Androgen Withdrawal in Patients Reduces Prostate Cancer Hypoxia: Implications for Disease Progression and Radiation Response Michael Milosevic, 1,5 Peter Chung, 1,5 Chris Parker, 9 Robert Bristow, 1,4,5,8 Ants Toi, 2,6 Tony Panzarella, 3,7 Padraig Warde, 1,5 Charles Catton, 1,5 Cynthia Menard, 1,5 Andrew Bayley, 1,5 Mary Gospodarowicz, 1,5 and Richard Hill 4,8 1 Radiation Medicine Program, Departments of 2 Medical Imaging, 3 Clinical Study Coordination and Biostatistics, and 4 Applied Molecular Oncology, Princess Margaret Hospital and the Ontario Cancer Institute; Departments of 5 Radiation Oncology, 6 Medical Imaging, 7 Public Health Sciences, and 8 Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; and 9 the Academic Oncology Unit, Institute of Cancer Research and Royal Marsden Hospital, Sutton, United Kingdom Abstract Hypoxia is a feature of many human malignancies, and leads to aggressive clinical behavior and recurrence after treatment. Here, we show for the first time that androgen withdrawal reduces prostate cancer hypoxia in patients. Oxygen measure- ments were done in 248 patients with clinically localized prostate cancer prior to radiotherapy, and showed hypoxia of potential biological and clinical significance. In 22 of these patients, prostate oxygen levels were measured both before and after 30 to 145 days of the androgen antagonist bicalutamide. There was a significant reduction in tumor hypoxia with androgen withdrawal (P = 0.005). The median pO 2 increased from 6.4 to 15 mm Hg, and the hypoxic proportion decreased from 40% to 31%. However, the response was heterogeneous, with improvement in 12 patients, stable oxygen readings in 9 patients and worsening hypoxia in 1 patient. Among the responding patients, the median pO 2 increased from 4.9 to 33 mm Hg, and the hypoxic proportion decreased from 51% to 23%. There was no apparent relationship between the change in oxygenation and baseline prostatic volume, Tcategory, Gleason score, prostate-specific antigen levels, the duration of treat- ment with bicalutamide, or the change in prostate-specific antigen levels with bicalutamide. These results might, in part, explain the improved patient outcome that has been observed in clinical trials of radiotherapy and hormones, and suggest a role for novel therapeutic agents that block the molecular response to hypoxia in prostate cancer either alone or in combination with other established treatments. [Cancer Res 2007;67(13):6022–5] Introduction Prostate cancer is the most common malignancy among North American men. At diagnosis, most patients have tumors that are clinically confined to the prostate gland. Depending on comorbid- ities and individual preferences, they are candidates for potentially curative treatment with either radical prostatectomy or radiother- apy. Despite technical advances in both of these treatments, f25% of radically treated patients will develop progressive disease either locally in the pelvis or at remote sites, most commonly in bone (1). This underscores the importance of better understanding the biological factors that are responsible for malignant progression, the development of metastases, and the failure of currently avail- able treatments. Androgens play an important role in the growth and progression of prostate cancer. Androgen withdrawal through surgical or medical castration causes tumor regression in most patients. Several phase III studies have shown improved tumor control and patient survival when radiotherapy is combined with androgen withdrawal to treat prostate cancer (2), and combined treatment is widely used in clinical practice. Despite this, the biological mechanisms responsible for the favorable interaction between radiotherapy and androgen deprivation remain ill-defined. Hypoxia is a feature of many human malignancies. In general, patients with hypoxic primary tumors at diagnosis are at greater risk of developing progressive disease and dying regardless of whether initial treatment is with surgery or radiotherapy (3). These clinicalobservationsareconsistentwithhypoxia-mediatedchanges in DNA repair, genomic instability, and abnormal expression of genes that promote both malignant progression and metastasis formation (4). Faulty DNA repair is an important determinant of genetic instability and contributes to chromosomal rearrangement, oncogene activation, and tumor suppressor gene inactivation (5). Repair-deficient cells are more likely to acquire a mutator pheno- type characterized by greater biological and clinical aggressiveness. Indeed, preclinical data have shown that hypoxia could lead to the selection of aggressive cancer cells with decreased sensitivity to apoptotic and DNA repair pathways and increased genetic insta- bility, angiogenesis, proliferation, and metastatic capability (4, 5). We and others have previously reported that many prostate can- cersarehypoxic(6–8).Here,weshowforthefirsttimethatandrogen withdrawal reduces prostate cancerhypoxia in patients, and discuss the implications of this for prostate cancer development and prog- ression, metastasis formation, and response to radiotherapy. Materials and Methods A total of 248 patients with cT 1c –T 2c ,N 0 ,M 0 (UICC-TNM Classification, 6th Edition, 2002) prostate cancer participated in this prospective study of tumorhypoxiapriortotreatmentwithescalated-doseconformalorintensity- modulated radiotherapy. The characteristics of these patients are summa- rized in Table 1. The study was approved by the University Health Network Research Ethics Board, and informed consentwas obtained in all cases. Prostate cancer hypoxia was measured prior to any treatment using an ultrasound-guided transrectal needle-electrode technique, as previously described (7). Between 40 and 80 individual oxygen readings were obtained along two to four linear measurement tracks 1.5 to 2 cm in length through regions of the prostate gland likely to contain tumor based on information from previous diagnostic biopsies, digital rectal examination, and real-time Requests for reprints: Michael Milosevic, Radiation Medicine Program, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9. Phone: 416-946-2125; Fax: 416-946-6566; E-mail: mike.milosevic@rmp.uhn.on.ca. I2007 American Association for Cancer Research. doi:10.1158/0008-5472.CAN-07-0561 Cancer Res 2007; 67: (13). 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