Chirayu Shah

Inhibition of Mammalian Target of Rapamycin Is Required for Optimal Antitumor Effect of HER2 Inhibitors against HER2-Overexpressing Cancer Cells

Purpose: A significant fraction of HER2-overexpressing breast cancers exhibit resistance to the HER2 antibody trastuzumab. Hyperactivity of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway confers trastuzumab resistance, and mammalian target of rapamycin (mTOR) is a major downstream effector of PI3K/AKT. Therefore, we examined whether mTOR inhibitors synergize with trastuzumab. Experimental Design: Immunocompetent mice bearing HER2+ mammary tumors were treated with trastuzumab, the mTOR inhibitor rapamycin, or the combination. Mice were imaged for tumor cell death using an optical Annexin-V probe and with [18F]FDG positron emission tomography. The signaling and growth effects of the mTOR inhibitor RAD001 on HER2+ cells treated with trastuzumab or lapatinib were evaluated. Results: Treatment of mice with trastuzumab plus rapamycin was more effective than single-agent treatments, inducing complete regression of 26 of 26 tumors. The combination induced tumor cell death (Annexin-V binding) and inhibited FDG uptake. Rapamycin inhibited mTOR and tumor cell proliferation as determined by phosphorylated S6 and Ki-67 immunohistochemistry, respectively. In culture, the combination of RAD001 plus trastuzumab inhibited cell growth more effectively than either drug alone. Trastuzumab partially decreased PI3K but not mTOR activity. Knockdown of TSC2 resulted in HER2-independent activation of mTOR and dampened the response to trastuzumab and lapatinib. Treatment with the HER2 inhibitor lapatinib decreased phosphorylated S6 and growth in TSC2-expressing cells but not in TSC2-knockdown cells. Conclusions: Inhibition of PI3K and mTOR are required for the growth-inhibitory effect of HER2 antagonists. These findings collectively support the combined use of trastuzumab and mTOR inhibitors for the treatment of HER2+ breast cancer. (Clin Cancer Res 2009;15(23):7266–76)

Molecular Imaging of Therapeutic Response to Epidermal Growth Factor Receptor Blockade in Colorectal Cancer

Purpose: To evaluate noninvasive molecular imaging methods as correlative biomarkers of therapeutic efficacy of cetuximab in human colorectal cancer cell line xenografts grown in athymic nude mice. The correlation between molecular imaging and immunohistochemical analysis to quantify epidermal growth factor (EGF) binding, apoptosis, and proliferation was evaluated in treated and untreated tumor-bearing cohorts. Experimental Design: Optical imaging probes targeting EGF receptor (EGFR) expression (NIR800-EGF) and apoptosis (NIR700-Annexin V) were synthesized and evaluated in vitro and in vivo. Proliferation was assessed by 3′-[18F]fluoro-3′-deoxythymidine ([18F]FLT) positron emission tomography. Assessment of inhibition of EGFR signaling by cetuximab was accomplished by concomitant imaging of NIR800-EGF, NIR700-Annexin V, and [18F]FLT in cetuximab-sensitive (DiFi) and insensitive (HCT-116) human colorectal cancer cell line xenografts. Imaging results were validated by measurement of tumor size and immunohistochemical analysis of total and phosphorylated EGFR, caspase-3, and Ki-67 immediately following in vivo imaging. Results: NIR800-EGF accumulation in tumors reflected relative EGFR expression and EGFR occupancy by cetuximab. NIR700-Annexin V accumulation correlated with cetuximab-induced apoptosis as assessed by immunohistochemical staining of caspase-3. No significant difference in tumor proliferation was noted between treated and untreated animals by [18F]FLT positron emission tomography or Ki-67 immunohistochemistry. Conclusions: Molecular imaging can accurately assess EGF binding, proliferation, and apoptosis in human colorectal cancer xenografts. These imaging approaches may prove useful for serial, noninvasive monitoring of the biological effects of EGFR inhibition in preclinical studies. It is anticipated that these assays can be adapted for clinical use.

Imaging Biomarkers Predict Response to Anti-HER2 (ErbB2) Therapy in Preclinical Models of Breast Cancer

Purpose: To evaluate noninvasive imaging methods as predictive biomarkers of response to trastuzumab in mouse models of HER2-overexpressing breast cancer. The correlation between tumor regression and molecular imaging of apoptosis, glucose metabolism, and cellular proliferation was evaluated longitudinally in responding and nonresponding tumor-bearing cohorts. Experimental Design: Mammary tumors from MMTV/HER2 transgenic female mice were transplanted into syngeneic female mice. BT474 human breast carcinoma cell line xenografts were grown in athymic nude mice. Tumor cell apoptosis (NIR700-Annexin V accumulation), glucose metabolism [2-deoxy-2-[18F]fluoro-d-glucose positron emission tomography ([18F]FDG-PET)], and proliferation [3′-[18F]fluoro-3′-deoxythymidine-PET ([18F]FLT-PET)] were evaluated throughout a biweekly trastuzumab regimen. Imaging metrics were validated by direct measurement of tumor size and immunohistochemical analysis of cleaved caspase-3, phosphorylated AKT, and Ki67. Results: NIR700-Annexin V accumulated significantly in trastuzumab-treated MMTV/HER2 and BT474 tumors that ultimately regressed but not in nonresponding or vehicle-treated tumors. Uptake of [18F]FDG was not affected by trastuzumab treatment in MMTV/HER2 or BT474 tumors. [18F]FLT-PET imaging predicted trastuzumab response in BT474 tumors but not in MMTV/HER2 tumors, which exhibited modest uptake of [18F]FLT. Close agreement was observed between imaging metrics and immunohistochemical analysis. Conclusions: Molecular imaging of apoptosis accurately predicts trastuzumab-induced regression of HER2+ tumors and may warrant clinical exploration to predict early response to neoadjuvant trastuzumab. Trastuzumab does not seem to alter glucose metabolism substantially enough to afford [18F]FDG-PET significant predictive value in this setting. Although promising in one preclinical model, further studies are required to determine the overall value of [18F]FLT-PET as a biomarker of response to trastuzumab in HER2+ breast cancer.

68Ga-DOTATATE Compared with 111In-DTPA-Octreotide and Conventional Imaging for Pulmonary and Gastroenteropancreatic Neuroendocrine Tumors: A Systematic Review and Meta-Analysis.

Neuroendocrine tumors (NETs) are uncommon tumors with increasing incidence and prevalence. Current reports suggest that 68Ga-DOTATATE PET/CT imaging improves diagnosis and staging of NETs compared with 111In-DTPA-octreotide and conventional imaging. We performed a systematic review of 68Ga-DOTATATE for safety and efficacy compared with octreotide and conventional imaging to determine whether available evidence supports U.S. Food and Drug Administration approval. Methods: Medline, EMBASE, Web of Science, and Cochrane Reviews electronic databases were searched from January 1999 to September 2015. Results were restricted to human studies comparing diagnostic accuracy of 68Ga-DOTATATE with octreotide or conventional imaging for pulmonary or gastroenteropancreatic NET and for human studies reporting safety/toxicity for 68Ga-DOTATATE with 10 subjects or more thought to have NETs. Direct communication with corresponding authors was attempted to obtain missing information. Abstracts meeting eligibility criteria were collected by a research librarian and assembled for reviewers; 2 reviewers independently determined whether or not to include each abstract. If either reviewer chose inclusion, the abstract was accepted for review. Results: Database and bibliography searches yielded 2,479 articles, of which 42 were eligible. Three studies compared the 2 radiopharmaceuticals in the same patient, finding 68Ga-DOTATATE to be more sensitive than octreotide. Nine studies compared 68Ga-DOTATATE with conventional imaging. 68Ga-DOTATATE estimated sensitivity, 90.9% (95% confidence interval, 81.4%–96.4%), and specificity, 90.6% (95% confidence interval, 77.8%–96.1%), were high. Five studies were retained for safety reporting only. Report of harm possibly related to 68Ga-DOTATATE was rare (6 of 974), and no study reported major toxicity or safety issues. Conclusion: No direct comparison of octreotide and 68Ga-DOTATATE imaging for diagnosis and staging in an unbiased population of NETs has been published. Available information in the peer-reviewed literature regarding diagnostic efficacy and safety supports the use of 68Ga-DOTATATE for imaging of NETs where it is available.

How much CT is needed in nuclear medicine

There is a major trend toward reducing the cost of medical care. One of the ways to meet this challenge is to diagnose and treat diseases in their infancy. With the advent of multislice computerized tomography (CT) scans, exquisite anatomical detail is available in shorter time intervals. However, anatomical changes are, by definition, the result of disease process and are thus evident only after the disease has progressed significantly. This has led to a major paradigm shift toward functional and physiologic imaging. We, in nuclear medicine, have the privilege of being able to detect physiological and pathophysiological changes that occur as a result of disease process long before anatomical changes are appreciated. With the emergence of molecular imaging, we are now researching targeted imaging and therapeutic agents that will enable us to visualize these changes at the molecular and cellular levels so as to diagnose diseases in their infancy before they progress or complications arise, resulting in both improved and efficient patient care at reduced cost. However, one of the well-known drawbacks of nuclear medicine and functional imaging, in general, is that this targeted approach sacrifices both anatomical details and landmarks that are needed for the accurate interpretation of the information. As we know, functional imaging with single photon emission computed tomography (SPECT) has the limitations of poor anatomic resolution and nonspecificity. Various methods of coregistration have been developed to improve anatomical localization. Initial attempts resulted in the development of dedicated software and workstations to coregister results of studies performed separately by different modalities such as SPECT and CT. However, problems with reproducing the exact positioning between different modalities, especially in the abdomen, have made this a difficult endeavor. This led to the development of dedicated single gantry, emission–transmission imaging systems using an array of high-purity germanium detectors and SPECT/CT scanners. The Millennium VG with “Hawkeye” by GE Healthcare Technology, a dual-head gamma camera equipped with an integrated X-ray transmission system introduced in the year 2000, was the first fully integrated clinical SPECT/CT hybrid system. It included slip ring capability allowing for continuous SPECT and CT scanning. Vanderbilt was one of the first sites to perform clinical imaging using this system. As the study is acquired on the same machine in registered format without changes in patient position, it allows for effortless superimposition of the SPECT images with CT images without the challenge of coregistrating results from different patient positioning. The transmission data obtained with the CT component are also used for attenuation correction of images acquired by SPECT. Newer generations of hybrid SPECT/CT systems utilize multidetector spiral CT allowing for better anatomic resolution, greater contrast, and quicker scan times. Almost all of the new positron emission tomography (PET) scanners sold nowadays are combined with multidetector CT scanners capable of acquiring up to 64 slices in one rotation. Exquisite anatomical details acquired by these scanners, such as those obtained from CT coronary angiography, can now be combined with functional/physiologic imaging, such as the myocardial perfusion study, allowing for better diagnostic accuracy. To generate an accurate, concise report for images acquired from these newer generations of hybrid systems, the nuclear medicine physician needs to be comfortable interpreting the diagnostic Eur J Nucl Med Mol Imaging (2008) 35:1759–1760 DOI 10.1007/s00259-008-0843-9

Detrimental effects of nitroglycerin use during regadenoson vasodilator stress testing: A cautionary tale

Vasodilator agents such as adenosine and regadenoson are commonly used pharmacologic stressors to assess for ischemia in patients undergoing myocardial perfusion studies. The recommended reversal agent for this mode of stress is aminophylline, although nitroglycerin is commonly administered as an attempt to reverse the symptoms or electrocardiographic (EKG) changes during the stress test. We demonstrate through two cases that incorrect administration of nitroglycerin can induce hypotension and worsen coronary steal, whereas appropriate administration of aminophylline can reverse the effects of pharmacologic vasodilators. While nitroglycerin is often used in patients with organic angina, it has the potential to worsen ischemia in the setting of pharmacologic vasodilator administration. These cases underscore the importance of administering the correct reversal agent for pharmacologic stress tests.

Dysfunctional neobladder causing pulmonary toxicity after combination chemotherapy for lymphoma

A 75-year-old man with transitional cell bladder carcinoma status post cystoprostatectomy with neobladder creation from the sigmoid colon was diagnosed with Stage IVA diffuse large B-cell lymphoma involving the kidney in an evaluation for acute-on-chronic renal failure. A [18F] fluorodeoxyglucose positron emission tomography (FDG-PET) and computed tomography (CT) scan at presentation revealed lymphadenopathy above and below the diaphragm. Bone marrow biopsy showed no lymphoma. Worsening renal failure from lymphadenopathy prompted treatment of his lymphoma. Due to Stage IV chronic kidney disease and cardiac ejection fraction of 38%, he received renal-dose adjusted cyclophosphamide, etoposide, vincristine, rituximab, and prednisone (R-CEOP). He received a total of 2 L IV fluid volume with his chemotherapy. His usual chronic in-dwelling Foley catheter was in place before, during, and after chemotherapy. On Day 5 of chemotherapy, he developed gross hemoptysis, hypoxia, and diffuse bilateral rales. Hemoglobin decreased from 10.8 g/dL to 6.3 g/dL with normal platelets and coagulation panel. Infection evaluation was negative. A CT scan demonstrated bilateral ground glass opacities. He was diagnosed with diffuse alveolar hemorrhage Figure 1. A: Axial CT done as a part of the initial diagnostic FDG PET-CT shows small bilateral pleural effusions and relatively normal lung parenchyma. B: Follow-up CT after second episode of hypoxia shows bilateral ground glass opacities, interlobular septal thickening, architectural distortion, and bronchiectasis with associated increased FDG uptake (not shown). C, D: PET-CT fusion and CT images demonstrate retained FDG containing urine in the neobladder despite the presence of a Foley catheter (arrow in D). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]