Abstract 1068: SDX-7320, a novel inhibitor of methionine aminopeptidase 2 (MetAP2), inhibits MCF-7 tumor growth in combination with palbociclib (Ibrance®)
Authors: Cornelius Peter , Mayes Benjamin , Dufour Pierre , Little Sara , Slee Andrew , Nir Raphael , Nir Adam , Carver Bradley J. , Shanahan James 
Published: July 2021

Abstract
Small molecule MetAP2 inhibitor TNP-470 previously showed clinical anti-tumor activity, however CNS side effects and poor drug-like properties limited its development. SDX-7320 is a polymer-drug conjugate of a novel MetAP2 inhibitor (SDX-7539), intended to improve biodistribution (limit CNS penetration) and pharmacokinetics relative to small molecule MetAP2 inhibitors. SDX-7320 has recently completed a phase I trial in late-stage cancer patients (NCT02743637). SDX-7320 was previously shown to inhibit the growth of syngeneic EO771 triple-negative breast cancers (TNBC) accelerated by obesity/metabolic dysfunction (“metabo-oncology”). In addition SDX-7320 synergized with the PI3Kα inhibitor alpelisib (Piqray®) to block the growth of ER+/Her2- MCF-7 xenografts. Here, we show that SDX-7320 inhibits the growth of MCF-7 xenografts alone and in combination with the CDK4/6 inhibitor Palbociclib (Ibrance®). Nude mice were implanted with slow release estrogen pellets and then injected with MCF-7 cells in the fourth mammary gland. Treatment began (n=10/group) when tumors exceeded 100 mm³: SDX-7320 (sc/q4d, 8 mg/kg), palbociclib (po, qd, 20 or 40 mg/kg), SDX-7320 plus palbociclib (20 mg/kg), SDX-7320 plus palbociclib (40 mg/kg). MCF-7 tumor growth inhibition at day 31 relative to vehicle-treated mice: SDX-7320, 29% (NS); palbociclib, 24% and 54% at 20 and 40 mg/kg respectively (NS); SDX-7320 plus palbociclib (20 mg/kg), 64% (p&lt;0.05); and SDX-7320 plus palbociclib (40 mg/kg), 82%, (p&lt;0.01). Tumor samples were homogenized in RIPA buffer containing protease and phosphatase inhibitors for analysis of proteins (by WES). Cell-cycle proteins (cyclin E1, E2, cdk2, cdk4) were decreased in tumor tissue from SDX-7320-treated mice relative to vehicle, and were typically lower in tumors from mice treated with SDX-7320 plus palbociclib (40 mg/kg) compared to either vehicle-treated or SDX-7320-treated mice. A key growth factor-signaling protein Akt was reduced in SDX-7320-treated groups (alone and in combination) as was estrogen receptor alpha (ERα). pAkt (S473) was lowest in SDX-7320-treated tumors and in tumors treated with SDX-7320 plus palbociclib (40 mg/kg). The autophagy marker LC3B was elevated in response to palbociclib (20 and 40 mg/kg) but in combination with SDX-7320, the increase was significantly attenuated. Intracellular pathways and proteins linked to emergence of resistance to palbociclib include cell cycle (cyclin E1), growth factor and hormone signaling (Akt, ERα) and autophagy (LC3B). The protein changes observed (representative of these pathways) suggest that combining SDX-7320 with palbociclib (Ibrance®) may extend the period of progression-free survival in patients with ER+/Her2- breast cancer relative to treatment with palbociclib (Ibrance®) alone.
Citation Format: Peter Cornelius, Benjamin Mayes, Pierre Dufour, Sara Little, Andrew Slee, Raphael Nir, Adam Nir, Bradley J. Carver, James Shanahan. SDX-7320, a novel inhibitor of methionine aminopeptidase 2 (MetAP2), inhibits MCF-7 tumor growth in combination with palbociclib (Ibrance®) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1068.