Abstract P4-01-03: HDACi (vorinostat) in metastatic breast cancer to restore sensitivity to ER-directed (AI) therapy: A phase II clinical trial with FES imaging correlates

Background: Histone deacetylase inhibitors (HDACi) have shown pre-clinical promise in estrogen receptor(ER)-modulation and restoring sensitivity to endocrine manipulation, suggesting potential clinical benefit (Sabnis 2011) (Huang 2000) in ER+ breast cancer. Vorinostat is an FDA-approved HDACi for CTCL, and could have a beneficial role in restoring ER-signaling in endocrine-resistant tumors (Munster 2011) (Yardley 2011). [F-18]fluoroestradiol (FES) PET imaging may be used to monitor regional tumor ER expression in patients with breast cancer (Linden 2011).

Methods: Patients with metastatic breast cancer with prior clinical benefit from endocrine manipulation who progressed on an AI therapy are eligible for this ongoing trial. In part A, patients were given vorinostat for 2 weeks, then resumed AI for 6 W. In part B (reflecting results of prior HDACi trials) patients are given vorinostat 400mg po daily 5/7 days 3/4 weeks while AI is given continuously. Paired FES and FDG PET are performed at baseline, week 2 and 8; clinical/radiologic assessment of disease is also performed at week 8. Patients with clinical benefit (response or stable disease) may continue on treatment until progressive disease or study withdrawal. Lesion-level analysis of the association between baseline FES uptake (logged) and FES/FDG ratio used generalized estimating equations (GEE) with small-sample adjustments to standard errors.

Results: 12/ 20 planned patients have accrued, and the treatment is well tolerated. Enrolled women were postmenopausal, the majority with primary infiltrating ductal tumors, bone/soft tissue dominant with longstanding metastatic disease, exposed to multiple endocrine and chemotherapy regimens. Five patients have had clinical benefit (2/4 on part B with greater HDACi exposure). One patient withdrew from the study due to toxicity. FES and FDG uptake was analyzed in 42 lesions in 11 patients. Average FES uptake was 2.0 (SULmean) for patients with clinical benefit, and 1.2 in patients with progressive disease by 8 weeks (p = 0.09). FES/FDG ratio at baseline was also associated with response (p = 0.04).

Conclusions: HDACi therapy is promising in relapsed ER+ breast cancer. Imaging of metabolic pathways in parallel with clinical trials may accelerate understanding of the underlying tumor biology and refine treatment selection.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-03.

Abstract P4-01-02: The role of FLT PET early assessment of response to endocrine therapy for early stage breast cancer

Background: In estrogen receptor positive (ER+) tumors, a low proliferative index (Ki-67) two weeks into endocrine therapy predicts response. FLT PET non-invasively measures tumor proliferation in vivo. The pre-operative window is an opportunity to assess impact of systemic therapies. We tested associations between FLT PET qualitative and quantitative measures and Ki-67 following two weeks of aromatase inhibitor (AI) therapy.

Methods: Women with clinical stage I-II ER+ HER2– breast cancer underwent “run-in” of AI monotherapy prior to definitive surgery. Premenopausal women were given GNRH agonist treatment 2 W prior to AI therapy. FLT PET was performed before AI therapy, and 1-7 days before surgery. Ki-67 was measured in baseline core biopsy and surgical specimens.

Results: Fourteen patients (8 postmenopausal, 6 premenopausal) have been enrolled. All have undergone baseline FLT PET imaging; 11 have completed imaging and surgery, including one premenopausal patient with no residual invasive carcinoma following 26 days of AI therapy. The majority harbored ductal carcinomas (n = 9, 5 with lobular histology) with the majority histologic grade ≥ 2 (n = 11). The median number of days exposed to AI was 19 (range, 9-42). Baseline SUVmax ranged from 1.2 to 3.9 (median 2.2), and post run-in SUV (6-64 days later) ranged from 1.2 to 2.8 (median 1.8). Baseline Ki-67 ranged from 6-26.2, median 11.6; surgical Ki-67 post AI therapy ranged from 0- 20.3 median 3.7, with seven below 5%. SUV and flux declined in most patients, as did Ki-67.

Quantitative FLT flux correlated with tumor response assessed by proliferative index (Ki-67) before the “run-in” period, with a stronger correlation at surgery, Pearson correlation coefficients = 0.41 and 0.82, respectively. FLT SUV and qualitative changes were not strongly associated with Ki-67.

Conclusions: Both pre and postmenopausal women with early stage breast cancer showed imaging and tissue response to endocrine therapy. Quantitative, but not qualitative FLT is a promising tool to assess tumor proliferation and response to therapy. Accrual is ongoing and updated results will be reported.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-01-02.

Abstract B147: Tumor response imaging with [F-18] fluorothymidine (FLT)

Background: Current cancer treatments have different mechanisms and variable responses in most histologic groups. The ability to determine treatment response at the molecular level by measuring tumor thymidine kinase 1 activity is being evaluated with FLT PET in groups of patients with different tumor histology.

Methods: Under FDA IND approved protocols, patients treated on standard clinical and clinical trial protocols for glioblastoma, carcinoma brain metastases, breast cancer, and AML underwent quantitative PET imaging with FLT at baseline, mid-therapy, and post therapy. Dynamic acquisitions of the sites of known tumor were acquired for 60 minutes, followed by a whole-body static image survey. All images were reconstructed with CT attenuation correction. Regions of interest for the tumor, liver, and surrounding tissues were analyzed for uptake at each data time. Regional tissue FLT uptake was described as the tissue standard uptake variable (SUV), and FLT transport (K1) and flux using a compartmental model analysis. The tumor K1 values were generated to quantify FLT delivery to tumor. Comparisons were made between FLT-PET obtained at sequential times in individual patients and with clinical response.

Results: At this time, 19 patients with primary brain tumors, 3 patients with brain metastases, 9 breast cancer patients, and 7 AML patients have been enrolled; at least one post-therapy image has been completed in all but 2 patients. The results have been analyzed semi-quantitatively as SUV and quantitatively by compartmental modeling to determine K1 and flux values for tumor baseline and post therapy comparisons. In most tumors, uptake by either SUV or flux declined in response to treatment but trends in tumor SUV values were not consistent with FLT flux values. In several cases, the FLT K1 and flux values were divergent, emphasizing the requirement to account for FLT delivery changes in observed tumor activity in response to therapy. This effect was most prominent in brain tumors and AML patients. Tumor blood flow/delivery is likely an independent response parameter that can be estimated from analysis of dynamic FLT PET. The poster will show evaluation of the predictive ability of baseline FLT studies as well as the role of pre/post comparisons.

Conclusions: FLT PET imaging shows increased tumor uptake across several histologic types. This uptake decreases significantly with therapy, however the flow/delivery parameters and flux values from imaging are important uptake parameters to consider individually to understand changes in response to therapy.

Supported by NIH/NCI P01 CA042045-23 and S10 RR017229.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B147.

Citation Format: Janet F. Eary, Jeanne M. Link, Mark Muzi, Finbarr O'Sullivan, Jason K. Rockhill, James R. Fink, Hannah M. Linden, Kenneth A. Krohn. Tumor response imaging with [F-18] fluorothymidine (FLT). [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B147.

Abstract B149: Quantitative FMISO imaging to assess regional tumor hypoxia as a predictor of response to therapy

Hypoxia is associated with resistance to RT and chemotherapy in malignant tumors, where the burden of hypoxic tumor present before as well as after RT influences treatment outcome. Due to the low retention in normal oxygenated tissue, FMISO is an effective quantitative imaging agent for tumor hypoxia. Because FMISO has a partition coefficient near one, the concentrations in oxygenated tissue and blood rapidly equilibrate and are essentially identical. Normalizing the FMISO uptake data to blood activity, has permitted the generation of a threshold value, above which indicates tissue hypoxia. Through our earlier work using FMISO in tumor cells in culture, animal tumor models and human patient studies, we have determined empirically that blood-normalized tissue uptake (T/B) above a threshold can reliably be used to indicate tissue hypoxia and predict outcome [reviewed in Krohn et al. J Nucl Med 49(suppl 2):129S-148S, 2008]. Over the time course of FMISO uptake after injection, vascularized normoxic tissues tend to equilibrate with blood activity and the ratio of tissue-to-blood tends toward a mean of slightly less than 1. In the collection of FMISO regional tissue activity from normoxic tissue types (muscle, cerebellum, breast, lung; n > 400), the T/B values were consistently (> 90%) less than 1. In the examination of various hypoxic thresholds from normoxic brain tissue, a value of 1.1 results in 10% hypoxia, which is unrealistic for normal functioning brain tissue; a value of 1.2 results in ∼2.5% hypoxia and 0% for T/B=1.3. Thus a FMISO T/B ratio threshold of 1.2 adequately characterizes normoxic tissue; a FMISO T/B value >1.2 indicates hypoxia. Applying a hypoxic threshold T/B value for FMISO permits the determination of hypoxic volume (HV, mL) of a tissue region that can be determined as the volume of pixels within the tissue VOI above the hypoxic threshold. This simple static image analysis is one of the strengths of FMISO-PET; it captures both the intensity and spatial distribution of tumor hypoxia. In this imaging procedure, a static scan of 20 min duration is acquired 2 hrs after tracer injection during which three venous blood samples are acquired. The quantitative parameters from FMISO imaging that describe tissue hypoxia are the maximum value (T/Bmax) determined from the pixel within the tumor that has the highest uptake, and HV. HV depicts the extent of tumor that has crossed the threshold for hypoxia and T/Bmax depicts the severity of the hypoxia. In general HV and T/Bmax are correlated within an individual patient. Quantitative FMISO imaging can be used to select patients with hypoxic tumors and to identify regions of hypoxia that might be subjected to more intense therapy. Kaplan-Meier survival analysis and multivariate Cox regressions were used to show that T/Bmax or HV are independent predictors of TTP and survival, where progression was defined by clinical criteria. Serial FMISO studies can also be used to follow the reoxygenation response after radiation or chemotherapies such as anti-VEGF treatments.

Supported by NIH Grant P01 CA042045-23.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B149.

Citation Format: Mark Muzi, Janet O'Sullivan, Janet F. Eary, Kenneth A. Krohn. Quantitative FMISO imaging to assess regional tumor hypoxia as a predictor of response to therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B149.

Quantifying the impact of antiangiogenic therapy on hypoxia and implications for radiation therapy in glioblastoma multiforme with a biomathematical model

e13028

Background: Glioblastoma multiforme (GBM) is the most aggressive form of primary brain tumor. As angiogenesis is a major hallmark of GBM, it can be inferred that hypoxia plays a prominent role in the progression of the disease. However, due to difficulty in assessing hypoxia, the development and evolution of hypoxia has not been well studied for GBM. 18F-Fluoromisonidazole (FMISO) PET indirectly measures hypoxia. It is known that hypoxia reduces the efficacy of radiation therapy, and one current strategy being explored is to combine anti-angiogenic therapy and radiation therapy. However, it is unclear whether anti-angiogenic therapy is ultimately reducing or increasing hypoxia nor is it clear how long the effects last. Methods: We have developed a spatio-temporal biomathematical model for glioma proliferation and invasion that incorporates the angiogenic cascade. In this context, we can simulate the action of anti-angiogenic treatment, such as bevacizumab, by modifying the availability of angiogenic factors. By applying a pharmacokinetic model for the uptake of FMISO to the simulation results, we can generate the corresponding FMISO-PET images during and after anti-angiogenic therapy to compare with what would be seen in the clinic. Results: Simulation results for a wide range of tumor kinetics demonstrated that hypoxia in general decreased during anti-angiogenic therapy. However, the rates at which it decreased and the time for the hypoxia to return to pre-treatment levels were not uniform. Conclusions: Dynamic understanding of anti-angiogenic therapy effects on vascular normalization and hypoxia suggest that optimal timing of radiation therapy and anti-angiogenic therapies would vary by patient. This biomathematical model can be tuned to individual patients’ tumors and provide similar information as a FMISO-PET image and also give insight into the dynamics of the hypoxia over time. Such insight could be invaluable to patient-specific treatment planning for combining radiation with antiangiogenics.

A robust automated measure of average antibody staining in immunohistochemistry images

Identifying and scoring cancer markers plays a key role in oncology, helping to characterize the tumor and predict the clinical course of the disease. The current method for scoring immunohistochemistry (IHC) slides is labor intensive and has inherent issues of quantitation. Although multiple attempts have been made to automate IHC scoring in the past decade, a major limitation in these efforts has been the setting of the threshold for positive staining. In this report, we propose the use of an averaged threshold measure (ATM) score that allows for automatic threshold setting. The ATM is a single multiplicative measure that includes both the proportion and intensity scores. It can be readily automated to allow for large-scale processing, and it is applicable in situations in which individual cells are hard to distinguish. The ATM scoring method was validated by applying it to simulated images, to a sequence of images from the same tumor, and to tumors from different patient biopsies that showed a broad range of staining patterns. Comparison between the ATM score and manual scoring by an expert pathologist showed that both methods resulted in essentially identical scores when applied to these patient biopsies. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Abstract P6-04-03: Changes in breast tumor metabolism and estradiol binding as measured by FES PET in patients treated with the histone deacetylace inhibitor vorinostat and aromatase inhibitor therapy

Background: Some estrogen receptor-positive (ER+) metastatic breast cancers are bone and soft tissue dominant, indolent, and controlled by endocrine therapy. However, these tumors eventually become refractory to endocrine therapy and need a mechanism to reset the “estrogen-dependence” to allow continued benefit upon progression. Histone deacetylase inhibitors (HDACi) act as modulators of gene expression that are promising therapeutic agents for this group of tumors (Huang 2000, Sabnis 2011). Preclinical and clinical data demonstrate in ER-poor tumors and cell lines ER up-regulation and consequently enhanced lethality to endocrine agents. The optimal dose and schedule are not known, but two promising phase II studies show benefit in a continuous schedule (Yardley 2011, Munster 2011). FES PET is a promising imaging agent used as a biomarker to determine which patients will benefit from endocrine therapy, and to monitor estradiol binding during therapy (Mortimer 2001, Linden 2011).

Methods: Patients with ER+ HER2− metastatic breast cancer with prior aromatase inhibitor (AI) exposure and clinical benefit of endocrine therapy were eligible for a phase II study of HDACi therapy to restore sensitivity to AI therapy. Following baseline FDG PET, FES PET and standard imaging (CT, MRI, ultrasound and/or bone scan as indicated by tumor location), patients received 2 weeks of vorinostat therapy (400 mg po daily). FES PET was performed at 2 weeks while on HDACi therapy. Patients then received 6 weeks of AI monotherapy. FDG PET, FES PET and response assessment were performed at 8 weeks. Patients with clinical benefit (stable disease or response) continued on the regimen, 2 weeks of vorinostat followed by 6 weeks of AI.

Results: To date, 8 patients have been enrolled of whom 6 have completed the first 8 weeks of treatment and all correlative imaging studies. FES biomarker imaging results are mixed, with some patients showing an increase in tumor estradiol concentrating ability by FES PET on HDACi therapy, and decline in metabolic activity by FDG. Two patients continue on treatment with clinical benefit. Results will be updated as accrual continues.

Conclusions: Changes in estradiol binding are measured by serial FES PET in patients on HDACi therapy support preclinical concept of HDACi modulation of ER expression in metastatic breast cancer. Molecular imaging is a promising tool to monitor Estradiol binding pharmacodynamics, and Vorinostat HDACi therapy is a promising novel approach to allow patients to avoid toxicities of traditional chemotherapy once their tumor has progressed on endocrine therapy.

Funding: P01, MKA, Merck

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-03.

Levels of human equilibrative nucleoside transporter-1 are higher in proliferating regions of A549 tumor cells grown as tumor xenografts in vivo

3'-Fluoro-3'-deoxythymidine (FLT) has been proposed for positron emission tomography (PET)-based identification of tumor chemosensitivity that is mediated by the human equilibrative nucleoside transporter-1 (ENT1). ENT1 facilitates transport of FLT into cells and elevated levels of FLT are associated with both larger FLT-PET signals and increased response to nucleoside-based chemotherapies. FLT-PET is also used as a measure of tumor proliferation. The present study examined the extent to which ENT1 levels vary in a proliferation-dependent manner in tumor cells in vivo.

METHODS

The human adenocarcinoma cell line A549 was used to establish tumor xenografts in nude mice. FLT uptake was measured in vivo using PET, and further examined ex vivo using autoradiography. FLT uptake patterns were compared to immunohistochemical (IHC) analysis of ENT1 and the proliferation markers Ki67 and BrdU.

RESULTS

Regional differences in FLT uptake matched differences in IHC proliferation markers. All cells stained for ENT1, but the staining intensity was twice as high for Ki67(+) cells than for Ki67(-) cells.

CONCLUSIONS

Under in vivo conditions, proliferating regions of tumors show increased FLT uptake and higher ENT1 levels than nonproliferating tumor regions.

The effects of 5-fluoruracil treatment on 3'-fluoro-3'-deoxythymidine (FLT) transport and metabolism in proliferating and non-proliferating cultures of human tumor cells

3'-Fluoro-3'-deoxythymidine (FLT) positron emission tomography (PET) has been proposed for imaging thymidylate synthase (TS) inhibition. Agents that target TS and shut down de novo synthesis of thymidine monophosphate increase the uptake and retention of FLT in vitro and in vivo because of a compensating increase in the salvage pathway. Increases in both thymidine kinase-1 (TK1) and the equilibrative nucleoside transporter hENT1 have been reported to underlie this effect. We examined whether the effects of one TS inhibitor, 5-fluorouracil (5FU), on FLT uptake require proliferating cells and whether the effects are limited to increasing TK1 activity.

METHODS

The effects of 5FU on FLT transport and metabolism, TK1 activity, and cell cycle progression were evaluated in the human tumor cell line, A549, maintained as either a proliferating or non-proliferating culture.

RESULTS

There were dose-dependent increases in FLT uptake that peaked after a 10 μM 5FU exposure and then declined to baseline levels or below at higher doses in both proliferating and non-proliferating cultures. The dose-dependence for FLT uptake was mirrored by changes in TK1 activity. S phase fraction did not correlate with FLT uptake in proliferating cultures. Chemical inhibition of hENT1 reduced overall levels of FLT uptake but did not affect the low dose increase in FLT uptake.

CONCLUSIONS

5FU only affects FLT uptake in proliferating A549 cells and increases in FLT uptake are directly related to increased TK1 activity. Our studies did not support a role for hENT1 in the increased uptake of FLT after exposure to 5FU. Our studies with A549 cells support the suggestion that FLT-PET could provide a measure of TS inhibition in vivo.

Abstract SY42-02: Novel PET imaging in the clinic: Selecting patient cohorts and measuring early response

Molecular imaging with PET is most commonly associated with tumor detection and staging, currently with [F-18]-fluorodeoxyglucose (FDG-PET) to measure energy metabolism. However other imaging agents can be used to measure important characteristics of tumors that have the potential to guide in therapy selection or provide an early indication of response to therapy. Even though there are enthusiastic predictions of the role that “omics” biomarkers will play in personalized medicine, imaging biomarkers have some practical advantages over tissue and serum biomarkers. Imaging characterizes the entire tumor burden in the context of its environment and it can be repeated frequently. Several new PET agents are becoming widely available to probe important aspects of the tumor phenotype. The UW NCI-sponsored program project is developing PET to image tumor cancer biology with new agents that examine the tumor phenotype and how it changes in response to therapy.

There are many biological factors that can influence response of an individual patient to cancer therapy. Evaluation of these factors provides the questions and hypotheses posed in the UW PPG. The group focuses on investigations of reasons for poor tumor response to treatment. Hypoxia, cellular proliferation, low abundance of therapeutic targets (e.g. estrogen receptors) and acquired multidrug resistance (MDR/P-gp) are some of the imaging targets. These tumor variables can be quantified by PET imaging with [F-18]-fluoromisonidazole, [F-18]-3′-fluoro-3′-deoxythymidine, [F-18]-16α-fluoroestradiol and [C-11]-verapamil, respectively. Because hypoxia is a common characteristic of tumors but it is heterogeneous within a tumor mass and differs between tumor sites in a patient, imaging has an important role in assessing regional tumor tissue oxygenation. [F-18]-Fluoromisonidazole (FMISO) developed by our group is a PET hypoxia-imaging probe that accumulates at low PO2. Imaging results with this agent have demonstrated tumor hypoxic volume is an independent predictor of overall survival in patients with head and neck cancer, soft tissue sarcoma and primary brain tumors.

PET can also be used to image the response mechanism of a tumor to therapy. Current therapies are cytotoxic or cytostatic, with some combinations that are overlapping or aimed at a particular phosphokinase pathway. Uncontrolled tumor growth results from dysregulation of cellular proliferation and/or deficiencies in programmed cell death. FDG has been advocated for monitoring this net process but there are many contributors to energy metabolism in tumors, thus reducing the specificity of FDG-PET for evaluating tumor response. Thymidine and its analogs can be used to image the salvage pathway of cellular proliferation (DNA synthesis) with better specificity because these nucleosides are accumulated and phosphorylated during cellular S-phase. The UW PET group developed [F-18]-3′-fluoro-3′-deoxythymidine (FLT) for this purpose.

Our recent studies have focused on the challenge of distinguishing whether clinical symptoms and standard imaging appearance after therapy is predominantly a result of tumor progression or radionecrosis/pseudoprogression in patients with primary brain tumors. This application of FLT-PET emphasizes the value of dynamic imaging to separate the blood flow or delivery phase of the imaging agent from its tumor incorporation as a flux through the DNA salvage pathway. Segmentation algorithms and compartmental analyses are being used to generate parametric maps of regional tumor transport and synthetic flux. In several study results, the flux parametric image in recurrent brain tumors shows much higher FLT accumulation (salvage pathway activity) than in tumors with pseudo-progression whereas the transport images overlap between the two groups.

Imaging the P-gp drug resistance mechanism is performed using [C-11]-verapamil, a substrate for the transporter similar to the anthracyclines, which are the mainstay of many chemotherapy regimens. Preliminary work in sarcoma patients has shown that levels of P-gp activity are variable in tumors at presentation and change in response to therapy, usually resulting in an increase in activity. This increase in P-gp activity may confirm clinical suspicion that drug resistance has been induced in an individual as an important contributor to treatment resistance.

In summary, PET imaging provides an important tool for selecting patients with specific mechanisms of resistance to cancer therapy so that new drugs can be used with maximum effectiveness. PET imaging results can also provide useful biomarkers for tumor response to standard and experimental therapy, and will be important contributors towards the goal of personalized medicine for cancer patients. The UW PET group has worked with NCI-CIP to develop INDs for FMISO and FLT that are now used in multicenter trials. The group has also developed methods for analysis of FMISO and FLT images and provides a resource for image analysis in the trials. Both of these imaging agents, and approaches to acquiring and analyzing their images, are widely available to nuclear medicine clinical research groups to contribute toward progress in understanding cancer and its response to therapy.

The research results to be presented were supported by P01 CA042045-22.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY42-02. doi:1538-7445.AM2012-SY42-02

Between-patient and within-patient (site-to-site) variability in estrogen receptor binding, measured in vivo by 18F-fluoroestradiol PET

Heterogeneity of estrogen receptor (ER) expression may be an important predictor of breast cancer therapeutic response. (18)F-fluoroestradiol PET produces in vivo quantitative measurements of regional estrogen binding in breast cancer tumors. We describe within-patient (site-to-site) and between-patient heterogeneity of lesions in patients scheduled to receive endocrine therapy.

METHODS

In 91 patients with a prior ER-positive biopsy, 505 lesions were analyzed for both (18)F-fluoroestradiol and (18)F-FDG uptake and the (18)F-fluoroestradiol/(18)F-FDG uptake ratio. Standardized uptake values (SUVs) were recorded for up to 16 lesions per patient, of 1.5 cm or more and visible on (18)F-FDG PET or conventional staging. Linear mixed-effects regression models examined associations between PET parameters and patient or lesion characteristics and estimated variance components. A reader study of SUV measurements for 9 scans further examined sources of within-patient variability.

RESULTS

Average (18)F-fluoroestradiol uptake and (18)F-fluoroestradiol/(18)F-FDG ratio varied greatly across these patients, despite a history of ER-positive disease: about 37% had low or absent (18)F-fluoroestradiol uptake even with marked (18)F-FDG uptake. (18)F-fluoroestradiol SUV and (18)F-fluoroestradiol/(18)F-FDG ratio measurements within patients with multiple lesions were clustered around the patient's average value in most cases. Summarizing these findings, the intraclass correlation coefficient (proportion of total variation that is between-patient) was 0.60 (95% confidence interval, 0.50-0.69) for (18)F-fluoroestradiol SUV and 0.65 (95% confidence interval, 0.56-0.73) for the (18)F-fluoroestradiol/(18)F-FDG ratio. Some within-patient variation in PET measures (22%-44%) was attributable to interobserver variability as measured by the reader study. A subset of patients had mixed uptake, with widely disparate (18)F-fluoroestradiol SUV or (18)F-fluoroestradiol/(18)F-FDG ratio for lesions in the same scan.

CONCLUSION

(18)F-fluoroestradiol uptake and the (18)F-fluoroestradiol/(18)F-FDG ratio varied greatly between patients but were usually consistent across lesions in the same scan. The average (18)F-fluoroestradiol SUV and (18)F-fluoroestradiol/(18)F-FDG ratio for a limited sample of lesions appear to provide a reasonable summary of synchronous ER expression for most patients. However, imaging the entire disease burden remains important to identify the subset of patients with mixed uptake, who may be at a critical point in their disease evolution.

Fluoroestradiol positron emission tomography reveals differences in pharmacodynamics of aromatase inhibitors, tamoxifen, and fulvestrant in patients with metastatic breast cancer

PURPOSE

To determine, by molecular imaging, how in vivo pharmacodynamics of estrogen-estrogen receptor (ER) binding differ between types of standard endocrine therapy.

EXPERIMENTAL DESIGN

The ER has been a highly successful target for breast cancer treatment. ER-directed treatments include lowering ligand concentration by using aromatase inhibitors (AI) and blocking the receptor with agents like tamoxifen (TAM) or fulvestrant (FUL). We measured regional estrogen-ER binding by using positron emission tomography with (18)F-fluoroestradiol (FES PET) prior to and during treatment with AI, TAM, or FUL in a series of 30 metastatic breast cancer patients. FES PET measured in vivo estrogen binding at all tumor sites in heavily pretreated women with metastatic bone soft tissue-dominant breast cancer. In patients with uterus (n = 16) changes in uterine FES uptake were also measured.

RESULTS

As expected, tumor FES uptake declined more markedly on ER blockers (TAM and FUL, average 54% decline) compared with a less than 15% average decline on estrogen-depleting AIs (P < 0.001). The rate of complete tumor blockade [FES standardized uptake value (SUV) ≤1.5] following TAM (5/5 patients) was greater than the blockade rate following FUL (4/11; 2-sided mid P = 0.019). Percent FES SUV change in the uterus showed a strong association with tumoral change (ρ = 0.63, P = 0.01).

CONCLUSIONS

FES PET can assess the in vivo pharmacodynamics of ER-targeted agents and may give insight into the activity of established therapeutic agents. Imaging revealed significant differences between agents, including differences in the efficacy of blockade by different ER antagonists in current clinical use.

Applying a patient-specific bio-mathematical model of glioma growth to develop virtual [18F]-FMISO-PET images

Glioblastoma multiforme (GBM) is a class of primary brain tumours characterized by their ability to rapidly proliferate and diffusely infiltrate surrounding brain tissue. The aggressive growth of GBM leads to the development of regions of low oxygenation (hypoxia), which can be clinically assessed through [18F]-fluoromisonidazole (FMISO) positron emission tomography (PET) imaging. Building upon the success of our previous mathematical modelling efforts, we have expanded our model to include the tumour microenvironment, specifically incorporating hypoxia, necrosis and angiogenesis. A pharmacokinetic model for the FMISO-PET tracer is applied at each spatial location throughout the brain and an analytical simulator for the image acquisition and reconstruction methods is applied to the resultant tracer activity map. The combination of our anatomical model with one for FMISO tracer dynamics and PET image reconstruction is able to produce a patient-specific virtual PET image that reproduces the image characteristics of the clinical PET scan as well as shows no statistical difference in the distribution of hypoxia within the tumour. This work establishes proof of principle for a link between anatomical (magnetic resonance image [MRI]) and molecular (PET) imaging on a patient-specific basis as well as address otherwise untenable questions in molecular imaging, such as determining the effect on tracer activity from cellular density. Although further investigation is necessary to establish the predicitve value of this technique, this unique tool provides a better dynamic understanding of the biological connection between anatomical changes seen on MRI and biochemical activity seen on PET of GBM in vivo.

Multiagent PET for risk characterization in sarcoma

A major goal of molecular imaging in cancer is to evaluate patient tumors for risk of treatment resistance and poor outcome using biologically specific PET agents. This approach was investigated using a multiagent imaging protocol for which patients were imaged in a single session to minimize changes in tumor parameters caused by multiple-day and -setting observation differences.

METHODS

We present data from a pilot study in 10 soft-tissue sarcoma patients imaged with (11)C-thymidine for cellular proliferation, (18)F-fluoromisonidazole (FMISO) for tissue hypoxia, and (11)C-verapamil for P-glycoprotein activity, in comparison with (15)O-water for blood flow and (11)C-CO(2) for metabolite analysis and (18)F-FDG clinical scans. Several patients underwent repeated imaging after adriamycin-based chemotherapy.

RESULTS

Quantitative imaging results showed that tumor uptake parameters vary between patients and with respect to each other in individual patients, suggesting that each patient's tumor biologic profile is unique. Specific tumor characteristics such as variable cellular proliferation, hypoxic volume, and upregulated P-glycoprotein activity were identified.

CONCLUSION

This study shows that multiagent PET is feasible and yields unique and potentially complementary biologic information on individual tumors.

Different modes of transport for 3H-thymidine, 3H-FLT, and 3H-FMAU in proliferating and nonproliferating human tumor cells

The basis for the use of nucleoside tracers in PET is that activity of the cell-growth-dependent enzyme thymidine kinase 1 is the rate-limiting factor driving tracer retention in tumors. Recent publications suggest that nucleoside transporters might influence uptake and thereby affect the tracer signal in vivo. Understanding transport mechanisms for different nucleoside PET tracers is important for evaluating clinical results. This study examined the relative role of different nucleoside transport mechanisms in uptake and retention of [methyl-(3)H]-3'-deoxy-3'-fluorothymidine ((3)H-FLT), [methyl-(3)H]-thymidine ((3)H-thymidine), and (3)H-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-methyluracil ((3)H-FMAU).

METHODS

Transport of (3)H-FLT, (3)H-thymidine, and (3)H-FMAU was examined in a single human adenocarcinoma cell line, A549, under both nongrowth and exponential-growth conditions.

RESULTS

(3)H-Thymidine transport was dominated by human equilibrative nucleoside transporter 1 (hENT1) under both growth conditions. (3)H-FLT was also transported by hENT1, but passive diffusion dominated its transport. (3)H-FMAU transport was dominated by human equilibrative nucleoside transporter 2. Cell membrane levels of hENT1 increased in cells under exponential growth, and this increase was associated with a more rapid rate of uptake for both (3)H-thymidine and (3)H-FLT. (3)H-FMAU transport was not affected by changes in growth conditions. All 3 tracers concentrated in the plateau phase, nonproliferating cells at levels many-fold greater than their concentration in buffer, in part because of low levels of nucleoside metabolism, which inhibited tracer efflux.

CONCLUSION

Transport mechanisms are not the same for (3)H-thymidine, (3)H-FLT, and (3)H-FMAU. Levels of hENT1, an important transporter of (3)H-FLT and (3)H-thymidine, increase as proliferating cells enter the cell cycle.

Abstract A230: Exploring novel PET agents for support of experimental cancer therapy: Selecting patient cohorts and monitoring response to therapy

The time course of biodistribution of PET radiopharmaceuticals, when analyzed by appropriate models, can be used to image molecular differences between tumors and normal tissues. Understanding important molecular differences and how they change during treatment should lead to better characterization of tumor biology and ultimately better treatment outcome. Four examples will show the value of PET to image specific aspects of the tumor phenotype.

Proliferation imaging started with [C-11]-thymidine and later with our development of [F-18]-FLT. The salvage pathway provides a robust measure of the growth rate of tumors. As an example, standard therapy for newly diagnosed glioblastoma multiforme is 60 Gy RT plus concurrent temozolomide. Many patients who complete therapy show MRIs consistent with tumor progression but they improve on continued TMZ. This pseudoprogression is an important problem; clinicians armed with MRI alone may wrongly conclude that standard treatment is failing. Misdiagnosing tumor progression could risk entering patients into trials of new agents, leading to falsely positive outcomes. FLT PET may help clarify this dilemma since preliminary studies have shown promise in distinguishing radionecrosis from recurrent disease. In these studies, we assessed FLT flux and transport as well as SUV and MRI and found that only FLT flux was an independent variable to distinguish the two groups.

Anthracycline based therapy continues to be a mainstay for solid cancers but many of these tumors have variable levels of multiple drug resistance. Pglycoprotein is a membrane pump to exclude anthracyclines from intracellular accumulation. We use PET to quantify Pgp activity using a transporter substrate, [C-11]-verapamil. Pilot studies of sarcoma patients showed a range of uptake kinetics in tumors before treatment compared with after exposure to chemotherapy. Our initial data shows that the extent of acquired MDR measured by PET correlates with survival.

Hypoxia is an important resistance factor in treatment. [F-18]-FMISO is an imaging agent that accumulates in hypoxia but not in necrosis. In outcomes studies of patients with brain tumors, FMISO was an independent predictor of outcome. Glioma patients with hypoxic volumes &gt;15 cc had a median survival of ∼4 mo while patients with less hypoxia had a median survival of ∼15 mo compared to 12–14 mo with current standard therapy. These data argue that better treatments directed at hypoxic disease deserve serious attention. We have also imaged recurrent malignant gliomas before and after treatment with bevacizumab plus irinotecan and correlated FMISO changes with survival. Our preliminary results argue that anti-angiogenic therapy may reduce hypoxia and lower resistance to radiotherapy and chemotherapy.

We are imaging estrogen receptors using [F-18]-fluoroestradiol to select breast cancer patients for targeted therapy. FES predicts response to endocrine therapy in metastatic breast cancer. It shows a pharmacodynamic difference between two ER blocking agents, tamoxifen and fulvestrant. We are beginning to explore the value of FES PET in novel therapy intended to re-express ER in breast cancer tumors refractory to endocrine therapy using a HDAC inhibitor.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A230.

Nonparametric Residue Analysis of Dynamic PET Data With Application to Cerebral FDG Studies in Normals

Kinetic analysis is used to extract metabolic information from dynamic positron emission tomography (PET) uptake data. The theory of indicator dilutions, developed in the seminal work of Meier and Zierler (1954), provides a probabilistic framework for representation of PET tracer uptake data in terms of a convolution between an arterial input function and a tissue residue. The residue is a scaled survival function associated with tracer residence in the tissue. Nonparametric inference for the residue, a deconvolution problem, provides a novel approach to kinetic analysis-critically one that is not reliant on specific compartmental modeling assumptions. A practical computational technique based on regularized cubic B-spline approximation of the residence time distribution is proposed. Nonparametric residue analysis allows formal statistical evaluation of specific parametric models to be considered. This analysis needs to properly account for the increased flexibility of the nonparametric estimator. The methodology is illustrated using data from a series of cerebral studies with PET and fluorodeoxyglucose (FDG) in normal subjects. Comparisons are made between key functionals of the residue, tracer flux, flow, etc., resulting from a parametric (the standard two-compartment of Phelps et al. 1979) and a nonparametric analysis. Strong statistical evidence against the compartment model is found. Primarily these differences relate to the representation of the early temporal structure of the tracer residence-largely a function of the vascular supply network. There are convincing physiological arguments against the representations implied by the compartmental approach but this is the first time that a rigorous statistical confirmation using PET data has been reported. The compartmental analysis produces suspect values for flow but, notably, the impact on the metabolic flux, though statistically significant, is limited to deviations on the order of 3%-4%. The general advantage of the nonparametric residue analysis is the ability to provide a valid kinetic quantitation in the context of studies where there may be heterogeneity or other uncertainty about the accuracy of a compartmental model approximation of the tissue residue.

Quantitative metrics of net proliferation and invasion link biological aggressiveness assessed by MRI with hypoxia assessed by FMISO-PET in newly diagnosed glioblastomas

Glioblastoma multiforme (GBM) are aggressive and uniformly fatal primary brain tumors characterized by their diffuse invasion of the normal-appearing parenchyma peripheral to the clinical imaging abnormality. Hypoxia, a hallmark of aggressive tumor behavior often noted in GBMs, has been associated with resistance to therapy, poorer survival, and more malignant tumor phenotypes. Based on the existence of a set of novel imaging techniques and modeling tools, our objective was to assess a hypothesized quantitative link between tumor growth kinetics [assessed via mathematical models and routine magnetic resonance imaging (MRI)] and the hypoxic burden of the tumor [assessed via positron emission tomography (PET) imaging]. Our biomathematical model for glioma kinetics describes the spatial and temporal evolution of a glioma in terms of concentration of malignant tumor cells. This model has already been proven useful as a novel tool to dynamically quantify the net rates of proliferation (rho) and invasion (D) of the glioma cells in individual patients. Estimates of these kinetic rates can be calculated from routinely available pretreatment MRI in vivo. Eleven adults with GBM were imaged preoperatively with (18)F-fluoromisonidazole (FMISO)-PET and serial gadolinium-enhanced T1- and T2-weighted MRIs to allow the estimation of patient-specific net rates of proliferation (rho) and invasion (D). Hypoxic volumes were quantified from each FMISO-PET scan following standard techniques. To control for tumor size variability, two measures of hypoxic burden were considered: relative hypoxia (RH), defined as the ratio of the hypoxic volume to the T2-defined tumor volume, and the mean intensity on FMISO-PET scaled to the blood activity of the tracer (mean T/B). Pearson correlations between RH and the net rate of cell proliferation (rho) reached significance (P < 0.04). Moreover, highly significant positive correlations were found between biological aggressiveness ratio (rho/D) and both RH (P < 0.00003) and the mean T/B (P < 0.0007).

NCI-sponsored trial for the evaluation of safety and preliminary efficacy of 3'-deoxy-3'-[18F]fluorothymidine (FLT) as a marker of proliferation in patients with recurrent gliomas: preliminary efficacy studies

PURPOSE

3'-Deoxy-3'-[18F]fluorothymidine ([18F]FLT) is being developed for imaging cellular proliferation. The goals were to explore the capacity of FLT-positron emission tomography (PET) to distinguish between recurrence and radionecrosis in gliomas and compare the results to those obtained with 2-fluoro-2-deoxy-D: -glucose (FDG).

PROCEDURES

Fifteen patients with tumor recurrence and four with radionecrosis, determined by clinical course and magnetic resonance imaging results, were studied by dynamic [18F]FLT-PET with arterial blood sampling. A two-tissue compartment four-rate constant model was used to determine metabolic flux (K (FLT)), blood to tissue transport (K (1)), and phosphorylation (k (3)). FDG-PET scans were obtained 75-90 min postinjection.

RESULTS

K (FLT) and k (3), but not K (1) or k (3)/k (2) + k (3), reached significance for separating the recurrence from radionecrosis groups. Standardized uptake value and visual analyses of FLT or FDG images did not reach significance.

CONCLUSIONS

K (FLT) (flux) appears to distinguish recurrence from radionecrosis better than other parameters, FLT and FDG semiquantitative approaches, or visual analysis of images of either tracer.

Complementary but distinct roles for MRI and 18F-fluoromisonidazole PET in the assessment of human glioblastomas

Glioblastoma multiforme is a primary brain tumor known for its rapid proliferation, diffuse invasion, and prominent neovasculature and necrosis. This study explores the in vivo link between these characteristics and hypoxia by comparing the relative spatial geometry of developing vasculature inferred from gadolinium-enhanced T1-weighted MRI (T1Gd), edematous tumor extent revealed on T2-weighted MRI (T2), and hypoxia assessed by 18F-fluoromisonidazole PET (18F-FMISO). Given the role of hypoxia in upregulating angiogenic factors, we hypothesized that the distribution of hypoxia seen on 18F-FMISO is correlated spatially and quantitatively with the amount of leaky neovasculature seen on T1Gd.

METHODS

A total of 24 patients with glioblastoma underwent T1Gd, T2, and 18F-FMISO-11 studies preceded surgical resection or biopsy, 7 followed surgery and preceded radiation therapy, and 11 followed radiation therapy. Abnormal regions seen on the MRI scan were segmented, including the necrotic center (T0), the region of abnormal blood-brain barrier associated with disrupted vasculature (T1Gd), and infiltrating tumor cells and edema (T2). The 18F-FMISO images were scaled to the blood 18F-FMISO activity to create tumor-to-blood ratio (T/B) images. The hypoxic volume (HV) was defined as the region with T/Bs greater than 1.2, and the maximum T/B (T/Bmax) was determined by the voxel with the greatest T/B value.

RESULTS

The HV generally occupied a region straddling the outer edge of the T1Gd abnormality and into the T2. A significant correlation between HV and the volume of the T1Gd abnormality that relied on the existence of a large outlier was observed. However, there was consistent correlation between surface areas of all MRI-defined regions and the surface area of the HV. The T/Bmax, typically located within the T1Gd region, was independent of the MRI-defined tumor size. Univariate survival analysis found the most significant predictors of survival to be HV, surface area of HV, surface area of T1Gd, and T/Bmax.

CONCLUSION

Hypoxia may drive the peripheral growth of glioblastomas. This conclusion supports the spatial link between the volumes and surface areas of the hypoxic and MRI regions; the magnitude of hypoxia, T/Bmax, remains independent of size.

Regional hypoxia in glioblastoma multiforme quantified with [18F]fluoromisonidazole positron emission tomography before radiotherapy: correlation with time to progression and survival

PURPOSE

Hypoxia is associated with resistance to radiotherapy and chemotherapy and activates transcription factors that support cell survival and migration. We measured the volume of hypoxic tumor and the maximum level of hypoxia in glioblastoma multiforme before radiotherapy with [(18)F]fluoromisonidazole positron emission tomography to assess their impact on time to progression (TTP) or survival.

EXPERIMENTAL DESIGN

Twenty-two patients were studied before biopsy or between resection and starting radiotherapy. Each had a 20-minute emission scan 2 hours after i.v. injection of 7 mCi of [(18)F]fluoromisonidazole. Venous blood samples taken during imaging were used to create tissue to blood concentration (T/B) ratios. The volume of tumor with T/B values above 1.2 defined the hypoxic volume (HV). Maximum T/B values (T/B(max)) were determined from the pixel with the highest uptake.

RESULTS

Kaplan-Meier plots showed shorter TTP and survival in patients whose tumors contained HVs or tumor T/B(max) ratios greater than the median (P < or = 0.001). In univariate analyses, greater HV or tumor T/B(max) were associated with shorter TTP or survival (P < 0.002). Multivariate analyses for survival and TTP against the covariates HV (or T/B(max)), magnetic resonance imaging (MRI) T1Gd volume, age, and Karnovsky performance score reached significance only for HV (or T/B(max); P < 0.03).

CONCLUSIONS

The volume and intensity of hypoxia in glioblastoma multiforme before radiotherapy are strongly associated with poorer TTP and survival. This type of imaging could be integrated into new treatment strategies to target hypoxia more aggressively in glioblastoma multiforme and could be applied to assess the treatment outcomes.

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.