Kenneth A. Krohn

Quantifying regional hypoxia in human tumors with positron emission tomography of [18F]fluoromisonidazole: A pretherapy study of 37 patients

PURPOSE To assess pretreatment hypoxia in a variety of tumors using positron emission tomography (PET) after injection of the hypoxia-binding radiopharmaceutical [18F]fluoromisonidazole ([18F]FMISO). METHODS AND MATERIALS Tumor fractional hypoxic volume (FHV) was determined in 21 nonsmall cell lung cancer patients, 7 head and neck cancer patients, 4 prostate cancer patients, and 5 patients with other malignancies by quantitative PET imaging after injection of [18F]FMISO (0.1 mCi/kg). The FHV was defined as the proportion of pixels in the imaged tumor volume with a tissue:blood [18F] activity ratio > or = 1.4 at 120-160 min postinjection. A FHV > 0 was taken as evidence for tumor hypoxia. RESULTS Hypoxia was observed in 36 of 37 tumors studied with FMISO PET imaging; FHVs ranged from 0 to 94.7%. In nonsmall cell lung cancers (n = 21), the median FHV was 47.6% and the range, 1.3 to 94.7%. There was no correlation between tumor size and FHV. In the seven head and neck carcinomas, the median FHV was 8.8%, with a range from 0.2 to 18.9%. In the group of four prostate cancers, the median and range were 18.2% and 0 to 93.9%, while in a group of five tumors of different types the median FHV was 55.2% (range: 21.4 to 85.8%). CONCLUSIONS Hypoxia was present in 97% of the tumors studied and the extent of hypoxia varied markedly between tumors in the same site or of the same histology. Hypoxia also was distributed heterogeneously between regions within a single tumor. These results are consistent with O2 electrode measures with other types of human tumors. The intra- and intertumor variability indicate the importance of making oxygenation measures in individual tumors and the necessity to sample as much of the tumor volume as possible.

Hypoxia: importance in tumor biology, noninvasive measurement by imaging, and value of its measurement in the management of cancer therapy.

PURPOSE The Cancer Imaging Program of the National Cancer Institute convened a workshop to assess the current status of hypoxia imaging, to assess what is known about the biology of hypoxia as it relates to cancer and cancer therapy, and to define clinical scenarios in which in vivo hypoxia imaging could prove valuable. RESULTS Hypoxia, or low oxygenation, has emerged as an important factor in tumor biology and response to cancer treatment. It has been correlated with angiogenesis, tumor aggressiveness, local recurrence, and metastasis, and it appears to be a prognostic factor for several cancers, including those of the cervix, head and neck, prostate, pancreas, and brain. The relationship between tumor oxygenation and response to radiation therapy has been well established, but hypoxia also affects and is affected by some chemotherapeutic agents. Although hypoxia is an important aspect of tumor physiology and response to treatment, the lack of simple and efficient methods to measure and image oxygenation hampers further understanding and limits their prognostic usefulness. There is no gold standard for measuring hypoxia; Eppendorf measurement of pO(2) has been used, but this method is invasive. Recent studies have focused on molecular markers of hypoxia, such as hypoxia inducible factor 1 (HIF-1) and carbonic anhydrase isozyme IX (CA-IX), and on developing noninvasive imaging techniques. CONCLUSIONS This workshop yielded recommendations on using hypoxia measurement to identify patients who would respond best to radiation therapy, which would improve treatment planning. This represents a narrow focus, as hypoxia measurement might also prove useful in drug development and in increasing our understanding of tumor biology.

Molecular Imaging of Hypoxia

Hypoxia, a condition of insufficient O2 to support metabolism, occurs when the vascular supply is interrupted, as in stroke or myocardial infarction, or when a tumor outgrows its vascular supply. When otherwise healthy tissues lose their O2 supply acutely, the cells usually die, whereas when cells gradually become hypoxic, they adapt by up-regulating the production of numerous proteins that promote their survival. These proteins slow the rate of growth, switch the mitochondria to glycolysis, stimulate growth of new vasculature, inhibit apoptosis, and promote metastatic spread. The consequence of these changes is that patients with hypoxic tumors invariably experience poor outcome to treatment. This has led the molecular imaging community to develop assays for hypoxia in patients, including regional measurements from O2 electrodes placed under CT guidance, several nuclear medicine approaches with imaging agents that accumulate with an inverse relationship to O2, MRI methods that measure either oxygenation directly or lactate production as a consequence of hypoxia, and optical methods with NIR and bioluminescence. The advantages and disadvantages of these approaches are reviewed, along with the individual strategies for validating different imaging methods. Ultimately the proof of value is in the clinical performance to predict outcome, select an appropriate cohort of patients to benefit from a hypoxia-directed treatment, or plan radiation fields that result in better local control. Hypoxia imaging in support of molecular medicine has become an important success story over the last decade and provides a model and some important lessons for development of new molecular imaging probes or techniques.

l Brief Communication QUANTIFYING REGIONAL HYPOXIA IN HUMAN TUMQRS WITH POSITRON EMISSION TOMOGRAPHY OF ('*F)FLUUROMISONIDAZOLE: A PRETHERAPY STUDY OF 37 PATIENTS

PURPOSE To assess pretreatment hypoxia in a variety of tumors using positron emission tomography (PET) after injection of the hypoxia-binding radiopharmaceutical [18F]fluoromisonidazole ([18F]FMISO). METHODS AND MATERIALS Tumor fractional hypoxic volume (FHV) was determined in 21 nonsmall cell lung cancer patients, 7 head and neck cancer patients, 4 prostate cancer patients, and 5 patients with other malignancies by quantitative PET imaging after injection of [18F]FMISO (0.1 mCi/kg). The FHV was defined as the proportion of pixels in the imaged tumor volume with a tissue:blood [18F] activity ratio > or = 1.4 at 120-160 min postinjection. A FHV > 0 was taken as evidence for tumor hypoxia. RESULTS Hypoxia was observed in 36 of 37 tumors studied with FMISO PET imaging; FHVs ranged from 0 to 94.7%. In nonsmall cell lung cancers (n = 21), the median FHV was 47.6% and the range, 1.3 to 94.7%. There was no correlation between tumor size and FHV. In the seven head and neck carcinomas, the median FHV was 8.8%, with a range from 0.2 to 18.9%. In the group of four prostate cancers, the median and range were 18.2% and 0 to 93.9%, while in a group of five tumors of different types the median FHV was 55.2% (range: 21.4 to 85.8%). CONCLUSIONS Hypoxia was present in 97% of the tumors studied and the extent of hypoxia varied markedly between tumors in the same site or of the same histology. Hypoxia also was distributed heterogeneously between regions within a single tumor. These results are consistent with O2 electrode measures with other types of human tumors. The intra- and intertumor variability indicate the importance of making oxygenation measures in individual tumors and the necessity to sample as much of the tumor volume as possible.

Hypoxia and glucose metabolism in malignant tumors: evaluation by [18F]fluoromisonidazole and [18F]fluorodeoxyglucose positron emission tomography imaging.

Purpose: The aim of this study is to compare glucose metabolism and hypoxia in four different tumor types using positron emission tomography (PET). 18F-labeled fluorodeoxyglucose (FDG) evaluates energy metabolism, whereas the uptake of 18F-labeled fluoromisonidazole (FMISO) is proportional to tissue hypoxia. Although acute hypoxia results in accelerated glycolysis, cellular metabolism is slowed in chronic hypoxia, prompting us to look for discordance between FMISO and FDG uptake. Experimental Design: Forty-nine patients (26 with head and neck cancer, 11 with soft tissue sarcoma, 7 with breast cancer, and 5 with glioblastoma multiforme) who had both FMISO and FDG PET scans as part of research protocols through February 2003 were included in this study. The maximum standardized uptake value was used to depict FDG uptake, and hypoxic volume and maximum tissue:blood ratio were used to quantify hypoxia. Pixel-by-pixel correlation of radiotracer uptake was performed on coregistered images for each corresponding tumor plane. Results: Hypoxia was detected in all four patient groups. The mean correlation coefficients between FMISO and FDG uptake were 0.62 for head and neck cancer, 0.47 for breast cancer, 0.38 for glioblastoma multiforme, and 0.32 for soft tissue sarcoma. The correlation between the overall tumor maximum standardized uptake value for FDG and hypoxic volume was small (Spearman r = 0.24), with highly significant differences among the different tumor types (P < 0.005). Conclusions: Hypoxia is a general factor affecting glucose metabolism; however, some hypoxic tumors can have modest glucose metabolism, whereas some highly metabolic tumors are not hypoxic, showing discordance in tracer uptake that can be tumor type specific.

Treatment of refractory non-Hodgkin's lymphoma with radiolabeled MB-1 (anti-CD37) antibody.

The biodistribution, toxicity, and therapeutic potential of anti-CD37 monoclonal antibody (MoAb) MB-1 labeled with iodine 131 (131I) was evaluated in ten patients with advanced-, low- or intermediate-grade non-Hodgkins lymphomas who failed conventional treatment. Sequential dosimetric studies were performed with escalating amounts of antibody MB-1 (0.5, 2.5, 10 mg/kg) trace-labeled with 5 to 10 mCi 131I. Serial tumor biopsies and gamma camera imaging showed that the 10 mg/kg MoAb dose yielded the best MoAb biodistribution in the ten patients studied. Biodistribution studies in the five patients with splenomegaly and tumor burdens greater than 1 kg indicated that not all tumor sites would receive more radiation than normal organs, and these patients were therefore not treated with high-dose radioimmunotherapy. The other five patients did not have splenomegaly and had tumor burdens less than 0.5 kg; all five patients in this group showed preferential localization and retention of MoAb at tumor sites. Four of these patients have been treated with 131I (232 to 608 mCi) conjugated to anti-CD37 MoAb MB-1, delivering 850 to 4,260 Gy to tumor sites. Each of these four patients attained a complete tumor remission (lasting 4, 6, 11+, and 8+ months). A fifth patient, whose tumor did not express the CD37 antigen, was treated with 131I-labeled anti-CD20 MoAb 1F5 and achieved a partial response. Myelosuppression occurred 3 to 5 weeks after treatment in all cases, but there were no other significant acute toxicities. Normal B cells were transiently depleted from the bloodstream, but immunoglobulin (Ig) levels were not affected, and no serious infections occurred. Two patients required reinfusion of previously stored autologous, purged bone marrow. Two patients developed asymptomatic hypothyroidism 1 year after therapy. The tolerable toxicity and encouraging efficacy warrant further dose escalation in this phase I trial.

Evaluation of oxygenation status during fractionated radiotherapy in human nonsmall cell lung cancers using [F-18]fluoromisonidazole positron emission tomography

PURPOSE Recent clinical investigations have shown a strong correlation between pretreatment tumor hypoxia and poor response to radiotherapy. These observations raise questions about standard assumptions of tumor reoxygenation during radiotherapy, which has been poorly studied in human cancers. Positron emission tomography (PET) imaging of [F-18]fluoromisonidazole (FMISO) uptake allows noninvasive assessment of tumor hypoxia, and is amenable for repeated studies during fractionated radiotherapy to systematically evaluate changes in tumor oxygenation. METHODS AND MATERIALS Seven patients with locally advanced nonsmall cell lung cancers underwent sequential [F-18]FMISO PET imaging while receiving primary radiotherapy. Computed tomograms were used to calculate tumor volumes, define tumor extent for PET image analysis, and assist in PET image registration between serial studies. Fractional hypoxic volume (FHV) was calculated for each study as the percentage of pixels within the analyzed imaged tumor volume with a tumor:blood [F-18]FMISO ratio > or = 1.4 by 120 min after injection. Serial FHVs were compared for each patient. RESULTS Pretreatment FHVs ranged from 20-84% (median 58%). Subsequent FHVs varied from 8-79% (median 29%) at midtreatment, and ranged from 3-65% (median 22%) by the end of radiotherapy. One patient had essentially no detectable residual tumor hypoxia by the end of radiation, while two others showed no apparent decrease in serial FHVs. There was no correlation between tumor size and pretreatment FHV. CONCLUSIONS Although there is a general tendency toward improved oxygenation in human tumors during fractionated radiotherapy, these changes are unpredictable and may be insufficient in extent and timing to overcome the negative effects of existing pretreatment hypoxia. Selection of patients for clinical trials addressing radioresistant hypoxic cancers can be appropriately achieved through single pretreatment evaluations of tumor hypoxia.

Tumor Hypoxia Imaging with [F-18] Fluoromisonidazole Positron Emission Tomography in Head and Neck Cancer

Purpose: Advanced head and neck cancer shows hypoxia that results in biological changes to make the tumor cells more aggressive and less responsive to treatment resulting in poor survival. [F-18] fluoromisonidazole (FMISO) positron emission tomography (PET) has the ability to noninvasively quantify regional hypoxia. We investigated the prognostic effect of pretherapy FMISO-PET on survival in head and neck cancer. Experimental Design: Seventy-three patients with head and neck cancer had pretherapy FMISO-PET and 53 also had fluorodeoxyglucose (FDG) PET under a research protocol from April 1994 to April 2004. Results: Significant hypoxia was identified in 58 patients (79%). The mean FMISO tumor/bloodmax (T/Bmax) was 1.6 and the mean hypoxic volume (HV) was 40.2 mL. There were 28 deaths in the follow-up period. Mean FDG standard uptake value (SUV)max was 10.8. The median time for follow-up was 72 weeks. In a univariate analysis, T/Bmax (P = 0.002), HV (P = 0.04), and the presence of nodes (P = 0.01) were strong independent predictors. In a multivariate analysis, including FDG SUVmax, no variable was predictive at P < 0.05. When FDG SUVmax was removed from the model (resulting in n = 73 with 28 events), nodal status and T/Bmax (or HV) were both highly predictive (P = 0.02, 0.006 for node and T/Bmax, respectively; P = 0.02 and 0.001 for node and HV, respectively). Conclusions: Pretherapy FMISO uptake shows a strong trend to be an independent prognostic measure in head and neck cancer.

Quantitative Fluoroestradiol Positron Emission Tomography Imaging Predicts Response to Endocrine Treatment in Breast Cancer

PURPOSE In breast cancer, [(18)F]fluoroestradiol (FES) positron emission tomography (PET) correlates with estrogen receptors (ER) expression and predicts response to tamoxifen. We tested the ability of FES-PET imaging to predict response to salvage hormonal treatment in heavily pretreated metastatic breast cancer patients, predominantly treated with aromatase inhibitors. PATIENTS AND METHODS Initial FES uptake measurements in 47 patients with ER-positive tumors were correlated with subsequent tumor response to 6 months of hormonal treatment. Most patients had bone dominant disease and prior tamoxifen exposure. Response was compared to initial FES-PET uptake, measured qualitatively and quantitatively using standardized uptake value (SUV) and estradiol-binding flux. RESULTS Eleven of 47 patients (23%) had an objective response. While no patients with absent FES uptake had a response to treatment, the association between qualitative FES-PET results and response was not significant (P = .14). However, quantitative FES uptake and response were significantly associated; zero of 15 patients with initial SUV less than 1.5 responded to hormonal therapy, compared with 11 of 32 patients (34%) with SUV higher than 1.5 (P < .01). In the subset of patients whose tumors did not overexpress HER2/neu, 11 of 24 patients (46%) with SUV higher than 1.5 responded. CONCLUSION Quantitative FES-PET can predict response to hormonal therapy and may help guide treatment selection. Treatment selection using quantitative FES-PET in our patient series would have increased the rate of response from 23% to 34% overall, and from 29% to 46% in the subset of patients lacking HER2/neu overexpression. A multi-institutional collaborative trial would permit definitive assessment of the value of FES-PET for therapeutic decision making.

Imaging oxygenation of human tumours

Tumour hypoxia represents a significant challenge to the curability of human tumours leading to treatment resistance and enhanced tumour progression. Tumour hypoxia can be detected by non-invasive and invasive techniques but the inter-relationships between these remains largely undefined. 18F-MISO and Cu-ATSM-PET, and BOLD-MRI are the lead contenders for human application based on their non-invasive nature, ease of use and robustness, measurement of hypoxia status, validity, ability to demonstrate heterogeneity and general availability, these techniques are the primary focus of this review. We discuss where developments are required for hypoxia imaging to become clinically useful and explore potential new uses for hypoxia imaging techniques including biological conformal radiotherapy.