The hydrophobicity of many chemotherapeutic agents usually results in their nonselective passive distribution into healthy cells and organs causing collateral toxicity. Ligand-targeted drugs (LTDs) are a promising class of targeted anticancer agents. The hydrophilicity of the targeting ligands in LTDs limits its nonselective passive tissue distribution and toxicity to healthy cells. In addition, the small size of LTDs allows for better tumor penetration, especially in the case of solid tumors. However, the short circulation half-life of LTDs, due to their hydrophilicity and small size, remains a significant challenge for achieving their full therapeutic potential. Therefore, extending the circulation half-life of targeted chemotherapeutic agents while maintaining their hydrophilicity and small size will represent a significant advance toward effective and safe cancer treatment. Here, we present a new approach for enhancing the safety and efficacy of targeted chemotherapeutic agents. By endowing hydrophobic chemotherapeutic agents with a targeting moiety and a hydrophilic small molecule that binds reversibly to the serum protein transthyretin, we generated small hydrophilic drug conjugates that displayed enhanced circulation half-life in rodents and selectivity to cancer cells. To the best of our knowledge, this is the first demonstration of a successful approach that maintains the small size and hydrophilicity of targeted anticancer agents containing hydrophobic payloads while at the same time extending their circulation half-life. This was demonstrated by the superior in vivo efficacy and lower toxicity of our conjugates in xenograft mouse models of metastatic prostate cancer.

This work describes the enhancement of a novel antitumor therapeutic platform that combines advantages from small-molecule drug conjugates (SMDCs) and antibody drug conjugates (ADCs). Valine− citrulline (VCit) dipeptide linkers are commonly used cathepsin B cleavable linkers for ADCs. However, the instability of these linkers in mouse serum makes translating efficacy data from mouse to human more challenging. Replacing the VCit linker with glutamic acid−valine−citrulline (EVCit) has been reported to enhance the stability of ADCs in mouse serum. However, the effect of EVCit linker on the stability of SMDCs has not been reported. Here, we report that incorporating the EVCit linker in prostate-specific membrane antigen-targeting SMDCs, equipped with the transthyretin ligand AG10, resulted in conjugates with lower toxicity, an extended half-life, and superior therapeutic efficacy to docetaxel in a xenograft mouse model of prostate cancer. This should make SMDCs' preclinical toxicity and efficacy data from mice more reliable for predicting human results.

Protein drugs hold great promise as therapeutics for a wide range of diseases. Unfortunately, one of the greatest challenges to be addressed during clinical development of protein therapeutics is their short circulation half-life. Several protein conjugation strategies have been developed for half-life extension. However, these strategies have limitations and there remains room for improvement. Here, we report a novel nature-inspired strategy for enhancing the in vivo half-life of proteins. Our strategy involves conjugating proteins to a hydrophilic small molecule that binds reversibly to the plasma protein, transthyretin. We show here that our strategy is effective in enhancing the pharmacokinetic and pharmacodynamic properties of human interleukin 2 in rats, potentially opening the door for more effective and safer cancer immunotherapies. To our knowledge, this is the first example of successful use of a small-molecule that not only extends the half-life but also maintains the smaller size, binding potency, and hydrophilicity of proteins.

Interactions with many clinically active therapeutic agents with deoxyribonucleic acid (DNA) are well studied and it expedites deciphering the structure of DNA and to investigate the pathological implication of those molecules in a living organism. The interaction of dextromethorphan hydrobromide (DEX) with calf thymus DNA (ct DNA) was studied employing UV absorption and fluorescence spectroscopic techniques. The binding affinity of DEX to DNA was calculated at different temperatures and the stoichiometry of binding was characterized to be about 1 dextromethorphan molecule per nucleotide. Hypochromic effect was found in the absorption spectra of dextromethorphan, and its wavelength had no shift in the presence of DNA indicating external binding mode of dextromethorphan to DNA. Quenching constants 3532 L/ mol and 12446L/ mol at 298 K and 308 K respectively with correlation co-efficient of 0.974 and 0.976, using SternVolmer equation and the quenching mechanism was found to be dynamic. Fluorescence spectroscopic results showed the quenching of fluorescence intensity of DEX in the presence of DNA, indicating the interaction between DEX and DNA. Based on this, hydrophobic interaction were found to play the dominating role in DEX-DNA binding and those binding forces also indicate the binding site of dextromethorphan to be in the minor groove of DNA.

Several investigations into the sites of action of opioid analgesics have utilized peripherally acting mu-opioid receptor antagonists (PAMORAs), which have been incorrectly assumed to possess limited permeability across the blood-brain barrier. Unfortunately, the poor pharmacokinetic properties of current PAMORAs have resulted in misunderstandings of the role of central nervous system and gastrointestinal tract in precipitating side effects such as opioid-induced constipation. Here, we develop a drug delivery approach for restricting the passage of small molecules across the blood-brain barrier. This allows us to develop naloxone- and oxycodone-based conjugates that display superior potency, peripheral selectivity, pharmacokinetics, and efficacy in rats compared to other clinically used PAMORAs. These probes allow us to demonstrate that the mu-opioid receptors in the central nervous system have a fundamental role in precipitating opioid-induced constipation. Therefore, our conjugates have immediate use as pharmacological probes and potential therapeutic agents for treating constipation and other opioid-related side effects.