Serum biomarkers for personalization of nanotherapeutics-based therapy in different tumor and organ microenvironments

Enhanced permeation and retention (EPR) effect, the mechanism by which nanotherapeutics accumulate in tumors, varies in patients based on differences in the tumor and organ microenvironment. Surrogate biomarkers for the EPR effect will aid in selecting patients who will accumulate higher amounts of nanotherapeutics and show better therapeutic efficacy. Our data suggest that the differences in the vascular permeability and pegylated liposomal doxorubicin (PLD) accumulation are tumor type as well as organ-specific and significantly correlated with the relative ratio of MMP-9 to TIMP-1 in the circulation, supporting development of these molecules as biomarkers for the personalization of nanoparticle-based therapy.     

Enhanced delivery of macromolecular antitumor drugs to tumors by nitroglycerin application

Dose regimens of anticancer agents are usually designed on the basis of the maximum tolerable drug doses, and toxicity prevents drug usage at higher doses, even though the drugs may be more effective at the higher doses. We previously studied macromolecular anticancer drugs, i.e. those larger than 40 kDa, and observed their accelerated accumulation in tumors. Their concentration in tumors was more than 5–100-fold their blood concentration because of the enhanced permeability and retention (EPR) effect. Here, we report that the EPR effect was enhanced by applying nitroglycerin (NG) ointment on the skin of tumor-bearing animals. Tumors studied included breast cancer, which was induced in Sprague–Dawley rats by the chemical carcinogen 7,12-dimethylbenz[ a ]anthracene, and three different transplanted tumor models in mice. NG was applied on tumor or nontumorous normal skin as well. Two to three times more putative macromolecular drug (an Evans blue/albumin complex) was delivered to solid tumors with NG than without NG. We also demonstrated that NG enhanced tumor delivery with another macromolecular drug candidate, PZP, i.e. polyethylene glycol-conjugated zinc protoporphyrin IX, which inhibits heme oxygenase-1. In addition, we investigated the therapeutic effect of NG using a combination with low molecular weight anthracycline or high molecular weight PZP in mouse tumor models. NG had no apparent toxicity at the doses used, and showed significantly increased therapeutic effects in both cases. Regardless of its site of application, NG thus enhanced the delivery of the drug to tumors, and enhanced therapeutic effects. ( Cancer Sci 2009; 100: 2426–2430)     

The link between infection and cancer: Tumor vasculature,free radicals,and drug delivery to tumors via the EPR effect

This review focuses primarily on my own research, including pathogenic mechanisms of microbial infection, vascular permeability in infection and tumors, and effects of nitric oxide (NO), superoxide anion radical (), and 8‐nitroguanosine in the enhanced permeability and retention (EPR) effect for the tumor‐selective delivery of macromolecular agents (nanomedicines). Infection‐induced vascular permeability is mediated by activation of the kinin‐generating protease cascade (kallikrein–kinin) triggered by exogenous microbial proteases. A similar mechanism operates in cancer tissues and in carcinomatosis of the pleural and peritoneal cavities. Infection also stimulates generation via activation of xanthine oxidase while generating NO by inducing NO synthase. These chemicals function in mutation and carcinogenesis and promote inflammation, in which peroxynitrite (a product of and NO) activates MMP, damages DNA and RNA, and regenerates 8‐nitroguanosine and 8‐oxoguanosine. We showed vascular permeability by using macromolecular drugs, which are not simply extravasated through the vascular wall into the tumor interstitium but remain there for prolonged periods. We thus discovered the EPR effect, which led to the rational development of tumor‐selective delivery of polymer conjugates, micellar and liposomal drugs, and genes. Our styrene–maleic acid copolymer conjugated with neocarzinostatin was the first agent of its kind used to treat hepatoma. The EPR effect occurs not only because of defective vascular architecture but also through the generation of various vascular mediators such as kinin, NO, and vascular endothelial growth factor. Although most solid tumors, including human tumors, show the EPR effect, heterogeneity of tumor tissue may impede drug delivery. This review describes the barriers and countermeasures for improved drug delivery to tumors by using nanomedicines.     

Caveolin-1-deficient mice have increased tumor microvascular permeability, angiogenesis, and growth

Caveolin-1 (Cav-1) is a major structural protein that is essential to the formation of the organelle, caveolae. Cav-1 knockout (KO) mice were observed to be completely devoid of caveolae yet they exhibit a hyperpermeable vasculature. Given the nature of the hyperpermeable Cav-1 KO endothelium, we sought to investigate if tumors grown in Cav-1 KO mice would be leaky and grow faster. Indeed, Lewis lung carcinoma cells implanted into Cav-1 KO mice had increased tumor vascular permeability, measured by Evans blue extravasation and fibrinogen deposition compared with tumors implanted into wild-type (WT) mice. Cav-1 KO mice also had significantly higher tumor growth rates, attributable to increased tumor angiogenesis and decreased tumor cell death. Furthermore, administration of an antipermeability peptide, cavtratin, was able to correct the tumor hyperpermeability as well as attenuate the increased tumor growth. Mechanistically, endothelial cells isolated from Cav-1 KO mice exhibited increased tyrosine phosphorylation on vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2) and decreased association with the adherens junction protein, VE-cadherin. Thus, the loss of Cav-1 increases tumor permeability and growth and that may relate to enhanced VEGF signaling due to lack of Cav-1 inhibition of VEGFR-2 or decreased VE-cadherin mediated VEGFR-2 phosphorylation.     

Enhanced Vascular Permeability in Solid Tumor Is Mediated by Nitric Oxide and Inhibited by Both New Nitric Oxide Scavenger and Nitric Oxide Synthase Inhibitor

A newly discovered nitric oxide radical scavenger, an imidazolineoxyl N -oxide derivative, was used to investigate the role of nitric oxide radical (*NO) in the vascular permeability enhancement of solid tumor. Sarcoma-180 solid tumor in ddY mice was used for this experiment. Electron spin resonance spectroscopy was used to quantitate the reacted and unreacted scavenger. The results showed that extensive extravasation, assessed by intravenous injection of Evans blue, could be greatly suppressed by both *NO scavenger administered orally and *NO synthase inhibitor administrated intraperitoneally. This indicates that *NO is responsible for the vascular permeability in solid tumors.     

Effects of glucocorticoid and chemotherapy on the peritumoral edema and astrocytic reaction in experimental brain tumor

To study the effects of glucocorticoids and chemotherapeutic agents on the pathophysiology of the tumor-induced brain edema, the site of Evans blue-albumin extravasation, the distribution of extravasated serum albumin, and the extent of local astrocytic reaction were examined in a rat model of implanted brain tumor. Experimental brain tumors were produced by implanting small pellets of Walker 256 carcinosarcoma into the cerebral cortex of Wistar rats. In the steroid group, rats were administered with intraperitoneal methylprednisolone succinate (15 mg/kg) daily on and after the 6th day postimplantation, and sacrificed on the 14th day. In the chemotherapy group, rats were given an intravenous injection of cyclophosphamide (30 mg/kg) on the 14th day, and sacrificed on the 21st day. Rats in the untreated group were sacrificed on the 14th day without any therapy. Each animal was sacrificed by the transcardiac perfusion with paraformaldehyde 30 min after intravenous injection of Evans blue. Firstly, coronal blocks of the brain were examined for Evans blue staining macroscopically. Paraffin embedded sections were studied for the Evans blue fluorescence and for the immunohistochemical reaction to serum albumin and GFAP. The examination of Evans blue demonstrated that the origin of extravasation of serum albumin was the tumor and the adjacent brain with dense tumor cell infiltration in any group of rats. The extravasated serum albumin distributed widely and the astrocytic reaction was prominent in the brain of the untreated group. A positive correlation was observed between the intensity of albumin immunoreaction and the degree of astrocytic proliferation. Chemotherapy effectively decreased the size of tumor and reduced the extravasation of serum albumin. The astrocytic reaction was however, not reduced. In the steroid group, the size of tumor was not significantly affected but the albumin extravasation as well as astrocytic reaction was markedly reduced. It was concluded that glucocorticoid is an effective drug against tumor-induced brain edema, which not only reduces the extravasation of serum components but also prevents histologic alterations of the brain.     

The effects of hyperthermia on vascular permeability in experimental liver metastasis

The effects of hyperthermia on vascular permeability in Walker carcinosarcomas and host liver tissue were studied in Sprague-Dawley rats. A quantitative Evans blue technique was used to measure permeability. With tumors heated to 40 degrees C, a nontherapeutic level, no changes in tumor vascular permeability as compared to control levels were noted. However, with tumors heated to 43 degrees C, within the therapeutic range of hyperthermia, significant rises in tumor vascular permeability occurred. Permeability was increased at both time periods studied, 30 minutes and 6 hours after hyperthermia and injection of Evans blue. These changes are similar to those seen after physical damage from freeze-thaw. It is likely that alterations in tumor microcirculation play a role in the therapeutic effect of intense hyperthermia.     

Enhanced vascular permeability in solid tumor involving peroxynitrite and matrix metalloproteinases.

Peroxynitrite (ONOO(-)), which is generated from nitric oxide (NO) and superoxide anion (O(2)(.-)) under pathological conditions, plays an important role in pathophysiological processes. Activation of matrix metalloproteinases (MMPs) contributes to tumor angiogenesis and metastasis. NO mediates the enhanced vascular permeability and retention (EPR) effect in solid tumors, and ONOO(-)activates proMMP to MMP in vitro. In this study, we examined the role of ONOO(-)in the EPR effect in solid tumors and normal tissues as related to MMP activation. Authentic ONOO(-), at 50 nmol or higher concentrations, induced the enhanced vascular permeability in normal dorsal skin of mice. ONOO(-)scavengers ebselen and uric acid significantly suppressed the EPR effect in mouse sarcoma 180 (S-180) tumors. Indirect evidence for formation of ONOO(-)in S-180 and mouse colon adenocarcinoma (C-38) tumors included strong immunostaining for nitrotyrosine in the tumor tissue, predominantly surrounding the tumor vessels. MMP inhibitor BE16627B (66.6 mg / kg i.v., given 2 times) or SI-27 (10 mg / kg i.p., given 2 times) significantly suppressed the ONOO(-)-induced EPR effect in S-180 tumors and in normal skin. Soybean trypsin inhibitor (Kunitz type), broad-spectrum proteinase inhibitor ovomacroglobulin, and bradykinin receptor antagonist HOE 140 also significantly suppressed the ONOO(-)-induced EPR effect in normal skin tissues. These data suggest that ONOO(-)may be involved in and promote the EPR effect in tumors, which could be mediated partly through activation of MMPs and a subsequent proteinase cascade to generate potent vasoactive mediators such as bradykinin.     

Reducing endothelial NOS activation and interstitial fluid pressure with n-3 PUFA offset tumor chemoresistance

The aim of this study was to determine how n-3 polyunsaturated fatty acid (PUFAs) counteracted tumor chemoresistance by restoring a functional vascularization. Rats with chemically induced mammary tumors were divided into two nutritional groups: a control group and a group fed with an n-3 PUFA-enriched diet. Both groups were treated with docetaxel. Functional vascular parameters (ultrasounds, interstitial fluid pressure) were determined for both nutritional groups before (W(0)) and during docetaxel treatment [every 2 h up to 1 week (W(+1)) for interstitial fluid pressure, at W(+1) for Evans blue extravasation and at W(+2) and W(+6) for ultrasounds]. In vitro n-3 PUFA-induced changes in endothelial cell migration, permeability and phosphorylation of endothelial nitric oxide synthase were evaluated using human umbilical vein endothelial cells. Whereas docetaxel stabilized tumor growth in the rat control group, it induced a 50% tumor regression in the n-3 PUFA group. Ultrasounds parameters were consistently lower in the n-3 PUFA group at all time points measured, down to ～50% at W(+6). A single dose of docetaxel in the n-3 PUFA group markedly reduced interstitial fluid pressure from 2 h after injection up to W(+1) when Evans blue extravasation was increased by 3-fold. A decreased activation of endothelial nitric oxide synthase in tumors of the n-3 PUFA group, and in human umbilical vein endothelial cell cultured with n-3 PUFA, points toward a PUFA-induced disruption of nitric oxide signaling pathway. This normalization of tumor vasculature functions under n-3 PUFA diet indicates that such a supplementation, by improving drug delivery in mammary tumors, could be a complementary clinical strategy to decrease anticancer drug resistance.     

Enhanced Vascular Permeability in Solid Tumor Involving Peroxynitrite and Matrix Metalloproteinases

Peroxynitrite (ONOO -), which is generated from nitric oxide (NO) and superoxide anion (O₂-) under pathological conditions, plays an important role in pathophysiological processes. Activation of matrix metalloproteinases (MMPs) contributes to tumor angiogenesis and metastasis. NO mediates the enhanced vascular permeability and retention (EPR) effect in solid tumors, and ONOO- activates proMMP to MMP in vitro. In this study, we examined the role of ONOO- in the EPR effect in solid tumors and normal tissues as related to MMP activation. Authentic ONOO-, at 50 nmol or higher concentrations, induced the enhanced vascular permeability in normal dorsal skin of mice. ONOO- scavengers ebselen and uric acid significantly suppressed the EPR effect in mouse sarcoma 180 (S-180) tumors. Indirect evidence for formation of ONOO- in S-180 and mouse colon adenocarcinoma (C-38) tumors included strong immunostaining for nitrotyrosine in the tumor tissue, predominantly surrounding the tumor vessels. MMP inhibitor BE16627B (66.6 mg/kg i.v., given 2 tunes) or SI-27 (10 mg/kg i.p., given 2 times) significantly suppressed the ONOO-induced EPR effect in S-180 tumors and in normal skin. Soybean trypsin inhibitor (Kunitz type), broad-spectrum proteinase inhibitor ovomacroglobulin, and bradykinin receptor antagonist HOE 140 also significantly suppressed the ONOO-induced EPR effect in normal skin tissues. These data suggest that ONOO- may be involved in and promote the EPR effect in tumors, which could be mediated partly through activation of MMPs and a subsequent proteinase cascade to generate potent vasoactive mediators such as bradykinin.     

Contrast-enhanced magnetic resonance imaging of tumor-bearing mice treated with human recombinant tumor necrosis factor alpha

Pharmacological effects of recombinant human tumor necrosis factor alpha (TNF) were studied in a mouse fibrosarcoma model using magnetic resonance imaging enhanced with a macromolecular contrast agent, albumin(gadolinium-diethylenetriamine pentaacetic acid)35. TNF was administered i.v. in a dose of 150 micrograms/kg, 60 to 80 min prior to imaging. Contrast-enhanced and nonenhanced magnetic resonance images of TNF-treated (n = 10) and untreated (n = 8) Meth A fibrosarcomas were obtained at 2.0 Tesla using T1-weighted spin-echo pulse sequences. Serial images spanning an interval of 60 to 120 min after TNF administration showed that the TNF-treated tumors enhanced significantly more overall than did untreated tumors (43% versus 31%). The most marked differential tumor enhancement was observed in the tumor rim (59% versus 40%). Nontumorous tissue, including muscle and brain, revealed no significant enhancement differences between TNF-treated animals and controls. The observed tumor enhancement corresponded strongly with Evans blue staining; the TNF-treated tumors stained deep blue, while untreated tumors and normal tissues observed did not stain. The different enhancement and Evans blue staining patterns between TNF-treated tumors and untreated tumors are attributed to TNF-induced changes in tumor capillary integrity. The data indicate that TNF effects on tumors include an increased capillary permeability for macromolecules at early times after administration. The ability to detect changes in capillary permeability in vivo using contrast-enhanced magnetic resonance imaging may prove to be clinically useful to monitor tumor response to TNF.     

Liposome-based drug delivery in breast cancer treatment

Drug delivery systems can in principle provide enhanced efficacy and/or reduced toxicity for anticancer agents. Long circulating macromolecular carriers such as liposomes can exploit the 'enhanced permeability and retention' effect for preferential extravasation from tumor vessels. Liposomal anthracyclines have achieved highly efficient drug encapsulation, resulting in significant anticancer activity with reduced cardiotoxicity, and include versions with greatly prolonged circulation such as liposomal daunorubicin and pegylated liposomal doxorubicin. Pegylated liposomal doxorubucin has shown substantial efficacy in breast cancer treatment both as monotherapy and in combination with other chemotherapeutics. Additional liposome constructs are being developed for the delivery of other drugs. The next generation of delivery systems will include true molecular targeting; immunoliposomes and other ligand-directed constructs represent an integration of biological components capable of tumor recognition with delivery technologies.     

Reduced tumor oxygenation by treatment with vinblastine

Vinblastine (VLB) previously has been shown to perturb tumor blood flow, but the effect of these perturbations on tissue oxygenation is not known. The recent development of electron paramagnetic resonance (EPR) oximetry now has made it feasible to measure the effects of changes of perfusion on the pO(2) in tumors and normal tissues as a function of time and dose. We measured changes in tumor perfusion by Patent blue staining, tumor blood volume and microvascular permeability by contrast-enhanced magnetic resonance imaging, and tumor oxygenation by EPR in s.c. SA-1 murine tumors. We found that treatment with VLB induced dose-dependent reduction in tumor perfusion. One hour after i.p. treatment of mice with 2.5 mg/kg VLB, tumor perfusion was reduced to 20% of the pretreatment value and returned to close to original values within 48 h. A transient tumor blood flow-modifying effect of VLB was demonstrated also by contrast-enhanced magnetic resonance imaging; reduction of tumor blood volume and microvascular permeability was found. Reduced tumor oxygenation was found as measured by EPR oximetry, with the same time course of changes in tumor blood flow. Tumor oxygenation was reduced to 50% of pretreatment value 1 h after the treatment with 2.5 mg/kg VLB and returned to pretreatment levels within 24 h after the treatment. Although the directions of the changes in perfusion and oxygenation were similar, they were quantitatively different. Reduction in oxygenation of normal tissues, muscle, and subcutis also occurred but was smaller and returned to pretreatment values more quickly compared to the changes induced in the tumors. In conclusion, the present study demonstrates that VLB causes a profound reduction in tumor blood flow and oxygenation, which may have implications in controlling side effects of therapy and the planning of combined treatment with VLB, either with other chemotherapeutic drugs or with radiotherapy.     

The contribution of proangiogenic factors to the progression of malignant disease: role of vascular endothelial growth factor and its receptors

Vascular endothelial growth factor is a major inducer of angiogenesis and a vascular permeability inducing factor. Its expression is upregulated in many types of tumors and it is thought to be a major inducer of tumor angiogenesis. This article focuses on the role of vascular endothelial growth factor in tumor progression and on current efforts aimed at the inhibition of tumor progression through the inhibition of vascular endothelial growth factor activity.     

Myeloid heme oxygenase‐1 promotes metastatic tumor colonization in mice

Heme oxygenase-1 (HO-1) is a heme degradation enzyme with antioxidant and immune-modulatory functions. HO-1 promotes tumorigenesis by enhancing tumor cell proliferation and invasion. Whether HO-1 has an effect on cancer progression through stromal compartments is less clear. Here we show that the growth of tumor engrafted subcutaneously in syngeneic mice was not affected by host HO-1 expression. However, lung metastasis arisen from subcutaneous tumor or circulating tumor cells was significantly reduced in HO-1^+/− mice comparing to wild type (WT) mice. The reduced lung metastasis was also observed in B6 mice bearing HO-1^+/− bone marrow as comparing to WT chimeras, indicating that HO-1 expression in hematopoietic cells impacts tumor colonization at the metastatic site. Further experiments demonstrated that the numbers of myeloid cells recruited to pulmonary premetastatic niches and metastatic loci were significantly lower in HO-1^+/− mice than in WT mice. Likewise, the extents of tumor cell extravasation and colonization at the metastatic loci in the early phase of metastasis were significantly lower in HO-1^+/− mice. Mechanistic studies revealed that HO-1 impacted chemoattractant-induced myeloid cell migration by modulating p38 kinase signaling. Moreover, myeloid HO-1-induced expressions of vascular endothelial growth factor and interleukin-10 promoted tumor cell transendothelial migration and STAT3 activation in vitro. These data support a pathological role of myeloid HO-1 in metastasis and suggest a possibility of targeting myeloid HO-1 for cancer treatment.     

介入性热化疗对兔肝VX-2肿瘤血管渗透性的影响

背景及目的:研究表明,加热对兔VX-2细胞阿霉素化疗有增敏作用,加热可提高细胞内阿霉素的含量。本研究探讨介入性热化疗对正常肝组织及肿瘤肝组织血管渗透性的影响。方法:建立可供实验用的兔VX-2移植性肝癌模型30只,随机分为3组:非灌注组(插管后只注射1%伊文思蓝),常温灌注组(灌注液为25℃生理盐水)。热灌注组(灌注液为60℃生理盐水)。使用标准曲线和分光光度法测量各组组织中伊文思蓝含量(作为血管渗透性的指标)。结果:肿瘤组织与肝组织的EB含量在3组中均有差别(P<0.05);正常灌注组与非灌注组肝组织的EB含量、肿瘤组织的EB含量无明显差别(P>0.05);热灌注组与非灌注组、正常灌注组肝组织的EB含量、肿瘤组织的EB含量有明显差别(P<0.05)。结论:介入性热化疗可以增加肝组织及肿瘤组织的血管渗透性。     

Antivascular effects of TZT-1027 (Soblidotin) on murine Colon26 adenocarcinoma

We investigated the ability of TZT-1027 (Soblidotin), a novel antimicrotubule agent, to induce antivascular effects, because most vascular targeting agents that selectively disrupt tumor vasculature also inhibit tubulin polymerization. Treatment with 10(-7) g/mL TZT-1027 rapidly disrupted the microtubule cytoskeleton in human umbilical vascular endothelial cells (HUVEC), and significantly enhanced vascular permeability in HUVEC monolayers. In addition, single intravenous administration of 2 mg/kg TZT-1027 to mice bearing Colon26 tumors significantly reduced tumor perfusion and caused extravascular leakage of erythrocytes 1 h after administration. Subsequently, thrombus formation with deposition of fibrin and tumor necrosis was observed 3 and 24 h after administration, respectively. These results strongly suggest that TZT-1027 possesses antivascular effects. TZT-1027 induced apoptosis not only in HUVEC but also in C26 cancer cells (cell line of Colon26 solid tumor) in vitro, suggesting it exerts direct cytotoxicity against tumor cells in addition to its antivascular effects. A single intravenous administration of 1, 2 and 4 mg/kg TZT-1027 significantly prolonged the survival of mice with advanced-stage Colon26 tumors in a dose-dependent manner. Furthermore, TZT-1027 itself less markedly enhanced the permeability of normal vessels, but was additive with vascular endothelial growth factor, indicating the possibility that TZT-1027 selectively exerts its activity on tumor vessels. In summary, these results suggest that TZT-1027 exerts both an indirect antivascular effect and a direct cytotoxic effect, resulting in strong antitumor activity against advanced-stage tumors, and that TZT-1027 may be useful clinically for treating solid tumors.     

血红素加氧酶-1在肿瘤新生血管化中的作用

研究证明血红素加氧酶-1(HO-1)与一些促新生血管因子如血管内皮生长因子(VEGF)、基质细胞衍生因子-1等相互作用,促进肿瘤的新生血管化.另外,也有研究者认为血红素加氧酶-1可以通过抑制核因子-кB(NF-кB)转录来抑制肿瘤新生血管化过程.HO-1可能参与了肿瘤新生血管形成的病理生理过程,可能成为肿瘤治疗新的作用靶点.     

Vascular endothelial growth factor (VEGF)-C differentially affects tumor vascular function and leukocyte recruitment: role of VEGF-receptor 2 and host VEGF-A

Unlike vascular endothelial growth factor (VEGF)-A, the effect of VEGF-C on tumor angiogenesis, vascular permeability, and leukocyte recruitment is not known. To this end, we quantified in vivo growth and vascular function in tumors derived from two VEGF-C-overexpressing (VC+) and mock-transfected cell lines (T241 fibrosarcoma and VEGF-A-/- embryonic stem cells) grown in murine dorsal skinfold chambers. VC+ tumors grew more rapidly than mock-transfected tumors and exhibited parallel increases in tumor angiogenesis. Furthermore, VEGF-C overexpression elevated vascular permeability in T241 tumors, but not in VEGF-A-/- tumors. Surprisingly, unlike VEGF-A, VEGF-C did not increase leukocyte rolling or adhesion in tumor vessels. Administration of VEGF receptor (VEGFR)-2 neutralizing antibody DC101 reduced vascular density and permeability of both VC+ and mock-transduced T241 tumors. These data suggest that VEGFR-2 signaling is critical for tumor angiogenesis and vascular permeability and that VEGFR-3 signaling does not compensate for VEGFR-2 blockade. An alternate VEGFR, VEGFR-1 or neuropilin-1, may modulate adhesion of leukocytes to tumor vessels.     

Validation of tumour models for use in anticancer nanomedicine evaluation: the EPR effect and cathepsin B-mediated drug release rate

Purpose

Intravenously (i.v.) administered nanomedicines have the potential for tumour targeting due to the enhanced permeability and retention (EPR) effect, but in vivo tumour models are rarely calibrated with respect to functional vascular permeability and/or mechanisms controlling intratumoural drug release. Here the effect of tumour type and tumour size on EPR-mediated tumour localisation and cathepsin B-mediated drug release was studied.

Methods

Evans Blue (10 mg/kg) and an N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer–doxorubicin (Dox) conjugate (FCE28068) (5 mg/kg Dox-equiv) were used as probes and tumour levels (and Dox release) measured at 1 h after i.v. administration in a panel of murine and human xenograft tumours.

Results

Evans Blue and FCE28068 displayed similar tumour levels in the range of 2–18 % dose/g at 1 h for B16F10 and L1210. Approximately half of the tumour models evaluated exhibited tumour size-dependent accumulation of FCE28068; smaller tumours had the highest accumulation. Administration of free Dox (5 mg/kg) produced tumour levels of <2.5 % dose/g independent of tumour size. Whereas the degree of EPR-mediated targeting showed ~12-fold difference across the tumour models evaluated, Dox release from FCE28068 at 1 h displayed ~200-fold variation.

Conclusions

Marked heterogeneity was seen in terms of EPR effect and Dox release rate, underlining the need to carefully calibrate tumour models used to benchmark nanomedicines against known relevant standard agents and for optimal development of strategies for late pre-clinical and clinical development.