On September 30, 2019 X4 Pharmaceuticals, Inc. (Nasdaq: XFOR), a clinical-stage biopharmaceutical company focused on the development of novel therapeutics for the treatment of rare diseases, reported positive results from the Phase 2a portion of its open-label Phase 1/2 clinical trial of mavorixafor (X4P-001) in combination with axitinib (Inlyta) in patients with advanced clear cell renal cell carcinoma (ccRCC) (Press release, X4 Pharmaceuticals, SEP 30, 2019, View Source [SID1234539945]). Data were presented at the European Society for Medical Oncology (ESMO) (Free ESMO Whitepaper) 2019 Congress today in Barcelona.

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Combination therapy with mavorixafor and approved tyrosine kinase inhibitor (TKI) axitinib was generally well tolerated with a manageable safety profile and demonstrated clinical improvement with encouraging median progression free survival (mPFS) in a heavily pretreated advanced ccRCC patient population. Of the 65 patients in the trial, 49 patients (or 75%) received mavorixafor + axitinib as a third- to ninth-line therapy, having received between two and eight prior therapies with a TKI, immuno-oncology (IO) agent, or other systemic therapy. Fifty-seven of the 65 patients in the trial (or 88%) had an intermediate or poor prognosis.

Overall mPFS across clinically evaluable patients receiving mavorixafor + axitinib (n=62) was 7.4 months. Predefined subpopulations examined patients with immediate prior TKI and IO treatment. Patients treated in the subgroup with immediate prior TKI therapy (n=34) demonstrated an objective response rate (ORR) of 18% and an increased mPFS of 7.4 months. This is a greater than 50% improvement from the 4.8-month historical mPFS with axitinib alone.1 Patients treated with mavorixafor + axitinib in the subgroup with immediate prior IO therapy (n=18) had an ORR of 61% and an increased mPFS of 11.6 months. In addition, eight of the 65 patients remain on the combination therapy today, with durations of treatment of 17 months or longer. Results suggest mavorixafor may enhance clinical response to axitinib and other TKIs that target tumor angiogenesis, as well as immunotherapy agents.

"In recent years a growing number of vascular endothelial growth factor (VEGF) TKI-based therapies (e.g., axitinib + pembrolizumab), have improved outcomes for patients with ccRCC. Despite these advances, most patients eventually develop resistance to therapy, and new treatment options are necessary to meet this unmet medical need," commented David F. McDermott, M.D., Beth Israel Deaconess Medical Center, Harvard Medical School and lead investigator of the study. "In this trial of mavorixafor, a novel CXCR4 pathway inhibitor, and axitinib in patients with metastatic ccRCC who had failed prior therapy, the combination was well tolerated and the anti-tumor activity was encouraging. We look forward to confirming the efficacy of mavorixafor in a randomized trial."

This Phase 1/2, multi-center, open-label trial of mavorixafor in combination with axitinib included 65 patients with histologically confirmed advanced ccRCC, all of whom received at least one prior systemic therapy. The safety analyses included 65 patients from Phases 1/2 who were treated with 400 mg mavorixafor (200 mg twice daily or 400 mg once daily) + 5 mg axitinib twice daily. Treatment responses were assessed using Response Evaluation Criteria in Solid Tumor, or RECIST v1.1 (a validated set of criteria to assess changes in tumor burden), every eight weeks from day one for 80 weeks, and then every 12 weeks thereafter, by blinded, independent central review. Treatment-related serious adverse events were diarrhea, hyperkalemia and hypertension (n=2, or 3%) and blood creatinine increased, dehydration, fatigue, hepatic enzyme increase, nausea, sepsis, trachea-oesophageal fistula, and vomiting (n=1 each, or 1.5%).

"These promising results, especially among heavily pre-treated patients with poor prognoses, add to a published body of evidence supporting mavorixafor’s generally favorable safety and tolerability profile and its novel CXCR4 mechanism of action that has been shown to induce immune-mediated antitumor activity as a single agent and in combination with approved therapies," said Lynne Kelley, M.D., FACS, Chief Medical Officer of X4 Pharmaceuticals. "We are encouraged by these data, including the eight patients who remain on combination therapy with mavorixafor and axitinib for 17 months or longer. We look forward to continuing to explore the potential benefit of mavorixafor in underserved cancer patients with solid tumors, including as a potential triple combination agent in addition to TKI and checkpoint inhibitor therapies or in combination with other standard of care treatments."

Mavorixafor is a potentially first-in-class, once-daily, oral, small molecule antagonist of chemokine receptor CXCR4. CXCR4 signaling is thought to contribute to the lack or loss of tumor responsiveness to angiogenesis inhibitors, like axitinib. Elevated expression of CXCR4 by RCC tumors is also correlated with an overall poor prognosis. In xenograft models studied previously, mavorixafor in combination with axitinib, a VEGF receptor TKI, reduced myeloid-derived suppressor cell infiltration and proangiogenic signals, and demonstrated greater than additive antitumor activity.

Details of the investor conference call and webcast are as follows:
Time and Date: Monday, September 30 at 8:00 AM EDT / 2:00 PM CEST
US Toll-Free Dial-In Number: (866) 721-7655
International Dial-In Number: (409) 216-0009 / Spain 0934923253
Conference ID: 4787329
Webcast: A live audio webcast of the conference call may be accessed in the "Investors" section of the Company’s website at the following link: View Source

About Mavorixafor

X4 Pharmaceuticals’ lead product candidate, mavorixafor (X4P-001), is a potentially first-in-class, once-daily, oral inhibitor of CXCR4, currently in Phase 2 development for the treatment of clear cell renal cell carcinoma (ccRCC). Mavorixafor has demonstrated single and combination agent activity and proof of mechanism in Phase 1b and Phase 2a trials, respectively, along with a favorable safety and tolerability profile. Mavorixafor is also in development for the treatment of WHIM syndrome, as well as Severe Congenital Neutropenia (SCN) and Waldenström’s macroglobulinemia (WM). Mavorixafor was designated orphan drug status by the U.S. Food and Drug Administration in 2018 and by the European Commission in 2019 for the treatment of WHIM syndrome.