Inhibition of mouse mammary adenocarcinoma (EMT6) growth and metastases inmice by a modified form of C-reactive protein

Mice were injected in the hind limb with a mouse mammary adenocarcinoma cel l line, EMT6, and tumor growth at the primary site as well as the incidence of lung metastases were measured. Groups of animals were treated with the acute-phase reactant C-reactive protein, (native-CRP), or a conformationall y modified form of CRP (mCRP) made by dissociating CRP subunits under chela ting, denaturing conditions. Each form of CRP was injected (intravenously) through the tail vein, encapsulated in large unilamellar lipid vesicles mad e by an extrusion technique (LUVETs), mCRP was also injected without the LU VET carrier. Mice not treated, or treated with LUVETs alone, exhibited both progressive tumor growth at the primary site and a high incidence of metas tatic lung tumors quantified at necropsy. Treatment with native-CRP encapsu lated in LUVETs had little or no effect on either tumor growth or metastase s. Treatment with mCRP, however, alone or encapsulated in LUVETs, effective ly slowed or stopped the progression of tumor growth, and in some mice, sho wed a decrease in tumor size. After cessation of mCRP injections, tumor gro wth resumed at a rate comparable to that measured in untreated animals. Fif ty to 85% of mice treated with mCRP or mCRP in LUVETs developed necrotic le sions at the primary tu mor site with in 24-48 h following the initial inje ction of protein. Furthermore, at necropsy, only 6% of mice treated with mC RP in LUVETs and 40% of mice treated with mCRP alone showed evidence of lun g metastases compared to 67-80% of animals in no-treatment, native-CRP in L UVETs and in LUVET control group animals. These results show that the proto typic acute-phase reactant, CRP, has therapeutic anticancer and antimetasta tic activity only when the native pentameric subunit structure is dissociat ed to form the mCRP conformer.