Selpercatinib in Patients With RET Fusion-Positive Non-Small-Cell Lung Cancer: Updated Safety and Efficacy From the Registrational LIBRETTO-001 Phase I/II Trial.

PURPOSE: Selpercatinib, a first-in-class, highly selective, and potent CNS-active RET kinase inhibitor, is currently approved for the treatment of patients with RET fusion-positive non-small-cell lung cancer (NSCLC). We provide a registrational data set update in more than double (n = 316) of the original reported population (n = 144) and better characterization of long-term efficacy and safety. METHODS: Patients were enrolled to LIBRETTO-001, a phase I/II, single-arm, open-label study of selpercatinib in patients with RET-altered cancers. An analysis of patients with RET fusion-positive NSCLC, including 69 treatment-naive and 247 with prior platinum-based chemotherapy, was performed. The primary end point was objective response rate (ORR; RECIST v1.1, independent review committee). Secondary end points included duration of response (DoR), progression-free survival (PFS), overall survival, and safety. RESULTS: In treatment-naive patients, the ORR was 84% (95% CI, 73 to 92); 6% achieved complete responses (CRs). The median DoR was 20.2 months (95% CI, 13.0 to could not be evaluated); 40% of responses were ongoing at the data cutoff (median follow-up of 20.3 months). The median PFS was 22.0 months; 35% of patients were alive and progression-free at the data cutoff (median follow-up of 21.9 months). In platinum-based chemotherapy pretreated patients, the ORR was 61% (95% CI, 55 to 67); 7% achieved CRs. The median DoR was 28.6 months (95% CI, 20.4 to could not be evaluated); 49% of responses were ongoing (median follow-up of 21.2 months). The median PFS was 24.9 months; 38% of patients were alive and progression-free (median follow-up of 24.7 months). Of 26 patients with measurable baseline CNS metastasis by the independent review committee, the intracranial ORR was 85% (95% CI, 65 to 96); 27% were CRs. In the full safety population (n = 796), the median treatment duration was 36.1 months. The safety profile of selpercatinib was consistent with previous reports. CONCLUSION: In a large cohort with extended follow-up, selpercatinib continued to demonstrate durable and robust responses, including intracranial activity, in previously treated and treatment-naive patients with RET fusion-positive NSCLC.

Preclinical Evaluation and Phase Ib Study of Prexasertib, a CHK1 Inhibitor, and Samotolisib (LY3023414), a Dual PI3K/mTOR Inhibitor.

PURPOSE: Prexasertib, a checkpoint kinase 1 inhibitor (CHK1), exhibited modest monotherapy antitumor activity in previous studies. Preclinical data were generated to support the clinical combination of prexasertib + samotolisib, a PI3K/mTOR inhibitor. PATIENTS AND METHODS: Prexasertib + samotolisib was first evaluated in triple-negative breast cancer (TNBC) cells, MDA-MB-231 orthotopic xenograft tumors, and TNBC patient-derived xenograft (PDX) mouse models. In the phase Ib trial, following dose escalation, the initial expansion arm (E1, solid tumors) explored prexasertib 105 mg/m2 intravenously every 14 days + samotolisib 200 mg orally twice daily. Subsequent expansion arms evaluated samotolisib 150 mg twice daily in patients carrying PIK3CA mutations (E2, solid tumors) or with TNBC (E3). Safety and antitumor activity were assessed. RESULTS: Prexasertib + samotolisib inhibited cell proliferation in TNBC lines and primary tumor growth in the MDA-MB-231 model. Prexasertib + samotolisib exhibited synergistic or additive effects in 30 of 38 PDX single-mouse ("n = 1") models, and provided rationale for clinical evaluation. In the phase Ib study, 53 patients were enrolled (escalation, n = 13; E1, n = 9; E2, n = 15; and E3, n = 16). No dose-limiting toxicities (DLT) were observed during escalation; however, DLT-equivalent toxicities were observed in E1, leading to samotolisib dose reduction (150 mg twice daily) in E2/E3. Common treatment-related adverse events were leukopenia/neutropenia (94.3%), thrombocytopenia (62.3%), and nausea (52.8%). During escalation, 2 patients achieved partial response for an overall response rate (ORR) of 15.4%, and ORRs were 13.3% for E2 (PIK3CA) and 25% for E3 (TNBC). CONCLUSIONS: Prexasertib + samotolisib showed antitumor activity in preclinical models and preliminary efficacy in heavily pretreated patients. The clinical combination was associated with toxicity, suggesting supportive measures may be required. However, these data may inform future trials using other CHK1 and PI3K pathway inhibitors.

A randomized, phase 2 evaluation of the CHK1 inhibitor, LY2603618, administered in combination with pemetrexed and cisplatin in patients with advanced nonsquamous non-small cell lung cancer.

This phase 2 portion of a phase 1/2 study examined the efficacy and safety of LY2603618, a selective checkpoint kinase 1 inhibitor, combined with pemetrexed and cisplatin (LY+Pem+Cis) in patients with advanced nonsquamous non-small cell lung cancer (NSCLC). This multicenter, randomized, controlled, open-label study (NCT01139775) enrolled patients with stage IV nonsquamous NSCLC and an Eastern Cooperative Oncology Group performance status ≤1. Patients were randomized (2:1) to LY+Pem+Cis or pemetrexed and cisplatin (Pem+Cis). Induction therapy comprised four 21-day cycles of 500 mg/m2 pemetrexed and 75mg/m2 cisplatin on Day 1 (both arms) and 275mg LY2603618 on Day 2 (LY+Pem+Cis arm). Maintenance therapy comprised 500mg/m2 pemetrexed on Day 1 (both arms) and 275mg LY2603618 on Day 2 (LY+Pem+Cis arm) until disease progression. The primary endpoint was progression-free survival (PFS). Enrollment was permanently halted before target enrollment was met due to a greater number of thromboembolic events in the LY+Pem+Cis arm. Sixty-two patients were enrolled (LY+Pem+Cis, n=39; Pem+Cis, n=23). Bayesian and frequentist analysis demonstrated superior PFS in the LY+Pem+Cis arm vs the Pem+Cis arm (median [90% confidence interval]: LY+Pem+Cis, 4.7 months [4.-7.1]; Pem+Cis, 1.5 months [1.3-2.9]; P=0.022). Seven patients in the LY+Pem+Cis arm (vs 0 in the Pem+Cis arm) experienced serious thromboembolic events: pulmonary embolism (n=5), ischemic stroke (n=1), and cerebrovascular accident (n=1). Although the primary endpoint was met, the combination of LY2603618+Pem+Cis will not be further developed for treating advanced nonsquamous NSCLC due to the potential increased risk of thromboembolic events with this combination. ClinicalTrials.gov Identifier: NCT01139775.

The Checkpoint Kinase 1 Inhibitor Prexasertib Induces Regression of Preclinical Models of Human Neuroblastoma.

Purpose: Checkpoint kinase 1 (CHK1) is a key regulator of the DNA damage response and a mediator of replication stress through modulation of replication fork licensing and activation of S and G2-M cell-cycle checkpoints. We evaluated prexasertib (LY2606368), a small-molecule CHK1 inhibitor currently in clinical testing, in multiple preclinical models of pediatric cancer. Following an initial assessment of prexasertib activity, this study focused on the preclinical models of neuroblastoma.Experimental Design: We evaluated the antiproliferative activity of prexasertib in a panel of cancer cell lines; neuroblastoma cell lines were among the most sensitive. Subsequent Western blot and immunofluorescence analyses measured DNA damage and DNA repair protein activation. Prexasertib was investigated in several cell line-derived xenograft mouse models of neuroblastoma.Results: Within 24 hours, single-agent prexasertib promoted γH2AX-positive double-strand DNA breaks and phosphorylation of DNA damage sensors ATM and DNA-PKcs, leading to neuroblastoma cell death. Knockdown of CHK1 and/or CHK2 by siRNA verified that the double-strand DNA breaks and cell death elicited by prexasertib were due to specific CHK1 inhibition. Neuroblastoma xenografts rapidly regressed following prexasertib administration, independent of starting tumor volume. Decreased Ki67 and increased immunostaining of endothelial and pericyte markers were observed in xenografts after only 6 days of exposure to prexasertib, potentially indicating a swift reduction in tumor volume and/or a direct effect on tumor vasculature.Conclusions: Overall, these data demonstrate that prexasertib is a specific inhibitor of CHK1 in neuroblastoma and leads to DNA damage and cell death in preclinical models of this devastating pediatric malignancy. Clin Cancer Res; 23(15); 4354-63. ©2017 AACR.

Phase I Study of CHK1 Inhibitor LY2603618 in Combination with Gemcitabine in Patients with Solid Tumors.

OBJECTIVE: LY2603618, a selective inhibitor of checkpoint kinase 1 (CHK1) and key regulator of the DNA damage checkpoint, may enhance the effects of antimetabolites. This phase I study defined the recommended phase II dose of LY2603618 combined with gemcitabine. PATIENTS AND METHODS: Patients with advanced/metastatic disease were administered doses of LY2603618 (70-250 mg/m2 or flat-fixed doses of 200 or 230 mg) after gemcitabine (1,000 mg/m2). Safety and pharmacokinetics (PK) were assessed. RESULTS: Among the 50 patients enrolled, frequent adverse events possibly related to study drug treatment included fatigue (44%), decreased platelets (42%), decreased neutrophils (32%), nausea (26%), and decreased hemoglobin (20%). Systemic exposure of LY2603618 increased dose dependently, while clearance was relatively dose independent. The mean LY2603618 half-life varied; however, the durations were still suitable for maintaining human exposures while minimizing accumulation. LY2603618 PK were not altered by gemcitabine administration. Plasma exposures that correlate with the maximal pharmacodynamic effect in nonclinical models were achieved for all doses. One patient with non-small cell lung cancer carcinoma achieved a partial response; 22 patients had stable disease. CONCLUSIONS: The maximum tolerated dose of LY2603618 combined with gemcitabine was 200 mg/m2, but a fixed LY2603618 dose of 230 mg combined with gemcitabine was selected as the recommended phase II dose.