Purpose: Tumor cell targeting is a promising strategy for enhancing the therapeutic potential of chemotherapy agents. Polyethylene glycol (PEG)-coated (sterically stabilized) liposomes show enhanced accumulation on the surface of tumors, but steric hindrance by PEGylation reduces the association of the liposome-bound ligand with its receptor. To increase folate receptor (FR) targeting, we optimized the concentration and PEG spacer length of folate-PEG-lipid in liposomes. Experimental Design: Three types of folate-linked liposomal doxorubicin were designed and prepared by optimizing the concentration and PEG spacer length of folate-PEG-lipid in PEGylated or non-PEGylated liposomes and by masking folate-linked liposomes where the folate ligand is ''masked'' by adjacent PEG spacers. The liposome targeting efficacy was evaluated in vitro and in vivo. Results: In human oral carcinoma KB cells, which overexpress FR, modification with sufficiently long PEG spacer and a high concentration of folate ligand to non-PEGylated liposomes increased the FR-mediated association and cytotoxicity more than with PEGylated and masked folate-linked liposomes. On the contrary, in mice bearing murine lung carcinoma M109, modification with the folate ligand in PEGylated and masked folate-linked liposomes showed significantly higher antitumor effect than with non-PEGylated liposomes irrespective of the length of time in the circulation after intravenous injection. Conclusions:The results of this study will be beneficial for the design and preparation of ligand-targeting carriers for cancer treatment.

Tumor cell targeting of drug carriers is a promising strategy and uses the attachment of various ligands to enhance the therapeutic potential of chemotherapy agents. Folic acid is a high-affinity ligand for folate receptor, which is a functional tumor-specific receptor. The transforming growth factor (TGF)-b type I receptor (TbR-I) inhibitor A-83-01 was expected to enhance the accumulation of nanocarriers in tumors by changing the microvascular environment. To enhance the therapeutic effect of folate-linked liposomal doxorubicin (F-SL), we co-administrated F-SL with A-83-01. Intraperitoneally injected A-83-01-induced alterations in the cancer-associated neovasculature were examined by magnetic resonance imaging (MRI) and histological analysis. The targeting efficacy of single intravenous injections of F-SL combined with A-83-01 was evaluated by measurement of the biodistribution and the antitumor effect in mice bearing murine lung carcinoma M109. A-83-01 temporarily changed the tumor vasculature around 3 h post injection. A-83-01 induced 1.7-fold higher drug accumulation of F-SL in the tumor than liposome alone at 24 h post injection. Moreover F-SL co-administrated with A-83-01 showed significantly greater antitumor activity than F-SL alone. This study shows that co-administration of TbR-I inhibitor will open a new strategy for the use of FR-targeting nanocarriers for cancer treatment. (Cancer Sci 2010; 101: 2207-2213

Supplementary Data from Design of Folate-Linked Liposomal Doxorubicin to its Antitumor Effect in Mice

<div>Abstract<p><b>Purpose:</b> Tumor cell targeting is a promising strategy for enhancing the therapeutic potential of chemotherapy agents. Polyethylene glycol (PEG)-coated (sterically stabilized) liposomes show enhanced accumulation on the surface of tumors, but steric hindrance by PEGylation reduces the association of the liposome-bound ligand with its receptor. To increase folate receptor (FR) targeting, we optimized the concentration and PEG spacer length of folate-PEG-lipid in liposomes.</p><p><b>Experimental Design:</b> Three types of folate-linked liposomal doxorubicin were designed and prepared by optimizing the concentration and PEG spacer length of folate-PEG-lipid in PEGylated or non-PEGylated liposomes and by masking folate-linked liposomes where the folate ligand is “masked” by adjacent PEG spacers. The liposome targeting efficacy was evaluated <i>in vitro</i> and <i>in vivo</i>.</p><p><b>Results:</b> In human oral carcinoma KB cells, which overexpress FR, modification with sufficiently long PEG spacer and a high concentration of folate ligand to non-PEGylated liposomes increased the FR-mediated association and cytotoxicity more than with PEGylated and masked folate-linked liposomes. On the contrary, in mice bearing murine lung carcinoma M109, modification with the folate ligand in PEGylated and masked folate-linked liposomes showed significantly higher antitumor effect than with non-PEGylated liposomes irrespective of the length of time in the circulation after intravenous injection.</p><p><b>Conclusions:</b> The results of this study will be beneficial for the design and preparation of ligand-targeting carriers for cancer treatment.</p></div>

<div>Abstract<p><b>Purpose:</b> Tumor cell targeting is a promising strategy for enhancing the therapeutic potential of chemotherapy agents. Polyethylene glycol (PEG)-coated (sterically stabilized) liposomes show enhanced accumulation on the surface of tumors, but steric hindrance by PEGylation reduces the association of the liposome-bound ligand with its receptor. To increase folate receptor (FR) targeting, we optimized the concentration and PEG spacer length of folate-PEG-lipid in liposomes.</p><p><b>Experimental Design:</b> Three types of folate-linked liposomal doxorubicin were designed and prepared by optimizing the concentration and PEG spacer length of folate-PEG-lipid in PEGylated or non-PEGylated liposomes and by masking folate-linked liposomes where the folate ligand is “masked” by adjacent PEG spacers. The liposome targeting efficacy was evaluated <i>in vitro</i> and <i>in vivo</i>.</p><p><b>Results:</b> In human oral carcinoma KB cells, which overexpress FR, modification with sufficiently long PEG spacer and a high concentration of folate ligand to non-PEGylated liposomes increased the FR-mediated association and cytotoxicity more than with PEGylated and masked folate-linked liposomes. On the contrary, in mice bearing murine lung carcinoma M109, modification with the folate ligand in PEGylated and masked folate-linked liposomes showed significantly higher antitumor effect than with non-PEGylated liposomes irrespective of the length of time in the circulation after intravenous injection.</p><p><b>Conclusions:</b> The results of this study will be beneficial for the design and preparation of ligand-targeting carriers for cancer treatment.</p></div>