On October 16, 2018 Five Prime Therapeutics, Inc. (Nasdaq: FPRX), a biotechnology company discovering and developing innovative immuno-oncology protein therapeutics, reported that it initiated patient dosing in the dose exploration cohort of its ongoing Phase 1 clinical trial of FPA150 (FPA150-001; NCT03514121), a targeted, first-in-class immuno-oncology antibody that targets B7-H4 (Press release, Five Prime Therapeutics, OCT 16, 2018, View Source [SID1234529927]).

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"We’re excited to be ahead of schedule in opening up our dose exploration basket cohort for FPA150, our first-in-class B7-H4 antibody, in patients whose tumors overexpress B7-H4," said Helen Collins, M.D., Senior Vice President and Chief Medical Officer of Five Prime. "B7-H4 is generating excitement in investigators because it’s expressed in tumor types that are currently not well served by immunotherapy, including breast and gynecologic cancers. We’re hopeful that a targeted therapy like FPA150 will provide clinical benefit in these patients who have limited treatment options."

B7-H4 is in the same family of checkpoint molecules as PD-L1 and, like PD-L1, appears to inhibit T-cells in preclinical models. FPA150 has a dual mechanism of action: it blocks a T cell checkpoint pathway and delivers antibody-dependent cell-mediated cytotoxicity (ADCC) against B7-H4-expressing tumor cells.

FPA150-001 is an ongoing Phase 1a/1b dose escalation and expansion clinical trial of FPA150 monotherapy in patients with advanced solid tumors. The exploratory basket cohort is a part of that trial and will include up to 10 patients whose tumors overexpress B7-H4, as assessed by an immunohistochemistry (IHC) assay. The objective of this cohort is to evaluate a range of FPA150 doses to gain additional data on safety, pharmacokinetics (PK) and potential preliminary clinical activity. All patients will undergo pre- and on-treatment biopsies to assess the pharmacodynamic effects of FPA150 on the tumor and the tumor microenvironment.

The Phase 1a dose-escalation portion of FPA150-001 in unselected patients with any solid tumor is currently ongoing. The primary objective of this portion of the trial is to identify a maximum tolerated dose (MTD) or recommended dose (RD) for FPA150 monotherapy.

Once the MTD/RTD has been identified, the company will initiate a Phase 1b dose-expansion portion of the trial in B7-H4 positive tumors, including in breast cancer, ovarian cancer and endometrial cancer. The Phase 1b dose expansion endpoints include objective response rate, as well as safety and PK.

About FPA150

FPA150 is a novel, fully human, afucosylated monoclonal antibody targeting B7-H4. B7-H4 expression is observed in multiple solid tumors, including breast and gynecologic cancers. FPA150 is designed with a dual mechanism of action: blocking the T cell checkpoint activity of B7-H4 as well as delivering ADCC against tumor cells expressing B7-H4.