Methods for determining the cause of somatic mutagenesis
The invention relates generally to methods for determining the likelihood that targeted somatic mutagenesis of a nucleic acid molecule by a mutagenic agent has occurred, and the likelihood that a mutagenic agent is a cause of targeted somatic mutagenesis of a nucleic acid molecule. The invention further relates to methods for diagnosing cancer in a subject and/or determining the likelihood that a subject has or will develop cancer, and methods for treating subjects diagnosed with cancer or determined to be likely to have or to develop cancer. In further aspects, the invention relates to methods for identifying motifs in nucleic acid molecules that are recognized or targeted by mutagenic agents.
1. A method for treating a cancer in a human subject, the method comprising:
selecting a human subject on the basis of the occurrence of targeted somatic mutagenesis, wherein the occurrence of targeted somatic mutagenesis indicates that the subject is likely to have or to develop cancer; and
exposing the subject to a therapy for treating the cancer, wherein
targeted somatic mutagenesis has occurred when there is a higher than expected percentage or number of mutations of a mutation type at one of three positions in a codon in a plurality of mutated codons in a nucleic acid molecule in a biological sample taken from the subject, wherein:
the nucleic acid molecule comprises the whole exome;
the mutations are at a motif recognized or targeted by APOBEC3G;
the number or percentage of observed G>A mutations in CG motifs at MC-2 sites in the non-transcribed strand of the nucleic acid molecule is higher than expected, or the number or percentage of observed C>T mutations in CG motifs at MC-1 sites in the non-transcribed strand of the nucleic acid molecule is higher than expected;
the cancer is selected from the group consisting of breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic and ovarian cancer; and the biological sample comprises, respectively, breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic or ovarian tissue or cells; and
the therapy comprises radiotherapy, surgery, chemotherapy, hormone ablation therapy, pro-apoptosis therapy and/or immunotherapy,
thereby treating the cancer.
2. The method of claim 1 , wherein the liver cancer is hepatocellular carcinoma, or wherein the skin cancer is melanoma.
3. The method of claim 1 , wherein prior to selecting the subject, the method further comprises analyzing a sequence of the nucleic acid molecule in a biological sample taken from the subject to determine for a plurality of mutations of a mutation type at one or more motifs recognized or targeted by a mutagenic agent the codon context of those mutations to thereby identify the location of a mutation and mutation type for each of a plurality of mutated codons in the nucleic acid molecule, wherein the codon context of an individual mutation is determined by determining at which of the three positions of a corresponding mutated codon the individual mutation occurs, and determining that targeted somatic mutagenesis is likely to have occurred when there is a higher than expected percentage or number of mutations of a mutation type at one of the three positions in the plurality of mutated codons, and determining that the subject is likely to have or to develop cancer when targeted somatic mutagenesis has occurred.
4. The method of claim 3 , wherein prior to analyzing the sequence of the nucleic acid molecule in a biological sample, the method further comprises sequencing the nucleic acid molecule.
5. A method for treating a cancer in a human subject, the method comprising:
isolating a nucleic acid molecule from a biological sample obtained from a human subject;
determining the sequence of the nucleic acid molecule;
determining whether targeted somatic mutagenesis has occurred, wherein targeted somatic mutagenesis has occurred when there is a higher than expected percentage or number of mutations of a mutation type at one of three positions in a codon in a plurality of mutated codons in the nucleic acid molecule, wherein:
the nucleic acid molecule comprises the whole exome;
the mutations are at a motif recognized or targeted by APOBEC3G; and
the number or percentage of observed G>A mutations in CG motifs at MC-2 sites in the non-transcribed strand of the nucleic acid molecule is higher than expected, or the number or percentage of observed C>T mutations in CG motifs at MC-1 sites in the non-transcribed strand of the nucleic acid molecule is higher than expected;
selecting the subject as being likely to have cancer when targeted somatic mutagenesis has occurred; and
exposing the subject to a therapy for treating the cancer; wherein the therapy comprises radiotherapy, surgery, chemotherapy, hormone ablation therapy, pro-apoptosis therapy and/or immunotherapy,
thereby treating the cancer, wherein the cancer is selected from the group consisting of breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic and ovarian cancer; and the biological sample comprises, respectively, breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic or ovarian tissue or cells.