Boron delivery agents for neutron capture therapy of cancer

Boron neutron capture therapy(BNCT)is a binary radiotherapeutic modality based on the nuclear capture and fission reactions that occur when the stable isotope,boron-10,is irradiated with neutrons to produce high energy alpha particles.This review will focus on tumor-targeting boron delivery agents that are an essential component of this binary system.Two low molecular weight boron-containing drugs currently are being used clinically,boronopheny-lalanine(BPA)and sodium borocaptate(BSH).Although they are far from being ideal,their therapeutic efficacy has been demonstrated in patients with high grade gliomas,recurrent tumors of the head and neck region,and a much smaller number with cutaneous and extra-cutaneous melanomas.Because of their limitations,great effort has been expended over the past 40 years to develop new boron delivery agents that have more favorable biodistribution and uptake for clinical use.These include boron-containing porphyrins,amino acids,polyamines,nucleosides,peptides,monoclonal antibodies,liposomes,nanoparticles of various types,boron cluster compounds and co-polymers.Cur-rently,however,none of these have reached the stage where there is enough convincing data to warrant clinical biodistribution studies.Therefore,at present the best way to further improve the clinical efficacy of BNCT would be to optimize the dosing paradigms and delivery of BPA and BSH,either alone or in combination,with the hope that future research will identify new and better boron delivery agents for clinical use.

Imaging tumor hypoxia:Blood-borne delivery of imaging agents is fundamentally different in hypoxia subtypes

Dedicated to the memory of Professor Briton Chance on the ccasion of his 100th birthday(July24 th,2013),and remembering mary erciting discussions on the orygenation of breast cancer,ontumor hyporia in general and imaging of the orygenation status of malignant tumors.Hypoxic tissue subvolumes are a hallmark feat ure of solid malignant tumors,relevant for cancertherapy and patient outcome because they increase both the intrinsic aggressiveness of tumor cells and their resist ance to several commonly used anticancer strategies.Pathogenetic mech-anisms leading to hypoxia are diverse,may coexist within the same tumor and are commonlygrouped according to the duration of their ffects.Chronic hypoxia is mainly caused by difusionlimitations resulting from enlarged intercapilary distances and adverse difusion geometriesand--to a lsser extent--by hypoxemia,compromised perfusion or long-lasting microregionalfow stops.Conversely,acute hypoxia preferentilly results from transient disruptions in per.fusion.While each of these features of the tumor microenvironment can contribute to a criticalreduction of oxy gen availability,the delivery of imaging agents(as well as nutrients and anti-cancer agents)may be compromised or remain unaffected,Thus,a critial appraisal of the ffectsof the various mechanisms leading to hypoxia with regard to the blood-bome delivery of imagingagents is necessary to judge their ability to correctly represent the hypoxic phenotype of solidmalignancies.

In Vivo Therapeutic Silencing of Hypoxia-Inducible Factor 1 Alpha(HIF-1)Using Single-Walled Carbon Nanotubes Noncovalently Coated with siRNA

A new approach is described for delivering small interfering RNA(siRNA)into cancer cells by noncovalently complexing unmodifi ed siRNA with pristine single-walled carbon nanotubes(SWCNTs).The complexes were prepared by simple sonication of pristine SWCNTs in a solution of siRNA,which then served both as the cargo and as the suspending agent for the SWCNTs.When complexes containing siRNA targeted to hypoxia-inducible factor 1 alpha(HIF-1)were added to cells growing in serum containing culture media,there was strong specific inhibition of cellular HIF-1 activity.The ability to obtain a biological response to SWCNT/siRNA complexes was seen in a wide variety of cancer cell types.Moreover,intratumoral administration of SWCNT-HIF-1 siRNA complexes in mice bearing MiaPaCa-2/HRE tumors signifi cantly inhibited the activity of tumor HIF-1.As elevated levels of HIF-1 are found in many human cancers and are associated with resistance to therapy and decreased patient survival,these results imply that SWCNT/siRNA complexes may have value as therapeutic agents.