On June 4, 2018 CytomX Therapeutics, Inc. (Nasdaq:CTMX) a clinical-stage oncology-focused biopharmaceutical company pioneering a novel class of investigational antibody therapeutics based on its Probody therapeutic technology platform, reported that preliminary clinical results from two arms of the PROCLAIM (PRObody CLinical Assessment In Man) module, PROCLAIM-072 (Press release, CytomX Therapeutics, JUN 4, 2018, View Source [SID1234527137]). PROCLAIM-072 is an ongoing Phase 1/2 trial evaluating CX-072, a Probody therapeutic targeting PD-L1, as monotherapy and in combination with Yervoy (ipilimumab) or Zelboraf (vemurafenib) in patients with advanced, unresectable solid tumors. Data from the CX-072 monotherapy arm and ipilimumab combination arm were presented today in two posters as part of the Developmental Therapeutics—Immunotherapy Session at the 2018 Annual Meeting of the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) in Chicago, Illinois.
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"These first clinical results mark a major milestone for CytomX as we advance our Probody platform and introduce a fundamentally new approach to antibody therapeutic drug development," said Sean McCarthy D.Phil., president and chief executive officer of CytomX Therapeutics. "The findings presented today show that our lead wholly-owned program, the PD-L1 targeting Probody therapeutic, CX-072, has the potential to become a new centerpiece of combination cancer therapy. These preliminary results suggest that CX-072 as monotherapy and in combination with ipilimumab has a favorable safety profile and encouraging antitumor efficacy in late-stage, heavily pretreated cancer patients. Moreover, these clinical data check important boxes for the development of our core platform technology by showing that CX-072 remains stable in circulation over extended periods of dosing and elicits anti-tumor effects within the tumor microenvironment. Based on these initial results, we have initiated multiple monotherapy expansion cohorts to further explore the safety and efficacy of this potentially differentiated PD-L1 inhibitor."
Preliminary Results of the First-In-Human, Dose-Finding PROCLAIM-072 Trial of the PD-L1 Probody Therapeutic CX-072 as Monotherapy in Patients with Advanced Solid Tumors
Session: Developmental Therapeutics—Immunotherapy (Poster #285)
Presenter: Karen A. Autio, M.D., MSc., Memorial Sloan Kettering Cancer Center
The primary objectives of this first-in-human, dose-escalation, monotherapy arm are to assess safety and tolerability, including determination of the maximum tolerated dose (MTD) and the dose-limiting toxicity (DLT) of CX-072 as monotherapy. At the completion of escalation, the arm had enrolled 22 patients, with an average of four prior anti-cancer treatments in a variety of tumor types for which no anti-PD-1 or anti-PD-L1 agents are available for their disease. Patients received escalating doses of CX-072 from 0.03 mg/kg to 30 mg/kg. Enrollment is complete and patient follow-up is ongoing.
Monotherapy Well Tolerated
The maximum tolerated dose (MTD) was not reached. As of an April 20, 2018 data cutoff, results showed that the administration of monotherapy CX-072 was well tolerated with the majority of treatment-related adverse events (TRAEs) as Grade 1/2. Grade 3/4 TRAEs were reported in two patients: neutropenia and thrombocytopenia in a patient with thymic cancer (3 mg/kg) and transaminase elevation in a patient with breast cancer (30 mg/kg). Both events were successfully managed with therapeutic intervention including steroids and discontinuation of CX-072.
Evidence of Activity
As of an April 20, 2018 data cutoff, results showed that among 20 evaluable patients who received CX-072, objective responses by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1, a commonly used guideline for evaluating tumors, were observed in 3 (15%) patients: thymoma (unconfirmed PR (uPR); 3 mg/kg), PD-L1 negative TNBC (confirmed PR; 10 mg/kg) and cervical cancer (uPR; 10 mg/kg) (all partial responses (PR)). Stable disease was observed in 8 patients (40%) for a disease control rate of 55%. Decreased target lesions were observed in 42% (8/19) of all evaluable patients with measurable disease at baseline and in 60% (6/10) of the subset of patients who received > 3 mg/kg of CX-072. Two of the responders were still on treatment (8 months each) at the time of the data cutoff.
Evidence of Probody Platform Performance
Results from a preliminary single-dose pharmacokinetic analysis of single-agent CX-072 suggest that, as designed, CX-072 circulates predominantly as the intact masked prodrug across all dose levels. Further, CX-072 is only minimally influenced by target mediated drug disposition at low doses, suggesting that masking is effective in blocking interaction with PD-L1 in the periphery.
Based on these preliminary safety, efficacy and translational data, further evaluation of CX-072 monotherapy (10 mg/kg every two weeks) is now underway in 8 expansion cohorts in a variety of cancer types.
Preliminary Interim Results of the First-In-Human, Dose-Finding PROCLAIM-072 Trial of the PD-L1 Probody Therapeutic CX-072 in Combination with Ipilimumab in Patients with Advanced Solid Tumors
Session: Developmental Therapeutics—Immunotherapy (Poster #286)
Presenter: Rachel E. Sanborn, M.D., Earle A. Chiles Research Institute, Providence Cancer Center
The primary objectives of this ongoing arm of the study are to assess safety and tolerability, and to determine the MTD and DLT of CX-072 when administered in a concomitant combination schedule with ipilimumab. At the April 20, 2018 data cutoff, the study had enrolled 16 immunotherapy naïve patients who had received an average of four prior anti-cancer treatments in a variety of tumor types for which no anti-PD-1 or PD-L1 agents were available for their disease. Patients received the combination ipilimumab (3 mg/kg) and CX-072 (escalating doses of 0.3 mg/kg to 10 mg/kg) every three weeks for four cycles followed by monotherapy CX-072 every two weeks.
Combination with Ipilimumab Well Tolerated
As of the April 20, 2018 data cutoff date, the MTD had not yet been reached and no new safety signals were observed beyond those expected for each component of the ipilimumab plus CX-072 combination. The majority of TRAEs were Grade 1/2. Of the 16 treated patients, 5 (31%) reported a Grade 3/4 TRAE, a rate similar to that reported previously for 3 mg/kg ipilimumab monotherapy1. These events included: Grade 3 colitis (n=1), Grade 3 dyspnea/pneumonitis (n=1), Grade 3 headache/Grade 3 hyponatremia (n=1), and Grade 3 amylase/Grade 4 lipase (n=1)2. A dose limiting toxicity of Grade 3 dyspnea was reported in one patient. The study is still ongoing with enrollment and dose escalation continuing.
Evidence of Activity
As of an April 20, 2018 data cutoff, results also showed that among 12 evaluable patients who received ipilimumab (3 mg/kg) combined with CX-072 (0.3 to 10 mg/kg), 3 (25%) achieved objective responses by RECIST v1.1, including patients with: anal cancer (confirmed complete response (CR); 0.3 mg/kg CX-072), testicular cancer (uPR; 1 mg/kg CX-072) and cancer of unknown primary (uPR; 3 mg/kg CX-072). Stable disease was observed in 8% of patients for a disease control rate of 33%. All 3 of the responders remained on treatment (10, 6 and 5 months, respectively) at the data cutoff.
Preliminary Single-Dose Clinical Pharmacokinetics of an anti-PD-L1 Probody Therapeutic in Cancer Patients
ASCO Supplement of the Journal of Clinical Oncology [J Clin Oncol 36, 2018 (suppl; abst 214558)]. (Abstract #e14558)
Preliminary pharmacokinetic clinical data showed that single-agent, single-dose CX-072 behaved as designed and circulated predominantly as the intact antibody prodrug and is only minimally affected by target-mediated drug disposition, consistent with being effectively masked in circulation.
Conference Call and Webcast
CytomX will host a conference call and live webcast with slides today, Monday, June 4, 2018, beginning at 5:00 p.m. CT/ 6:00 p.m. ET to discuss these data presentations. This event can be accessed in three ways:
From the CytomX website: View Source Please access the website 15 minutes prior to the start of the call to download and install any necessary audio software.
By telephone: Participants can access the call by dialing 1-877-809-6037 (United States) or 1-615-247-0221 (International) referencing Conference ID 4294667.
By replay: A replay of the webcast will be located under the Investor Relations section of CytomX’s website approximately two hours after the conclusion of the live call and will be available for 30 days following the call.
About PROCLAIM
PROCLAIM (Probody Clinical Assessment In Man) is an international umbrella program designed to evaluate CytomX’s Probody therapeutics. The first module is the PROCLAIM-CX-072 clinical program, an open-label, dose-finding Phase 1/2 trial evaluating CX-072 as monotherapy and in combination with Yervoy (ipilimumab) or Zelboraf(vemurafenib) in patients with metastatic or locally advanced unresectable solid tumors or lymphomas. CytomX aims to achieve three goals as part of the PROCLAIM-072 clinical trial:
Tolerability: Demonstrate that CX-072 is well tolerated in patients and potentially improves safety, particularly in the combination setting.
Anti-cancer activity: Demonstrate initial evidence of CX-072’s anti-cancer activity as monotherapy and in combination.
Translational program and Probody platform proof-of-concept: Explore mechanistic aspects of Probody activity in patients as observed in preclinical models.