Poster Presentation NSW State Cancer Conference 2023

Investigation of modified glutamine transport via ASCT2 in Xenopus laevis oocytes.  (#130)

Vinitha M 1 , Adnan Bani-saad 1 , Chelsea Briot 2 , Trevor Hambley 1 , Renae Ryan 2
  1. School of Chemistry , The University of Sydney, Faculty of Science, Camperdown, NSW, Australia
  2. School of Medical Sciences, The University of Sydney, Faculty of Medicine and Health, Sydney , NSW, Australia

Background: Platinum(II) drugs are widely used to treat cancers.1,2 However, these drugs can cause harmful side effects3,4 and drug resistance5. Platinum(IV) complexes have the potential to overcome these limitations.6 Oxidation of platinum(II) allows the addition of two axial ligands which can be modified to increase their selectivity for cancer cells.7,8 Cancer cells are known to experience “glutamine addiction”9 and can die without an exogenous supply of glutamine.10,11 ASCT2 is one of 14 known mammalian glutamine transporters and is overexpressed in many cancers to meet their increased glutamine demands12,13. Platinum(IV)-glutamine complexes may improve selective drug delivery into cancer cells using ASCT2 as an entry route. Prior to synthesising platinum(IV)-complexes, we first use modified glutamine compounds to understand if modification of glutamine affects transport via ASCT2. Compound 1 was synthesised by attaching a polyethylene glycol (PEG) linker to glutamine. Theanine, an analog of glutamine was also examined.

 

Aim: To study the transport of modified glutamine compounds via ASCT2.

 

Method: Compound 1 and theanine were applied to Xenopus laevis oocytes expressing human ASCT2. Known substrates of ASCT2 – glutamine and serine and a known inhibitor – benzylserine were used as control compounds. Two-electrode voltage clamp electrophysiology was used to measure substrate elicited currents over a range of membrane potentials.

 

Results: No measurable currents were detected when 300 µM and 1 mM of compound 1 were applied to oocytes expressing ASCT2. Currents activated by the application of 100 µM serine in the presence of 300 µM compound 1 showed no significant difference. Application of 1 mM theanine to oocytes expressing ASCT2 produced an inward current similar to that observed when 1 mM benzylserine was applied. Application of 100 µM serine in presence of 1 mM benzylserine revealed reduced currents.

 

Discussion: Compound 1 is neither a substrate nor an inhibitor of ASCT2. Modification of glutamine with the PEG linker could be preventing its binding to ASCT2. Theanine has been identified as an inhibitor of ASCT2. Currents observed during application of 1 mM theanine suggest that it is binding to ASCT but is acting as an inhibitor and competing with substrates for binding.

 

Conclusion: Modification of glutamine affects its transport by ASCT2. Synthesising platinum(IV)-glutamine complexes to selectively deliver drugs into cancer cells through ASCT2 may not be possible. Other glutamine transporters that are also overexpressed in cancers should be investigated as alternative routes.

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