Inhibition of lysine acetyltransferase KAT6 in ER+HER2- metastatic breast cancer: a phase 1 trial.

Inhibition of histone lysine acetyltransferases (KATs) KAT6A and KAT6B has shown antitumor activity in estrogen receptor-positive (ER+) breast cancer preclinical models. PF-07248144 is a selective catalytic inhibitor of KAT6A and KAT6B. In the present study, we report the safety, pharmacokinetics (PK), pharmacodynamics, efficacy and biomarker results from the first-in-human, phase 1 dose escalation and dose expansion study (n = 107) of PF-07248144 monotherapy and fulvestrant combination in heavily pretreated ER+ human epidermal growth factor receptor-negative (HER2-) metastatic breast cancer (mBC). The primary objectives of assessing the safety and tolerability and determining the recommended dose for expansion of PF-07248144, as monotherapy and in combination with fulvestrant, were met. Secondary endpoints included characterization of PK and evaluation of antitumor activity, including objective response rate (ORR) and progression-free survival (PFS). Common treatment-related adverse events (any grade; grades 3-4) included dysgeusia (83.2%, 0%), neutropenia (59.8%, 35.5%) and anemia (48.6%, 13.1%). Exposure was approximately dose proportional. Antitumor activity was observed as monotherapy. For the PF-07248144-fulvestrant combination (n = 43), the ORR (95% confidence interval (CI)) was 30.2% (95% CI = 17.2-46.1%) and the median PFS was 10.7 (5.3-not evaluable) months. PF-07248144 demonstrated a tolerable safety profile and durable antitumor activity in heavily pretreated ER+HER2- mBC. These findings establish KAT6A and KAT6B as druggable cancer targets, provide clinical proof of concept and reveal a potential avenue to treat mBC. clinicaltrial.gov registration: NCT04606446 .

Newly Approved and Emerging Agents in HER2-Positive Metastatic Breast Cancer.

Human epidermal growth factor receptor 2-positive breast cancer (HER2+ BC) is an aggressive tumor type, accounting for 15% to 20% of the approximately 300,000 new BC cases in the United States each year. The goal of this review is to discuss the evolving landscape of therapies for HER2+ metastatic BC (mBC). Targeted therapies that have been the standard of care (SOC) for HER2+ mBC for almost a decade have greatly improved patient outcomes. The SOC for the first-line treatment of HER2+ mBC continues to be HER2-targeted monoclonal antibodies (mAbs) + a taxane, but recent updates in the second-line setting favor use of a newer HER2-targeted antibody-drug conjugate (ADC), trastuzumab deruxtecan, versus the prior SOC ADC, trastuzumab emtansine. Numerous options are now available in the third line and beyond, including tyrosine kinase inhibitor (TKI) regimens, newer mAbs, and other ADCs. The optimal course of treatment for individual patients can be guided by location of metastases, prior therapies, concomitant biomarkers, and monitoring and management of adverse events. Ongoing trials will further the evolution of the HER2+ mBC treatment landscape. Furthermore, next-generation ADCs, TKIs, and classes of drugs that have not been approved for the treatment of HER2+ mBC, including immune checkpoint inhibitors and cyclin-dependent kinase 4 and 6 inhibitors, are also being evaluated for their efficacy in the first and second line. Although the influx of new drugs may complicate treatment decisions for physicians, having a multitude of options will undoubtedly further improve patient outcomes and patient-centered care.

Response of Leptomeningeal Metastasis of Breast Cancer With a HER2/neu Activating Variant to Tucatinib: A Case Report.

Metastatic breast cancer demonstrates HER2/neu amplification approximately 15% of the time. However, HER2 mutations, which often stimulate tumor growth, occur in only 3% to 5% of patients, and are seen more frequently in metastatic versus primary tumors. They are more frequent in lobular carcinoma, including triple-negative lobular cancer. Many of these variants are resistant to trastuzumab and lapatinib. However, neratinib can be efficacious, and recent data suggest that antibody-drug conjugates (ADCs) such as ado-trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan may also be helpful. Laboratory and clinical data raise the possibility that simultaneous treatment with ADCs plus neratinib may be even more efficacious. Tucatinib, which has demonstrated significant activity in the central nervous system, has also been shown in vitro to be active against a number of these HER2 variants. This report describes a patient with metastatic estrogen receptor-positive, HER2-nonamplified breast cancer with an activating HER2 mutation whose tumor became resistant to neratinib as well as capecitabine, but whose subsequent leptomeningeal disease had a dramatically successful response to tucatinib plus capecitabine. As the frequency of HER2 mutations increases during the evolution of metastatic breast cancer, it is important to obtain genomic evaluation on these tumors with either repeat tissue or liquid biopsy as they progress over time.

18F-Fluoroestradiol PET Imaging in a Phase II Trial of Vorinostat to Restore Endocrine Sensitivity in ER+/HER2- Metastatic Breast Cancer.

Histone deacetylase inhibitors (HDACIs) may overcome endocrine resistance in estrogen receptor-positive (ER+) metastatic breast cancer. We tested whether 18F-fluoroestradiol PET imaging would elucidate the pharmacodynamics of combination HDACIs and endocrine therapy. Methods: Patients with ER+/human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer with prior clinical benefit from endocrine therapy but later progression on aromatase inhibitor (AI) therapy were given vorinostat (400 mg daily) sequentially or simultaneously with AI. 18F-fluoroestradiol PET and 18F-FDG PET scans were performed at baseline, week 2, and week 8. Results: Eight patients were treated sequentially, and then 15 simultaneously. Eight patients had stable disease at week 8, and 6 of these 8 patients had more than 6 mo of stable disease. Higher baseline 18F-fluoroestradiol uptake was associated with longer progression-free survival. 18F-fluoroestradiol uptake did not systematically increase with vorinostat exposure, indicating no change in regional ER estradiol binding, and 18F-FDG uptake did not show a significant decrease, as would have been expected with tumor regression. Conclusion: Simultaneous HDACIs and AI dosing in patients with cancer resistant to AI alone showed clinical benefit (6 or more months without progression) in 4 of 10 evaluable patients. Higher 18F-fluoroestradiol PET uptake identified patients likely to benefit from combination therapy, but vorinostat did not change ER expression at the level of detection of 18F-fluoroestradiol PET.

Complete and Durable Responses in Primary Central Nervous System Posttransplant Lymphoproliferative Disorder with Zidovudine, Ganciclovir, Rituximab, and Dexamethasone.

Purpose: Primary central nervous system posttransplant lymphoproliferative disorder (PCNS-PTLD) is a complication of solid organ transplantation with a poor prognosis and typically associated with Epstein-Barr virus (EBV). We hypothesized EBV lytic-phase protein expression would allow successful treatment with antiviral therapy.Patients and Methods: Thirteen patients were treated with zidovudine (AZT), ganciclovir (GCV), dexamethasone, and rituximab in EBV+ PCNS-PTLD. Twice-daily, intravenous AZT 1,500 mg, GCV 5 mg/kg, and dexamethasone 10 mg were given for 14 days. Weekly rituximab 375 mg/m2 was delivered for the first 4 weeks. Twice-daily valganciclovir 450 mg and AZT 300 mg started day 15. Lytic and latent protein expression was assessed using in situ hybridization and immunohistochemistry. Immunoblot assay assessed lytic gene activation. Cells transfected with lytic kinase vectors were assessed for sensitivity to our therapy using MTS tetrazolium and flow cytometry.Results: The median time to response was 2 months. Median therapy duration was 26.5 months. Median follow-up was 52 months. The estimated 2-year overall survival (OS) was 76.9% (95% CI, 44.2%-91.9%). Overall response rate (ORR) was 92% (95% CI, 64%-100%). BXLF1/vTK and BGLF4 expression was found in the seven tumor biopsies evaluated. Lytic gene expression was induced in vitro using the four-drug regimen. Transfection with viral kinase cDNA increased cellular sensitivity to antiviral therapy.Conclusions: EBV+ PCNS-PTLD expressed lytic kinases and therapy with AZT, GCV, rituximab and dexamethasone provided durable responses. Induction of the lytic protein expression and increased cellular sensitivity to antiviral therapy after transfection with viral kinase cDNA provides a mechanistic rationale for our approach. Clin Cancer Res; 24(14); 3273-81. ©2018 AACR.

Targeted Drugs as Maintenance Therapy after Autologous Stem Cell Transplantation in Patients with Mantle Cell Lymphoma.

The treatment landscape for mantle cell lymphoma (MCL) is rapidly evolving toward the incorporation of novel and biologically targeted pharmaceuticals with improved disease activity and gentler toxicity profiles compared with conventional chemotherapeutics. Upfront intensive treatment of MCL includes autologous stem cell transplantation (SCT) consolidation aimed at deepening and lengthening disease remission, but subsequent relapse occurs. Maintenance therapy after autologous SCT in patients with MCL in remission features lower-intensity treatments given over extended periods to improve disease outcomes. Targeted drugs are a natural fit for this space, and are the focus of considerable clinical investigation. This review summarizes recent advances in the field and their potential impact on treatment practices for MCL.

Selective inhibition of protein arginine methyltransferase 5 blocks initiation and maintenance of B-cell transformation.

Epigenetic events that are essential drivers of lymphocyte transformation remain incompletely characterized. We used models of Epstein-Barr virus (EBV)-induced B-cell transformation to document the relevance of protein arginine methyltransferase 5 (PRMT5) to regulation of epigenetic-repressive marks during lymphomagenesis. EBV(+) lymphomas and transformed cell lines exhibited abundant expression of PRMT5, a type II PRMT enzyme that promotes transcriptional silencing of target genes by methylating arginine residues on histone tails. PRMT5 expression was limited to EBV-transformed cells, not resting or activated B lymphocytes, validating it as an ideal therapeutic target. We developed a first-in-class, small-molecule PRMT5 inhibitor that blocked EBV-driven B-lymphocyte transformation and survival while leaving normal B cells unaffected. Inhibition of PRMT5 led to lost recruitment of a PRMT5/p65/HDAC3-repressive complex on the miR96 promoter, restored miR96 expression, and PRMT5 downregulation. RNA-sequencing and chromatin immunoprecipitation experiments identified several tumor suppressor genes, including the protein tyrosine phosphatase gene PTPROt, which became silenced during EBV-driven B-cell transformation. Enhanced PTPROt expression following PRMT5 inhibition led to dephosphorylation of kinases that regulate B-cell receptor signaling. We conclude that PRMT5 is critical to EBV-driven B-cell transformation and maintenance of the malignant phenotype, and that PRMT5 inhibition shows promise as a novel therapeutic approach for B-cell lymphomas.

Genetic validation of the protein arginine methyltransferase PRMT5 as a candidate therapeutic target in glioblastoma.

Glioblastoma is the most common and aggressive histologic subtype of brain cancer with poor outcomes and limited treatment options. Here, we report the selective overexpression of the protein arginine methyltransferase PRMT5 as a novel candidate theranostic target in this disease. PRMT5 silences the transcription of regulatory genes by catalyzing symmetric dimethylation of arginine residues on histone tails. PRMT5 overexpression in patient-derived primary tumors and cell lines correlated with cell line growth rate and inversely with overall patient survival. Genetic attenuation of PRMT5 led to cell-cycle arrest, apoptosis, and loss of cell migratory activity. Cell death was p53-independent but caspase-dependent and enhanced with temozolomide, a chemotherapeutic agent used as a present standard of care. Global gene profiling and chromatin immunoprecipitation identified the tumor suppressor ST7 as a key gene silenced by PRMT5. Diminished ST7 expression was associated with reduced patient survival. PRMT5 attenuation limited PRMT5 recruitment to the ST7 promoter, led to restored expression of ST7 and cell growth inhibition. Finally, PRMT5 attenuation enhanced glioblastoma cell survival in a mouse xenograft model of aggressive glioblastoma. Together, our findings defined PRMT5 as a candidate prognostic factor and therapeutic target in glioblastoma, offering a preclinical justification for targeting PRMT5-driven oncogenic pathways in this deadly disease.

Protein arginine methyltransferase 5 (PRMT5) inhibition induces lymphoma cell death through reactivation of the retinoblastoma tumor suppressor pathway and polycomb repressor complex 2 (PRC2) silencing.

Epigenetic regulation mediated by lysine- and arginine-specific enzymes plays an essential role in tumorigenesis, and enhanced expression of the type II protein arginine methyltransferase PRMT5 as well as the polycomb repressor complex PRC2 has been associated with increased cell proliferation and survival. Here, we show that PRMT5 is overexpressed in three different types of non-Hodgkin lymphoma cell lines and clinical samples as well as in mouse primary lymphoma cells and that it up-regulates PRC2 expression through inactivation of the retinoblastoma proteins RB1 and RBL2. Although PRMT5 epigenetically controls RBL2 expression, it indirectly promotes RB1 phosphorylation through enhanced cyclin D1 expression. Furthermore, we demonstrate that PRMT5 knockdown in non-Hodgkin lymphoma cell lines and mouse primary lymphoma cells leads to RBL2 derepression and RB1 reactivation, which in turn inhibit PRC2 expression and trigger derepression of its CASP10, DAP1, HOXA5, and HRK pro-apoptotic target genes. We also show that reduced PRMT5 expression leads to cyclin D1 transcriptional repression via loss of TP53K372 methylation, which results in decreased BCL3 expression and enhanced recruitment of NF-κB p52-HDAC1 repressor complexes to the cyclin D1 promoter. These findings indicate that PRMT5 is a master epigenetic regulator that governs expression of its own target genes and those regulated by PRC2 and that its inhibition could offer a promising therapeutic strategy for lymphoma patients.

PRMT5 is upregulated in malignant and metastatic melanoma and regulates expression of MITF and p27(Kip1.).

Protein arginine methyltransferase-5 (PRMT5) is a Type II arginine methyltransferase that regulates various cellular functions. We hypothesized that PRMT5 plays a role in regulating the growth of human melanoma cells. Immunohistochemical analysis indicated significant upregulation of PRMT5 in human melanocytic nevi, malignant melanomas and metastatic melanomas as compared to normal epidermis. Furthermore, nuclear PRMT5 was significantly decreased in metastatic melanomas as compared to primary cutaneous melanomas. In human metastatic melanoma cell lines, PRMT5 was predominantly cytoplasmic, and associated with its enzymatic cofactor Mep50, but not STAT3 or cyclin D1. However, histologic examination of tumor xenografts from athymic mice revealed heterogeneous nuclear and cytoplasmic PRMT5 expression. Depletion of PRMT5 via siRNA inhibited proliferation in a subset of melanoma cell lines, while it accelerated growth of others. Loss of PRMT5 also led to reduced expression of MITF (microphthalmia-associated transcription factor), a melanocyte-lineage specific oncogene, and increased expression of the cell cycle regulator p27(Kip1). These results are the first to report elevated PRMT5 expression in human melanoma specimens and indicate this protein may regulate MITF and p27(Kip1) expression in human melanoma cells.

Combination anti-CD74 (milatuzumab) and anti-CD20 (rituximab) monoclonal antibody therapy has in vitro and in vivo activity in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy with a median survival of 3 years despite chemoimmunotherapy. Rituximab, a chimeric anti-CD20 monoclonal antibody (mAb), has shown only modest activity as single agent in MCL. The humanized mAb milatuzumab targets CD74, an integral membrane protein linked with promotion of B-cell growth and survival, and has shown preclinical activity against B-cell malignancies. Because rituximab and milatuzumab target distinct antigens and potentially signal through different pathways, we explored a preclinical combination strategy in MCL. Treatment of MCL cell lines and primary tumor cells with immobilized milatuzumab and rituximab resulted in rapid cell death, radical oxygen species generation, and loss of mitochondrial membrane potential. Cytoskeletal distrupting agents significantly reduced formation of CD20/CD74 aggregates, cell adhesion, and cell death, highlighting the importance of actin microfilaments in rituximab/milatuzumab-mediated cell death. Cell death was independent of caspase activation, Bcl-2 family proteins or modulation of autophagy. Maximal inhibition of p65 nuclear translocation was observed with combination treatment, indicating disruption of the NF-κB pathway. Significant in vivo therapeutic activity of combination rituximab and milatuzumab was demonstrated in a preclinical model of MCL. These data support clinical evaluation of combination milatuzumab and rituximab therapy in MCL.

The search for an optimal DNA, RNA, and protein detection by in situ hybridization, immunohistochemistry, and solution-based methods.

Clinical trials and correlative laboratory research are increasingly reliant upon archived paraffin-embedded samples. Therefore, the proper processing of biological samples is an important step to sample preservation and for downstream analyses like the detection of a wide variety of targets including micro RNA, DNA and proteins. This paper analyzed the question whether routine fixation of cells and tissues in 10% buffered formalin is optimal for in situ and solution phase analyses by comparing this fixative to a variety of cross linking and alcohol (denaturing) fixatives. We examined the ability of nine commonly used fixative regimens to preserve cell morphology and DNA/RNA/protein quality for these applications. Epstein-Barr virus (EBV) and bovine papillomavirus (BPV)-infected tissues and cells were used as our model systems. Our evaluation showed that the optimal fixative in cell preparations for molecular hybridization techniques was "gentle" fixative with a cross-linker such as paraformaldehyde or a short incubation in 10% buffered formalin. The optimal fixatives for tissue were either paraformaldehyde or low concentration of formalin (5% of formalin). Methanol was the best of the non cross-linking fixatives for in situ hybridization and immunohistochemistry. For PCR-based detection of DNA or RNA, some denaturing fixatives like acetone and methanol as well as "gentle" cross-linking fixatives like paraformaldehyde out-performed other fixatives. Long term fixation was not proposed for DNA/RNA-based assays. The typical long-term fixation of cells and tissues in 10% buffered formalin is not optimal for combined analyses by in situ hybridization, immunohistochemistry, or--if one does not have unfixed tissues--solution phase PCR. Rather, we recommend short term less intense cross linking fixation if one wishes to use the same cells/tissue for in situ hybridization, immunohistochemistry, and solution phase PCR.

Strong inverse correlation between microRNA-125b and human papillomavirus DNA in productive infection.

Infection by the human papillomavirus (HPV) is a cause of cervical intraepithelial neoplasia (CIN) and cancer. microRNA (miRNA) in situ analysis of the transformation zone epithelia, the site of initial cervical HPV infection, showed that miRNAs let-7c, -99a, 26a, and 125b were the most abundantly expressed. In situ testing of CIN 1 showed a dramatic reduction in miR-125b expression in the koilocytes, the cytologic marker of productive HPV infection. A marked reduction in miR-125b was likewise observed in the HPV-infected cells of the condyloma acuminatum, verruca vulgaris, and epidermodysplasia verruciformis. Reverse transcriptase in situ polymerase chain reaction (PCR) showed that the pre-miRNA 125b was present in the koilocyte, suggesting direct inactivation of the mature miRNA. HEK cells transfected with only the antimiR-125b showed perinuclear halos equivalent to HPV-infected koilocytes. NIH 3T3 cells transfected with the HPV 16 full-length genome and mimetic miR-125b showed a marked reduction in viral DNA and protein synthesis by quantitative PCR and in situ-based analyses, respectively (P=0.002). Alternatively, cotransfection with anti-miR-125b and HPV 16 markedly increased HPV DNA (P=0.002). Sequence analyses showed strong homology between L2 of different HPV genotypes and miR-125b. Transfection with HPV 16 L2 resulted in a marked reduction in miR-125b levels in the NIH 3T3 cells. HPV L2-induced inactivation of miR-125b is associated with the classic cytologic changes of the koilocyte, and the exogenous application of mimetic miR-125b markedly inhibits HPV DNA synthesis.

FTY720 shows promising in vitro and in vivo preclinical activity by downmodulating Cyclin D1 and phospho-Akt in mantle cell lymphoma.

PURPOSE: Despite the progress that has been made in the treatment of mantle cell lymphoma (MCL), all patients invariably relapse with the currently available therapies. Because of the absence of curative therapy for MCL, we explored FTY720 as a novel agent against MCL. EXPERIMENTAL DESIGN: The cytotoxic effect of FTY720 in primary MCL tumor cells and cell lines were evaluated in vitro. The effects of FTY720 on caspase activation, generation of reactive oxygen species, and modulation of Cyclin D1 and Akt, which are implied in the pathogenesis of MCL, were investigated. The in vivo efficacy of FTY720 was evaluated in a Jeko-severe combined immunodeficient xenograft model of human MCL. RESULTS: FTY720 mediated time- and dose-dependent cytotoxicity in primary MCL tumor cells and MCL cell lines in vitro. FTY720-induced cytotoxicity occured independent of caspase activation but dependent on the generation of ROS in MCL. In addition, FTY720 treatment resulted in the time-dependent downmodulation of Cyclin D1 and accumulation of cells in G(0)-G(1) and G(2)-M phases of the cell cycle with concomitant decrease in S-phase entry. Furthermore, concentrations of FTY720 that induced cytotoxicity led to decreased phospho-Akt in primary MCL cells and cell lines. Most importantly, the in vivo therapeutic activity of FTY720 was shown in severe combined immunodeficient mice engrafted with the Jeko MCL cell line. CONCLUSIONS: These results provide the first evidence for a potential use of FTY720 in targeting key pathways that are operable in the pathogenesis of MCL and warrant further investigation of FTY720 in clinical trials to treat patients with MCL.