Abstract 3127: Negative impact of paclitaxel on human breast tumor microenvironment and its reversal by the combination of interferon-α with TLR3 agonist rintatolimod
Authors: Gandhi Shipra , Grimm Melissa , Slomba Ronald , Takabe Kazuaki , Kalinski Pawel 
Published: June 2022

Abstract
Background: Taxanes are extensively used in the chemotherapy of breast cancer in the neoadjuvant, adjuvant and metastatic settings. Paclitaxel is known to have both immunostimulatory and immunosuppressive effects, but its impact on the chemokine system within the tumor microenvironment (TME) remains unclear. In the breast TME treated with neoadjuvant taxane chemotherapy, high levels of the cytotoxic T cell (CTL) attractants CXCL9, CXCL10 and their common receptor CXCR3 predict higher probability of pathological complete response (pCR) and improved long term outcomes. We previously developed a chemokine modulatory regimen (CKM) combining interferon-α with TLR3 agonist rintatolimod to selectively increase CTL-attracting chemokines in the TME but reduce the production of chemokines attracting myeloid-derived suppressor cells (MDSC) and regulatory T cells (Treg) in the TME. Here we evaluated paclitaxel’s impact on chemokine production in the human breast TME and CKM’s ability to eliminate undesirable aspects of taxane chemotherapy.
Methods: Fresh breast cancer tissues obtained during routine surgeries, breast cancer cell lines BT-549 and MDA-MD-231 and peripheral blood monocyte-derived macrophages were analyzed immediately or cultured ex vivo for 24 hours in the absence or presence of paclitaxel and/or CKM components. The expression of chemokine genes and secretion of chemokines by freshly harvested and ex vivo-treated tumor explants, cancer cell lines and macrophages were analyzed by quantitative PCR (Taqman) and ELISA. Paired student t-test was used for statistical analyses.
Results: Breast cancer explants spontaneously expressed high levels of MDSC/Treg-attractants CXCL12 and CCL22, but only marginal levels of CTL and natural killer (NK) cell attractants CXCL9, CXCL10, CXCL11 and CCL5. Unexpectedly, paclitaxel treatment resulted in further elevation of granulocyte/MDSC-attractant CXCL8 and CCL22, which was reversed by the combination of paclitaxel with CKM. At the same time, while paclitaxel alone did not induce any of the CTL attractants tested, its combination with the CKM was highly effective in inducing CXCL9, CXCL10, CXCL11 and CCL5.
Conclusions: Our results identify an undesirable aspect of paclitaxel’s impact on breast cancer. The ability of CKM to enhance the expression of CTL/NK cell attractants and suppress the production of Treg/MDSC attractants produced by paclitaxel provides a strong rationale for combined use of CKM in taxane-based chemo-immunotherapy of breast cancer and potentially other diseases.
Citation Format: Shipra Gandhi, Melissa Grimm, Ronald Slomba, Kazuaki Takabe, Pawel Kalinski. Negative impact of paclitaxel on human breast tumor microenvironment and its reversal by the combination of interferon-α with TLR3 agonist rintatolimod [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3127.