Synthesis and activity of folate conjugated didemnin B for potential treatment of inflammatory diseases

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

RNA Nanotechnology to Solubilize Hydrophobic Antitumor Drug for Targeted Delivery

Small-molecule drugs are used extensively in clinics for cancer treatment; however, many antitumor chemical drugs dissolve poorly in aqueous solution. Their poor solubility and nonselective delivery in vivo often cause severe side effects. Here, the application of RNA nanotechnology to enhance the solubility of hydrophobic drugs, using camptothecin (CPT) for proof-of-concept in targeted delivery for cancer treatment is reported. Multiple CPT prodrug molecules are conjugated to RNA oligos via a click reaction, and the resulting CPT-RNA conjugates efficiently self-assemble into thermodynamically stable RNA three-way junction (3WJ) nanoparticles. The RNA 3WJ is covalently linked with seven hydrophobic CPT prodrug molecules through cleavable ester bonds and a folic acid ligand for specific tumor targeting while remaining soluble in aqueous solutions without detectable aggregation at therapeutic dose. This CPT-RNA nanoparticle exhibits efficient and specific cell binding and internalization, leading to cell apoptosis. Tumor growth is effectively inhibited by CPT-RNA nanoparticles; the targeted delivery, strengthened by tumor ligand, further enhances tumor suppression. Compared with the traditional formulation, solubilization of CPT in aqueous buffer using RNA nanoparticles as a carrier is found to be safe and efficacious, demonstrating that RNA nanoparticles are a promising platform for the solubilization and the delivery of hydrophobic antitumor drugs.

Novel Small Molecule Probes for Metastatic Melanoma

Actively targeting probe 1b, an unsymmetrical bivalent dipeptide mimic, selectively bound melanoma over healthy skin tissue in histological samples from patients and Sinclair swine. Modifications to 1b gave agents 2-4 that contain a near-IR aza-BODIPY fluor. Contrary to our expectations, symmetrical probe 3 gave the highest melanoma-to-healthy skin selectivity in histochemistry and experiments with live cells; this was surprising because 2, not 3, is unsymmetrical like the original lead 1. Optical imaging of 3 in a mouse melanoma model failed to show tumor accumulation in vivo, but the probe did selectively accumulate in the tumor (some in lung and less in the liver) as proven by analysis of the organs post mortem.

Comparison of nanoparticle penetration into solid tumors and sites of inflammation: studies using targeted and nontargeted liposomes

AIM

The vast majority of nanomedicine research is focused on the use of nanoparticles for the diagnosis and treatment of cancer. However, the dense extracellular matrix of solid tumors restricts nanoparticle penetration, raising the question of whether the best applications of nanomedicines lie in oncology.

MATERIALS & METHODS

In this study, the uptake of folate-conjugated liposomes was compared between folate receptor-expressing tumors and folate receptor+ inflammatory lesions within the same mouse.

RESULTS

We demonstrate here that both folate-targeted and nontargeted liposomes accumulate more readily at sites of inflammation than in solid tumors.

CONCLUSION

These data suggest that nanosized imaging and therapeutic agents may be better suited for the treatment and diagnosis of inflammatory/autoimmune diseases than cancer.

Folate-based radiotracers for PET imaging--update and perspectives

The folate receptor (FR) is expressed in many tumor types, among those ovarian and lung cancer. Due to the high FR affinity of folic acid, it has been used for targeting of FR-positive tumors, allowing specific delivery of attached probes to the malignant tissue. Therefore, nuclear imaging of FR-positive cancer is of clinical interest for selecting patients who could benefit from innovative therapy concepts based on FR-targeting. Positron emission computed tomography (PET) has become an established technique in clinical routine because it provides an increased spatial resolution and higher sensitivity compared to single photon emission computed tomography (SPECT). Therefore, it is of critical importance to develop folate radiotracers suitable for PET imaging. This review article updates on the design, preparation and pre-clinical investigation of folate derivatives for radiolabeling with radioisotopes for PET. Among those the most relevant radionuclides so far are fluorine-18 (t_1/2: 110 min, E_avβ⁺: 250 keV) and gallium-68 (t_1/2: 68 min, E_av β⁺: 830 keV). Recent results obtained with new PET isotopes such as terbium-152 (t_1/2: 17.5 h, Eβ⁺: 470 keV) or scandium-44 (t_1/2: 3.97 h, E_av β⁺: 632 keV) are also presented and discussed. Current endeavors for clinical implementation of PET agents open new perspectives for identification of FR-positive malignancies in patients.