A first-in-class, first-in-human, phase I trial of p28, a non-HDM2-mediated peptide inhibitor of p53 ubiquitination in patients with advanced solid tumours

Abstract

Background: This first-in-human, phase I clinical trial of p28 (NSC745104), a 28-amino-acid fragment of the cupredoxin azurin, investigated the safety, tolerability, pharmacokinetics and preliminary activity of p28 in patients with p53(+) metastatic solid tumours.

Methods: A total of 15 patients were administered p28 i.v. as a short infusion three times per week for 4 weeks followed by a 2-week rest under an accelerated titration 3+3 dose escalation design until either a grade 3-related adverse event occurred or the maximum tolerated dose (MTD) was reached. Single-dose and steady-state serum pharmacokinetics were characterised. Assessments included toxicity, best objective response by RECIST 1.1 Criteria, and overall survival.

Results: No patients exhibited any dose-limiting toxicities (DLTs), significant adverse events or exhibited an immune response (IgG) to the peptide. The No Observed Adverse Effect Level (NOAEL) and MTD were not reached. Seven patients demonstrated stable disease for 7-61 weeks, three a partial response for 44-125 weeks, and one a complete response for 139 weeks. Three patients are still alive at 158, 140, and 110 weeks post therapy completion.

Conclusion: p28 was tolerated with no significant adverse events. An MTD was not reached. Evidence of anti-tumour activity indicates a highly favourable therapeutic index and demonstrates proof of concept for this new class of non-HDM2-mediated peptide inhibitors of p53 ubiquitination.

Figure 1

Model for stabilisation of p53 through a formation of p28 : p53 complex. p28 binds to a specific motif within the p53 DNA-binding domain that inhibits p53 proteasomal degradation and stabilizes p53, independently of HDM2. The increase in p53 transcriptionally regulates downstream genes, p21, p27, leading to inhibition of the cancer cell cycle at G₂/M.

Figure 2

Escalating dose phase I clinical trial of p28 in patients (N=15) with advanced, refractory, p53-positive (>10% cells; IHC) solid tumours.

Figure 3

Lack of immunogenicity of p28 in patients. Serum samples taken after 12 injections of p28 at each treatment level were diluted 1 : 200 to 1 : 25 000 for each assay. O.D. at 450 nm was measured with substrate, PNPP. Values represent the mean±s.e.m. of each patient in three replicates. Pre-treatment control (black), Level 1 (white), Level 2 (red), Level 3 (blue), Level 4 (green), and Level 5 (orange). Standard curve for anti-p28 antibody at 1 : 70 000 dilution was generated by direct ELISA (inset). The 96-well plates were coated with p28 (0, 0.25, 2.5, 5.0, 10, 25, 50, 100, 250, 500, and 1000 ng per well).

Figure 4

Tumour Response to p28. (A) Best response (%) of target lesions by patient. Before study entry, all patients underwent physical examination, laboratory measurements, and computed tomography scans as baseline. Tumour lesions were accurately measured in at least one dimension (longest diameter) with a minimum size of 10 mm by CT scan. Tumour response and progression were evaluated by Response Evaluation Criteria in Solid Tumours (RECIST 1.1). Complete Response (CR) was defined as disappearance of all target lesions. Partial response (PR) was defined as a 30% or above decrease in the sum of the longest diameters of target lesions, excluding complete disappearance of disease. Progressive disease (PD) was defined as a 20% or above increase in the sum of the longest diameters of target lesions. Stable disease (SD) was defined as small changes that did not meet the criteria for a PR or PD. M=melanoma, C=colon, P=prostate, S=sarcoma and Pa=pancreatic cancer. CR=green, PR=red, SD=blue, PD=black. *, Alive. All patients with tumour reduction evaluated as stable, PR and CR received either the highest or multiple levels of p28 (RECIST guideline, version 1.1; Eisenhauer et al, 2009). Values below each bar indicate the dose level (range) each patient received. ^#, progressive disease 28 December 2011, ^‡, Cancer recurrence 23 July 2012. (B,C) Representative CT images of the head region (B) prior (baseline) and (C) post trial completion (dose level 3–5). (D–F) Another subject receiving dose levels 2–5 during the trial showed complete regression of an intramuscular nodule (D), red circle=target lesion; histological examinations of target lesion in left flank before p28 administration (E) and after receiving dose levels 2–5 during the trial (F). (G) An image of a polypoid metastatic lesion in the proximal ilium that recurred after completion of the study.

Figure 5

Patient overall survival as of 4 December 2012. Survival of each patient was measured from the date the first dose of p28 was administered until death from any cause or last follow-up. M=melanoma, C=colon, P=prostate, S=sarcoma and Pa=pancreatic cancer. *Alive (green bars). CR=complete response, PR=partial response, SD=stable and PD=progressive disease. Median overall survival: 28 weeks. Range alive: 110–158 weeks, median 140 weeks. Range of date of death (DOD) for deceased patients: 7–71 weeks, Median 19 weeks. Values within each bar represent the dose level (range) each patient received. ^#, progressive disease 28 December 2011. ^‡, Cancer recurrence 23 July 2012.

Figure 6

Concentration profiles of p28 after i.v infusion. Plot of p28 concentration–time in patients receiving increasing dose levels. Serum samples were taken from patients at 0, 5, 10, 20, 30, 60, and 120 min after p28 i.v. infusion. p28 concentration in the serum was determined by LC/MS/MS assay.

Figure 7

Relationship between p53 status and patient response and survival. Complete response=green, partial response=red, stable disease=blue and progressive disease=black. *, Alive. Tissue sections representative of each patient's primary tumour were analysed for p53 status by IHC. ^#, Progressive disease 28 December 2011. ^‡, Cancer recurrence 23 July 2012.