SN12PM6

Carbazochrome Sodium Sulfonate (CBZ) Inhibits Renal Cell Carcinoma Bone Metastasis and Promotes Osteoblast Differentiation via BIGH3 Modulation

Renal cell carcinoma bone metastases (RCCBM) are primarily osteolytic, driven in part by tumor-secreted BIGH3 (TGFBI), which suppresses osteoblast (OSB) differentiation. To test whether BIGH3 modulation could alter tumor behavior, human SN12PM6 cells—which normally express low levels of BIGH3—were engineered to overexpress BIGH3 (SN12PM6/BG). Overexpression was confirmed by real-time RT-PCR (Fig. 1A), with no significant effect on cell proliferation (Fig. 1B). In vitro treatment with carbazochrome sodium sulfonate (CBZ; 50 or 100 nmol/L) for up to 5 days did not inhibit the growth of either SN12PM6/Vector or SN12PM6/BG cells (Fig.1C).

In vivo, mice received intrafemoral injections of SN12PM6/Vector or SN12PM6/BG cells. After 2 weeks of tumor establishment, CBZ treatment was administered for 21 days. Bioluminescence imaging (BLI) showed progressive tumor growth in control groups, whereas CBZ significantly reduced BLI signals in both cell lines (Fig. 1D, E), indicating inhibition of tumor growth in bone.

Bone histomorphometry of SN12PM6/BG-bearing femurs revealed that CBZ treatment increased OSB numbers per osteoid perimeter (N.Ob/O.Pm), bone volume (BV/TV%), and trabecular thickness (Tb.Th) (Fig. 1F). CBZ also reduced blood vessel density (BVS/BVV) (Fig. 1G) and significantly decreased osteoclast numbers (Oc Number, N.Oc/B.Pm), with a trend toward reduced osteoclasts per erosion perimeter (N.Oc/E.Pm) (Fig. 1H).

These findings demonstrate that CBZ suppresses RCCBM progression in bone by promoting OSB differentiation, inhibiting angiogenesis, and reducing osteoclastogenesis, independently of direct effects on tumor cell proliferation. This highlights CBZ as a potential therapeutic agent for mitigating the osteolytic bone microenvironment in renal cell carcinoma.