Engineered gp120 immunogens that elicit VRC01-like antibodies by vaccination

Background: One of the great challenges for an HIV vaccine is to elicit broadly neutralizing antibodies specific for conserved epitopes from which the virus cannot easily escape. The CD4 binding site is one such epitope against which several antibodies (e.g. b12, VRC01) have been isolated. In macaques infected with SHIV, passive immunization with these CD4-directed neutralizing antibodies fails to control the virus, but prophylactic administration is highly protective. Similarly, patients who generate neutralizing antibodies over the course of an HIV infection derive no clinical benefit from them, but eliciting such antibodies prophylactically by vaccination may prevent the virus from establishing its lethal foothold

An engineered protein antagonist of K-Ras/B-Raf interaction

Ras is at the hub of signal transduction pathways controlling cell proliferation and survival. Its mutants, present in about 30% of human cancers, are major drivers of oncogenesis and render tumors unresponsive to standard therapies. Here we report the engineering of a protein scaffold for preferential binding to K-Ras G12D. This is the first reported inhibitor to achieve nanomolar affinity while exhibiting specificity for mutant over wild type (WT) K-Ras. Crystal structures of the protein R11.1.6 in complex with K-Ras WT and K-Ras G12D offer insight into the structural basis for specificity, highlighting differences in the switch I conformation as the major defining element in the higher affinity interaction. R11.1.6 directly blocks interaction with Raf and reduces signaling through the Raf/MEK/ERK pathway. Our results support greater consideration of the state of switch I and provide a novel tool to study Ras biology. Most importantly, this work makes an unprecedented contribution to Ras research in inhibitor development strategy by revealing details of a targetable binding surface. Unlike the polar interfaces found for Ras/effector interactions, the K-Ras/R11.1.6 complex reveals an extensive hydrophobic interface that can serve as a template to advance the development of high affinity, non-covalent inhibitors of K-Ras oncogenic mutants.National Institutes of Health (U.S.) (Grant 5-R01-CA096504-15

Single cells from human primary colorectal tumors exhibit polyfunctional heterogeneity in secretions of ELR+ CXC chemokines

Cancer is an inflammatory disease of tissue that is largely influenced by the interactions between multiple cell types, secreted factors, and signal transduction pathways. While single-cell sequencing continues to refine our understanding of the clonotypic heterogeneity within tumors, the complex interplay between genetic variations and non-genetic factors ultimately affects therapeutic outcome. Much has been learned through bulk studies of secreted factors in the tumor microenvironment, but the secretory behavior of single cells has been largely uncharacterized. Here we directly profiled the secretions of ELR+ CXC chemokines from thousands of single colorectal tumor and stromal cells, using an array of subnanoliter wells and a technique called microengraving to characterize both the rates of secretion of several factors at once and the numbers of cells secreting each chemokine. The ELR+ CXC chemokines are highly redundant, pro-angiogenic cytokines that signal via the CXCR1 and CXCR2 receptors, influencing tumor growth and progression. We find that human primary colorectal tumor and stromal cells exhibit polyfunctional heterogeneity in the combinations and magnitudes of secretions for these chemokines. In cell lines, we observe similar variance: phenotypes observed in bulk can be largely absent among the majority of single cells, and discordances exist between secretory states measured and gene expression for these chemokines among single cells. Together, these measures suggest secretory states among tumor cells are complex and can evolve dynamically. Most importantly, this study reveals new insight into the intratumoral phenotypic heterogeneity of human primary tumors.Janssen Pharmaceutical Ltd.National Cancer Institute (U.S.) (Cancer Center Support (Core) Grant P30-CA14051)National Science Foundation (U.S.). Graduate Research FellowshipSingapore. Agency for Science, Technology and ResearchSwiss National Science Foundation (Fellowship for Advanced Researchers PA00P3 139659

Theranostic pretargeted radioimmunotherapy of colorectal cancer xenografts in mice using picomolar affinity 86Y- or 177Lu-DOTA-Bn binding scFv C825/GPA33 IgG bispecific immunoconjugates

Purpose: GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pretargeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn–(radiolanthanide metal) complex. Methods: PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent, and the C825 haptens [superscript 177]Lu-or [superscript 86]Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model. Results: Using optimized PRIT, therapeutic indices (TIs) for tumor radiation-absorbed dose of 73 (tumor/blood) and 12 (tumor/kidney) were achieved. Estimated absorbed doses (cGy/MBq) to tumor, blood, liver, spleen, and kidney for single-cycle PRIT were 65.8, 0.9 (TI 73), 6.3 (TI 10), 6.6 (TI 10), and 5.3 (TI 12), respectively. Two cycles of PRIT (66.6 or 111 MBq [superscript 177]Lu-DOTA-Bn) were safe and effective, with a complete response of established s.c. tumors (100 – 700 mm³) in nine of nine mice, with two mice alive without recurrence at >140 days. Tumor log kill in this model was estimated to be 2.1 – 3.0 based on time to 500-mm³ tumor recurrence. In addition, PRIT dosimetry/diagnosis was performed by PET imaging of the positron-emitting DOTA hapten [superscript 86]Y-DOTA-Bn. Conclusion: We have developed anti-GPA33 PRIT as a triplestep theranostic strategy for preclinical detection, dosimetry, and safe targeted radiotherapy of established human colorectal mouse xenografts.National Institute of Mental Health (U.S.) (Grant R01-CA-101830

Pathways of cellular internalisation of liposomes delivered siRNA and effects on siRNA engagement with target mRNA and silencing in cancer cells

Design of an efficient delivery system is a generally recognised bottleneck in translation of siRNA technology into clinic. Despite research efforts, cellular processes that determine efficiency of siRNA silencing achieved by different delivery formulations remain unclear. Here, we investigated the mechanism(s) of cellular internalisation of a model siRNA-loaded liposome system in a correlation to the engagement of delivered siRNA with its target and consequent silencing by adopting siRNA molecular beacon technology. Probing of cellular internalisation pathways by a panel of pharmacological inhibitors indicated that clathrin-mediated (dynamin-dependent) endocytosis, macropinocytosis (dynamine independent), and cell membrane cholesterol dependent process(es) (clathrin and caveolea-independent) all play a role in the siRNA-liposomes internalization. The inhibition of either of these entry routes was, in general, mirrored by a reduction in the level of siRNA engagement with its target mRNA, as well as in a reduction of the target gene silencing. A dramatic increase in siRNA engagement with its target RNA was observed on disruption of endosomal membrane (by chloroquine), accompanied with an increased silencing. The work thus illustrates that employing molecular beacon siRNA technology one can start to assess the target RNA engagement – a stage between initial cellular internalization and final gene silencing of siRNA delivery systems

Rolling Adhesion of Yeast Engineered to Express Cell Adhesion Molecules

Selectins are cell adhesion molecules that mediate capture of leukocytes on vascular endothelium as an essential component of the inflammatory response. Here we describe a method for yeast surface display of selectins, together with a functional assay that measures rolling adhesion of selectin-expressing yeast on a ligand-coated surface. E-selectin-expressing yeast roll specifically on surfaces bearing sialyl-Lewisx ligands. Observation of yeast rolling dynamics at various stages of their life cycle indicates that the kinematics of yeast motion depends on the ratio of the bud radius to the parent radius (B/P). Large-budded yeast walk across the surface, alternately pivoting about bud and parent. Small-budded yeast wobble across the surface, with bud pivoting about parent. Tracking the bud location of budding yeast allows measurement of the angular velocity of the yeast particle. Comparison of translational and angular velocities of budding yeast demonstrates that selectin-expressing cells are rolling rather than slipping across ligand-coated surfaces

Fluorescent RNA cytosine analogue - an internal probe for detailed structure and dynamics investigations

The bright fluorescent cytosine analogue tCO stands out among fluorescent bases due to its virtually unquenched fluorescence emission in duplex DNA. However, like most reported base analogues, it has not been thoroughly characterized in RNA. We here report on the first synthesis and RNA-incorporation of tCO, and characterize its base-mimicking and fluorescence properties in RNA. As in DNA, we find a high quantum yield inside RNA duplexes (<?F> = 0.22) that is virtually unaffected by the neighbouring bases (?F = 0.20-0.25), resulting in an average brightness of 1900 M-1 cm-1. The average fluorescence lifetime in RNA duplexes is 4.3 ns and generally two lifetimes are required to fit the exponential decays. Fluorescence properties in ssRNA are defined by a small increase in average quantum yield (<?F > = 0.24) compared to dsRNA, with a broader distribution (?F = 0.17-0.34) and slightly shorter average lifetimes. Using circular dichroism, we find that the tCO-modified RNA duplexes form regular A-form helices and in UV-melting experiments the stability of the duplexes is only slightly higher than that of the corresponding natural RNA (<?T m> = + 2.3 °C). These properties make tCO a highly interesting fluorescent RNA base analogue for detailed FRET-based structural measurements, as a bright internal label in microscopy, and for fluorescence anisotropy measurements of RNA dynamics

Both intratumoral regulatory T cell depletion and CTLA-4 antagonism are required for maximum efficacy of anti-CTLA-4 antibodies

Anti-CTLA-4 antibodies have successfully elicited durable tumor regression in the clinic; however, long-term benefit is limited to a subset of patients for select cancer indications. The incomplete understanding of their mechanism of action has hindered efforts at improvement, with conflicting hypotheses proposing either antagonism of the CTLA-4:B7 axis or Fc effector-mediated regulatory T cell (Treg) depletion governing efficacy. Here, we report the engineering of a nonantagonistic CTLA-4 binding domain (b1s1e2) that depletes intratumoral Tregs as an Fc fusion. Comparison of b1s1e2-Fc to 9d9, an antagonistic anti-CTLA-4 antibody, allowed for interrogation of the separate contributions of CTLA-4 antagonism and Treg depletion to efficacy. Despite equivalent levels of intratumoral Treg depletion, 9d9 achieved more long-term cures than b1s1e2-Fc in MC38 tumors, demonstrating that CTLA-4 antagonism provided additional survival benefit. Consistent with prior reports that CTLA-4 antagonism enhances priming, treatment with 9d9, but not b1s1e2-Fc, increased the percentage of activated T cells in the tumor-draining lymph node (tdLN). Treg depletion with either construct was restricted to the tumor due to insufficient surface CTLA-4 expression on Tregs in other compartments. Through intratumoral administration of diphtheria toxin in Foxp3-DTR mice, we show that depletion of both intratumoral and nodal Tregs provided even greater survival benefit than 9d9, consistent with Treg-driven restraint of priming in the tdLN. Our data demonstrate that anti-CTLA-4 therapies require both CTLA-4 antagonism and intratumoral Treg depletion for maximum efficacy-but that potential future therapies also capable of depleting nodal Tregs could show efficacy in the absence of CTLA-4 antagonism