The primary objective of this study is to determine the safety and tolerability of utilizing the insulin-like growth factor-1-methotrexate conjugate, 765IGF-MTX for the treatment of advanced, previously treated myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML) and oligoblastic acute myelogenous leukemia (oligoblastic AML or O-AML), including determining the maximum tolerated dose (MTD).