Higher sensitivity to patupilone versus paclitaxel chemotherapy in primary uterine serous papillary carcinoma cell lines with high versus low HER-2/neu expression in vitro

Abstract

Objective: To compare the in vitro sensitivity/resistance to patupilone versus paclitaxel in uterine serous papillary carcinoma (USPC) with high versus low HER-2/neu expression.

Methods: Six primary USPC cell lines, half of which overexpress HER-2/neu at a 3+ level, were evaluated for growth rate and tested for their in vitro sensitivity/resistance to patupilone versus paclitaxel by MTS assays. Quantitative RT-PCR was used to identify potential mechanisms underlying the differential sensitivity/resistance to patupilone versus paclitaxel in primary USPC cell lines.

Results: Cell lines overexpressing HER-2/neu showed higher proliferation when compared to low HER-2/neu-expressing cell lines. Compared to low-expressing cell lines, high HER-2/neu expressors were significantly more sensitive to patupilone than to paclitaxel (P<0.0002). In contrast, there was no appreciable difference in sensitivity to patupilone versus paclitaxel in primary USPC cell lines with low HER-2/neu expression. Higher levels of β-tubulin III (TUBB3) and P-glycoprotein (ABCB1) were detected in USPC cell lines with high versus low HER-2/neu expression (P<0.05).

Conclusions: USPC overexpressing HER-2/neu display greater in vitro sensitivity to patupilone and higher levels of the patupilone molecular target TUBB3 when compared to low HER-2/neu expressors. Due to the adverse prognosis associated with HER-2/neu overexpression in USPC patients, patupilone may represent a promising novel drug to combine to platinum compounds in this subset of aggressive endometrial tumors.

Figure 1. Growth curves of primary USPC cell lines

High HER-2/neu expressors (USPC-ARK-1, USPC-ARK-2, USPC-ARK-3) versus Low HER-2/neu expressors (USPC-ARK-4, USPC-ARK-5, USPC-ARK-6).

Figure 2. Representative dose-response curves following exposure to patupilone versus paclitaxel of USPC primary cell lines with High versus Low HER-2/neu expression

Survival was assessed by MTS assay as described in the Methods section. Each point on the cell line graph represents the mean of 3 estimations + SE.

Figure 3. IC₅₀s of Patupilone and Paclitaxel in six USPC cell lines

Symbols (error bars) denote means (standard deviations) of IC₅₀s. Text to the left of the symbols denotes the cell line, its paclitaxel/patupilone ratio of IC₅₀s, and the ratio’s P value. Note that the individual ratios are significant (at P<0.05) for the cell lines that show HER-2/neu amplification by FISH, but not significant in the cell lines that don’t. As a class, the three HER-2/neuamplified lines taken together showed significantly lower IC₅₀s for patupilone compared to paclitaxel (P=0.0002), whereas the three unamplified lines taken together did not (P=0.54).

Figure 4. P-glycoprotein (ABCB1) and β-tubulin class III (TUBB3) expression by RT-PCR in high versus low HER-2/neu expressor cell lines

Upper panel: ABCB1; Lower panel: TUBB3. Symbols (error bars) denote the geometric means (SDs) of relative expression in USPC-ARK-1 through ARK-6 ordered from left to right-respectively; symbol shapes and figure brackets denote groupings of cell lines into high and low HER-2/neu expressor groups as indicated by the legends. In each panel, the text between expressor groups reports the geometric mean fold change and P value between high and low expressor groups.