Transient Protection of Normal Cells During Chemotherapy

A method of reducing the effect of chemotherapy on healthy cells in a subject being treated for cyclin-dependent kinase 4/6 (CDK4/6) replication independent cancer or abnormal cell proliferation, wherein said healthy cells are hematopoietic stem cells or hematopoietic progenitor cells, the method comprising administering to the subject an effective amount of a compound of the formula:

• wherein R is C(H)X, NX, C(H)Y, or C(X)2;
• where X is a straight, branched or cyclic C1 to C5 alkyl group, and
• Y is NR1R2 wherein R1 and R2 are independently X, or wherein R1 and R2 are alkyl groups that together form a bridge that includes one or two heteroatoms (N, O, or S);
• and
• wherein two X groups can together form an alkyl bridge or a bridge that includes one or two heteroatoms (N, S, or O) to form a spiro compound;
• or
• a pharmaceutically acceptable salt thereof.