CRUK is testing a MCT1i produced by AstraZeneca (NCT01791595) and some data have been presented in the past [1]. The reason I mention this is because a second (MCT4i) is likely going to be moved forward into the clinic [2] and this paper tested both with metformin [3].

A second company is also active in this space. Some data on their lead [4] and they are working on a second (MTC1i).

Refs:

1 https://ascopubs.org/doi/10.1200/JCO.2017.35.15_suppl.2516

2 https://cancerres.aacrjournals.org/content/79/13_Supplement/1207

3 https://www.cell.com/cell-reports/fulltext/S2211-1247(18)31806-0

4 https://www.phenex-pharma.com/wp-content/uploads/2020/01/AACR_2019_MCT4.pdf