M344 is a histone deacetylase (HDAC) inhibitor also known as D237 or MS 344. It inhibits human HDACs, and shows a three-fold selectivity for inhibition of HDAC6 over HDAC1. M344 has been found to increase the sensitivity of human squamous carcinoma cells to radiation. It has also been found to promote cell cycle arrest and apoptosis in human ovarian cancer cells and endometrial cancer. M344 can also inhibit maize HDAC.