MacroGenics falls on early stage cancer data: ASCO

 

• Dose escalation: anti-tumor activity observed in melanoma (including one confirmed partial response) and in mCRPC patients

• Cohort expansion in mCRPC: 11/22 (50%) patients have ≥ 50% PSA reduction; anti-tumor activity observed in four of seven patients evaluated (including one unconfirmed partial response)

• Conference call and webcast with external guest presenters on Friday, June 4, 2021 at 4:30 P.M. ET

MacroGenics, Inc. (NASDAQ: MGNX), a biopharmaceutical company focused on developing and commercializing innovative monoclonal antibody-based therapeutics for the treatment of cancer, today announced preliminary safety and anti-tumor activity data from the Company’s ongoing Phase 1 clinical trial of MGC018. This investigational antibody-drug conjugate (ADC) was designed to deliver a DNA alkylating duocarmycin payload to both dividing and non-dividing cells in a B7-H3-dependent manner. The dataset will be presented in a poster titled “Phase 1 Dose Escalation Study of MGC018, an anti-B7-H3 Antibody-Drug Conjugate (ADC), In Patients with Advanced Solid Tumors” (Abstract #2631) at the upcoming 2021 American Society of Clinical Oncology (ASCO) Annual Meeting to be held June 4-8, 2021.

Dose Escalation Results Update

The ASCO abstract included data as of January 21, 2021; updated data as of a May 3, 2021 cut-off are included below and will be presented at ASCO.

A total of 29 patients with advanced solid tumors were enrolled in five dose escalation cohorts with MGC018 at 0.5 to 4.0 mg/kg, administered intravenously every three weeks. This included six patients at the 4.0 mg/kg cohort enrolled subsequent to the 2020 ASCO poster presentation. A recommended Phase 2 dose (RP2D) was defined as 3.0 mg/kg every three weeks.

mCRPC. Preliminary evidence of anti-tumor activity by MGC018 has been observed, most notably in patients with advanced metastatic castration-resistant prostate cancer (mCRPC). Reductions in prostate-specific antigen (PSA) levels of ≥ 50% were observed in five of nine mCRPC patients treated in dose escalation, including one with substantial regression of bone disease. Of the nine patients with mCRPC, eight were evaluated for tumor response, all of whom demonstrated a best response of stable disease. Two of these eight patients had measurable disease; both had reductions in target lesions, including a 29% reduction in one patient. The nine mCRPC patients treated in dose escalation received a median of four therapies prior to MGC018, including taxane chemotherapy (eight patients) and next generation hormonal agents (all patients had previously received abiraterone, enzalutamide or both). All nine mCRPC patients in dose escalation are off therapy. Of the five patients who had ≥ 50% PSA reduction, one withdrew consent (without disease progression) at 4 months, one had new bone lesions at 6 months, one initiated subsequent therapy at 6 months, and two had no progression at 7 months.

Safety. Adverse events for the dose escalation cohorts of 0.5 mg/kg to 4.0 mg/kg as of the May 3, 2021 data cut-off were generally consistent with those previously reported at ASCO 2020. MGC018-related toxicities included hematologic and skin toxicities that have been clinically manageable. In dose escalation overall, at least one treatment-related adverse event was experienced by 27 of 29 patients (93%). At 4.0 mg/kg, one patient developed a dose-limiting toxicity manifested by Grade 3 fatigue that lasted for more than 72 hours and as previously reported, a Grade 4 neutropenia occurred in a patient in the 2.0 mg/kg cohort.

Conference Call

MacroGenics’ management will host a conference call and webcast with external guest presenters to discuss the preliminary MGC018 results on Friday, June 4, 2021 at 4:30 P.M. ET. To participate in the conference call, please dial (877) 303-6253 (domestic) or (973) 409-9610 (international) ten minutes prior to the start of the call and provide the Conference ID: 1583522. The listen-only audio and slide webcast of the conference call can be accessed under "Events & Presentations" in the Investor Relations section of the Company's website at http://ir.macrogenics.com/events.cfm. A replay of the webcast will be available shortly after the conclusion of the call and archived on the Company's website for 30 days.

ASCO Presentation

The abstract for MacroGenics’ MGC018 poster presentation was submitted to ASCO in February 2021 and is available on the ASCO website at https://conferences.asco.org/am/abstracts. The poster will be available for on-demand viewing on the ASCO website and on the Events & Presentations page on MacroGenics’ website at http://ir.macrogenics.com/events.cfm on or around June 4, 2021.

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