PhD Discussions: Srivatsava Viswanadha Venkata Naga Sai and Madhura Murar

Mechanical characterization of murine pluripotency dissolution

Srivatsava Viswanadha Venkata Naga Sai, Cellular and Molecular Mechanobiology Group

Mouse Embryonic Stem Cells (mESCs) can be maintained in ground/naïve state when grown in a defined N2B27 media with the supplementation of two inhibitors (2i) for MEK/Erk and GSK3β. Upon 2i withdrawal, mESCs exit naïve state and become functionally mature, acquiring differentiation competence. From a mechanical point of view, the instruction for initiating ground state exit is the integrin mediated mechano-sensing of extra cellular matrix (ECM). Although laminin has been found to be the pivotal ECM ligand for pluripotency dissolution, the down-stream mechano-responses accompanying its sensing, their spatio-temporal evolution and, their regulatory role in mESC maturation remain unclear. In this work, we combine mechanical measurements, functional characterization, and live cell imaging to unravel the role of mESCs-ECM interactions during naïve state exit and pluripotency dissolution. We employ a Rex1::GFPd2 expressing mESC line to monitor naïve state exit in real time, combined with a laminin-rich ECM environment. During naïve state exit, we observe a progressive increase in cell-ECM interaction, marked by an increase in traction forces, growth of focal adhesions, and the reorganization of the basal actin from a mesh-like network into an oriented filamentous morphology reminiscent of stress fibres. Furthermore, inhibition of non-muscle myosin-II using blebbistatin significantly delayed naïve state exit, suggesting a regulatory role of cell contractility in mESC maturation. We finally investigate the role of these changes in cell-ECM interactions in mediating nuclear mechanoresponses, and their influence in mESC pluripotency dissolution.

Dual peptide-mediated design of polymeric nanoparticles: towards precision prostate cancer targeting

Madhura Murar, Nanoscopy for Nanomedicine Group

A key bottleneck of current cancer treatments is the lack of selective targeting of cancer cells to reduce undesirable side-effects. Nanoparticles (NPs) allow for the design of ligand-coated materials that can fulfil this function but have not yet shown consistent clinical results to make the ‘magic bullet’ theory a paradigm. The inconsistencies may be due to a range of biological factors like differences in disease models or expression levels of target receptor(s). NP design parameters could play a key role in alleviating these inconsistencies and significantly influence the therapeutic efficacy. To further improve this efficacy, multi-ligand targeting strategies have been proposed, however, they remain controversial as they involve an intricate interplay between multitude of factors such as choice of ligands, their receptor binding affinities, NP surface densities, stoichiometric ratios etc., thereby calling for a thorough understanding of the impact of these properties to improve their targeting potential.

Within this context, we employ two cell targeting peptides (WQP and GE11) having different binding affinities to PSMA and EGFR receptors, which are known PCa biomarkers. We evaluate the effect of multivalency of low affinity WQP peptide over its monomeric form on PSMA targeting. We find that by increasing the valency of WQP on NP surface, we observe a higher cellular uptake of WQP-NPs over the monomeric form, attributing to a stronger avidity. Next, we assess the effect of two conjugation strategies using the high affinity GE11 peptide and study their impact on EGFR targeting in a systematic manner. We observe that conjugating GE11 peptide to PLGA-PEG polymer prior to NP formulation (pre-conjugation) allows for a higher and more controlled GE11 content on NP surface than conjugating it to formulated PLGA-PEG NPs (post-conjugation), consequently leading to a higher cellular uptake.

Based on these findings, we report a synthetic strategy for dual peptide-NPs with systematically varied properties, specifically surface valencies and ratios, and establish their impact on selective targeting in a prostate cancer (PCa) model. First, we study the impact of peptide valencies on NP surface of dual NPs in comparison to single peptide-NPs on the selective cellular uptake in different PCa cell lines. Once we establish optimal surface valency, we check the effect of different surface peptide ratios on cellular uptake and determine the optimal ratio for enhanced targeting of only those cells over-expressing both receptors, by the virtue of improved selectivity. Somewhat counterintuitively, we observe an increase in tumor cell uptake of NPs with lower peptide density, which can be attributed to improved surface distribution of the peptide, allowing for an enhanced availability to react with target receptor. This increase in uptake is a result of the two peptides acting in co-operation, as opposed to simply an additive effect. Our findings demonstrate that through refined design and well-characterized NP formulations, dual-peptide targeted nanosystems hold potential to provide precise cancer treatments.

This PhD Discussion session will be held at Tower I, 11th floor Baobab room, at 10:00am.

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