Professional Education

  • PhD, University of Missouri - Columbia, Synthetic Bio-/Organic Chemistry (2014)
  • Bachelor of Science, Trinity University, Biochemistry & Molecular Biology (2002)
  • Bachelor of Arts, Trinity University, Philosophy - Metaphysics & Epistemology (2002)

Stanford Advisors

All Publications

  • A NIR fluorescent smart probe for imaging tumor hypoxia. Cancer reports (Hoboken, N.J.) Hettie, K. S., Klockow, J. L., Moon, E. J., Giaccia, A. J., Chin, F. T. 2021: e1384


    BACKGROUND: Tumor hypoxia is a characteristic of paramount importance due to low oxygenation levels in tissue negatively correlating with resistance to traditional therapies. The ability to noninvasively identify such could provide for personalized treatment(s) and enhance survival rates. Accordingly, we recently developed an NIR fluorescent hypoxia-sensitive smart probe (NO2 -Rosol) for identifying hypoxia via selectively imaging nitroreductase (NTR) activity, which could correlate to oxygen deprivation levels in cells, thereby serving as a proxy. We demonstrated proof of concept by subjecting a glioblastoma (GBM) cell line to extreme stress by evaluating such under radiobiological hypoxic (pO2 ≤~0.5%) conditions, which is a far cry from representative levels for hypoxia for brain glioma (pO2 = ~1.7%) which fluctuate little from physiological hypoxic (pO2 = 1.0-3.0%) conditions.AIM: We aimed to evaluate the robustness, suitability, and feasibility of NO2 -Rosol for imaging hypoxia in vitro and in vivo via assessing NTR activity in diverse GBM models under relevant oxygenation levels (pO2 = 2.0%) within physiological hypoxic conditions that mimic oxygenation levels in GBM tumor tissue in the brain.METHODS: We evaluated multiple GBM cell lines to determine their relative sensitivity to oxygenation levels via measuring carbonic anhydrase IX (CAIX) levels, which is a surrogate marker for indirectly identifying hypoxia by reporting on oxygen deprivation levels and upregulated NTR activity. We evaluated for hypoxia via measuring NTR activity when employing NO2 -Rosol in in vitro and tumor hypoxia imaging studies in vivo.RESULTS: The GBM39 cell line demonstrated the highest CAIX expression under hypoxic conditions representing that of GBM in the brain. NO2 -Rosol displayed an 8-fold fluorescence enhancement when evaluated in GBM39 cells (pO2 = 2.0%), thereby establishing its robustness and suitability for imaging hypoxia under relevant physiological conditions. We demonstrated the feasibility of NO2 -Rosol to afford tumor hypoxia imaging in vivo via it demonstrating a tumor-to-background of 5 upon (i) diffusion throughout, (ii) bioreductive activation by NTR activity in, and (iii) retention within, GBM39 tumor tissue.CONCLUSION: We established the robustness, suitability, and feasibility of NO2 -Rosol for imaging hypoxia under relevant oxygenation levels in vitro and in vivo via assessing NTR activity in GBM39 models.

    View details for DOI 10.1002/cnr2.1384

    View details for PubMedID 33811473

  • Near-Infrared Fluorophores for Thrombosis Diagnosis and Therapy ADVANCED THERAPEUTICS Sun, B., Hettie, K. S., Zhu, S. 2021
  • A Role for Extracellular Vesicles in SARS-CoV-2 Therapeutics and Prevention. Journal of neuroimmune pharmacology : the official journal of the Society on NeuroImmune Pharmacology Machhi, J., Shahjin, F., Das, S., Patel, M., Abdelmoaty, M. M., Cohen, J. D., Singh, P. A., Baldi, A., Bajwa, N., Kumar, R., Vora, L. K., Patel, T. A., Oleynikov, M. D., Soni, D., Yeapuri, P., Mukadam, I., Chakraborty, R., Saksena, C. G., Herskovitz, J., Hasan, M., Oupicky, D., Das, S., Donnelly, R. F., Hettie, K. S., Chang, L., Gendelman, H. E., Kevadiya, B. D. 2021


    Extracellular vesicles (EVs) are the common designation for ectosomes, microparticles and microvesicles serving dominant roles in intercellular communication. Bothviableand dying cells release EVs to the extracellular environment for transfer of cell, immune and infectious materials. Defined morphologically as lipid bi-layered structures EVs show molecular, biochemical, distribution, and entry mechanisms similarto viruses within cells and tissues. In recent years their functional capacities have been harnessed to deliver biomolecules and drugs and immunological agents to specific cells and organs of interest or disease. Interest in EVs as putative vaccines or drug delivery vehicles are substantial. The vesicles have properties of receptors nanoassembly on their surface. EVs can interact with specific immunocytes that include antigen presenting cells (dendritic cells and other mononuclear phagocytes) to elicit immune responses or affect tissue and cellular homeostasis or disease. Due to potential advantages like biocompatibility, biodegradation and efficient immune activation, EVs have gained attraction for the development of treatment or a vaccine system against the severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) infection. In this review efforts to use EVs to contain SARS CoV-2 and affect the current viral pandemic are discussed. An emphasis is made on mesenchymal stem cell derived EVs' as a vaccine candidate delivery system.

    View details for DOI 10.1007/s11481-020-09981-0

    View details for PubMedID 33544324

  • Nanocarrier Vaccines for SARS-CoV-2. Advanced drug delivery reviews Machhi, J., Shahjin, F., Das, S., Patel, M., Abdelmoaty, M. M., Cohen, J. D., Singh, P. A., Baldi, A., Bajwa, N., Kumar, R., Vora, L. K., Patel, T. A., Oleynikov, M. D., Soni, D., Yeapuri, P., Mukadam, I., Chakraborty, R., Saksena, C. G., Herskovitz, J., Hasan, M., Oupicky, D., Das, S., Donnelly, R. F., Hettie, K. S., Chang, L., Gendelman, H. E., Kevadiya, B. D. 2021


    The SARS-CoV-2 global pandemic has seen rapid spread, disease mobidities and death associated with substantive social, economic and societal impact. Treatments rely on re-purposed antivirals and immune modulatory agents focusing on attenuating the acute respiratory distress syndrome. No curative therapies exist. Vaccines remain the best hope for disease control and elimination and the principal global effort with success now being realized. Herein, we summarize those developments with a focus on the role played by nanocarrier delivery.

    View details for DOI 10.1016/j.addr.2021.01.002

    View details for PubMedID 33428995

  • Targeting Contrast Agents With Peak Near-Infrared-II (NIR-II) Fluorescence Emission for Non-invasive Real-Time Direct Visualization of Thrombosis. Frontiers in molecular biosciences Hettie, K. S. 2021; 8: 670251


    Thrombosis within the vasculature arises when pathological factors compromise normal hemostasis. On doing so, arterial thrombosis (AT) and venous thrombosis (VT) can lead to life-threatening cardio-cerebrovascular complications. Unfortunately, the therapeutic window following the onset of AT and VT is insufficient for effective treatment. As such, acute AT is the leading cause of heart attacks and constitutes 80% of stroke incidences, while acute VT can lead to fatal therapy complications. Early lesion detection, their accurate identification, and the subsequent appropriate treatment of thrombi can reduce the risk of thrombosis as well as its sequelae. As the success rate of therapy of fresh thrombi is higher than that of old thrombi, detection of the former and accurate identification of lesions as thrombi are of paramount importance. Magnetic resonance imaging, x-ray computed tomography (CT), and ultrasound (US) are the conventional non-invasive imaging modalities used for the detection and identification of AT and VT, but these modalities have the drawback of providing only image-delayed indirect visualization of only late stages of thrombi development. To overcome such limitations, near-infrared (NIR, ca. 700-1,700 nm) fluorescence (NIRF) imaging has been implemented due to its capability of providing non-invasive real-time direct visualization of biological structures and processes. Contrast agents designed for providing real-time direct or indirect visualization of thrombi using NIRF imaging primarily provide peak NIR-I fluorescence emission (ca. 700-1,000 nm), which affords limited tissue penetration depth and suboptimal spatiotemporal resolution. To facilitate the enhancement of the visualization of thrombosis via providing detection of smaller, fresh, and/or deep-seated thrombi in real time, the development of contrast agents with peak NIR-II fluorescence emission (ca. 1000-1,700 nm) has been recently underway. Currently, however, most contrast agents that provide peak NIR-II fluorescence emissions that are purportedly capable of providing direct visualization of thrombi or their resultant occlusions actually afford only the indirect visualization of such because they only provide for the (i) measuring of the surrounding vascular blood flow and/or (ii) simple tracing of the vasculature. These contrast agents do not target thrombi or occlusions. As such, this mini review summarizes the extremely limited number of targeting contrast agents with peak NIR-II fluorescence emission developed for non-invasive real-time direct visualization of thrombosis that have been recently reported.

    View details for DOI 10.3389/fmolb.2021.670251

    View details for PubMedID 34026844

  • Near-infrared Fluorophores for Thrombosis Diagnosis and Therapy. Advanced therapeutics Sun, B. n., Hettie, K. S., Zhu, S. n. 2021; 4 (5)


    Thrombosis is an adverse physiological event wherein the resulting thrombus and thrombus-induced diseases collectively result in high morbidity and mortality rates. Currently, nano-medicines that incorporate fluorophores emitting in the near-infrared-I (NIR-I, 700-900 nm) spectral region into their systems have been adopted to afford thrombosis theranostics. However, several unsolved problems such as limited penetration depth and image quality severely impede further applications of such nano-medicine systems. Fortunately, the ability to incorporate fluorophores emitting in the NIR-II (1000-1700 nm) window into nano-medicine systems can unambiguously identify biological processes with high signal-to-noise, deep tissue penetration depth, and high image resolution. Considering the inherently favorable properties of NIR-II fluorophores, we believe such have enormous potential to quickly become incorporated into nano-medicine systems for thrombosis theranostics. In this review, we i) discuss the development of NIR fluorescence as an imaging modality and fluorescent agents; ii) comprehensively summarize the recent development of NIR-I fluorophore-based nano-medicine systems for thrombosis theranostics; iii) highlight the state-of-the-art NIR-II fluorophores that have been designed for the specific purpose of affording thrombotic diagnosis; iv) speculate on possible forward avenues for the use of NIR-II fluorophores towards thrombosis diagnosis and therapy; and v) discuss the potential for their clinical translation.

    View details for DOI 10.1002/adtp.202000278

    View details for PubMedID 33997270

    View details for PubMedCentralID PMC8115206

  • Off-Peak Near-Infrared-II (NIR-II) Bioimaging of an Immunoconjugate Having Peak Fluorescence Emission in the NIR-I Spectral Region for Improving Tumor Margin Delineation ACS APPLIED BIO MATERIALS Hettie, K. S., Teraphongphom, N., Ertsey, R., Chin, F. T. 2020; 3 (12): 8658–66
  • Targeting intracranial patient-derived glioblastoma (GBM) with a NIR-I fluorescent immunoconjugate for facilitating its image-guided resection RSC ADVANCES Hettie, K. S., Teraphongphom, N., Ertsey, R. D., Rosenthal, E. L., Chin, F. T. 2020; 10 (69): 42413–22

    View details for DOI 10.1039/d0ra07245a

    View details for Web of Science ID 000592897600049

  • An activatable NIR fluorescent rosol for selectively imaging nitroreductase activity SENSORS AND ACTUATORS B-CHEMICAL Klockow, J. L., Hettie, K. S., LaGory, E. L., Moon, E., Giaccia, A. J., Graves, E. E., Chin, F. T. 2020; 306
  • Multiplexed NIR-II Probes for Lymph Node-Invaded Cancer Detection and Imaging-Guided Surgery. Advanced materials (Deerfield Beach, Fla.) Tian, R., Ma, H., Zhu, S., Lau, J., Ma, R., Liu, Y., Lin, L., Chandra, S., Wang, S., Zhu, X., Deng, H., Niu, G., Zhang, M., Antaris, A. L., Hettie, K. S., Yang, B., Liang, Y., Chen, X. 2020: e1907365


    Tumor-lymph node (LN) metastasis is the dominant prognostic factor for tumor staging and therapeutic decision-making. However, concurrently visualizing metastasis and performing imaging-guided lymph node surgery is challenging. Here, a multiplexed-near-infrared-II (NIR-II) is reported in vivo imaging system using nonoverlapping NIR-II probes with markedly suppressed photon scattering and zero-autofluorescence, enabling visualization of the metastatic tumor and the tumor metastatic proximal LNs resection. A bright and tumor-seeking donor-acceptor-donor (D-A-D) dye, IR-FD, is screened for primary/metastatic tumor imaging in the NIR-IIa (1100-1300 nm) window. This optimized D-A-D dye exhibits greatly improved quantum yield of organic D-A-D fluorophores in aqueous solutions (6.0%) and good in vivo performance. Ultrabright PbS/CdS core/shell quantum dots (QDs) with dense polymer coating are used to visualize cancer-invaded sentinel LNs in the NIR-IIb (>1500 nm) window. Compared to clinically used indocyanine green, the QDs show superior brightness and photostability (no obvious bleaching even after continuous laser irradiation for 5 h); thus, only a picomolar dose is required for sentinel LNs detection. This combination of dual-NIR-II image-guided surgery can be performed under bright light, adding to its convenience and appeal in clinical use.

    View details for DOI 10.1002/adma.201907365

    View details for PubMedID 32022975

  • Targeting intracranial patient-derived glioblastoma (GBM) with a NIR-I fluorescent immunoconjugate for facilitating its image-guided resection. RSC advances Hettie, K. S., Teraphongphom, N. T., Ertsey, R. D., Rosenthal, E. L., Chin, F. T. 2020; 10 (69): 42413–22


    Glioblastoma multiforme (GBM) is the most aggressive form of primary brain tumor type and is associated with a high mortality rate borne out of such affording a survival rate of only 15 months. GBM aggressiveness is associated with the overexpression of epidermal growth factor receptor (EGFR) and its mutants. Targeting GBM with therapeutics is challenging because the blood-brain barrier (BBB) permits primarily select small-molecule entities across its semipermeable blockade. However, recent preclinical data suggest that large biomolecules, such as the anti-EGFR antibody therapeutic, cetuximab, could be capable of bypassing the BBB despite the relative enormity of its size. As such, we set forth to establish the feasibility of utilizing an EGFR-targeting near-infrared-I (NIR-I) fluorescent construct in the form of an immunoconjugate (cetuxmimab-IRDye800) to achieve visual differentiation between diseased brain tissue arising from a low-passage patient-derived GBM cell line (GBM39) and healthy brain tissue via utilizing orthotopic intracranial murine GBM39 tumor models for in vivo and ex vivo evaluation such that by doing so would establish proof of concept for ultimately facilitating its in vivo fluorescence-guided resection and ex vivo surgical back-table pathological confirmation in the clinic. As anticipated, we were not capable of distinguishing between malignant tumor tissue and healthy tissue in resected intact and slices of whole brain ex vivo under white-light illumination (WLI) due to both the diseased tissue and healthy tissue appearing virtually identical to the unaided eye. However, we readily observed over an average 6-fold enhancement in the fluorescence emission in the resected intact whole brain ex vivo when performing NIR-I fluorescence imaging (FLI) on the cohort of GBM39 tumor models that were administered the immunoconjugate compared to controls. In all, we laid the initial groundwork for establishing that NIR-I fluorescent immunoconjugates (theranostics) such as cetuximab-IRDye800 can bypass the BBB to visually afford GBM39 tumor tissue differentiation for its image-guided surgical removal.

    View details for DOI 10.1039/d0ra07245a

    View details for PubMedID 33391732

    View details for PubMedCentralID PMC7747479

  • An Activatable NIR Fluorescent Rosol for Selectively Imaging Nitroreductase Activity. Sensors and actuators. B, Chemical Klockow, J. L., Hettie, K. S., LaGory, E. L., Moon, E. J., Giaccia, A. J., Graves, E. E., Chin, F. T. 2020; 306


    Hypoxia (pO2 ≤ ~1.5%) is an important characteristic of tumor microenvironments that directly correlates with resistance against first-line therapies and tumor proliferation/infiltration. The ability to accurately identify hypoxic tumor cells/tissue could afford tailored therapeutic regimens for personalized treatment, development of more-effective therapies, and discerning the mechanisms underlying disease progression. Fluorogenic constructs identifying aforesaid cells/tissue operate by targeting the bioreductive activity of primarily nitroreductases (NTRs), but collectively present photophysical and/or physicochemical shortcomings that could limit effectiveness. To overcome these limitations, we present the rational design, development, and evaluation of the first activatable ultracompact xanthene core-based molecular probe (NO 2 -Rosol) for selectively imaging NTR activity that affords an "OFF-ON" near-infrared (NIR) fluorescence response (> 700 nm) alongside a remarkable Stokes shift (> 150 nm) via NTR activity-facilitated modulation to its energetics whose resultant interplay discontinues an intramolecular d-PET fluorescence-quenching mechanism transpiring between directly-linked electronically-uncoupled π-systems comprising its components. DFT calculations guided selection of a suitable fluorogenic scaffold and nitroaromatic moiety candidate that when adjoined could (i) afford such photophysical response upon bioreduction by upregulated NTR activity in hypoxic tumor cells/tissue and (ii) employ a retention mechanism strategy that capitalizes on an inherent physical property of the NIR fluorogenic scaffold for achieving signal amplification. NO 2 -Rosol demonstrated 705 nm NIR fluorescence emission and 157 nm Stokes shift, selectivity for NTR over relevant bioanalytes, and a 28-/12-fold fluorescence enhancement in solution and between cells cultured under different oxic conditions, respectively. In establishing feasibility for NO 2 -Rosol to provide favorable contrast levels in solutio/vitro, we anticipate NO 2 -Rosol doing so in preclinical studies.

    View details for DOI 10.1016/j.snb.2019.127446

    View details for PubMedID 32265579

    View details for PubMedCentralID PMC7138224

  • Near-Infrared Fluorescent Rosol Dye Tailored toward Lymphatic Mapping Applications ANALYTICAL CHEMISTRY Hettie, K. S., Klockow, J. L., Glass, T. E., Chin, F. T. 2019; 91 (4): 3110–17


    An optical molecular imaging contrast agent that is tailored toward lymphatic mapping techniques implementing near-infrared (NIR) fluorescence image-guided navigation in the planning and surgical treatment of cancers would significantly aid in enabling the real-time visualization of the potential metastatic tumor-draining lymph node(s) for their needed surgical biopsy and/or removal, thereby ensuring unmissed disease to prevent recurrence and improve patient survival rates. Here, the development of the first NIR fluorescent rosol dye (THQ-Rosol) tailored to overcome the limitations arising from the suboptimal properties of the generic molecular fluorescent dyes commonly used for such applications is described. In developing THQ-Rosol, we prepared a progressive series of torsionally restrictive N-substituted non-NIR fluorescent rosol dyes based on density functional theory (DFT) calculations, wherein we discerned high correlations amongst their calculated energetics, modeled N-C3' torsion angles, and evaluated properties. We leveraged these strong relationships to rationally design THQ-Rosol, wherein DFT calculations inspired an innovative approach and synthetic strategy to afford an uncharged xanthene core-based scaffold/molecular platform with an aptly elevated p Ka value alongside NIR fluorescence emission (ca.700-900 nm). THQ-Rosol exhibited 710 nm NIR fluorescence emission, a 160 nm Stokes shift, robust photostability, and an aptly elevated p Ka value (5.85) for affording pH-insensitivity and optimal contrast upon designed use. We demonstrated the efficacy of THQ-Rosol for lymphatic mapping with in vitro and in vivo studies, wherein it revealed timely tumor drainage and afforded definitive lymph node visualization upon its administration and accumulation. THQ-Rosol serves as a proof-of-concept for the effective tailoring of an uncharged xanthene core-based scaffold/molecular platform toward a specific imaging application using rational design.

    View details for PubMedID 30669835

  • Albumin-chaperoned cyanine dye yields superbright NIR-II fluorophore with enhanced pharmacokinetics. Science advances Tian, R. n., Zeng, Q. n., Zhu, S. n., Lau, J. n., Chandra, S. n., Ertsey, R. n., Hettie, K. S., Teraphongphom, T. n., Hu, Z. n., Niu, G. n., Kiesewetter, D. O., Sun, H. n., Zhang, X. n., Antaris, A. L., Brooks, B. R., Chen, X. n. 2019; 5 (9): eaaw0672


    NIR-II fluorescence imaging greatly reduces scattering coefficients for nearly all tissue types at long wavelengths, benefiting deep tissue imaging. However, most of the NIR-II fluorophores suffer from low quantum yields and/or short circulation time that limit the quality of NIR-II imaging. Here, we engineered a supramolecular assembly of protein complex with lodged cyanine dyes to produce a brilliant NIR-II fluorophore, providing a NIR-II quantum yield of 21.2% with prolonged circulation time. Computational modeling revealed the mechanism for fluorescence enhancement and identified key parameters governing albumin complex for NIR-II fluorophores. Our complex afforded high-resolution microvessel imaging, with a 3-hour imaging window compared to 2 min for free dye alone. Furthermore, the complexation strategy was applied to an antibody-derived assembly, offering high-contrast tumor imaging without affecting the targeting ability of the antibody. This study provides a facile strategy for producing high-performance NIR-II fluorophores by chaperoning cyanine dyes with functional proteins.

    View details for DOI 10.1126/sciadv.aaw0672

    View details for PubMedID 31548981

    View details for PubMedCentralID PMC6744268