Markus Steinbauer

Rapamycin inhibits primary and metastatic tumor growth by antiangiogenesis: involvement of vascular endothelial growth factor

Conventional immunosuppressive drugs have been used effectively to prevent immunologic rejection in organ transplantation. Individuals taking these drugs are at risk, however, for the development and recurrence of cancer. In the present study we show that the new immunosuppressive drug rapamycin (RAPA) may reduce the risk of cancer development while simultaneously providing effective immunosuppression. Experimentally, RAPA inhibited metastatic tumor growth and angiogenesis in in vivo mouse models. In addition, normal immunosuppressive doses of RAPA effectively controlled the growth of established tumors. In contrast, the most widely recognized immunosuppressive drug, cyclosporine, promoted tumor growth. From a mechanistic perspective, RAPA showed antiangiogenic activities linked to a decrease in production of vascular endothelial growth factor (VEGF) and to a markedly inhibited response of vascular endothelial cells to stimulation by VEGF. Thus, the use of RAPA, instead of cyclosporine, may reduce the chance of recurrent or de novo cancer in high-risk transplant patients.

Rapamycin Protects Allografts From Rejection While Simultaneously Attacking Tumors In Immunosuppressed Mice

Cancer is an increasingly recognized problem associated with immunosuppression. Recent reports, however, suggest that the immunosuppressive agent rapamycin has anti-cancer properties that could address this problem. Thus far, rapamycin’s effects on immunity and cancer have been studied separately. Here we tested the effects of rapamycin, versus cyclosporine A (CsA), on established tumors in mice simultaneously bearing a heart allograft. In one tumor-transplant model, BALB/c mice received subcutaneous syngenic CT26 colon adenocarcinoma cells 7 days before C3H ear–heart transplantation. Rapamycin or CsA treatment was initiated with transplantation. In a second model system, a B16 melanoma was established in C57BL/6 mice that received a primary vascularized C3H heart allograft. In vitro angiogenic effects of rapamycin and CsA were tested in an aortic ring assay. Results show that CT26 tumors grew for 2 weeks before tumor complications occurred. However, rapamycin protected allografts, inhibited tumor growth, and permitted animal survival. In contrast, CsA-treated mice succumbed to advancing tumors, albeit with a functioning allograft. Rapamycin’s antitumor effect also functioned in severe combined immunodeficient BALB/c mice. Similar effects of the drugs occurred with B16 melanomas and primary vascularized C3H allografts in C57BL/6 mice. Furthermore, in this model, rapamycin inhibited the tumor growth-enhancing effects of CsA. Moreover, in vitro experiments showed that CsA promotes angiogenesis by a transforming growth factor-β–related mechanism, and that this effect is abrogated by rapamycin. This study demonstrates that rapamycin simultaneously protects allografts from rejection and attacks tumors in a complex transplant-tumor situation. Notably, CsA protects allografts from rejection, but cancer progression is promoted in transplant recipients.

Rapamycin-Induced Endothelial Cell Death and Tumor Vessel Thrombosis Potentiate Cytotoxic Therapy against Pancreatic Cancer

Purpose: Despite current chemotherapies, pancreatic cancer remains an uncontrollable, rapidly progressive disease. Here, we tested an approach combining a recently described antiangiogenic drug, rapamycin, with standard gemcitabine cytotoxic therapy on human pancreatic tumor growth. Experimental Design: Tumor growth was assessed in rapamycin and gemcitabine-treated nude mice orthotopically injected with metastatic L3.6pl human pancreatic cancer cells. H&E staining was performed on tumors, along with Ki67 staining for cell proliferation and immunohistochemical terminal deoxynucleotidyl transferase-mediated nick end labeling and CD31 analysis. Rapamycin-treated tumor vessels were also directly examined in dorsal skin-fold chambers for blood flow after thrombosis induction. Cell death in human umbilical vein endothelial cells was assessed by flow cytometry after annexin-V staining. Results: Rapamycin therapy alone inhibited tumor growth and metastasis more than gemcitabine, with remarkable long-term tumor control when the drugs were combined. Mechanistically, H&E analysis revealed tumor vessel endothelium damage and thrombosis with rapamycin treatment. Indeed, dorsal skin-fold chamber analysis of rapamycin-treated tumors showed an increased susceptibility of tumor-specific vessels to thrombosis. Furthermore, terminal deoxynucleotidyl transferase-mediated nick end labeling/CD31 double staining of orthotopic tumors demonstrated apoptotic endothelial cells with rapamycin treatment, which also occurred with human umbilical vein endothelial cells in vitro. In contrast, gemcitabine was not antiangiogenic and, despite its known cytotoxicity, did not reduce proliferation in orthotopic tumors; nevertheless, rapamycin did reduce tumor proliferation. Conclusions: Our data suggest a novel mechanism whereby rapamycin targets pancreatic tumor endothelium for destruction and thrombosis. We propose that rapamycin-based vascular targeting not only reduces tumor vascularization, it decreases the number of proliferating tumor cells to be destroyed by gemcitabine, thus introducing a new, clinically feasible strategy against pancreatic cancer.

Dosing of rapamycin is critical to achieve an optimal antiangiogenic effect against cancer

Rapamycin has antiangiogenic activity against tumors. This has been discussed while addressing the problem of cancer in organ transplantation. Here we investigated effective dosing schedules against tumors and angiogenesis. Growth of established CT‐26 colon adenocarcinoma tumors was measured in Balb/c mice treated with total equivalent rapamycin doses (1.5 mg/kg/day) given once a day, once every 3 days, or by continuous infusion. Tumors were most inhibited with continuous rapamycin infusion, and less by bolus dosing. Interestingly, however, continuous dosing produced the lowest rapamycin blood levels (15 ng/ml). As rapamycin‐sensitive p70S6‐kinase intracellular signaling is critical for angiogenesis, p70S6‐kinase activation was measured in endothelial cells by Western blotting. Maximal p70S6‐kinase inhibition occurred from 1–5 ng/ml rapamycin. These same rapamycin concentrations optimally blocked vessel‐sprouting from cultured aortic rings. Therefore, low‐level rapamycin dosing most effectively controls tumors in mice. Importantly, antiangiogenic rapamycin levels are compatible with immunosuppressive doses, supporting its potential use in transplant patients with cancer.

Blockage of 2-Deoxy-d-Ribose-Induced Angiogenesis with Rapamycin Counteracts a Thymidine Phosphorylase-Based Escape Mechanism Available for Colon Cancer under 5-Fluorouracil Therapy

Purpose: Colorectal neoplasms remain a leading cause of cancer-related deaths. A recognized weakness of conventional 5-fluorouracil (5-FU) therapy relates to expression of the intracellular enzyme, thymidine phosphorylase (TP). Although TP promotes 5-FU cytotoxicity, TP-derived 2-deoxy-d-ribose (dRib) counterproductively stimulates tumor angiogenesis. Here, the newly discovered antiangiogenic drug rapamycin was combined with 5-FU to counteract the potential escape mechanism of dRib-induced angiogenesis. Experimental Design: Orthotopic tumor growth was assessed in rapamycin and 5-FU-treated BALB/c mice with TP-expressing CT-26 colon adenocarcinoma cells. To examine liver metastasis, green-fluorescent protein-transfected CT-26 cells were visualized by fluorescence microscopy after intraportal injection. Cell counting and Ki67 staining were used to determine in vitro and in vivo cell expansion, respectively. In vitro angiogenic effects of dRib were assessed with endothelial cell migration and aortic ring assays. Western blotting detected dRib effects on p70/S6 kinase activation. Results: Rapamycin treatment of mice bearing orthotopic tumors inhibited tumor growth more than did 5-FU, and mice treated with both drugs typically developed no tumors. In the liver metastasis assay, combination therapy blocked metastatic expansion of solitary tumor cells. Interestingly, complex drug activities were suggested by tumor-cell proliferation being more sensitive to 5-FU than to rapamycin in vitro, but more sensitive to rapamycin in vivo. With regard to angiogenesis, dRib-induced endothelial cell migration and aortic ring formation were completely abrogated by rapamycin, correlating with blockage of dRib-induced p70/S6 kinase activation in endothelial cells. Conclusions: Inhibition of dRib-induced angiogenesis with rapamycin counteracts a potential TP-based escape mechanism for colorectal cancer under 5-FU therapy, introducing a novel, clinically feasible, combination treatment option for this common neoplasm.

Alert for increased long-term follow-up after carotid artery stenting: results of a prospective, randomized, single-center trial of carotid artery stenting vs carotid endarterectomy.

BACKGROUND Carotid endarterectomy (CEA) has been shown to be effective in stroke prevention for patients with symptomatic or asymptomatic carotid artery stenosis. Although several prospective randomized trials indicate that carotid artery stenting (CAS) is an alternative but not superior treatment modality, there is still a significant lack of long-term data comparing CAS with CEA. This study presents long-term results of a prospective, randomized, single-center trial. METHODS Between August 1999 and April 2002, 87 patients with a symptomatic high-grade internal carotid artery stenosis (>70%) were randomized to CAS or CEA. After a median observation time of 66 +/- 14.2 months (CAS) and 64 +/- 12.1 months (CEA), 42 patients in each group were re-evaluated retrospectively by clinical examination and documentation of neurologic events. Duplex ultrasound imaging was performed in 61 patients (32 CAS, 29 CEA), and patients with restenosis >70% were re-evaluated by angiography. RESULTS During the observation period, 23 patients (25.2%) died (10 CAS, 13 CEA), and three were lost to follow up. The incidence of strokes was higher after CAS, with four strokes in 42 CAS patients vs none in 42 CEA patients. One transient ischemic attack occurred in each group. A significantly higher rate of restenosis >70% (6 of 32 vs 0 of 29) occurred after CAS compared with CEA. Five of 32 CAS patients (15.6%) presented with high-grade (>70%) restenosis as an indication for secondary intervention or surgical stent removal, and three presented with neurologic symptoms. No CEA patients required reintervention (P < .05 vs CAS). A medium-grade (<70%) restenosis was detected in eight of 32 CAS patients (25%) and in one of 29 CEA patients (3.4%). In five of 32 CAS (15.6%) and three of 29 CEA patients (10.3%), a high-grade stenosis of the contralateral carotid artery was observed and treated during the observation period. CONCLUSION The long-term results of this prospective, randomized, single-center study revealed a high incidence of relevant restenosis and neurologic symptoms after CAS. CEA seems to be superior to CAS concerning the development of restenosis and significant prevention of stroke. However, the long-term results of the ongoing multicenter trials have to be awaited for a final conclusion.

Surgical strategy in aortoesophageal fistulae : Endovascular stentgrafts and in situ repair of the aorta with cryopreserved homografts

Objective:The surgical treatment of aortoesophageal fistulae (AEF) has a high morbidity and mortality rate. We report our experience with the sequential use of endovascular thoracic stentgrafts and cryopreserved aortic homografts for in situ repair of the descending thoracic aorta. Methods:In a 7-year period, 6 patients with AEF were treated at our center. After primary endovascular repair in all cases, 4 patients subsequently underwent in situ repair of the descending thoracic aorta with cryopreserved homografts. Long-term antibiotic therapy was given in all cases. Recent clinical status and radiologic findings on follow-up studies of each patient were analyzed. The mean follow-up time was 35 months (range, 2–76). Results:Endovascular stentgraft repair was technically successful in all cases. Two patients were not candidates for open surgical repair because of their medical condition; they both died within 8 weeks after discharge from the hospital, 1 from recurrent septic episodes, and the other from upper gastrointestinal bleeding. One of 4 patients who had undergone open surgical repair died 1 year later from upper gastrointestinal bleeding that occurred presumably due to an infectious degeneration of the homograft after secondary infection with a methacillin-resistant Staphyloccocus aureus. In 1 case persistent paraplegia and in another case persistent renal failure occurred. Conclusion:The use of cryopreserved homografts is a valuable alternative to in situ repair with prosthetic vascular grafts or extra-anatomic reconstructions in the surgical treatment of AEF. Endovascular stentgraft placement plays a role as a bridging procedure in emergency situations.

Overexpression of melanoma inhibitory activity (MIA) enhances extravasation and metastasis of A-mel 3 melanoma cells in vivo

The secreted MIA protein is strongly expressed by advanced primary and metastatic melanomas but not in normal melanocytes. Previous studies have shown that MIA serum levels correlate with clinical tumour progression in melanoma patients. To provide direct evidence that MIA plays a role in metastasis of malignant melanomas, A-mel 3 hamster melanoma cells were transfected with sense- and antisense rhMIA cDNA and analysed subsequently for changes in their tumorigenic and metastatic potential. Enforced expression of MIA in A-mel 3 cells significantly increased their metastatic potential without affecting primary tumour growth, cell proliferation or apoptosis rate in hamsters, compared with control or antisense transfected cells. Additionally, MIA overexpressing transfectants showed a higher rate of both tumour cell invasion and extravasation. Cells transfected with MIA antisense generally exerted an opposite response. The above changes in function attributed to the expression of MIA may underlie the contribution of MIA to the malignant phenotype.

Mycophenolate mofetil inhibits tumor growth and angiogenesis in vitro but has variable antitumor effects in vivo, possibly related to bioavailability.

Background. Identifying immunosuppressive agents with antitumor effects could help address the problem of posttransplant malignancy. Here we tested for potential inhibitory effects of mycophenolate mofetil (MMF) on tumors in vitro and in vivo. Methods. Mouse CT26 colon adenocarcinoma, B16 melanoma, and human TMK1 gastric adenocarcinoma cells were tested for in vitro growth in the presence of MMF. In vitro angiogenesis was tested with a rat aortic-ring assay. Tumor cells were implanted into dorsal skinfold chambers (DSFC) to assess in vivo angiogenesis. Subcutaneous tumor growth was determined in mice receiving MMF. Results. MMF caused a dose-dependent reduction in tumor cell numbers in vitro, starting between 0.1 to 1 μM. Vessel sprouting from aortic rings was markedly blocked by similar concentrations of MMF. In vivo, however, DSFC results showed a marginal reduction in CT26 tumor angiogenesis with MMF doses of 40 or 80 mg/kg/day, although MMF did inhibit TMK1 vascularity. Moreover, 80 mg/kg/day MMF did not reduce subcutaneous CT26 tumor volumes, but did slightly inhibit B16 and TMK1 expansion. Interestingly, the mycophenolic acid (MPA) blood level 2 hr after 80 mg/kg/day MMF bolus dosing was near 14 mg/L, but decreased dramatically thereafter, suggesting a drug availability issue. Indeed, intermittent 2-hr MMF pulses in tumor-cell cultures substantially reduced the antiproliferative effect of MPA. Conclusion. MMF strongly inhibits tumor cell growth and angiogenesis in vitro, but only marginally inhibits tumors in vivo. These contrasting results may relate to drug availability, where intermittent exposure of tumor cells to immunosuppressive doses of MMF substantially reduce its potential antitumor effects.

Differential effects of short-term ace- and AT1-receptor inhibition on postischemic injury and leukocyte adherence in vivo and in vitro.

ABSTRACT There is recent evidence that angiotensin‐converting enzyme (ACE) inhibition reduces post‐ischemic injury and angiotensin II receptor inhibition may have similar effects. We therefore further charac‐terized the role of ACE‐ vs. AT1‐receptor inhibition on cell injury and temporal association of leukocyte endothelial interaction in response to ischemia‐reperfusion. A combined in vivo and in vitro study comparing the ACE inhibitor enalapril and the AT1‐receptor antagonist losartan was performed. The extent and temporal correlation of cellular damage (propidium‐iodide staining), microvascular perfusion failure and leukocyte‐endothelial interaction (leukocyte adherence) were investigated by means of intravital microscopy, after the application of hemodynamically ineffective doses of enalapril and losartan (5 mg/kg). A hamster dorsal skinfold model with a 4‐h tourniquet ischemia was used. In vitro, the effect of enalapril and losartan on polymorphonuclear cell (PMN) adherence, as well as adhesion molecule expression (ICAM‐1, VCAM‐1), on hypoxia‐ or IL‐1&bgr;‐stimulated endothelial cells (HUVEC) was assessed using a PMN‐adhesion assay and flow cytometry, respectively. Ischemia‐reperfusion responses revealed a biphasic pattern, comprised of an early phase (30 min) of acute cellular damage and microvascular perfusion failure, followed by a late increase (240 min) in leukocyte adherence in vivo. Enalapril significantly reduced early cellular damage, microvascular perfusion failure, and leukocyte adherence in response to ischemia‐reperfusion. Conversely, AT1 receptor inhibition with losartan proved to be ineffective at attenuating postischemic microcirculatory disorders (leukocyte‐endothelial interactions, microvascular perfusion failure) and aggravated cellular injury. In vitro, enalapril reduced PMN adherence and ICAM‐1 and VCAM‐1 expression, while losartan was ineffective in the same respect. Following ischemia‐reperfusion injury, ACE‐ versus AT1‐receptor inhibition induce differential effects concerning the extent and temporal association of cell injury and leukocyte‐endothelial interaction. The use of enalapril combines the beneficial effects of preventing cell and vascular injury immediately after reperfusion, with a delayed inhibition of the inflammatory response. Since the AT1‐receptor inhibitor losartan did not mimic effects obtained with ACE inhibition, it is conceivable that the responses in ischemia‐reperfusion are mediated by a non‐angiotensin II‐AT1 receptor‐dependent mechanism.