Targeting acute hypoxic cancer cells by doxorubicin-immunoliposomes directed by monoclonal antibodies specific to RON receptor tyrosine kinase.

PURPOSE

Hypoxia contributes to acquired drug resistance in various cancer cells. The underlying mechanism is cellular insensitivity regulated by hypoxia-inducible factors (HIF), which impairs drug uptake, transport, and metabolism. The current study determines anti-RON antibody-directed cytotoxicity of doxorubicin (Dox)-immunoliposomes (IL) in hypoxic colon cancer cells.

METHODS

Cells were cultured under hypoxia (1% O(2), 5% CO(2), and 96% N(2)) for 24 h. Dox-loaded IL were formulated followed by post-insertion of monoclonal antibody Zt/g4 specific to RON. Western blotting was used to detect HIF-1α and RON expression. Cellular uptake of Zt/g4-conjugated IL was determined by confocal and internalization assays. Cell viability was assessed by the MTT assay.

RESULTS

RON and HIF-1α expression were observed in hypoxic colon HCT116 and SW620 cells. Resistance to Dox-induced cytotoxicity was acquired in hypoxic cells with increased IC(50) values. However, acquired resistance was attenuated by Zt/g4-directed Dox-IL, which displays increased cytotoxic activities. IL binding and uptake revealed that hypoxic RON expression is functional, which mediates high levels of Zt/g4-Dox-IL binding and cytoplasmic internalization. Zt/g4-Dox-IL is effective in killing hypoxic HCT116 and SW620 cells with reduced IC(50) values compared to Dox and pegylated-liposomal Dox. These effects were dependent on hypoxic RON expression. HCC1937 cells with diminished RON expression under hypoxia were insensitive to Zt/g4-Dox-IL-induced cytotoxic effect.

CONCLUSIONS

RON expressed by hypoxic colon cancer cells is thus a potential targeting molecule for delivery of chemotherapeutics. The ability of anti-RON mAb to direct Dox-IL cytotoxicity could be developed for attenuating hypoxia-acquired drug resistance in various cancer cells.