Activation of Inflammatory Responses Correlate With Hedgehog Activation and Precede Expansion of Cancer Stem-Like Cells in an Animal Model of Residual Triple Negative Breast Cancer after Neoadjuvant Chemotherapy

Abstract

Triple Negative Breast Cancer (TNBC) is characterized as a lack of expression of the
hormonal receptors, estrogen and progesterone, and Human epidermal growth factor receptor
2 (HER2) and as such is unresponsive to current targeted therapy. Resistance of breast cancers
to treatment is thought to be due to a sub-population of tumor cells called Breast Cancer Stem
Cells (BCSCs) and contributes to poor prognosis and increased risk of recurrence. Previously,
we have shown that hedgehog activation is induced by chemotherapy and promotes expansion
of a stem-like population in breast cancer cell lines. In addition, chemotherapy can induce an
inflammatory response and inflammatory factors can lead to activation of Hedgehog (HH) at
sites of tissue injury. Therefore, we wanted to investigate how chemotherapy altered hedgehog
signaling and correlated with the release of inflammatory cytokines in a mouse model of breast
cancer. Patient derived triple negative breast tumor bearing mice were treated with weekly
doses of docetaxel. Following treatment, tumor volume decreased reaching a nadir around 15
days after the start of treatment and increased back to pre-treatment size 35-39 days post treatment.
Immunohistochemical staining of mice tumors revealed that Sonic hedgehog and nuclear
Gli-1 expression transiently increased following docetaxel treatment, reached peak expression
at day 8, and subsequently decreased to almost pre-treatment levels following regrowth of the
tumor. Similarly, Interleukin 6 (IL-6) and Interleukin 8 (IL-8) expression transiently increased,
peaked around day 8, and decreased upon tumor regrowth, however, remained above pre-treatment
levels. Expression of the stem cell marker ALDH1A3 proceeded activation of hedgehog
signaling and expression of inflammatory cytokines, increasing around day 15 post treatment
and continued to be elevated during tumor regrowth. Thus, chemotherapy treatment resulted in
activation of the hedgehog pathway and release of inflammatory cytokines leading to long-term
expansion of ALDH1A3 positive stem cells, which can contribute to the regrowth of the tumor
and promote resistance to treatment.