This study is for patients that have been diagnosed with relapsed and refractory multiple myeloma (RRMM). This study is testing and investigational drug called KTX-1001. "Investigational" means it has not been approved by the United States Food and Drug Administration (FDA). The primary purpose of this study is to test the safety and tolerability of KTX-1001 and to find out how it is processed by the body. The drug is given to participants by mouth. Participants in this study can expect to be in this study until disease progression, unacceptable toxicity, or withdrawal from the study. The total duration of the study may be approximately 4 years.