The pH-Low Insertion Peptide (pHLIP) offers the potential to deliver drugs selectively to the cytoplasm of cancer cells based on tumor acidosis. The WT pHLIP inserts into membrane with a pH50 of 6.1 while most solid tumors have extracellular pH (pHe) of 6.5-7.0. To close this gap, a SAR study was carried out to search for pHLIP variants with improved pH-response. We learned that (a) replacing Asp25 with α-aminoadipic acid (Aad) adjusts the pH50 to 6.74, matching average tumor acidity, and (b) replacing Asp14 with γ-carboxyglutamic acid (Gla) increases the sharpness of pH-response (i.e. transition over 0.5 instead of 1 pH unit). These effects are additive — the Asp14Gla/Asp25Aad double variant shows a pH50 of 6.79, with sharper transition than Asp25Aad. Further, the advantage of the double variant over WT pHLIP in terms of cargo delivery was demonstrated in turn-on fluorescence assays and anti-proliferation studies (using paclitaxel as cargo) in A549 lung cancer cells at pH 6.6.

Single-walled carbon nanotubes are of interest in biomedicine for imaging and molecular sensing applications, and as shuttles for various cargos such as chemotherapeutic drugs, peptides, proteins, and oligonucleotides. Carbon nanotube surface chemistry can be modulated for subcellular targeting while preserving photoluminescence for label-free visualization in complex biological environments, making them attractive materials for such studies. The cell nucleus is a potential target for many pathologies including cancer and infectious diseases. Understanding mechanisms of nanomaterial delivery to the nucleus may facilitate diagnostics, drug development, and gene editing tools. Currently, there are no systematic studies to understand how these nanomaterials gain access to the nucleus. Herein, we developed carbon nanotube-based hybrid material which elucidated a distinct mechanism of nuclear translocation of a nanomaterial in cultured cells. We developed a nuclear-targeted nanotube via cloaking photoluminescent single-walled carbon nanotubes in a guanidinium-functionalized helical polycarbodiimide. We found that the nuclear entry of the nanotubes was mediated by the import receptor importin β without the aid of importin α and not by the more common importin α/β pathway. Additionally, the nanotube photoluminescence exhibited distinct red-shifting upon entry to the nucleus, potentially functioning as a reporter of the importin β-mediated nuclear transport process. This work delineates a non-canonical mechanism for nanomaterial delivery to the nucleus and provides a reporter for the study of nucleus-related pathologies.

We describe three new strategies for determining heterogeneous reaction rates using photomicroscopy to measure the rate of retreat of metal surfaces: (i) spheres in a stirred solution, (ii) microscopic powder in an unstirred solution, and (iii) spheres on a rotating shaft. The strategies are applied to indium-mediated allylation (IMA), which is a powerful tool for synthetic chemists because of its stereoselectivity, broad applicability, and high yields. The rate-limiting step of IMA, reaction of allyl halides at indium metal surfaces, is shown to be fast, with a minimum value of the heterogeneous rate constant of 1 × 10(-2) cm/s, an order of magnitude faster than the previously determined minimum value. The strategies described here can be applied to any reaction in which the surface is retreating or advancing, thereby broadening the applicability of photomicroscopy to measuring heterogeneous reaction kinetics.

Polycarbodiimide cloaking of photoluminescent single-walled carbon nanotubes modulates their surface chemistry, protein corona, and uptake in cancer cells.