Cancer-selective targeting and cytotoxicity by liposomal-coupled lysosomal saposin C protein.
OBJECTIVE
Saposin C is a multifunctional protein known to activate lysosomal enzymes and induce membrane fusion in an acidic environment. Excessive accumulation of lipid-coupled saposin C in lysosomes is cytotoxic. Because neoplasms generate an acidic microenvironment, caused by leakage of lysosomal enzymes and hypoxia, we hypothesized that saposin C may be an effective anticancer agent. We investigated the antitumor efficacy and systemic biodistribution of nanovesicles comprised of saposin C coupled with dioleoylphosphatidylserine in preclinical cancer models.


METHODS
Neuroblastoma, malignant peripheral nerve sheath tumor and, breast cancer cells were treated with saposin C-dioleoylphosphatidylserine nanovesicles and assessed for cell viability, ceramide elevation, caspase activation, and apoptosis. Fluorescently labeled saposin C-dioleoylphosphatidylserine was i.v. injected to determine in vivo tumor-targeting specificity. Antitumor activity and toxicity profile of saposin C-dioleoylphosphatidylserine were evaluated in xenograft models.


RESULTS
Saposin C-dioleoylphosphatidylserine nanovesicles, with a mean diameter of approximately 190 nm, showed specific tumor-targeting activity shown through in vivo imaging. Following i.v. administration, saposin C-dioleoylphosphatidylserine nanovesicles preferentially accumulated in tumor vessels and cells in tumor-bearing mice. Saposin C-dioleoylphosphatidylserine induced apoptosis in multiple cancer cell types while sparing normal cells and tissues. The mechanism of saposin C-dioleoylphosphatidylserine induction of apoptosis was determined to be in part through elevation of intracellular ceramides, followed by caspase activation. In in vivo models, saposin C-dioleoylphosphatidylserine nanovesicles significantly inhibited growth of preclinical xenografts of neuroblastoma and malignant peripheral nerve sheath tumor. I.v. dosing of saposin C-dioleoylphosphatidylserine showed no toxic effects in nontumor tissues.


CONCLUSIONS
Saposin C-dioleoylphosphatidylserine nanovesicles offer promise as a novel, nontoxic, cancer-targeted, antitumor agent for treating a broad range of cancers.
Qi
Xiaoyang
X
Division and Program in HumanGenetics, 3333 Burnet Avenue, Cincinnati, Ohio 45229-3039, USA. xiaoyang.qi@cchmc.org
Chu
Zhengtao
Z
Mahller
Yonatan Y
YY
Stringer
Keith F
KF
Witte
David P
DP
Cripe
Timothy P
TP
D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D004195:Disease Models, Animal; D004354:Drug Screening Assays, Antitumor; D064420:Drug-Related Side Effects and Adverse Reactions; D005260:Female; D006801:Humans; D008081:Liposomes; D008247:Lysosomes / Q000737:chemistry*; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000473:pathology; D018317:Nerve Sheath Neoplasms / Q000188:drug therapy / Q000473:pathology; D009447:Neuroblastoma / Q000188:drug therapy / Q000473:pathology; D010718:Phosphatidylserines / Q000737:chemistry*; D049231:Saposins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology* / Q000627:therapeutic use*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D008081:Liposomes; D010718:Phosphatidylserines; D049231:Saposins; C042511:1,2-dioleoylphosphatidylserine