Abstract P1-19-08: Neratinib + trastuzumab + fulvestrant for HER2-mutant, hormone receptor-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT ‘basket’ trial

Background: HER2 mutations define a subset of metastatic breast cancers (MBCs) with a unique mechanism of oncogenic addiction to HER2 signaling. Neratinib, an irreversible pan-HER tyrosine kinase inhibitor, has been shown to have encouraging clinical activity when combined with fulvestrant in HER2-mutant, hormone receptor-positive (HR+) MBC [Smyth et al. SABCS 2018]. Genomic analyses suggest that acquired resistance to neratinib may occur by the acquisition of additional HER2 alterations, which may amplify HER2 pathway signaling [Won et al. AACR 2019]. We therefore explored whether dual HER2-targeted therapy may improve clinical benefit in this setting. Here we describe initial results from a cohort of patients with HER2-mutant, HR+ MBC treated with neratinib + trastuzumab + fulvestrant (N+T+F) from the phase 2 SUMMIT ‘basket’ trial (NCT01953926). Methods: Patients with HR+ MBC and known oncogenic driver HER2 mutations identified by genomic sequencing were eligible to receive combination treatment with oral neratinib 240 mg daily, intravenous trastuzumab 8 mg/kg initially followed by 6 mg/kg every 3 weeks, and intramuscular fulvestrant 500 mg on days 1 and 15 of month 1, then on day 1 every 4 weeks (N+T+F). Loperamide prophylaxis was mandatory during cycle 1. There was no restriction on the number of prior lines of systemic treatment for MBC. Efficacy endpoints included: confirmed objective response rate and clinical benefit rate - all defined according to RECIST v1.1 - as well as duration of response and progression-free survival. Genomic profiling from fresh/archival tumor tissues and/or plasma cfDNA was performed retrospectively by next-generation sequencing (MSK-IMPACT). Results: As of 01-May-2019, 19 patients were enrolled into the N+T+F cohort and received study treatment (safety population). 20 HER2 mutations were identified in the 19 patients: 14 kinase domain missense mutations, 3 extracellular domain missense mutations, and 3 exon-20 insertion mutations. Median number of prior systemic regimens for metastatic disease was 4 (range 0-10) and histologies were evenly split between lobular and ductal carcinomas. While the majority of patients remain on study treatment (n=15), only 13 of the 19 enrolled patients are efficacy evaluable at this time (having had ≥1 post-baseline tumor assessment). Clinical activity is summarized in the Table. Diarrhea was the most commonly reported adverse event (84.2% any grade) with 5 patients reporting Grade 3 diarrhea (there were no Grade 4 diarrhea events). Three patients (15.8%) reduced neratinib dose due to diarrhea but no patient discontinued treatment due to diarrhea. Conclusions: The combination of N+T+F resulted in an encouraging response rate and was a well-tolerated regimen in predominantly heavily pretreated HER2-mutant HR+ breast cancers. Based on a pre-planned interim analysis, the cohort has been expanded to enroll a total of 50 patients. Updated efficacy and safety data will be presented.

Neratinib + trastuzumab + fulvestrant(n=13)Confirmed objective response rate, % (95% CI)39 (13.9-68.4)Complete response0Partial response5 (39)Duration of responses range, months4.2*-10.4*Median progression-free survivala,b, months (95% CI)NA (1.9-NA)*Response ongoing; aKaplan-Meier analysis; bincludes all patients enrolled (n=19); NA, not applicable.

Citation Format: Hans Wildiers, Valentina Boni, Cristina Saura, Mafalda Oliveira, Komal Jhaveri, Helen Won, François-Clément Bidard, Adam M Brufsky, Mark E Burkard, Andrés Cervantes, Carlos Fernández-Martos, Barbara Haley, Sherene Loi, Iben Spanggaard, Stefano Panni, Janice Lu, Melanie E Dujka, Feng Xu, Sonia Macia, Lisa D Eli, Alshad S Lalani, Sarina Piha-Paul, Funda Meric-Bernstam, David B Solit, David M Hyman. Neratinib + trastuzumab + fulvestrant for HER2-mutant, hormone receptor-positive, metastatic breast cancer: Updated results from the phase 2 SUMMIT ‘basket’ trial [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-08.

ATM and p53 are essential in the cell-cycle containment of DNA breaks during V(D)J recombination in vivo

V(D)J recombination is essential for the maturation of lymphocytes. Because of the involvement of cutting and joining DNA double strands, this recombination activity is strictly contained within the noncycling phases of the cell cycle. Such containment is crucial for the maintenance of genomic integrity. The ataxia telangiectasia mutated (ATM) gene is known to have a central role in sensing general DNA damage and mediating cell-cycle checkpoint. In this study, we investigated the role of ATM and its downstream targets in the cell-cycle control of V(D)J recombination in vivo. Our results revealed the persistence of double-strand breaks (DSBs) throughout the cell cycle in ATM(-/-) and p53(-/-) thymocytes, but the cell-cycle regulation of a V(D)J recombinase, Rag-2, was normal. The histone variant H2AX, which is phosphorylated during normal V(D)J recombination, was dispensable for containing DSBs. H2AX was still phosphorylated at V(D)J loci in the absence of ATM. Therefore, V(D)J recombination, a physiological DNA rearrangement process, activates the ATM/p53 pathway to contain DNA breaks within the noncycling cells and surprisingly this pathway is not important for containing Rag-2 activity. This study shows the dynamic multiple functions of ATM in maintaining genomic stability and preventing tumorigenesis in developing lymphocytes.

Mutations within the kinase domain and truncations of the epidermal growth factor receptor are rare events in bladder cancer: implications for therapy

PURPOSE

It has previously been reported that the patient response to gefitinib depends on the presence of mutations within the kinase domain of epidermal growth factor receptor (EGFR) or the expression of its truncated form, EGFR variant III (EGFRvIII). The focus of this study was to determine if these alterations are present within the tyrosine kinase and ligand-binding domain of EGFR in urothelial carcinoma.

EXPERIMENTAL DESIGN

The kinase domain found within exons 18 to 21 of the EGFR from 11 bladder cancer cell lines and 75 patient tumors were subjected to automated sequencing. EGFRvIII expression was determined by immunohistochemistry using a urothelial carcinoma tissue microarray, and its expression was subsequently verified by reverse transcription PCR, real-time PCR, and Western blot analysis, using an EGFRvIII-transfected glioblastoma cell line and glioblastoma tumors as positive controls.

RESULTS

Our analysis failed to detect mutations within the tyrosine kinase domain of EGFR in the 11 cell lines and 75 patients tested. The initial analysis of EGFRvIII expression by immunohistochemistry revealed that at least 50% of the patient tumors expressed EGFRvIII in a urothelial carcinoma tissue microarray. Conflicting reports exist, however, regarding the extent of EGFRvIII expression in tissues owing to the specificity of the antibodies and the methodologies used. Therefore, we sought to validate this observation by reverse transcription PCR, real-time PCR, and Western blot analysis. In these assays, none of the samples were positive for EGFRvIII except for control transfectants and glioblastomas.

CONCLUSIONS

When our results are taken together, we conclude that alterations within the tyrosine kinase domain and expression of EGFRvIII are rare events in bladder cancer. The present study has clinical implications in selecting tyrosine kinase inhibitors for the therapy of urothelial carcinoma.

DNA damage-induced cellular senescence is sufficient to suppress tumorigenesis: a mouse model

Tumor suppressor p53-dependent apoptosis is critical in suppressing tumorigenesis. Previously, we reported that DNA double-strand breaks (DSBs) at the V(D)J recombination loci induced genomic instability in the developing lymphocytes of nonhomologous end-joining (NHEJ)–deficient, p53-deficient mice, which led to rapid lymphomagenesis. To test the ability of p53-dependent cell cycle arrest to suppress tumorigenesis in the absence of apoptosis in vivo, we crossbred NHEJ-deficient mice into a mutant p53R172P background; these mice have defects in apoptosis induction, but not cell cycle arrest. These double-mutant mice survived longer than NHEJ/p53 double-null mice and, remarkably, were completely tumor free. We detected accumulation of aberrant V(D)J recombination–related DSBs at the T cell receptor (TCR) locus, and high expression levels of both mutant p53 and cell cycle checkpoint protein p21, but not the apoptotic protein p53-upregulated modulator of apoptosis. In addition, a substantial number of senescent cells were observed among both thymocytes and bone marrow cells. Cytogenetic studies revealed euploidy and limited chromosomal breaks in these lymphoid cells. The results indicate that precursor lymphocytes, which normally possess a high proliferation potential, are able to withdraw from the cell cycle and undergo senescence in response to the persistence of DSBs in a p53–p21–dependent pathway; this is sufficient to inhibit oncogenic chromosomal abnormality and suppress tumorigenesis.

Role of ATM in V(D)J recombination and cell cycle control (35.10)

V(D)J recombination is a process specific to developing B- and T- lymphocytes in which double strand breaks (DSBs) are introduced into germline DNA and upon repair generate rearranged gene segments. This recombination event is cell cycle regulated and is confined to the noncycling G0/G1 phase of cell cycle. The protein kinase Ataxia Telangiectasia Mutated (ATM) is a vital mediator in both the DNA damage response and cell cycle. ATM was found localized at V(D)J mediated break sites, suggesting an additional function for ATM in recombination. In the absence of ATM, mice develop thymic lymphomas with chromosomal translocations. Therefore, we hypothesize a role for ATM in the cell cycle control of V(D)J recombination. Thymic lymphomas from Atm null mice revealed cells harbored multiple chromosomal translocations near sites of recombination. Wildtype and Atm null thymocytes were separated into cell cycle fractions of G0/G1 and S/G2/M. V(D)J mediated DSBs, indicative of recombination, were observed at the T cell receptor α, δ, and β loci in both cell cycle fractions of Atm null thymocytes but were found only in the G0/G1 fraction of wildtype thymocytes. Together, these results indicate the involvement of ATM in the cell cycle control of V(D)J recombination. Loss of this control can lead to sustained DNA DSBs and translocations, which could contribute to tumorigenesis.

NPI-0052, a novel proteasome inhibitor, induces caspase-8 and ROS-dependent apoptosis alone and in combination with HDAC inhibitors in leukemia cells

The proteasome has been successfully targeted for the treatment of multiple myeloma and mantle cell lymphoma; however, in other hematologic malignancies, bortezomib has been less effective as a single agent. Here, we describe effects of NPI-0052, a novel proteasome inhibitor, in leukemia model systems. In cell lines, NPI-0052 inhibits all 3 proteolytic activities associated with the proteasome: chymotrypsin-, trypsin-, and caspase-like. NPI-0052 also induces DNA fragmentation in leukemia lines and in mononuclear cells from a Ph + acute lymphoblastic leukemia (ALL) patient. Caspase-3 activation by NPI-0052 was seen in wild-type Jurkat cells, but was significantly lessened in Fas-associated death domain (FADD)-deficient or caspase-8-deficient counterparts. NPI-0052-induced apoptosis was further probed using caspase-8 inhibitors, which were more protective than caspase-9 inhibitors. N-acetyl cysteine (NAC) also conferred protection against NPI-0052-induced apoptosis, indicating a role for oxidative stress by NPI-0052. In support of the drug's in vitro activities, biweekly treatment with NPI-0052 lessened total white blood cell (WBC) burden over 35 days in leukemic mice. Interestingly, combining NPI-0052 with either MS-275 or valproic acid (VPA) induced greater levels of cell death than the combination of bortezomib with these histone deacetylase inhibitors (HDACi). These effects of NPI-0052, alone and in combination with HDACi, warrant further testing to determine the compound's clinical efficacy in leukemia.