p66ShcA potentiates the cytotoxic response of triple-negative breast cancers to PARP inhibitors
Eduardo Cepeda Cañedo, Stephanie Totten, Ryuhjin Ahn, Paul Savage, Deanna MacNeil, Jesse Hudson, Chantal Autexier, Genevieve Deblois, Morag Park, Michael Witcher, Josie Ursini-Siegel
Eduardo Cepeda Cañedo, Stephanie Totten, Ryuhjin Ahn, Paul Savage, Deanna MacNeil, Jesse Hudson, Chantal Autexier, Genevieve Deblois, Morag Park, Michael Witcher, Josie Ursini-Siegel
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Research Article Cell biology Oncology

p66ShcA potentiates the cytotoxic response of triple-negative breast cancers to PARP inhibitors

Abstract

Triple-negative breast cancers (TNBCs) lack effective targeted therapies, and cytotoxic chemotherapies remain the standard of care for this subtype. Owing to their increased genomic instability, poly (ADP-ribose) polymerase (PARP) inhibitors (PARPi) are being tested against TNBCs. In particular, clinical trials are now interrogating the efficacy of PARPi combined with chemotherapies. Intriguingly, while response rates are low, cohort of patients do respond to PARPi in combination with chemotherapies. Moreover, recent studies suggest that an increase in levels of ROS may sensitize cells to PARPi. This represents a therapeutic opportunity, as several chemotherapies, including doxorubicin, function in part by producing ROS. We previously demonstrated that the p66ShcA adaptor protein is variably expressed in TNBCs. We now show that, in response to therapy-induced stress, p66ShcA stimulated ROS production, which, in turn, potentiated the synergy of PARPi in combination with doxorubicin in TNBCs. This p66ShcA-induced sensitivity relied on the accumulation of oxidative damage in TNBCs, rather than genomic instability, to potentiate cell death. These findings suggest that increasing the expression of p66ShcA protein levels in TNBCs represents a rational approach to bolster the synergy between PARPi and doxorubicin.

Authors

Eduardo Cepeda Cañedo, Stephanie Totten, Ryuhjin Ahn, Paul Savage, Deanna MacNeil, Jesse Hudson, Chantal Autexier, Genevieve Deblois, Morag Park, Michael Witcher, Josie Ursini-Siegel

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Figure 1

p66ShcA sensitizes TNBC cells to doxorubicin/PARPi combination therapies.

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p66ShcA sensitizes TNBC cells to doxorubicin/PARPi combination therapies...
(A) ShcA and tubulin immunoblot analysis of VC- (p66ShcA null) and p66ShcA-expressing cells. (B) Hs578T cells were cultured in DMSO, doxorubicin (1 nM), and PARPi (50–600 nM) alone or in combination for 5 days. Viable cells were quantified by trypan blue exclusion. Data are shown as the mean of mean fold change in cell viability relative to DMSO (mean ± SEM) (n = 3 independent experiments). (C) Excess-over-Bliss scores. (D) Soft agar assay to assess the tumorigenic potential of Hs578T-VC– and p66ShcA-expressing cells cultured in the presence of DMSO, doxorubicin (1 nM), and PARPi (300 nM) alone or in combination for 10 days. Data are representative of 2 independent experiments. The total number of foci and average area of each foci ± SD (n = 2 experiments, with 6 technical repeats each) (original magnification, ×40). (E) VC- or p66ShcA-expressing Hs578T cells were injected into the mammary fat pads of SCID-Beige mice. At 150mm3, mice were randomized into 4 treatment groups: (a) DMSO, (b) 2.5 mg/kg doxorubicin, (c) 25 mg/kg PARPi, or (d) doxorubicin and PARPi combination therapy. Data are shown as fold increase in tumor volume relative to the start of treatment (day 0) ± SEM (n = 20–22 tumors per group). Measurements were taken every second or third day following the start of treatment. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 by 2-tailed t test (B), 1-way ANOVA/Tukey’s multiple comparisons test (D), and mixed-effect analysis/Sidak’s multiple comparison tests (E).