Modification of tumor blood flow: current status and future directions

A Review of Chemotherapy and Photodynamic Therapy for Lung Cancer Treatment

Cancer is among the leading causes of mortality and morbidity worldwide. Among the different types of cancers, lung cancer is considered to be the leading cause of death related to cancer and the most commonly diagnosed form of such disease. Chemotherapy remains a dominant treatment modality for many types of cancers at different stages. However, in many cases, cancer cells develop drug resistance and become nonresponsive to chemotherapy, thus, necessitating the exploration of alternative and /or complementary treatment modalities. Photodynamic Therapy (PDT) has emerged as an effective treatment modality for various malignant neoplasia and tumors. In PDT, the photochemical interaction of light, Photosensitizer (PS) and molecular oxygen produces Reactive Oxygen Species (ROS), which induces cell death. Combination therapy, by using PDT and chemotherapy, can promote synergistic effect against this fatal disease with the elimination of drug resistance, and enhancement of the efficacy of cancer eradication. In this review, we give an overview of chemotherapeutic modalities, PDT, and the different types of drugs associated with each therapy. Furthermore, we also explored the combined use of chemotherapy and PDT in the course of lung cancer treatment and how this approach could be the last resort for thousands of patients that have been diagnosed by this fatal disease.

Equilibria, kinetics and mechanism for the degradation of the cytotoxic compound L-NG-nitroarginine

L-N^G-nitroarginine (LNNA), an analog of L-arginine, is a competitive inhibitor of nitric oxide synthase which causes the selective reduction of blood flow to tumor cells. Despite the potential of LNNA to function as an adjuvant in cancer therapies, its poor solubility and stability have hindered the development of an injectable formulation of LNNA that is suitable for human administration. This work, for the first time, details a systematic study on the determination of equilibrium K_a constants and the rate law of LNNA degradation. The four K_a values of LNNA were determined to be 1.03, 1.10 × 10^-2, 2.51 × 10^-10, and 1.33 × 10^-13 M. From the kinetic and equilibrium studies, we have shown that the deprotonated form of LNNA is the main form of LNNA that undergoes degradation in aqueous media at room temperature. The rate law of LNNA degradation was found to be first order with respect to OH^- concentration and first order with respect to LNNA^- concentration. The rate constant at 25 °C and 1 atm was determined to be 0.04453 M^-1min^-1. A base catalyzed mechanism of LNNA degradation was proposed based on the kinetic study. The mechanism was found to be very useful in explaining the discrepancies and changes of the rate law at different pH values. It is thus recommended that LNNA should be formulated as a concentrated solution in acidic conditions for maximum chemical stability during storage and be diluted with a basic solution to near physiological pH just before administration.

Intravenous vasopressin for the prevention of nontarget gastrointestinal embolization during liver-directed cancer treatment: experimental study in a porcine model

PURPOSE

The aim of this study was to evaluate the potential for intravenous vasopressin to reduce the risk of nontarget gastrointestinal embolization during transcatheter liver-directed cancer therapies in a porcine model.

MATERIALS AND METHODS

An angiographic catheter was used to select the celiac or common hepatic artery under fluoroscopic guidance in six anesthetized pigs. After angiography of the hepatic and splanchnic territories was performed, technetium-99m macroaggregated albumin ((99m)Tc-MAA) was injected through the catheter. Serial arteriograms were obtained before, every 5 minutes during, and after peripheral intravenous vasopressin infusion at 0.4 U/min for a minimum of 20 minutes. After 10 minutes of infusion, indium-111 ((111)In)-MAA was injected through the arterial catheter. Quantitative comparisons of liver and gastrointestinal activity using dual-isotope single-photon emission computed tomography (SPECT)/CT imaging were performed.

RESULTS

Catheter angiography demonstrated reduced blood flow to the splanchnic vasculature while maintaining blood flow through the hepatic arteries during vasopressin infusion. Angiographic findings correlated with the relative distribution of (99m)Tc-MAA (before the vasopressin infusion) and (111)In-MAA (after the vasopressin infusion) on SPECT/CT. The increased ratio of liver to gastrointestinal tract activity during the vasopressin infusion was statistically significant (6.2:11.4, respectively; P = .018).

CONCLUSIONS

Intravenous vasopressin reduces arterial blood flow to the splanchnic vasculature while preserving hepatic arterial blood flow in a healthy porcine model. Intraprocedural vasopressin administration has the potential to benefit liver-directed cancer therapies by enhancing tumor targeting as well as preventing the unintended delivery of bland embolic, chemoembolic, or radioembolic agents into the gastrointestinal vascular territories.

Antivascular effects of electrochemotherapy: implications in treatment of bleeding metastases

Solid tumors of various etiologies can be treated efficiently by electrochemotherapy (ECT), a combined use of electroporation (EP) and chemotherapeutic drugs, such as bleomycin and cisplatin. EP alone and ECT in particular, induce a profound reduction in tumor blood flow, which contributes to the antitumor effect. After EP and ECT, the time course of blood flow changes and follows the same two-phase pattern. The first rapid and short-lived vasoconstriction phase is followed by the second much longer-lived phase resulting from disrupted cytoskeletal structures and a compromised barrier function of the microvascular endothelium. In the case of ECT, however, tumor vascular endothelial cells are also affected by the chemotherapeutic drug, which leads to irrecoverable damage to tumor vessels and to a further decrease in tumor blood flow within hours after application of ECT. Tumor cells surviving the direct effects of ECT are consequently exposed to lack of oxygen and nutrients and are pushed into the secondary cascade of induced cell death. Clinically, the antitumor effectiveness of ECT has been proven extensively in the treatment of melanoma metastases, with 70-80% complete responses. The antivascular effects of ECT were also exploited for palliative treatment of bleeding melanoma metastases, with immediate cessation of bleeding and very good antitumor effectiveness. The antivascular effect of ECT is of utmost importance for translation of ECT into the treatment of deep-seated tumors, especially in well vascularized organs, such as the liver, where it prevents bleeding of the treated area.

Blood supply in melanoma xenografts is governed by the morphology of the supplying arteries

Tumor blood supply was related to the morphology of the tumor microvasculature and the supplying arteries (SAs) of A-07-GFP and D-12-GFP melanoma xenografts growing in window chamber preparations in BALB/c nu/nu mice. Blood supply and morphologic parameters were determined from first-pass imaging movies and vascular maps recorded after a bolus of 155-kDa tetramethylrhodamine isothiocyanate-labeled dextran had been administered intravenously. Poorly supplied tumors showed microvascular networks that did not differ from those of well-supplied tumors in vessel tortuosity, diameter, and density. Conversely, the SAs of poorly supplied tumors were more tortuous and had a smaller diameter than those of well-supplied tumors, resulting in lower plasma velocities in the downstream tumor vessels. Consequently, the blood supply of A-07-GFP and D-12-GFP tumors was governed by the geometric resistance of the SAs rather than by the geometric resistance or the vessel density of the tumor microvasculature. The present study suggests that the SAs may represent an important target for physiological interventions of tumors and that it may be beneficial to focus on the tumor SAs rather than the tumor microvasculature when searching for novel therapeutic strategies for modifying tumor blood supply.

Thrombospondin 1 and vasoactive agents indirectly alter tumor blood flow

Nitric oxide (NO) plays important physiological roles in the vasculature to regulate angiogenesis, blood flow, and hemostasis. In solid tumors, NO is generally acknowledged to mediate angiogenic responses to several growth factors. This contrasts with conflicting evidence that NO can acutely increase tumor perfusion through local vasodilation or diminish perfusion by preferential relaxation of peripheral vascular beds outside the tumor. Because thrombospondin 1 (TSP1) is an important physiological antagonist of NO in vascular cells, we examined whether, in addition to inhibiting tumor angiogenesis, TSP1 can acutely regulate tumor blood flow. We assessed this activity of TSP1 in the context of perfusion responses to NO as a vasodilator and epinephrine as a vasoconstrictor. Nitric oxide treatment of wild type and TSP1 null mice decreased perfusion of a syngeneic melanoma, whereas epinephrine transiently increased tumor perfusion. Acute vasoactive responses were also independent of the level of tumor-expressed TSP1 in a melanoma xenograft, but recovery of basal perfusion was modulated by TSP1 expression. In contrast, overexpression of truncated TSP1 lacking part of its CD47 binding domain lacked this modulating activity. These data indicate that TSP1 primarily regulates long-term vascular responses in tumors, in part, because the tumor vasculature has a limited capacity to acutely respond to vasoactive agents.

IRL-1620, a tumor selective vasodilator, augments the uptake and efficacy of chemotherapeutic agents in prostate tumor rats

BACKGROUND

IRL-1620, a potent endothelin B receptor agonist, enhanced the efficacy of paclitaxel in a breast tumor model, but its effect in prostate cancer is not known. The present study was conducted to evaluate the effect of IRL-1620 on tumor perfusion, uptake of [(14)C]-doxorubicin in the tumor and efficacy of doxorubicin (DOX), and 5-flurouracil (5-FU) in a rat prostate tumor model.

METHODS

JHU-4 (Mat-Lu) cells inoculated prostate tumor model in Copenhagen rats was used for the study.

RESULTS

Administration of IRL-1620 (3 nmol/kg, i.v) significantly increased (102.8%) prostate tumor perfusion and tumor uptake of [(14)C]-doxorubicin (115%) compared to vehicle treated rats. Results of the efficacy study demonstrate that IRL-1620 administration 15 min prior to DOX (5 mg/kg) or 5-FU (50 mg/kg) on every third day for a total of four doses significantly reduced tumor volume compared to vehicle treated rats.

CONCLUSIONS

IRL-1620 significantly enhanced the uptake and efficacy of anticancer agents in prostate cancer.

Irradiation promotes Akt-targeting therapeutic gene delivery to the tumor vasculature

PURPOSE

To determine whether radiation-induced increases in nitric oxide (NO) production can influence tumor blood flow and improve delivery of Akt-targeting therapeutic DNA lipocomplexes to the tumor.

METHODS AND MATERIALS

The contribution of NO to the endothelial response to radiation was identified using NO synthase (NOS) inhibitors and endothelial NOS (eNOS)-deficient mice. Reporter-encoding plasmids complexed with cationic lipids were used to document the tumor vascular specificity and the efficacy of in vivo lipofection after irradiation. A dominant-negative Akt gene construct was used to evaluate the facilitating effects of radiotherapy on the therapeutic transgene delivery.

RESULTS

The abundance of eNOS protein was increased in both irradiated tumor microvessels and endothelial cells, leading to a stimulation of NO release and an associated increase in tumor blood flow. Transgene expression was subsequently improved in the irradiated vs. nonirradiated tumor vasculature. This effect was not apparent in eNOS-deficient mice and could not be reproduced in irradiated cultured endothelial cells. Finally, we combined low-dose radiotherapy with a dominant-negative Akt gene construct and documented synergistic antitumor effects.

CONCLUSIONS

This study offers a new rationale to combine radiotherapy with gene therapy, by directly exploiting the stimulatory effects of radiation on NO production by tumor endothelial cells. The preferential expression of the transgene in the tumor microvasculature underscores the potential of such an adjuvant strategy to limit the angiogenic response of irradiated tumors.

Reversal of temporal and spatial heterogeneities in tumor perfusion identifies the tumor vascular tone as a tunable variable to improve drug delivery

Maturation of tumor vasculature involves the recruitment of pericytes that protect the endothelial tubes from a variety of stresses, including antiangiogenic drugs. Mural cells also provide mature tumor blood vessels with the ability to either relax or contract in response to substances present in the tumor microenvironment. The observed cyclic alterations in tumor blood flow and the associated deficit in chemotherapeutic drug delivery could in part arise from this vasomodulatory influence. To test this hypothesis, we focused on endothelin-1 (ET-1), which, besides its autocrine effects on tumor cell growth, is a powerful vasoconstrictor. We first document that an ET(A) receptor antagonist induced relaxation of microdissected tumor arterioles and selectively and quantitatively increased tumor blood flow in experimental tumor models. We then combined dye staining of functional vessels, fluorescent microsphere-based mapping, and magnetic resonance imaging to identify heterogeneities in tumor blood flow and to examine the reversibility of such phenomena. Data from all these techniques concurred to show that administration of an ET(A) receptor antagonist could reduce the extent of underperfused tumor areas, proving the key role of vessel tone variations in tumor blood flow heterogeneity. We also provide evidence that ET(A) antagonist administration could, despite an increase in tumor interstitial fluid pressure, improve access of cyclophosphamide to the tumor compartment and significantly influence tumor growth. In conclusion, tumor endogenous ET-1 production participates largely in the temporal and spatial variations in tumor blood flow. ET(A) antagonist administration may wipe out such heterogeneities, thus representing an adjuvant strategy that could improve the delivery of conventional chemotherapy to tumors.

Hypoxia regulates cross-talk between Syk and Lck leading to breast cancer progression and angiogenesis

Hypoxia is a key parameter that controls tumor angiogenesis and malignant progression by regulating the expression of several oncogenic molecules. The nonreceptor protein-tyrosine kinases Syk and Lck play crucial roles in the signaling mechanism of various cellular processes. The enhanced expression of Syk in normal breast tissue but not in malignant breast carcinoma has prompted us to investigate its potential role in mammary carcinogenesis. Accordingly, we hypothesized that hypoxia/reoxygenation (H/R) may play an important role in regulating Syk activation, and Lck may be involved in this process. In this study, we have demonstrated that H/R differentially regulates Syk phosphorylation and its subsequent interaction and cross-talk with Lck in MCF-7 cells. Moreover, Syk and Lck play differential roles in regulating Sp1 activation and expressions of melanoma cell adhesion molecule (MelCAM), urokinase-type plasminogen activator (uPA), matrix metalloproteinase-9 (MMP-9), and vascular endothelial growth factor (VEGF) in response to H/R. Overexpression of wild type Syk inhibited the H/R-induced uPA, MMP-9, and VEGF expression but up-regulated MelCAM expression. Our data also indicated that MelCAM acts as a tumor suppressor by negatively regulating H/R-induced uPA secretion and MMP-9 activation. The mice xenograft study showed the cross-talk between Syk and Lck regulated H/R-induced breast tumor progression and further correlated with the expressions of MelCAM, uPA, MMP-9, and VEGF. Human clinical specimen analysis supported the in vitro and in vivo findings. To our knowledge, this is first report that the cross-talk between Syk and Lck regulates H/R-induced breast cancer progression and further suggests that Syk may act as potential therapeutic target for the treatment of breast cancer.

RNA interference targeting Akt promotes apoptosis in hypoxia-exposed human neuroblastoma cells

Overactivation of the PI3 kinase/Akt pathway plays an essential role in the development and progression of various tumors. Akt is a key component of this pathway and hyperactivated in different tumors including neuroblastoma and glioma. In the present study, we tested the therapeutic efficacy of siRNA targeting Akt in inducing apoptotic cell death in NBFL cells (a human neuroblastoma cell line) subjected to anoxia/reoxygenation (A/R), a process that has been shown to modulate growth and progression of malignant tumors. We observed that siRNA targeting Akt effectively induced apoptotic cell death in NBFL cells (as determined by TUNEL assay and activated caspase-3 immunoreactivity) under normoxic conditions, an effect that was greatly enhanced under conditions of A/R. These findings underscore the importance of Akt signaling in promoting survival of neuroblastoma cells and may have potential therapeutic applications.

Endothelin B receptor agonist, IRL 1620, enhances the anti-tumor efficacy of paclitaxel in breast tumor rats

Pharmacological agents that increase tumor blood flow could be utilized to promote the delivery of anti-cancer drugs. We have demonstrated that administration of endothelin-1 (ET-1) to breast tumor bearing rats transiently increased tumor blood flow by stimulating endothelin B (ET(B)) receptors. The present study evaluated the effect of ET(B) receptor agonist, IRL 1620, on breast tumor perfusion, concentration of [3H]paclitaxel in tumor and tissues, and efficacy of paclitaxel in N-methyl nitrosourea induced breast tumor bearing rats. Administration of IRL 1620 (3 and 9 nmol/kg) significantly increased (203 and 140%, respectively) breast tumor perfusion. BQ 788, an ET(B) receptor antagonist, pretreatment completely abolished IRL 1620 induced increase in tumor perfusion. Tumor [3H]paclitaxel concentration was increased by 308% when [3H]paclitaxel was administered 15 min after IRL 1620 (3 nmol/kg) compared to vehicle treated rats. However, IRL 1620 did not increase [3H]paclitaxel concentrations in other organs. Efficacy study showed that paclitaxel (5 mg/kg) administration on every third day for a total of five doses produced 60.0, 4.5 and 0% reduction in tumor volume, tumor progression and complete tumor remission, respectively, compared to saline treated rats. However, paclitaxel (5 mg/kg) when administered 15 min after IRL 1620 (3 nmol/kg) produced 268.9, 210.3 and 20% reduction in tumor volume, tumor progression and complete remission of tumors, respectively, compared to saline treated rats. In conclusion, IRL 1620 significantly enhanced delivery and effectiveness of paclitaxel in an animal model of breast cancer.

The endothelin B (ETB) receptor agonist IRL 1620 is highly vasoconstrictive in two syngeneic rat tumour lines: potential for selective tumour blood flow modification

The vascular effects of the endothelin B (ET_B) receptor agonist IRL 1620 were investigated in the rat P22 carcinosarcoma and a range of normal tissues in BDIX rats. Tissue blood flow rate was calculated from measurements of tissue uptake of radiolabelled iodoantipyrine. A comparison of vascular effects in the P22 tumour and the HSN sarcoma growing in CBH/CBi rats was made using laser Doppler flowmetry, showing similar effects of IRL 1620, with red cell flux rapidly decreasing by 50–60% and then returning to control levels within approximately 30 min. This corresponded to similar levels but different spatial organisation of ET_B binding sites in the two tumours, as measured by autoradiography. The decrease in tumour blood flow and an increase in vascular resistance suggest that the vascular component of ET_B receptors in the P22 tumour is localised on contractile elements rather than on endothelial cells. ET_A receptors were also identified. Vasoconstriction occurred uniformly throughout the P22 tumour mass, consistent with a measured homogeneous distribution of ET_B receptors. IRL 1620 caused vasoconstriction in normal skeletal muscle, kidney and small intestine of the BDIX rat as well as in tumour, but did not affect blood flow in other tissues. These effects could be useful for limiting toxicity of certain chemotherapeutic agents. Fully functional ET_B receptors are clearly expressed on tumour vasculature and IRL 1620 shows promise for short-term modification of tumour blood flow. Expression levels of ET_B receptors on the tumour vasculature could be useful for predicting which tumours are likely to respond to IRL 1620.

Quantifying transient hypoxia in human tumor xenografts by flow cytometry

Transient hypoxia is a poorly understood and potentially important factor that may limit tumor response to various forms of therapy. We assessed transient hypoxia on a global scale in two different human tumor xenografts by sequentially administering two hypoxia markers followed by quantification of hypoxic cells using flow cytometry. High levels of the first hypoxia marker (pimonidazole) were maintained in the circulation over an 8-hour period by multiple hourly injections, providing a "time-integrated" hypoxia measure showing an asymptotic increase in the total number of hypoxic cells. Subsequent administration of a second hypoxia marker (CCI-103F) showed that substantial numbers of the previously pimonidazole-labeled cells were no longer hypoxic during the circulation lifetime of the second marker. The overall fraction of tumor cells that demonstrated changes in hypoxic status with time increased with different kinetics and by different magnitudes in the two xenograft systems. Specifically, up to 20% of the cells in SiHa (human cervical squamous cell carcinoma) tumors and up to 8% of the cells in WiDr (human colon adenocarcinoma) tumors were intermittently hypoxic over an 8-hour period. Also, the tumor cells that demonstrated transient hypoxia were typically not adjacent to functional tumor blood vessels. Similar approaches could be used in the clinic to provide information on the duration of intermittent hypoxia episodes and the fraction of transiently hypoxic tumor cells, which would, in turn, have important implications for the strategic improvement of cancer therapy.

Vascular endothelial growth factor and other signaling pathways in developmental and pathologic angiogenesis

The field of angiogenesis received a huge boost in 2003 with the announcement of positive results in a phase III clinical trial using a vascular endothelial growth factor (VEGF)-blocking antibody for the treatment of cancer. Although the VEGF pathway has emerged as a central signaling pathway in normal and pathologic angiogenesis, several other pathways are also now recognized as playing essential roles. This review focuses on 2 specific areas. First, we summarize some of the work on newly discovered angiogenic signaling pathways by primarily describing the molecular biology of the pathways and the evidence for their involvement in vascular development. Second, we describe progress in therapeutic antiangiogenesis in cancer, particularly with agents that block the VEGF pathway.

Endothelin-1 Is a Critical Mediator of Myogenic Tone in Tumor Arterioles

Although derived from the host tissue, the tumor vasculature is under the influence of the tumor microenvironment and needs to adapt to the resistance to blood flow inherent to the dynamics of tumor growth. Such vascular remodeling can offer selective targets to pharmacologically modulate tumor perfusion and thereby improve the efficacy of conventional anticancer treatments. Radiotherapy and chemotherapy can, indeed, take advantage of a better tumor oxygenation and drug delivery, respectively, both partly dependent on the tumor blood supply. Here, we showed that isolated tumor arterioles mounted in a pressure myograph have the ability, contrary to size-matched healthy arterioles, to contract in response to a transluminal pressure increase. This myogenic tone was exquisitely dependent on the endothelin-1 pathway because it was completely abolished by the selective endothelin receptor A (ETA) antagonist BQ123. This selectivity was additionally supported by the large increase in endothelin-1 abundance in tumors and the higher density of the ETA receptors in tumor vessels. We also documented by using laser Doppler microprobes and imaging that administration of the ETA antagonist led to a significant increase in tumor blood flow, whereas the perfusion in control healthy tissue was not altered. Finally, we provided evidence that acute administration of the ETA antagonist could significantly stimulate tumor oxygenation, as determined by electron paramagnetic resonance oximetry, and increase the efficacy of low-dose, clinically relevant fractionated radiotherapy. Thus, blocking the tumor-selective increase in the vascular endothelin-1/ETA pathway led us to unravel an important reserve of vasorelaxation that can be exploited to selectively increase tumor response to radiotherapy.

EPR oximetry of tumors in vivo in cancer therapy

The partial oxygen pressure (pO2) in tumors is considered to be one of important factors that affect the response of tumors to different treatment. Therefore, we anticipate that the information about the variation of oxygen concentration in tumors can be used as a guide for individualizing radiotherapy, chemotherapy, and especially the combined therapies. There is thus a need to obtain quantitative data on the effects of different therapies on tumor oxygenation under in vivo conditions. One of the methods, which enable these measurements is EPR oximetry. In this work basic principles of the method will be described as well as some examples of tumor oxygenation changes after application of chemotherapeutic drugs (vinblastine, cisplatin, bleomycin) or electric pulses in combination with cisplatin or bleomycin to fibrosarcoma SA-1 tumors in mice. A paramagnetic probe, a char of Bubinga tree, was implanted into the tumor (center and periphery) and in the muscle or subcutis. EPR spectra line-width, which is proportional to oxygen concentration, was measured with time after the treatments. Tumor oxygenation was reduced for 58% of pretreatment value 1 h after intraperitoneal injection of 2.5 mg kg(-1) VLB and returned to pretreatment level within 24 h. Reduction in oxygenation of muscle and subcutis was much smaller and returned to pretreatment value faster as in tumors. With cisplatin (4 mg kg(-1)) and bleomicyn (1 mg kg(-1)) the reduction was less than 15%, but increases in combined therapy to 70%. Similar reduction was observed also with electric pulses alone (eight pulses, 1300 V cm(-1), 100 micros, 1 Hz) with fast recovery of 8h. After electrochemotherapy the recovery was slower and occurs only after 48 h. This study demonstrates that EPR oximetry is a sensitive method for monitoring changes in tissue oxygenation after different treatments, which may have implications in controlling side effects of therapy and in the planning of combined treatments.

Combretastatin A-4 phosphate enhances CPT-11 activity independently of the administration sequence

We evaluated the effect of different intervals and sequences of the vascular targeting agent combretastatin A-4 disodium phosphate (CA4DP) and CPT-11 administration on tumour growth delay and intratumoral uptake of CPT-11 using a syngeneic rhabdomyosarcoma tumour model. Irrespective of the administration sequence, the combination of CA4DP and CPT-11 significantly increases tumour growth delay in comparison with both drugs alone (P<0.001). Intratumoral CPT-11 concentration generally decreased (up to 5-fold) in the combination groups, while SN-38, the active metabolite of CPT-11, increased up to 9-fold. However, the increased amount of intratumoral SN-38 trapping after CA4DP injection did not correlate with the observed tumour growth delay. In conclusion, CA4DP significantly enhances the antitumour effect of CPT-11, which is not greatly influenced by the administration sequence, and which lacks a correlation with the intratumoral trapping of CPT-11 or SN-38. Mechanisms other than trapping are likely to be involved in the chemosensitising capacity of CA4DP.

Assessment of pharmacodynamic vascular response in a phase I trial of combretastatin A4 phosphate

PURPOSE

Clinical evaluation of novel agents that target tumor blood vessels requires pharmacodynamic end points that measure vascular damage. Positron emission tomography (PET) was used to measure the effects of the vascular targeting agent combretastatin A4 phosphate (CA4P) on tumor and normal tissue perfusion and blood volume.

PATIENTS AND METHODS

Patients with advanced solid tumors were enrolled onto part of a phase I, accelerated-titration, dose-escalation study. The effects of 5 to 114 mg/m2 CA4P on tumor, spleen, and kidney were investigated. Tissue perfusion was measured using oxygen-15 (15O)-labeled water and blood volume was measured using 15O-labeled carbon monoxide (C15O). Scans were performed immediately before, and 30 minutes and 24 hours after the first infusion of each dose level of CA4P. All statistical tests were two sided.

RESULTS

PET data were obtained for 13 patients with intrapatient dose escalation. Significant dose-dependent reductions were seen in tumor perfusion 30 minutes after CA4P administration (mean change, -49% at >or= 52 mg/m2; P =.0010). Significant reductions were also seen in tumor blood volume (mean change, -15% at >or= 52 mg/m2; P =.0070). Although by 24 hours there was tumor vascular recovery, for doses >or= 52 mg/m2 the reduction in perfusion remained significant (P =.013). Thirty minutes after CA4P administration borderline significant changes were seen in spleen perfusion (mean change, -35%; P =.018), spleen blood volume (mean change, -18%; P =.022), kidney perfusion (mean change, -6%; P =.026), and kidney blood volume (mean change, -6%; P =.014). No significant changes were seen at 24 hours in spleen or kidney.

CONCLUSION

CA4P produces rapid changes in the vasculature of human tumors that can be assessed using PET measurements of tumor perfusion.

Effects of tin-protoporphyrin IX on blood flow in a rat tumor model

Carbon monoxide (CO), one of the products of heme oxygenase (HO) catalyzed heme degradation, is a vasodilator. The aim of the present study was to clarify the role of HO in blood flow maintenance in tumors. Male BD9 rats bearing subcutaneous transplants of the P22 carcinosarcoma tumor were treated intraperitoneally (i.p.) with either tin-protoporphyrin IX (SnPP; 45 micromol/kg), a selective inhibitor of HO or copper-protoporphyrin IX (CuPP; 45 micromol/kg), used as a negative control. The extent of HO activity inhibition was measured using a spectrophotometric assay of bilirubin production and blood flow rates to the tumor and a range of normal tissues were assessed using the uptake of the radiolabelled tracer, iodo-antipyrine ((125)I-IAP). The animals were cannulated under fentanyl citrate/fluanisone (Hypnorm)/midazolam anesthesia. In the P22 tumor, SnPP, but not CuPP, caused a complete inhibition of HO activity 15 min post-treatment. Administration of SnPP 15 min before blood flow measurements reduced tumor blood flow by 17%, with no effects in any of the normal tissues studied. However, CuPP induced a greater reduction in tumor blood flow than SnPP (45% decrease). Furthermore, CuPP caused a reduction in blood flow to the skin and small intestine but a significant increase to skeletal muscle. The current findings conclusively establish only a minor role played by the HO/CO system in the maintenance of blood flow in this tumor system, despite relatively high levels of HO-1 protein and HO activity. The results also highlight the potential usefulness of CuPP as a tumor blood flow modifier.

Carbon dioxide reactivity of computed tomography functional parameters in rabbit VX2 soft tissue tumour

Tumour blood flow is one of the important factors limiting the efficacy of radiation therapy (hypoxic radioresistance), chemotherapy (drug delivery) and thermal therapy (heat dissipation) in treating cancer. The modification of tumour blood flow has been an area of intense investigation. In the current study, the arterial carbon dioxide tension (PaCO2) was changed in order to investigate the tumour vascular response to carbon dioxide. Functional maps of blood flow, blood volume and mean transit time were generated at four PaCO2 levels in VX2 tumour in the rabbit thigh and normal soft tissue. The PaCO2 levels investigated were normocapnia (PaCO2 = 40.9 +/- 1.2 mmHg), hypocapnia (27.2 +/- 2.3 and 33.5 +/- 2.3 mmHg) and hypercapnia (54.9 +/- 4.4 mmHg). The carbon dioxide reactivity of the global tumour blood flow and mean transit time showed significant differences between normocapnia and the two levels of hypocapnia, but not between normocapnia and hypercapnia. The average fractional change of blood flow from normocapnia for the two levels of hypocapnia was -0.41 +/- 0.06 and -0.29 +/- 0.08, respectively (P < 0.05). In the case of mean transit time the fractional change was +0.39 +/- 0.30 and +0.23 +/- 0.24, respectively (P < 0.05). The fractional change of blood volume from normocapnia, however, was not significantly different at any capnic level, as was the case with respect to each of the functional parameters in normal tissue. The ability to reduce blood flow and increase mean transit time through hypocapnia has significant implications in thermal therapy, since heat dissipation is a major factor in limiting the effectiveness of treatment.

Nitric oxide-mediated increase in tumor blood flow and oxygenation of tumors implanted in muscles stimulated by electric pulses

PURPOSE

Oxygen deficiency in tumors reduces the efficacy of nonsurgical treatment modalities. We tested the hypothesis that electrical stimulation of the sciatic nerve could modify the oxygenation status and the blood flow of tumors implanted in the thigh of mice.

MATERIALS AND METHODS

The sciatic nerve was electrically stimulated at 5 Hz. Local transplantable liver tumor (TLT) and fibrosarcoma (FSaII) tumor oxygen pressure (pO(2)) and perfusion measurements were carried out using electron paramagnetic resonance (EPR) oximetry and the OxyLite/OxyFlo technique. The radiosensitizing effect of the protocol was assessed by irradiating FSaII tumors with X-rays.

RESULTS

Tumor pO(2) increased from approximately 3 mm Hg to approximately 8 mm Hg, and relative tumor blood flow was increased by 241% and 162% for TLT and FSaII tumor models, respectively. The effect on the tumor oxygenation was inhibited by a nitric oxide synthase (NOS) inhibitor, and an increase in the tumor nitric oxide (NO) content was observed using EPR spin-trapping. The tumor oxygen consumption rate was decreased after the stimulation protocol. In addition, the electrical stimulation of the host tissue increased regrowth delays by a factor of 1.65.

CONCLUSIONS

This increase in tumor oxygenation is due to the temporary increase in tumor blood flow, but particularly to a decrease in the tumor oxygen consumption rate (inhibition of respiration) that is mediated by a local production of NO during the protocol. Those tumor hemodynamic changes resulted in a radiosensitizing effect.

Perturbation of blood flow as a mechanism of anti-tumour action of direct current electrotherapy

Anti-tumour effects of direct current electrotherapy are attributed to different mechanisms depending on the electrode configuration and on the parameters of electric current. The effects mostly arise from the electrochemical products of electrolysis. Direct toxicity of these products to tumour tissue is, however, not a plausible explanation for the observed tumour growth retardation in the case when the electrodes are placed into healthy tissue surrounding the tumour and not into the tumour itself. The hypothesis that the anti-tumour effectiveness of electrotherapy could result from disturbed blood flow in tumours was tested by the measurement of changes in blood perfusion and oxygenation in tumours with three different methods (in vivo tissue staining with Patent Blue Violet dye, polarographic oximetry, near-infrared spectroscopy). The effects induced by electrotherapy were evaluated in two experimental tumour models: Sa-1 fibrosarcoma in A/J mice and LPB fibrosarcoma in C57B1/6 mice. We found that perfusion and oxygenation were significantly decreased after electrotherapy. Good agreement between the results of different methods was observed. The effect of electrotherapy on local perfusion of tumours is probably the prevalent mechanism of anti-tumour action for the particular type of electrotherapy used in the study. The importance of this effect should be considered for the optimization of electrotherapy protocols in experimental and clinical trials. The non-invasive technique of near-infrared spectroscopy proved to be a reliable method for detecting perfusion and oxygenation changes in small solid tumours.

Modulation of the tumor vasculature functionality by ionizing radiation accounts for tumor radiosensitization and promotes gene delivery

The ultimate goal of radiotherapy is to induce irreversible damages in genetically unstable, fast-growing cancer cells while minimizing the cytotoxic effects on host tissues. The satus of the tumor vasculature is particular because it is located within the tumor but mostly arises from host cells. The aim of this study was to characterize the effects of low-dose irradiation on the function of endothelial cells lining tumor vessels. Using isolated arterioles mounted on a pressure myograph, we first documented that the nitric oxide (NO)-mediated vasorelaxation that was defective in tumor vessels was completely restored following local tumor irradiation. Immunoblot analyses revealed that this was attributable to an increase in the abundance of the endothelial NO synthase while the expression of its physiological inhibitor, caveolin-1, was reduced. We further showed that the potentiation of the NO-dependent pathway induced a marked increase in tumor blood flow and oxygenation that determined the higher sensitivity of the tumor to further irradiation. Finally, we documented that the NO-mediated effects of irradiation on the tumor vasculature increased the delivery and expression of a reporter gene into the tumor. Thus, low-dose irradiation of endothelial cells within a tumor is a key determinant of the effectiveness of radiotherapy and may offer a new strategy to increase gene and/or drug delivery to the tumor.

Reduced blood flow and oxygenation in SA-1 tumours after electrochemotherapy with cisplatin

Electrochemotherapy is an antitumour treatment that utilises locally delivered electric pulses to increase cytotoxicity of chemotherapeutic drugs. Besides increased drug delivery, application of electric pulses affects tumour blood flow. The aim of this study was to determine tumour blood flow modifying effects of electrochemotherapy with cisplatin, its effects on tumour oxygenation and to determine their relation to antitumour effectiveness. Electrochemotherapy of SA-1 subcutaneous tumours was performed by application of electric pulses to the tumours, following administration of cisplatin. Tumour blood flow modifying effects of electrochemotherapy were determined by measurement of tumour perfusion using the Patent blue staining technique, determination of tumour blood volume, and microvascular permeability using contrast enhanced magnetic resonance imaging, and tumour oxygenation using electron paramagnetic resonance oximetry. Antitumour effectiveness was determined by tumour growth delay and the extent of tumour necrosis and apoptosis. Tumour treatment by electrochemotherapy induced 9.4 days tumour growth delay. Tumour blood flow was reduced instantaneously and persisted for several days. This reduction in tumour blood flow was reflected in reduced tumour oxygenation. The maximal reduction in partial oxygen pressure (pO2) levels was observed at 2 h after the treatment, with steady recovery to the pretreatment level within 48 h. The reduced tumour blood flow and oxygenation correlated well with the extent of tumour necrosis and tumour cells apoptosis induced by electrochemotherapy with cisplatin. Therefore, the data indicate that antitumour effectiveness of electrochemotherapy is not only due to increased cytotoxicity of cisplatin due to electroporation of tumour cells, but also due to anti-vascular effect of electrochemotherapy, which resulted in reduced tumour blood flow and oxygenation.

Hypoxia/reoxygenation induction of monocyte chemoattractant protein-1 in melanoma cells: involvement of nuclear factor-kappaB, stimulatory protein-1 transcription factors and mitogen-activated protein kinase pathways

Monocyte chemoattractant protein-1 (MCP-1) expression is found in malignant melanoma and melanoma metastases. Since areas of hypoxia/reoxygenation (H/R) are a common feature of malignant tumours and metastases, we addressed the question whether melanoma cells produce MCP-1 upon exposure to H/R. In the present study, we show that melanoma cells up-regulate MCP-1 mRNA and protein under H/R. By means of reporter gene analysis, we further demonstrate that H/R induces transcriptional activation of the MCP-1 promoter carrying a stimulatory protein-1 (SP1) and two nuclear factor-kappaB (NF-kappaB) binding motifs. Accordingly, H/R-stimulated melanoma cells showed enhanced binding activity of both transcription factors NF-kappaB and SP1 in electrophoretic mobility-shift assay. A common upstream activator of NF-kappaB, inhibitory kappaBalpha kinase, was not significantly activated under H/R conditions. Further analysis of upstream signalling events revealed that members of the mitogen-activated protein kinases family, namely extracellular signal-regulated protein kinase, c-Jun N-terminal kinase/ stress-activated protein kinase and p38 stress kinase, may be involved in MCP-1 transcriptional regulation under H/R. In summary, we conclude that H/R induces MCP-1 production in melanoma cells via the co-operative action of both transcription factors NF-kappaB and SP1, and involves mitogen-activated protein kinase signalling pathways. Functionally, H/R-induced MCP-1 production may contribute to tumour progression by committing selective pressure on tumour cells via chemoattraction and activation of tumour-infiltrating monocytes/macrophages.

The development and testing of a new temperature-sensitive drug delivery system for the treatment of solid tumors

Our laboratories have been working together in close collaboration for over 10 years concerning the design and performance of lipid-based drug delivery systems. Over the past 3 years we have conceived of, developed, and tested pre-clinically, a new liposome-based temperature-sensitive drug delivery system for the treatment of solid tumors. This work is reported in a series of four publications: "J. Liposome Res. 9 (1999) 491; Cancer Res. Adv. Brief 60(5) (2000) 1197; Cancer Res. 6(9) (2000) 748; and Cancer Res. 60 (2000) 6950". Following a brief introduction concerning the motivations behind the work, this article will review these studies, including some of our earlier work that led to these ideas, and will present the rational design of the new liposome formulation from a materials engineering perspective.

Regulation of tumour drug delivery by blood flow chronobiology

The chronobiology of various physiological phenomena that impact tumour drug delivery has not been established. Since the delivery of therapeutic agents is directly influenced in part by tumour vascular volume (VV), vascular permeability (VP) and local blood flow (BF), we have performed a series of studies to assess the natural rhythms of these functions in tumour and normal tissues. Preliminary results by Hori et al. Cancer Res 1992, 52, 912-916, have demonstrated fluctuations in tumour blood flow in subcutaneous (s.c.) rat tumours with a higher rate at 15-21 h after light onset (HALO) compared with 3-9 HALO. We used the GW-39 and LS174T human colon carcinoma xenografts grown s.c. in nude mice for these studies. VV, VP and BF were determined at 3, 7, 10, 13, 17, 20 and 23 HALO. In separate studies, dosing with a small therapeutic agent ([3H]-5-fluorouracil (5-FU)) or a macromolecule ([131I]-131-MN-14-anti carcinoembryonic antigen (CEA) immunoglobulin G (IgG)) was done at 10 and 17 HALO and 3, 10 and 17 HALO, respectively, and tissue and tumour uptake was determined in each group. Well-defined peaks and nadirs were observed for all three vascular functions. The peaks for VV and VP were similar in tumour and normal tissue whereas BF rate had a unique rhythm in tumour. Using cosinor analysis of the BF rate, we have found that the acrophase (peak) for tumour BF occurs at approximately 17 HALO in both tumour xenografts, while maximal liver, lung and kidney BF occurred at 10-13 HALO. Tumour BF rate ranged from the lowest value of 1.34+/-0.54 microliter/g/min at 20 HALO to the highest value of 2.79+/-0.57 microliter/g/min at 17 HALO. Liver BF rate ranged from 4.1+/-1.1 microliter/g/min at 3 HALO to 10.22+/-1.31 microliter/g/min at 10 HALO, and was 5.83+/-1.37 microliter/g/min at 17 HALO. Thus, the rhythm of tumour and normal tissue BF are different, creating a window of opportunity when tumours can be targeted with a therapeutic agent. At 3 h postinjection, the %ID/g of 5-FU in tumour at 10 HALO was 0.14+/-0.09 and at 17 HALO was 0.32+/-0.12 (P<0.02). In liver at 10 HALO, uptake was 0.13+/-0.06 and at 17 HALO was 0. 07+/-0.03 (P<0.05). At 24 h postinjection, the %ID/g of [131I]-MN-14 IgG in tumour at 10 HALO was 11.50+/-1.58 and at 17 HALO was 1. 5-fold higher at 16.96+/-2.35 (P<0.001). In liver at 10 HALO, uptake was 6.47+/-0.49 and at 17 HALO was 30% lower at 4.48+/-0.81 (P<0.01). These results suggest that small shifts in the chronobiology of BF in tumour and in normal tissue can have a sizeable impact on the distribution of chemotherapeutics and antibody-based drugs.

Tumor hypoxia--a confounding or exploitable factor in interstitial brachytherapy? Effects of tissue trauma in an experimental rat tumor model

PURPOSE

To evaluate the potential effects of tumor hypoxia induced by afterloading catheter implantation on the effectiveness of brachytherapy in a rat tumor model.

METHODS AND MATERIALS

Afterloading catheters (4) were implanted in subcutaneously growing R1M rhabdomyosarcoma in female Wag/Rij rats. A MicroSelectron (Nucletron) was used for interstitial high-dose-rate irradiation ((192)Ir). Tumor oxygenation, perfusion, and cell survival were assessed by pO(2) histography (Eppendorf), Tc-99m injection, and excision assay, respectively.

RESULTS

Tumor perfusion was markedly reduced at 1 h after catheter implantation (33.9 +/- 6.0% (SEM, n = 9) of control) and partly recovered after 5 h (61.5 +/- 12.2%). At 24 h, the perfusion level reached control values (100.6 +/- 25.7%), but was highly variable with some of the tumors showing hardly any recovery at all. Tumor oxygenation showed a similar pattern, but with less recovery. Median pO(2) readings were 13.5, 1.2, and 5.3 mm Hg before and at 1 and 24 h after implantation, respectively (7 tumors). The percentages of pO(2) readings </= 2.5 mm Hg were 18.9%, 55.6%, and 41.3% at these time points. The difference in cell survival after irradiation (10 Gy) at 1 or 24 h after implantation was compatible with a radiobiological oxygen effect.

CONCLUSION

Implantation of brachytherapy afterloading catheters induces an increased level of hypoxia for several hours by disrupting tumor perfusion, causing both a modest degree of direct cell kill and a significant reduction of the radiation effect. This transient hypoxia might be exploited by combining irradiation with properly timed treatments targeting hypoxic cells.

Computer simulation of cytotoxic and vascular effects of radiosurgery in solid and necrotic brain metastases

PURPOSE

Solid and necrotic brain tumors respond to radiosurgery, although necrotic lesions often contain a significant proportion of hypoxic cells which cannot become reoxygenated during the short overall treatment time of single dose application. In addition to the direct cytotoxic action, delayed vascular occlusion followed by ischemic tumor cell death could contribute to the effect of radiosurgery.

MATERIALS AND METHODS

In order to determine the impact of the two possible effects on tumor response, a 3-dimensional computer simulation was developed and fitted to response data obtained from 90 patients who were treated by LINAC radiosurgery for 1-3 brain metastases with median marginal doses of 20 Gy. Complete response rates were as follows: small, solid lesions (diameter 0.4-1 cm), 52% (12/23); large solid lesions (1.1-5.2 cm), 28% (17/60); large necrotic lesions, 12% (6/50). The 3-dimensional computer model simulated the growth of small solid and large, solid or necrotic tumors situated in a vascularized stroma. Oxygen supply, tumor cell division (cell cycle time 5 days), neovascularization, tumor cell kill by single dose irradiation (linear-quadratic model, alpha/beta=10 Gy, oxygen enhancement ratio 3.0) and time-dependent vascular occlusion (alpha/beta=3 Gy) were modeled by Monte-Carlo simulation techniques.

RESULTS

In the presence of neovascularization, solid tumors with a hypoxic fraction of 1-2% developed. Without neoangiogenesis, central necrosis occurred, and tumors had a hypoxic fraction of 20-25%. Assuming a pure cytotoxic effect of radiosurgery, neither the dose-response relationship for the solid lesions of different size nor that for the large lesions with solid or necrotic appearance could be reproduced for any given level of radiosensitivity. This was only possible by introducing a vascular effect that led to the occlusion of >/=99% of the vessels at the border of the target volume within 1 year after irradiation. In the presence of the vascular effect, the apparent radiosensitivity of the tumor cells was increased by 50-100%. Calculations of the dose-equivalent for the vascular effect show that it contributes 19-33% of the overall effect of single dose radiosurgery.

CONCLUSION

This simulation study suggests that the therapeutic effect of single radiosurgery in malignant brain tumors cannot be understood without the consideration of vascular effects. The computer model might serve as a basis for exploring new treatment modalities that modify both cytotoxic and vascular effects of radiosurgery.

Clinical outcome and tumour microenvironmental effects of accelerated radiotherapy with carbogen and nicotinamide

Experimental studies have shown an almost 2-fold increase in effectiveness if accelerated radiotherapy combined with carbogen and nicotinamide (ARCON) was compared with standard radiotherapy. This combination was chosen in order to overcome repopulation of clonogens during radiotherapy and to minimize tumour hypoxia. Analysis of microenvironmental parameters is required to identify tumours that can benefit from these new treatment approaches. In this study 124 patients with stage III or IV head and neck squamous cell carcinomas received ARCON treatment. Vascular architecture, perfusion, proliferation and oxygenation were studied in two human laryngeal squamous cell carcinoma xenograft lines and the effects of carbogen and nicotinamide were analysed. Loco-regional control for stage III-IV larynx carcinomas was 85%, for hypopharynx carcinomas 50% and for oral cavity and oropharynx carcinomas 65%. In the experimental studies, carbogen treatment resulted in one tumour line in a decrease of blood perfusion, which was reversed if nicotinamide was added. The other tumour line showed no perfusion changes after carbogen or nicotinamide treatment. Both tumour lines showed a drastic reduction of hypoxia after carbogen breathing only or carbogen breathing plus nicotinamide. The ARCON schedule results in high loco-regional tumour control rates. Analysis of tumour microenvironmental parameters showed differences in response to carbogen and nicotinamide between different tumour lines of similar histology and site of origin. This indicates that it may be advantageous to base the selection of patients for oxygenation modifying treatment on microenvironmental tumour characteristics.

Vascular architecture and microenvironmental parameters in human squamous cell carcinoma xenografts: effects of carbogen and nicotinamide

BACKGROUND AND PURPOSE

A better understanding of the vascular architecture and the microenvironmental parameters (VAMP) will allow the identification of tumours that can be more effectively treated by intensified fractionated radiotherapy or modifiers of blood flow and oxygenation or combinations of these approaches.

MATERIALS AND METHODS

Proliferation (BrdUrd), vascular architecture (endothelial marker), perfusion (Hoechst 33342) and oxygenation (NITP) were studied in two human laryngeal squamous cell carcinoma tumour lines grown as xenografts in nude mice. The effects of carbogen and nicotinamide on these parameters were evaluated.

RESULTS

Carbogen treatment resulted in a decrease of the number of perfused blood vessels from 66% to 55% in one of the two tumour lines. In this tumour line nicotinamide prevented this reduction of tumour blood flow by carbogen. In both tumour lines the labelling index (LI) decreased after treatment with carbogen for 1 h, from 11-13% to 5-7%. Both tumour lines showed a drastic reduction of hypoxia by carbogen alone or by carbogen plus nicotinamide.

CONCLUSIONS

In both laryngeal squamous cell carcinoma xenograft tumour lines carbogen was very effective in reducing diffusion limited hypoxia. Only in one of the two tested tumour lines carbogen also caused a reduction of tumour blood perfusion, which could be compensated for by nicotinamide. In addition, carbogen reduced tumour cell proliferation. The fact that differences in response to nicotinamide and carbogen were observed and that they can be studied in vivo provides a basis for further development of a 'predictive profile' which will guide the clinician to select the optimal treatment for individual patients or groups of patients.