Preclinical Study Finds Cancer Stem Cell Inhibitor Sensitizes Colon Cancer Cells To Immunotherapy

MedicalResearch.com Interview with:
Dr. Yuan Gao

Assistant Investigator at Boston Biomedical

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Colorectal cancer (CRC) is the third most commonly diagnosed malignant disease and third most frequent cause of cancer-related death in the United States. Standard treatment for unresectable metastatic CRC currently includes first and second line 5-fluorouracil (5-FU)-based chemotherapy regimens. However, CRC patients often develop chemoresistance. Recently, immunotherapy has emerged as a revolutionary new treatment for CRC. However, with the exception of a small percentage of CRC patients that display microsatellite instability (MSI), the vast majority of colorectal cancer patients have been found to be resistant to immune checkpoint therapies.

Cancer stem cells (CSCs), a highly malignant tumor cell subpopulation capable of self-renewal, are considered to be fundamentally responsible for malignant growth and tumor recurrence. Emerging evidence indicates that CSCs and cancer stemness pathways, such as STAT3, beta-Catenin, CD44 and Nanog, are involved in the immune evasion of cancers. BBI-608 (napabucasin) is an orally-administered first-in-class cancer stemness inhibitor that works by targeting STAT3. In this study, we investigated the effect of cancer stemness inhibition on sensitizing colorectal cancer to immune checkpoint inhibitors in preclinical models.

In the syngeneic microsatellite stable (MSS) tumor model, CT26, an anti-PD-1 antibody delivered as a monotherapy, produced low level and temporary antitumor activity with rapid development of complete resistance to anti-PD-1 treatment. The anti-PD-1 antibody-treated CT26 tumors exhibited increased p-STAT3 activation and overexpression of a variety of stemness factors, as well as enrichment of sphere-forming stemness-high cancer cells. Napabucasin was able to reduce basal as well as anti-PD1-induced STAT3 activation and other CSC features within CT26 tumors. The combination of a stemness inhibitor – napabucasin – with the anti-PD-1 antibody led to tumor complete response (CR) in all treated CT26 tumors, with 40 percent of the mice remaining tumor-free for 30 days following treatment termination. This combination also had a synergistic effect on the influx of tumor infiltrating CD8+ T cells, which likely contributed to the rapid tumor regression. Finally, mice CR-induced by napabucasin and the anti-PD-1 antibody were able to reject CT26 tumors upon re-challenge, but not the unrelated breast cancer 4T1 tumors.

MedicalResearch.com: What should readers take away from your report?

Response: Our data suggest cancer stemness pathways contribute to immunotherapy resistance in MSS CRC, a subtype representing the vast majority of colorectal cancer cases. Furthermore, inhibition of cancer stemness by BBI-608 sensitizes colorectal cancer to immune checkpoint inhibition, producing striking regression in a large proportion of the tumors treated.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: This study provides compelling preclinical evidence to support the investigation of the combination of napabucasin with immune checkpoint inhibitors in CRC. While this study specifically investigated the combination with anti-PD-1, the combination with other immunotherapies could be studied as well.

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.

Citation: AACR 2017 Abstract

Inhibition of cancer stemness sensitizes colorectal cancer to immune checkpoint inhibitors
Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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