Establishment and Characterization of an Epstein-Barr Virus-positive Cell Line from a Non-keratinizing Differentiated Primary Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC), a cancer that is etiologically associated with the Epstein-Barr virus (EBV), is endemic in Southern China and Southeast Asia. The scarcity of representative NPC cell lines owing to the frequent loss of EBV episomes following prolonged propagation and compromised authenticity of previous models underscores the critical need for new EBV-positive NPC models. Herein, we describe the establishment of a new EBV-positive NPC cell line, designated NPC268 from a primary non-keratinizing, differentiated NPC tissue. NPC268 can undergo productive lytic reactivation of EBV and is highly tumorigenic in immunodeficient mice. Whole-genome sequencing revealed close similarities with the tissue of origin, including large chromosomal rearrangements, while whole-genome bisulfite sequencing and RNA sequencing demonstrated a hypomethylated genome and enrichment in immune-related pathways, respectively. Drug screening of NPC268 together with six other NPC cell lines using 339 compounds, representing the largest high-throughput drug testing in NPC, revealed biomarkers associated with specific drug classes. NPC268 represents the first and only available EBV-positive non-keratinizing differentiated NPC model, and extensive genomic, methylomic, transcriptomic, and drug response data should facilitate research in EBV and NPC, where current models are limited.

SIGNIFICANCE

NPC268 is the first and only EBV-positive cell line derived from a primary non-keratinizing, differentiated nasopharyngeal carcinoma, an understudied but important subtype in Southeast Asian countries. This model adds to the limited number of authentic EBV-positive lines globally that will facilitate mechanistic studies and drug development for NPC.

Abstract 1704: Interferon inducible ADAR1 is essential for the survival of oral squamous cell carcinoma

Treating oral squamous cell carcinoma (OSCC) remains challenging due to limited knowledge of the critical genes that could affect cell survival in OSCC. We have previously utilized genome-wide CRISPR-Cas9 knockout functional screens to explore the genetic vulnerabilities of OSCC and identified Adenosine deaminase acting on RNA (ADAR1) as one of the top fitness genes. ADAR1 is an interferon-stimulated gene (ISG) that catalyses adenosine-to-inosine (A-to-I) editing of double-stranded RNA (dsRNA), which suppresses dsRNA sensing mechanism from triggering cell death. ADAR1 gene encodes for two isoforms, the constitutively expressed P110 and the interferon-inducible P150. Given that deleting ADAR1 severely impacts OSCC viability, we aimed to elucidate key molecular mechanisms underlying this gene dependency which may provide opportunities for developing better treatment strategies. Here, we validated ADAR1 dependency via competitive co-culture assay using single-guide RNA (sgRNA) knockout in selected OSCC cell lines. We also confirmed that sgRNA-mediated ADAR1 knockout resulted in prominent cell lethality through increased apoptosis and inhibition of colony formation. Cell lethality is evident in ADAR1 KO cells in conjunction with the phosphorylation of a dsRNA sensor, protein kinase R (PKR) which regulates cell death mechanism. In ADAR1-less dependent cells, IFN-β treatment increased the expression of ISGs including ADAR1, and sensitized the cells to ADAR1 KO-induced cell death. Overexpression of ADAR1-P150 but not ADAR1-P110 rescued cell lethality in ADAR1-depleted cells, suggesting that ADAR1-P150 is required for OSCC survival. We also demonstrate that the deaminase function of ADAR1 is important in conferring survival to a subset of OSCC lines. In addition to PKR, the melanoma differentiation-associated protein 5 (MDA5) dsRNA sensor is also important in mediating ADAR1 KO-induced cell lethality OSCC and co-deleting both PKR and MDA5 enabled the partial rescue of cell death compared to when each gene was knocked out individually. Collectively, our results uncover the essentiality of IFN-inducible ADAR1-P150 for OSCC survival, and reveal that the activation of PKR and MDA5 dsRNA sensing pathways underlie the cell lethality caused by ADAR1 deletion.

Citation Format: Pei San Yee, Annie Wai Yeeng Chai, Shi Mun Yee, Shi Yin Ooi, Yee Hua Tan, Mathew Garnett, Siew Kit Ng, Sok Ching Cheong. Interferon inducible ADAR1 is essential for the survival of oral squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1704.

Rational Combinations of Targeted Therapy and Immune Checkpoint Inhibitors in Head and Neck Cancers

Immunotherapy, especially the immune checkpoint inhibitors (ICIs) such as the pembrolizumab and nivolumab have contributed to significant improvements in treatment outcomes and survival of head and neck cancer (HNC) patients. Still, only a subset of patients benefits from ICIs and hence the race is on to identify combination therapies that could improve response rates. Increasingly, genetic alterations that occur within cancer cells have been shown to modulate the tumor microenvironment resulting in immune evasion, and these have led to the emergence of trials that rationalize a combination of targeted therapy with immunotherapy. In this review, we aim to provide an overview of the biological rationale and current strategies of combining targeted therapy with the approved ICIs in HNC. We summarize the ongoing combinatorial clinical trials and discuss emerging immunomodulatory targets. We also discuss the challenges and gaps that have yet to be addressed, as well as future perspectives in combining these different drug classes.

Abstract 1226: Targeting OSCC fitness genes YAP1 and WWTR1 via synergistic killing of CA3 in combination with cisplatin

Oral squamous cell carcinoma (OSCC) is one of the most common forms of head and neck cancer, with more than half of the global mortality occurring in Asia. The current treatment regimens for OSCC are of limited benefit to the patients and the development of new targeted therapies is very much needed. In our previous study using genome-wide CRISPR/Cas9 screen to identify the genetic vulnerabilities for OSCC, we have successfully identified two key fitness genes - YAP1 and WWTR1 (TAZ) of the Hippo signaling pathway as potential therapeutic targets for OSCC. We discovered that CRISPR/Cas9-mediated knockout of either YAP1 or WWTR1 in the YAP1- or WWTR1-dependent OSCC cell lines resulted in the down-regulation of pro-proliferative genes such as the CTGF and CYR61. Further, both YAP1 and WWTR1 have separately been implicated as potential mediators of resistance to cisplatin, a common chemotherapy used for the treatment of OSCC patients. Inhibition of the interaction between either YAP1 or WWTR1 with their downstream binding partners, such as the transcription factor, TEAD, has been one of the main focus for therapeutic intervention. However, this has not been examined in the context of OSCC. We, therefore, aim to i) identify and evaluate the anti-proliferative effect of existing YAP1/WWTR1 inhibitors on YAP1/WWTR1-dependent OSCC, ii) evaluate the synergistic effect of combining the YAP1/WWTR1 inhibitors with cisplatin in controlling OSCC growth. We identify two putative inhibitors of YAP/WWTR1/TEAD - Verteporfin and CA3. We show that compared to Verteporfin, the new inhibitor, CA3 exerts a more prominent anti-proliferative effect on the OSCC models that are dependent on either YAP1 or WWTR1, with IC50 in the nanomolar range. We then test the effect of combining CA3 (at 0.5µM and 1µM) with various dosages of cisplatin and demonstrated strong synergistic effects in OSCC across most combinations. We show that CA3 sensitizes OSCC cells to cisplatin at concentrations as low as 0.5µM. Our results further confirm that YAP1/TAZ are important therapeutic targets in OSCC and the treatment of YAP1/TAZ inhibitors could sensitize the OSCC cells to cisplatin. Further investigation is warranted to uncover the mechanism underlying YAP/TAZ-mediated cisplatin sensitivity in OSCC to improve the proportion of OSCC patients who could respond to cisplatin.

Citation Format: Annie Wai Yeeng Chai, Pei San Yee, Shi Mun Yee, Sok Ching Cheong. Targeting OSCC fitness genes YAP1 and WWTR1 via synergistic killing of CA3 in combination with cisplatin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1226.

Genome-wide CRISPR screens of oral squamous cell carcinoma reveal fitness genes in the Hippo pathway

New therapeutic targets for oral squamous cell carcinoma (OSCC) are urgently needed. We conducted genome-wide CRISPR-Cas9 screens in 21 OSCC cell lines, primarily derived from Asians, to identify genetic vulnerabilities that can be explored as therapeutic targets. We identify known and novel fitness genes and demonstrate that many previously identified OSCC-related cancer genes are non-essential and could have limited therapeutic value, while other fitness genes warrant further investigation for their potential as therapeutic targets. We validate a distinctive dependency on YAP1 and WWTR1 of the Hippo pathway, where the lost-of-fitness effect of one paralog can be compensated only in a subset of lines. We also discover that OSCCs with WWTR1 dependency signature are significantly associated with biomarkers of favorable response toward immunotherapy. In summary, we have delineated the genetic vulnerabilities of OSCC, enabling the prioritization of therapeutic targets for further exploration, including the targeting of YAP1 and WWTR1.

IFITM3 knockdown reduces the expression of CCND1 and CDK4 and suppresses the growth of oral squamous cell carcinoma cells

PURPOSE

Oral squamous cell carcinoma (OSCC) is a challenging disease to treat. Up to 50% of OSCC patients with advanced disease develop recurrences. Elucidation of key molecular mechanisms underlying OSCC development may provide opportunities to target specific genes and, thus, to improve patient survival. In this study, we examined the expression and functional role of interferon transmembrane protein 3 (IFITM3) in OSCC development.

METHODS

The expression of IFITM3 in OSCC and normal oral mucosal tissues was assessed by qRT-PCR and immunohistochemistry. The role of IFITM3 in driving OSCC cell proliferation and survival was examined using siRNA-mediated gene knockdown, and the role of IFITM3 in driving cell cycle regulators was examined using Western blotting.

RESULTS

We found that IFITM3 is overexpressed in more than 79% of primary OSCCs. We also found that IFITM3 knockdown led to impaired OSCC cell growth through inhibition of cell proliferation, induction of cell cycle arrest, senescence and apoptosis. In addition, we found that IFITM3 knockdown led to reduced expressions of CCND1 and CDK4 and reduced RB phosphorylation, leading to inhibition of OSCC cell growth. This information may be instrumental for the design of novel targeted therapeutic strategies.

CONCLUSIONS

From our data we conclude that IFITM3 is overexpressed in OSCC and may regulate the CCND1-CDK4/6-pRB axis to mediate OSCC cell growth.

The 4717C > G polymorphism in periplakin modulates sensitivity to EGFR inhibitors

The use of EGFR inhibitors on oral squamous cell carcinoma (OSCC) as monotherapy yielded modest clinical outcomes and therefore would benefit from biomarkers that could predict which patient subsets are likely to respond. Here, we determined the efficacy of erlotinib in OSCC cell lines, and by comparing sensitive and resistant lines to identify potential biomarkers. We focused on the 4717C > G polymorphism in periplakin (PPL) where the CC genotype was associated with erlotinib resistance. To validate this, erlotinib-resistant cell lines harbouring CC genotype were engineered to overexpress the GG genotype and vice versa. Isogenic cell lines were then studied for their response to erlotinib treatment. We demonstrated that overexpression of the GG genotype in erlotinib-resistant lines sensitized them to erlotinib and inhibition of AKT phosphorylation. Similarly, the expression of the CC genotype conferred resistance to erlotinib with a concomitant increase in AKT phosphorylation. We also demonstrated that cell lines with the CC genotype generally are more resistant to other EGFR inhibitors than those with the GG genotype. Overall, we showed that a specific polymorphism in the PPL gene could confer resistance to erlotinib and other EGFR inhibitors and further work to evaluate these as biomarkers of response is warranted.

Effects of palbociclib on oral squamous cell carcinoma and the role of PIK3CA in conferring resistance

Objective

Lack of effective therapies remains a problem in the treatment of oral squamous cell carcinoma (OSCC), especially in patients with advanced tumors. OSCC development is driven by multiple aberrancies within the cell cycle pathway, including amplification of cyclin D1 and loss of p16. Hence, cell cycle inhibitors of the CDK4/6-cyclin D axis are appealing targets for OSCC treatment. Here, we determined the potency of palbociclib and identified genetic features that are associated with the response of palbociclib in OSCC.

Methods

The effect of palbociclib was evaluated in a panel of well-characterized OSCC cell lines by cell proliferation assays and further confirmed by in vivo evaluation in xenograft models. PIK3CA-mutant isogenic cell lines were used to investigate the effect of PIK3CA mutation towards palbociclib response.

Results

We demonstrated that 80% of OSCC cell lines are sensitive to palbociclib at sub-micromolar concentrations. Consistently, palbociclib was effective in controlling tumor growth in mice. We identified that palbociclib-resistant cells harbored mutations in PIK3CA. Using isogenic cell lines, we showed that PIK3CA mutant cells are less responsive to palbociclib as compared to wild-type cells with concurrent upregulation of CDK2 and cyclin E1 protein levels. We further demonstrated that the combination of a PI3K/mTOR inhibitor (PF-04691502) and palbociclib completely controlled tumor growth in mice.

Conclusions

This study demonstrated the potency of palbociclib in OSCC models and provides a rationale for the inclusion of PIK3CA testing in the clinical evaluation of CDK4/6 inhibitors and suggests combination approaches for further clinical studies.

Zerumbone targets the CXCR4-RhoA and PI3K-mTOR signaling axis to reduce motility and proliferation of oral cancer cells

BACKGROUND

The CXCR4-RhoA and PI3K-mTOR signaling pathways play crucial roles in the dissemination and tumorigenesis of oral squamous cell carcinoma (OSCC). Activation of these pathways have made them promising molecular targets in the treatment of OSCC. Zerumbone, a bioactive monocyclic sesquiterpene isolated from the rhizomes of tropical ginger, Zingiber zerumbet (L.) Roscoe ex Sm. has displayed promising anticancer properties with the ability to modulate multiple molecular targets involved in carcinogenesis. While the anticancer activities of zerumbone have been well explored across different types of cancer, the molecular mechanism of action of zerumbone in OSCC remains largely unknown.

PURPOSE

Here, we investigated whether OSCC cells were sensitive towards zerumbone treatment and further determined the molecular pathways involved in the mechanism of action.

METHODS

Cytotoxicity, anti-proliferative, anti-migratory and anti-invasive effects of zerumbone were tested on a panel of OSCC cell lines. The mechanism of action of zerumbone was investigated by analysing the effects on the CXCR4-RhoA and PI3K-mTOR pathways by western blotting.

RESULTS

Our panel of OSCC cells was broadly sensitive towards zerumbone with IC₅₀ values of less than 5 µM whereas normal keratinocyte cells were less responsive with IC₅₀ values of more than 25 µM. Representative OSCC cells revealed that zerumbone inhibited OSCC proliferation and induced cell cycle arrest and apoptosis. In addition, zerumbone treatment inhibited migration and invasion of OSCC cells, with concurrent suppression of endogenous CXCR4 protein expression in a time and dose-dependent manner. RhoA-pull down assay showed reduction in the expression of RhoA-GTP, suggesting the inactivation of RhoA by zerumbone. In association with this, zerumbone also inhibited the PI3K-mTOR pathway through the inactivation of Akt and S6 proteins.

CONCLUSION

We provide evidence that zerumbone could inhibit the activation of CXCR4-RhoA and PI3K-mTOR signaling pathways leading to the reduced cell viability of OSCC cells. Our results suggest that zerumbone is a promising phytoagent for development of new therapeutics for OSCC treatment.

Genetically-defined novel oral squamous cell carcinoma cell lines for the development of molecular therapies

Emerging biological and translational insights from large sequencing efforts underscore the need for genetically-relevant cell lines to study the relationships between genomic alterations of tumors, and therapeutic dependencies. Here, we report a detailed characterization of a novel panel of clinically annotated oral squamous cell carcinoma (OSCC) cell lines, derived from patients with diverse ethnicity and risk habits. Molecular analysis by RNAseq and copy number alterations (CNA) identified that the cell lines harbour CNA that have been previously reported in OSCC, for example focal amplications in 3q, 7p, 8q, 11q, 20q and deletions in 3p, 5q, 8p, 18q. Similarly, our analysis identified the same cohort of frequently mutated genes previously reported in OSCC including TP53, CDKN2A, EPHA2, FAT1, NOTCH1, CASP8 and PIK3CA. Notably, we identified mutations (MLL4, USP9X, ARID2) in cell lines derived from betel quid users that may be associated with this specific risk factor. Gene expression profiles of the ORL lines also aligned with those reported for OSCC. By focusing on those gene expression signatures that are predictive of chemotherapeutic response, we observed that the ORL lines broadly clustered into three groups (cell cycle, xenobiotic metabolism, others). The ORL lines noted to be enriched in cell cycle genes responded preferentially to the CDK1 inhibitor RO3306, by MTT cell viability assay. Overall, our in-depth characterization of clinically annotated ORL lines provides new insight into the molecular alterations synonymous with OSCC, which can facilitate in the identification of biomarkers that can be used to guide diagnosis, prognosis, and treatment of OSCC.

Common oncogenic mutations are infrequent in oral squamous cell carcinoma of Asian origin

OBJECTIVES

The frequency of common oncogenic mutations and TP53 was determined in Asian oral squamous cell carcinoma (OSCC).

MATERIALS AND METHODS

The OncoCarta(™) panel v1.0 assay was used to characterize oncogenic mutations. In addition, exons 4-11 of the TP53 gene were sequenced. Statistical analyses were conducted to identify associations between mutations and selected clinico-pathological characteristics and risk habits.

RESULTS

Oncogenic mutations were detected in PIK3CA (5.7%) and HRAS (2.4%). Mutations in TP53 were observed in 27.7% (31/112) of the OSCC specimens. Oncogenic mutations were found more frequently in non-smokers (p = 0.049) and TP53 truncating mutations were more common in patients with no risk habits (p = 0.019). Patients with mutations had worse overall survival compared to those with absence of mutations; and patients who harbored DNA binding domain (DBD) and L2/L3/LSH mutations showed a worse survival probability compared to those patients with wild type TP53. The majority of the oncogenic and TP53 mutations were G:C > A:T and A:T > G:C base transitions, regardless of the different risk habits.

CONCLUSION

Hotspot oncogenic mutations which are frequently present in common solid tumors are exceedingly rare in OSCC. Despite differences in risk habit exposure, the mutation frequency of PIK3CA and HRAS in Asian OSCC were similar to that reported in OSCC among Caucasians, whereas TP53 mutations rates were significantly lower. The lack of actionable hotspot mutations argue strongly for the need to comprehensively characterize gene mutations associated with OSCC for the development of new diagnostic and therapeutic tools.

Relationship of the train-of-four fade ratio to clinical signs and symptoms of residual paralysis in awake volunteers

BACKGROUND

Recovery of the train-of-four (TOF) ratio to a value > 0.70 is synonymous with adequate return of neuromuscular function, but there is little information available concerning the subjective experience that accompanies residual neuromuscular block wherein the TOF ratio is in the range of 0.70 to 0.90.

METHODS

Ten American Society of Anesthesiologists' (ASA) physical status 1 volunteers were studied. Control measurements including grip strength in kilograms and ability to perform a 5-s head- and leg-lift. In addition, a standard wooden tongue depressor was placed between each subject's incisor teeth, and he or she was told not to let the investigator remove it. All subjects were easily able to retain the device despite vigorous attempts to dislodge it. Neuromuscular function was monitored with a Datex (Datex Medical Instrumentation, Inc., Tewksbury, MA) 221 electromyographic (EMG) monitor. TOF stimulation was given every 20 s, and the measured TOF fade ratio was continuously recorded. A 5 mg/kg bolus of mivacurium was then administered, and an infusion at 2 mg.kg-1.min-1 was begun. The infusion was continued until the TOF ratio decreased to < 0.70 and was adjusted to keep it in the range of 0.65 to 0.75. Signs and symptoms of weakness were recorded when the TOF ratio had been stable +/-0.03 for at least 10 min during an interval when there were no adjustments in the infusion. All tests noted previously were repeated at this time. The TOF ratio was then allowed to recover to 0.85-0.90. When stable at this level, all tests were repeated, and the infusion was discontinued. TOF measurements were continued until a ratio of 1.0 was attained and until a final set of observations was recorded.

RESULTS

The TOF ratio in all subjects was reduced to < 0.70. No volunteers required intervention to maintain a patient airway, and the hemoglobin oxygen saturation while breathing air was > or = 96% at all times. TOF ratios < or = 0.90 were accompanied by diplopia and difficulty in tracking moving objects in all subjects. The ability to strongly oppose the incisor teeth did not return until the TOF ratio (on average) exceeded 0.85. A sustained 5-s head-lift was not achieved until the TOF ratio averaged 0.60 (range, 0.45-0.75). At a TOF ratio of 0.70, grip strength averaged 59% of control (range, 50-75%). With certain exceptions (vision, ability to clench the teeth tightly), there was wide variation in symptomatology between patients for any given TOF ratio. It is impossible to give reliable TOF break-points at which symptoms and signs will be present or absent.

CONCLUSIONS

All subjects had significant signs and symptoms of residual block at a TOF ratio of 0.70; none considered themselves remotely "street ready" at this time. The authors believe that satisfactory recovery of neuromuscular function after mivacurium-induced neuromuscular block requires return of the TOF ratio to a value > 0.90 and ideally to unity.

Residual postoperative paralysis. Pancuronium versus mivacurium, does it matter?

BACKGROUND

Based on a train-of-four (TOF) ratio greater than 0.70 as the standard of acceptable clinical recovery, undetected postoperative residual paralysis occurs frequently in postanesthesia care units. In most published studies, detailed information regarding anesthetic management is not provided. The authors reexamined the incidence of postoperative weakness after the administration of long- and short-acting neuromuscular blockers because few, if any, such comparative studies are available.

METHODS

Ninety-one adult patients were studied. In group 1 (mivacurium, n = 35), anesthesia was induced with propofol/ fentanyl and maintained with nitrous oxide, desflurane, and opioid supplementation. The response of the adductor pollicis to ulnar nerve stimulation was estimated by palpating the thumb. Mivacurium (0.20 mg/kg) was administered for tracheal intubation, and an infusion was adjusted to maintain the TOF count at 1. When surgery was completed, the infusion was discontinued. When a second twitch could be detected, 7.0 micrograms/kg atropine and then 0.5 mg/kg edrophonium were administered. At 5 and 10 min, the mechanical TOF response was measured. Additional measurements were recorded if possible. Patients were tracheally extubated and discharged from the operating room when they could respond to verbal commands and no TOF fade was palpable. In group 2 (pancuronium-desflurane anesthesia, n = 29), the protocol was identical to that of group 1, except that 0.07 mg/kg pancuronium was administered for tracheal intubation. Additional increments (0.5 to 1 mg) were given as needed. Antagonism was accomplished with 0.05 mg/kg neostigmine and 0.01 mg/kg glycopyrrolate. In group 3 (pancuronium propofol-opioid, n = 27), the protocol was identical to that of group 2, except that anesthesia was maintained with nitrous oxide and a propofol-alfentanil infusion. In all groups, patients were assessed until a TOF ratio of 0.90 or more was achieved.

RESULTS

All of the patients in group 1 had TOF ratios greater than 0.80 on arrival in the postanesthesia care unit. Twenty of 35 patients had TOF ratios 0.90 or more while they were still in the operating room. Thirty-three of 35 patients had TOF ratios 0.90 or more within 30 min of reversal, and this value was reached in all patients by 45 min. Recovery parameters in groups 2 and 3 did not differ from each other. Hence data from these groups were pooled. Fifty-four of 56 patients who received pancuronium had TOF values of 0.70 or more, the remaining two patients had values of 0.6 to 0.7. In contrast to the mivacurium group, however, only four patients achieved a TOF ratio of 0.90 or greater while still in the operating room. Finally, eight of these patients did not achieve this degree of recovery within 90 min of reversal.

CONCLUSIONS

These results suggest that if nondepolarizing neuromuscular blockers are administered using tactile evaluation of the TOF count as a guide, critical episodes of postoperative weakness in the postanesthesia care unit should occur infrequently even with long-acting relaxants. Nevertheless, if full recovery is defined as return to a TOF ratio of 0.90 or more, then short-acting agents would appear to offer a wider margin of safety.