11: A Humanized Monoclonal Antibody to Secreted Frizzled-Related Protein 2 Inhibits TNBC Lung Metastases

A promising novel target for breast cancer is secreted frizzled-related protein 2 (SFRP2), which blocks tumor apoptosis, promotes T-cell exhaustion, and induces tumor angiogenesis. The prevalence of SFRP2 in triple negative breast cancer (TNBC) has not been studied. We developed a humanized monoclonal antibody to SFRP2, (hSFRP2 mAb) that inhibits primary breast cancer growth in vivo. We hypothesize that  SFRP2 is a target in human TNBC, that hSFRP2 mAb is effective at inhibiting the growth of  metastatic TNBC, and that hSFRP2 mAb remains effective in chemotherapy resistant TNBC cells.


Methods:

SFRP2 immunohistochemistry (IHC) on an FFPE 88 core human TNBC tissue microarray (TMA). The TMA was stained with antibody to SFRP2 and intensity was quantified using spatial analysis. Results were analyzed as described for analyses of ER and PR receptor positivity; categories are: 0-negative ; low positive (0-10%), and positive >10%.

Efficacy of hSFRP2 mAb in doxorubicin (dox)-resistant cells. MDA-MB-231 cells were treated with 4nM dox which was increased 2nM at a time until resistant to 10µM dox over one year. Wild type (WT) and dox-resistant cells were then treated for 4 hours with hSFRP2 mAb (10uM) or IgG control (10uM) (n=6). Apoptotic cells were detected with Promokine Apoptosis kit.

hSFRP2 mAb treatment of metastatic TNBC. PY8119 and E0771 TNBC cells were injected iv into C57BL/6 mice. Mice were treated with IgG1 8 mg/kg iv or hSFRP2 mAb 8 mg/kg iv every 3 days. After 4 weeks, lungs were removed, and surface metastases quantified.  


Results:

SFRP2 is present in human TNBC. Of 88 cores, 83 were positive for SFRP2, 4 were minimally positive, and 1 was negative.

Efficacy of hSFRP2 mAb in dox-resistant cells For WT cells, apoptotic cell count in control cells was 11.5 ± 3.7 and in hSFRP2 mAb cells was 76.6 ± 5.0  (p< 0.001, n=9). For dox-resistant cells, apoptotic count in control cells was 16.7 ± 6.0, and in hSFRP2 mAb cells was 68.4 ± 6.4 (p< 0.001, n=9).

hSFRP2 mAb inhibits metastatic TNBC growth in vivo. For E0771, the surface met count in the control group was 8.9 ±2.8 and in the hSFRP2 mAb group was 4.9 ± 1.1 (p< 0.05, n=15). For PY8119 tumors the control group had 6.4 ± 1.0 metastases, and the hSFRP2 mAb group had 3.6 ± 0.9  (p< 0.05, n=11).


Conclusions:

SFRP2 protein is present in the majority of human TNBC. hSFRP2 mAb reduces TNBC lung metastases in two in vivo models and induces apoptosis in doxo- resistant TNBC cells. SFRP2 is a therapeutic target for de novo and dox-resistant TNBC.