Tumor Interstitial Pressure Research Articles

Correlation of blood and physiologic markers with effect of bevacizumab (BV) with chemoradiation therapy in rectal cancer (RC)

4096 Background: A phase I/II study of neoadjuvant BV with 5-fluorouracil (5-FU) and radiation therapy (RT) in patients with locally advanced RC tested the hypothesis that standard therapy plus inhibition of VEGF results in clinical benefit and that this effect is correlated with a set of angiogenic biomarkers. Methods: 25 patients with endoscopic US or surface coil MRI staged T3/4 RC were enrolled on this trial from 2002. Patients received 4 cycles of neoadjuvant therapy consisting of: 1) BV infusion on day 1 (cycles 1–4); 2) infusional 5-FU (225 mg/m2/24 hours, cycles 2–4); 3) external beam RT (50.4 Gy in 28 fractions, cycles 2–4; and 4) surgery 7–9 weeks after completion of neoadjuvant therapy. Correlative studies were undertaken to explore the biomarker value of angiogenic markers for this neoadjuvant therapy regimen in RC. Results: Histologic examination of the surgical specimen showed no residual cancer in the primary site in 5 patients (20%), 8 patients had rare scattered tumor cells (32%) and 6 patients exhibited more fibrosis than residual tumor (24%). In 14 patients all the lymph nodes were negative for malignancy, whereas 11 patients had microscopic nodal metastases. 3-year actuarial overall survival, disease free survival, and local control of these 25 patients were 100%, 88%, and 100%, respectively. There were no acute grade 4 toxicity events. The change in PlGF on BV alone and the pretreatment sVEGFR-1 in plasma correlated significantly (p<0.05) with extent of primary tumor regression. Presurgery CECs correlated with the extent of PET-FDG uptake decrease and was significantly higher in patients with residual disease compared to patients with pathCR (p<0.05). Changes in plasma VEGF and in tumor interstitial pressure correlated significantly (p<0.05) to extent of nodal regression in the surgical specimen. Conclusions: BV with standard chemo- radiation yields promising clinical results. The biomarkers identified in this study are the first ones shown to correlate with tumor response to combination of anti-VEGF and cytotoxic therapy. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration AstraZeneca, Dyax, Pfizer, Takeda AstraZeneca, Genentech

Pitfalls of the application of microdialysis in clinical oncology: Controversial findings with docetaxel

Microdialysis is a novel and minimally invasive sampling technique, based on the diffusion of analytes from the interstitial compartment through a semi-permeable membrane, and enables direct assessment of tissue disposition and penetration of drugs. Variable antitumor responses may be associated with differences in tumor vascularity, capillary permeability or tumor interstitial pressure resulting in variable delivery of anticancer agents. In preparation of pharmacokinetic studies, aimed at measuring docetaxel concentrations in healthy and malignant tissues in vivo, in pre-clinical as well as clinical studies, in vitro recovery experiments were performed. In contrast to published data, the recovery experiments suggest that docetaxel has a very low recovery as a result of non-specific binding to currently available microdialysis catheters. Here we discuss our findings with docetaxel in a historical perspective and we report on our experience using polysorbate 80 to eliminate the non-specific binding and its effects on the recovery of docetaxel.

Continuous Delivery of IFN-β Promotes Sustained Maturation of Intratumoral Vasculature

IFNs have pleiotropic antitumor mechanisms of action. The purpose of this study was to further investigate the effects of IFN-beta on the vasculature of human xenografts in immunodeficient mice. We found that continuous, systemic IFN-beta delivery, established with liver-targeted adeno-associated virus vectors, led to sustained morphologic and functional changes of the tumor vasculature that were consistent with vessel maturation. These changes included increased smooth muscle cell coverage of tumor vessels, improved intratumoral blood flow, and decreased vessel permeability, tumor interstitial pressure, and intratumoral hypoxia. Although these changes in the tumor vasculature resulted in more efficient tumor perfusion, further tumor growth was restricted, as the mature vasculature seemed to be unable to expand to support further tumor growth. In addition, maturation of the intratumoral vasculature resulted in increased intratumoral penetration of systemically administered chemotherapy. Finally, molecular analysis revealed increased expression by treated tumors of angiopoietin-1, a cytokine known to promote vessel stabilization. Induction of angiopoietin-1 expression in response to IFN-beta was broadly observed in different tumor lines but not in those with defects in IFN signaling. In addition, IFN-beta-mediated vascular changes were prevented when angiopoietin signaling was blocked with a decoy receptor. Thus, we have identified an alternative approach for achieving sustained vascular remodeling-continuous delivery of IFN-beta. In addition to restricting tumor growth by inhibiting further angiogenesis, maturation of the tumor vasculature also improved the efficiency of delivery of adjuvant therapy. These results have significant implications for the planning of combination anticancer therapy.

Lung Cancer

Lung Cancer

An update on phase I study of dose-escalating imatinib mesylate plus standard-dosed temozolomide for the treatment of patients with malignant glioma

1560 Background: Imatinib mesylate, a kinase inhibitor of the PDGF receptor has been shown to decrease tumor interstitial pressure resulting in enhanced delivery of cytotoxic therapy. Recent phase II trial demonstrated promising anti-glioma activity of imatinib mesylate in combination with chemotherapy, hydroxyurea. Methods: The current phase I study is designed to determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of imatinib mesylate when combined with temozolomide, a DNA methylator with established efficacy against gliomas. Eligibility criteria include: histologically confirmed malignant glioma; age of at least 18 years; KPS of at least 60%; less than grade 2 intratumoral hemorrhage; adequate hepatic, renal, and bone marrow function and lack of prior failure or significant toxicity following treatment with either imatinib mesylate or temozolomide. Temozolomide is dosed at 200 mg/m2 on days 4–8 of each 28-day cycle. Imatinib mesylate is administered on days 1–8 of each cycle and the dose is escalated in successive cohorts of 3–6 patients via a standard “3+3” dose escalation design. Patients are stratified based on concurrent use of enzyme-inducing anticonvulsants (EIAC) and both strata are independently escalated. Results: To date 47 patients have been enrolled including 40 with GBM and 7 with anaplastic gliomas. Median age is 53.9 years (range 28 to 72); 66% are male and 51% are on EIAC. The MTD has yet to be defined for either stratum. To date DLT of ALT elevation has been observed in one patient from non-EIAC stratum. Two patients discontinued therapy due to toxicities with one asymptomatic intracerebral hemorrhage and one severe hematologic toxicity. Pharmacokinetic sampling has been performed in approximately half of the patients. One patient completed the study (12 cycles) with stable disease. Eleven patients remain on study with one partial response and three patients have undergone more than 10 cycles of therapy with stable disease. Twenty-eight patients (59%) have developed progressive disease and discontinued therapy. Conclusions: Combination of imatinib mesylate and temozolomide is safe and well tolerated. Further accrual and dose escalation are ongoing. [Table: see text]

SWOG 0338: A phase II trial of imatinib mesylate in combination with capecitabine in metastatic breast cancer

10529 Background: Imatinib mesylate targets c-kit and platelet derived growth factor receptor (PDGFR) tyrosine kinases, and both are variably expressed in breast cancer. Inhibition of PDGFR by imatinib mesylate may decrease tumor interstitial pressure and improve delivery of chemotherapy. Based on preclinical synergy, SWOG conducted a phase II trial in metastatic breast cancer. Methods: Patients were eligible if they had adenocarcinoma of the breast that had progressed on at least 1 but ≤ 2 prior chemotherapy regimens for metastatic disease. No prior 5-FU or capecitabine for metastatic disease was allowed. Patients had to be &gt; 18 years with a Zubrod performance status ≤ 2 and have adequate organ function. Patients with brain metastases were ineligible. Patients received imatinib mesylate 400 mg orally daily and capecitabine 1000 mg/m2 orally twice daily on days 1–14 of a 21-day cycle. If tolerated, the imatinib mesylate was increased to 600 mg daily in subsequent cycles. This was a 2-stage design with 25 patients with measurable disease accrued in the first stage. A total of 70 patients was planned, including those with nonmeasurable disease, if accrual proceeded to the second stage. The primary endpoint was to determine the confirmed response rate (RR) to the combination therapy. Secondary endpoints were to estimate the 6-month progression free survival, to determine the toxicities, and to explore c-kit and PDGFR in this population. Results: 27 patients were accrued; 6 were ineligible. 19 patients received therapy and were evaluable for toxicity. The median age was 59 years (36–78). Four responses were seen: 1 complete, 1 confirmed partial, and 2 unconfirmed partial (RR 21%). The 6-month progression free survival was 16%. There were no grade 4 toxicities. The most common grade 3 toxicities, seen in 7 patients, were diarrhea, fatigue, and hand-foot syndrome. As 2 of the 4 responses were unconfirmed, accrual did not proceed to the second stage. Conclusions: The combination of imatinib mesylate and capecitabine was well tolerated in patients with metastatic breast cancer, but the RR was not better than was seen in a prior study of single agent capecitabine. Correlative studies to explore c-kit, PDGFR, and estrogen receptor expression and response are in progress. No significant financial relationships to disclose.

Intraperitoneal Immunotherapy for Metastatic Ovarian Carcinoma: Resistance of Intratumoral Collagen to Antibody Penetration

Convective transport of macromolecules from the peritoneal cavity into tumor is determined by its hydraulic permeability and the pressure gradient. Previous studies showed that establishing a pressure gradient into the tumor failed to result in significant penetration. This study addresses the hypothesis that the extracellular matrix is the major resistance to the penetration of an i.p. injected antibody. Human ovarian tumors (SKOV-3 and OVCAR-3) were established in the abdominal wall of athymic rats. After anesthesia, the tumor serosal surface was treated for 2 hours with Krebs solution (control), collagenase (37.5 unit/mL), or hyaluronidase (10 unit/mL) followed by 3 hours of convective delivery of radiolabeled IgG. Transport of antibody into the tumor was measured with quantitative autoradiography along with the tumor interstitial pressure, concentration of collagen and hyaluronic acid, and IgG volume of distribution. Antibody was excluded from 42% to 53% of tumor extracellular volume. Exposure of tumors to hyaluronidase did not enhance IgG transport despite removal of 90% of the hyaluronan from the exposed tumor. In contrast, collagenase reduced collagen content, lowered tumor interstitial pressure, and markedly enhanced antibody penetration. Reduction of collagen, but not hyaluronan, in the matrix of ovarian xenografts enhanced the transport of i.p. injected antibody. Although high interstitial pressure is a deterrent to convective transport of macromolecules into the tumor parenchyma, the structure of the interstitial matrix provides an inherent resistance, which must be overcome before effective delivery of an antibody.

Efficacy of imatinib mesylate plus hydroxyurea regimen in the treatment of recurrent malignant glioma: Phase II study results

1515 In this phase 2 study we evaluated the activity of imatinib mesylate (Gleevec), an inhibitor of the PDGF receptor tyrosine kinase with anti-angiogenic activity and the ability to decrease tumor interstitial pressure, combined with hydroxyurea in the treatment of patients with recurrent malignant glioma. Eligibility criteria include: recurrent malignant glioma; age > 18 years; KPS 60% or greater; less than grade 2 intratumoral hemorrhage; adequate hepatic, renal, and bone marrow function. Hydroxyurea is administered at 500 mg BID while Gleevec is administered at 500 mg BID for patients on enzyme-inducing anticonvulsants (EIAC; phenytoin, carbamazepine and phenobarbitol) and at 400 mg QD for those not on EIAC. A treatment cycle lasted 28 days and evaluations for response were performed after every other cycle. Enrollment includes 64 patients: 32 with recurrent GBM and 32 with recurrent AA/AO. The median age is 46 (range 21 to 68); 55% are male and 45% are on EIAC. All patients had prior XRT and the median number of prior chemotherapy agents was 3 (range, 1–5) while the median number of prior progressions was 2 (range, 1–7). Toxicity has included grade 3 or 4 hematologic events in 20% and 5% respectively, grade 3 edema in 8% and grade 3 LFT abnormalities in 3%. Nine percent of GBM patients achieved a radiographic response while 35% achieved stable disease. Median progression free survival (PFS) for patients with recurrent AA/AO and GBM are 10.9 and 14.4 weeks respectively. At 6 months, 26.3% of GBM patients are progression free. Among heavily pretreated patients with recurrent GBM enrolled on this study, the rate of radiographic response, median PFS and 6-mth PFS rate compare favorably to results achieved with temozolomide in first relapse indicating that a randomized trial of imatinib mesylate plus hydroxyurea versus temozolomide is warranted. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Novartis Novartis

A phase I dose escalation study of imatinib mesylate plus standard-dosed temozolomide in the treatment of patients with malignant glioma

1540 Imatinib mesylate (Gleevec), an inhibitor of the PDGF receptor tyrosine kinase with anti-angiogenic activity, has been shown to decrease tumor interstitial pressure resulting in enhanced delivery of cytotoxic therapy. The current phase I study is designed to determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of imatinib mesylate when combined with temozolomide, a DNA methylator with established anti-glioma activity, in patients with malignant glioma. Eligibility criteria include: histologically confirmed malignant glioma; age at least 18 years; KPS of at least 60%; less than grade 2 intratumoral hemorrhage; adequate hepatic, renal, and bone marrow function and lack of prior failure or significant toxicity following treatment with either imatinib mesylate or temozolomide. Temozolomide is dosed at 200 mg/m2 on days 1–5 of each 28-day cycle. Imatinib mesylate is administered on days 1–8 of each cycle and the dose is escalated in successive cohorts of 3–6 patients via a standard ...

Resistance of Tumor Interstitial Pressure to the Penetration of Intraperitoneally Delivered Antibodies into Metastatic Ovarian Tumors

Despite evidence that regional chemotherapy improves the treatment of metastatic peritoneal ovarian carcinoma, monoclonal antibodies have not shown significant success in i.p. delivery. The present study was designed to address the hypothesis that convective penetration of macromolecular antineoplastic agents depends on a positive pressure difference between the i.p. therapeutic solution and the tumor. Nude rats with human ovarian xenografts implanted in the abdominal wall were used in experiments to facilitate in vivo measurement of tumor pressure and the treatment of the tumor with i.p. solutions at high pressures. Penetration of (125)I-labeled trastuzumab was measured with quantitative autoradiography. Tumor pressure profiles showed peak pressures of 32 mm Hg with mean pressures (+/- SD, mm Hg) in 12 SKOV3 tumors of 9.7 +/- 8.3 and in 15 OVCAR3 tumors of 12.5 +/- 7.0. I.p. therapeutic dwells at 6 to 8 mm Hg (maximum feasible pressure) showed significantly less penetration of trastuzumab than in adjacent normal muscle. To establish a driving force for convection into the tumor, various maneuvers were attempted to reduce tumor pressure, including treatment with taxanes or prostaglandin E(1), elimination of tumor circulation, and removal of the tumor capsule. Tumor decapsulation decreased the pressure to zero but did not enhance the penetration of antibody. Binding to specific trastuzumab receptors on each tumor was shown to be not a significant barrier to antibody penetration. The results only partially support our hypothesis and imply that the microenvironment of the tumor is in itself a major barrier to delivery of charged macromolecules.

Improving chemotherapeutic drug penetration in tumors by vascular targeting and barrier alteration.

Drug delivery and penetration into neoplastic cells distant from tumor vessels are critical for the effectiveness of solid-tumor chemotherapy. We have found that targeted delivery to tumor vessels of picogram doses of TNF-alpha (TNF), a cytokine able to alter endothelial barrier function and tumor interstitial pressure, enhances the penetration of doxorubicin in tumors in murine models. Vascular targeting was achieved by coupling TNF with CNGRC, a peptide that targets the tumor neovasculature. This treatment enhanced eight- to tenfold the therapeutic efficacy of doxorubicin, with no evidence of increased toxicity. Similarly, vascular targeting enhanced the efficacy of melphalan, a different chemotherapeutic drug. Synergy with chemotherapy was observed with 3-5 ng/kg of targeted TNF (intraperitoneally), about 10(6)-fold lower than the LD(50) and 10(5)-fold lower than the dose required for nontargeted TNF. In addition, we have also found that targeted delivery of low doses of TNF to tumor vessels does not induce the release of soluble TNF receptors into the circulation. The delivery of minute amounts of TNF to tumor vessels represents a new approach for avoiding negative feedback mechanisms and preserving its ability to alter drug-penetration barriers. Vascular targeting could be a novel strategy for increasing the therapeutic index of chemotherapeutic drugs.

Improving chemotherapeutic drug penetration in tumors by vascular targeting and barrier alteration

Drug delivery and penetration into neoplastic cells distant from tumor vessels are critical for the effectiveness of solid-tumor chemotherapy. We have found that targeted delivery to tumor vessels of picogram doses of TNF-α (TNF), a cytokine able to alter endothelial barrier function and tumor interstitial pressure, enhances the penetration of doxorubicin in tumors in murine models. Vascular targeting was achieved by coupling TNF with CNGRC, a peptide that targets the tumor neovasculature. This treatment enhanced eight- to tenfold the therapeutic efficacy of doxorubicin, with no evidence of increased toxicity. Similarly, vascular targeting enhanced the efficacy of melphalan, a different chemotherapeutic drug. Synergy with chemotherapy was observed with 3–5 ng/kg of targeted TNF (intraperitoneally), about 106-fold lower than the LD50 and 105-fold lower than the dose required for nontargeted TNF. In addition, we have also found that targeted delivery of low doses of TNF to tumor vessels does not induce the release of soluble TNF receptors into the circulation. The delivery of minute amounts of TNF to tumor vessels represents a new approach for avoiding negative feedback mechanisms and preserving its ability to alter drug-penetration barriers. Vascular targeting could be a novel strategy for increasing the therapeutic index of chemotherapeutic drugs.

Improving chemotherapeutic drug penetration in tumors by vascular targeting and barrier alteration

Drug delivery and penetration into neoplastic cells distant from tumor vessels are critical for the effectiveness of solid-tumor chemotherapy. We have found that targeted delivery to tumor vessels of picogram doses of TNF-α (TNF), a cytokine able to alter endothelial barrier function and tumor interstitial pressure, enhances the penetration of doxorubicin in tumors in murine models. Vascular targeting was achieved by coupling TNF with CNGRC, a peptide that targets the tumor neovasculature. This treatment enhanced eight- to tenfold the therapeutic efficacy of doxorubicin, with no evidence of increased toxicity. Similarly, vascular targeting enhanced the efficacy of melphalan, a different chemotherapeutic drug. Synergy with chemotherapy was observed with 3–5 ng/kg of targeted TNF (intraperitoneally), about 106-fold lower than the LD50 and 105-fold lower than the dose required for nontargeted TNF. In addition, we have also found that targeted delivery of low doses of TNF to tumor vessels does not induce the release of soluble TNF receptors into the circulation. The delivery of minute amounts of TNF to tumor vessels represents a new approach for avoiding negative feedback mechanisms and preserving its ability to alter drug-penetration barriers. Vascular targeting could be a novel strategy for increasing the therapeutic index of chemotherapeutic drugs.

Relationship between tumor extracellular fluid exposure to topotecan and tumor response in human neuroblastoma xenograft and cell lines.

We have reported a 6-fold difference in the topotecan (TPT) lactone systemic exposure achieving a complete response in the human neuroblastoma xenografts NB-1691 and NB-1643. However, the relationship between tumor extracellular fluid (ECF) exposure to TPT and the antitumor activity in xenograft and in vitro models has not been established. TPT was given i.v. to mice bearing NB-1691 and NB-1643 tumors. Prior to dosing, microdialysis probes were placed in tumors of mice bearing NB-1691 and NB-1643 tumors. Plasma and tumor ECF concentrations of TPT lactone were assayed by high performance liquid chromatography. The inhibitory concentration (IC50) was determined for NB-1691 and NB-1643 cell lines in vitro. The TPT AUC(ECF) values determined for NB-1691 (n = 10) and NB-1643 (n = 11) were 7.3 +/- 0.84 and 25.6 +/- 0.76 ng h ml(-1), respectively (P < 0.05). TPT tumor ECF penetration in NB-1691 and NB-1643 was 0.04 +/- 0.04 and 0.15 +/- 0.11 (P < 0.05), respectively. The IC50 values recorded after 6 h of TPT exposure daily for 5 consecutive days for NB-1691 and NB-1643 were 2.7 +/- 1.1 and 0.53 +/- 0.19 ng/ml, respectively (P < 0.05). NB-1643 was more sensitive in vitro than NB-1691, and at similar plasma TPT exposures, NB-1643 had a greater degree of TPT tumor ECF exposure and penetration as compared with NB-1691. Potential factors affecting tumor TPT ECF disposition include tumor vascularity, capillary permeability, and interstitial pressure. The clinical importance of this study is underscored by the need to select anticancer agents with a high capacity for tumor penetration and to optimize drug administration to increase tumor penetration.

Pharmacologic Modification of Tumor Blood Flow and Interstitial Fluid Pressure in a Human Tumor Xenograft: Network Analysis and Mechanistic Interpretation

Various vasoactive agents have been used to modify tumor blood flow with the ultimate goal of improving cancer detection and treatment, with widely disparate results. Furthermore, the lack of mechanistic interpretations has hindered understanding of how these agents affect the different physiological parameters involved in perfusion. Thus, there is a need to develop a unified framework for understanding the interrelated physiological effects of pharmacological and physical agents, The goals of this study were (1) to develop a mathematical model which helps determine the location and magnitude of changes in the vascular resistance of tumor and normal tissues and (2) to test the model with our own experimental studies and by comparison with results from the literature. The systemic and interstitial pressures and relative tumor blood flow were measured before and after administration of angiotensin II, epinephrine, norepinephrine, nitroglycerin, and hydralazine in SCID mice bearing LS174T human colon adenocarcinoma xenografts. A mathematical model was developed in analogy to electrical circuits which examined the pressure, flow, and resistance relationships for arterial and venous segments of the vasculature of a tumor and surrounding normal tissue. Vasoconstrictor-induced increases in the mean arterial blood pressure led to increases in tumor blood flow and interstitial pressure with the magnitude of change dependent on the agent (percentage change in blood flow: angiotensin > epinephrine > norepinephrine). The vasodilating agents induced decreases in tumor blood flow in parallel to the induced decreases in the systemic pressure, but only the long-acting arterial vasodilator hydralazine was capable of effecting a decrease in tumor interstitial pressure. The model was also found to be consistent with other data available in the literature on norepinephrine, pentoxifylline, nicotinamide, and hemodilution, and was useful in providing input as to the location and degree of the physiological effects of these agents. The results of the data and model show that the steal phenomenon is the dominant mechanism for redistribution of host blood flow to the tumor. However, some degree of arterial control was found to be present in the tumors. Moreover, the parallel increases in tumor interstitial pressure and blood flow contradict any hypothesis suggesting that elevated interstitial fluid pressure precipitates chronic vascular collapse, thus decreasing blood flow.

Oxygen in Human Tumors: Correlations between Methods of Measurement and Response to Therapy: Summary of a Workshop Held November 19-20, 1992, at the National Cancer Institute, Bethesda, Maryland

Knowledge about the oxygenation of human tumors and its importance in the response to radiotherapy is crucial to the effort to develop improved treatment methods for radiotherapy. The measurement of oxygenation of human tumors and correlations with response to radiotherapy were the subjects of a recent workshop sponsored by the National Cancer Institute. The following methods for measuring oxygen or hypoxia, or a parameter related to either, were presented: polarographic oxygen electrodes, the comet and alkaline elution assays for radiation-induced DNA damage, nitroimidazole binding assays, hemoglobin saturation assays, magnetic resonance spectroscopy, electron spin resonance spectroscopy, phosphorescence imaging, and an assay for tumor interstitial pressure. The electron spin resonance, alkaline elution, and phosphorescence imaging methods have not been used in human tumors. The comet assay, nitroimidazole binding assays, magnetic resonance spectroscopy, cryospectroscopy, and near-infrared spectroscopy have been employed in human tumors, but correlations to treatment response have not been made. Polarographic measurements have indicated that the presence of hypoxia correlates with a poor response to radiotherapy in cervical cancers, but additional data are needed on early-stage disease, and with long-term follow-up on local control and survival. If these confirm the correlation between hypoxia and poor response to radiotherapy, additional tumor sites should be studied. Future clinical trials of treatments that sensitize, exploit, or kill hypoxic cells should identify and include the individual patients with hypoxic tumors. Fundamental unanswered questions regarding the assessment of tumor oxygenation concern the need for invasive procedures, the spatial resolution needed for prediction of response to radiotherapy, the importance of reoxygenation, differences between tumors in rates and degrees of reoxygenation, whether measurements made during a course of therapy are of value, and correlations among methods and with other predictive assays such as intrinsic radiosensitivity and potential doubling time.

The effects of photodynamic therapy using differently substituted zinc phthalocyanines on vessel constriction, vessel leakage and tumor response.

The effects of four different zinc phthalocyanines were studied during and after photodynamic therapy (PDT). Measurements of vessel constriction, vessel leakage, tumor interstitial pressure, eicosanoid release, and tumor response of chondrosarcoma were made in Sprague-Dawley rats. Animals were injected intravenously with 1 mumol/kg of mono-, di-, or tetrasulfonated zinc phthalocyanine, or 1 mumol/kg of a zinc phthalocyanine substituted with four tertiary butyl groups. Tissues were exposed to 400 J/cm2 670 nm light 24 h after photosensitizer injection. An additional group of animals was given indomethacin before treatment. The use of the monosulfonated and tertiary butyl substituted zinc phthalocyanines in PDT caused the release of specific eicosanoids, caused vessel constriction, and induced venule leakage and increases in tumor interstitial pressure. Tumor cures of 27% and 7% were observed. Photodynamic therapy using the disulfonated zinc phthalocyanine did not induce vessel constriction or the release of eicosanoids, however, tumor cure was 43%. The use of the tetrasulfonated zinc phthalocyanine caused intermediate effects between the mono- and disulfonated compounds. The administration of indomethacin to animals completely inhibited the effects of PDT using the monosulfonated compound but had minimal effects on treatment using the disulfonated compound. This suggests that the monosulfonated and disulfonated compounds act by different mechanisms of destruction.

THE EFFECTS OF ASPIRIN ON MICROVASCULATURE AFTER PHOTODYNAMIC THERAPY

The effects of aspirin (acetylsalicylic acid: ASA) on vessel behavior and tumor response were measured during and after photodynamic therapy (PDT). Changes to vessel constriction, macromolecular leakage, tumor interstitial pressure, and tumor response were examined. Animals were randomly placed into treatment groups and injected with 0-25 mg/kg Photofrin and given 0 or 135 J/cm2 light treatment. The light treatment was standardized to 75 mW/cm2 at 630 nm over a 30 min treatment interval (135 J/cm2). The treatment groups were further subdivided to receive Photofrin alone or Photofrin plus 100 mg/kg ASA. A cremaster muscle model in Sprague-Dawley rats was used to directly observe microvascular response and changes in vessel permeability to macromolecules. A tumor interstitial pressure model was designed to measure pressure changes in a chondrosarcoma tumor over time. This model indirectly measures macromolecular leakage, among other factors, in the tumor tissue. Groups of 10-20 rats were implanted subcutaneously with chondrosarcoma and were subjected to PDT to assess tumor response to the various treatments. Statistically significant differences in vessel leakage and changes in interstitial pressure were observed between animals given ASA plus PDT as compared to animals given PDT alone. The administration of ASA significantly inhibited venule leakage of albumin and reduced increases in interstitial pressure after treatment. The use of ASA had no effect on vessel constriction or tumor response after PDT. These findings suggest that the increases in vessel permeability observed during and after PDT, using Photofrin, do not significantly contribute to tumor response.

CHANGES IN TUMOR INTERSTITIAL PRESSURE INDUCED BY PHOTODYNAMIC THERAPY

This study has examined the changes in tumor interstitial pressure exhibited during and after photodynamic therapy (PDT). The kinetics of these changes are marked by an initial decrease, followed by a rapid rise in tumor interstitial pressure. We have also employed two inhibitory agents to evaluate the different components of the pressure curve. Specially designed pressure chambers were seeded with chondrosarcoma and implanted subcutaneously in rats. Animals were injected with 0-50 mg/kg Photofrin II (i.v.) 7 days post-implantation and tumors were exposed to 0-540 J/cm2 630 nm 24 h later. Interstitial pressure was monitored via a transducer connected to the implanted chamber. Additional groups of animals were injected with either indomethacin (an inhibitor of thromboxane synthesis) or Ketanserin (a serotonin antagonist) before light treatment. Porphyrin doses of 10 mg/kg and above (135 J/cm2), or light doses of 135 J/cm2 and above (25 mg/kg Photofrin II) were effective in modifying interstitial pressure. Porphyrin doses greater than 25 mg/kg, or light doses greater than 270 J/cm2 produced no further increases in interstitial pressure. Animals given indomethacin (10 mg/kg i.p.) exhibited the initial decrease in pressure during light treatment, but showed no increase past baseline levels. Animals given Ketanserin (10 mg/kg i.p.) demonstrated no decrease in pressure during PDT, but showed the same elevations in pressure as controls. This suggests that two independent mechanisms account for the different components of the pressure curve, and that serotonin release may occur during PDT.

Transcapillary passage of albumin in mammary tumours and in normal lactating mammary glands of the rat.

A triple-isotope technique was used to obtain albumin clearances and blood flow in DMBA induced mammary tumours, normal lactating mammary glands and various other tissues of the rat. Albumin clearance was high both in tumours (0.0337 ml/min/100 g) and in lactating mammary glands (0.0414 ml/min/100 g). Albumin extraction (defined as the ratio of clearance over plasma flow) was exceptionally high in tumours (23 X 10(-4)) and lactating glands (18 X 10(-4)) as compared to all other tissues (1-7 X 10(-4)). This probably reflects an increased capillary permeability to macromolecules and/or a change in the relation between blood flow and available capillary surface area, both in the physiological, hormonally induced gland and in the abnormal neoplasia derived from the same tissue. Increased extravasation of albumin, together with other changes (e.g. impaired lymph formation) may be important factors behind the production of increased tumour interstitial pressure, which tend to reduce nutritional blood flow in tumours.