Amivantamab plus lazertinib in osimertinib-relapsed EGFR-mutant advanced non-small cell lung cancer: a phase 1 trial

Patients with epidermal growth factor receptor (EGFR)-mutated non-small cell lung cancer (NSCLC) often develop resistance to current standard third-generation EGFR tyrosine kinase inhibitors (TKIs); no targeted treatments are approved in the osimertinib-relapsed setting. In this open-label, dose-escalation and dose-expansion phase 1 trial, the potential for improved anti-tumor activity by combining amivantamab, an EGFR-MET bispecific antibody, with lazertinib, a third-generation EGFR TKI, was evaluated in patients with EGFR-mutant NSCLC whose disease progressed on third-generation TKI monotherapy but were chemotherapy naive (CHRYSALIS cohort E). In the dose-escalation phase, the recommended phase 2 combination dose was established; in the dose-expansion phase, the primary endpoints were safety and overall response rate, and key secondary endpoints included progression-free survival and overall survival. The safety profile of amivantamab and lazertinib was generally consistent with previous experience of each agent alone, with 4% experiencing grade ≥3 events; no new safety signals were identified. In an exploratory cohort of 45 patients who were enrolled without biomarker selection, the primary endpoint of investigator-assessed overall response rate was 36% (95% confidence interval, 22-51). The median duration of response was 9.6 months, and the median progression-free survival was 4.9 months. Next-generation sequencing and immunohistochemistry analyses identified high EGFR and/or MET expression as potential predictive biomarkers of response, which will need to be validated with prospective assessment. ClinicalTrials.gov identifier: NCT02609776 .

Management of infusion-related reactions (IRRs) in patients receiving amivantamab in the CHRYSALIS study

BACKGROUND

Amivantamab, a fully humanized EGFR-MET bispecific antibody, has antitumor activity in diverse EGFR- and MET-driven non-small cell lung cancer (NSCLC) and a safety profile consistent with associated on-target activities. Infusion-related reaction(s) (IRR[s]) are reported commonly with amivantamab. We review IRR and subsequent management in amivantamab-treated patients.

METHODS

Patients treated with the approved dose of intravenous amivantamab (1050 mg, <80 kg; 1400 mg, ≥80 kg) in CHRYSALIS-an ongoing, phase 1 study in advanced EGFR-mutated NSCLC-were included in this analysis. IRR mitigations included split first dose (350 mg, day 1 [D1]; remainder, D2), reduced initial infusion rates with proactive infusion interruption, and steroid premedication before initial dose. For all doses, pre-infusion antihistamines and antipyretics were required. Steroids were optional after the initial dose.

RESULTS

As of 3/30/2021, 380 patients received amivantamab. IRRs were reported in 256 (67%) patients. Signs/symptoms of IRR included chills, dyspnea, flushing, nausea, chest discomfort, and vomiting. Most of the 279 IRRs were grade 1 or 2; grade 3 and 4 IRR occurred in 7 and 1 patients, respectively. Most (90%) IRRs occurred on cycle 1, D1 (C1D1); median time-to-first-IRR onset during C1D1 was 60 min; and first-infusion IRRs did not compromise subsequent infusions. Per protocol, IRR was mitigated on C1D1 with holding of infusion (56% [214/380]), reinitiating at reduced rate (53% [202/380]), and aborting infusion (14% [53/380]). C1D2 infusions were completed in 85% (45/53) of patients who had C1D1 infusions aborted. Four patients (1% [4/380]) discontinued treatment due to IRR. In studies aimed at elucidating the underlying mechanism(s) of IRR, no pattern was observed between patients with versus without IRR.

CONCLUSION

IRRs with amivantamab were predominantly low grade and limited to first infusion, and rarely occurred with subsequent dosing. Close monitoring for IRR with the initial amivantamab dose and early intervention at first IRR signs/symptoms should be part of routine amivantamab administration.

Amivantamab in patients with NSCLC with MET exon 14 skipping mutation: Updated results from the CHRYSALIS study

9008

Background: Amivantamab, a fully human bispecific antibody targeting epidermal growth factor receptor (EGFR) and MET, is approved for the treatment of non-small cell lung cancer (NSCLC) with EGFR exon 20 insertion after prior platinum-based chemotherapy. Given its bispecific nature, amivantamab is being explored in patients (pts) with primary MET exon 14 skipping mutation (METex14) in the MET-2 cohort of the CHRYSALIS study. Methods: CHRYSALIS (NCT02609776) is an ongoing phase 1 dose escalation/dose expansion study of amivantamab in pts with advanced NSCLC. Pts with primary METex14 whose disease progressed on or who declined current standard of care therapy were treated with amivantamab 1050 mg (pts <80 kg) or 1400 mg (pts ≥80 kg) weekly in cycle 1 and biweekly thereafter. Response was assessed by investigators using RECIST v1.1. Results: As of 2 Dec 2021, 43 pts with METex14 had received amivantamab. Median age was 70 y (range, 43-88), 58% were women, median prior lines of therapy was 2 (range, 0-10) [eg, crizotinib (n=13), capmatinib (n=11), tepotinib (n=5), anti-MET antibody (n=1)], and 23% had history of brain metastases at baseline. In 36 pts with ≥1 postbaseline disease assessment, median duration of follow-up was 5.8 months (range, 0.3-15.8); 6 pts had no prior treatment, 11 had no prior MET inhibitor, and 19 had a prior MET inhibitor. Overall response rate was 33% (50% [3/6] in treatment-naïve pts, 46% [5/11] in pts with no prior MET inhibitor, and 21% [4/19] in pts with prior MET inhibitor therapy). Clinical benefit rate was >54% regardless of prior treatment (Table). Median duration of response (DOR) was not reached (range, 2.1-12.2 months); 67% (8/13) had DOR ≥6 months. Ten of the 12 responders remain on treatment (6.0-14.4 months) with ongoing responses; 2 discontinued after 2 and 12 months, respectively. Safety profile was consistent with previously reported experience of amivantamab (Sabari 2021 JTO 16(3):S108-109). Treatment-related adverse events leading to dose reduction or discontinuation occurred in 3 pts, each. Conclusions: Amivantamab demonstrates anti-tumor activity in primary METex14 NSCLC including after prior MET inhibitor treatment. Enrollment is ongoing and updated data will be shown. Clinical trial information: NCT02609776. [Table: see text]

Amivantamab in EGFR Exon 20 Insertion-Mutated Non-Small-Cell Lung Cancer Progressing on Platinum Chemotherapy: Initial Results From the CHRYSALIS Phase I Study

PURPOSE

Non–small-cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) exon 20 insertion (Exon20ins) mutations exhibits inherent resistance to approved tyrosine kinase inhibitors. Amivantamab, an EGFR-MET bispecific antibody with immune cell–directing activity, binds to each receptor's extracellular domain, bypassing resistance at the tyrosine kinase inhibitor binding site.

METHODS

CHRYSALIS is a phase I, open-label, dose-escalation, and dose-expansion study, which included a population with EGFR Exon20ins NSCLC. The primary end points were dose-limiting toxicity and overall response rate. We report findings from the postplatinum EGFR Exon20ins NSCLC population treated at the recommended phase II dose of 1,050 mg amivantamab (1,400 mg, ≥ 80 kg) given once weekly for the first 4 weeks and then once every 2 weeks starting at week 5.

RESULTS

In the efficacy population (n = 81), the median age was 62 years (range, 42-84 years); 40 patients (49%) were Asian, and the median number of previous lines of therapy was two (range, 1-7). The overall response rate was 40% (95% CI, 29 to 51), including three complete responses, with a median duration of response of 11.1 months (95% CI, 6.9 to not reached). The median progression-free survival was 8.3 months (95% CI, 6.5 to 10.9). In the safety population (n = 114), the most common adverse events were rash in 98 patients (86%), infusion-related reactions in 75 (66%), and paronychia in 51 (45%). The most common grade 3-4 adverse events were hypokalemia in six patients (5%) and rash, pulmonary embolism, diarrhea, and neutropenia in four (4%) each. Treatment-related dose reductions and discontinuations were reported in 13% and 4% of patients, respectively.

CONCLUSION

Amivantamab, via its novel mechanism of action, yielded robust and durable responses with tolerable safety in patients with EGFR Exon20ins mutations after progression on platinum-based chemotherapy.

Amivantamab in combination with lazertinib for the treatment of osimertinib-relapsed, chemotherapy-naïve EGFR mutant (EGFRm) non-small cell lung cancer (NSCLC) and potential biomarkers for response

9006

Background: Preliminary efficacy was observed with the combination of amivantamab, an EGFR-MET bispecific antibody, and lazertinib, a 3rd-generation tyrosine kinase inhibitor, in both treatment-naïve and osimertinib (osi)-relapsed patients (pts) with EGFRm NSCLC (Cho Ann Oncol 2020;31:S813). We present updated results of the combination in osi-relapsed pts, including an analysis of potential biomarkers of response. Methods: Pts with EGFR exon 19 deletion or L858R mutation NSCLC, who had progressed on osi without intervening chemotherapy, were enrolled in the combination cohort of the ongoing CHRYSALIS study (NCT02609776). With pre-treatment tumor biopsies and ctDNA collected prospectively, pts received the combination dose of 1050/1400 mg amivantamab + 240 mg lazertinib to assess safety and efficacy in the osi-relapsed population. Response was assessed by investigator per RECIST v1.1. Osi-resistance mutations or amplifications in EGFR/MET identified by next-generation sequencing (NGS) in either ctDNA or tumor biopsy (biomarker-positive [pos]), were evaluated for enriching response. Immunohistochemistry (IHC) staining for EGFR and MET expression was also explored as a potential biomarker for response. Results: Of the 45 osi-relapsed pts, 36% (95% CI, 22–51) had a confirmed response (1 complete response and 15 partial responses [PR]). At a median follow-up of 8.2 mo (1.0–11.8), 20/45 pts (44%) remain on treatment. With 11/16 pts (69%) continuing in response (2.6–9.6+ mo), median duration of response has not been reached (NR). The median progression-free survival (mPFS) was 4.9 mo (95% CI, 3.7–8.3). In total, 44/45 pts were evaluable by ctDNA and 29/45 by tumor NGS. Genetic testing identified 17 biomarker-pos pts, of whom 8 (47%) responded. Of the remaining 28 pts, 8 (29%) responded. Among these 28 pts, 18 had unknown mechanisms of osi-resistance (8 PR) and 10 had non-EGFR/MET mechanisms of resistance identified (none responded). The mPFS (95% CI) for biomarker-pos and remaining pts was 6.7 mo (3.4–NR) and 4.1 mo (1.4–9.5), respectively. Adequate tissue was available for 20 pts to perform IHC testing for EGFR and MET–9/10 (90%) IHC high (combined EGFR+MET H score>400) pts responded to treatment, while 1/10 IHC low pts responded to treatment. Conclusions: Treatment with the combination of amivantamab and lazertinib yielded responses in 36% of chemotherapy-naïve pts who progressed on osi. Among these pts, genetic EGFR and MET-based biomarkers of resistance identified a subgroup of pts more likely to respond to amivantamab and lazertinib, although additional pts lacking identified resistance markers also responded. An IHC-based approach may identify pts most likely to benefit from the combination regimen, but further investigation is warranted. Clinical trial information: NCT02609776.

Amivantamab (JNJ-61186372), an anti-EGFR-MET bispecific antibody, in patients with EGFR exon 20 insertion (exon20ins)-mutated non-small cell lung cancer (NSCLC)

9512

Background: EGFR exon20ins-mutated NSCLC is generally refractory to EGFR tyrosine kinase inhibitors (TKIs) and is associated with poor prognosis. Amivantamab (JNJ-61186372) is a novel, fully human anti-EGFR-MET bispecific antibody whose mechanism of action can target both EGFR- and MET-driven disease and has shown monotherapy activity in patients (pts) with diverse EGFR mutant disease characterized by EGFR C797S, T790M, exon20ins, and MET amplification. We present preliminary results of pts with advanced NSCLC harboring exon20ins mutations from CHRYSALIS, an ongoing phase 1 study of amivantamab (NCT02609776). Methods: This study comprises a dose escalation phase in pts with advanced NSCLC and a dose expansion phase in pts with EGFR- and MET-mutated disease. This analysis includes all enrolled pts with exon20ins disease who received the recommended phase 2 dose (RP2D) of 1050 mg (1400 mg, pts ≥80 kg) amivantamab. Response was assessed by investigator per RECIST v1.1. Results: As of 30 Oct 2019, 50 pts with exon20ins mutations had received amivantamab at the RP2D. 39/50 pts were response-evaluable and had ≥2 disease assessments or had discontinued therapy prior to the assessment period; among these pts, 29 had prior platinum-based chemotherapy (PBCT). Median age for response-evaluable pts was 61 y (40–78), 51% were female, and median prior lines was 1 (0–7). In the 50 pts harboring exon20ins mutations treated at the RP2D, the most common adverse events (AEs) reported were rash (72%), infusion related reaction (60%), and paronychia (34%). Additional EGFR-related AEs included stomatitis (16%), pruritus (14%), and diarrhea (6%). Grade ≥3 AEs were reported in 36% of pts; 6% were treatment-related. One grade 3 diarrhea and no grade ≥3 rash was reported. Among the 39 response-evaluable pts, with a median follow-up of 4 months (1–26), the overall response rate (≥partial response [PR]) was 36% (95% CI, 21–53), and 41% (95% CI, 24–61) for the 29 pts who had prior PBCT. The clinical benefit rate (≥PR or stable disease ≥11 weeks) was 67% for response-evaluable pts and 72% for pts who had prior PBCT. Among all 14 responders, median duration of response was 10 months (1–16), with ongoing responses in 9 pts at data cutoff. Median progression-free survival was 8.3 months (95% CI, 3.0–14.8) for response-evaluable pts and 8.6 months (95% CI, 3.7–14.8) for pts who had prior PBCT. Conclusions: Amivantamab demonstrates robust and durable antitumor activity in pts with exon20ins disease, with a manageable safety profile. Clinical trial information: NCT02609776 .

Antitumor Activity of Amivantamab (JNJ-61186372), an EGFR-MET Bispecific Antibody, in Diverse Models of EGFR Exon 20 Insertion-Driven NSCLC

EGFR exon 20 insertion driver mutations (Exon20ins) in non-small cell lung cancer (NSCLC) are insensitive to EGFR tyrosine kinase inhibitors (TKI). Amivantamab (JNJ-61186372), a bispecific antibody targeting EGFR-MET, has shown preclinical activity in TKI-sensitive EGFR-mutated NSCLC models and in an ongoing first-in-human study in patients with advanced NSCLC. However, the activity of amivantamab in Exon20ins-driven tumors has not yet been described. Ba/F3 cells and patient-derived cells/organoids/xenograft models harboring diverse Exon20ins were used to characterize the antitumor mechanism of amivantamab. Amivantamab inhibited proliferation by effectively downmodulating EGFR-MET levels and inducing immune-directed antitumor activity with increased IFNγ secretion in various models. Importantly, in vivo efficacy of amivantamab was superior to cetuximab or poziotinib, an experimental Exon20ins-targeted TKI. Amivantamab produced robust tumor responses in two Exon20ins patients, highlighting the important translational nature of this preclinical work. These findings provide mechanistic insight into the activity of amivantamab and support its continued clinical development in Exon20ins patients, an area of high unmet medical need. SIGNIFICANCE: Currently, there are no approved targeted therapies for EGFR Exon20ins-driven NSCLC. Preclinical data shown here, together with promising clinical activity in an ongoing phase I study, strongly support further clinical investigation of amivantamab in EGFR Exon20ins-driven NSCLC.This article is highlighted in the In This Issue feature, p. 1079.

Decreased nuclear factor-kappaB DNA binding activity following permanent focal cerebral ischaemia in the rat

Many factors implicated in the pathogenesis of cerebral ischaemia such as glutamate, tumour necrosis factor and interleukin-1 have also been shown to activate nuclear factor-kappaB (NF-kappaB). In the present study we have investigated NF-kappaB activity at various times following permanent focal cerebral ischaemia in rats using immunohistochemistry, western blotting and electrophoretic mobility shift assay (EMSA). Three hours following middle cerebral artery occlusion nuclear translocation of NF-kappaB was detected using immunohistochemical and western blotting techniques. This was reflected in a trend towards increased NF-kappaB binding activity (EMSA) in the ischaemic cortex compared to histologically normal tissue. In contrast however, from 6 to 48 h post-occlusion nuclear translocation and NF-kappaB binding activity was decreased in the ischaemic cortex. Decreased NF-kappaB binding activity detected in degenerating neurones, suggests that decreased NF-kappaB activity may exacerbate ischaemia induced neuronal cell death.

Respective roles of the 14 kDa and 85 kDa phospholipase A2 enzymes in human monocyte eicosanoid formation

Human monocytes possess both the cytosolic 85 kDa phospholipase (PLA) A2 and a 14 kDa PLA2 and are capable of simultaneously producing prostanoids (PG), leukotrienes (LT) and platelet activating factor (PAF). As the exact roles of the two enzymes in monocyte lipid mediator formation was unclear, both selective PLA2 inhibitors and antisense were used to elucidate their respective roles. Reduction in 85 kDa PLA2 cellular protein levels by initiation site-directed antisense (SK 7111) or exposure to the 85 kDa PLA2 inhibitor, arachidonyl trifluormethyl ketone (AACOCF3), prevented A23187 or zymosan-stimulated monocytes prostanoid formation but not LTC4 or PAF production. This confirmed the important role of the 85 kDa PLA2 in prostanoid formation but indicated a less significant role in LT or PAF biosynthesis. Alternatively, treatment of monocytes with the selective, active-site-directed 14 kDa PLA2 inhibitor, SB 203347, totally inhibited LT and PAF formation, while prostanoid formation was not altered. Addition of 20 uM exogenous arachidonic acid (AA) to monocytes exposed to SB 203347 did not alter A23187-induced LTC4 generation, indicating that SB 203347 had no effect on downstream AA metabolizing enzymes in this setting. Taken together, these results provide evidence that the 14 kDa PLA2 provides substrate for monocyte LT and PAF formation, while the 85 kDa PLA2 plays a more significant role in the formation of PG.

An indolocarbazole inhibitor of human checkpoint kinase (Chk1) abrogates cell cycle arrest caused by DNA damage

Many cancer therapies cause DNA damage to effectively kill proliferating tumor cells; however, a major limitation of current therapies is the emergence of resistant tumors following initial treatment. Cell cycle checkpoints are involved in the response to DNA damage and specifically prevent cell cycle progression to allow DNA repair. Tumor cells can take advantage of the G2 checkpoint to arrest following DNA damage and avoid immediate cell death. This can contribute to acquisition of drug resistance. By abrogating the G2 checkpoint arrest, it may be possible to synergistically augment tumor cell death induced by DNA damage and circumvent resistance. This requires an understanding of the molecules involved in regulating the checkpoints. Human Chk1 is a recently identified homologue of the Schizosaccharomyces pombe checkpoint kinase gene, which is required for G2 arrest in response to DNA damage. Chk1 phosphorylates the dual specificity phosphatase cdc25C on Ser-216, and this may be involved in preventing cdc25 from activating cdc2/cyclinB and initiating mitosis. To further study the role of Chk1 in G2 checkpoint control, we identified a potent and selective indolocarbazole inhibitor (SB-218078) of Chk1 kinase activity and used this compound to assess cell cycle checkpoint responses. Limited DNA damage induced by gamma-irradiation or the topoisomerase I inhibitor topotecan was used to induce G2 arrest in HeLa cells. In the presence of the Chk1 inhibitor, the cells did not arrest following gamma-irradiation or treatment with topotecan, but continued into mitosis. Abrogation of the damage-arrest checkpoint also enhanced the cytotoxicity of topoisomerase I inhibitors. These studies suggest that Chk1 activity is required for G2 arrest following DNA damage.

Cytosolic 85-kDa phospholipase A2-mediated release of arachidonic acid is critical for proliferation of vascular smooth muscle cells

Recent evidence suggests that arachidonic acid (AA) may be involved in regulating cellular proliferation. The predominant mechanism of AA release from cellular phospholipids is via phospholipase A2 (PLA2) hydrolysis. The purpose of this study was to examine the roles of the distinct 14-kDa and 85-kDa PLA2 enzymes in human coronary artery vascular smooth muscle cell (hCAVSMC) proliferation. Cultured hCAVSMCs proliferate in the presence of growth medium with a typical doubling time of 30-40 h, grow at a slower proliferative rate upon reaching confluency (day 8), and eventually undergo contact inhibition of growth (day 10). Neither Type II 14-kDa PLA2 activity nor mass changed over a 10-day culture period. In contrast, 85-kDa PLA2 protein activity and mRNA decreased as time in culture progressed. This reduction in 85-kDa PLA2 correlated with reductions in DNA synthesis and suggested a possible association between 85-kDa PLA2 and proliferation. To directly evaluate the role of the 85-kDa PLA2 in proliferation we examined the effects of an 85-kDa PLA2 inhibitor (AACOCF3) and 85-kDa PLA2 antisense oligonucleotides on proliferation. Both reagents dose dependently inhibited proliferation, whereas a 14-kDa PLA2 inhibitor (SB203347), a calcium-independent PLA2 inhibitor (HELSS), an 85-kDa sense oligonucleotide, and a nonrelevant scrambled control oligonucleotide had no effect. The mechanism by which 85-kDa PLA2 influences cellular proliferation remains unclear. Inhibition of 85-kDa PLA2 activity produced neither phase-specific cell cycle arrest nor apoptosis (fluorescence-activated cell sorter analysis). Addition of AA (20 mu M) attenuated the effects of both AACOCF3 and 85-kDa antisense oligonucleotides implicating AA as a key mediator in cellular proliferation. However, although prostaglandin E2 (PGE2) was present in the culture medium, it peaked early (day 3) in culture, and indomethacin had no effect on cellular proliferation indicating that hCAVSMC proliferation was not mediated through PGE2. These data provide the first direct evidence that PLA2 is involved in control of VSMC proliferation and indicate that 85-kDa PLA2-mediated liberation of AA is critical for cellular proliferation.

Inhibition of NFkappaB-mediated interleukin-1beta-stimulated prostaglandin E2 formation by the marine natural product hymenialdisine

Exposure of human rheumatoid synovial fibroblasts (RSF) to interleukin 1beta (IL-1beta) results in the coordinate up-regulation of 85-kDa phospholipase A2 (PLA2) and mitogen-inducible cyclooxygenase (COX II) and subsequent biosynthesis of prostaglandin E2 (PGE2). We have recently demonstrated, through the use of oligonucleotide decoys and antisense, the participation of the proinflammatory transcription factor, nuclear factor kappaB (NFkappaB), in the regulation of the prostanoid-metabolizing enzymes. Hymenialdisine, a marine natural product has recently been characterized as an inhibitor of NFkappaB activation and exposure of IL-1-stimulated RSF-inhibited PGE2 production in a concentration-dependent manner (IC50 approximately 1 microM). Alternatively, both an analog, aldisine, and the protein kinase C inhibitor, RO 32-0432, were without affect. Direct action of hymenialdisine on IL-1-induced NFkappaB activation was demonstrated by a significant reduction (approximately 80%) in NFkappaB binding to the classical kappaB consensus motif (as assessed by electrophoretic mobility shift assay) and inhibition of stimulated p65 migration from the cytosol of treated cells (as assessed by Western analysis). Consistent with the role of NFkappaB in the transcriptional regulation of COX II and 85-kDa PLA2, hymenialdisine-treated RSF did not transcribe the respective mRNAs in response to IL-1. This led to reductions in their respective protein levels and subsequent reductions in the ability to produce PGE2. Specificity of action is suggested as IL-1-stimulated interleukin-8 (IL-8) production, which is known to be an NFkappaB-regulated event, was also inhibited by hymenialdisine, whereas IL-1-induced production of vascular endothelial growth factor, a non-NFkappaB-regulated gene, was not affected by exposure to hymenialdisine. Taken together, hymenialdisine inhibits IL-1-stimulated-RSF PGE2 formation acting predominately through modulation of NFkappaB activation and offers an interesting novel tool to evaluate the role of NFkappaB in inflammatory disease.

Depletion of human monocyte 85-kDa phospholipase A2 does not alter leukotriene formation

Human monocytes possess several acylhydrolase activities and are capable of producing both prostanoids (PG) and leukotriene (LT) products upon acute stimulation with calcium ionophore, A23187 or phagocytosis of zymosan particles. The cytosolic 85-kDa phospholipase (PLA) A2 co-exists with the 14-kDa PLA2 in the human monocyte, but their respective roles in LT production are not well understood. Reduction in 85-kDa PLA2 cellular protein levels by initiation site-directed antisense (SK 7111) or exposure to the 85-kDa PLA2 inhibitor, arachidonyl trifluoromethyl ketone (AACOCF3), prevented A23187 or zymosan-stimulated monocyte prostanoid formation. In contrast, neither treatment altered stimulated LTC4 production. This confirmed the important role of the 85-kDa PLA2 in prostanoid formation but suggests that it has less of a role in LT biosynthesis. Alternatively, treatment of monocytes with the selective, active site-directed 14-kDa PLA2 inhibitor, SB 203347, prior to stimulation had no effect on prostanoid formation at concentrations that totally inhibited LT formation. Addition of 20 microM exogenous arachidonic acid to monocytes exposed to SK 7111 or SB 203347 did not alter A23187-induced PGE2 or LTC4 generation, respectively, indicating that these agents had no effect on downstream arachidonic acid-metabolizing enzymes in this setting. Taken together, these results provide evidence that the 85-kDa PLA2 may play a more significant role in the formation of PG than LT. Further, utilization of SB 203347 provides intriguing data to form the hypothesis that a non-85-kDa PLA2 sn-2 acyl hydrolase, possibly the 14-kDa PLA2, may provide substrate for LT formation.

Suppression of human synovial fibroblast 85 kDa phospholipase A2 by antisense reduces interleukin-1 beta induced prostaglandin E2

OBJECTIVE

To evaluate the relative roles of rheumatoid synovial fibroblast phospholipases A2 (PLA2) in interleukin- 1beta (IL-1 beta) stimulated prostaglandin E2 (PGE2) production.

METHODS

The role of the cytosolic 85 kDa PLA2 in IL-1beta induced human rheumatoid synovial fibroblast PGE2 formation was directly evaluated using an antisense phosphorothioate oligonucleotide to the initiation site of the 85 kDa PLA2 mRNA. Contribution of the 14 kDa PLA2 was assessed using selective inhibitors or a neutralizing monoclonal antibody (Mab).

RESULTS

Antisense, but not sense, decreased IL-1beta upregulation of 85 kDa PLA2 activity and protein levels. The antisense effect was specific, since it did not affect 14 kDa PLA2 activity released into the media or induced cyclooxygenase II protein levels over 24 h. Antisense, but not sense, reduced PGE2 formation in a concentration dependent manner. IL-1 beta significantly upregulated cell associated 14 kDa PLA2 and its subsequent release. Specific inhibition of this enzyme by a neutralizing Mab or selective inhibitors of 14 kDA PLA2 activity did not alter IL-1beta induced PGE2 levels.

CONCLUSION

These data directly support a role for the 85 kDa PLA2, but not the 14 kDa PLA2, in IL- 1beta stimulated PGE2 production from human rheumatoid synovial fibroblast.

SB 203347, an inhibitor of 14 kDa phospholipase A2, alters human neutrophil arachidonic acid release and metabolism and prolongs survival in murine endotoxin shock

Phospholipase A2 (PLA2) catalyzes the hydrolysis of the sn-2 fatty acyl group [predominantly arachidonic acid (AA)] of membrane phospholipids, the products of which are further metabolized, forming a variety of eicosanoids and/or platelet-activating factor. PLA2 activity is significantly enhanced during inflammation and therefore offers an intriguing target in designing anti-inflammatory drugs. SB 203347 (2-[2-[3,5-bis (trifluoromethyl) sulfonamido]-4- trifluoromethylphenoxy] benzoic acid) potently inhibits rh type II 14 kDa PLA2 (IC50 = 0.5 microM) but exhibits a 40-fold weaker inhibition of 85 kDa PLA2 (IC50 = 20 microM) using [3H]-AA E. coli as substrate. A specific interaction with rh type II 14 kDa PLA2 was confirmed both by observing the pH dependence of its IC50 and by demonstrating linear inhibition in a "scooting" kinetic model using radiolabeled phospholipid reporter substrate in a 1,2-dimyristoyl phosphatidylmethanol vesicle. Before evaluating the effect of SB 203347 on AA metabolism in intact human neutrophil, we showed that it fully inhibits PLA2 activity in acid extracted-intact human neutrophil homogenate (IC50 = 4.7 microM). SB 203347 inhibited A23187-induced intact human neutrophil AA mass release in a concentration-dependent manner (IC50 = 1 microM), which coincided with reductions in the biosynthesis of platelet-activating factor (IC50 = 1.5 microM) and leukotriene B4 (IC50 = 2.3 microM). Finally, SB 203347 prolonged survival in a mouse model of endotoxin shock delivered i.p. Taken together, the data support a role of cellular 14 kDa PLA2 in the formation of AA-derived proinflammatory lipid mediator.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of monocyte 85-kDa phospholipase A2 by antisense and effects on endotoxin-induced prostaglandin biosynthesis

Studies were conducted to characterize a human monocyte model where the role of the 85-kDa phospholipase A2 (PLA2) in prostanoid formation could be evaluated. The presence of an immunologically related 85-kDa PLA2 and type II 14-kDa PLA2 was demonstrated in human monocytes and their roles examined in lipopolysaccharide (LPS)-induced monocyte prostaglandin E2 (PGE2) formation. Exposure of human monocytes to LPS over 18 h resulted in the up-regulation of the mitogen-inducible cyclooxygenase-2 and was accompanied by production and release of prostaglandin E2 but not leukotriene C4. This coincided with a 2-fold increase in the 85-kDa PLA2 protein and activity levels. In contrast, there was no effect on the type II 14-kDa-like PLA2 activity measured in the 100,000 x g particulate fraction nor did LPS induce the release of type II 14-kDa PLA2 into the medium. Treatment with cycloheximide over 18 h resulted in a time-dependent decrease in cytosolic 85-kDa PLA2 protein and activity (half-life = 4 h), but there was no change in the particulate type II 14-kDa-like PLA2 activity. Monocytes were therefore exposed to an 85-kDa PLA2 initiation site-directed antisense oligonucleotide which specifically decreased the cytosolic 85-kDa PLA2 protein levels and activity in a concentration-dependent manner. This had no effect on the cyclooxygenase-2 (protein mass or the ability to convert arachidonic acid to PGE2) or the particulate fraction sn-2 acylhydrolytic activity but was associated with a decrease in LPS-induced PGE2 production. Taken together, these data support a role for the cytosolic 85-kDa PLA2 in LPS-induced monocyte PGE2 formation.

Characterization of phospholipase A2 release by elicited-peritoneal macrophage and its relationship to eicosanoid production

Elicited guinea pig peritoneal macrophages released a soluble phospholipase A2 (PLA2) into conditioned media that was biochemically and pharmacologically similar to the recombinant human (rh) type II 14 kDa PLA2. The level of activity found in the 24 h media positively correlated with cell number and was reduced by actinomycin D and cycloheximide suggesting the enzyme was being constitutively synthesized. The enzyme protein accumulated in the media over 10-24 h and remained at maximal levels over 40 h as demonstrated by both activity and ELISA measurements. This was preceded by an increase in total cell-associated sn-2-acylhydrolytic activity which reached maximal levels by 12-17 h of culture and remained elevated to 40 h. Treatment of cell homogenate with dithiothreitol (DTT) revealed a rise in DTT-insensitive sn-2-acylhydrolytic activity which increased between 12 and 24 h. Prostaglandin (PG) E2 but not leukotriene (LT)B4 accumulated in the media and reached maximal levels by 24 h. This paralleled the release of secreted type II 14 kDa-like PLA2 and the rise in DTT-insensitive cell-associated activity, but not upregulation and formation of new cyclooxygenase after aspirin treatment. Overnight exposure to a non-cell permeable selective 14 kDa PLA2 inhibitor or neutralizing mAb interfered with expression of PLA2 activity but not PGE2 accumulation over 24 h. This indicated that the secreted PLA2 was not directly involved in PGE2 biosynthesis. Exposure of the elicited macrophages to the cell permeable 14 kDa PLA2 inhibitor, 12-epi-scalaradial also did not effect PGE2 accumulation. Taken together, elicited guinea-pig macrophages release 14 kDa PLA2 upon culture, but this activity appears not to be related to the concomitant accumulation in PGE2. The role of the cell-associated PLA2 activity(s) in PGE2 formation cannot be ruled out.

Characterization of phospholipase A2 from human nasal lavage

A secreted form of phospholipase A2 (PLA2) has been implicated in inflammatory disorders such as rheumatoid arthritis and sepsis. To determine if PLA2 may also play a role in allergic rhinitis, we have measured enzymic activity in nasal lavage from allergic subjects. Enhanced activity of PLA2 in the lavage was observed following nasal challenge with antigen or histamine. The PLA2 in the nasal lavage was partially purified by acid extraction, size exclusion chromatography, and ion exchange chromatography. The partially purified enzyme from nasal lavage was subsequently compared to a recombinant form of human PLA2 identified in synovial fluid from arthritic patients. The two enzymes showed similar molecular weights (15 to 16 kD) on SDS-PAGE, and both reacted with a rabbit polyclonal antiserum raised to a galactokinase-PLA2 fusion protein. The enzymatic activities of the two PLA2s were indistinguishable when compared for ionic dependence, substrate selectivity, and sensitivity to inhibitors. These results suggest that the PLA2 induced in nasal lavage in response to challenge by antigen is very similar to the extracellular PLA2 found in synovial fluid from subjects with rheumatoid arthritis and may play a role in the inflammatory processes associated with allergic rhinitis.

Effects of scalaradial, a type II phospholipase A2 inhibitor, on human neutrophil arachidonic acid mobilization and lipid mediator formation

The role of scalaradial (SLD) (or its 12-epi analog), a marine natural product purified from sponge (Cacospongia mollior) in human neutrophil (polymorphonuclear leukocyte, PMN) arachidonic acid metabolism was studied. SLD potently inhibited human recombinant (rh) type II-14 kDa-phospholipase A2 (PLA2) (IC50 = 0.07 microM) but displayed weak inhibition of U937 cell, 85 kDa-PLA2 (IC50 = 20 microM). Sn-2 acylhydrolytic activity expressed in human PMN acid extract, that was completely neutralized by anti-rh type II-14 kDa-PLA2 monoclonal antibody, was inhibited by SLD in a concentration-dependent manner (IC50 = 35 microM). Exposure of human PMN to SLD resulted in a concentration-dependent inhibition of calcium ionophore (A23187)-induced leukotriene B4 release (IC50 = 0.1-0.6 microM). In contrast to the action of selective 5-lipoxygenase inhibitors (WY 50295 or zileuton), SLD decreased A23187-induced PMN liberation of arachidonic acid mass and platelet-activating factor biosynthesis (IC50 = 1-2 microM). PMN acetyltransferase activity was not significantly affected by SLD suggesting that platelet-activating factor inhibition was due, predominantly, to inactivation of PLA2 activity. In vivo, topical application of SLD on mouse ear treated with phorbol ester, not only inhibited edema formation but also the increase in myeloperoxidase activity (an index of cellular infiltration). SLD had little or no effect on arachidonic acid-induced ear edema or myeloperoxidase which is consistent with an action on PLA2. Take together these data suggest that the predominant mechanism of SLD is via inhibition of 14 kDa-like-PLA2 and suggests that this enzyme may participate in PMN arachidonic acid liberation and lipid mediator formation.

Coexistence of two biochemically distinct phospholipase A2 activities in human platelet, monocyte, and neutrophil

The cell-associated phospholipase A2 (PLA2) activities of the human platelet, neutrophil, and monocyte were simultaneously characterized, utilizing the biochemical differences observed between the 14 kDa (kilodalton), type II PLA2 isolated from inflammatory human synovial joint fluid (HSF) and the arachidonic acid (AA) specific, 85-kDa high molecular mass (HMM) PLA2 isolated from the cytosol of a U937 monocytic cell line. The HSF PLA2 can be distinguished from the HMM PLA2 by its resistance to acid treatment, sensitivity to a sulfhydryl reducing agent, lack of preference for the fatty acid on the sn-2 position of phospholipid substrate, and inhibition by the C-7 phosphonate-phospholipid transition-state PLA2 inhibitor. Evaluation of all three cell types revealed that HMM-like PLA2 activity was found predominantly in the cytosolic fractions, although detection in neutrophil cytosol required more concentrated preparations and the use of high specific activity [3H]AA-labeled Escherichia coli. HSP-PLA2-like activity was measured in microsomal and cytosolic fractions of all three cell types, but was found in neutrophil cytosol only after treatment with acid. Further HMM-PLA2-specific interfering agents in neutrophil cytosol were observed and exemplifies one problem in assigning the existence of this enzyme in crude broken cell preparations using activity measurements alone. The role that these two enzymes play in eicosanoid production of the respective cell types remains to be studied.

Recombinant human secretory phospholipase A2: purification and characterization of the enzyme for active site studies

A secreted form of phospholipase A2 (PLA2) is thought to play an important role in inflammatory diseases. To characterize this enzyme the cDNA encoding a low molecular weight PLA2 was cloned from a human placental cDNA library. The cDNA encoding the human PLA2 was subcloned into an expression vector and subsequently transfected into Chinese hamster ovary (CHO) cells. A stable CHO cell clone, secreting ca 1 mg/L of recombinant PLA2 into the medium, was scaled up in culture to 180 L. The recombinant enzyme was purified from the cell supernatant to apparent homogeneity by a novel procedure combining adsorption to poly(vinylidene difluoride) membranes, ion exchange chromatography and size exclusion chromatography. The final recovery of PLA2 activity was 58%. A direct comparison between the purified recombinant human PLA2 and PLA2 purified from human synovial fluid, including molecular weight, antigenicity, ionic dependence, substrate specificity and sensitivity to known PLA2 inhibitors, indicated that the two enzymes exhibit identical biochemical properties. These results show that the recombinant PLA2 can be efficiently expressed and purified in sufficient quantities to characterize the enzyme active site, to aid in the rational development of PLA2 inhibitors as potential anti-inflammatory drugs, and to investigate further the role of PLA2 in inflammatory disease.