However, when anginex treatment followed radiation, this effect was not observed, yet tumor growth (quadrupling time) was delayed by 6.8 days compared with control. first 4 days of treatment with both anginex and bevacizumab. From treatment day 5 onward, tumor oxygenation in treated mice decreased significantly to below that in control mice. This tumor oxygenation windows occurred in all three tumor models varying in origin and growth rate. Moreover, during the treatment period, tumor microvessel density decreased and pericyte protection of vessels increased, supporting the idea of vessel normalization. We also found that the transient modulation of tumor physiology caused by either antiangiogenic therapy improved the effect of radiation treatment. Tumor growth delay was enhanced when single dose or fractionated radiotherapy was initiated within the tumor oxygenation windows as compared with other treatment schedules. Conclusions The results are of immediate translational importance because the clinical benefits of bevacizumab therapy might be increased by more precise treatment scheduling to ensure radiation is given during periods of peak radiosensitivity. The oxygen elevation in tumors by nonCgrowth factorCmediated peptide anginex suggests that vessel normalization might be a general phenomenon of agents directed at disrupting the tumor vasculature by a variety of mechanisms. Angiogenesis is usually involved in numerous pathologic disorders like malignancy, arthritis, diabetic retinopathy, and restenosis, but is also key to normal organ development (1). Agents that can inhibit angiogenesis in tumors have shown promise as therapeutics against malignancy. Although antiCvascular endothelial growth factor (VEGF) brokers PIK-293 like bevacizumab (Avastin, a humanized monoclonal antibody against VEGF; Genentech) are perhaps most discussed (2), many other antiangiogenic compounds targeting some aspects of VEGF signaling have been identified and are currently in various phases of clinical cancer trials according to the National Cancer Institute clinical trials website. Nevertheless, some angiogenesis inhibitors are ineffective or cause unwanted biological side effects (3), which underscores the need for better angiostatic compounds and/or treatment strategies. It is critical to recognize that antiangiogenesis treatment can take the form of more than VEGF pathway inhibition alone. Besides anti-VEGF compounds, which can be considered rather indirect angiogenesis inhibitors, one can categorize other inhibitors as direct antiangiogenesis compounds (i.e., affecting activated endothelial cells directly) or vascular disrupting brokers (e.g., combretastatin) as well as others (e.g., arsenic trioxide, interleukin 8, interleukin 2, and tumor necrosis factor ; ref. 4). Yet, currently, this is not reflected in clinical trials where predominantly VEGF inhibitors are being tested. At least in theory, the most encouraging angiogenesis inhibitors are those that take action directly on endothelial cells to inhibit tumor angiogenesis, reducing the risk of drug resistance and making them more therapeutically effective against a broad spectrum of tumors (1). In clinical trials thus far, the addition of Avastin to standard chemotherapy has generally improved survival and response rate by 10% to 15% and has been shown to cause clinically evaluable changes in tumor physiology (5, 6). However, not every combination study with Avastin has shown improved efficacy. Second- or third-line patients with metastatic breast cancer in a phase III trial did not benefit from the addition of bevacizumab to capecitabine (7). It PIK-293 is now generally accepted that tumors can evade the blockade of a single growth factor such as PIK-293 VEGF by relying more heavily on one or more of nearly a dozen other growth factors shown to be involved in angiogenesis and vascular homeostasis (8). Clearly, there is a need to diversify and investigate other angiogenesis mechanisms and targets and to optimize clinical translation of these exciting therapeutics in combination with radiation and chemotherapy. Numerous preclinical studies have indicated that this addition of various types of antiangiogenic or antivascular therapy to single-dose or fractionated radiotherapy can synergistically improve the response of human and murine tumors to treatment (5, 9C13). However, because there are multiple variables that contribute to the sensitivity of tumors to radiation or antiangiogenic treatment, it has been hard to clearly identify a method to combine these therapies (14C16). Some investigations revealed that blocking survival signaling in endothelial cells after irradiation is usually highly effective in increasing the radiation LAIR2 response (11, 17). Others show that sensitization and killing of endothelial cells just before PIK-293 exposure to radiation may be the most effective way to improve radiation response (12, 13, 18, 19). In any scenario of combination treatments, the effect of one therapy (such as induction of hypoxia via blood vessel damage) may be detrimental to another (such as hypoxic radioprotection or reduced access of chemotherapy to the tumor). A logical and clearly confirmed rationale for optimal multimodality therapy is usually a necessity for efficient translation of successful preclinical strategies to human clinical applications (14, 15). The accepted dogma is usually that antiangiogenic therapy destroys or blocks the function of tumor-associated vessels to deprive the tumor of oxygen and nutrients, thereby inhibiting tumor growth. However, current thinking prospects one to conclude that this results of any type of antiangiogenic therapy.
