Honors & Awards


  • Poster award winner at the Stanford Bio-X IIP Poster Session, Stanford Bio-X (March 2020)
  • Stanford Bio-X Travel Award, Stanford Bio-X (August 2019)
  • Student travel Award, World Molecular Imaging Congress (2018)
  • Vevo Travel Award, Molecular Imaging Track, Fujifilm/VisualSonics (2018)
  • Faculty of Health Sciences Graduate Programs Outstanding Thesis Award, McMaster University (2017)
  • Faculty of Health Sciences Graduate Programs Excellence Award, McMaster University (2016)
  • McMaster Graduate Studies International Excellence Award, McMaster University (2014-2015)
  • Outstanding Oral Presentation Award, Faculty of Health Sciences, McMaster University (2014)
  • Chemical Biology Travel Award, McMaster University (2012-2013)
  • McMaster Graduate Studies International Excellence Award, McMaster University (2012-2013)

Stanford Advisors


Patents


  • Aimen Zlitni, Gayatri Gowrishankar, Sanjiv Sam Gambhir. "United States Patent 20200061215 MALTOTRIOSE-BASED PROBES FOR FLUORESCENCE AND PHOTOACOUSTIC IMAGING OF BACTERIA", OTL, Feb 27, 2020
  • Aimen Zlitni, John F. Valliant. "CanadaTargeted Molecular Imaging Contrast Agents.", Aug 1, 2015

Projects


  • The development and evaluation of probes for multimodal molecular imaging of bacterial infections, Stanford University (12/2016 - Present)

    Imaging modalities include Photo-acoustic, fluorescence and PET imaging

    Location

    California

  • The preparation and evaluation of nanobubbles for photo-acoustic and Ultrasound molecular imaging of cancer, Stanford University (9/1/2016 - Present)

    Location

    California

  • Development and Evaluation of probes for Molecular Optical Imaging of cancer, Stanford University

    Location

    United States

  • Novel nanoparticle-based systems for gene and drug delivery, Stanford Univeristy

    Location

    United States

All Publications


  • Fundamentals and developments in fluorescence-guided cancer surgery. Nature reviews. Clinical oncology Mieog, J. S., Achterberg, F. B., Zlitni, A., Hutteman, M., Burggraaf, J., Swijnenburg, R., Gioux, S., Vahrmeijer, A. L. 2021

    Abstract

    Fluorescence-guided surgery using tumour-targeted imaging agents has emerged over the past decade as a promising and effective method of intraoperative cancer detection. An impressive number of fluorescently labelled antibodies, peptides, particles and other molecules related to cancer hallmarks have been developed for the illumination of target lesions. New approaches are being implemented to translate these imaging agents into the clinic, although only a few have made it past early-phase clinical trials. For this translational process to succeed, target selection, imaging agents and their related detection systems and clinical implementation have to operate in perfect harmony to enable real-time intraoperative visualization that can benefit patients. Herein, we review key aspects of this imaging cascade and focus on imaging approaches and methods that have helped to shed new light onto the field of intraoperative fluorescence-guided cancer surgery with the singular goal of improving patient outcomes.

    View details for DOI 10.1038/s41571-021-00548-3

    View details for PubMedID 34493858

  • Maltotriose-based probes for fluorescence and photoacoustic imaging of bacterial infections. Nature communications Zlitni, A. n., Gowrishankar, G. n., Steinberg, I. n., Haywood, T. n., Sam Gambhir, S. n. 2020; 11 (1): 1250

    Abstract

    Currently, there are no non-invasive tools to accurately diagnose wound and surgical site infections before they become systemic or cause significant anatomical damage. Fluorescence and photoacoustic imaging are cost-effective imaging modalities that can be used to noninvasively diagnose bacterial infections when paired with a molecularly targeted infection imaging agent. Here, we develop a fluorescent derivative of maltotriose (Cy7-1-maltotriose), which is shown to be taken up in a variety of gram-positive and gram-negative bacterial strains in vitro. In vivo fluorescence and photoacoustic imaging studies highlight the ability of this probe to detect infection, assess infection burden, and visualize the effectiveness of antibiotic treatment in E. coli-induced myositis and a clinically relevant S. aureus wound infection murine model. In addition, we show that maltotriose is an ideal scaffold for infection imaging agents encompassing better pharmacokinetic properties and in vivo stability than other maltodextrins (e.g. maltohexose).

    View details for DOI 10.1038/s41467-020-14985-8

    View details for PubMedID 32144257

  • Molecular imaging agents for ultrasound. Current opinion in chemical biology Zlitni, A., Gambhir, S. S. 2018; 45: 113–20

    Abstract

    Ultrasound (US) imaging is a safe, sensitive and affordable imaging modality with a wide usage in the clinic. US signal can be further enhanced by using echogenic contrast agents (UCAs) which amplify the US signal. Developments in UCAs which are targeted to sites of disease allow the use of US imaging to provide molecular information. Unfortunately, traditional UCAs are too large to leave the vascular space limiting the application of molecular US to intravascular markers. In this mini review, we highlight the most recent reports on the application of molecular US imaging in the clinic and summarize the latest nanoparticle platforms used to develop nUCAs. We believe that the highlighted technologies will have a great impact on the evolution of the US imaging field.

    View details for PubMedID 29631121

  • Development of prostate specific membrane antigen targeted ultrasound microbubbles using bioorthogonal chemistry. PloS one Zlitni, A. n., Yin, M. n., Janzen, N. n., Chatterjee, S. n., Lisok, A. n., Gabrielson, K. L., Nimmagadda, S. n., Pomper, M. G., Foster, F. S., Valliant, J. F. 2017; 12 (5): e0176958

    Abstract

    Prostate specific membrane antigen (PSMA) targeted microbubbles (MBs) were developed using bioorthogonal chemistry. Streptavidin-labeled MBs were treated with a biotinylated tetrazine (MBTz) and targeted to PSMA expressing cells using trans-cyclooctene (TCO)-functionalized anti-PSMA antibodies (TCO-anti-PSMA). The extent of MB binding to PSMA positive cells for two different targeting strategies was determined using an in vitro flow chamber. The initial approach involved pretargeting, where TCO-anti-PSMA was first incubated with PSMA expressing cells and followed by MBTz, which subsequently showed a 2.8 fold increase in the number of bound MBs compared to experiments performed in the absence of TCO-anti-PSMA. Using direct targeting, where TCO-anti-PSMA was linked to MBTz prior to initiation of the assay, a 5-fold increase in binding compared to controls was observed. The direct targeting approach was subsequently evaluated in vivo using a human xenograft tumor model and two different PSMA-targeting antibodies. The US signal enhancements observed were 1.6- and 5.9-fold greater than that for non-targeted MBs. The lead construct was also evaluated in a head-to-head study using mice bearing both PSMA positive or negative tumors in separate limbs. The human PSMA expressing tumors exhibited a 2-fold higher US signal compared to those tumors deficient in human PSMA. The results demonstrate both the feasibility of preparing PSMA-targeted MBs and the benefits of using bioorthogonal chemistry to create targeted US probes.

    View details for DOI 10.1371/journal.pone.0176958

    View details for PubMedID 28472168

  • In vivo Biodistribution of Radiolabeled Acoustic Protein Nanostructures. Molecular imaging and biology : MIB : the official publication of the Academy of Molecular Imaging Le Floc'h, J. n., Zlitni, A. n., Bilton, H. A., Yin, M. n., Farhadi, A. n., Janzen, N. R., Shapiro, M. G., Valliant, J. F., Foster, F. S. 2017

    Abstract

    Contrast-enhanced ultrasound plays an expanding role in oncology, but its applicability to molecular imaging is hindered by a lack of nanoscale contrast agents that can reach targets outside the vasculature. Gas vesicles (GVs)-a unique class of gas-filled protein nanostructures-have recently been introduced as a promising new class of ultrasound contrast agents that can potentially access the extravascular space and be modified for molecular targeting. The purpose of the present study is to determine the quantitative biodistribution of GVs, which is critical for their development as imaging agents.We use a novel bioorthogonal radiolabeling strategy to prepare technetium-99m-radiolabeled ([(99m)Tc])GVs in high radiochemical purity. We use single photon emission computed tomography (SPECT) and tissue counting to quantitatively assess GV biodistribution in mice.Twenty minutes following administration to mice, the SPECT biodistribution shows that 84 % of [(99m)Tc]GVs are taken up by the reticuloendothelial system (RES) and 13 % are found in the gall bladder and duodenum. Quantitative tissue counting shows that the uptake (mean ± SEM % of injected dose/organ) is 0.6 ± 0.2 for the gall bladder, 46.2 ± 3.1 for the liver, 1.91 ± 0.16 for the lungs, and 1.3 ± 0.3 for the spleen. Fluorescence imaging confirmed the presence of GVs in RES.These results provide essential information for the development of GVs as targeted nanoscale imaging agents for ultrasound.

    View details for DOI 10.1007/s11307-017-1122-6

    View details for PubMedID 28956265

  • Catching Bubbles: Targeting Ultrasound Microbubbles Using Bioorthogonal Inverse-Electron-Demand Diels-Alder Reactions ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Zlitni, A., Janzen, N., Foster, F. S., Valliant, J. F. 2014; 53 (25): 6459-6463

    View details for DOI 10.1002/anie.201402473

    View details for Web of Science ID 000337095900025

    View details for PubMedID 24829138

  • Ultra-high-frequency radio-frequency acoustic molecular imaging with saline nanodroplets in living subjects. Nature nanotechnology Chen, Y. S., Zhao, Y. n., Beinat, C. n., Zlitni, A. n., Hsu, E. C., Chen, D. H., Achterberg, F. n., Wang, H. n., Stoyanova, T. n., Dionne, J. n., Gambhir, S. S. 2021

    Abstract

    Molecular imaging is a crucial technique in clinical diagnostics but it relies on radioactive tracers or strong magnetic fields that are unsuitable for many patients, particularly infants and pregnant women. Ultra-high-frequency radio-frequency acoustic (UHF-RF-acoustic) imaging using non-ionizing RF pulses allows deep-tissue imaging with sub-millimetre spatial resolution. However, lack of biocompatible and targetable contrast agents has prevented the successful in vivo application of UHF-RF-acoustic imaging. Here we report our development of targetable nanodroplets for UHF-RF-acoustic molecular imaging of cancers. We synthesize all-liquid nanodroplets containing hypertonic saline that are stable for at least 2 weeks and can produce high-intensity UHF-RF-acoustic signals. Compared with concentration-matched iron oxide nanoparticles, our nanodroplets produce at least 1,600 times higher UHF-RF-acoustic signals at the same imaging depth. We demonstrate in vivo imaging using the targeted nanodroplets in a prostate cancer xenograft mouse model expressing gastrin release protein receptor (GRPR), and show that targeting specificity is increased by more than 2-fold compared with untargeted nanodroplets or prostate cancer cells not expressing this receptor.

    View details for DOI 10.1038/s41565-021-00869-5

    View details for PubMedID 33782588

  • Superiorized Photo-Acoustic Non-NEgative Reconstruction (SPANNER) for Clinical Photoacoustic Imaging. IEEE transactions on medical imaging Steinberg, I. n., Kim, J. n., Schneider, M. K., Hyun, D. n., Zlitni, A. n., Hooper, S. M., Klap, T. n., Sonn, G. A., Dahl, J. J., Kim, C. n., Gambhir, S. S. 2021; PP

    Abstract

    Photoacoustic (PA) imaging can revolutionize medical ultrasound by augmenting it with molecular information. However, clinical translation of PA imaging remains a challenge due to the limited viewing angles and imaging depth. Described here is a new robust algorithm called Superiorized Photo-Acoustic Non-NEgative Reconstruction (SPANNER), designed to reconstruct PA images in real-time and to address the artifacts associated with limited viewing angles and imaging depth. The method utilizes precise forward modeling of the PA propagation and reception of signals while accounting for the effects of acoustic absorption, element size, shape, and sensitivity, as well as the transducer's impulse response and directivity pattern. A fast superiorized conjugate gradient algorithm is used for inversion. SPANNER is compared to three reconstruction algorithms: delay-and-sum (DAS), universal back-projection (UBP), and model-based reconstruction (MBR). All four algorithms are applied to both simulations and experimental data acquired from tissue-mimicking phantoms, ex vivo tissue samples, and in vivo imaging of the prostates in patients. Simulations and phantom experiments highlight the ability of SPANNER to improve contrast to background ratio by up to 20 dB compared to all other algorithms, as well as a 3-fold increase in axial resolution compared to DAS and UBP. Applying SPANNER on contrast-enhanced PA images acquired from prostate cancer patients yielded a statistically significant difference before and after contrast agent administration, while the other three image reconstruction methods did not, thus highlighting SPANNER's performance in differentiating intrinsic from extrinsic PA signals and its ability to quantify PA signals from the contrast agent more accurately.

    View details for DOI 10.1109/TMI.2021.3068181

    View details for PubMedID 33755561

  • Real-time surgical margin assessment using ICG-fluorescence during laparoscopic and robot-assisted resections of colorectal liver metastases. Annals of translational medicine Achterberg, F. B., Sibinga Mulder, B. G., Meijer, R. P., Bonsing, B. A., Hartgrink, H. H., Mieog, J. S., Zlitni, A. n., Park, S. M., Farina Sarasqueta, A. n., Vahrmeijer, A. L., Swijnenburg, R. J. 2020; 8 (21): 1448

    Abstract

    Almost a third of the resections in patients with colorectal liver metastases (CRLM) undergoing curative surgery, end up being tumor-margin positive (≤1 mm margin). Near-infrared fluorescent (NIRF) imaging using the fluorescent contrast agent indocyanine green (ICG) has been studied for many different applications. When administered in a relatively low dose (10 mg) 24 hours prior to surgery, ICG accumulated in hepatocytes surrounding the CRLM. This results in the formation of a characteristic fluorescent 'rim' surrounding CRLM when located at the periphery of the liver. By resecting the metastasis with the entire surrounding fluorescent rim, in real-time guided by NIRF imaging, the surgeon can effectively acquire margin-negative (>1 mm) resections. This pilot study aims to describe the surgical technique for using near-infrared fluorescence imaging to assess tumor-margins in vivo in patients with CRLM undergoing laparoscopic or robot-assisted resections.Out of our institutional database we selected 16 CRLM based on margin-status (R0; n=8, R1; n=8), which were resected by a minimally-invasive approach using ICG-fluorescence. NIRF images acquired during surgery, from both the resection specimen and the wound bed, were analysed for fluorescent signal. We hypothesized that a protruding fluorescent rim at the parenchymal side of the resection specimen could indicate a too close proximity to the tumor and could be predictive for a tumor-positive surgical margin. NIRF images were correlated to final histopathological assessment of the resection margin.All lesions with a NIRF positive resection plane in vivo were reported as having a tumor-positive margin. Lesions that showcased no protruding rim in the wound bed in vivo were diagnosed as having a tumor-negative margin in 88% of cases. A 5-step surgical workflow is described to document the NIRF signal was used assess the resection margin in vivo for future clinical studies.The pilot study shows that image-guided surgery using real-time ICG-fluorescence has the potential to aid surgeons in achieving a tumor-negative margin in minimally invasive liver metastasectomies. The national multi-centre MIMIC-Trial will prospectively study the effect of this technique on surgical tumor-margins (Dutch Trial Register number NL7674).

    View details for DOI 10.21037/atm-20-1999

    View details for PubMedID 33313193

    View details for PubMedCentralID PMC7723628

  • Trop2 is a driver of metastatic prostate cancer with neuroendocrine phenotype via PARP1. Proceedings of the National Academy of Sciences of the United States of America Hsu, E. C., Rice, M. A., Bermudez, A. n., Marques, F. J., Aslan, M. n., Liu, S. n., Ghoochani, A. n., Zhang, C. A., Chen, Y. S., Zlitni, A. n., Kumar, S. n., Nolley, R. n., Habte, F. n., Shen, M. n., Koul, K. n., Peehl, D. M., Zoubeidi, A. n., Gambhir, S. S., Kunder, C. A., Pitteri, S. J., Brooks, J. D., Stoyanova, T. n. 2020

    Abstract

    Resistance to androgen deprivation therapy, or castration-resistant prostate cancer (CRPC), is often accompanied by metastasis and is currently the ultimate cause of prostate cancer-associated deaths in men. Recently, secondary hormonal therapies have led to an increase of neuroendocrine prostate cancer (NEPC), a highly aggressive variant of CRPC. Here, we identify that high levels of cell surface receptor Trop2 are predictive of recurrence of localized prostate cancer. Moreover, Trop2 is significantly elevated in CRPC and NEPC, drives prostate cancer growth, and induces neuroendocrine phenotype. Overexpression of Trop2 induces tumor growth and metastasis while loss of Trop2 suppresses these abilities in vivo. Trop2-driven NEPC displays a significant up-regulation of PARP1, and PARP inhibitors significantly delay tumor growth and metastatic colonization and reverse neuroendocrine features in Trop2-driven NEPC. Our findings establish Trop2 as a driver and therapeutic target for metastatic prostate cancer with neuroendocrine phenotype and suggest that high Trop2 levels could identify cancers that are sensitive to Trop2-targeting therapies and PARP1 inhibition.

    View details for DOI 10.1073/pnas.1905384117

    View details for PubMedID 31932422

  • I-125-Tetrazines and Inverse-Electron-Demand Diels-Alder Chemistry: A Convenient Radioiodination Strategy for Biomolecule Labeling, Screening, and Biodistribution Studies BIOCONJUGATE CHEMISTRY Albu, S. A., Al-Karmi, S. A., Vito, A., Dzandzi, J. P., Zlitni, A., Beckford-Vera, D., Blacker, M., Janzen, N., Patel, R. M., Capretta, A., Valliant, J. F. 2016; 27 (1): 207-216

    Abstract

    A convenient method to prepare radioiodinated tetrazines was developed, such that a bioorthogonal inverse electron demand Diels-Alder reaction can be used to label biomolecules with iodine-125 for in vitro screening and in vivo biodistribution studies. The tetrazine was prepared by employing a high-yielding oxidative halo destannylation reaction that concomitantly oxidized the dihydrotetrazine precursor. The product reacts quickly and efficiently with trans-cyclooctene derivatives. Utility was demonstrated through antibody and hormone labeling experiments and by evaluating products using standard analytical methods, in vitro assays, and quantitative biodistribution studies where the latter was performed in direct comparison to Bolton-Hunter and direct iodination methods. The approach described provides a convenient and advantageous alternative to conventional protein iodination methods that can expedite preclinical development and evaluation of biotherapeutics.

    View details for DOI 10.1021/acs.bioconjchem.5b00609

    View details for Web of Science ID 000368651600023

    View details for PubMedID 26699913

  • Synthesis, characterization and radiolabeling of carborane-functionalized tetrazines for use in inverse electron demand Diels-Alder ligation reactions JOURNAL OF ORGANOMETALLIC CHEMISTRY Genady, A. R., Tan, J., El-Zaria, M. E., Zlitni, A., Janzen, N., Valliant, J. F. 2015; 791: 204-213
  • The synthesis, magnetic purification and evaluation of Tc-99m-labeled microbubbles NUCLEAR MEDICINE AND BIOLOGY Lazarova, N., Causey, P. W., Lemon, J. A., Czorny, S. K., Forbes, J. R., Zlitni, A., Genady, A., Foster, F. S., Valliant, J. F. 2011; 38 (8): 1111-1118

    Abstract

    Ultrasound (US) contrast agents based on microbubbles (MBs) are being investigated as platforms for drug and gene delivery. A methodology for determining the distribution and fate of modified MBs quantitatively in vivo can be achieved by tagging MBs directly with (99m)Tc. This creates the opportunity to employ dual-modality imaging using both US and small animal SPECT along with quantitative ex vivo tissue counting to evaluate novel MB constructs.A (99m)Tc-labeled biotin derivative ((99m)TcL1) was prepared and incubated with streptavidin-coated MBs. The (99m)Tc-labeled bubbles were isolated using a streptavidin-coated magnetic-bead purification strategy that did not disrupt the MBs. A small animal scintigraphic/CT imaging study as well as a quantitative biodistribution study was completed using (99m)TcL1 and (99m)Tc-labeled bubbles in healthy C57Bl-6 mice.The imaging and biodistribution data showed rapid accumulation and retention of (99m)Tc-MBs in the liver (68.2±6.6 %ID/g at 4 min; 93.3±3.2 %ID/g at 60 min) and spleen (214.2±19.7 %ID/g at 4 min; 213.4±19.7 %ID/g at 60 min). In contrast, (99m)TcL1 accumulated in multiple organs including the small intestine (22.5±3.6 %ID/g at 4 min; 83.4±5.9 %ID/g at 60 min) and bladder (184.0±88.1 %ID/g at 4 min; 24.2±17.7 %ID/g at 60 min).A convenient means to radiolabel and purify MBs was developed and the distribution of the labeled products determined. The result is a platform which can be used to assess the pharmacokinetics and fate of novel MB constructs both regionally using US and throughout the entire subject in a quantitative manner by employing small animal SPECT and tissue counting.

    View details for DOI 10.1016/j.nucmedbio.2011.04.008

    View details for Web of Science ID 000298070400005

    View details for PubMedID 21741260