Promising drug candidates sometimes fail during clinical trials because of problems with their delivery. For instance, some compounds aren’t absorbed well by the body. Other candidates have poor target specificity: They spread through the body rather than making a beeline to the region where they’re needed. This can cause toxicity in healthy tissue. About 20 years ago, pharmaceutical firms began investigating nanomedicines as a potential solution to these problems. Because researchers can coat nanoparticles with targeting molecules and can design them to release therapeutic payloads over time, nanomedicines might one day overcome current drug delivery challenges. Here, we focus on three recently patented nano drug delivery systems.
Doctors typically treat castration-resistant prostate cancer (CRPC) with chemotherapy, but it does not relieve chronic inflammation or diminish tumors that have invaded bone, common occurrences in CRPC patients. To address these shortcomings, Shanta Dhar and Rakesh K. Pathak of the University of Georgia have designed a biodegradable polymer-based nanoparticle capable of delivering chemotherapy drugs, as well as anti-inflammatory agents and compounds that prevent bone degradation. The researchers target prostate cancer by attaching to the particles’ polymer coatings small molecules that bind to prostate-specific membrane antigen, a protein present on the surface of the cancer cells. They report that this new nanoparticle-based drug delivery system, carrying cisplatin as a chemotherapeutic and aspirin as an anti-inflammatory agent, kills prostate cancer cells more effectively than cisplatin and aspirin alone (WO 2014169007). In the patent, the authors describe how the particle might also be loaded with pamidronate, a compound that prevents bone breakdown.
One reason it’s been difficult to treat brain disorders is that it’s hard to slip large therapeutic agents through the brain’s protective barrier. Scientists have tried targeting transferrin receptors (TfRs), proteins that dot brain capillaries and transport iron inside the brain. By hijacking this transport machinery, researchers have been able to sneak antibodies across the blood-brain barrier. High doses are needed, though, to get therapeutically sufficient amounts into the brain. Mark E. Davis and colleagues at Caltech have been designing nanoparticles that interact with TfRs and that can carry a drug payload. In a recent patent (WO 2014185964), Davis and his group propose attaching transferrin to gold particles via a cleavable chemical linker. After the particle binds a TfR on a blood capillary cell, it would be drawn into a cell vesicle (shown). Then the linker would break because of the mildly acidic environment inside (pH 5–6). Eventually, the vesicle would release the particle on the other side of the blood-brain barrier. Because these particles attach strongly to TfRs but also release into the brain easily, the team thinks drug-loaded versions could be administered to patients at low doses.
Patent Picks is a collaborative effort by C&EN and CAS. This feature reports on trends CAS scientists observe from patents in CAS databases. Patents now generate more than 70% of the new substances appearing in the literature.
Some chemotherapy drugs work by disrupting DNA synthesis within tumors. One particular strategy inserts modified DNA building blocks—altered nucleotides made from bases such as cytosine—into a growing DNA strand. These imposter nucleotides halt DNA strand growth, killing the tumor cells to which they’ve been delivered. They do so because they contain bulky molecular groups that muck up the polymerase transcription machinery. To target these nucleotides to tumors, Vladislav Litosh and colleagues at the University of Cincinnati have designed a nano drug delivery system (WO 2014194250). The researchers attached modified nucleosides—nucleotides without phosphate groups—to the cyclodextrin-based polymer particles via acid-sensitive linkers. They also attached targeting molecules, such as antibodies, to guide the particles to tumor cells. Once a particle enters the acidic cells, the linker breaks, releasing the imposter nucleosides. These bulked-up nucleosides then get converted into nucleotides by the cell’s machinery. When tested, the particles inhibited the growth of a variety of cancer cell lines.