Maria Rusan

Development of covalent inhibitors that can overcome resistance to first-generation FGFR kinase inhibitors

Significance Inhibitors of the FGF receptors (FGFRs) are currently under clinical investigation for the treatment of various cancers. All currently approved kinase inhibitors eventually are rendered useless by the emergence of drug-resistant tumors. We used structure-based drug design to develop the first, to our knowledge, selective, next-generation covalent FGFR inhibitors that can overcome the most common form of kinase inhibitor resistance, the mutation of the so-called “gatekeeper” residue located in the ATP-binding pocket. We also describe a novel kinase inhibitor design strategy that uses a single electrophile to target covalently cysteines that are located in different positions within the ATP-binding pocket. These results have important implications for the design of covalent FGFR inhibitors that can overcome clinical resistance. The human FGF receptors (FGFRs) play critical roles in various human cancers, and several FGFR inhibitors are currently under clinical investigation. Resistance usually results from selection for mutant kinases that are impervious to the action of the drug or from up-regulation of compensatory signaling pathways. Preclinical studies have demonstrated that resistance to FGFR inhibitors can be acquired through mutations in the FGFR gatekeeper residue, as clinically observed for FGFR4 in embryonal rhabdomyosarcoma and neuroendocrine breast carcinomas. Here we report on the use of a structure-based drug design to develop two selective, next-generation covalent FGFR inhibitors, the FGFR irreversible inhibitors 2 (FIIN-2) and 3 (FIIN-3). To our knowledge, FIIN-2 and FIIN-3 are the first inhibitors that can potently inhibit the proliferation of cells dependent upon the gatekeeper mutants of FGFR1 or FGFR2, which confer resistance to first-generation clinical FGFR inhibitors such as NVP-BGJ398 and AZD4547. Because of the conformational flexibility of the reactive acrylamide substituent, FIIN-3 has the unprecedented ability to inhibit both the EGF receptor (EGFR) and FGFR covalently by targeting two distinct cysteine residues. We report the cocrystal structure of FGFR4 with FIIN-2, which unexpectedly exhibits a “DFG-out” covalent binding mode. The structural basis for dual FGFR and EGFR targeting by FIIN3 also is illustrated by crystal structures of FIIN-3 bound with FGFR4 V550L and EGFR L858R. These results have important implications for the design of covalent FGFR inhibitors that can overcome clinical resistance and provide the first example, to our knowledge, of a kinase inhibitor that covalently targets cysteines located in different positions within the ATP-binding pocket.

Fusobacterium necrophorum: most prevalent pathogen in peritonsillar abscess in Denmark.

BACKGROUND Group A streptococci are commonly regarded as the most prevalent cause of acute bacterial tonsillitis and peritonsillar abscess (PTA). However, the majority of PTA aspirates also contain strains of anaerobes, and accumulating evidence indicates that Fusobacterium necrophorum (FN) could be involved in acute tonsillitis. The purpose of the present study was to describe the epidemiology and bacteriology of PTA in Denmark, with particular emphasis on correlations between microbiological, clinical, and laboratory data. METHODS A retrospective study on all patients with PTA admitted to the ear, nose, and throat department at Aarhus University Hospitals from January 2001 through December 2006 was conducted. RESULTS In total, 847 patients were included in the study. The mean annual incidence of PTA was 41 cases/100,000 population. FN was the most frequently detected bacteria (in 23% of cultures), followed by group A streptococci (in 17%) and groups C and G streptococci (counted together, in 5%). Of the 191 FN isolates detected, 155 (81%) grew as pure culture. Patients infected with FN were significantly younger than patients infected with other strains of bacteria (P < .001). Patients with FN exhibited significantly higher neutrophil counts (P < .001) and C-reactive protein values (P = .01) than did patients infected with other bacteria. CONCLUSIONS To our knowledge, this study is the first report of FN being the most prevalent pathogen in PTA patients. The significantly higher neutrophil counts and C-reactive protein values strongly indicate the pathogenic importance of FN in PTA. The widespread reliance on rapid streptococcal antigen test in general practice to appoint patients for antibiotics and the highest PTA incidence ever reported raise concern that highly virulent bacteria may be left initially untreated.

Genomic Landscape of Human Papillomavirus–Associated Cancers

Recent next-generation sequencing studies have generated a comprehensive overview of the genomic landscape of human papillomavirus (HPV)–associated cancers. This review summarizes these findings to provide insight into the tumor biology of these cancers and potential therapeutic opportunities for HPV-driven malignancies. In addition to the tumorigenic properties of the HPV oncoproteins, integration of HPV DNA into the host genome is suggested to be a driver of the neoplastic process. Integration may confer a growth and survival advantage via enhanced expression of viral oncoproteins, alteration of critical cellular genes, and changes in global promoter methylation and transcription. Alteration of cellular genes may lead to loss of function of tumor suppressor genes, enhanced oncogene expression, loss of function of DNA repair genes, or other vital cellular functions. Recurrent integrations in RAD51B, NR4A2, and TP63, leading to aberrant forms of these proteins, are observed in both HPV-positive head and neck squamous cell carcinoma (HNSCC) and cervical carcinoma. Additional genomic alterations, independent of integration events, include recurrent PIK3CA mutations (and aberrations in other members of the PI3K pathway), alterations in receptor tyrosine kinases (primarily FGFR2 and FGFR3 in HPV-positive HNSCC, and ERBB2 in cervical squamous cell carcinoma), and genes in pathways related to squamous cell differentiation and immune responses. A number of the alterations identified are potentially targetable, which may lead to advances in the treatment of HPV-associated cancers. Clin Cancer Res; 21(9); 2009–19. ©2015 AACR.

The interplay between HPV and host immunity in head and neck squamous cell carcinoma.

Persistent infection with human papillomavirus (HPV) type 16 is a major risk factor for the development of head and neck squamous cell carcinoma (HNSCC), in particular oropharyngeal squamous cell carcinoma (OPSCC). The oropharyngeal epithelium differs from the mucosal epithelium at other commonly HPV16‐infected sites (i.e., cervix and anogenital region) in that it is juxtaposed with the underlying lymphatic tissue, serving a key immunologic function in the surveillance of inhaled and ingested pathogens. Therefore, the natural history of infection and immune response to HPV at this site may differ from that at other anatomic locations. This review summarizes the literature concerning the adaptive immune response against HPV in the context of HNSCC, with a focus on the T‐cell response. Recent studies have shown that a broad repertoire of tumor‐infiltrating HPV‐specific T‐cells are found in nearly all patients with HPV‐positive tumors. A systemic response is found in only a proportion of these. Furthermore, the local response is more frequent in OPSCC patients than in cervical cancer patients and HPV‐negative OPSCC patients. Despite this, tumor persistence may be facilitated by abnormalities in antigen processing, a skewed T‐helper cell response, and an increased local prevalence of T‐regulatory cells. Nonetheless, the immunologic profile of HPV‐positive vs. HPV‐negative HNSCC is associated with a significantly better outcome, and the HPV‐specific immune response is suggested to play a role in the significantly better response to therapy of HPV‐positive patients. Immunoprofiling may prove a valuable prognostic tool, and immunotherapy trials targeting HPV are underway, providing hope for decreasing treatment‐related toxicity.

Suppression of Adaptive Responses to Targeted Cancer Therapy by Transcriptional Repression

Acquired drug resistance is a major factor limiting the effectiveness of targeted cancer therapies. Targeting tumors with kinase inhibitors induces complex adaptive programs that promote the persistence of a fraction of the original cell population, facilitating the eventual outgrowth of inhibitor-resistant tumor clones. We show that the addition of a newly identified CDK7/12 inhibitor, THZ1, to targeted therapy enhances cell killing and impedes the emergence of drug-resistant cell populations in diverse cellular and in vivo cancer models. We propose that targeted therapy induces a state of transcriptional dependency in a subpopulation of cells poised to become drug tolerant, which THZ1 can exploit by blocking dynamic transcriptional responses, promoting remodeling of enhancers and key signaling outputs required for tumor cell survival in the setting of targeted therapy. These findings suggest that the addition of THZ1 to targeted therapies is a promising broad-based strategy to hinder the emergence of drug-resistant cancer cell populations.Significance: CDK7/12 inhibition prevents active enhancer formation at genes, promoting resistance emergence in response to targeted therapy, and impedes the engagement of transcriptional programs required for tumor cell survival. CDK7/12 inhibition in combination with targeted cancer therapies may serve as a therapeutic paradigm for enhancing the effectiveness of targeted therapies. Cancer Discov; 8(1); 59-73. ©2017 AACR.See related commentary by Carugo and Draetta, p. 17This article is highlighted in the In This Issue feature, p. 1.

The role of viruses in the pathogenesis of peritonsillar abscess

Peritonsillar abscess (PTA) is the most frequent complication of acute tonsillitis and a prevalent cause for acute admission to otorhinolaryngology departments. Our aim was to examine the role of viruses in the pathogenesis of PTA, as this has not previously been considered. We examined both palatine tonsils from 25 patients undergoing acute tonsillectomy for PTA, using PCR-based assays for herpes simplex virus-1 and -2 (HSV-1 and -2), adenovirus, Epstein-Barr virus (EBV), influenza A and B, and respiratory syncytial virus (RSV) A and B. We similarly examined tonsils from 55 patients undergoing elective tonsillectomy due to chronic tonsillar conditions. These patients served as a control group, as they did not have a clinically apparent infection at the time of surgery. Only HSV-1 (5/80, 6.3%), adenovirus (11/80, 13.8%), and EBV (71/80, 88.8%) were detected in our study population. There was no statistically significant difference in the frequency of these viruses across different diagnostic groups. Quantification of EBV load demonstrated no differences between the PTA and the elective tonsillectomy group, nor between the abscessed and non-abscessed tonsil of PTA patients. In summary, our data do not support a significant role for the examined viruses in the pathogenesis of PTA.

ER stress signaling promotes the survival of cancer 'persister cells' tolerant to EGFR tyrosine kinase inhibitors

An increasingly recognized component of resistance to tyrosine kinase inhibitors (TKI) involves persistence of a drug-tolerant subpopulation of cancer cells that survive despite effective eradication of the majority of the cell population. Multiple groups have demonstrated that these drug-tolerant persister cells undergo transcriptional adaptation via an epigenetic state change that promotes cell survival. Because this mode of TKI drug tolerance appears to involve transcriptional addiction to specific genes and pathways, we hypothesized that systematic functional screening of EGFR TKI/transcriptional inhibitor combination therapy would yield important mechanistic insights and alternative drug escape pathways. We therefore performed a genome-wide CRISPR/Cas9 enhancer/suppressor screen in EGFR-dependent lung cancer PC9 cells treated with erlotinib + THZ1 (CDK7/12 inhibitor) combination therapy, a combination previously shown to suppress drug-tolerant cells in this setting. As expected, suppression of multiple genes associated with transcriptional complexes (EP300, CREBBP, and MED1) enhanced erlotinib/THZ1 synergy. Unexpectedly, we uncovered nearly every component of the recently described ufmylation pathway in the synergy suppressor group. Loss of ufmylation did not affect canonical downstream EGFR signaling. Instead, absence of this pathway triggered a protective unfolded protein response associated with STING upregulation, promoting protumorigenic inflammatory signaling but also unique dependence on Bcl-xL. These data reveal that dysregulation of ufmylation and ER stress comprise a previously unrecognized TKI drug tolerance pathway that engages survival signaling, with potentially important therapeutic implications.Significance: These findings reveal a novel function of the recently described ufmylation pathway, an ER stress survival signaling in drug-tolerant persister cells, which has important biological and therapeutic implications. Cancer Res; 78(4); 1044-57. ©2017 AACR.

Peritonsillar Abscess Complication of Acute Tonsillitis or Weber’s Glands Infection?

Objective To review the literature concerning the 2 primary hypotheses put forth to explain the pathogenesis of peritonsillar abscess: “the acute tonsillitis hypothesis” (peritonsillar abscess is a complication of acute tonsillitis) and “the Weber gland hypothesis” (peritonsillar abscess is an infection of Weber’s glands). Data Sources PubMed, EMBASE. Review Methods Data supporting or negating one hypothesis or the other were elicited from the literature. Conclusions Several findings support the acute tonsillitis hypothesis. First, the 2 main pathogens in peritonsillar abscess have been recovered from pus aspirates and bilateral tonsillar tissues with high concordance rates, suggesting that both tonsils are infected in patients with peritonsillar abscess. Second, studies report signs of acute tonsillitis in the days prior to and at the time of peritonsillar abscess. Third, antibiotic treatment reduces the risk of abscess development in patients with acute tonsillitis. However, some findings suggest involvement of the Weber’s glands in peritonsillar abscess pathogenesis. First, high amylase levels have been found in peritonsillar pus. Second, the majority of peritonsillar abscesses are located at the superior tonsillar pole in proximity of the Weber’s glands. We propose a unified hypothesis whereby bacteria initially infect the tonsillar mucosa and spread via the salivary duct system to the peritonsillar space, where an abscess is formed. Implications for Practice Our findings support the rationale for antibiotic treatment of patients with severe acute tonsillitis to reduce the risk of abscess development. Improved understanding of peritonsillar abscess pathogenesis is important for the development of efficient prevention strategies.

Worldwide Prevalence of Human Papillomavirus in Tonsillar Squamous Cell Carcinoma and Tumor-Free Tonsillar Tissue

Human Papillomavirus (HPV) is the etiological agent in cervical cancer and a significant proportion of anogenital cancers. It appears to also be associated with a subset of head and neck cancers, in particular tonsillar squamous cell carcinoma (TSCC). The overall prevalence of HPV and the type-specific prevalence at the cervical level vary geographically. It is unclear whether this is also the case in tonsillar infection with HPV and in HPV-associated TSCC. This review provides an overview of the current literature with regards to the prevalence and types of HPV found in TSCC, and in tumor-free tonsillar tissue, globally. The HPV prevalence in TSCC is highly variable from region to region, ranging from 0 to 100%. The majority of studies from Europe, however, report an HPV prevalence of 40-60%. A similar prevalence of 35-65% is reported in North America. The only study from Australia reports a comparable prevalence of 46%. In contrast, the prevalence in China and Taiwan is between 0 and 13%. No data is available from Latin America, Africa, Eastern Europe, and other parts of Asia. The predominant type identified is HPV 16, with the majority of studies detecting HPV 16 in over 80% of HPV-positive samples. HPV 33 is the second most frequent type. Other high-risk and low-risk types are only rarely isolated. Co-infections with multiple types are also rare. Several Western European countries, USA and Australia, have reported an increase in the incidence of TSCC cases. There is evidence that this is attributable to an increase in HPV- associated TSCC cases. In tumor-free tissue the overall HPV prevalence ranges between 0 and 9%, and the most frequent type identified is HPV 16. HPV 11 has also occasionally been isolated. The interpretation of these results is complicated by the small sample size of many studies and by heterogeneous methodology.

RAS-MAPK reactivation facilitates acquired resistance in FGFR1-amplified lung cancer and underlies a rationale for upfront FGFR-MEK blockade

The FGFR kinases are promising therapeutic targets in multiple cancer types, including lung and head and neck squamous cell carcinoma, cholangiocarcinoma, and bladder cancer. Although several FGFR kinase inhibitors have entered clinical trials, single-agent clinical efficacy has been modest and resistance invariably occurs. We therefore conducted a genome-wide functional screen to characterize mechanisms of resistance to FGFR inhibition in a FGFR1-dependent lung cancer cellular model. Our screen identified known resistance drivers, such as MET, and additional novel resistance mediators including members of the neurotrophin receptor pathway (NTRK), the TAM family of tyrosine kinases (TYRO3, MERTK, AXL), and MAPK pathway, which were further validated in additional FGFR-dependent models. In an orthogonal approach, we generated a large panel of resistant clones by chronic exposure to FGFR inhibitors in FGFR1- and FGFR3-dependent cellular models and characterized gene expression profiles employing the L1000 platform. Notably, resistant clones had enrichment for NTRK and MAPK signaling pathways. Novel mediators of resistance to FGFR inhibition were found to compensate for FGFR loss in part through reactivation of MAPK pathway. Intriguingly, coinhibition of FGFR and specific receptor tyrosine kinases identified in our screen was not sufficient to suppress ERK activity or to prevent resistance to FGFR inhibition, suggesting a redundant reactivation of RAS–MAPK pathway. Dual blockade of FGFR and MEK, however, proved to be a more powerful approach in preventing resistance across diverse FGFR dependencies and may represent a therapeutic opportunity to achieve durable responses to FGFR inhibition in FGFR-dependent cancers. Mol Cancer Ther; 17(7); 1526–39. ©2018 AACR.