Prevention of cancer recurrence in tumor margins by stopping microcirculation in the tumor and tumor-host interface.

Combretastatins interrupt blood flow of solid tumor vascular networks and lead to necrosis by blocking nutrients. However, tumors recover from tumor blood flow interruption-induced damage and develop viable rims. To investigate why cancer recurs and its prevention, we used a combretastatin derivative, Cderiv (=AC7700), and analyzed changes in tumor-host interface (T-HI) vessels, which were closest to cancer cells in the tumor margin after tumor vessel disruption, and the microenvironment surrounding them. Treatment with Cderiv (10 mg/kg) interrupted tumor blood flow in all regions of LY80 (a variant of Yoshida sarcoma) tumor, but not T-HI vessel blood flow. The same Cderiv dose given 72 h after 5 Gy irradiation stopped T-HI vessel blood flow and prevented cancer recurrence. Treatment in the reverse order, however, did not affect T-HI vessel blood flow. The greatest difference between the two treatments was the occurrence of gradual T-HI edema with the former. Severe T-HI edema compressed T-HI blood vessels, so that circulation stopped. Thus, the distance between a tumor margin and its nearest functioning host vessel became much larger, and the tumor marginal region became a microenvironment that lacked a nutritional supply. Cancer cells in tumor margins received nutrients through two circulation routes: tumor vessels and T-HI vessels. Our starvation methods, which involved treatment with Cderiv 72 h after 5 Gy irradiation, blocked both circulation routes and may have great potential as a clinical strategy to prevent cancer recurrence.

Starvation tactics for solid tumors: tumor blood flow interruption via a combretastatin derivative (Cderiv), and its microcirculation mechanism.

Combretastatin can prevent the supply of nutrients to cancer cells by selectively interrupting tumor blood flow (TBF). Therefore, combretastatin may serve as a new anticancer drug that utilizes starvation tactics to attack solid tumors. Among combretastatin compounds, combretastatin A-4 and a combretastatin A-4 derivative (Cderiv) are now in phase III clinical trials. These two combretastatin compounds have similar chemical structures and provide marked TBF interruption. However, their mechanisms of action are reportedly quite different and remain controversial. Precise mechanisms of action of these agents must be elucidated so as to develop safe clinical treatments and wider clinical applications. By using various kinds of rodent tumors, we showed that Cderiv produced potent interruption of TBF in all primary tumors and metastatic foci, without exception, and had beneficial therapeutic effects including significantly improved survival. Cderiv caused host arterioles to constrict. However, a tumor vascular bed scarcely reacted to a direct topical application of Cderiv. In addition, the fact that Cderiv did not have cytotoxic drug-like accumulated toxicity usually caused by repeated administration means that inhibition of tubulin polymerization by Cderiv may not occur to a great degree in vivo. Therefore, at least for Cderiv, our studies demonstrated that TBF interruption was mainly caused indirectly, via enhancement of vascular resistance of host arterioles, rather than being caused by a direct effect of Cderiv on tumor vessels. In this review, I describe cancer therapy that utilizes such TBF interruption, which leads to Cderiv-induced necrosis, and discuss details of its microcirculation mechanism.

Tumor environment changed by combretastatin derivative (Cderiv) pretreatment that leads to effective tumor targeting, MRI studies, and antitumor activity of polymeric micelle carrier systems.

PURPOSE: To evaluate effect of a vascular disrupting agent, a combretastatin derivative (Cderiv), on tumor targeting for polymeric micelle carrier systems, containing either a diagnostic MRI contrast agent or a therapeutic anticancer drug. METHODS: Cderiv was pre-administered 72 h before polymeric micelle MRI contrast agent injection. Accumulation of the MRI contrast agent in colon 26 murine tumor was evaluated with or without pretreatment of Cderiv by ICP and MRI. RESULTS: Significantly higher accumulation of the MRI contrast agent was found in tumor tissues when Cderiv was administered at 72 h before MRI contrast agent injection. T(1)-weighted images of the tumor exhibited substantial signal enhancement in tumor area at 24 h after the contrast agent injection. In T(1)-weighted images, remarkable T(1)-signal enhancements were observed in part of tumor, not in whole tumor. These results indicate that Cderiv pretreatment considerably enhanced the permeability of the tumor blood vessels. Antitumor activity of adriamycin encapsulated polymeric micelles with the Cderiv pretreatment suppressed tumor growth in 44As3 human gastric scirrhous carcinoma-bearing nude mice. CONCLUSIONS: Pretreatment of Cderiv enhanced tumor permeability, resulting in higher accumulation of polymeric micelle carrier systems in solid tumors.

Tumor blood flow interruption after radiotherapy strongly inhibits tumor regrowth.

To clarify the therapeutic significance of interrupting tumor blood flow after irradiation, we investigated X-irradiation-induced changes in hemodynamic parameters (blood flow, extravasation and washout of fluorescein isothiocyanate-dextran, and interstitial fluid pressure) in a variant of Yoshida sarcoma, LY80. Tumors in anesthetized male Donryu rats received local irradiation (10 Gy). At 48 h after irradiation, tumor blood flow increased significantly; at 72-96 h after irradiation, a 2-2.5-fold increase was observed. All parameters then consistently showed improved tumor microcirculation, which probably contributed to regrowth of cancer because certain cells survived irradiation. Rats received an intravenous dose (10 mg/kg) of a combretastatin derivative, AC7700 (AVE8062), which interrupts tumor blood flow and disrupts tumor vessels. At all times evaluated after irradiation, AC7700 completely stopped tumor blood flow. Radiotherapy efficacy was significantly enhanced when combined with AC7700: AC7700 given 48 h after irradiation, when tumor blood flow increased significantly, remarkably suppressed tumor regrowth compared with AC7700 given 48 h before irradiation. Also, postirradiation AC7700 completely inhibited not only primary tumor regrowth but also regional lymph node metastases in half of tumor-bearing rats and led to a significant improvement in survival. These results strongly suggest that the combination effect was enhanced via interruption of increased tumor blood flow after irradiation. This therapeutic combination and timing may have important benefits, even in tumors with low sensitivity to either treatment alone, because the effect was considerably greater than additive. Our data thus show that destruction of tumor microcirculation after irradiation is quite effective for preventing cancer recurrence.

Effect of irradiation on neovascularization in rat skinfold chambers: implications for clinical trials of low-dose radiotherapy for wet-type age-related macular degeneration.

PURPOSE: Wet-type age-related macular degeneration is a refractory eye disease that involves choroidal neovascularization. Randomized controlled trials of low-dose radiotherapy for this disease performed in Japan showed that, at 12 months of follow-up, visual acuity was significantly well preserved and the neovascular membrane size decreased. Because understanding the effect of irradiation on new vascular networks is an important prerequisite for clinical trials, we used a rat skinfold chamber technique to investigate X-ray-induced changes in neovasculature microcirculation. METHODS AND MATERIALS: Neovascularization was induced in rat skinfold chambers via polyvinyl chloride resin plates. Neovessels were irradiated in a single 10-Gy dose, after which, changes in vascular density, blood velocity, tissue blood flow, and interstitial fluid pressure (IFP), were measured. RESULTS: Vascular density, tissue blood flow, and IFP measurements in resin-induced inflammatory tissue were much higher than those measurements in normal tissue. Although overall blood velocity was low and sluggish or blood-flow stasis occurred in the neovascular network, after a single 10-Gy dose of radiation, the velocity increased, stasis improved markedly, and many dilated vessels narrowed. Thereafter, vascular density, blood flow, and IFP significantly decreased and approached normal values. CONCLUSION: These findings may help explain clinical results related to radiotherapy-induced changes in neovascular membranes in age-related macular degeneration. Both vascular morphology and vascular function in inflammatory tissue returned to normal, without vessel destruction, after an appropriate radiation dose.

Role of peroxiredoxin III in the pathogenesis of pre-eclampsia as evidenced in mice.

As a member of peroxiredoxin (Prx) family, PrxIII has been demonstrated to play an important role in scavenging intracellular reactive oxygen species (ROS). Since PrxIII knockout mice exhibited oxidative stress in placentas resembling pathophysiologic changes in placentas of human pre-eclampsia, we measured blood pressure through the carotid artery and detected oxidative status by Western blotting in pregnant mice. We did not notice hypertension in pregnant PrxIII knockout mice as compared with wild-type littermates, although endothelin-1 was over-expressed in PrxIII-deficient placentas. Our results indicate that PrxIII is not involved in pre-eclamptic development. Instead, PrxIII is an indispensable antioxidant in placentas where oxidative stress exists.

Vital microscopic analysis of polymeric micelle extravasation from tumor vessels: macromolecular delivery according to tumor vascular growth stage.

Particles larger than a specific size have been thought to extravasate from tumor vessels but not from normal vessels. Therefore, various nanoparticles incorporating anticancer drugs have been developed to realize selective drug delivery to solid tumors. However, it is not yet clear whether nanoparticles extravasate readily from all tumor vessels including vessels of microtumors. To answer this question, we synthesized new polymeric micelles labeled with fluorescein isothiocyanate (FITC) and injected them into the tail vein of rats with implanted skinfold transparent chambers. We also analyzed, by means of time-lapse vital microscopy with image analysis, extravasation of FITC micelles from tumor vessels at different stages of growth of Yoshida ascites sarcoma LY80. Polymeric micelles readily leaked from vessels at the interface between normal and tumor tissues and those at the interface between tumor tissues and necrotic areas. The micelles showed negligible extravasation, however, from the vascular network of microtumors less than 1 mm in diameter and did not accumulate in the microtumor. Our results suggest that we must develop a novel therapeutic strategy that can deliver sufficient nanomedicine to microtumors.

The combretastatin derivative (Cderiv), a vascular disrupting agent, enables polymeric nanomicelles to accumulate in microtumors.

A previous study found almost no leakage of polymeric nanomicelles from vessels in microtumors. If such vessels become leaky, sufficient nanomedicines may be delivered to microtumors and large tumors. To create leaky vessels, a combretastatin derivative (Cderiv), a vascular disrupting agent, was used. Via vital microscopy with fluorescein isothiocyanate (FITC)-labeled nanomicelles, the effect of Cderiv pretreatment on changes in micelle extravasation was investigated. Whether such treatment would prolong microtumor retention of micelles was also examined. FITC-albumin was used for comparison. The degree of extravasation from intact vessels in microtumors (rat sarcoma LY80) was extremely low and comparable to that from normal vessels. Cderiv pretreatment (1 or 3 days before administration of FITC-labeled compounds) markedly enhanced extravasation of such nanomicelles and albumin from vessels that survived treatment and had restored blood flow. A high concentration of extravasated macromolecules remained even 24 h later in tissue areas whose microcirculatory function had collapsed. Tumors receiving 10 Gy irradiation 3 days before the macromolecules evidenced gradual removal of extravasated macromolecules, which did not accumulate in those areas, despite extravasation from tumor vessels. Our results strongly suggest that pretreatment with Cderiv is quite effective for maintaining microtumor concentrations of nanomicelles and albumin associated with anticancer or diagnostic drugs.

Antineoplastic strategy: irreversible tumor blood flow stasis induced by the combretastatin A-4 derivative AVE8062 (AC7700).

Despite extensive research efforts, effective therapies for refractive cancers have not yet been established, and development of successful treatment strategies remains the most important task in the field of oncology. We recently showed that AVE8062 (formerly AC7700), a derivative of combretastatin A-4, achieved irreversible stasis of tumor blood flow (TBF), thereby causing necrosis of tumor tissue by halting the supply of nutrients. Such effects were unrelated to cancer type. In this review, we summarize our experiments on antivascular and antitumor effects by AVE8062. We maintain that such starvation tactics against solid tumors constitute a new therapeutic strategy for all solid tumors, including refractory cancers.