Mipsagargin, a novel thapsigargin-based PSMA-activated prodrug: results of a first-in-man phase I clinical trial in patients with refractory, advanced or metastatic solid tumours.
BACKGROUND
Mipsagargin (G-202; (8-O-(12-aminododecanoyl)-8-O-debutanoyl thapsigargin)-Asp-γ-Glu-γ-Glu-γ-GluGluOH)) is a novel thapsigargin-based targeted prodrug that is activated by PSMA-mediated cleavage of an inert masking peptide. The active moiety is an inhibitor of the sarcoplasmic/endoplasmic reticulum calcium adenosine triphosphatase (SERCA) pump protein that is necessary for cellular viability. We evaluated the safety of mipsagargin in patients with advanced solid tumours and established a recommended phase II dosing (RP2D) regimen.


METHODS
Patients with advanced solid tumours received mipsagargin by intravenous infusion on days 1, 2 and 3 of 28-day cycles and were allowed to continue participation in the absence of disease progression or unacceptable toxicity. The dosing began at 1.2 mg m(-2) and was escalated using a modified Fibonacci schema to determine maximally tolerated dose (MTD) with an expansion cohort at the RP2D. Plasma was analysed for mipsagargin pharmacokinetics and response was assessed using RECIST criteria.


RESULTS
A total of 44 patients were treated at doses ranging from 1.2 to 88 mg m(-2), including 28 patients in the dose escalation phase and 16 patients in an expansion cohort. One dose-limiting toxicity (DLT; Grade 3 rash) was observed in the dose escalation portion of the study. At 88 mg m(-2), observations of Grade 2 infusion-related reaction (IRR, 2 patients) and Grade 2 creatinine elevation (1 patient) led to declaration of 66.8 mg m(-2) as the recommended phase II dose (RP2D). Across the study, the most common treatment-related adverse events (AEs) were fatigue, rash, nausea, pyrexia and IRR. Two patients developed treatment-related Grade 3 acute renal failure that was reversible during the treatment-free portion of the cycle. To help ameliorate the IRR and creatinine elevations, a RP2D of 40 mg m(-2) on day 1 and 66.8 mg m(-2) on days 2 and 3 with prophylactic premedications and hydration on each day of infusion was established. Clinical response was not observed, but prolonged disease stabilisation was observed in a subset of patients.


CONCLUSIONS
Mipsagargin demonstrated an acceptable tolerability and favourable pharmacokinetic profile in patients with solid tumours.
University of Texas Health Science Center San Antonio, Cancer Therapy and Research Center, 7979 Wurzbach Road, U639, Mail Code 8232, San Antonio, TX 78229, USA.
D
D
Mahalingam
University of Wisconsin Comprehensive Cancer Center, Madison, WI, USA.
G
G
Wilding
Johns Hopkins University, Baltimore, MD, USA.
S
S
Denmeade
University of Texas Health Science Center San Antonio, Cancer Therapy and Research Center, 7979 Wurzbach Road, U639, Mail Code 8232, San Antonio, TX 78229, USA.
J
J
Sarantopoulas
Johns Hopkins University School of Medicine, Sidney Kimmel Comprehensive Cancer Center, Bunting/Blaustein Building, 1650 Orleans Street, Baltimore, MD 21231-1000, USA.
D
D
Cosgrove
University of Wisconsin Comprehensive Cancer Center, Madison, WI, USA.
J
J
Cetnar
Johns Hopkins University School of Medicine, Sidney Kimmel Comprehensive Cancer Center, Bunting/Blaustein Building, 1650 Orleans Street, Baltimore, MD 21231-1000, USA.
N
N
Azad
Department of Oncology, University of Wisconsin Carbone Cancer Center, 7057 Wisconsin Institutes for Medical Research, 1111 Highland Avenue, Madison, WI 53705, USA.
J
J
Bruce
Genspera Inc., Medical Monitor, 2511 North Loop 1604 W, Suite 204, San Antonio, TX 78258, USA.
M
M
Kurman
Genspera Inc., Medical Monitor, 2511 North Loop 1604 W, Suite 204, San Antonio, TX 78258, USA.
V E
VE
Allgood
Johns Hopkins University School of Medicine, Sidney Kimmel Comprehensive Cancer Center, Bunting/Blaustein Building, 1650 Orleans Street, Baltimore, MD 21231-1000, USA.
M
M
Carducci
D000368:Aged; D000369:Aged, 80 and over; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000188:drug therapy*; D011355:Prodrugs / Q000627:therapeutic use*; D019284:Thapsigargin / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*
D004791:Enzyme Inhibitors; D011355:Prodrugs; D019284:Thapsigargin