-enhanced HIFU-mediated heating. In this study, we investigate the acoustic droplet vaporization of a DDFP nanoemulsion in tissue-mimicking gels and demonstrate the ability to nucleate inertial cavitation (IC) and enhance HIFU-mediated heating. The nanoemulsion was dispersed throughout albumin-acrylamide gel phantoms and sonicated with microsecond-length HIFU pulses ( f = 2 MHz). The pressure threshold needed to vaporize the nanoemulsion was measured as a function of degree of superheat, pulse length and nanoemulsion concentration. It was determined that the vaporization threshold was inversely proportional with degree of superheat and independent of pulse length and concentration within the range of values tested. It was also shown that the bubbles formed from vaporized nanoemulsions reduced the IC threshold in the gel phantoms. Finally, it was demonstrated that cavitation from vaporized nanoemulsions accelerated HIFU-mediated heating. The results from this study demonstrate that phase-shift nanoemulsions can be combined with HIFU to provide a high degree of spatial and temporal control of bubble-enhanced heating. (E-mail: tmp@bu.edu)