Antitumor activity of 5'-O-dipalmitoylphosphatidyl 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine is enhanced by long-circulating liposomalization.
We previously synthesized the 5'-O-diacylphosphatidyl derivative of 2'-C-cyano-2'-deoxy-1-beta-D-arabino-pentofuranosylcytosine (CNDAC), a novel antitumor nucleoside, and observed it to have a high antitumor activity. Since this compound is readily incorporated into liposomal membranes, we liposomalized the compound using a formulation for conventional and long-circulating liposomes, and investigated the antitumor activity of liposomal 5'-O-dipalmitoylphosphatidyl CNDAC (DPP-CNDAC). Long-circulating liposomes composed of DPP-CNDAC, dipalmitoylphosphatidylcholine, cholesterol and palmityl-D-glucuronide (PGlcUA) (2:2:2:1 as a molar ratio), as well as liposomes containing dipalmitoylphosphatidylglycerol (DPPG) instead of palmityl-D-glucuronide and those composed of only DPP-CNDAC, were injected intravenously into Meth A sarcoma-bearing mice. DPP-CNDAC showed suppression of tumor growth, whereas CNDAC did not at the same concentration, suggesting that 5'-phosphatidylation is useful to enhance therapeutic efficacy. Furthermore, liposomal DPP-CNDAC reduced the acute toxicity, and liposomes containing PGlcUA showed more enhanced activities of reducing tumor growth and increasing the lifetime of the mice than liposomes containing DPPG. To obtain a higher therapeutic efficacy, we injected long-circulating liposomal DPP-CNDAC 5 times. The tumor growth was suppressed to 13.2% (86.8% inhibition), and the survival time of the tumor-bearing mice increased to 128.5% with one completely cured mouse out of five. Next, the effect of DPP-CNDAC incorporation on the in vivo behavior of PGlcUA and DPPG liposomes was examined by a non-invasive method using positron emission tomography (PET). Liposomes were labeled with [2-(18)F]-2-fluoro-2-deoxy-D-glucose, and administered to tumor-bearing mice. PET images and time-activity curves indicated that DPP-CNDAC/PGlcUA-liposomes tended to accumulate in tumor tissues a little bit more than DPP-CNDAC/DPPG-liposomes, although the difference between the two kinds of liposomal distribution was not as marked as between PGlcUA and DPPG liposomes, suggesting that DPP-CNDAC incorporation partly affected the liposomal behavior in vivo but that the long-circulating character of PGlcUA-liposomes might not be fully abolished. Thus, the enhanced therapeutic efficacy of long circulating liposomalized DPP-CNDAC observed here may be due to passive targeting of DPP-CNDAC to the tumor tissue, making this formulation of DPP-CNDAC useful for cancer chemotherapy.
Department of Radiobiochemistry, School of Pharmaceutical Sciences, University of Shizuoka, Yada, Japan.
T
T
Asai
K
K
Kurohane
S
S
Shuto
H
H
Awano
A
A
Matsuda
H
H
Tsukada
Y
Y
Namba
S
S
Okada
N
N
Oku
D000818:Animals; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D001088:Arabinonucleotides / Q000008:administration & dosage / Q000627:therapeutic use*; D003692:Delayed-Action Preparations; D004337:Drug Carriers; D008081:Liposomes; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D012513:Sarcoma, Experimental / Q000188:drug therapy*
D000970:Antineoplastic Agents; D001088:Arabinonucleotides; D003692:Delayed-Action Preparations; D004337:Drug Carriers; D008081:Liposomes; C114869:dpp-cndac