Enhancing standard of care chemotherapy efficacy using DNA-dependent protein kinase (DNA-PK) inhibition in preclinical models of Ewing sarcoma

Disruption of DNA damage repair via impaired homologous recombination is characteristic of Ewing sarcoma (EWS) cells. We hypothesize that this disruption results in increased reliance on non-homologous end joining (NHEJ) to repair DNA damage. In this study, we investigated if pharmacological inhibition of the enzyme responsible for NHEJ, the DNA-PK holoenzyme, alters the response of EWS cells to genotoxic standard of care chemotherapy. We used analyses of cell viability and proliferation to investigate the effects of clinical DNA-PK inhibitors (DNA-PKi) in combination with six therapeutic or experimental agents for EWS. We performed calculations of synergy using the Loewe Additivity Model. Immunoblotting evaluated treatment effects on DNA-PK, DNA damage, and apoptosis. Flow cytometric analyses evaluated effects on cell cycle and fate. We used orthotopic xenograft models to interrogate tolerability, drug mechanism, and efficacy in vivo. DNA-PKi demonstrated on-target activity, reducing phosphorylated DNA-PK levels in EWS cells. DNA-PKi sensitized EWS cell lines to agents that function as topoisomerase 2 (TOP2) poisons and enhanced the DNA damage induced by TOP2 poisons. Nanomolar concentrations of single agent TOP2 poisons induced G2M arrest and little apoptotic response, while adding DNA-PKi mediated apoptosis. In vivo, the combination of AZD-7648 and etoposide had limited tolerability but resulted in enhanced DNA damage, apoptosis, and EWS tumor shrinkage. The combination of DNA-PKi with standard of care TOP2 poisons in EWS models is synergistic, enhances DNA damage and cell death, and may form the basis of a promising future therapeutic strategy for EWS.

Inhibition of NAD+-Dependent Metabolic Processes Induces Cellular Necrosis and Tumor Regression in Rhabdomyosarcoma Models

PURPOSE

Deregulated metabolism in cancer cells represents a vulnerability that may be therapeutically exploited to benefit patients. One such target is nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the NAD+ salvage pathway. NAMPT is necessary for efficient NAD+ production and may be exploited in cells with increased metabolic demands. We have identified NAMPT as a dependency in rhabdomyosarcoma (RMS), a malignancy for which novel therapies are critically needed. Here we describe the effect of NAMPT inhibition on RMS proliferation and metabolism in vitro and in vivo.

EXPERIMENTAL DESIGN

Assays of proliferation and cell death were used to determine the effects of pharmacologic NAMPT inhibition in a panel of ten molecularly diverse RMS cell lines. Mechanism of the clinical NAMPTi OT-82 was determined using measures of NAD+ and downstream NAD+-dependent functions, including energy metabolism. We used orthotopic xenograft models to examine tolerability, efficacy, and drug mechanism in vivo.

RESULTS

Across all ten RMS cell lines, OT-82 depleted NAD+ and inhibited cell growth at concentrations ≤1 nmol/L. Significant impairment of glycolysis was a universal finding, with some cell lines also exhibiting diminished oxidative phosphorylation. Most cell lines experienced profound depletion of ATP with subsequent irreversible necrotic cell death. Importantly, loss of NAD and glycolytic activity were confirmed in orthotopic in vivo models, which exhibited complete tumor regressions with OT-82 treatment delivered on the clinical schedule.

CONCLUSIONS

RMS is highly vulnerable to NAMPT inhibition. These findings underscore the need for further clinical study of this class of agents for this malignancy.

Abstract 6718: Exploiting metabolic vulnerabilities of pediatric rhabdomyosarcoma with novelnicotinamide phosphoribosyltransferase (NAMPT) inhibitor OT-82

Purpose: A hallmark of cancer cells is altered metabolism. Therapeutically, these alterations may be exploited by targeting metabolic vulnerabilities specific to cancer cells. Efficient production of NAD through the NAD salvage pathway is one such potential vulnerability, as some tumor cells demonstrate a high need for rapid NAD turnover. Nicotinamide phosphoribosyltransferase (NAMPT) is the pharmacologically targetable rate-limiting enzyme in this pathway. We report on the effect of targeting NAMPT in models of pediatric rhabdomyosarcoma (RMS), a cancer for which novel therapeutics remain an unmet need.

Experimental Procedures: The relative sensitivity of RMS cell lines to NAMPT inhibitors was first compared to NAMPT inhibitor sensitivity of other cancer cell lines using viability assays. A panel of ten molecularly diverse RMS cell lines was used for the remainder of the evaluations. In vitro activity of NAMPT inhibition was evaluated using assays of proliferation and cell death. Measurements of NAD and functional assessment of NAD-dependent processes, such as glucose metabolism, were used to study the mechanistic activity of NAMPT inhibition in these models. In vivo studies included assessments of toxicity, efficacy, and mechanism of action of a clinical NAMPT inhibitor, OT-82, in four orthotopic RMS models.

Results: RMS cells showed striking sensitivity to NAMPT inhibition with IC-50 values in the low nanomolar range. In vitro, NAMPT inhibition resulted in NAD depletion and impaired cellular proliferation. Effects on glucose metabolism included decreases in glycolytic activity and glycolytic capacity in all cell lines tested, as well as decreased oxidative phosphorylation in a subset of cell lines. The majority of cell lines exhibited ATP depletion and irreversible necrotic cell death. Apoptotic cell death was not observed. In vivo, the effects of OT-82 treatment delivered on the human clinical schedule replicated those seen in vitro, including loss of glycolytic activity as measured using hyperpolarized 13C MRI spectroscopy. In all four xenograft models, complete tumor regressions were observed at multiple doses and with minimal toxicity.

Conclusions: NAMPT inhibition with OT-82 was highly effective in decreasing RMS proliferation and impairing glucose metabolism both in vitro and in vivo. Given these results, there is a critical need for further clinical study of this class of agents for RMS.

Citation Format: Grace McKay-Corkum, Victor J. Collins, Choh Yeung, Takeshi Ito, Sameer H. Issaq, Arnulfo Mendoza, Kazutoshi Yamamoto, Murali Cherukuri, Len Neckers, Christine M. Heske. Exploiting metabolic vulnerabilities of pediatric rhabdomyosarcoma with novelnicotinamide phosphoribosyltransferase (NAMPT) inhibitor OT-82 [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 6718.

Hippocampal ceRNA networks from chronic intermittent ethanol vapor-exposed male mice and functional analysis of top-ranked lncRNA genes for ethanol drinking phenotypes

The molecular mechanisms regulating the development and progression of alcohol use disorder (AUD) are largely unknown. While noncoding RNAs have previously been implicated as playing key roles in AUD, long-noncoding RNA (lncRNA) remains understudied in relation to AUD. In this study, we first identified ethanol-responsive lncRNAs in the mouse hippocampus that are transcriptional network hub genes. Microarray analysis of lncRNA, miRNA, circular RNA, and protein coding gene expression in the hippocampus from chronic intermittent ethanol vapor- or air- (control) exposed mice was used to identify ethanol-responsive competing endogenous RNA (ceRNA) networks. Highly interconnected lncRNAs (genes that had the strongest overall correlation to all other dysregulated genes identified) were ranked. The top four lncRNAs were novel, previously uncharacterized genes named Gm42575, 4930413E15Rik, Gm15767, and Gm33447, hereafter referred to as Pitt1, Pitt2, Pitt3, and Pitt4, respectively. We subsequently tested the hypothesis that CRISPR/Cas9 mutagenesis of the putative promoter and first exon of these lncRNAs in C57BL/6J mice would alter ethanol drinking behavior. The Drinking in the Dark (DID) assay was used to examine binge-like drinking behavior, and the Every-Other-Day Two-Bottle Choice (EOD-2BC) assay was used to examine intermittent ethanol consumption and preference. No significant differences between control and mutant mice were observed in the DID assay. Female-specific reductions in ethanol consumption were observed in the EOD-2BC assay for Pitt1, Pitt3, and Pitt4 mutant mice compared to controls. Male-specific alterations in ethanol preference were observed for Pitt1 and Pitt2. Female-specific increases in ethanol preference were observed for Pitt3 and Pitt4. Total fluid consumption was reduced in Pitt1 and Pitt2 mutants at 15% v/v ethanol and in Pitt3 and Pitt4 at 20% v/v ethanol in females only. We conclude that all lncRNAs targeted altered ethanol drinking behavior, and that lncRNAs Pitt1, Pitt3, and Pitt4 influenced ethanol consumption in a sex-specific manner. Further research is necessary to elucidate the biological mechanisms for these effects. These findings add to the literature implicating noncoding RNAs in AUD and suggest lncRNAs also play an important regulatory role in the disease.

Factors influencing choice between tracheostomy and prolonged translaryngeal intubation in acute respiratory failure: a prospective study

One of the problems of prolonged ventilatory therapy in acute respiratory failure (ARF) is the need to choose between tracheostomy after 48 to 72 hours of translaryngeal (TL) tracheal intubation or the continuous use of the TL tube for a period of 10 days. Too often the choice has been based on retrospective studies or personal preference. To investigate this problem prospectively, 52 adults in ARF were divided sequentially into 2 groups on their 3rd day of TL intubation. Patients in group I (G-I) retained the TL tube for a total of 11 days; those in group II (G-II) were tracheostomized on the 3rd day. The following factors ere used to evaluate the efficiency and complications in each group: patient's epidemiologic variables, daily pulmonary functions, severity of respiratory infections, and scores of post-intubation airway lesions. No consistent statistically significant differences between the two procedures were seen in the pulmonary functions or the range of individual patient variables. However, with an early tracheostomy, there was an eightfold greater incidence of contamination of the airway by new organisms, airway lesions were more frequent and severe, and the need for the tracheal tube was extended. To identify the epidemiologic variables and the pulmonary functions that discriminate between patients with serious airway lesions and those with mild lesions, and to evaluate the ability of these variables to differentiate the patients who died from those who survived, the distribution of all factors was compared in the two categories. The epidemiologic variables separated the patients according to their airway lesions only, while the difference in pulmonary functions was statistically significant only between the patients who died and those who survived.

Cardiac arrest related to anesthesia. Contributing factors in infants and children

A collaborative retrospective study undertaken to investigate cardiac arrest related to pediatric anesthesia in seven institutions between 1960 and 1972 showed 73 instances in which anesthesia was thought to have been either directly responsible or had played an important contributing role. About two thirds of these patients were successfully resuscitated. Cases were found to fit into one of two major categories: cardiovascular and respiratory. Among cardiovascular factors, blood loss, preoperative anemia, inappropriate administration of succinylcholine, and accidental administration of potassium were important contributing causes. Respiratory factors included failure to maintain a patent airway and ventilatory problems. In retrospect, most of these accidents were preventable. Such information should indicate where research emphasis needs to be placed and that our current methods of teaching and training need to be reevaluated.