Abstract 935: Oral cancer cells may hijack stem cell altruism to survive during extreme hypoxia, and exposure to chemotherapeutic drugs

Abstract

The mechanism of tumor hypoxia induced reprogramming of cancer cells are not understood well. Hypoxia might activate evolutionary preserved cellular defense mechanism that could contribute to tumor progression and metastasis. We recently described that during hypoxia/oxidative stress, human embryonic stem cells (hES) exhibit an altruistic defense mechanism, where a few cells reprogram to a highly undifferentiated state, and secrete glutathione to protect rest of the community of cells from oxidative stress induced DNA damage (Das B et al, Stem Cells, 2012). The altruistic stem cells phenotype exhibited high HIF-2alpha and low p53 activity. After a few weeks, the reprogrammed cells, although highly fit to survives, underwent spontaneous apoptosis/differentiation by re-activating the p53/MDM2 oscillation. Thus, the reprogrammed cells sacrificed its own fitness to enhance the fitness of the rest of the community, an altruistic behavior (Das B et al. Stem Cells, 2012). Here, we investigated the potential hijacking of the altruistic defense mechanism by oral cancer cells during exposure to hypoxia. We exposed the four oral cancer cell lines SCC-25, SCC-15, SCC-9 and SCC-5 to extreme hypoxia followed by re-oxygenation for 72 hours. We found that while majority of cancer cells underwent apoptosis, a few cancer cell lines survived, exhibited side-population (SP) phenotype, high level of HIF-2alpha, Nanog, Sox-2 and MYC. The SP cells exhibited migratory activity, as well as high tumorigenic and metastatic activity in NOD/SCID mice. ChIP assay indicated that HIF-2alhpa interact with MYC and NOTCH1. The conditioned media of SP cells exhibited high level of glutathione, and ability to protect non-SP cells from cisplatin-induced toxicity. These results indicate that HIF-2alpha and MYC may cooperate to reprogram a few oral cancer cells to altruistic stemness phenotype. The altruistic phenotype that exhibited cytoprotective activity against cisplatin mediated toxicity. Thus, similar to bacteria, where altruistic biofilm exhibit novel drug resistance mechanism, stem cell altruism may serve as a novel drug resistance mechanism in oral cancer. Citation Format: Rashmi Bhuyan, Hong Li, Sukanya Gayan, Bidisha Pal, Reza Bayat-Mokhtari, Jyotirmoy Phukan, Debabrata Baishya, Anupam Sarma, Joyeeta Talukdar, Manaf Muhammad Alkurdi, Wael Tasabehji, Seema Bhuyan, Gayatri Gogoi, Ista Pulu, Herman Yeger, Bikul Das. Oral cancer cells may hijack stem cell altruism to survive during extreme hypoxia, and exposure to chemotherapeutic drugs. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 935.

Targeting tumor stemness switch phenotype by activating pathogen induced stem cell niche defense

“…Next, we evaluated the in vivo potency of bystander apoptosis of ABCG2+ CSC in a SCC-25 derived xenograft model of NOD/SCID mice, which we recently characterized [8], [41]. The BCG-CM, BCG+Rif-CM or saline (1 ml/week/i.p.)…”

“…Others also reported drug-induced stemness in several tumor models [6], [7]. Subsequently, using a SCC-25 oral cancer derived CSC model, we showed that chemotherapy-induced TSS enable CSCs to modulate TME for rapid tumor progression and immune suppression [8], [9]. In addition, we found that oral CSCs undergo inflammation and bacteria mediated TSS phenotype [10], [11], which also contribute to rapid tumor progression.…”

Targeting hypoxia-induced tumor stemness by activating pathogen-induced stem cell niche defense

“…To test this hypothesis, we have utilized several cancer cell line-derived xenograft models, where we characterized the TS phenotype. In these xenografts of neuroblastoma (SKN-BE-2), sarcoma (HOS and RH4), small cell lung cancer (H-146), colon cancer (LOVO), breast cancer (MCF-7), and oral squamous cell cancer (SCC-25), we found that migratory side population cells (SPm) enriched in ABCG2+ CSCs having high tumorigenic activity reside in the hypoxic TME niche and exhibit TS phenotype (5)(6)(7)11). We previously obtained this highly tumorigenic SPm+/ABCG2+/ABCG2+ CSCs from SP cells (25) when exposed to 24 h of hypoxia followed by 24 h of reoxygenation (5).…”

“…These results indicate that the replication of BCG intracellular to EpCAM+/ABCG2+ CSCs is required for the CM of these cells to induce bystander apoptosis. Next, we evaluated the in vivo potency of bystander apoptosis of EpCAM+/ABCG2+ CSCs in a SCC-25-derived xenograft model of NOD/SCID mice (n = 7), which we recently characterized (11). The BCG-CM, BCG + Rif-CM, or saline (1 ml/week/i.p.)…”

“…Others also reported drug-induced stemness in several tumor models ( 9 , 10 ). Subsequently, using a SCC-25 oral cancer–derived CSC model, we showed that hypoxia/reoxygenation or chemotherapy-induced TS enables ABCG2-positive sub-fraction of EpCAM+/ALDH1+/CD44v3+ CSCs to modulate TME for rapid tumor progression and immune suppression ( 11 , 12 ). In addition, we found that oral cancer EpCAM+/ABCG2+ cells undergo inflammation and bacteria-mediated TS phenotype ( 13 ), which also contribute to rapid tumor progression.…”