Rapidly growing cells show an increased demand for nutrients and vitamins. The objective of our work is to exploit the supply route of vitamin B12 to deliver new derivatives of this vital vitamin to hyperproliferative cells. To date, radiolabeled ( 57 Co and 111 In) vitamin B12 derivatives showed labeling of tumor tissue but also undesired high accumulation of radioactivity in normal tissue. By abolishing the interaction of a tailored vitamin B12 derivative to its transport protein transcobalamin II and therefore interrupting transcobalamin II receptor and megalin mediated uptake in normal tissue, preferential accumulation of a radiolabeled vitamin in cancer tissue could be accomplished. We identified transcobalamin I on tumors as a possible new receptor for this preferential accumulation of vitamin-mediated targeting. The low systemic distribution of radioactivity and the high tumor to blood ratio opens the possibility of a more successful clinical application of vitamin B12 for imaging or therapy.

From a strain of Aspergillus nidulans var. echinulatus, A 32204, echinocandin, a novel polypeptide antibiotic complex with high and specific anti‐yeast activity was isolated. The main component, echinocandin B, was separated by counter‐current distribution. A tentative molecular formula C52H81N7O18 is discussed. The antibiotic is characterized by its IR. and NMR. spectra and by its characteristic hydrolytic degradation products: linoilic acid, L‐4‐hydroxyproline, L‐4‐oxoproline, (2S, 3S, 4S)‐4‐methyl‐3‐hydroxy‐proline, L‐threonine (2 mols), and 1‐(p‐hydroxyphenyl)‐3‐amino‐propan‐2‐one.

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