Safety and efficacy of tazemetostat, an enhancer of zeste-homolog 2 inhibitor, in patients with relapsed or refractory malignant mesothelioma

9058

Background: Breast cancer gene 1 (BRCA1)-associated protein 1 (BAP1), a nuclear deubiquitinase, is commonly inactivated in malignant mesothelioma. Preclinical data showed that BAP1 inactivation sensitizes mesothelial cells to inhibition of enhancer of zeste-homolog 2 (EZH2), a methyltransferase implicated as an oncogenic driver in this tumor. This study evaluated the safety and efficacy of tazemetostat (TAZ), a potent and selective EZH2 inhibitor, in relapsed/refractory (R/R) malignant mesothelioma with BAP1-inactivation. Methods: EZH-203 (NCT02860286) was a 2-part, open-label, phase 2 study that assessed the pharmacokinetics (PK), safety, and efficacy of TAZ in pts with R/R malignant mesothelioma. In part 1, pts received TAZ 800 mg QD on day 1 (D1) and 800 mg BID, beginning day 2 of cycle 1 (C1). In part 2, pts received 800 mg of TAZ BID on D1 of C1. A two-stage Green-Dahlberg design was used for part 2. Primary endpoints were PK profiling of TAZ in all pts (part 1), and disease control rate (DCR) at week 12 in pts with BAP1-deficient R/R malignant mesothelioma (part 2). Secondary endpoints included safety, overall response rate (ORR), progression-free survival, overall survival, and duration of response (DOR). Results: The study enrolled 74 pts with R/R malignant mesothelioma, 70 pts (95%) were centrally confirmed to be BAP1-deficient. Median prior lines of therapy were 2 (range, 1-9). Observed clinical data in the presence of CYP3A4 inhibitors and inducers suggest a low DDI potential of TAZ. The 12 week DCR was 47% (n = 35). The ORR per RECIST version 1.1 was 3% [complete response: 0%; partial response (PR): 3% (n = 2)]. Of the 2 patients with PR, 1 had a DOR of 21 weeks and the other is ongoing (15.3 weeks at data cut off). 47 pts (64%) and 21 pts (28%) had stable disease (SD) and progressive disease, respectively. Overall, 91% pts discontinued, either due to disease progression (n = 65), death (n = 5), or treatment discontinuation (n = 1). Grade ≥3 treatment-emergent adverse events (TEAEs) occurred in ≤5% of patients, most commonly anemia (5%) and dyspnea (4%). No pts discontinued due to TEAEs. There were no treatment related deaths. Conclusions: Based on disease control rate and stable disease, TAZ showed antitumor activity in pts with BAP1-deficient R/R malignant mesothelioma. TAZ monotherapy was generally well-tolerated. The current data support further clinical evaluation of TAZ in these pts. Furthermore, this trial presents an optimal paradigm for drug development in molecularly-enriched cohorts in mesothelioma. Clinical trial information: NCT02860286.

Phase 1 dose-expansion study of pegylated arginine deiminase, cisplatin, and pemetrexed in patients with argininosuccinate synthetase 1 (ASS1)–deficient non-squamous non-small cell lung cancer

9097

Background: Pegylated arginine deiminase (ADI-PEG20) targets ASS1-ve tumors, including non–small-cell lung cancer (NSCLC), by potentiating pemetrexed cytotoxicity via arginine depletion. In Beddowes et al (JCO 2017) we showed a 100% disease control rate in thoracic cancers treated with ADI-PEG20, cisplatin and pemetrexed (ADIPemCis). Thus, we tested ADIPemCis in a phase I dose-expansion cohort study of patients (pts) with non-squamous NSCLC. Methods: Good performance (ECOG 0-1) advanced non-squamous NSCLC pts were enrolled at the maximum tolerated dose (MTD) of ADIPemCis, using tumoral ASS1 loss as a selection biomarker. Pem (500mg/m2) and Cis (75mg/m2) were given every 3 weeks with weekly IM ADI-PEG20 (36mg/m2) for up to 4 cycles with maintenance ADI-PEG20 or Pem in responding pts. Primary endpoint was tumor response rate (RR by RECIST 1.1), with secondary endpoints including progression-free survival (PFS), overall survival (OS), and toxicity. We also measured plasma [arginine] and [citrulline], anti-ADI-PEG20 antibodies, and PD-L1 expression. Results: 21 of 70 screened pts (median age 60.1) were enrolled between April 15 and August 17. A confirmed partial response (PR) was observed in 55.6 % (n = 10/18 evaluable pts). Median PFS and OS were 4 months (95% CI 2.9-4.8) and 7.2 months (95% CI 5.1-18.4), respectively. 9% (n = 2/21) remain alive on subsequent therapies. 43% (n = 9/21) experienced grade 3/4 treatment-related toxicities, commonly non-febrile neutropenia. Plasma [arginine] declined rapidly and [citrulline] increased; both changes persisted at 16 weeks. 55% of pts’ tumors (n = 6/11 ) were PD-L1 < 1% by immunohistochemistry. Conclusions: The ADIPemCis regimen is active and safe in ASS1-ve NSCLC pts almost doubling the expected RR. However, the short survival compared with ASS1-agnostic historical controls indicates that ASS1 (and frequent PD-L1) loss selects for a biologically more aggressive and immunorefractory NSCLC phenotype. The iTRAP study opening Q2 of 2019 will assess the safety and tolerability of ADIPemPlatinum(Carbo) with atezolizumab in pts with ASS1-deficient non-squamous NSCLC. Clinical trial information: NCT02029690.

Expansion study of ADI-PEG 20, pemetrexed and cisplatin in patients with ASS1-deficient malignant pleural mesothelioma (TRAP)

8553

Background: Argininosuccinate synthetase 1 (ASS1)-deficient malignant pleural mesothelioma (MPM) cells are sensitive to arginine deprivation with pegylated arginine deiminase (ADI-PEG20), which also potentiates the cytotoxic effect of pemetrexed (PEM). In the phase I dose-escalation TRAP study (NCT02029690) we showed that ADI-PEG20 with first-line PEM and cisplatin (CIS) chemotherapy (ADIPEMCIS) produced a 100% disease control rate (DCR) in patients (pts; n = 9) with ASS1-deficient thoracic cancers, with no additional toxicity (Beddowes et al 2017). Here, we present the TRAP expansion cohort experience in MPM. Methods: Good performance (ECOG 0-1) MPM pts with non-resectable disease and measurable by modified RECIST, were enrolled in a phase I TRAP expansion cohort at the maximum tolerated dose (MTD) of ADIPEMCIS, using tumoral ASS1 loss as a selection biomarker. PEM (500mg/m2) and CIS (75mg/m2) were given every 3 weeks with weekly IM ADI-PEG20 (36mg/m2) for a maximum of 6 cycles with maintenance ADI-PEG20 in responding pts. Primary endpoint was tumor response rate (modified RECIST), with secondary endpoints including progression-free survival (PFS), overall survival (OS), and toxicity. We measured plasma arginine and citrulline concentrations, ADI-PEG20 antibodies, and biopsied patients on progression to explore resistance mechanisms. Results: 31 ASS1-deficient MPM pts (median age 67) were enrolled (11 epithelioid, 10 biphasic and 10 sarcomatoid) out of 92 screened pts. Plasma arginine decreased with a reciprocal increase in plasma citrulline. The partial response rate was 35.5% (95% CI 19.2%-54.6%) with a DCR of 93.5% (95% CI 78.6%-99.2%). Median PFS was 5.6 months (95% CI 4-6) and median OS was 10.1 months (95% CI 6.7-17.7). 10/31 pts (32.3%) experienced grade 3/4 treatment-related toxicities, the most common being neutropenia (16.1%). Upregulation of ASS1 expression was observed in 2/3 biopsies on progression. Conclusions: The ADIPEMCIS regimen is active in ASS1-deficient MPM pts, including non-epithelioid disease. Based on these data the ATOMIC-meso phase 2/3 trial has opened comparing ADIPEMCIS versus PEMCISPlacebo, focusing on pts with non-epithelioid MPM. Clinical trial information: NCT02029690.

ATOMIC-Meso: A randomized phase 2/3 trial of ADI-PEG20 or placebo with pemetrexed and cisplatin in patients with argininosuccinate synthetase 1-deficient non-epithelioid mesothelioma

TPS8582

Background: Argininosuccinate synthetase 1 (ASS1)-deficient malignant pleural mesothelioma (MPM) is sensitive to arginine deprivation therapy with pegylated arginine deiminase (ADI-PEG20), which also enhances the cytotoxicity of pemetrexed. The TRAP Phase 1 trial (NCT02029690) of ADI-PEG 20 combined with 1st-line pemetrexed (PEM) and cisplatin (CDDP) chemotherapy revealed a 94% disease control rate in non-epithelioid (biphasic and sarcomatoid) MPM subtypes characterized by a 75% rate of ASS1 loss. Thus, we plan to assess the efficacy of ADI-PEG20 or placebo combined with PEM and CDDP in patients (pts) with poor prognosis MPM in a randomized, placebo-controlled, double-blind phase 2/3 global trial. Methods: Up to 386 good performance (ECOG 0-1) pts with non-epithelioid malignant pleural mesothelioma will be enrolled in a phase 2/3 adaptive, biomarker-driven study design. Biopsies will be required prior to randomization: ASS1-agnostic pts will be enrolled initially (phase 2 stage) with an option to restrict enrolment to ASS1-deficient MPM (phase 3 stage). Pts will be randomized to receive weekly ADI-PEG20 (36 mg/m2 IM) or placebo with standard doses of PEM and CDDP for a maximum of 18 weeks (6 cycles) of treatment. Pts who develop CDDP toxicity may be switched to carboplatin. Pts will be assessed every 6 weeks using modified RECIST (RECIST 1.1 allowed for pts with significant extrathoracic disease). The primary endpoint for the phase 2 stage will be overall response rate (ORR) with secondary endpoints of overall survival (OS), safety and toxicity. The phase 2 will test ORR proportions with the placebo triplet set at 15% vs. 35% for the ADI-PEG 20 triplet, with a 1:1 randomization, 80% power. After recruitment of 176 pts, the phase 2 will convert to a phase 3 study with the primary endpoint of OS. In summary, ATOMIC-Meso is the first triplet chemotherapy study to assess the role of targeted arginine deprivation in aggressive subtypes of mesothelioma. Pt accrual has commenced across the US and Asia, with enrolment due in Europe and Australia by 2nd quarter of 2017. [Trial sponsored by Polaris Group]. Clinical trial information: NCT02709512.

Epigenetic inactivation to target the arginine biosynthetic pathway in multiple myeloma

e18567

Background: Argininoosuccinate synthetase-1 (ASS1) catalyses the rate-limiting step in arginine biosynthesis, the conversion of citruline to arginine. Argininosuccinate lyase (ASL) is an enzyme that catalyses the reversible breakdown of arginosuccinate producing arginine and fumerate. Arginine deprivation using arginine deiminase (ADI-PEG20) is currently considered as a novel therapeutic intervention for cancer. In this perspective, we investigated the methylation status of the ASS1 and ASL CpG islands in multiple myeloma (MM) and analyzed for clinical relevance. Methods: Genomic DNA was extracted from bone marrow aspirate samples from 46 MM patients (28 male, 18 female, median age 64 years) obtained at diagnosis. Methylation-specific PCR was employed to study the methylation in the ASS1 and ASL CpG islands. DNA was isolated and bisulphite modified using commercially available kits. Logistic regression analyses were used to measure the association between gene methylation and sex, age>65, ISS stage, presence of extramedullary disease, renal failure and bone disease. Kaplan-Meier curves were used to estimate the probabilities of survival and the Log-rank test to assess the statistical significance of differences in event rates. Results: Methylation in the CpG island of ASS1 was detected in 71.7% patients and of ASL in 37% patients, while simultaneous methylation in both genes was present in 10 patients. None of the two genes was detectably methylated in the control group. Patients with ASS1 methylation were less likely to have bone disease (p=0.04, OR=0.22) and extramedullary disease (p=0.05, OR=0.22) and a trend was also noted that these patients were less likely to be >65 years of age (p=0.2, OR=0.37). We did not detect any statistically significant difference in overall survival by methylation status of the studied genes in this small study size. Conclusions: We demonstrate for the first time that arginine biosynthesis genes ASS1 and ASL are methylated in MM.Methylation of ASS1 was found to be more frequent and negatively associated with bone or extramedullary disease. Further evaluation of ASS1 and ASL is warranted in MM and supports the expansion of arginine deprivation trials in these patients

Potential applications of gene therapy in the patient with cancer

The elderly population has much to gain from the advances of molecular medicine, although at present genetic pharmacology remains mostly at the conceptual level. Cancer, in particular, is an increasing health burden and the majority (over 70%) of gene therapy trials are aimed at tackling this problem. Available strategies employ both viral and synthetic vectors with the selective delivery and expression of therapeutic genes a pivotal requirement. Clinical trials are now in progress with a view to modulating disease at many different levels, including the direct replacement of abnormal genes. suicide-gene formulations, and the delivery of 'gain of function' genes, which seek to alter the malignant phenotype by indirect means, such as, immunopotentiation and stromal reorganisation. Early data from these studies is tantalising and we must remain optimistic that gene therapy will benefit the patient with cancer by both reducing morbidity and extending life.

Effective treatment of a patient with a high-grade endometrial stromal sarcoma with an accelerated regimen of carboplatin and paclitaxel

The rarity of endometrial stromal sarcoma (ESS) and its poor response to treatment provides fertile ground for investigational therapies. An accelerated regimen of carboplatin and paclitaxel is investigated. A patient with a recent history of treated tuberculosis of the lung represented with infertility and acute abdominal pain from suspected fibroids, and underwent a laparotomy with a diagnosis of a high-grade ESS. A novel therapeutic approach using a regimen of carboplatin and paclitaxel with the reinfusion of filgrastim-mobilized peripheral blood progenitor cells is described. A partial response was observed following six cycles of chemotherapy. Grade IV thrombocytopenia occurred after the last cycle, with recovery prior to pelvic radiotherapy. The patient remained well 1 year post-diagnosis. High-grade ESS is responsive to combination chemotherapy with paclitaxel and carboplatin, and requires further evaluation. The use of an accelerated regimen may also have contributed to the response and this question awaits randomized trials.