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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Gene-silencing RNAs Targeting CTNNB1 and PD-L1 May Attack a Variety of Cancers

MedicalResearch.com Interview with:
Dr. Youzhi Li

Vice President at Boston Biomedical 

MedicalResearch.com: What are the main findings?

Response: RNAi (RNA interference) technology has the potential to target any genes causing disease, including conventionally “undruggable” targets in cancer. One particularly interesting RNAi target in oncology is the CTNNBI oncogene, which encodes the β-Catenin protein whose nuclear form acts as a transcription factor promoting tumorigenesis. Aberrant β-Catenin signaling has been demonstrated in 90 percent of colorectal carcinomas, 40 percent of hepatocellular carcinoma, and 90 percent of non-ductal pancreatic carcinomas. Recent research also suggests active β-Catenin contributes to tumor immune evasion and to the recurrence of melanoma in patients post the check-point blockage immunotherapy.

However, the direct blockade of β-Catenin activity has proved difficult with conventional approaches. While the application of traditional RNAi technology has the potential to block this pathway, in clinical cancer therapy, this approach has proven challenging due to the difficulty in systemic delivery of RNAi to tumor sites located in various organs.

We have recently developed BBI-801, a lipid-based nanoparticle that encapsulates therapeutic aiRNAs targeting CTNNB1 and PD-L1 to simultaneously target immune evasion via both these pathways. Here, we investigate the in vivo delivery and anti-tumor activity of BBI-801.

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Model of RAF Inhibitor Action Provides Roadmap For Resistant Colon and Thyroid Cancer Treatment

MedicalResearch.com Interview with:

Poulikos I. Poulikakos, PhD Assistant Professor Department of Oncological Sciences Department of Dermatology The Tisch Cancer Institute Icahn School of Medicine at Mount Sinai

Dr. Poulikakos

Poulikos I. Poulikakos, PhD
Assistant Professor
Department of Oncological Sciences
Department of Dermatology
The Tisch Cancer Institute
Icahn School of Medicine at Mount Sinai

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

Response: Mutations in the oncoprotein kinase BRAF are found in about 8% of human tumors, including more than 50% of melanomas. Small molecule RAF inhibitors prolonged survival of melanoma patients with mutant-BRAF tumors, but resistance limits their effectiveness. Further, RAF inhibitors showed only modest efficacy in patients with colorectal and thyroid mutant-BRAF tumors. Previous studies have suggested that the complex biochemical mechanisms of action of RAF inhibitors account for both sensitivity and major mechanisms of resistance to these drugs. Recently, a number of next generation RAF inhibitors have entered preclinical or clinical development, but the most appropriate clinical context for their use remained elusive.

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Effect of Centralization on Health Disparities in Lung and Bladder Cancer Surgery

MedicalResearch.com Interview with:

Emanuela Taioli MD PhD Professor, Population Health Science and Policy, and Thoracic Surgery Director, Institute for Translational Epidemiology Director, Center for the Study of Thoracic Diseases Outcome Director, Division of Social Epidemiology Icahn Medical Institute, New York, NY 10029

Dr. Taioli

Emanuela Taioli MD PhD
Professor, Population Health Science and Policy, and Thoracic Surgery
Director, Institute for Translational Epidemiology
Director, Center for the Study of Thoracic Diseases Outcome
Director, Division of Social Epidemiology
Icahn Medical Institute,
New York, NY 10029 

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

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We investigated the effects of centralization on HV hospital utilization and surgical outcomes for lung (n = 28,047 White; n = 2,638 Black) and bladder (n = 7,593 White; n = 567 Black) cancer patients over a 15 year time span (1997-2011) in New York State. We hypothesized that centralization has improved utilization of HV hospitals and outcomes for both black and white patients, but significant disparities remain between black and white patients.

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