Efficacy of doxorubicin thermosensitive liposomes (40 degrees C) and local hyperthermia on rat rhabdomyosarcoma.

The efficacy of novel thermosensitive liposomes (40 degrees C) containing doxorubicin (Dox-Lip) together with local hyperthermia (HT) was studied on solid growing rat rhabdomyosarcomas. Tumor response and systemic toxicity were evaluated by comparing to free doxorubicin (Free Dox) with or without hyperthermia. Tumors were heated with infrared-A-radiation and drugs were infused intravenously after preheating the tumors followed by a further 60 min of heating at 42.5 degrees C. Recorded temperatures at various locations in the tumors indicated that all intratumoral temperatures, especially at the back rim, were definitely >40 degrees C. After single doses, tumor growth was further inhibited by Dox-Lip+HT compared to Free Dox+HT or Free Dox alone. Repeated treatments with Dox-Lip+HT (2x2.5 mg/kg+HT/2 weeks) resulted in a statistically significant tumor growth delay and was associated with a much lower systemic toxicity. Uptake studies of drugs in blood, tumor and normal tissues showed that Dox-liposomes (40 degrees C) are long circulating liposomes in the blood. However, the enhanced tumor response did not correlate with an increased uptake of Dox-Lip+HT in the tumor. The findings suggest that repeated applications of thermosensitive liposomal doxorubicin (40 degrees C) and local hyperthermia can control primary rat rhabdomyosarcomas while reducing the systemic toxicity of free doxorubicin.

Zone-specific remodeling of tumor blood vessels affects tumor growth.

BACKGROUND: Chaotic organization, abnormal leakiness, and structural instability are characteristics of tumor vessels. However, morphologic events of vascular remodeling in relation to tumor growth are not sufficiently studied yet. METHODS: By using the rat rhabdomyosarcoma tumor model vascular morphogenesis was studied by light and electron microscopy and immunohistochemistry in relation to tumor regions such as tumor surrounding (TSZ), marginal (TMZ), intermediate (TIZ), and center (TCZ) zones. RESULTS: The analyses revealed that blood vessels of TSZ display a regular ultrastructure, whereas blood vessels of TMZ showed a chaotic organization and unstable structure with a diffuse or even lacking basal lamina, and missing or irregular assembled periendothelial cells. In contrast, blood vessels of TIZ and TCZ exhibited a more or less stabilized vessel structure with increased diameter. Correspondingly, normal assembly of alpha-smooth-muscle-actin (alpha-SMA)-positive cells into the vessel wall was observed in blood vessels of TSZ, TIZ, and TCZ. Also, Ang1 immunostaining was strongest in large vessels of TIZ and TCZ, whereas Ang2 staining was prominent in small vessels of TIZ. Tie2 staining was detectable in small and large vessels of all tumor zones. Immunostaining for alpha(v)beta(3)-integrin was strongest in small vessels of TMZ, whereas large vessels of TIZ and TCZ were almost negative. CONCLUSIONS: The results indicate a zone-specific remodeling of tumor blood vessels by stabilization of vessels in TIZ and TCZ, whereas small vessels of these zones obviously undergo regression leading to tumor necrosis. Thus, a better understanding of vascular remodeling and stabilization in tumors would enable new strategies in tumor therapy and imaging.

Oxygenation of tumor recurrences following fractionated radiotherapy of primary tumors. Studies on the rhabdomyosarcoma R1H of the rat.

BACKGROUND AND PURPOSE: Tumor oxygenation is well recognized as a major factor of tumor response to radiotherapy. In this respect, a number of studies have examined the response of primary tumors, whereas little is known about the oxygenation of tumor recurrences after radiotherapy. It was the aim of this study to investigate the oxygenation of tumor recurrences after preceding irradiation of the primary tumor. MATERIAL AND METHODS: Tumor oxygenation in primary tumors and recurrences of rat rhabdomyosarcomas R1H was measured by using pO(2) probes and Eppendorf pO(2) histography. Primary tumors were irradiated at a (60)Co radiotherapy facility with a total dose of 75 Gy, given in 30 fractions over 6 weeks. Oxygenation was measured in R1H tumors before and directly after completion of irradiation. In R1H recurrences oxygenation was determined, when they reached the same size as the previously treated primary tumors (V(o) = 3.1 +/- 0.5 cm(3)). Additionally, tumor microvessel density and the intercapillary distance of tumor blood vessels were determined on histological sections using a counting grid. RESULTS: Tumor oxygenation in R1H recurrences was significantly lower when compared to primary R1H tumors. In primary tumors a median pO(2) of 17 +/- 7 mmHg was measured. By contrast, the median pO(2) in R1H recurrences was only 5 +/- 5 mmHg (p < 0.05). The high frequency of pO(2) values < 5 mmHg indicated that R1H recurrences were significantly more hypoxic (58 +/- 5%) in comparison to primary tumors (22 +/- 4%). The histological sections of the R1H recurrences showed a higher heterogeneity in their tissue structure than primary nonirradiated tumors. The morphometric studies demonstrated a reduced microvessel density (91 +/- 21/9.04 mm(2) in the tumor periphery; p = 0.0001) compared with recurrent tumors (68 +/- 26) and an enhanced mean distance of tumor blood vessels, especially in the center of the R1H recurrences (184 +/- 20 vs. 243 +/- 70 mm; p = 0.0001). CONCLUSION: In R1H rhabdomyosarcomas tumor oxygenation in recurrent tumors following radiation therapy is significantly lower than in primary tumors. This observation has to be taken into account in cases of tumor recurrences where repeated radiotherapy, chemotherapy or combined treatment modalities are used.

Pentoxifylline enhances tumor oxygenation and radiosensitivity in rat rhabdomyosarcomas during continuous hyperfractionated irradiation.

PURPOSE: To examine the influence of the hemorrheologic agent pentoxifylline (PTX) on tumor oxygenation and radiosensitivity. MATERIAL AND METHODS: Tumor oxygenation in rat rhabdomyosarcomas R1H after PTX administration (50 mg/kg body weight) was measured using interstitial pO(2) probes (Licox CMP system and Eppendorf pO(2)-Histograph). Tumors were irradiated with (60)Co gamma-irradiation using single doses (15 and 30 Gy), conventional fractionation (60 Gy/30 fractions/6 weeks), and continuous hyperfractionation (54 Gy/36 fractions/18 days) in combination with PTX or an equivalent volume of physiological saline. Radiation effects were determined by tumor growth delay (2V(o)), and by partial and complete tumor remission. RESULTS: PTX increased tumor oxygenation for up to 45 min after administration of the drug. Single doses of 15 and 30 Gy of irradiation, when combined with PTX, produced little radiosensitization of the R1H tumors as indicated by dose-modifying factors (DMFs) of 1.11 and 1.04, respectively. In conventional fractionated irradiation with PTX, a DMF of 1.10 was obtained only. However, in continuous hyperfractionated irradiation with 18 x 50 mg/kg of PTX, the DMF with respect to tumor growth delay was found to be 1.37. Local tumor control was not influenced by PTX. In vitro studies identified R1H cells as p53 wildtype and showed a G1 arrest in response to irradiation. When 2 mM PTX was given prior to irradiation, it did not improve radiosensitivity of R1H cells as measured by clonogenic survival assays. CONCLUSION: PTX effectively enhances tumor oxygenation and radiosensitivity of R1H rhabdomyosarcomas, especially during continuous hyperfractionated irradiation. Given to rats as an adjuvant to fractionated irradiation, PTX does not enhance acute or late skin reactions or tumor metastasis. No radiosensitization was observed in vitro, when oxygen was not limiting. The observed radiosensitization by PTX is caused mainly by improved tumor oxygenation.