A phase Ib study of the combination regorafenib with PF-03446962 in patients with refractory metastatic colorectal cancer (REGAL-1 trial)

This was a dose-escalation phase Ib and biomarker study to assess the combination of regorafenib (Bayer Health Care Pharmaceuticals, Inc) and PF-03446962 (Pfizer, Inc.) in patients with refractory metastatic colorectal cancer. A standard “3 + 3” dose escalation was used to establish the MTD/RPTD of regorafenib and PF-03446962. The MTD was defined around toxicities in the first 28 day cycle. There was a planned escalation cohort of 6–15 additional subjects planned to enroll at the RPTD to assess safety and tolerability; however, this cohort was not opened. The cycles were 28 days long, and treatment continued until disease progression, patient refusal, or unacceptable toxicity, whichever occurred first. Patients were first treated with 120 mg of regorafenib and 4.5 mg/kg of PF-03446962. Once two subjects experienced DLT, the dose level was lowered to 3 mg/kg of PF-03446962. Archived paraffin-embedded tissue and blood were collected for future analysis of factors related to tumor growth and angiogenesis that may predict response, resistance, or toxicity.

Eligible patients were required to have histologically and/or cytologically confirmed and radiographically evaluable refractory metastatic colorectal adenocarcinoma for which regorafenib would be considered a therapeutic option. Additional inclusion criteria included: measureable disease per RECIST 1.1 criteria; age ≥ 18 years; ECOG 0 or 1; life expectancy of at least 3 months; adequate bone marrow function (as shown by ANC ≥ 1.5 × 10⁹, platelets ≥ 100 × 10⁹/L, Hgb ≥ 9 g/dL); adequate liver function (as shown by serum bilirubin ≤ 1.5 × ULN, PT/PTT/INR ≤ 1.5 × ULN; ALT and AST ≤ 2.5 × ULN); adequate renal function (CrCl ≥ 50 cc/min by Cockroft Gault or 24 h urine; presence of an archived tumor sample. Exclusion criteria included: prior failure to tolerate regorafenib at 120 mg/day; current or previous anticancer therapy within 4 weeks from D1 of study drug; major surgery or traumatic injury within 4 weeks from D1 of study drug; not recovering from the side effects of any major surgery; anticipated to have major surgery during the course of the study; hypersensitivity reactions to regorafenib and/or structural compound, biological agent, or formulation; grade 3–4 AE associated with prior anti-VEGF therapy; history of grade 3 or higher hypersensitivity attributed to humanized and/or chimeric monoclonal antibodies; patients receiving chronic, systemic treatment with corticosteroids; active brain or leptomeningeal metastases; severe COPD or other pulmonary disease with hypoxemia; poorly controlled atrial fibrillation; previous history of CVA, TIA, angina pectoris, acute MI, or history of recent re-perfusion procedures, pulmonary embolus, or untreated DVT within 6 months from start of study drug; known CAD or PVD or CVD; congestive heart failure (NYHA classification III–IV); proteinuria at screening (UA > 1+ and 24 h urine protein ≥ 1 g/24 h); severely impaired lung function; active or uncontrolled severe infection requiring treatment with IV antibiotics; liver disease; poorly controlled hypertension; impaired GI function that may significantly alter absorption of oral medications; significant vascular disease; history of hemoptysis; history of abdominal fistula or GI perforation within 6 months prior to D1 of study drug; active peptic ulcer disease, IBD, or other GI condition with increased risk of perforation or GI bleeding; use or need for full-dose anticoagulation; serious, non-healing wound, active ulcer, or untreated bone fracture; active bleeding diathesis; endobronchial lesions and/or lesions infiltrating major pulmonary vessels that increase the risk of pulmonary hemorrhage; known history of HIV, hepatitis B or C; female patients who are pregnant or breast feeding or adults of reproductive potential not willing to use effective birth control; concomitant use of CYP3A4 strong inducers or strong inhibitors; corrected QTc interval > 500 ms; history of Osler–Weber–Rendu syndrome or Hereditary Hemorrhagic Telangiectasia.

This was a single-center study approved by the Duke Institutional Review Board and following the guidelines of the Helsinki Declaration. All patients provided informed written consent prior to any study-related procedure and were treated at Duke Cancer Institute. Subject accrual took place from Sept 2014 to Nov 2015.

All subjects completed the following baseline assessments to determine eligibility prior to receiving study drug: extensive medical history, physical exam, vital signs, height and weight, ECOG performance status, baseline symptom assessment, CBC with differential, serum chemistry, pregnancy test (females of childbearing potential), PT/PTT/INR, phosphorus (if clinically indicated), TSH (if clinically indicated), amylase and lipase (if clinically indicated), urinalysis or UPCR, EKG, radiographic tumor assessment, tumor blood markers, and confirmation of archived paraffin tumor sample availability. Throughout the study treatment phase, subjects received all of the above listed assessments within 72 h prior of drug administration on D1 of the cycle, with the exception of height, EKG, radiographic tumor assessment, tumor blood markers, and confirmation of tumor availability. Subjects were also assessed for adverse events and concomitant medication administration throughout their participation in the study. On D15 of each cycle, subjects had the following assessments prior to infusion: vital signs, CBC with differential, serum chemistry, phosphorus (if clinically indicated), TSH (if clinically indicated), and amylase and lipase (if clinically indicated). Every 8 weeks, subjects were restaged and received and EKG, radiographic tumor assessment, and tumor blood markers.

Tumor response was assessed via computed tomography (CT) scan or magnetic resonance imaging (MRI) every 8 weeks using response evaluation criteria in solid tumor (RECIST) criteria (version 1.1). General symptom management and supportive care were provided as clinically indicated. Clinical activity was defined as complete response (CR), partial response (PR), or stable disease (SD).

The NCI common toxicity criteria version 4.0 was used to grade adverse events. If study treatment-related and occurring during cycle 1, the following adverse events were considered to be DLTs: hematologic toxicity (defined as any grade 4 neutropenia, thrombocytopenia, or anemia, or grade ≥ 3 neutropenia or thrombocytopenia lasting over 7 days); any grade 3 thrombocytopenia associated with bleeding; neutropenic fever; nausea/vomiting/diarrhea of grade 3 or greater lasting 3 days or more despite adequate supportive care; grade ≥ 3 ALT or AST elevation > 7 days; other non-hematologic toxicity ≥ grade 3, excluding alopecia, anorexia, fatigue, hypertension, isolated (non-clinically significant) lab abnormalities, and/or rare, idiosyncratic reactions to any study drug; treatment delay of ≥ 14 days for cycle 2 due to unresolved treatment-related toxicity; less than 75% dose intensity of regorafenib. Patients were considered evaluable for toxicity if they received any study treatment and evaluable for DLT/MTD determinations if they completed cycle 1, or experienced DLT in cycle 1.

Double-spun, platelet poor plasma was collected at baseline, every restaging, and at the time the subject came off-treatment and stored at − 80 °C. Baseline and longitudinal samples were analyzed for factors related to tumor growth and angiogenesis, including 24 blood biomarkers (supplemental). All biomarkers were measured using the CiraScan multiplex platform (Aushon Biosystems, Inc., Billerica, MA, USA), except for BMP-9 and TGFβ-R3. TGFβ-R3 [10] and BMP-9 [11] were assessed as previously described.

The objectives of this study were to assess the MTD/RPTD of PF-03446962 in combination with regorafenib, describe the safety and tolerability profile, evaluate the clinical efficacy, and explore genetic changes potentially associated with treatment. The MTD was defined by the frequency of DLTs based on the standard “3 + 3” dose-escalation study design. Adverse events (AEs) summarized safety and tolerability using frequencies and percentages. Clinical efficacy was evaluated using tumor response, progression-free survival (PFS), and overall survival (OS). Tumor response was defined by RECIST criteria v 1.1 and summarized using frequencies and percentages. The endpoint for PFS was disease progression or death from any cause. The endpoint for OS was death from any cause. The medians and confidence intervals for OS and PFS were estimated using the Kaplan–Meier method.

Plasma samples from all 11 patients were analyzed to assess the expression of 24 biomarkers related to angiogenesis and inflammation (Table 5). Markers were assessed at three time points, including baseline (prior to any treatment), during cycle 1 of therapy, and during cycle 2 of therapy. We noted that nine biomarkers (BMP-9, PlGF, TGF-β2, TGFβ-R3, TSP-2, VCAM-1, VEGF-A, VEGF-R2, and VEGF-R3) significantly changed from baseline during the first cycle of this regimen. As shown in Fig. 2a, PlGF increased (p = 0.0039), while TSP-2 decreased (p = 0.027) in the majority of patients. At later time points, we observed a reversal of these changes; levels of PlGF were decreased at cycle 2 compared to cycle 1 (p = 0.039) and levels of TSP-2 were increased at cycle 2 compared to cycle 1 (p = 0.0078) (Fig. 2b). Of the 11 patients evaluated, 2 patients exhibited SD, while 9 patients exhibited PD or were inevaluable. Dichotomizing the patients into these two groups (SD vs PD/inevaluable), we explored the potential relationship between biomarker expression and response. Due to the very small number of patients assessed, these results are considered hypothesis-generating only and highly preliminary. Nevertheless, as shown in Fig. 3, the two SD patients demonstrated higher expression of TGF-β1, PDGF-AA, and PDGF-BB compared to PD and inevaluable patients.