Alternative Lengthening of Telomeres in Cancer Confers a Vulnerability to Reactivation of p53 Function

A subset of cancers across multiple histologies with predominantly poor outcomes use the alternative lengthening of telomeres (ALT) mechanism to maintain telomere length, which can be identified with robust biomarkers. ALT has been reported to be prevalent in high-risk neuroblastoma and certain sarcomas, and ALT cancers are a major clinical challenge that lack targeted therapeutic approaches. Here, we found ALT in a variety of pediatric and adult cancer histologies, including carcinomas. Patient-derived ALT cancer cell lines from neuroblastomas, sarcomas, and carcinomas were hypersensitive to the p53 reactivator eprenetapopt (APR-246) relative to telomerase-positive (TA+) models. Constitutive telomere damage signaling in ALT cells activated ataxia-telangiectasia mutated (ATM) kinase to phosphorylate p53, which resulted in selective ALT sensitivity to APR-246. Treatment with APR-246 combined with irinotecan achieved complete responses in mice xenografted with ALT neuroblastoma, rhabdomyosarcoma, and breast cancer and delayed tumor growth in ALT colon cancer xenografts, while the combination had limited efficacy in TA+ tumor models. A large number of adult and pediatric cancers present with the ALT phenotype, which confers a uniquely high sensitivity to reactivation of p53. These data support clinical evaluation of a combinatorial approach using APR-246 and irinotecan in ALT patients with cancer.

SIGNIFICANCE

This work demonstrates that constitutive activation of ATM in chemotherapy-refractory ALT cancer cells renders them hypersensitive to reactivation of p53 function by APR-246, indicating a potential strategy to overcome therapeutic resistance.

Abstract 6228: APR-246, which restores p53 function, is highly active against alternative lengthening of telomere (ALT) cell lines and PDXs

Introduction: Most cancers proliferate by activating telomerase (TA+) while 10% of cancers utilize alternate lengthening of telomeres (ALT). ALT has been associated with resistance to DNA damaging agents, p53 loss-of-function (p53LOF), ATRX mutations, and very poor survival. ATM kinase, which activates functional p53, is constitutively activated in ALT cancers (Science Translational Medicine 18:eabd5750, 2021). We hypothesized that the constitutive activation of ATM kinase in ALT cancers would confer high sensitivity to pharmacological reactivation of p53 function.

Methods: We used patient-derived ALT (telomeric DNA C-circle positive) and TA+ neuroblastoma, sarcoma, colorectal, and breast cancer cell lines and xenografts treated with the clinical-stage p53 reactivator eprenetapopt (APR-246) and irinotecan. In vitro cytotoxicity was assayed by DIMSCAN digital imaging microscopy, ATM activation by immunofluorescence microscopy, and protein expression by western blotting.

Results: ALT p53LOF cell lines were significantly (p<0.05) less sensitive to DNA-damaging agents relative to TA+ p53LOF comparators. Constitutive phosphorylation (activation) of ATM kinase and the DNA damage marker 53BP1 were observed at telomeres in ALT but not TA+ cell lines. APR-246 induced p53 targets p21 and NOXA and was significantly more cytotoxic (p<0.001) for ALT relative to TA+ cell lines, regardless of TP53 status. Overexpression of p53 in a TP53-null ALT cell line increased sensitivity (p<0.0001) to APR-246. Knockdown of p53 or ATM kinase in ALT TP53 mutated and wild-type cell lines antagonized (p<0.0001) APR-246 activity. Induction of telomere dysfunction in a TA+ p53LOF neuroblastoma cell line using dominant-negative TRF2 (a shelterin protein that blocks ATM activation at telomeres) activated ATM and sensitized cells to APR-246 (p<0.01). APR-246 enhanced the cytotoxicity of irinotecan (as SN38) in ALT cell lines in vitro to a higher degree than in TA+ p53LOF cell lines (p<0.05). Single-agent APR-246 significantly (p<0.0001) increased event-free survival (EFS) of mice with ALT xenografts relative to controls. APR-246 enhanced (p<0.0001) the activity of irinotecan in 3 neuroblastoma, 2 rhabdomyosarcoma, 1 colorectal, and 1 triple-negative breast ALT xenograft models with most mice (47/56) achieving complete responses and an EFS of >100 days (45/56) compared to no complete responses (median EFS ~ 34 days) in mice treated with only irinotecan (p<0.0001). APR-246 + irinotecan had no significant effect relative to irinotecan alone (p=0.08) on EFS of mice with TA+ p53LOF xenografts (median EFS ~ 40 days).

Conclusion: ALT cancers of a variety of histologies are highly resistant to DNA damaging agents, have p53LOF, and constitutive activation of ATM kinase, which confers high sensitivity to p53 reactivation by APR-246. APR-246 warrants clinical testing in patients with ALT cancers.

Citation Format: Shawn J. Macha, Balakrishna Koneru, Trevor Burrow, Charles Zhu, Dzmitry Savitski, Jonas Nance, Kristyn McCoy, Cody Eslinger, C Patrick Reynolds. APR-246, which restores p53 function, is highly active against alternative lengthening of telomere (ALT) cell lines and PDXs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6228.

Telomere Maintenance Mechanisms Define Clinical Outcome in High-Risk Neuroblastoma

Neuroblastoma is a childhood cancer with heterogeneous clinical outcomes. To comprehensively assess the impact of telomere maintenance mechanism (TMM) on clinical outcomes in high-risk neuroblastoma, we integrated the C-circle assay [a marker for alternative lengthening of telomeres (ALT)], TERT mRNA expression by RNA-sequencing, whole-genome/exome sequencing, and clinical covariates in 134 neuroblastoma patient samples at diagnosis. In addition, we assessed TMM in neuroblastoma cell lines (n = 104) and patient-derived xenografts (n = 28). ALT was identified in 23.4% of high-risk neuroblastoma tumors and genomic alterations in ATRX were detected in 60% of ALT tumors; 40% of ALT tumors lacked genomic alterations in known ALT-associated genes. Patients with high-risk neuroblastoma were classified into three subgroups (TERT-high, ALT+, and TERT-low/non-ALT) based on presence of C-circles and TERT mRNA expression (above or below median TERT expression). Event-free survival was similar among TERT-high, ALT+, or TERT-low/non-ALT patients. However, overall survival (OS) for TERT-low/non-ALT patients was significantly higher relative to TERT-high or ALT patients (log-rank test; P < 0.01) independent of current clinical and molecular prognostic markers. Consistent with the observed higher OS in patients with TERT-low/non-ALT tumors, continuous shortening of telomeres and decreasing viability occurred in low TERT-expressing, non-ALT patient-derived high-risk neuroblastoma cell lines. These findings demonstrate that assaying TMM with TERT mRNA expression and C-circles provides precise stratification of high-risk neuroblastoma into three subgroups with substantially different OS: a previously undescribed TERT-low/non-ALT cohort with superior OS (even after relapse) and two cohorts of patients with poor survival that have distinct molecular therapeutic targets. SIGNIFICANCE: These findings assess telomere maintenance mechanisms with TERT mRNA and the ALT DNA biomarker C-circles to stratify neuroblastoma into three groups, with distinct overall survival independent of currently used clinical risk classifiers.

Genomic Profiling of Childhood Tumor Patient-Derived Xenograft Models to Enable Rational Clinical Trial Design

Accelerating cures for children with cancer remains an immediate challenge as a result of extensive oncogenic heterogeneity between and within histologies, distinct molecular mechanisms evolving between diagnosis and relapsed disease, and limited therapeutic options. To systematically prioritize and rationally test novel agents in preclinical murine models, researchers within the Pediatric Preclinical Testing Consortium are continuously developing patient-derived xenografts (PDXs)-many of which are refractory to current standard-of-care treatments-from high-risk childhood cancers. Here, we genomically characterize 261 PDX models from 37 unique pediatric cancers; demonstrate faithful recapitulation of histologies and subtypes; and refine our understanding of relapsed disease. In addition, we use expression signatures to classify tumors for TP53 and NF1 pathway inactivation. We anticipate that these data will serve as a resource for pediatric oncology drug development and will guide rational clinical trial design for children with cancer.

Chitinase activity and a novel population of CXCR3 expressing alternatively activated macrophages in the CNS during chronic Toxoplasma gondii infection. (56.33)

During infection with Toxoplasma gondii, an IFN-γ dependent polarization of classically activated macrophages (CaM) is required to control parasite growth during the acute phase of infection. These macrophages produce high levels of cytokines such as IL-12 and TNF-α and other effector molecules such as nitric oxide that act to induce stage conversion to bradyzoites resulting in a sustained chronic infection in the brain. Cytokines such as IL-4 as well as the presence of exogenous polymers such as chitin, induce alternatively activated macrophage (AMac) phenotypes involved in tissue remodeling and wound healing responses. Here we demonstrate the presence of AMac macrophages during Toxoplasma infection at a time point associated with chronic infection and substantial tissue remodeling in the brain. This population preferentially expressed the chemokine receptor CXCR3, scavenger receptors, MMR and stabilin-1. In vivo blockade of CXCR3 and CXCL10 decreased not only T cell infiltration and resulted in an increase in parasite burden but macrophage migration to the brain was also diminished. Finally, we demonstrate chitinase activity in the Toxoplasma infected brain associated with the presence of AMac and chitin in the cyst wall. These results indicate that chitin in the parasitic cyst wall locally stimulates a population of CXCR3 expressing AMac that are required for tissue remodeling and immunity in the brain during Toxoplasma infection and inflammation.

CCL21 dependent CD4+ T cell migration plays a role in protective immune responses against Toxoplasma infection in the brain. (99.22)

The chemokine receptor, CCR7 and interactions with its ligands CCL19 and CCL21 are well known to facilitate priming of T cells in lymphoid tissue. Our data demonstrate upregulation of CCR7, CCL19 and CCL21 in the brain during Toxoplasma gondii infection at a time point coincident with the peak of T cell infiltration in the CNS. CNS resident astrocytes significantly upregulate CCL21 following direct infection with Toxoplasma tachyzoites and in the absence of CCL21, plt/plt mice were less efficient in controlling parasite replication during chronic infection. Although T cells enter the infected brain in a CCR7 independent manner, migration of extravasated CD4+T cells from the perivascular area into the CNS parenchyma is CCL21-dependent. Our data also demonstrate accumulation of CD4+CCR7 expressing T cells in the infected brain. A significant proportion of these CCR7+T cells express memory T cell markers including IL-7R (Interleukin 7 Receptor) and CD103 (tissue resident memory phenotype). These data indicate CCR7-CCL21 interactions play a role in guiding CD4+CCR7+ memory T cell migration in the brain to prevent parasite reactivation and disease. Analysis of the behavior and phenotype of this memory T cell population in the absence of CCR7 or CCL21 will be presented. These data address the potential contribution of CCR7/CCL21 mediated interactions to maximize memory responses in the brain during Toxoplasma infection.

spe-29 encodes a small predicted membrane protein required for the initiation of sperm activation in Caenorhabditis elegans

Caenorhabditis elegans spermatids complete a dramatic morphogenesis to crawling spermatozoa in the absence of an actin- or tubulin-based cytoskeleton and without synthesizing new gene products. Mutations in three genes (spe-8, spe-12, and spe-27) prevent the initiation of this morphogenesis, termed activation. Males with mutations in any of these genes are fertile. By contrast, mutant hermaphrodites are self-sterile when unmated due to a failure in spermatid activation. Intriguingly, mutant hermaphrodites form functional spermatozoa and become self-fertile upon mating, suggesting that spermatids can be activated by male seminal fluid. Here we describe a mutation in a fourth gene, spe-29, which mimics the phenotype of spe-8, spe-12, and spe-27 mutants. spe-29 sperm are defective in the initiation of hermaphrodite sperm activation, yet they maintain the ability to complete the morphogenetic rearrangements that follow. Mutant alleles of spe-12, spe-27, and spe-29 exhibit genetic interactions that suggest that the wild-type products of these genes function in a common signaling pathway to initiate sperm activation. We have identified the spe-29 gene, which is expressed specifically in the sperm-producing germ line and is predicted to encode a small, novel transmembrane protein.

A global profile of germline gene expression in C. elegans

We used DNA microarrays to profile gene expression patterns in the C. elegans germline and identified 1416 germline-enriched transcripts that define three groups. The sperm-enriched group contains an unusually large number of protein kinases and phosphatases. The oocyte-enriched group includes potentially new components of embryonic signaling pathways. The germline-intrinsic group, defined as genes expressed similarly in germlines making only sperm or only oocytes, contains a family of piwi-related genes that may be important for stem cell proliferation. Finally, examination of the chromosomal location of germline transcripts revealed that sperm-enriched and germline-intrinsic genes are nearly absent from the X chromosome, but oocyte-enriched genes are not.

spe-12 encodes a sperm cell surface protein that promotes spermiogenesis in Caenorhabditis elegans

During spermiogenesis, Caenorhabditis elegans spermatids activate and mature into crawling spermatozoa without synthesizing new proteins. Mutations in the spe-12 gene block spermatid activation, rendering normally self-fertile hermaphrodites sterile. Mutant males, however, are fertile. Surprisingly, when mutant hermaphrodites mate with a male, their self-spermatids activate and form functional spermatozoa, presumably due to contact with male seminal fluid. Here we show that, in addition to its essential role in normal activation of hermaphrodite-derived spermatids, SPE-12 also plays a supplementary but nonessential role in mating-induced activation. We have identified the spe-12 gene, which encodes a novel protein containing a single transmembrane domain. spe-12 mRNA is expressed in the sperm-producing germ line and the protein localizes to the spermatid cell surface. We propose that SPE-12 functions downstream of both hermaphrodite- and male-derived activation signals in a spermatid signaling pathway that initiates spermiogenesis.

Osteopathia striata with cranial sclerosis: highly variable phenotypic expression within a family

We report a four-generation family, with five individuals affected by osteopathia striata with cranial sclerosis (OS-CS). The family illustrates the wide spectrum of gene expression in this autosomal dominant condition. Of particular note is the unusually severe expression in the proband, who exhibits virtually all of the reported associations of the syndrome. Proximal osteolysis of the fibula and congenital urological abnormalities, in the proband, and holoprosencephaly sequence, in the proband's sister, have not previously been described in the syndrome.

An interdisciplinary team approach to implementing the ketogenic diet for the treatment of seizures

The ketogenic diet is becoming a more recognized method of treating seizures in some children with epilepsy. Texas Scottish Rite Hospital for Children (TSRHC) developed an interdisciplinary team that uses a comprehensive approach to implementing this innovative therapy. Anticipated outcomes of this unique approach are increased family satisfaction and improved dietary compliance, which maximizes the diet to its fullest potential. These outcomes are validated by anecdotal information by families' reports of satisfaction and successful diet maintenance for increased number of months (this population from 3-31 months). Of the 27 children ages 1-16 years, approximately 40% have experienced reduction of seizures of more than 50%, 25% are seizure free, and 35% have discontinued the diet for a variety of reasons including difficulty in consistently maintaining the diet. Originally introduced in the 1920s, the ketogenic diet has once again become cutting edge treatment for nonresponsive seizure activity.

Post-hospitalization concerns of medical-surgical patients

In response to the phenomenon of earlier-than-ever discharge, the post-hospitalization concerns of medical-surgical patients were investigated in a descriptive survey conducted in physicians' offices and clinics. The 150 recently discharged patients typically identified multiple concerns including understanding their progress, activity, insurance, medications, and pain control. Differences were found in number of concerns according to age, gender, length of hospital stay, type of treatment (medical or surgical), and perceived presence or absence of discharge planning.

Emergency department nursing management of patients with orthopedic fractures resulting from motor vehicle accidents

Nursing management of patients with orthopedic fractures resulting from motor vehicle accidents is a frequent challenge for nurses in an emergency department setting. The nurse must have knowledge of the mechanics of injury, the classification of the resulting fracture types, and the usual medical interventions. In addition, emergency department nurses should follow plans of care that are based on nursing diagnoses so that appropriate nursing interventions can be determined and consistently provided. Initiation of these care plans must not be delayed until the patient is admitted to an inpatient nursing unit, but should be begun in the emergency unit setting. This article presents information that the emergency room nurse needs in order to make plans for nursing care, and discusses seven nursing diagnoses that are almost always appropriate for patients seen in the emergency department who are experiencing orthopedic fractures resulting from motor vehicle accidents.

Amoxicillin: in vitro and pharmacological studies

Amoxicillin is a new semisynthetic penicillin which is active in vitro against gram-positive cocci (except penicillin G-resistant Staphylococcus aureus) and most isolates of Proteus mirabilis and Escherichia coli. Its in vitro activity is quite similar to ampicillin, but it produces higher serum levels after oral administration. The mean peak serum levels of amoxicillin in 11 normal volunteers were 2.30 mug/ml after 125 mg, 3.43 mug/ml after 250 mg, 6.75 mug/ml after 500 mg, and 9.90 mug/ml after 1 g. About 70% of the drug was excreted in the urine during the first 6 hr.