Figure 4.

Involvement of PDGF-BB/PDGFR-β in CSC/MSC interactions leads to platinum resistance and can be inhibited with sunitinib. (A) Increased amounts of PDGF-BB were detected via ELISA in CSC/MSC heterospheroids, compared to CSC mono-spheroids (n ≥ 3). (B) Gene expression analysis of the receptor PDGFRB demonstrated a significant (*** p < 0.0001, t-test, n ≥ 3) >two-fold upregulation in OVCAR3 CSC co-cultured with MSCs compared to OVCAR3 CSC mono-cultures. (C) PDGFR-β expression was confirmed using flow cytometry, and in corroboration with qPCR data, demonstrated a non-significant increase in PDGFR-β expression in CSC/MSC heterospheroids (* p < 0.05, one-way ANOVA followed by Tukey’s test, n ≥ 3). (D) Representative flow cytometry plots from the quantification in (C). (E) CSC were treated with various doses of carboplatin and 5 µM of sunitinib, a PDGFR-β inhibitor, to determine the change in IC₅₀ with MSC co-culture. (F) Tabulation of the IC₅₀ values, indicating that sunitinib treatment significantly lowers carboplatin IC₅₀ in CSC/CA-MSC heterospheroids.