Identification of compounds that selectively target highly chemotherapy refractory neuroblastoma cancer stem cells.

Relapse of cancer months or years after an apparently successful therapy is probably caused by cancer stem cells (CSCs) due to their intrinsic features like dormant periods, radiorefraction, and acquired multidrug resistance (MDR) phenotypes, among other mechanisms of cellular drug evasiveness. Thus, the lack of currently efficacious interventions remains a major problem in the treatment of malignancies, together with the inability of existing drugs to destroy specifically CSCs. Neuroblastomas per se are highly chemotherapy-refractory extracranial tumors in infants with very low survival rates. So far, no effective cytostatics against this kind of tumors are clinically available. Therefore, we have put much effort into the development of agents to efficiently combat this malignancy. For this purpose, we tested several compounds isolated from Cuban propolis on induced CSCs (iCSC) derived from LAN-1 neuroblastoma cells which expressed several characteristics of tumor-initiating cells both in in-vitro and in-vivo models. Some small molecules such as flavonoids and polycyclic polyprenylated acylphloroglucinols (PPAP) were isolated using successive RT-HPLC cycles and identified employing mass spectrometry and NMR spectroscopic techniques. Their cytotoxicity was first screened in sensitive cell systems by MTT proliferation assays and afterwards studied in less sensitive neuroblastoma iCSC models. We found several compounds with considerable anti-iCSC activity, most of them belonging to the PPAP class. The majority of the compounds act in a pleiotropic manner on the molecular biology of tumors although their specific targets remain unclear. Nevertheless, two substances, one of them a flavonoid, induced a strong disruption of tubulin polymerization. In addition, an unknown compound strongly inhibited replicative enzymes like toposimerases I/II and DNA polymerase. Here, we report for the first time cytotoxic activities of small molecules isolated from Caribbean propolis which could be promising therapeutics or lead structures against therapy-refractory neuroblastoma entities. *Contributed equally.

(R)-Di-tert-butyl 1,1'-binaphthyl-2,2'-dicarboxyl-ate.

The crystal structure of the title compound, C(30)H(30)O(4), comprises two crystallographically independent half-mol-ecules which are completed by crystallographic twofold symmetry. The dihedral angles between the naphthalene ring planes are 85.83 (3) and 83.69 (3)° for the two molecules. The atoms of the tert-butyl group of one mol-ecule are disordered over two sets of sites with occupancies of 0.60:0.40. The crystal packing is achieved via π-π stacking inter-actions between the naphthyl groups of adjacent mol-ecules, with a separation of 3.790 (1) Šbetween the centroids of the rings.

Crystal Structure of a Peptide-Steroid Macrocycle-Intramolecular Attraction between Steroids and Peptidic ß(I) Turns.

Two molecules of the steroid lithocholic acid and two dipeptides (Phe-Phe) make up the macrocycle 1, in which the two steroidal surfaces approach each other so that the peptide parts fold into ß(I) turns. Thus, the structure of a cyclic steroid-peptide compound was determined in the solid state for the first time. The structure of 1 is stabilized in the crystal through intra- and intermolecular hydrogen bonds as well as through π stacking of the side-chain phenyl rings of Phe(i+1).