Clinical Focus

  • Fellow
  • Hematology
  • Medical Oncology

Professional Education

  • Fellowship, Stanford University School of Medicine, Hematology and Medical Oncology (2024)
  • Board Certification, American Board of Internal Medicine, Internal Medicine (2021)
  • Residency, Stanford University School of Medicine, Internal Medicine (2021)
  • MD, Duke University School of Medicine (2018)
  • PhD, Duke University School of Medicine, Pharmacology (2018)
  • MA, Harvard University, Chemistry (2009)
  • BA, Harvard University, Chemistry and Physics (2009)

All Publications

  • Development of Circulating Tumor DNA (ctDNA) for Molecular Measurable Residual Disease (MRD) in Acute Myeloid Leukemia (AML) Gunaratne, R., Zhou, C., Tai, J. W., Schwede, M., Tanaka, K., Alkaitis, M., Yin, R., Sworder, B. J., Mannis, G., Majeti, R., Khodadoust, M. S., Kurtz, D. M., Zhang, T. Y. AMER SOC HEMATOLOGY. 2023
  • Combining Heparin and a FX/Xa Aptamer to Reduce Thrombin Generation in Cardiopulmonary Bypass and COVID-19. Nucleic acid therapeutics Chabata, C. V., Frederiksen, J. W., Olson, L. B., Naqvi, I. A., Hall, S. E., Gunaratne, R., Kraft, B. D., Que, L. G., Chen, L., Sullenger, B. A. 1800


    Known limitations of unfractionated heparin (UFH) have encouraged the evaluation of anticoagulant aptamers as alternatives to UFH in highly procoagulant settings such as cardiopulmonary bypass (CPB). Despite progress, these efforts have not been totally successful. We take a different approach and explore whether properties of an anticoagulant aptamer can complement UFH, rather than replace it, to address shortcomings with UFH use. Combining RNA aptamer 11F7t, which targets factor X/Xa, with UFH (or low molecular weight heparin) yields a significantly enhanced anticoagulant cocktail effective in normal and COVID-19 patient blood. This aptamer-UFH combination (1) supports continuous circulation of human blood through an ex vivo membrane oxygenation circuit, as is required for patients undergoing CPB and COVID-19 patients requiring extracorporeal membrane oxygenation, (2) allows for a reduced level of UFH to be employed, (3) more effectively limits thrombin generation compared to UFH alone, and (4) is rapidly reversed by the administration of protamine sulfate, the standard treatment for reversing UFH clinically following CPB. Thus, the combination of factor X/Xa aptamer and UFH has significantly improved anticoagulant properties compared to UFH alone and underscores the potential of RNA aptamers to improve medical management of acute care patients requiring potent yet rapidly reversible anticoagulation.

    View details for DOI 10.1089/nat.2021.0077

    View details for PubMedID 35021888

  • Utilizing nucleic-acid scavengers (NASs) to inhibit proinflammatory and proinvasive signaling in triple-negative breast cancer Eteshola, E. O., Naqvi, I. A., Gunaratne, R., Moreno, A., Nair, S. K., Sullenger, B. A. AMER ASSOC CANCER RESEARCH. 2019
  • Emerging applications of aptamers for anticoagulation and hemostasis. Current opinion in hematology Chabata, C. V., Frederiksen, J. W., Sullenger, B. A., Gunaratne, R. 2018; 25 (5): 382-388


    Since the selection of the first thrombin-binding aptamer in 1992, the use of nucleic acid aptamers to target specific coagulation factors has emerged as a valuable approach for generating novel anticoagulant and procoagulant therapeutics. Herein, we highlight the most recent discoveries involving application of aptamers for those purposes.Learning from the successes and pitfalls of the FIXa-targeting aptamer pegnivacogin in preclinical and clinical studies, the latest efforts to develop antidote-controllable anticoagulation strategies for cardiopulmonary bypass that avoid unfractionated heparin involve potentiation of the exosite-binding factor X (FX)a aptamer 11F7t by combination with either a small molecule FXa catalytic site inhibitor or a thrombin aptamer. Recent work has also focused on identifying aptamer inhibitors of contact pathway factors such as FXIa and kallikrein, which may prove to be well tolerated and effective antithrombotic agents in certain clinical settings. Finally, new approaches to develop procoagulant aptamers to control bleeding associated with hemophilia and other coagulopathies involve targeting activated protein C and tissue plasminogen activator.Overall, these recent findings exemplify the versatility of aptamers to modulate a variety of procoagulant and anticoagulant factors, along with their capacity to be used complementarily with other aptamers or drugs for wide-ranging applications.

    View details for DOI 10.1097/MOH.0000000000000452

    View details for PubMedID 30015643

  • Combination of aptamer and drug for reversible anticoagulation in cardiopulmonary bypass. Nature biotechnology Gunaratne, R., Kumar, S., Frederiksen, J. W., Stayrook, S., Lohrmann, J. L., Perry, K., Bompiani, K. M., Chabata, C. V., Thalji, N. K., Ho, M. D., Arepally, G., Camire, R. M., Krishnaswamy, S., Sullenger, B. A. 2018; 36 (7): 606-613


    Unfractionated heparin (UFH), the standard anticoagulant for cardiopulmonary bypass (CPB) surgery, carries a risk of post-operative bleeding and is potentially harmful in patients with heparin-induced thrombocytopenia-associated antibodies. To improve the activity of an alternative anticoagulant, the RNA aptamer 11F7t, we solved X-ray crystal structures of the aptamer bound to factor Xa (FXa). The finding that 11F7t did not bind the catalytic site suggested that it could complement small-molecule FXa inhibitors. We demonstrate that combinations of 11F7t and catalytic-site FXa inhibitors enhance anticoagulation in purified reaction mixtures and plasma. Aptamer-drug combinations prevented clot formation as effectively as UFH in human blood circulated in an extracorporeal oxygenator circuit that mimicked CPB, while avoiding side effects of UFH. An antidote could promptly neutralize the anticoagulant effects of both FXa inhibitors. Our results suggest that drugs and aptamers with shared targets can be combined to exert more specific and potent effects than either agent alone.

    View details for DOI 10.1038/nbt.4153

    View details for PubMedID 29863725

    View details for PubMedCentralID PMC6349032

  • Polymer-Mediated Inhibition of Pro-invasive Nucleic Acid DAMPs and Microvesicles Limits Pancreatic Cancer Metastasis. Molecular therapy : the journal of the American Society of Gene Therapy Naqvi, I., Gunaratne, R., McDade, J. E., Moreno, A., Rempel, R. E., Rouse, D. C., Herrera, S. G., Pisetsky, D. S., Lee, J., White, R. R., Sullenger, B. A. 2018; 26 (4): 1020-1031


    Nucleic acid binding polymers (NABPs) have been extensively used as vehicles for DNA and RNA delivery. More recently, we discovered that a subset of these NABPs can also serve as anti-inflammatory agents by capturing pro-inflammatory extracellular nucleic acids and associated protein complexes that promote activation of toll-like receptors (TLRs) in diseases such as lupus erythematosus. Nucleic-acid-mediated TLR signaling also facilitates tumor progression and metastasis in several cancers, including pancreatic cancer (PC). In addition, extracellular DNA and RNA circulate on or within lipid microvesicles, such as microparticles or exosomes, which also promote metastasis by inducing pro-tumorigenic signaling in cancer cells and pre-conditioning secondary sites for metastatic establishment. Here, we explore the use of an NABP, the 3rd generation polyamidoamine dendrimer (PAMAM-G3), as an anti-metastatic agent. We show that PAMAM-G3 not only inhibits nucleic-acid-mediated activation of TLRs and invasion of PC tumor cells in vitro, but can also directly bind extracellular microvesicles to neutralize their pro-invasive effects as well. Moreover, we demonstrate that PAMAM-G3 dramatically reduces liver metastases in a syngeneic murine model of PC. Our findings identify a promising therapeutic application of NABPs for combating metastatic disease in PC and potentially other malignancies.

    View details for DOI 10.1016/j.ymthe.2018.02.018

    View details for PubMedID 29550075

    View details for PubMedCentralID PMC6079560

  • Identifying protein kinase target preferences using mass spectrometry. American journal of physiology. Cell physiology Douglass, J., Gunaratne, R., Bradford, D., Saeed, F., Hoffert, J. D., Steinbach, P. J., Knepper, M. A., Pisitkun, T. 2012; 303 (7): C715-27


    A general question in molecular physiology is how to identify candidate protein kinases corresponding to a known or hypothetical phosphorylation site in a protein of interest. It is generally recognized that the amino acid sequence surrounding the phosphorylation site provides information that is relevant to identification of the cognate protein kinase. Here, we present a mass spectrometry-based method for profiling the target specificity of a given protein kinase as well as a computational tool for the calculation and visualization of the target preferences. The mass spectrometry-based method identifies sites phosphorylated in response to in vitro incubation of protein mixtures with active recombinant protein kinases followed by standard phosphoproteomic methodologies. The computational tool, called "PhosphoLogo," uses an information-theoretic algorithm to calculate position-specific amino acid preferences and anti-preferences from the mass-spectrometry data ( The method was tested using protein kinase A (catalytic subunit α), revealing the well-known preference for basic amino acids in positions -2 and -3 relative to the phosphorylated amino acid. It also provides evidence for a preference for amino acids with a branched aliphatic side chain in position +1, a finding compatible with known crystal structures of protein kinase A. The method was also employed to profile target preferences and anti-preferences for 15 additional protein kinases with potential roles in regulation of epithelial transport: CK2, p38, AKT1, SGK1, PKCδ, CaMK2δ, DAPK1, MAPKAPK2, PKD3, PIM1, OSR1, STK39/SPAK, GSK3β, Wnk1, and Wnk4.

    View details for DOI 10.1152/ajpcell.00166.2012

    View details for PubMedID 22723110

    View details for PubMedCentralID PMC3774550

  • Changes in the tension in dsDNA alter the conformation of RecA bound to dsDNA-RecA filaments. Nucleic acids research Conover, A. J., Danilowicz, C., Gunaratne, R., Coljee, V. W., Kleckner, N., Prentiss, M. 2011; 39 (20): 8833-43


    The RecA protein is an ATPase that mediates recombination via strand exchange. In strand exchange a single-stranded DNA (ssDNA) bound to RecA binding site I in a RecA/ssDNA filament pairs with one strand of a double-stranded DNA (dsDNA) and forms heteroduplex dsDNA in site I if homology is encountered. Long sequences are exchanged in a dynamic process in which initially unbound dsDNA binds to the leading end of a RecA/ssDNA filament, while heteroduplex dsDNA unbinds from the lagging end via ATP hydrolysis. ATP hydrolysis is required to convert the active RecA conformation, which cannot unbind, to the inactive conformation, which can unbind. If dsDNA extension due to RecA binding increases the dsDNA tension, then RecA unbinding must decrease tension. We show that in the presence of ATP hydrolysis decreases in tension induce decreases in length whereas in the absence of hydrolysis, changes in tension have no systematic effect. These results suggest that decreases in force enhance dissociation by promoting transitions from the active to the inactive RecA conformation. In contrast, increases in tension reduce dissociation. Thus, the changes in tension inherent to strand exchange may couple with ATP hydrolysis to increase the directionality and stringency of strand exchange.

    View details for DOI 10.1093/nar/gkr561

    View details for PubMedID 21768124

    View details for PubMedCentralID PMC3203582

  • Single-molecule studies of the stringency factors and rates governing the polymerization of RecA on double-stranded DNA. Nucleic acids research Feinstein, E., Danilowicz, C., Conover, A., Gunaratne, R., Kleckner, N., Prentiss, M. 2011; 39 (9): 3781-91


    RecA is a key protein in homologous recombination. During recombination, one single-stranded DNA (ssDNA) bound to site I in RecA exchanges Watson-Crick pairing with a sequence-matched ssDNA that was part of a double-stranded DNA molecule (dsDNA) bound to site II in RecA. After strand exchange, heteroduplex dsDNA is bound to site I. In vivo, direct polymerization of RecA on dsDNA through site I does not occur, though it does in vitro. The mechanisms underlying the difference have been unclear. We use single-molecule experiments to decouple the two steps involved in polymerization: nucleation and elongation. We find that elongation is governed by a fundamental clock that is insensitive to force and RecA concentration from 0.2 and 6 µM, though rates depend on ionic conditions. Thus, we can probe nucleation site stability by creating nucleation sites at high force and then measuring elongation as a function of applied force. We find that in the presence of ATP hydrolysis a minimum force is required for polymerization. The minimum force decreases with increasing RecA or ATP concentrations. We propose that force reduces the off-rate for nucleation site binding and that nucleation site stability is the stringency factor that prevents in vivo polymerization.

    View details for DOI 10.1093/nar/gkr013

    View details for PubMedID 21245047

    View details for PubMedCentralID PMC3089484

  • c-Abl mediates high NaCl-induced phosphorylation and activation of the transcription factor TonEBP/OREBP. FASEB journal : official publication of the Federation of American Societies for Experimental Biology Gallazzini, M., Yu, M. J., Gunaratne, R., Burg, M. B., Ferraris, J. D. 2010; 24 (11): 4325-35


    The transcription factor TonEBP/OREBP promotes cell survival during osmotic stress. High NaCl-induced phosphorylation of TonEBP/OREBP at tyrosine-143 was known to be an important factor in increasing its activity in cell culture. We now find that TonEBP/OREBP also is phosphorylated at tyrosine-143 in rat renal inner medulla, dependent on the interstitial osmolality. c-Abl seemed likely to be the kinase that phosphorylates TonEBP/OREBP because Y143 is in a consensus c-Abl phosphorylation site. We now confirm that, as follows. High NaCl increases c-Abl activity. Specific inhibition of c-Abl by imatinib, siRNA, or c-Abl kinase dead drastically reduces high NaCl-induced TonEBP/OREBP activity by reducing its nuclear location and transactivating activity. c-Abl associates with TonEBP/OREBP (coimmunoprecipitation) and phosphorylates TonEBP/OREBP-Y143 both in cell and in vitro. High NaCl-induced activation of ataxia telangiectasia mutated, previously known to contribute to activation of TonEBP/OREBP, depends on c-Abl activity. Thus, c-Abl is the kinase responsible for high NaCl-induced phosphorylation of TonEBP/OREBP-Y143, which contributes to its increased activity.

    View details for DOI 10.1096/fj.10-157362

    View details for PubMedID 20585028

    View details for PubMedCentralID PMC2974425

  • Study of force induced melting of dsDNA as a function of length and conformation. Journal of physics. Condensed matter : an Institute of Physics journal Danilowicz, C., Hatch, K., Conover, A., Ducas, T., Gunaratne, R., Coljee, V., Prentiss, M. 2010; 22 (41): 414106


    We measure the constant force required to melt double-stranded (ds) DNA as a function of length for lengths from 12 to 100,000 base pairs, where the force is applied to the 3'3' or 5'5' ends of the dsDNA. Molecules with 32 base pairs or fewer melt before overstretching. For these short molecules, the melting force is independent of the ends to which the force is applied and the shear force as a function of length is well described by de Gennes theory with a de Gennes length of less than 10 bp. Molecules with lengths of 500 base pairs or more overstretch before melting. For these long molecules, the melting force depends on the ends to which the force is applied. The melting force as a function of length increases even when the length exceeds 1000 bp, where the length dependence is inconsistent with de Gennes theory. Finally, we expand de Gennes melting theory to 3'5' pulling and compare the predictions with experimental results.

    View details for DOI 10.1088/0953-8984/22/41/414106

    View details for PubMedID 21386589

    View details for PubMedCentralID PMC4752207

  • Quantitative phosphoproteomic analysis reveals cAMP/vasopressin-dependent signaling pathways in native renal thick ascending limb cells. Proceedings of the National Academy of Sciences of the United States of America Gunaratne, R., Braucht, D. W., Rinschen, M. M., Chou, C. L., Hoffert, J. D., Pisitkun, T., Knepper, M. A. 2010; 107 (35): 15653-8


    Quantitative mass spectrometry was used to identify hormone-dependent signaling pathways in renal medullary thick ascending limb (mTAL) cells via phosphoproteomic analysis. Active transport of NaCl across the mTAL epithelium is accelerated by hormones that increase cAMP levels (vasopressin, glucagon, parathyroid hormone, and calcitonin). mTAL suspensions from rat kidneys were exposed (15 min) to a mixture of these four hormones. Tryptic phosphopeptides (immobilized metal affinity chromatography-enriched) were identified and quantified by mass spectrometry (LTQ-Orbitrap) using label-free methodology. We quantified a total of 654 phosphopeptides, of which 414 were quantified in three experimental pairs (hormone vs. vehicle). Of these phosphopeptides, 82% were statistically unchanged in abundance in response to the hormone mixture. In contrast, 48 phosphopeptides were significantly increased, whereas 28 were significantly decreased. The population of up-regulated phosphopeptides was highly enriched in basophilic kinase substrate motifs (AGC or calmodulin-sensitive kinase families), whereas the down-regulated sites were dominated by "proline-directed" motifs (cyclin-dependent or MAP kinase families). Bioinformatic classification uncovered overrepresentation of transmembrane transporters, protein phosphatase regulators, and cytoskeletal binding proteins among the regulated proteins. Immunoblotting with phospho-specific antibodies confirmed cAMP/vasopressin-dependent phosphorylation at Thr96, Ser126, and Ser874 of the Na(+):K(+):2Cl(-) cotransporter NKCC2, at Ser552 of the Na(+):H(+) exchanger NHE3, and at Ser552 of beta-catenin. Vasopressin also increased phosphorylation of NKCC2 at both Ser126 (more than fivefold) and Ser874 (more than threefold) in rats in vivo. Both sites were phosphorylated by purified protein kinase A during in vitro assays. These results support the view that, although protein kinase A plays a central role in mTAL signaling, additional kinases, including those that target proline-directed motifs, may be involved.

    View details for DOI 10.1073/pnas.1007424107

    View details for PubMedID 20713729

    View details for PubMedCentralID PMC2932563