SPL-108 Mediates Metastasis and Chemoresistance in High-Grade Serous Tubo-Ovarian Carcinoma

Objectives: Overcoming chemoresistance will improve outcomes for all women with tubo-ovarian carcinomas. Mechanisms of chemoresistance are multifactorial and heterogeneous. ABCB1 (MDR1) represents one common resistance mechanism in tubo-ovarian carcinomas and is under the regulation of CD44. In the present study we examined the effects of a novel CD44 modulator, SPL-108, in a panel of ovarian cancer cell lines. Methods: We assessed chemosensitivity and migration effects of SPL-108 in a panel of ovarian cancer cell lines with (OVCAR5, OVCAR8, OVCAR3) and without (OVCAR4, CAOV3) MDR1 expression. In vitro experiments (cell viability assay, Western blot analysis, Calcein AM fluorescence assay, and migration assay) were carried out to determine the functional effects of SPL-108. Results: Higher expression of CD44 was seen in OVCAR5 and OVCAR8 on Western Blot analysis. In transwell migration assay, treatment with SPL-108 decreased the number of migrating cells compared to control in OVCAR8 (mean ± SEM, 149.1 ± 22.8 vs 89.0 ± 16.5 cells, p=0.04), OVCAR5 (177.7 ± 15.4 vs 134.5 ± 14.7 cells, p=0.04) and OVCAR3 (111.2 ± 12.4 vs 50.5 ± 9.4 cells, p<0.01) cell lines. Migratory response was independent of CD44 expression. SPL-108 led to the accumulation of MDR1 substrate, as measured by the Calcein AM assay, in OVCAR5 (1.9 fold, p<0.01), OVCAR8 (1.6 fold, p<0.001) and OVCAR3 (1.2 fold, p=0.01) cells lines compared to controls. Retention of the MDR1 substrate after SPL-108 treatment positively correlated with MDR1 protein expression and no Calcein retention was seen in cells that lacked MDR1 expression. Co-treatment of OVCAR5 cells with paclitaxel and SPL-108 decreased the percentage of viable cells from 94% when treated with paclitaxel alone to 63% with combination therapy. No toxicity was observed with SPL-108 monotherapy. Conclusions: SPL-108 treatment has anti-metastatic properties and suppresses chemoresistance in preclinical models of ovarian cancer. Ongoing studies in animal models will help to guide the further clinical development of SPL-108. Overcoming chemoresistance will improve outcomes for all women with tubo-ovarian carcinomas. Mechanisms of chemoresistance are multifactorial and heterogeneous. ABCB1 (MDR1) represents one common resistance mechanism in tubo-ovarian carcinomas and is under the regulation of CD44. In the present study we examined the effects of a novel CD44 modulator, SPL-108, in a panel of ovarian cancer cell lines. We assessed chemosensitivity and migration effects of SPL-108 in a panel of ovarian cancer cell lines with (OVCAR5, OVCAR8, OVCAR3) and without (OVCAR4, CAOV3) MDR1 expression. In vitro experiments (cell viability assay, Western blot analysis, Calcein AM fluorescence assay, and migration assay) were carried out to determine the functional effects of SPL-108. Higher expression of CD44 was seen in OVCAR5 and OVCAR8 on Western Blot analysis. In transwell migration assay, treatment with SPL-108 decreased the number of migrating cells compared to control in OVCAR8 (mean ± SEM, 149.1 ± 22.8 vs 89.0 ± 16.5 cells, p=0.04), OVCAR5 (177.7 ± 15.4 vs 134.5 ± 14.7 cells, p=0.04) and OVCAR3 (111.2 ± 12.4 vs 50.5 ± 9.4 cells, p<0.01) cell lines. Migratory response was independent of CD44 expression. SPL-108 led to the accumulation of MDR1 substrate, as measured by the Calcein AM assay, in OVCAR5 (1.9 fold, p<0.01), OVCAR8 (1.6 fold, p<0.001) and OVCAR3 (1.2 fold, p=0.01) cells lines compared to controls. Retention of the MDR1 substrate after SPL-108 treatment positively correlated with MDR1 protein expression and no Calcein retention was seen in cells that lacked MDR1 expression. Co-treatment of OVCAR5 cells with paclitaxel and SPL-108 decreased the percentage of viable cells from 94% when treated with paclitaxel alone to 63% with combination therapy. No toxicity was observed with SPL-108 monotherapy. SPL-108 treatment has anti-metastatic properties and suppresses chemoresistance in preclinical models of ovarian cancer. Ongoing studies in animal models will help to guide the further clinical development of SPL-108.