Neocarzinostatin

The anti-tumor antibiotics neocarzinostatin and bleomycin specifically oxidize deoxyribose in DNA at the C-5' and C-4' positions, respectively. The resulting DNA lesions include strand breaks and apyrimidinic sites. Both agents are broad specificity mutagens, inducing, in various systems, base substitutions, frameshifts and deletions. Sequencing studies in bacterial systems have suggested that the base substitutions may result primarily from replicative bypass of the oxidized apyrimidinic sites.

A new zinc(II)-cofactor coupled to a testosterone anchor, zinc(II)-N,N-bis(2-pyridylmethyl)-1,3-diamino-propa-2-ol-N'(17'-succinimidyltestosterone) (Zn-Testo-BisPyPol) 1-Zn has been synthesized and fully characterized. It has been further associated with a neocarzinostatin variant, NCS-3.24, to generate a new artificial metalloenzyme following the so-called 'Trojan horse' strategy. This new 1-Zn-NCS-3.24 biocatalyst showed an interesting catalytic activity as it was found able to catalyze the hydrolysis of the RNA model HPNP with a good catalytic efficiency (kcat/KM=13.6M(-1)s(-1) at pH 7) that places it among the best artificial catalysts for this reaction. Molecular modeling studies showed that a synergy between the binding of the steroid moiety and that of the BisPyPol into the protein binding site can explain the experimental results, indicating a better affinity of 1-Zn for the NCS-3.24 variant than testosterone and testosterone-hemisuccinate themselves. They also show that the artificial cofactor entirely fills the cavity, the testosterone part of 1-Zn being bound to one the two subdomains of the protein providing with good complementarities whereas its metal ion remains widely exposed to the solvent which made it a valuable tool for the catalysis of hydrolysis reactions, such as that of HPNP. Some possible improvements in the 'Trojan horse' strategy for obtaining better catalysts of selective reactions will be further studied.

A variety of treatments have recently been introduced to improve the prognosis of hepatocellular carcinoma (HCC). These anticancer therapies include the oily carcinostatic agent styrene maleic acid neocarzinostatin (SMANCS). SMANCS is a chemical conjugate of a synthetic copolymer of styrene maleic acid (SMA) and the proteinaceous anti-cancer agent neocarzinostatin (NCS), which dissolves in organic solvents such as pyridine and acetone, and particularly in Lipiodol. NCS is a simple protein capable of inhibiting DNA synthesis and inducing DNA degradation. Lipiodol is an ethyl ester of iodinated poppy seed oil in which most of the unsaturated double bonds in oleic, linoleic and linolenic acid are almost completely iodinated. When a homogeneous suspension of SMANCS with Lipiodol (SMANCS/Lipiodol) is administered intra-arterially, Lipiodol acts as a carrier of SMANCS. Many studies have demonstrated the clinical efficacy of SMANCS/Lipiodol in the treatment of HCC. We have shown that transcatheter arterial infusion (TAI) with SMANCS/Lipiodol has a more favorable focal therapeutic effect than does epirubicin in Lipiodol in the initial treatment of HCC. However, recent clinical studies have indicated that SMANCS causes severe adverse reactions and complications. We have also reported a case of HCC in which multifocal hepatic infarction developed after TAI with SMANCS/Lipiodol. Arterial administration of SMANCS/Lipiodol, therefore, should be given as peripherally as possible via the tumor feeding arteries, to enhance the efficacy of the agent and to reduce the adverse effects.

The unstability of neocarzinostatin (NCS), apo-NCS and NCS-chromophore (NCS-chr) has been investigated by using an extra-weak chemiluminescence (CL) analyzer. A significantly high emission intensity (10,840 counts/10 seconds) was detected from NCS under dark conditions at 20 degrees C, while no significant emission was observed in other antitumor antibiotics, such as, mitomycin C and pepleomycin. This high emission intensity of NCS was due to NCS-chr I (epoxide form) but not apo-NCS. The functional group generating the high extra-weak CL of NCS-chr I is probably the epoxide in the molecule, since the emission intensity of NCS-chr I (epoxide form) is much higher than that of NCS-chr II (hydrochloride adduct form). The extra-weak CL emission of NCS decreased under a nitrogen atmosphere and it was greatly enhanced under an oxygen atmosphere. The spectral analysis of NCS showed emission peaks around 460 and 570 nm. These observations strongly suggest that one of the emission species of NCS-chr may be due to singlet oxygen.