Cytotoxic ribonuclease variants
Cytotoxic variants of human ribonuclease 1 (RNase 1) identified through analysis of the interaction between RNase 1 and the human ribonuclease inhibitor (hRI) as defined by the three dimensional (3-D) atomic structure of the RNase1 hRI complex are disclosed. Also disclosed is the 3-D structure of the hRI.RNase 1 complex and methods for designing and using the RNase 1 variants.
1. A method for inhibiting the proliferation of cancer cells, comprising delivering to the cells an effective amount of an engineered human ribonuclease (RNase 1), wherein said RNase 1 comprises a variant of SEQ ID NO:2, wherein said variant matches SEQ ID NO:2 at all positions other than positions 4, 7, 11, 31, 32, 38, 39, 41, 42, 66, 67, 71, 85-94, 111, and 118 and wherein said variant has at least four amino acid substitutions relative to SEQ ID NO:2 at positions selected from the group consisting of 4, 7, 11, 31, 32, 38, 39, 41, 42, 66, 67, 71, 85-94, 111, and 118, wherein said substitutions include at least:
(a) one amino acid substitution located within residues 85 to 94 of SEQ ID NO:2;
(b) the amino acid substitution G38R at residue 38 of SEQ ID NO:2; and
(c) two amino acid substitutions at amino acid residues selected from the group consisting of residues 4, 7, 11, 31, 32, 39, 41, 42, 66, 67, 71, 111 and 118 of SEQ ID NO:2.
2. The method of claim 1 , wherein at least one of the amino acid substitutions located within residues 85 to 94 of SEQ ID NO: 2 is at an amino acid residue selected from the group consisting of residues 88, 89 and 91 of SEQ ID NO: 2.
3. The method of claim 2 , wherein at least one of the amino acid substitutions located within residues 85 to 94 of SEQ ID NO:2 is selected from the group consisting of substitutions at residues 88 and 91 of SEQ ID NO:2.
4. The method of claim 2 , wherein each of the amino acid substitutions located within residues 85 to 94 of SEQ ID NO:2 are at amino acid residues selected from the group consisting of residues 88, 89 and 91 of SEQ ID NO:2.
5. The method of claim 4 , wherein the amino acid substitutions located within residues 85 to 94 of SEQ ID NO:2 consist of three amino acid substitutions at residues 88, 89, and 91 of SEQ ID NO:2.
6. The method of claim 5 , wherein the difference in amino acid sequence from an RNase 1 protein comprising SEQ ID NO:2 consists of the following substitutions of SEQ ID NO:2: R4C/G38R/R39G/N67R/N88L/G89R/R91GN118C.
7. The method of claim 4 , wherein the amino acid substitutions located within residues 85 to 94 of SEQ ID NO:2 consist of one amino acid substitution at residue 88 of SEQ ID NO:2.
8. The method of claim 7 , wherein the amino acid substitutions at amino acid residues selected from the group consisting of residues 4, 7, 11, 31, 32, 39, 41, 42, 66, 67, 71, 111 and 118 of SEQ ID NO: 2 consist of two amino acid substitutions at residues 39 and 67 of SEQ ID NO: 2.
9. The method of claim 8 , wherein the difference in amino acid sequence from an RNase 1 protein comprising SEQ ID NO:2 consists of the following substitutions of SEQ ID NO:2: G38R/R39G/N67R/N88R.
10. The method of claim 1 , wherein the engineered RNase 1 retains ribonucleolytic activity relative to SEQ ID NO:2.
11. The method of claim 1 , wherein the engineered RNase 1 exhibits enhanced cytotoxic activity relative to SEQ ID NO: 2.
12. The method of claim 1 , wherein the engineered RNase 1 exhibits a lower binding affinity for hRI than SEQ ID NO:2.
13. The method of claim 1 , wherein the engineered RNase 1 retains ribonucleolytic activity, exhibits enhanced cytotoxic activity relative to SEQ ID NO: 2, and has a lower binding affinity for hRI than SEQ ID NO:2.