Abstract P1-08-07: Educational Opportunities to Improve HER2 Testing and Use of Newer Therapies for HER2-Positive MBC Among Community Healthcare Professionals

Background: The management of HER2-positive (HER2+) metastatic breast cancer (MBC) has continued to evolve, with multiple FDA approvals of novel HER2-targeted agents since late 2019. Considering the growing HER2+ MBC treatment armamentarium and the emerging HER2-low MBC subtype, we undertook an analysis of the current implementation of guideline and expert recommendations for HER2 testing and treatment of HER2+ MBC with recently approved agents among oncology healthcare professionals (HCPs) participating in educational programs on these topics.

Methods: Between January 2020 and April 2022, we conducted several expert-designed educational activities for HCPs focusing on recommended HER2 testing and treatment of HER2+ MBC. Polling questions on HCP knowledge, practice patterns, and confidence in the evaluation of HER2 status and the use of newer targeted therapies in the setting of HER2+ MBC were assessed across the activities and compared with expert recommendations.

Results: Among 129 HCPs participating in 2 educational activities held from July 2020 to March 2021, 53% reported confidence to appropriately apply current HER2 testing guidelines to patient care. Similarly, among 407 HCPs who participated in 4 educational programs from May 2020 to January 2021, 24% reported confidence to incorporate recently approved drugs (including trastuzumab deruxtecan [T-DXd], neratinib, and tucatinib) into the care of patients with HER2+ MBC. The percentage of HCPs reporting confidence in the use of these new drugs remained low over this time period.

Comparison of treatment recommendations for various HER2+ MBC case scenarios across 7 educational activities from January 2020 through April 2022 showed considerable discordance between experts and HCPs regarding the implementation of newly approved HER2-targeted regimens (Table 1). For patients with disease progression after 2 lines of therapy and no central nervous system (CNS) metastases, 27% to 57% of HCPs (n = 571) chose T-DXd in agreement with experts. For patients with disease progression after 2 lines of therapy with CNS metastases, 27% to 42% of HCPs (n = 597) chose a tucatinib-based regimen in agreement with experts. Treatment choice concurrence between HCPs and experts did not increase over the course of this study for either of these patient scenarios.

Conclusions: These data suggest that some HCPs are challenged to optimally incorporate recommendations for HER2 testing and the implementation of novel HER2-targeted therapies in the care of patients with HER2+ MBC. Educational activities designed to improve the knowledge and confidence of HCPs would benefit patients with HER2+ MBC. A detailed analysis of trends over time and by role on the care team will be presented.

Table 1. Expert and HCP Treatment Selections for Case Scenarios in HER2+ MBC.

Citation Format: Ryan P. Topping, Rachael M. Andrie, Kristen Rosenthal, Timothy A. Quill. Educational Opportunities to Improve HER2 Testing and Use of Newer Therapies for HER2-Positive MBC Among Community Healthcare Professionals [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-08-07.

Pyrenophora bromi, causal agent of brownspot of bromegrass, expresses a gene encoding a protein with homology and similar activity to Ptr ToxB, a host-selective toxin of wheat

Ptr ToxB, encoded by ToxB, is one of multiple host-selective toxins (HST) produced by the wheat pathogen Pyrenophora tritici-repentis. Homologs of ToxB are found in several ascomycetes, including sister species Pyrenophora bromi, causal agent of brownspot of bromegrass. Due to the close evolutionary relatedness of P. tritici-repentis and P. bromi and that of their grass hosts, we hypothesized that homologs of ToxB in P. bromi may act as HST in the disease interaction between P. bromi and bromegrass. A representative set of transcriptionally active P. bromi ToxB genes were heterologously expressed in Pichia pastoris and the resultant proteins tested for their ability to act as HST on bromegrass. The tested Pyrenophora bromi ToxB (Pb ToxB) proteins were not toxic to bromegrass; thus, Pb ToxB does not appear to function as an HST in the P. bromi-bromegrass interaction. Instead, we revealed that the Pb ToxB proteins can be toxic to Ptr ToxB-sensitive wheat, at levels similar to Ptr ToxB, and the corresponding P. bromi ToxB genes are expressed in P. bromi-inoculated wheat. Our data suggest that P. bromi possesses the potential to become a wheat pathogen and highlights the importance of investigating the interaction between P. bromi and wheat.

The Ascomycota tree of life: a phylum-wide phylogeny clarifies the origin and evolution of fundamental reproductive and ecological traits

We present a 6-gene, 420-species maximum-likelihood phylogeny of Ascomycota, the largest phylum of Fungi. This analysis is the most taxonomically complete to date with species sampled from all 15 currently circumscribed classes. A number of superclass-level nodes that have previously evaded resolution and were unnamed in classifications of the Fungi are resolved for the first time. Based on the 6-gene phylogeny we conducted a phylogenetic informativeness analysis of all 6 genes and a series of ancestral character state reconstructions that focused on morphology of sporocarps, ascus dehiscence, and evolution of nutritional modes and ecologies. A gene-by-gene assessment of phylogenetic informativeness yielded higher levels of informativeness for protein genes (RPB1, RPB2, and TEF1) as compared with the ribosomal genes, which have been the standard bearer in fungal systematics. Our reconstruction of sporocarp characters is consistent with 2 origins for multicellular sexual reproductive structures in Ascomycota, once in the common ancestor of Pezizomycotina and once in the common ancestor of Neolectomycetes. This first report of dual origins of ascomycete sporocarps highlights the complicated nature of assessing homology of morphological traits across Fungi. Furthermore, ancestral reconstruction supports an open sporocarp with an exposed hymenium (apothecium) as the primitive morphology for Pezizomycotina with multiple derivations of the partially (perithecia) or completely enclosed (cleistothecia) sporocarps. Ascus dehiscence is most informative at the class level within Pezizomycotina with most superclass nodes reconstructed equivocally. Character-state reconstructions support a terrestrial, saprobic ecology as ancestral. In contrast to previous studies, these analyses support multiple origins of lichenization events with the loss of lichenization as less frequent and limited to terminal, closely related species.

Homologs of ToxB, a host-selective toxin gene from Pyrenophora tritici-repentis, are present in the genome of sister-species Pyrenophora bromi and other members of the Ascomycota

Pyrenophora tritici-repentis requires the production of host-selective toxins (HSTs) to cause the disease tan spot of wheat, including Ptr ToxA, Ptr ToxB, and Ptr ToxC. Pyrenophora bromi, the species most closely related to P. tritici-repentis, is the causal agent of brown leaf spot of bromegrass. Because of the relatedness of P. bromi and P. tritici-repentis, we investigated the possibility that P. bromi contains sequences homologous to ToxA and/or ToxB, the products of which may be involved in its interaction with bromegrass. Multiplex polymerase chain reaction (PCR) revealed the presence of ToxB-like sequences in P. bromi and high-fidelity PCR was used to clone several of these loci, which were subsequently confirmed to be homologous to ToxB. Additionally, Southern analysis revealed ToxB from P. bromi to have a multicopy nature similar to ToxB from P. tritici-repentis. A combination of phylogenetic and Southern analyses revealed that the distribution of ToxB extends further into the Pleosporaceae, and a search of available fungal genomes identified a distant putative homolog in Magnaporthe grisea, causal agent of rice blast. Thus, unlike most described HSTs, ToxB homologs are present across a broad range of plant pathogenic ascomycetes, suggesting that it may have arose in an early ancestor of the Ascomycota.

A Combination of Phenotypic and Genotypic Characterization Strengthens Pyrenophora tritici-repentis Race Identification

ABSTRACT Pyrenophora tritici-repentis, causal agent of tan spot of wheat, produces multiple host-selective toxins (HSTs), including Ptr ToxA, Ptr ToxB, and Ptr ToxC. The specific complement of HSTs produced by a particular isolate determines its host cultivar specificity. Each unique specificity profile, represented by the differential induction of necrosis or chlorosis on a standard set of wheat differentials, defines a unique race. Eight races of P. tritici-repentis have been formally published, although additional races are under investigation. Although visual assessment of disease phenotype is often used in race designation of P. tritici-repentis, our results suggest that it has the potential to be misleading. Inoculation of the P. tritici-repentis isolates SO3 and PT82 on the current wheat differential set indicated classification as race 2 and race 8, respectively; however, genetic characterization revealed that these isolates do not possess the associated HSTs expected for these race assignments. Despite sharing disease phenotypes similar to known races, SO3 and PT82 were genotypically distinct from these previously characterized races of P. tritici-repentis. To ensure detection of the breadth of physiological variation among the isolates of P. tritici-repentis, our results indicate that race classification, where possible, should include both phenotypic and genotypic analyses and eventual expansion of the differential set.

Development of ToxA and ToxB promoter-driven fluorescent protein expression vectors for use in filamentous ascomycetes

The green fluorescent protein (GFP) has been established as the premier in vivo reporter for investigations of gene expression, protein localization, and cell and organism dynamics. The fungal transformation vector pCT74, with sGFP under the control of the ToxA promoter from Pyrenophora tritici-repentis, effectively expresses GFP in a diverse group of filamentous ascomycetes. Due to the versatility of ToxA promoter-driven expression of GFP, we constructed an additional set of fluorescent protein expression vectors to expand the color palette of fluorescent markers for use in filamentous fungi. EYFP, ECFP and mRFP1 were successfully expressed from the ToxA promoter in its fungus of origin, P. tritici-repentis, and a distant relative, Verticillium dahliae. Additionally the ToxB promoter from P. tritici-repentis drove expression of sGFP in V. dahliae, suggesting a similar potential to the ToxA promoter for heterologous expression in ascomycetes. The suite of fungal transformation vectors presented here promise to be useful for a variety of fungal research applications.

Ptr ToxA requires multiple motifs for complete activity

Ptr ToxA was the first proteinaceous necrosis-inducing toxin identified and cloned from the wheat pathogen, Pyrenophora tritici-repentis. How this protein causes necrosis in sensitive wheat cultivars is not known. In an effort to understand the structural features of Ptr ToxA required for induction of necrosis, we employed a combination of site-directed mutagenesis and peptide inhibition studies. Mutagenesis was carried out on conserved motifs within the active domain of Ptr ToxA. Proteins with mutations of potential casein kinase 2 phosphorylation sites but not protein kinase C phosphorylation sites have significantly reduced activity. Additionally, mutations in a region with high homology to amino acids surrounding and including the RGD cell attachment motif of vitronectin result in proteins with significantly less activity than Ptr ToxA. The importance of the vitronectin-like motif was confirmed by a decrease of Ptr ToxA-induced activity when coinfiltrated with peptides corresponding to amino acids within this motif. Reduction in Ptr ToxA activity by competition with mutant proteins demonstrates the necessity of multiple motifs for Ptr ToxA activity.