Phase 1 study of the pan-RAF inhibitor tovorafenib in patients with advanced solid tumors followed by dose expansion in patients with metastatic melanoma

PURPOSE

Genomic alterations of BRAF and NRAS are oncogenic drivers in malignant melanoma and other solid tumors. Tovorafenib is an investigational, oral, selective, CNS-penetrant, small molecule, type II pan‑RAF inhibitor. This first-in-human phase 1 study explored the safety and antitumor activity of tovorafenib.

METHODS

This two-part study in adult patients with relapsed or refractory advanced solid tumors included a dose escalation phase and a dose expansion phase including molecularly defined cohorts of patients with melanoma. Primary objectives were to evaluate the safety of tovorafenib administered once every other day (Q2D) or once weekly (QW), and to determine the maximum-tolerated and recommended phase 2 dose (RP2D) on these schedules. Secondary objectives included evaluation of antitumor activity and tovorafenib pharmacokinetics.

RESULTS

Tovorafenib was administered to 149 patients (Q2D n = 110, QW n = 39). The RP2D of tovorafenib was defined as 200 mg Q2D or 600 mg QW. In the dose expansion phase, 58 (73%) of 80 patients in Q2D cohorts and 9 (47%) of 19 in the QW cohort had grade ≥ 3 adverse events. The most common of these overall were anemia (14 patients, 14%) and maculo-papular rash (8 patients, 8%). Responses were seen in 10 (15%) of 68 evaluable patients in the Q2D expansion phase, including in 8 of 16 (50%) patients with BRAF mutation-positive melanoma naïve to RAF and MEK inhibitors. In the QW dose expansion phase, there were no responses in 17 evaluable patients with NRAS mutation-positive melanoma naïve to RAF and MEK inhibitors; 9 patients (53%) had a best response of stable disease. QW dose administration was associated with minimal accumulation of tovorafenib in systemic circulation in the dose range of 400-800 mg.

CONCLUSIONS

The safety profile of both schedules was acceptable, with QW dosing at the RP2D of 600 mg QW preferred for future clinical studies. Antitumor activity of tovorafenib in BRAF-mutated melanoma was promising and justifies continued clinical development across multiple settings.

CLINICALTRIALS

GOV IDENTIFIER

NCT01425008.

Abstract 1836: RBN-2397, a novel, potent, and selective PARP7 inhibitor, induces tumor-intrinsic type I interferon responses and adaptive immunity in patient tumors

Background: PARP7 is a mono-ART that is upregulated in response to cellular stress (e.g., viral infection, cigarette smoke), and suppresses the Type I interferon (IFN) response following cytosolic nucleic acid sensing. RBN-2397 is a first-in-class PARP7 inhibitor, inducing cancer cell autonomous and immune stimulatory effects in preclinical models through enhanced Type I IFN signaling in cancer cells. Moreover, RBN-2397 induces CD8 T cell-dependent tumor-specific immune memory in an immunocompetent mouse cancer model [1]. RBN-2397 is currently being tested in an ongoing Phase I clinical study (NCT04053673) [2]. Here we present evidence of proof of mechanism in the paired biopsies of tumors from Phase 1 patients.

Methods: Plasma CXCL10 from patients was measured by MSD while ISG expression in PBMCs was measured by NanoString. Baseline and on-treatment patient tumor biopsies were analyzed by NanoString, CD8/GZMB IHC, and MIBI-TOF to characterize immune changes in the tumor microenvironment.

Results: In peripheral blood from patients treated with RBN-2397, neither plasma nor PBMC CXCL10 increased more than 2-fold over baseline. Expression of 42 ISGs was not consistently induced in a dose-dependent manner in PBMCs. However, in tumor types of interest (e.g., cancers of the upper aerodigestive tract), CXCL10 expression increased, with similar effects observed for a subset of ISGs in multiple evaluable paired biopsy samples. Confirming preclinical studies [1], increases in CD8 T cell infiltration along with induction of granzyme B expression were observed in several evaluable paired patient tumor biopsies by immunohistochemistry. Using the MIBI-TOF technology, we observed up to 50-fold increases in intratumoral activated T cells as well as monocytes and M1 macrophages, most strikingly in two NSCLC patients.

Conclusions: In patients treated with RBN-2397 pharmacodynamic effects were preferentially observed in tumor tissue relative to the periphery, including an increase in immune infiltration into the tumor microenvironment. These data provide evidence for induction of an adaptive immune response and confirm the tumor-intrinsic, immunomodulatory mechanism of action of RBN-2397 in patients.

References: 1. Gozgit et al. PARP7 negatively regulates the Type I interferon response in cancer cells and its inhibition triggers antitumor immunity. Cancer Cell. 2021 2. Falchook et al. A First-In-Human Phase 1 Study of a Novel PARP7 Inhibitor RBN-2397 in Patients with Advanced Solid Tumors. ASCO 2021 oral presentation

Citation Format: Kristy Kuplast-Barr, Melissa L. Johnson, Manish R. Patel, Timothy A. Yap, Gerald S. Falchook, Patricia LoRusso, Ryan Abo, Chang Liu, Erika L. Manyak, Lisa Cleary, Viviana Bozon, Sudha Parasuraman, Heike Keilhack, Kristen McEachern. RBN-2397, a novel, potent, and selective PARP7 inhibitor, induces tumor-intrinsic type I interferon responses and adaptive immunity in patient tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1836.

866 RBN-2397, a novel, potent, and selective PARP7 inhibitor, induces tumor-intrinsic type I interferon responses and adaptive immunity in preclinical models and patient tumors

Background

PARP7 is a mono-ART that is upregulated in response to cellular stress (e.g., viral infection, cigarette smoke), and suppresses the Type I interferon (IFN) response following cytosolic nucleic acid sensing. RBN-2397 is a first-in-class PARP7 inhibitor, inducing cancer cell autonomous and immune stimulatory effects in preclinical models through enhanced Type I IFN signaling in cancer cells. Moreover, RBN-2397 induces CD8 T cell-dependent tumor-specific immune memory in an immunocompetent mouse cancer model.1 RBN-2397 is currently being tested in an ongoing Phase I clinical study (NCT04053673).2 Here we aimed to compare biomarker results from preclinical models and patient samples.

Methods

In preclinical models, interferon-stimulated gene (ISG) expression was assessed by qPCR, NanoString, or ELISA. Plasma CXCL10 from patients was measured by MSD while ISG expression in PBMCs was measured by NanoString. Baseline and on-treatment patient tumor biopsies were analyzed by NanoString, CD8/GZMB IHC, and MIBI-TOF to characterize immune changes in the tumor microenvironment.

Results

RBN-2397 potently restored tumoral Type I IFN signaling in preclinical models as demonstrated by increases in ISGs, namely CXCL10, which were not observed in non-tumor tissue (e.g. spleen, PBMCs). In peripheral blood from patients treated with RBN-2397, neither plasma nor PBMC CXCL10 increased more than 2-fold over baseline. Expression of 42 ISGs was not consistently induced in a dose-dependent manner in PBMCs. However, in tumor types of interest (e.g. cancers of the upper aerodigestive tract), CXCL10 expression increased 1.5 to 8-fold, with similar effects observed for a subset of ISGs in 5 evaluable paired biopsy samples.Confirming preclinical studies [1], up to 8-fold increases in CD8 T cell infiltration along with induction of granzyme B expression were observed in 4 of 5 paired patient tumor biopsies by immunohistochemistry. Using the MIBI-TOF technology, we observed up to 50-fold increases in intratumoral activated T cells as well as monocytes and M1 macrophages, most strikingly in two NSCLC patients.

Conclusions

Inhibition of PARP7 with RBN-2397 restores tumor-intrinsic Type I IFN signaling in preclinical models leading to enhanced adaptive immunity, resulting in CD8 T cell-dependent durable tumor regressions. These observations are mirrored in samples from patients treated with RBN-2397 in that pharmacodynamic effects of RBN-2397 were preferentially observed in tumor tissue relative to the periphery, including an increase in immune infiltration into the tumor microenvironment. These data provide evidence for induction of an adaptive immune response and confirm the tumor-intrinsic, immunomodulatory mechanism of action of RBN-2397 in patients.

References

Gozgit, et al. PARP7 negatively regulates the type I interferon response in cancer cells and its inhibition triggers antitumor immunity. Cancer Cell 2021; In press.

Falchook, et al. A first-in-human phase 1 study of a novel PARP7 inhibitor RBN-2397 in patients with advanced solid tumors. ASCO 2021; oral presentation.

Abstract CT131: A Phase I safety and tolerance study of FN-1501, a novel FLT3 inhibitor, in patients with advanced solid tumors and acute myeloid leukemia

Background: FLT3 mutations are found in approximately 30% of adult patients with Acute Myeloid Leukemia (AML) and to a lesser degree, in certain solid tumors. FN-1501 is a potent inhibitor of FLT3 and other tyrosine kinases such as CDK4/6, KIT, PDGFR, ALK and RET proteins, with demonstrated anti-tumor activity in several leukemia and colon cancer xenograft models. An ongoing, open-label, Phase I study (NCT03690154) is evaluating FN-1501 as monotherapy in patients with various advanced solid tumors and relapsed, refractory (R/R) AML. The objectives of the trial are to assess safety and tolerability, establish a Recommended Phase 2 Dose (RP2D), and evaluate preliminary anti-tumor activity. Methods: Pts received FN-1501 by IV thrice weekly for 2 weeks followed by 1 week off treatment in 21-day cycles. The dose escalation phase follows a standard 3+3 design. Primary objectives include determinations of dose-limiting toxicity (DLT), maximum tolerated dose (MTD), safety, and RP2D. Secondary objectives include pharmacokinetics (PK) and anti-tumor activity. Exploratory objectives include the relationship between pharmacogenetic mutations (e.g. FLT3, TP53, KRAS, NRAS, etc) and safety/efficacy. Expansion cohorts have been added to the ongoing protocol amendment to confirm safety and evaluate preliminary efficacy at RP2D. Results: At the time of data cut-off (Nov 17, 2020), 40 pts (n=1 AML; n=39 solid tumors) were enrolled at doses ranging from 2.5 to 128 mg. Median number of prior lines of treatment was 5 (range 1-12). Thirty-four patients met the minimum exposure criterion for DLT assessment. No DLTs were reported and MTD was not reached. Treatment-related adverse events (TRAEs) were reported in 58% of pts. The most common TRAEs in ≥10% of patients included fatigue (20%), nausea (15%), infusion related reaction (10%), mostly reversible grade 1 or 2. Grade ≥3 TRAEs consisting of anemia, fatigue and serum creatinine increase were observed in 3 pts. TRAEs resulted in dose delay/interruption in 4 pts (10%) but no treatment discontinuations. No serious TRAEs were observed. The exposure of FN-1501 (AUC and Cmax) increased in a dose proportional manner. Mean t1/2 was estimated to be 12-19 hours. Among 25 response-reportable pts, 1 had a best overall response of PR (47% target lesion shrinkage), 10 had stable disease and 14 had progressive disease. The confirmed PR (duration > 4 months) occurred at the 40 mg dose level in a pt with endometrial carcinoma. Conclusion: FN-1501 has demonstrated reasonable safety/tolerability across all doses tested, with promising anti-tumor activity in pts with certain advanced, heavily pre-treated solid tumors. Enrollment of pts into the dose escalation part of the study is continuing and updated safety, PK and molecular biomarker results will be presented at the meeting.

Citation Format: Gary Edward Richardson, Stephen K. Williamson, Misako Nagasaka, Viviana Bozon, Maria Margarita Corvez, Chao Li, Wei Li, Jiao Wei, Ai-Min Hui. A Phase I safety and tolerance study of FN-1501, a novel FLT3 inhibitor, in patients with advanced solid tumors and acute myeloid leukemia [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 CT131.

A first-in-human phase 1 study of a novel PARP7 inhibitor RBN-2397 in patients with advanced solid tumors

3000

Background: Targeting cytosolic nucleic acid sensing pathways and the Type I interferon (IFN) response is an emerging therapeutic strategy in oncology. PARP7 is a member of the monoPARP class of enzymes and a newly identified negative regulator of nucleic acid sensing in tumor cells. PARP7 expression is increased by cellular stress and aromatic hydrocarbons, and the PARP7 gene is amplified in multiple cancers. RBN-2397 is a potent, selective inhibitor of PARP7. In preclinical models, RBN-2397 restored Type I IFN signaling in tumors, caused complete tumor regressions, and induced adaptive immunity. Methods: Patients (pts) with advanced solid tumors were treated with RBN-2397 on either a continuous or 14-of-21-day intermittent schedule using a 3+3 dose escalation design. Primary objective: establish MTD and/or RP2D. Secondary obj.: safety, activity, PK of unmicronized/micronized tablets. Exploratory obj.: Pd. Results: As of 4 January 2021, 47 pts were treated: 25 pts in the intermittent schedule (25 to 500 mg BID) and 22 patients in the continuous schedule (100 to 400 mg BID). The most frequent RBN-2397-related AEs (all grades) were dysgeusia (26%), decreased appetite (13%), fatigue (11%), and diarrhea (11%). Gr 3/4 RBN-2397-related AEs all occurred in 7 pts (15%) at doses ≥ 200 mg: diarrhea (2 pts, 4%), increased ALT, AST, and bilirubin (1 pt, 2%), and fatigue, anemia, neutropenia, and thrombocytopenia in 1 pt (2%) each. The 2 DLTs were Gr 3 febrile neutropenia (400 mg continuous schedule) and Gr 4 increase in ALT/AST (500 mg intermittent schedule). Plasma exposures generally increased dose dependently with the majority at or above the projected efficacious range based on animal studies. All evaluable baseline tumor biopsies showed evidence of PARP7 expression as measured by mRNA in situ hybridization (n = 11; Median tumor H score: 128). In 5 evaluable tumor biopsy pairs, increases in interferon-stimulated gene expression were observed post RBN-2397, consistent with activation of Type I IFN. CXCL10 mRNA increased in all evaluable on-treatment biopsies (1.5 to 8-fold). Several on-treatment biopsies showed enrichment for immune response gene sets that was accompanied by an increase in CD8+ T cells and Granzyme B expression, evidence for induction of an adaptive immune response post RBN-2397. This increase in immune response related genes and CD8+ T cells was observed in a pt with metastatic squamous NSCLC who has been on study for 16+ months. 1 pt with HR+, HER2- breast cancer achieved a confirmed PR at 100 mg and 8 pts had SD for ≥18 weeks (RECIST 1.1). Conclusions: To date, RBN-2397 is well tolerated and demonstrates dose dependent increases in plasma exposures, evidence of target inhibition, and preliminary signs of clinical activity. Determination of MTD/RP2D is imminent and study expansion is planned to evaluate safety and efficacy in squamous NSCLC, HNSCC, HR+ breast cancer, and PARP7 amplified tumors. Clinical trial information: NCT04053673.

FIH phase I dose escalation study of FN1501, an investigational FLT-3 inhibitor with multiple targets in patients with relapsed or refractory solid tumors and acute myeloid leukemia

e15656

Background: FN1501 inhibits various tyrosine kinases as CDK4/6, KIT, PDGFR, ALK and RET proteins, particularly potent on FLT3 and EGFR2. A Ph1 FIH trial for patients (pts) with solid tumors and Acute Myeloid Leukemia (AML) is on-going1. Preclinical data showed that FN1501 inhibits the phosphorylation of FLT3 and its downstream kinase STAT5 in human acute leukemia cell lines, arrests the cell cycle inducing apoptosis and inhibits growth and proliferation of leukemia cells. It has anti-proliferation activity against other leukemia cell lines bearing FLT3 mutations, and lymphoma cell lines2, 3. Methods: 26 pts with advanced solid tumors or AML enrolled in the escalation phase and received IV FN1501 on days 1, 3, 5, 8, 10 and 12 on 21-day cycles. Primary objectives are safety and MTD, secondary objectives include preliminary activity, PK and PD. Plasma PK were assessed at different timepoints pre and post dose in C1 and C2. Results: As of 6FEB20, 26 pts have been treated in 7 ascending doses of 2.5mg, 5mg, 10mg, 15mg, 22.5mg, 30mg and 40mg. A 54 mg dose cohort is on-going. No DLTs, no SAEs or deaths associated to FN1501 have been reported. 12 pts (46%) had one grade 3 or higher TEAE and 7 pts (27%) had dose interruptions due to a TEAE. Administration of FN1501 to pts with metastatic solid tumors has resulted in anti-tumor activity. 9 pts had durable stable disease across 4 doses in renal, endometrial, ovarian, gastric, appendix and thymic malignancies. One pt with serous endometrial carcinoma achieved a cPR after 2 cycles at 40mg with a 47% tumor size reduction (target lesions). As of 26Oct19 preliminary PK data showed a t1/2 of approximately 12.7-19.0 hours post-dose. Mean Cmax and AUC increased proportionally with dose and Clearance is consistent among all doses. Conclusions: This on-going Ph1trial of FN1501 is providing evidence of dose or exposure effects as a single agent in patients with solid tumors. Since FN1501 targets multiple kinases on addition to FLT3, antitumor activity beyond AML is also being observed, suggesting that the potent inhibitory effects of other tyrosine kinases, including EGFR2 may be playing a role in the regulation of cellular functions, cell growth, differentiation and angiogenesis effects. FN1501 has been well tolerated and AEs are manageable. Genomic alterations investigations are underway to identify candidate biomarkers useful for predicting sensitivity to the multiple FN1501 tyrosine kinases. Further development of FN1501 is warranted. Clinical trial information: NCT03690154.

A phase I clinical study to evaluate the safety, tolerability, pharmacokinetics (PK), and antitumor activity of FN-1501 monotherapy in patients with advanced solid tumors

TPS3150

Background: Receptor tyrosine kinases (RTK), a group of transmembrane proteins, are responsible for growth factor signaling transduction in normal cellular functions. Abnormal RTK functions are associated with human tumorigenesis. FMS-like tyrosine kinase 3 (FLT3) belongs to the type III receptor tyrosine kinase family and plays a well-established role in normal growth and differentiation of hematopoietic precursor cells. FLT3 mutations have been reported to occur in approximately 30% newly diagnosed AML patients. The internal tandem duplications mutation (FLT3/ITD) is the major mutation and correlated with more aggressive progress and poor prognosis. FN-1501 is an inhibitor of various tyrosine kinases such as cyclin-dependent kinase 4/6(CDK4/6), platelet-derived growth factor receptor (PDGFR), KIT protein, anaplastic lymphoma kinase (ALK) and RET protein, particularly potent on FLT3. The preclinical data generated from biochemical, cell based and animal in vivo studies suggest that FN-1501 as a single agent could offer cancer patients clinical benefit by inhibiting multiple tyrosine kinases including FLT3, PDGFR, KIT, ALK, and RET. Methods: This is a Phase1, open label, multicenter, dose-escalation study that will evaluate the safety, pharmacokinetics (PK), and preliminary efficacy of FN-1501 in up to 33 cancer patients with solid tumors. There is a dose escalation phase that will be followed by an expansion cohort. The dose escalation phase utilizes a standard “3 + 3” design where doses of FN-1501 will be escalated up to the Maximum-Tolerated Dose (MTD) or until the Recommended Phase 2 dose (RP2D) is identified. Once the MTD or RP2D dose is identified, an expansion cohort including patients with hematologic malignancies will be enrolled to further evaluate the safety and efficacy of FN-1501. Key exploratory analyses will include an evaluation of safety and efficacy and levels of expression and/or amplification of FLT3 mutations. As of February 8, 2019, cohorts 1 and 2 have been completed without a dose limiting toxicity (DLT). A total of 11 patients have been treated. Enrollment to cohort 3 is on-going. Clinical trial information: NCT03690154.

Phase 1b/2 study of binimetinib (BINI) in combination with nivolumab (NIVO) or NIVO plus ipilimumab (IPI) in patients (pts) with previously treated microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) with RAS mutation

TPS870

Background: Approximately 96% of CRCs have an MSS phenotype, which results in more immunologically quiescent tumors for which immunotherapies are largely ineffective (Lee et al. 2015; Overman et al. 2016). Pts with MSS CRC and activating RAS mutation (35%–45% of CRCs) have treatment options limited still further because anti-EGFR monoclonal antibodies (eg, cetuximab) are ineffective owing to dominant activation of RAS in the MAPK pathway (Douillard et al. 2014). However, preclinical and preliminary clinical data suggest that MAPK pathway inhibition enhances antigen presentation and T-cell cytotoxicity to positively modulate the efficacy of checkpoint inhibitors (Brea et al. 2016; Bendell et al. 2014). The main objective of this open-label multicenter phase 1b/2 study is to evaluate whether the potential positive modulation of NIVO or NIVO plus IPI, when combined with BINI, translates into clinically meaningful overall response in pts with MSS mCRC and RAS mutation. Methods: The study will enroll ~90 previously treated pts (1 or 2 prior regimens), ~42 in phase 1b and ~48 in phase 2. The primary objective of phase 1b will be to determine the recommended phase 2 dose (RP2D) of BINI in combination with NIVO ± IPI. Dose finding in the doublet arm will begin with BINI 45 mg BID + NIVO 480 mg Q4W; the triplet arm will begin with the BINI RP2D from the doublet arm + NIVO 480 mg Q4W + IPI 1 mg/kg Q8W. In phase 2, pts will be randomized 1:1 to doublet or triplet arms, incorporating the BINI RP2Ds found in phase 1b; treatment will continue in 28-day cycles until disease progression, unacceptable toxicity, withdrawal of consent, initiation of subsequent anticancer therapy, loss to follow-up, or death. The primary objective for phase 2 will be to assess response by RECIST version 1.1. The study will also characterize safety and PK. CT.gov Identifier: Clinical trial information: NCT03271047.

Phase 1b/2 trial of ribociclib+binimetinib in metastatic NRAS-mutant melanoma: Safety, efficacy, and recommended phase 2 dose (RP2D)

9519

Background: Simultaneous inhibition of MEK and CDK4/6 may suppress MAPK pathway activation and cell-cycle checkpoint dysregulation in NRAS-mutant melanoma, resulting in enhanced antitumor activity. Phase 1b data are reported. Methods: The phase 1b primary objective was to determine maximum tolerated dose (MTD)/RP2D. A 28-d cycle of oral ribociclib (RIBO) once daily (QD) for 21 d + oral binimetinib (BINI) twice daily (BID) for 28 d, and a 21-d cycle of RIBO QD + BINI BID, both for 14 d per cycle, were evaluated. Secondary objectives were to evaluate efficacy, safety and pharmacodynamics. Results: Based on dose escalation (van Herpen, ESMO 2015), MTD was 600mg RIBO/45mg BINI for the 21-d and 200/45 for the 28-d regimens. Due to promising activity, the 28-d cycle was selected as RP2D(unconfirmed partial response [PR] with limited follow-up occurred in 35% of pts). This finding was supported by comparable and manageable safety and the Bayesian logistic regression model.As of Jan 2017, the RP2D was received by 16 pts in phase 1b (ECOG PS 0/1/2, 63%/31%/6%; elevated lactate dehydrogenase, 44%; stage IVM1c disease, 50%; prior ipilimumab [ipi], 44%; prior anti–programmed death [PD]-1/PD-L1, 31%). Median (range) exposure was 4 (0–13) mo. Common adverse events (AEs) were increased blood creatine phosphokinase, elevated AST, peripheral edema, acneiform dermatitis, diarrhea and fatigue. Common grade 3/4 AEs were elevated AST and ALT (19%/6%), nausea (19%/0%), rash (19%/0%), vomiting (6%/6%) and neutropenia (12%/0%). Confirmed PR (cPR) occurred in 4 pts (25%; time to response, 48–168 d), stable disease in 7 pts (44%), disease progression in 3 pts (19%); 2 pts (12%) were not evaluable. Among cPR pts, 3 had prior ipi and/or anti–PD-1/PD-L1. Median progression-free survival (mPFS) was 6.7 (95% CI, 3.5–9.2) mo. Sequence analysis of synchronous non- RAS genetic alterations will be presented. Conclusions: Combined RIBO/BINI at the selected RP2D had a manageable safety profile and favorable efficacy (based on mPFS) for NRAS-mutant melanoma in phase 1b. Based on these promising data, the phase 2 expansion is underway to assess antitumor activity at the RP2D. Clinical trial information: NCT01781572.

Design, synthesis and biological evaluation of fluorescent ligands for MT1 and/or MT2 melatonin receptors

Fluorescent melatoninergic ligands have been designed by associating the 4-azamelatonin ligands with different fluorophores.

MLN2480, an investigational oral pan-RAF kinase inhibitor, in patients (pts) with relapsed or refractory solid tumors: Phase I study

2547

Background: MLN2480 is an investigational pan-RAF kinase inhibitor. In vivo, MLN2480 showed antitumor activity in melanoma, colon, lung, and pancreatic cancer xenograft models. This first-in-human study aimed to evaluate the safety of MLN2480, determine the MTD/recommended phase 2 dose (RP2D), and evaluate pharmacokinetics (PK) and preliminary efficacy. Methods: Pts aged ≥18 yrs with advanced solid tumors who had failed/were not candidates for standard therapy received oral MLN2480 every other day (Q2D) in 22-d cycles, with dose escalation (3+3 design) based on DLTs in cycle 1. AEs were graded per NCI-CTCAE v4.03. Blood samples for plasma PK assessment were taken pre-dose and at multiple times post-dose, d 1 and 21, cycle 1. Results: 24 pts (10 male, median age 64.5 yrs [range 37–83]) have been treated at 20, 40, 80, 135, 200, and 280 mg (n=4, 3, 3, 3, 4, and 7), respectively. The most common tumors included colorectal cancer in 11 pts and non-small-cell lung cancer in 2 pts. Pts received a median of 2 (range 1–6) cycles. 2 pts treated at 280 mg had DLTs: grade 3 macular rash and grade 3 periorbital edema. 20 pts had drug-related AEs, including fatigue 46%, arthralgia 25%, maculopapular rash 21%, and myalgia 17%. 4 pts had drug-related grade ≥3 AEs, which included the 2 DLTs listed above, anemia, dyspnea, and fatigue. No keratocanthomas/ squamous cutaneous carcinomas have been seen to date. 4 pts discontinued due to AEs. There were 3 on-study deaths (1 treatment-related per investigator; dyspnea and respiratory failure). At 20–200 mg MLN2480 PK data (13 pts) exhibited rapid absorption (median Tmax 2 hr), low fluctuation at steady state (mean peak to trough ratio 2.1), and mean accumulation half-life of 67 hr. Overall mean accumulation was 2.6-fold following repeated Q2D dosing for 21 d. Steady-state (d 21) exposures increased in an approximately dose-proportional manner over 20–200 mg range. No pts had an objective response to date; no pts with BRAF mutation enrolled to date. Conclusions: In this first-in-human study (n=24), the safety profile of MLN2480 up to 200 mg Q2D was acceptable. Accrual continues at 200 mg to confirm the MTD. Melanoma expansion cohorts are planned at the RP2D using a Q2D 28-d cycle. Clinical trial information: NCT01425008.

Phase I, dose-escalation study of the investigational drug TAK-733, an oral MEK inhibitor, in patients (pts) with advanced solid tumors

2528

Background: This first-in-human study evaluated the safety, pharmacokinetics (PK), pharmacodynamics (PD), MTD, and efficacy of TAK-733 – an oral, selective, allosteric inhibitor of MEK1/2 – in pts with advanced solid tumors (NCT00948467; completed study). Methods: Eligibility: age ≥18 y; ECOG PS 0–2; evaluable tumors. Pts received escalating doses of TAK-733 QD in a modified 3+3 design for 21 d in a 28-d cycle to determine the MTD based on DLTs in cycle 1. Plasma (PK) and peripheral blood samples (PD: pERK reduction in PBMCs) were obtained pre-dose (d 1, 8, 15, 21) and post-dose (d 1, 21) in cycle1. Results: 51 pts (median age 58 y; 51% M) received escalating doses of TAK-733 (0.2–22 mg; median 2 cycles, range 1–11 [5 pts ≥6 cycles]). 4 pts had DLTs: grade 3 acneiform dermatitis, 1 each at 11.8 and 16mg; grade 3 pustular rash and grade 2 rash/stomatitis (qualifying as a DLT) at 22mg, leading to the 16 mg dose being selected as MTD. 45 pts (88%) had a drug-related AE; most frequent was acneiform dermatitis (47%). 10 pts (20%) had a grade ≥3 drug-related AE; most frequent were creatine phosphokinase increase and acneiform dermatitis (each n=3, 6%). 7 pts discontinued due to AEs. TAK-733 exhibited a moderately fast absorption with a median Tmax of 3 hr. Steady-state exposure of TAK-733 (0.2–22mg) did not increase in a dose proportional manner based on the power model analysis. The mean terminal t1/2 (11.8, 16, and 22 mg) was 43 hr. Overall mean accumulation ratio was 3.5 following QD dosing for 21 d. On d 21, Emax of blood pERK modulation was 56–99%, and time-averaged modulation over the dosing interval at steady-state was 76–98% at MTD. This range correlates well to the 76–89% for pERK modulation associated with maximal efficacy in xenograft models. 1 pt (16 mg) with melanoma (BRAF L597R) had a confirmed partial response after 4 cycles (treated for 9 cycles). 15 pts had a best response of stable disease (4–11.7 months in 6 pts). Conclusions: From preliminary data, TAK-733 appears generally well tolerated, pharmacodynamically active and shows signs of anti-tumor activity in pts with advanced solid tumors. MTD was associated with significant pERK inhibition in peripheral blood. Clinical trial information: NCT00948467.

BRAF(L597) mutations in melanoma are associated with sensitivity to MEK inhibitors

Kinase inhibitors are accepted treatment for metastatic melanomas that harbor specific driver mutations in BRAF or KIT, but only 40% to 50% of cases are positive. To uncover other potential targetable mutations, we conducted whole-genome sequencing of a highly aggressive BRAF (V600) and KIT (W557, V559, L576, K642, and D816) wild-type melanoma. Surprisingly, we found a somatic BRAF(L597R) mutation in exon 15. Analysis of BRAF exon 15 in 49 tumors negative for BRAF(V600) mutations as well as driver mutations in KIT, NRAS, GNAQ, and GNA11, showed that two (4%) harbored L597 mutations and another two involved BRAF D594 and K601 mutations. In vitro signaling induced by L597R/S/Q mutants was suppressed by mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibition. A patient with BRAF(L597S) mutant metastatic melanoma responded significantly to treatment with the MEK inhibitor, TAK-733. Collectively, these data show clinical significance to BRAF(L597) mutations in melanoma.

SIGNIFICANCE

This study shows that cells harboring BRAF(L597R) mutants are sensitive to MEK inhibitor treatment, providing a rationale for routine screening and therapy of BRAF(L597R)-mutant melanoma.

Surveillance of the eye and vision in clinical trials of CP-675,206 for metastatic melanoma

PURPOSE

To determine the ocular safety of CP-675,206 (Pfizer, New York, New York, USA), a fully human anti-cytotoxic T lymphocyte-associated antigen 4 monoclonal antibody in clinical trials of immunotherapy of metastatic melanoma.

DESIGN

Prospective, nonrandomized study of the eye and vision in phase I/II clinical trials of CP-675,206 in metastatic melanoma conducted at the University of California, Los Angeles.

METHODS

Patients with regional or distant metastatic melanoma were enrolled in phase I/II clinical trials evaluating the safety and antitumor efficacy of CP-675,206 alone or in combination with melanoma antigen peptide-pulsed dendritic cell vaccines. Ophthalmic evaluation was performed at the onset of CP-675,206 immunotherapy (baseline evaluation), two months or more after the onset of CP-675,206 immunotherapy (end-study evaluation), and at two- to three-month intervals thereafter in patients who continued to receive CP-675,206 immunotherapy (poststudy evaluation). Baseline and end-study evaluations included comprehensive ophthalmic examination, psychophysical and electrophysiologic visual function assessment, fundus photography, fluorescein angiography, and visual function assessment.

RESULTS

Twenty patients with metastatic melanoma arising from the skin, mucosa, eye, or unknown site were evaluated. Systemic toxicity attributed to CP-675,206 included dermatologic manifestations, diarrhea, and autoimmune hepatitis with panhypopituitarism. A subset of patients receiving CP-675,206 demonstrated antitumor efficacy with partial response or complete response of metastatic melanoma. Comparison of ophthalmic baseline with end-study evaluations in all 20 patients and limited-term poststudy evaluations showed no adverse effect of CP-675,206 immunotherapy on the eye or vision.

CONCLUSIONS

In this study, CP-675,206 immunotherapy for metastatic melanoma did not adversely affect the eye or vision.

Dose and schedule selection for the anti-CTLA4 monoclonal antibody ticilimumab in patients (pts) with metastatic melanoma

8032

Background: Ticilimumab therapy has demonstrated anti-tumor activity in pts with metastatic melanoma. Its indirect, immune-mediated antitumor effects pose unique challenges for dose/regimen selection. Methods: It was our original intention to select the clinical dose/regimen of ticilimumab based on (1) clinical safety and tolerability and (2) attainment of target plasma concentrations derived from pre-clinical work using an ex vivo assay of ticilimumab-induced enhancement of cytotoxic T-cell function. Because numerous pts with metastatic melanoma experienced clinical benefit (i.e., durable objective responses [OR] and/or long-term survival) in early clinical trials of ticilimumab, we are using (1) safety and tolerability and (2) clinical benefit to guide dose/regimen selection. Data for evaluating these criteria come from a single-dose Phase 1 trial (0.01, 0.1, 1, 3, 6, 10 and 15 mg/kg) and an ongoing multiple-dose Phase 1/2 trial in pts with melanoma (Phase 1 portion: 3, 6 and 10 mg/kg Q1M; Phase 2 portion: 10 mg/kg Q1M and 15 mg/kg Q3M). Results: In the single-dose Phase 1 trial, 10 mg/kg was the Protocol-defined MTD but a high rate of clinical benefit was seen in the 15 mg/kg dose cohort (6/6 pts). Because the DLTs seen at 15 mg/kg (Gr 3 diarrhea, Gr 3 rash) were moderate and resolved completely within 3 months of dosing, 15 mg/kg Q3M was proposed as a safe and tolerable dose and is being studied in the Phase 2 portion of the multiple-dose Phase 1/2 trial. The Phase 1 portion of the multiple-dose Phase 1/2 trial revealed that 10 mg/kg is safe and tolerable with monthly dosing so 10 mg/kg Q1M is also being studied in the Phase 2 portion of the trial. At the end of the Simon Optimum-defined Stage 1 of the Phase 2 portion of the ongoing trial, the OR rate (3/18 pts) is the same for both dosing regimens. However, with 15 mg/kg Q3M, Gr 3/4 adverse events were less frequent (6% versus 34%). Conclusions: 15 mg/kg Q3M is proposed as the clinical dose/regimen for ticilimumab in metastatic melanoma. This dose/regimen appears to have anti-tumor activity approximately equal to 10 mg/kg Q1M but it appears to have a superior safety profile.

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Antigen-specific T cell responses in patients with melanoma treated with the CTLA4 blocking mAb ticilimumab

8033

Background: We previously defined the magnitude of the minimum statistically significant change in value for the MHC tetramer and ELISPOT assays (Comin-Anduix, Clin Cancer Res 2006). We used those reference change values (RCV) to determine if the administration of ticilimumab to patients with melanoma expands the circulating populations of tumor antigen-specific T cells. Methods: HLA-A2.1+ pts with sIIIc or IV melanoma and baseline circulating MART-1-specific T cells above the low limit of detection by tetramer assay (LLD, 0.03% of CD8+ T cells) received ticilimumab at 10 mg/kg monthly. Two 40 ml blood samples were collected at baseline, and one at 1 and 2 weeks after each dose for 4 cycles. Primary endpoint was immune response for MART-1 by tetramer assay, for which the RCV is 80% (expressed as percent change from baseline). Results: Of 15 pts (2 sIIIc, 5 sIVa, 2 sIVb, 6 sIVc), 1 was not treated and 2 received only 1 dose due to rapid progression. The 12 remaining pts received 2–11 doses. Clinical immunologic response to ticilimumab was evidenced by immune-related toxicity (G3 diarrhea in 2 pts, G2 hypophysitis in 1 pt, G3 hepatitis in 2 pts) and by anti-tumor activity: CR in 1 pt (15+ mo), PR in 2 pts (9+, 8 mo), and SD in 3 pts (11, 8+ and 4 mo); the rest had PD at 4 mo or less. A mean of 2 baseline and 7 follow up (range 5–9) time points were tested by tetramer and ELISPOT assays. 4 pts had an increase in MART-1-specific T cells beyond the RCV on 1 or more occasions, but no pt had a consistent pattern of change over time. Indeed, there was no consistent pattern of change in any pt in circulating T cells specific for MART-1, gp100, tyrosinase, EBV, or CMV by tetramer or by ELISPOT assay. One pt had accessible regressing lesions which on biopsy showed heavy infiltration by CD8+/Granzyme B+ CTL and a 10-fold enrichment of gp100-specific T cells compared to his peripheral blood. Conclusion: Ticilimumab administered monthly induces immune-related phenomena and tumor responses in patients with melanoma without a demonstrable expansion of circulating melanoma antigen-specific T cells. Evaluation of melanoma antigen-specific T cells within the tumor may be a better way to study the mechanism of antitumor activity of CTLA4 blocking mAb.

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Phase I clinical trials of ticilimumab: Tumor responses are sufficient but not necessary for prolonged survival

8036

Background: Clinical studies examining anti-CTLA4 monoclonal antibodies (mAb) provide evidence of the biologic and clinical activity of this class of agents. Two Phase 1 studies with ticilimumab, a fully human anti-CTLA4 mAb, have been reported previously. In both studies, objective responses (OR) were seen in some patients (pts) with melanoma. In addition, we observed highly favorable outcomes among several pts who did not experience objective responses. This may indicate a positive impact of ticilimumab on melanoma in these pts, not well reflected by traditional response criteria. Long-term follow-up data on survival for pts enrolled in these Phase 1 studies is now reported. Methods: We studied the safety, pharmacokinetics, immunostimulatory activity, and clinical activity of ticilimumab in 53 pts with solid malignancies. Ticilimumab was administered, as a single agent, at single dose levels ranging from 0.01 to 15 mg/kg and at multiple dose levels ranging from 3 to 15 mg/kg. The dosing regimens included either a single dose, multiple doses given q3 months, or multiple doses given q1 month. Results: The two studies included 43 pts with measurable melanoma. Ticilimumab proved safe and overall was well tolerated (Ribas et al. ProcASCO 2005, and JCO Dec2005). Of the 43 pts with measurable melanoma, 18 were alive at >12 months (range: 13 - 42+) after initial treatment with ticilimumab. This includes 5 pts with an OR who continue on ticilimumab, either on-study or as part of a single IND, and 13 pts without an objective response. Among the pts who did not experience an OR, 5 had surgical resection of metastatic lesions and remain relapse free, and 8 are alive with disease. Conclusions: In pts with melanoma treated with ticilimumab, long-term survival has been achieved by all 5 pts who experienced an OR and in 13 pts who did not experience an OR. These findings suggest that lack of objective response is a poor predictor of long-term survival following ticilimumab therapy.

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Agonist-like activity of antibodies directed against the second extracellular loop of the human cardiac serotonin 5-HT4(e) receptor in transfected COS-7 cells

We have previously reported that antipeptide antibodies directed against the second extracellular loop of the cardiac h5-HT4 receptor could block the activation of the L-type Ca channel in human atrial cardiomyocytes. In this paper we investigate the immunological and physiological activity of these antibodies, in a cell system expressing a larger amount of receptors than the atrial cells. The recombinant receptor was expressed at the surface of COS-7 cells under an active form (serotonin, EC50 = 1.81 x 10(-7) M), at a high level (375 +/- 25 fmol receptor/mg total protein) and was able to bind a specific ligand (GR113808) with a high affinity (Kd = 0.28 +/- 0.05 nM). In this system, the same anti-peptide antibodies used for the cardiac cells induced an "agonist-like" effect on the recombinant h5-HT4 receptor. These results are in line with those shown for others G-protein coupled receptors, as adrenoreceptors. In addition, this work showed that the effect of the antibodies is not only dependent on the epitopic region recognised but also on the molecular density and/or the cellular environment of the target receptors. Finally, our results support the hypothesis that the h5-HT4 receptor could be a new target for autoantibodies in patients with atrial arrhythmia.

Critical relationship between glycosylation of recombinant lutropin receptor ectodomain and its secretion from baculovirus-infected insect cells

The lutropin receptor ectodomain overexpressed under the control of the powerful polyhedrin promoter in baculovirus-infected Sf9 insect cells, is mainly found in an inactive, intracellularly-aggregated form. It is secreted in an active form under the control of the P10 promoter, a somewhat weaker and earlier promoter, at the price of a lower production. The apparent molecular masses of the two species encoded by the same cDNA are 48 kDa and 60-68 kDa, respectively. The relationship between the extent and type of glycosylation and the extracellular targeting for the recombinant lutropin receptor ectodomains was investigated precisely with endoglycosidases, lectins of various specificities, and a glycosylation inhibitor, and tested with monoclonal and polyclonal antibodies. The results indicate that the strong polyhedrin promoter probably overwhelms the processing capacity of the ER in Sf9 cells, so that only a high-mannose precursor is expressed in large amounts. Only a minute amount of protein is secreted, which has been processed by Sf9 exoglycosidases/glycosyltransferases and bears complex/hybrid oligosaccharides. The weaker P10 promoter allows secretion of a mature and active receptor ectodomain, bearing complex glycosylation. An important O-linked glycosylation is also added post-translationally on this species. In particular, beta-galactose and sialic acid residues were specifically detected in the secreted species, evidence of the induction of the corresponding glycosyltransferases or of their genes. These results suggest that Sf9 cells should eventually be engineered with chaperones and glycosyltransferases in order to improve the production of demanding glycoproteins such as the porcine lutropin ectodomain, so as to open the way to resolution of the three-dimensional structures of these receptors.

Endocytosis of lutropin by Leydig cells through a pathway distinct from the high-affinity receptor

In porcine Leydig cells in primary culture, 95% of the internalization of [125I]porcine lutropin ([125I]pLH, which bears sulfated GalNAc) could not be ascribed to the high-affinity LH receptor (LHR). In contrast, >40% of [125I]human choriogonadotropin (hCG, with sialylated sugar chains) uptake was performed by the LHR itself. When the LHR was down-regulated by excess unlabeled hormone, the LHR-independent incorporation of [125I]pLH could be inhibited in a dose-dependent fashion by sulfated polysaccharides such as fucoidan or chondroitin-(4 or 6)-sulfate, but not by other polyanionic compounds, nor by sulfated chondroitin disaccharides. Endocytosis occurred through a clathrin-dependent pathway and was inhibited by low temperature, endocytosis inhibitors, increased ionic strength, or by EDTA and dithiothreitol. Taken together, these results suggest that a Leydig cell membrane protein (possibly a lectin, or a glycosaminoglycan receptor) could perform specific LH clearance in the testis via recognition of its sulfated sugars.

Mapping of HCG-receptor complexes

Molecular forms of the porcine LH/CG receptor (pLHR) and complexes between hCG and either the full-length pLHR or its extracellular domain (ectodomain) have been produced in various recombinant systems. In COS cells and in the baculovirus insect cells system, the co-expression of the ecto- and endo-domains reconstituted a functional receptor where the association of the two domains seems to depend upon the presence of disulfide bridges. According to previous observations [39], synthetic peptides mimicking three regions of the ectodomain (21-38, 100-115, 250-272) were found to inhibit hormone binding and stimulation of cAMP production. Antisera raised against these peptides contained anti-peptide antibodies (Ab) able to interfere with hormone signalling. Moreover, the results of peptide mapping indicated that some peptides stretches may be more involved in signalling rather than in binding. Immunochemical mapping based on monoclonal antibodies (mAbs) was used to probe the hCG-ectodomain complex. It appeared that mAbs directed to epitopes present on the 'beta-tip' of hCG (assembled from the beta subunit loops 3 and 1, and previously designated site IIIb) and on the 'alpha-tip' (alpha subunit loops 1 and 3, site IIIa) bound to hCG-receptor complexes, whereas a conformational epitope (defined by the alpha-beta interface between beta seat belt C-terminus and alpha loop 2, site II) was masked. Interestingly, we and others previously reported that, in the hCG-full length receptor complex, site IIIa was shielded to mAb binding. A peptide mimicking the second extracellular loop (EL2) of the receptor endodomain was found to prevent the binding of a mAb directed to site IIIa, suggesting that this region of the endodomain may be interacting with the 'alpha-tip'. In the full-length, membrane anchored pLHR, the EL2 peptide inhibited hCG-induced cAMP production, but not binding. The possibility of inhibiting stimulation without inhibition of binding gives support to the 'negative specificity' hypothesis [6]. Thus, the ectodomain of the glycoprotein hormone receptors might be considered as a screening device preventing access of any glycoprotein hormone to the signalling peptide keys of the endodomain, which otherwise would be sensitive to any alpha subunit stimulation. Finally, antibody binding to site IIIa on the hCG-ectodomain complex was also hindered by an anti-peptide mAb directed against a peptide encoded by the eighth exon (pE x 8) of the LHR. This suggests that pEx8 is vicinal to the alpha-tip of hCG and to EL2 in the hCG-full length receptor complex. Altogether, these observations help to build up a topological model of the hCG-receptor complex.

A defined epitope on the human choriogonadotropin alpha-subunit interacts with the second extracellular loop of the transmembrane domain of the lutropin/choriogonadotropin receptor

The monoclonal antibody, HT13 recognizes human choriogonadotropin (CG) bound to the extracellular domain of its receptor, but not to the full-length receptor. The HT13 epitope is located in the regions of residues 15-17 and 73-75 of the human CG alpha-subunit. Only one synthetic peptide, lutropin (LH)/CG-receptor-(481-497)-peptide (EL2 peptide), which spans the second putative extracellular loop of the LH/CG-receptor endodomain, prevents recognition of human CG by HT13 mAb. EL2 peptide decreases hormone-induced cAMP production, but not high-affinity binding. An anti-EL2 serum also displays the capacity to inhibit human CG-stimulated cAMP production. These results suggest that the second extracellular loop of the receptor is in contact with the HT13 epitope of human CG alpha-subunit and is involved in signal transduction. A relative orientation of the hormone versus the endodomain is proposed.

Peptide and immunochemical mapping of the ectodomain of the porcine LH receptor

The LH/hCG receptor is a G protein-coupled receptor with an N-terminal extracellular domain involved in hormone-receptor interaction. The recombinant porcine receptor, stably expressed in Chinese hamster ovary (CHO) cells, has the same characteristics (Kd and cAMP production) as in Leydig cells. Six synthetic peptides derived from the receptor ectodomain and two polyclonal anti-peptide sera were tested in the homologous system porcine LH and porcine LH receptor. Their ability to inhibit hormone binding and signal transduction on CHO cells expressing the recombinant receptor was evaluated. Peptides 25-40 and 107-121 exhibited a high transduction inhibition as compared with hormone binding, peptides 21-36, 102-111, and 102-121 inhibited hormone binding more efficiently than signal transduction, and peptide 7-24 exhibited inhibition of both hormone binding and hormone-induced cAMP production. Immunoglobulins against peptides 21-36 and 102-111 inhibited both hormone binding and receptor activation suggesting that these sequences are located on the receptor surface. The data suggest that multiple, discontinuous regions of the extracellular domain of porcine LH receptor are involved in hormone binding and signal transduction. Two minimum critical sequences, 21-24 and 102-107, are involved in hormone binding and vicinal segments may be implicated in signal transduction.

The porcine follitropin receptor: cDNA cloning, functional expression and chromosomal localization of the gene

The porcine follitropin receptor-encoding cDNA (pFSHR) was cloned using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA from porcine granulosa cells was used as template. Two overlapping cDNA fragments encoding, respectively, aa 1 to 290 and aa 191 to 694 of the pFSHR were obtained. Taken together, the two fragments represented the whole coding sequence, assuming a comparable length for the FSHR from the porcine, rat and human species. Functionality of the cloned receptor was assessed by expression experiments; COS cells transfected with the pFSHR cDNA exhibited high-affinity specific binding for [125I]hFSH and FSH-dependent cAMP production. The primary sequence of the porcine FSHR N-terminal hormone-binding domain showed high percentages of identity with the sequences from ovine, human, and rat origins. A truncated form of the pFSHR cDNA, lacking aa 75 to 124 in the N-terminal domain, was also cloned and sequenced. A PCR-derived cDNA fragment of 1.45 kb was used as gene-specific hybridisation probe to map the pFSHR-encoding gene by radioactive in situ hybridization. This gene was found co-localized (as in human) with the porcine lutropin hormone receptor (pLHR)-encoding gene on the q2.2-q2.3 region of pig chromosome 3.

Influence of promoter and signal peptide on the expression and secretion of recombinant porcine LH extracellular domain in baculovirus/lepidopteran cells or the caterpillar system

Overexpression of the porcine LH receptor (pLHR) ectodomain has been achieved using the baculovirus-insect cell system but mostly in an aggregated form with no secretion. In order to carry this out, new baculoviruses were selected to produce the pLHR ectodomain in insect Sf9 cells and caterpillars. In pLHR-P10-297 and pLHR-mel-319 baculoviruses, pLHR cDNA was under the control of the P10 promoter and the polyhedrin gene promoter respectively. The constructs contained either the porcine signal peptide (pLHR-P10-297) or the insect signal peptide of melittin (pLHR-mel-319). Infected cells produced 1 x 10(5)-3 x 10(5) receptors/cell 3 days after infection. The recombinant LH receptor ectodomains produced were secreted in a biologically active form and bound the hormone with high affinity. Infected caterpillars produced a larger amount of active pLHR ectodomain that insect cells. The products were not secreted into the haemolymph however. Promoter and/or signal peptide modifications therefore enabled pLHR recombinant ectodomain secretion in a biologically active form, using the baculovirus-lepidopteran cell system. Moreover, moderate levels of expression seem to allow the production of biologically active ectodomain.

High-level expression of recombinant porcine LH receptor in baculovirus-infected insect cells or caterpillars

Porcine LH receptor ectodomain was overexpressed in insect cells and lepidopteran larvae using the recombinant baculovirus expression system. A low multiplicity of infection yielded the largest active production, of approximately 10(7) receptors/cell or 3 micrograms active receptor/mg total protein in infected cells. The truncated ectodomain solubilized with Triton X-100 bound its ligand with a high affinity which was comparable with that of the native membrane receptor. Increasing the multiplicity of infection resulted in an optimum protein production of 0.6 mg receptor/mg total protein in infected cells. This receptor was largely inactive, probably trapped within aggregation pools. Active receptor could be recovered by dilution of the samples. No secretion of recombinant receptor was ever observed whatever the conditions of infection. Expression of the recombinant receptor in insect larvae was also tested. This low-cost system failed both to increase the amount of active receptor and to induce secretion into the haemolymph. Two methods remain for producing sizeable amounts of active receptor with this baculovirus/insect cell system. One relies on immunoaffinity purification of the active protein and requires large-scale production, and the other is based on the purification of overexpressed inactive receptor followed by renaturation.

Suppression of fertility in male mice by immunization against LH receptor

We have investigated the potential contraceptive effects of immunization against the luteinizing hormone (LH) receptor in male mice at the prepubertal stage. Two N-terminal fragments of the porcine LH receptor encoding amino acids 1-297 and 1-370 were produced in large quantities through the Baculovirus insect cell system. We have immunized three-week-old mice from two Balb/c stocks of differing fecundity with Sf9 insect cells producing the short (1-297) or long (1-370) recombinant LH receptor. A booster injection was performed at six weeks using purified antigens. Ten days later, the immunized male mice were mated over a period of two weeks with adult untreated females. After weaning of the first litters, the same partners were mated once again under the same conditions. There was no decrease in the antiserum titers against the antigens over a two-month period. The circulating testosterone decreased as the anti-LH receptor antibodies increased. The fertility of the treated male mice was reduced up to 75%, depending on the mouse stock, the antigen used and the time separating immunization and mating. The impaired fertility was mostly due to male sterilization (up to 60% of sterile mates). The delay between mating and birth was enhanced by the treatment, reflecting delayed fertility and/or delayed male behaviour acquisition.

Reconstitution of a high-affinity functional lutropin receptor by coexpression of its extracellular and membrane domains

The glycoprotein hormone receptors differ from other G protein-coupled receptors by their large extracellular domain which mediates ligand binding. Cooperation between the G-protein coupled membrane domain, the extracellular domain and the hormone in establishing high-affinity binding and efficient transduction is likely to exist. Expression plasmids encoding the full-length porcine LH-hCG receptor (1-696), its extracellular (1-297) and membrane domain (298-696), as well as the alpha and beta subunits of hCG were constructed. We report that coexpression in COS cells of the two LH-hCG receptor domains restores cell surface high-affinity hormone binding and hormone dependent adenylyl cyclase activation, suggesting sufficient interactions between the two receptor domains to reconstitute a complete functional molecule. Moreover, the two hormone subunits and the two receptor domains are able to associate within coexpressing COS cells into an active complex.