Michael Höckel

Bio: Michael Höckel is an academic researcher from University of Mainz. The author has contributed to research in topics: Tumor hypoxia & Tumor Oxygenation. The author has an hindex of 15, co-authored 23 publications receiving 5668 citations. Previous affiliations of Michael Höckel include Leipzig University.

Association between Tumor Hypoxia and Malignant Progression in Advanced Cancer of the Uterine Cervix

Abstract: Experimental tumors contain a significant fraction of microregions that are chronically or transiently hypoxic. Experimental evidence showing that hypoxia (and subsequent reoxyenation) may have a profound impact on malignant progression and on responsiveness to therapy is growing. The clinical relevance of tumor oxygenation in human solid malignancies is under investigation. We have developed and validated a clinically applicable method for measurement of tumor oxygenation in locally advanced cancer of the uterine cervix using a computerized polarographic electrode system. Applying this procedure in patients with cervical cancers ≥3 cm in diameter, who gave informed consent, we have been studying the clinical relevance of tumor oxygenation prospectively since 1989. As of June 1995, 103 patients with advanced cancers of the uterine cervix [Federation Internationale des Gynaecologistes et Obstetristes (FIGO) stages Ib, bulky ( n = 13), IIa and IIb ( n = 51), IIIa and IIIb ( n = 34), and IVa and IVb ( n = 5)] had entered the study. Fifty % of the patients had carcinomas with median pO 2 readings hypoxic tumors. Tumor oxygenation was found to be independent of various patient demographics and also of pretreatment tumor characteristics, such as clinical tumor stage and size, histological type, and differentiation. However, histopathological examination of the surgical specimens following radical tumor resection in 47 patients showed that low-pO 2 tumors exhibited larger tumor extensions and more frequent (occult) parametrial spread, as well as lymph-vascular space involvement, compared to well-oxygenated tumors of similar clinical stage and size. Forty-two patients completing primary radiation therapy and 47 patients who underwent radical surgery were analyzed for treatment outcome after a median observation period of 28 months (range, 3–76 months). Patients with hypoxic tumors had significantly worse disease-free and overall survival probabilities compared to patients with nonhypoxic tumors. Cox regession analysis identified tumor oxygenation and FIGO stage as the most important independent prognostic factors. The poorer outcome of the patients with hypoxic tumors was mainly due to locoregional failures with and without distant metastases, irrespective of whether surgery or radiation was applied as primary treatment. Tumor oxygenation as measured with a standardized polarographic method proved to be a powerful new pretherapeutic prognostic parameter providing important information on malignant progression in terms of extracervical tumor spread and radioresistance in advanced cervical cancers.

Oxygenation of Human Tumors: Evaluation of Tissue Oxygen Distribution in Breast Cancers by Computerized O2 Tension Measurements

Abstract: Direct oxygen partial pressure (pO2) readings in breast cancers, in fibrocystic disease, and in the normal breast have been obtained using a novel technique which allows for the systematic evaluation of the oxygenation status as a function of pathological staging and histological grading. Measurements were performed in awake pre- and postmenopausal patients with well-defined arterial blood gas status. The measuring procedure encompasses a computerized electrode movement in the tissue which avoids significant compression artifacts and allows routine measurement in human tumors before, during, and after treatment. Using this reliable technique, pO2 measurements in the normal breast and in fibrocystic disease resulted in oxygenation patterns which were characteristic for normal, adequately supplied tissues. The median pO2 values were 65 and 67 mm Hg, respectively, with no pO2 readings below 12.5 mm Hg in the normal breast, and less than or equal to 5 mm Hg in fibrocystic disease, respectively. In contrast, in breast cancers the median pO2 value was 30 mm Hg (pooled data for pathological stages T1-T4). To date, 6 of 15 breast cancers exhibited pO2 values between zero and 2.5 mm Hg, i.e., tissue areas with less than half-maximum radiosensitivity. The oxygenation pattern in breast cancers and the occurrence of hypoxia and/or anoxia did not correlate with either the pathological stages and histological grades or with a series of clinically relevant parameters. No significant differences were found between pre- and postmenopausal tumors and between lobular and ductal carcinomas. Tumor-to-tumor variability in the oxygenation pattern was more pronounced than intra-tumor heterogeneity. pO2 variations within a tumor cannot be predicted, e.g., as a function of the measuring site (tumor center versus periphery).

Angiogenesis in cancer and other diseases

Abstract: Pathological angiogenesis is a hallmark of cancer and various ischaemic and inflammatory diseases Concentrated efforts in this area of research are leading to the discovery of a growing number of pro- and anti-angiogenic molecules, some of which are already in clinical trials The complex interactions among these molecules and how they affect vascular structure and function in different environments are now beginning to be elucidated This integrated understanding is leading to the development of a number of exciting and bold approaches to treat cancer and other diseases But owing to several unanswered questions, caution is needed

Tumor hypoxia: definitions and current clinical, biologic, and molecular aspects.

Abstract: Tissue hypoxia results from an inadequate supply of oxygen (O(2)) that compromises biologic functions. Evidence from experimental and clinical studies increasingly points to a fundamental role for hypoxia in solid tumors. Hypoxia in tumors is primarily a pathophysiologic consequence of structurally and functionally disturbed microcirculation and the deterioration of diffusion conditions. Tumor hypoxia appears to be strongly associated with tumor propagation, malignant progression, and resistance to therapy, and it has thus become a central issue in tumor physiology and cancer treatment. Biochemists and clinicians (as well as physiologists) define hypoxia differently; biochemists define it as O(2)-limited electron transport, and physiologists and clinicians define it as a state of reduced O(2) availability or decreased O(2) partial pressure that restricts or even abolishes functions of organs, tissues, or cells. Because malignant tumors no longer execute functions necessary for homeostasis (such as the production of adequate amounts of adenosine triphosphate), the physiology-based definitions of the term "hypoxia" are not necessarily valid for malignant tumors. Instead, alternative definitions based on clinical, biologic, and molecular effects that are observed at O(2) partial pressures below a critical level have to be applied.

Exploiting tumour hypoxia in cancer treatment.

Abstract: Solid tumours contain regions at very low oxygen concentrations (hypoxia), often surrounding areas of necrosis. The cells in these hypoxic regions are resistant to both radiotherapy and chemotherapy. However, the existence of hypoxia and necrosis also provides an opportunity for tumour-selective therapy, including prodrugs activated by hypoxia, hypoxia-specific gene therapy, targeting the hypoxia-inducible factor 1 transcription factor, and recombinant anaerobic bacteria. These strategies could turn what is now an impediment into a significant advantage for cancer therapy.

Regulation of transport pathways in tumor vessels: Role of tumor type and microenvironment

Abstract: Novel anti-neoplastic agents such as gene targeting vectors and encapsulated carriers are quite large (approximately 100–300 nm in diameter) An understanding of the functional size and physiological regulation of transvascular pathways is necessary to optimize delivery of these agents Here we analyze the functional limits of transvascular transport and its modulation by the microenvironment One human and five murine tumors including mammary and colorectal carcinomas, hepatoma, glioma, and sarcoma were implanted in the dorsal skin-fold chamber or cranial window, and the pore cutoff size, a functional measure of transvascular gap size, was determined The microenvironment was modulated: (i) spatially, by growing tumors in subcutaneous or cranial locations and (ii) temporally, by inducing vascular regression in hormone-dependent tumors Tumors grown subcutaneously exhibited a characteristic pore cutoff size ranging from 200 nm to 12 μm This pore cutoff size was reduced in tumors grown in the cranium or in regressing tumors after hormone withdrawal Vessels induced in basic fibroblast growth factor-containing gels had a pore cutoff size of 200 nm Albumin permeability was independent of pore cutoff size These results have three major implications for the delivery of therapeutic agents: (i) delivery may be less efficient in cranial tumors than in subcutaneous tumors, (ii) delivery may be reduced during tumor regression induced by hormonal ablation, and (iii) permeability to a molecule is independent of pore cutoff size as long as the diameter of the molecule is much less than the pore diameter

Overexpression of Hypoxia-inducible Factor 1α in Common Human Cancers and Their Metastases

Abstract: Neovascularization and increased glycolysis, two universal characteristics of solid tumors, represent adaptations to a hypoxic microenvironment that are correlated with tumor invasion, metastasis, and lethality. Hypoxia-inducible factor 1 (HIF-1) activates transcription of genes encoding glucose transporters, glycolytic enzymes, and vascular endothelial growth factor. HIF-1 transcriptional activity is determined by regulated expression of the HIF-1α subunit. In this study, HIF-1α expression was analyzed by immunohistochemistry in 179 tumor specimens. HIF-1α was overexpressed in 13 of 19 tumor types compared with the respective normal tissues, including colon, breast, gastric, lung, skin, ovarian, pancreatic, prostate, and renal carcinomas. HIF-1α expression was correlated with aberrant p53 accumulation and cell proliferation. Preneoplastic lesions in breast, colon, and prostate overexpressed HIF-1α, whereas benign tumors in breast and uterus did not. HIF-1α overexpression was detected in only 29% of primary breast cancers but in 69% of breast cancer metastases. In brain tumors, HIF-1α immunohistochemistry demarcated areas of angiogenesis. These results provide the first clinical data indicating that HIF-1α may play an important role in human cancer progression.