Selpercatinib (LOXO-292) and pralsetinib (BLU-667) are highly potent RET-selective protein tyrosine kinase inhibitors (TKIs) for treating advanced RET-altered thyroid cancers and non-small-cell lung ...cancer (NSCLC). It is critical to analyze RET mutants resistant to these drugs and unravel the molecular basis to improve patient outcomes.
Cell-free DNAs (cfDNAs) were analyzed in a RET-mutant medullary thyroid cancer (MTC) patient and a CCDC6-RET fusion NSCLC patient who had dramatic response to selpercatinib and later developed resistance. Selpercatinib-resistant RET mutants were identified and cross-profiled with pralsetinib in cell cultures. Crystal structures of RET-selpercatinib and RET-pralsetinib complexes were determined based on high-resolution diffraction data collected with synchrotron radiation.
RETG810C/S mutations at the solvent front and RETY806C/N mutation at the hinge region were found in cfDNAs of an MTC patient with RETM918T/V804M/L, who initially responded to selpercatinib and developed resistance. RETG810C mutant was detected in cfDNAs of a CCDC6-RET-fusion NSCLC patient who developed acquired resistance to selpercatinib. Five RET kinase domain mutations at three non-gatekeeper residues were identified from 39 selpercatinib-resistant cell lines. All five selpercatinib-resistant RET mutants were cross-resistant to pralsetinib. X-ray crystal structures of the RET-selpercatinib and RET-pralsetinib complexes reveal that, unlike other TKIs, these two RET TKIs anchor one end in the front cleft and wrap around the gate wall to access the back cleft.
RET mutations at the solvent front and the hinge are resistant to both drugs. Selpercatinib and pralsetinib use an unconventional mode to bind RET that avoids the interference from gatekeeper mutations but is vulnerable to non-gatekeeper mutations.
•Resistance to selpercatinib and pralsetinib are found at the solvent front and hinge sites of the RET kinase domain.•The identified selpercatinib-resistant RET mutants are cross-resistant to pralsetinib.•Selpercatinib and pralsetinib use an unprecedented binding mode to dock into the RET kinase.•The new kinase inhibitor binding mode avoids the interference from gatekeeper mutations but remains vulnerable to non-gatekeeper mutations.
The phase I/II FIGHT-101 study (NCT02393248) evaluated safety, pharmacokinetics, pharmacodynamics, and preliminary efficacy of pemigatinib, a potent and selective fibroblast growth factor receptor ...(FGFR) 1-3 inhibitor, as monotherapy or in combination therapy, for refractory advanced malignancies, with and without fibroblast growth factor (FGF) and receptor (FGFR) gene alterations.
Eligible, molecularly unselected patients with advanced malignancies were included in part 1 (dose escalation; 3 + 3 design) to determine the maximum tolerated dose. Part 2 (dose expansion) evaluated the recommended phase II dose in tumors with or where FGF/FGFR activity is relevant.
Patients (N = 128) received pemigatinib 1-20 mg once daily intermittently (2 weeks on/1 week off; n = 70) or continuously (n = 58). No dose-limiting toxicities were reported. Doses ≥4 mg were pharmacologically active (maximum tolerated dose not reached; recommended phase II dose 13.5 mg once daily). The most common treatment-emergent adverse event (TEAE) was hyperphosphatemia (75.0%; grade ≥3, 2.3%); the most common grade ≥3 TEAE was fatigue (10.2%). Dose interruption, dose reduction, and TEAE-related treatment discontinuation occurred in 66 (51.6%), 14 (10.9%), and 13 (10.2%) patients, respectively. Overall, 12 partial responses were achieved, most commonly in cholangiocarcinoma (n = 5) as well as in a broad spectrum of tumors including head and neck, pancreatic, gallbladder, uterine, urothelial carcinoma, recurrent pilocytic astrocytoma, and non-small-cell lung cancer (each n = 1); median duration of response was 7.3 months 95% confidence interval (CI) 3.3-14.5 months. Overall response rate was highest for patients with FGFR fusions/rearrangements n = 5; 25.0% (95% CI 8.7% to 49.1%), followed by those with FGFR mutations n = 3; 23.1% (95% CI 5.0% to 53.8%).
Pemigatinib was associated with a manageable safety profile and pharmacodynamic and clinical activity, with responses seen across tumors and driven by FGFR fusions/rearrangements and mutations. These results prompted a registrational study in cholangiocarcinoma and phase II/III trials in multiple tumor types demonstrating the benefit of precision therapy, even in early phase trials.
•Pemigatinib (selective FGFR 1-3 inhibitor; 13.5 mg QD) was safe and demonstrated pharmacologic/clinical activity.•Active across a broad spectrum of tumors, most commonly in cholangiocarcinoma.•The results supported those of FIGHT-202 that led to pemigatinib approval for advanced FGFR2-rearranged cholangiocarcinoma.•Pemigatinib may also have potential benefit in multiple other cancers with FGFR rearrangements and/or mutations.
Combined therapy with dabrafenib plus trametinib was approved in several countries for treatment of BRAF V600E-mutant anaplastic thyroid cancer (ATC) based on an earlier interim analysis of 23 ...response-assessable patients in the ATC cohort of the phase II Rare Oncology Agnostic Research (ROAR) basket study. We report an updated analysis describing the efficacy and safety of dabrafenib plus trametinib in the full ROAR ATC cohort of 36 patients with ∼4 years of additional study follow-up.
ROAR (NCT02034110) is an open-label, nonrandomized, phase II basket study evaluating dabrafenib plus trametinib in BRAF V600E-mutant rare cancers. The ATC cohort comprised 36 patients with unresectable or metastatic ATC who received dabrafenib 150 mg twice daily plus trametinib 2 mg once daily orally until disease progression, unacceptable toxicity, or death. The primary endpoint was investigator-assessed overall response rate (ORR) per Response Evaluation Criteria in Solid Tumors version 1.1. Secondary endpoints were duration of response (DOR), progression-free survival (PFS), overall survival (OS), and safety.
At data cutoff (14 September 2020), median follow-up was 11.1 months (range, 0.9-76.6 months). The investigator-assessed ORR was 56% (95% confidence interval, 38.1% to 72.1%), including three complete responses; the 12-month DOR rate was 50%. Median PFS and OS were 6.7 and 14.5 months, respectively. The respective 12-month PFS and OS rates were 43.2% and 51.7%, and the 24-month OS rate was 31.5%. No new safety signals were identified with additional follow-up, and adverse events were consistent with the established tolerability of dabrafenib plus trametinib.
These updated results confirm the substantial clinical benefit and manageable toxicity of dabrafenib plus trametinib in BRAF V600E-mutant ATC. Dabrafenib plus trametinib notably improved long-term survival and represents a meaningful treatment option for this rare, aggressive cancer.
•The phase II ROAR basket trial led to regulatory approvals of dabrafenib plus trametinib in BRAF V600E-mutant ATC.•This updated analysis includes the full enrollment of 36 patients and ∼4 years of additional study follow-up.•Investigator-assessed responses were observed in 56% of patients, with 50% of responders still in response at 12 months.•Median OS was 15 months, with the 12-month rate of 52% being notable given historic median OS of <6 months.•This updated analysis confirms the definitive benefit of dabrafenib plus trametinib in ATC with long-term follow-up.
Aberrant activation of RET is a critical driver of growth and proliferation in diverse solid tumours. Multikinase inhibitors (MKIs) showing anti-RET activities have been tested in RET-altered tumours ...with variable results. The low target specificity with consequent increase in side-effects and off-target toxicities resulting in dose reduction and drug discontinuation are some of the major issues with MKIs. To overcome these issues, new selective RET inhibitors such as pralsetinib (BLU-667) and selpercatinib (LOXO-292) have been developed in clinical trials, with selpercatinib recently approved by the Food and Drug Administration (FDA). The results of these trials showed marked and durable antitumour activity and manageable toxicity profiles in patients with RET-altered tumours. The European Society for Medical Oncology (ESMO) Translational Research and Precision Medicine Working Group (TR and PM WG) launched a collaborative project to review the available methods for the detection of RET gene alterations, their potential applications and strategies for the implementation of a rational approach for the detection of RET fusion genes and mutations in human malignancies. We present here recommendations for the routine clinical detection of targetable RET rearrangements and mutations.
•New selective RET inhibitors have activity and favourable toxicity profiles in RET-altered solid tumours.•There is a need to identify the optimal techniques to detect RET alterations.•In those tumours where RET fusions or mutations are highly recurrent, FISH or RT-PCR could be used.•In cancers rarely RET rearranged, broad panel assays query RET fusions to allow screening in a histotype-agnostic manner.
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