** Mayne Pharma MYX.AX slides as much as 12.5% to A$4.14, lowest since November 21, 2024
** Co gets purported notice to terminate $432 million acquisition offer from U.S.-based Cosette Pharmaceuticals
** Says it intends to reject termination notice as invalid
** Stock set for biggest intraday pct loss since May 21, when MYX posted its worst day in 16 years, plunging 30%, after Cosette initiated a review of its buyout offer
** About 3.4 mln shares traded in stock's busiest day since May 21
** MYX last down 5.7%, takes YTD losses to ~10%