Paul A. Wender

Conjugation of arginine oligomers to cyclosporin A facilitates topical delivery and inhibition of inflammation

Many systemically effective drugs such as cyclosporin A are ineffective topically because of their poor penetration into skin. To surmount this problem, we conjugated a heptamer of arginine to cyclosporin A through a pH-sensitive linker to produce R7–CsA. In contrast to unmodified cyclosporin A, which fails to penetrate skin, topically applied R7–CsA was efficiently transported into cells in mouse and human skin. R7–CsA reached dermal T lymphocytes and inhibited cutaneous inflammation. These data establish a general strategy for enhancing delivery of poorly absorbed drugs across tissue barriers and provide a new topical approach to the treatment of inflammatory skin disorders.

Synthesis at the molecular frontier

Driven by remarkable advances in the understanding of structure and reaction mechanisms, organic synthesis will be increasingly directed to producing bioinspired and newly designed molecules.

The design of guanidinium-rich transporters and their internalization mechanisms ☆

The ability of a drug or probe to cross a biological barrier has historically been viewed to be a function of its intrinsic physical properties. This view has largely restricted drug design and selection to agents within a narrow log P range. Molecular transporters offer a strategy to circumvent these restrictions. In the case of guanidinium-rich transporters (GRTs), a typically highly water-soluble conjugate is found to readily pass through the non-polar membrane of a cell and for some across tissue barriers. This activity opens a field of opportunities for the use of GRTs to enable delivery of polar and non-polar drugs or probes as well as to enhance uptake of those of intermediate polarity. The field of transporter enabled or enhanced uptake has grown dramatically in the last decade. Some GRT drug conjugates have been advanced into clinical trials. This review will provide an overview of recent work pertinent to the design and mechanism of uptake of GRTs.

Overcoming multidrug resistance of small-molecule therapeutics through conjugation with releasable octaarginine transporters

Many cancer therapeutic agents elicit resistance that renders them ineffective and often produces cross-resistance to other drugs. One of the most common mechanisms of resistance involves P-glycoprotein (Pgp)-mediated drug efflux. To address this problem, new agents have been sought that are less prone to inducing resistance and less likely to serve as substrates for Pgp efflux. An alternative to this approach is to deliver established agents as molecular transporter conjugates into cells through a mechanism that circumvents Pgp-mediated efflux and allows for release of free drug only after cell entry. Here we report that the widely used chemotherapeutic agent Taxol, ineffective against Taxol-resistant human ovarian cancer cell lines, can be incorporated into a releasable octaarginine conjugate that is effective against the same Taxol-resistant cell lines. It is significant that the ability of the Taxol conjugates to overcome Taxol resistance is observed both in cell culture and in animal models of ovarian cancer. The generality and mechanistic basis for this effect were also explored with coelenterazine, a Pgp substrate. Although coelenterazine itself does not enter cells because of Pgp efflux, its octaarginine conjugate does so readily. This approach shows generality for overcoming the multidrug resistance elicited by small-molecule cancer chemotherapeutics and could improve the prognosis for many patients with cancer and fundamentally alter search strategies for novel therapeutic agents that are effective against resistant disease.

Molecular transporters for peptides: delivery of a cardioprotective ϵPKC agonist peptide into cells and intact ischemic heart using a transport system, R7

BACKGROUND Recently, we reported a novel oligoguanidine transporter system, polyarginine (R(7)), which, when conjugated to spectroscopic probes (e.g., fluorescein) and drugs (e.g., cyclosporin A), results in highly water-soluble conjugates that rapidly enter cells and tissues. We report herein the preparation of the first R(7) peptide conjugates and a study of their cellular and organ uptake and functional activity. The octapeptide (psi)(epsilon)RACK was selected for this study as it is known to exhibit selective epsilon protein kinase C isozyme agonist activity and to reduce ischemia-induced damage in cardiomyocytes. However, (psi)(epsilon)RACK is not cell-permeable. RESULTS Here we show that an R(7)-(psi)(epsilon)RACK conjugate readily enters cardiomyocytes, significantly outperforming (psi)(epsilon)RACK conjugates of the transporters derived from HIV Tat and from Antennapedia. Moreover, R(7)-(psi)(epsilon)RACK conjugate reduced ischemic damage when delivered into intact hearts either prior to or after the ischemic insult. CONCLUSIONS Our data suggest that R(7) converts a peptide lead into a potential therapeutic agent for the ischemic heart.

Molecular Transporters: Synthesis of Oligoguanidinium Transporters and Their Application to Drug Delivery and Real-Time Imaging

Biological barriers are of fundamental importance in understanding evolution, systems biology, and the prevention, ACHTUNGTRENNUNGdetection, and treatment of disease. Methods to enhance or ACHTUNGTRENNUNGcontrol selective passage of therapeutics or probes into or through such barriers are a key to the future of drug therapy and many fundamental advances in science. Research in this area offers the possibility of improving the bioavailability of existing drugs, enabling the delivery of new cargoes and drug candidates (e.g. , RNAi, shRNA, DNA, proteins, imaging agents, and sensors), accessing difficult sites (e.g. , the blood–brain barrier and eye), achieving tissueor cell-selective entry, modulating the activity of agents and controlling their release, and avoiding or minimizing toxicity and metabolism—all of which could dramatically enhance human therapy and our fundamental understanding of living systems. Biological barriers have evolved to perform many functions. They provide compartmentalization and are critical to the ACHTUNGTRENNUNGselective import, concentration, and export of compounds needed for sustenance, protection, movement, adherence, and replication. However, these very functions often present a formidable challenge for chemotherapy, limiting or precluding the uptake, and therefore the therapeutic benefit, of a variety of drugs. The perceived effectiveness of barriers is so great that most approaches to drug design select only drug candidates that fall into a rather narrow logP range so as to allow passage of the molecule through the polar extracellular milieu and diffusion across the relatively nonpolar membrane of a cell. A not uncommon view is that polar molecules cannot cross the nonpolar membrane of a cell. Reinforcing these selection criteria are the problems often encountered with molecules that fall outside of the preferred logP range. Poorly water-soluble taxol, for example, must be formulated in ethanol :Cremophor EL, and, at the other end of the polarity range, charged polar molecules, like oligonucleotides, often must be modified into less polar analogues to achieve cellular uptake. Thus, while much emphasis in recent years has been placed on “diversity” in drug discovery, many drug discovery strategies achieve only structural diversity while maintaining physical property (logP) homogeneity. In contrast, Nature utilizes molecules that cover a wide range of physical properties and structural diversity, offering important inspirations for new approaches to cell entry and hence to drug delivery. Several physical and molecular techniques have been developed over the years to enable drug or probe uptake into cells and tissue. The needle is one of the most commonly used devices for this purpose, although high pressure injections and other mechanical techniques have also been deployed more recently. Molecular approaches to enable or enhance drug uptake have traditionally centered on adjusting the physical properties of the drug candidate through the synthesis of numerous analogues from which those with optimal logP and absorption, distribution, metabolism and excretion (ADME) characteristics are selected for advancement. This is a synthesis and time intensive exercise, as often hundreds if not thousands of analogues are made before an optimal candidate is identified. The time and effort involved in this approach have contributed to the increasing interest in other strategies. Encapsulation of drugs, even those with suboptimal physical properties, by using, for example, liposomes, provides an increasingly important means of overriding the problematic solubility characteristics of a drug candidate while often also offering advantages with respect to distribution and metabolism. Nature provides inspiration for other strategies for cell penetration as it has evolved a wide variety of delivery techniques ranging from the remarkably exquisite mechanism of fertilization to various entry mechanisms, including macropinocytosis, clathrinand caveolin-mediated entry, and receptor-mediated uptake. Folate, for example, is actively imported into cells. By attaching folic acid to a drug that cannot enter cells, or does so only poorly, a conjugate can be prepared that readily enters

Practical Synthesis of Prostratin, DPP, and Their Analogs, Adjuvant Leads Against Latent HIV

Although antiretroviral therapies have been effective in decreasing active viral loads in AIDS patients, the persistence of latent viral reservoirs prevents eradication of the virus. Prostratin and DPP (12-deoxyphorbol-13-phenylacetate) activate the latent virus and thus represent promising adjuvants for antiviral therapy. Their limited supply and the challenges of accessing related structures have, however, impeded therapeutic development and the search for clinically superior analogs. Here we report a practical synthesis of prostratin and DPP starting from phorbol or crotophorbolone, agents readily available from renewable sources, including a biodiesel candidate. This synthesis reliably supplies gram quantities of the therapeutically promising natural products, hitherto available only in low and variable amounts from natural sources, and opens access to a variety of new analogs.

The practical synthesis of a novel and highly potent analogue of bryostatin.

Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer.

Designed, synthetically accessible bryostatin analogues potently induce activation of latent HIV reservoirs in vitro

Bryostatin is a unique lead in the development of potentially transformative therapies for cancer, Alzheimer’s disease, and the eradication of HIV/AIDS. However, the clinical use of bryostatin has been hampered by its limited supply, difficulties in accessing clinically-relevant derivatives, and side effects. Herein, we address these problems through the step-economical syntheses of seven members of a new family of designed bryostatin analogues utilizing a highly convergent Prins-macrocyclization strategy. We also demonstrate for the first time that such analogues effectively induce latent HIV activation in vitro with potencies similar to or better than bryostatin. Significantly, these analogues are up to 1000-fold more potent in inducing latent HIV expression than prostratin, the current clinical candidate for latent virus induction. This study provides the first demonstration that designed, synthetically-accessible bryostatin analogues could serve as superior candidates for the eradication of HIV/AIDS through induction of latent viral reservoirs in conjunction with current antiretroviral therapy.

Efficient Synthetic Access to a New Family of Highly Potent Bryostatin Analogues via a Prins-Driven Macrocyclization Strategy

The step-economical synthesis of a new class of bryostatin analogues that contain the complete oxycarbocyclic core ring system of the bryostatin natural products is reported. These agents are convergently assembled via a highly efficient, functional-group-tolerant, and stereoselective Prins-driven macrocyclization. These tetrahydropyranyl B-ring analogues are among our most potent and efficacious analogues to date, exhibiting nanomolar and picomolar activities in protein kinase C affinity assays as well as in cellular antiproliferation assays.