A phase I study to evaluate the safety, pharmacokinetics, and pharmacodynamics of PF-06939999 (PRMT5 inhibitor) in patients with selected advanced or metastatic tumors with high incidence of splicing factor gene mutations

BACKGROUND

Protein arginine methyltransferase 5 (PRMT5) methylates multiple substrates dysregulated in cancer, including spliceosome machinery components. PF-06939999 is a selective small-molecule PRMT5 inhibitor.

PATIENTS AND METHODS

This phase I dose-escalation and -expansion trial (NCT03854227) enrolled patients with selected solid tumors. PF-06939999 was administered orally once or twice a day (q.d./b.i.d.) in 28-day cycles. The objectives were to evaluate PF-06939999 safety and tolerability to identify maximum tolerated dose (MTD) and recommended part 2 dose (RP2D), and assess pharmacokinetics (PK), pharmacodynamics [changes in plasma symmetric dimethylarginine (SDMA) levels], and antitumor activities.

RESULTS

In part 1 dose escalation, 28 patients received PF-06939999 (0.5 mg q.d. to 6 mg b.i.d.). Four of 24 (17%) patients reported dose-limiting toxicities: thrombocytopenia (n = 2, 6 mg b.i.d.), anemia (n = 1, 8 mg q.d.), and neutropenia (n = 1, 6 mg q.d.). PF-06939999 exposure increased with dose. Steady-state PK was achieved by day 15. Plasma SDMA was reduced at steady state (58%-88%). Modulation of plasma SDMA was dose dependent. No MTD was determined. In part 2 dose expansion, 26 patients received PF-06939999 6 mg q.d. (RP2D). Overall (part 1 + part 2), the most common grade ≥3 treatment-related adverse events included anemia (28%), thrombocytopenia/platelet count decreased (22%), fatigue (6%), and neutropenia (4%). Three patients (6.8%) had confirmed partial response (head and neck squamous cell carcinoma, n = 1; non-small-cell lung cancer, n = 2), and 19 (43.2%) had stable disease. No predictive biomarkers were identified.

CONCLUSIONS

PF-06939999 demonstrated a tolerable safety profile and objective clinical responses in a subset of patients, suggesting that PRMT5 is an interesting cancer target with clinical validation. However, no predictive biomarker was identified. The role of PRMT5 in cancer biology is complex and requires further preclinical, mechanistic investigation to identify predictive biomarkers for patient selection.

Abstract CT016: Clinical activity of single-agent ZN-c3, an oral WEE1 inhibitor, in a phase 1 dose-escalation trial in patients with advanced solid tumors

Introduction: ZN-c3 is a selective and orally bioavailable small molecule WEE1 inhibitor. WEE1 is a crucial component of the G2/M cell cycle checkpoint preventing cells from entering mitosis to allow repair of DNA damage before cell cycle progression. ZN-c3 has demonstrated significant growth inhibition in vitro in multiple cell lines from various cancer types and antitumor activity in vivo in human xenograft tumor models. Methods: ZN-c3-001 (NCT04158336) is a dose escalation, open-label, multicenter, Phase 1 clinical trial evaluating the safety, tolerability, and efficacy of ZN-c3 in subjects with advanced or metastatic solid tumors, refractory to standard therapy or for whom no standard therapy is available. ZN-c3 dosing was escalated from 25mg to 450mg administered orally QD. The primary objective of this study is to determine the schedule, Maximum Tolerated Dose (MTD), and Recommended Phase 2 Dose (RP2D) of ZN-c3. Subjects underwent imaging every 9 weeks to assess disease response. Here we report early signal of clinical activity of ZN-c3. Results: As of 30Nov2020 there were 39 subjects treated and of those, 30 experienced treatment related adverse events (TRAEs), the most frequently reported TRAEs were nausea, diarrhea, vomiting, and fatigue. Of the 16 subjects with post-baseline tumor assessments, 5 patients had stable disease (SD) and 2 subjects had partial responses (PR), as per RECIST 1.1. One was a 63-yo Caucasian male with Stage IV colorectal cancer with metastases to the liver, lymph nodes, and pleura who achieved a PR with 42% reduction in overall tumor burden. Carcinoembryonic Antigen tumor marker decreased from 327 ng/mL at baseline to less than 50 ng/mL after 3 weeks on treatment. The second subject was a 72-yo Caucasian female with Stage IV ovarian cancer with metastases to the pleura, peritoneum, and retroperitoneum who achieved a PR with a 56% reduction in overall tumor burden. CA-125 dropped from 610 kU/L at baseline to 125 kU/L within 4 weeks after first dose and normalized 3 weeks later. Based on MTD, as determined by the Bayesian Continual Reassessment model, the overall tolerability and toxicity, and the dose dependent pharmacokinetic profile, the recommended RP2D for ZN-c3 is determined to be 300mg, given orally as continuous once daily dosing. Conclusions: ZN-c3 shows early signal of clinical activity in heavily pretreated advanced solid tumor subjects. It appears safe and tolerable as a single agent at the identified RP2D. An expansion cohort will be included in this Phase 1 study to treat additional subjects. In addition, a Phase 2 clinical study is being planned to enroll additional subjects to further evaluate the efficacy of ZN-c3. Ongoing correlative studies will continue to determine specific mechanisms and biomarkers of response to ZN-c3.

Citation Format: Anthony Tolcher, Hirva Mamdani, Pavani Chalasani, Funda Meric-Bernstam, Mihaela Gazdoiu, Lukas Makris, Philippe Pultar, Dimitris Voliotis. Clinical activity of single-agent ZN-c3, an oral WEE1 inhibitor, in a phase 1 dose-escalation trial in patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT016.

Ribociclib, a CDK 4/6 inhibitor, plus endocrine therapy in Asian women with advanced breast cancer

The ongoing, Phase Ib MONALEESASIA study is evaluating the efficacy and safety of ribociclib plus endocrine therapy in Asian patients with hormone receptor‐positive, human epidermal growth factor receptor 2‐negative advanced breast cancer. Eligible patients from Japan, Hong Kong, and Singapore were enrolled in this 2‐phase study consisting of a dose‐escalation phase to determine the maximum‐tolerated dose and the recommended Phase II dose of ribociclib plus letrozole, and a dose‐expansion phase to evaluate safety and tolerability of ribociclib plus letrozole, fulvestrant, or tamoxifen. An exploratory biomarker analysis evaluating expression of target genes was also conducted. In the dose‐escalation phase, the maximum‐tolerated/recommended Phase II doses of ribociclib were lower in Japanese patients (300 mg) than in Asian non‐Japanese patients (600 mg). Ribociclib plus endocrine therapy at the recommended Phase II dose had a manageable safety profile, with neutropenia and elevated liver transaminases being the most common adverse events leading to dose modifications or discontinuations, and it demonstrated evidence of clinical activity in both Japanese and Asian non‐Japanese patients. Preliminary efficacy in Asian populations is similar to that observed in White populations studied in previous ribociclib (MONALEESA) trials. Biomarker analysis demonstrated suppression of pharmacodynamic biomarker gene expression, indicating inhibition of target genes by ribociclib combined with endocrine therapy. Results from the ongoing study support the use of ribociclib in combination with letrozole in Asian non‐Japanese patients at the same dose (600 mg) as White patients. In Japanese patients, a lower dose of ribociclib (300 mg) should be considered. Clinicaltrials.gov: NCT02333370.

Abstract CT143: Baseline circulating tumor DNA (ctDNA) analysis in Asian women with HR+/HER2- advanced breast cancer (ABC) receiving ribociclib + endocrine therapy in the Phase Ib MONALEESASIA trial

Background: MONALEESASIA (NCT02333370) is an ongoing Phase Ib study in which Asian patients (pts) with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) ABC are treated with ribociclib (a cyclin-dependent kinase 4/6 inhibitor) and either letrozole (all pts), fulvestrant, or tamoxifen (Japanese pts). Tumor biomarker analysis in MONALEESASIA using NanoString technology for gene expression was presented previously (Yap YS, et al. ESMO Asia 2018 [Abstract 400]). Here we report additional biomarker analysis of baseline ctDNA.

Methods: Plasma samples were collected at baseline and end of treatment; ctDNA was extracted and used to generate next-generation sequencing libraries. The DNA libraries were then enriched for a specific 2.9 Mb of the human genome containing ≈550 oncogenes and tumor suppressor genes. Captured libraries were then combined in equimolar pools and sequenced, targeting ≥70 million sequencing reads per sample to ensure that unique coverage of the genes was >1000× or approached the maximal complexity of the library.

Results: ctDNA was analyzed in baseline plasma samples collected from 77 pts (49 Japanese and 28 non-Japanese). Similar gene alteration frequencies were observed in Japanese and non-Japanese pts except for ESR1 alterations, which were more common in Japanese pts (Table). TP53 alterations were more common in pts with progressive disease, and the frequencies of TP53, ESR1, and FAT1 were slightly lower in pre- vs postmenopausal pts; however, these differences were not statistically significant. Response rates by genetic alteration are shown in the table.

Conclusion: There appeared to be a trend toward a higher likelihood of alterations in TP53 and PIK3CA in pts with poorer responses, although the sample size was small. These data are hypothesis generating, and additional analysis is ongoing.

Gene AlterationsPIK3CATP53CCND1FAT1ESR1FGFR1CDH1Frequency, n (%)Japanesen=4917 (35)11 (22)5 (10)3 (6)7 (14)5 (10)4 (8)Non-Japanesen=288 (29)7 (25)3 (11)5 (18)02 (7)0Best Overall Response, n of Patients with Alteration (% Response Type)PRn=359 (26)6 (17)5 (14)3 (9)2 (6)4 (11)0SDn=299 (31)7 (24)1 (3)3 (10)3 (10)03 (10)NCRNPDn=63 (50)1 (17)002 (33)1 (17)1 (17)PDn=74 (57)4 (57)2 (29)2 (29)02 (29)0CCND1, cyclin D1; CDH1, cadherin 1; ESR1, estrogen receptor 1; FAT1, FAT atypical cadherin 1; FGFR1, fibroblast growth factor receptor 1; NCRNPD, not complete response nor progressive disease; PD, progressive disease; PIK3CA, phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit α; PR, partial response; SD, stable disease; TP53, tumor protein p53.

Citation Format: Yoon-Sim Yap, Faye Su, Nadia Solovieff, Yoshinori Ito, Norikaza Masuda, Takashi Ishikawa, Tomoyuki Aruga, Seung Jin Kim, Wei He, Mihaela Gazdoiu, Joanne Chiu. Baseline circulating tumor DNA (ctDNA) analysis in Asian women with HR+/HER2- advanced breast cancer (ABC) receiving ribociclib + endocrine therapy in the Phase Ib MONALEESASIA trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT143.

Inhibition of Cathepsin S by Fsn0503 enhances the efficacy of chemotherapy in colorectal carcinomas

Cathepsin S is a lysosomal cysteine protease implicated in tumourigenesis with key roles in invasion and angiogenesis. We have previously shown that the specific inhibition of Cathepsin S using a monoclonal antibody (Fsn0503) blocks colorectal carcinoma tumour growth and angiogenesis in vivo. We investigated whether Cathepsin S expression levels were affected by chemotherapy in human cancer cell lines by RT-PCR. Using colorectal xenograft models, we examined the therapeutic benefit of Cathepsin S inhibition using Fsn0503 in combination with a metronomic dosing regimen of CPT-11. We analysed the effects of the combination therapy on tumour progression and on tumour vascularisation by immunohistochemical staining of tumours. Cathepsin S expression levels are upregulated in HCT116, LoVo, Colo205 cell lines and HUVECs after exposure to CPT-11 in vitro. The administration of Fsn0503 in combination with CPT-11 significantly attenuated tumour growth in comparison to CPT-11 alone in colorectal HCT116 xenograft models. Furthermore, analysis of tumour vascularisation revealed that this was also significantly disrupted by the combination treatment. These results show that the combination of Cathepsin S inhibition with CPT-11 enhances the therapeutic effect of the chemotherapy. This rationale may have clinical application in the treatment of colorectal cancer upon further evaluation.

Slc25a12 disruption alters myelination and neurofilaments: a model for a hypomyelination syndrome and childhood neurodevelopmental disorders

BACKGROUND

SLC25A12, a susceptibility gene for autism spectrum disorders that is mutated in a neurodevelopmental syndrome, encodes a mitochondrial aspartate-glutamate carrier (aspartate-glutamate carrier isoform 1 [AGC1]). AGC1 is an important component of the malate/aspartate shuttle, a crucial system supporting oxidative phosphorylation and adenosine triphosphate production.

METHODS

We characterized mice with a disruption of the Slc25a12 gene, followed by confirmatory in vitro studies.

RESULTS

Slc25a12-knockout mice, which showed no AGC1 by immunoblotting, were born normally but displayed delayed development and died around 3 weeks after birth. In postnatal day 13 to 14 knockout brains, the brains were smaller with no obvious alteration in gross structure. However, we found a reduction in myelin basic protein (MBP)-positive fibers, consistent with a previous report. Furthermore, the neocortex of knockout mice contained abnormal neurofilamentous accumulations in neurons, suggesting defective axonal transport and/or neurodegeneration. Slice cultures prepared from knockout mice also showed a myelination defect, and reduction of Slc25a12 in rat primary oligodendrocytes led to a cell-autonomous reduction in MBP expression. Myelin deficits in slice cultures from knockout mice could be reversed by administration of pyruvate, indicating that reduction in AGC1 activity leads to reduced production of aspartate/N-acetylaspartate and/or alterations in the dihydronicotinamide adenine dinucleotide/nicotinamide adenine dinucleotide(+) ratio, resulting in myelin defects.

CONCLUSIONS

Our data implicate AGC1 activity in myelination and in neuronal structure and indicate that while loss of AGC1 leads to hypomyelination and neuronal changes, subtle alterations in AGC1 expression could affect brain development, contributing to increased autism susceptibility.

Interactions between the L1 cell adhesion molecule and ezrin support traction-force generation and can be regulated by tyrosine phosphorylation

An Ig superfamily cell-adhesion molecule, L1, forms an adhesion complex at the cell membrane containing both signaling molecules and cytoskeletal proteins. This complex mediates the transduction of extracellular signals and generates actin-mediated traction forces, both of which support axon outgrowth. The L1 cytoplasmic region binds ezrin, an adapter protein that interacts with the actin cytoskeleton. In this study, we analyzed L1-ezrin interactions in detail, assessed their role in generating traction forces by L1, and identified potential regulatory mechanisms controlling ezrin-L1 interactions. The FERM domain of ezrin binds to the juxtamembrane region of L1, demonstrated by yeast two-hybrid interaction traps and protein binding analyses in vitro. A lysine-to-leucine substitution in this domain of L1 (K1147L) shows reduced binding to the ezrin FERM domain. Additionally, in ND7 cells, the K1147L mutation inhibits retrograde movement of L1 on the cell surface that has been linked to the generation of the traction forces necessary for axon growth. A membrane-permeable peptide consisting of the juxtamembrane region of L1 that can disrupt endogenous L1-ezrin interactions inhibits neurite extension of cerebellar cells on L1 substrates. Moreover, the L1-ezrin interactions can be modulated by tyrosine phosphorylation of the L1 cytoplasmic region, namely, Y1151, possibly through Src-family kinases. Replacement of this tyrosine together with Y1176 with either aspartate or phenylalanine changes ezrin binding and alters colocalization with ezrin in ND7 cells. Collectively, these data suggest that L1-ezrin interactions mediated by the L1 juxtamembrane region are involved in traction-force generation and can be regulated by the phosphorylation of L1.

MAP kinase pathway-dependent phosphorylation of the L1-CAM ankyrin binding site regulates neuronal growth

The growth of neuronal processes depends critically on the function of adhesion proteins that link extracellular ligands to the cytoskeleton. The neuronal adhesion protein L1-CAM serves as a receptor for nerve growth-promoting proteins, a process that is inhibited by the interaction between L1-CAM and the cytoskeleton adaptor ankyrin. Using a novel reporter based on intramolecular bioluminescence resonance energy transfer, we have determined that the MAP kinase pathway regulates the phosphorylation of the FIGQY motif in the adhesion protein L1-CAM and its interaction with ankyrin B. MAP kinase pathway inhibitors block L1-CAM-mediated neuronal growth. However, this blockade is partially rescued by inhibitors of L1-CAM-ankyrin binding. These results demonstrate that the MAP kinase pathway regulates L1-CAM-mediated nerve growth by modulating ankyrin binding, suggesting that nerve growth can be regulated at the level of individual receptors.

Identification and characterization of murine alternatively spliced tissue factor

Tissue factor (TF) is a transmembrane glycoprotein that initiates coagulation and plays a critical role in regulating hemostasis and thrombosis. We have recently reported a naturally occurring, soluble form of human tissue factor (asTF) generated by alternative splicing. This splice variant has a novel C-terminus with no homology to that of the full-length TF (flTF), lacks a transmembrane domain, and is active in the presence of phospholipids. Mouse models offer unique opportunities to examine the relative importance of flTF and asTF in mediating thrombosis, the response to arterial injury, and ischemic damage. To that end, we have identified and characterized murine asTF (masTF). Like the human splice variant, masTF lacks a transmembrane domain and has a unique C-terminus. We have generated antibodies specific to masTF and murine flTF (mflTF) to examine the expression of both forms of TF. masTF antigen is widely and abundantly expressed, with a pattern similar to that of mflTF, in adult tissues, in experimentally induced thrombi, and during development. These studies demonstrate that masTF contributes to the pool of total TF and may thus play an important role in mediating TF-dependent processes.

MCP-1 deficiency is associated with reduced intimal hyperplasia after arterial injury

Monocyte chemoattractant protein (MCP)-1 is abundant in smooth muscle cells (SMC) and macrophages of atherosclerotic plaques and in the injured arterial wall. MCP-1 and its receptor, CCR2, are important mediators of macrophage accumulation and atherosclerotic plaque progression. We have recently reported that CCR2(-/-) mice have a approximately 60% decrease in intimal hyperplasia and medial DNA synthesis in response to femoral arterial injury. We have now examined the response to femoral arterial injury in MCP-1(-/-) mice. MCP-1 deficiency was associated with a approximately 30% reduction in intimal hyperplasia at 4 weeks and was not associated with diminished medial DNA synthesis. Despite inducing tissue factor in SMC culture, MCP-1 deficiency was not associated with a decrease in neointimal tissue factor after injury. These data suggest that MCP-1 and CCR2 deficiencies have distinct effects on arterial injury. The effects of MCP-1 on intimal hyperplasia may be mediated largely through SMC migration.