Abstract
Normal human genomic DNA (N-DNA) and mutated DNA (M-DNA) from K562 leukemic cells show different thermodynamic properties and binding affinities on interaction with anticancer drugs; adriamycin (ADR) and daunomycin (DNM). Isothermal calorimetric thermograms representing titration of ADR/DNM with N-DNA and M-DNA on analysis best fitted with sequential model of four and three events respectively. From Raman spectroscopy it has been identified that M-DNA is partially transformed to A form owing to mutations and N-DNA on binding of drugs too undergoes transition to A form of DNA. A correlation of thermodynamic contribution and structural data reveal the presence of different binding events in drug and DNA interactions. These events are assumed to be representative of minor groove complexation, reorientation of the drug in the complex, DNA deformation to accommodate the drugs and finally intercalation. Dynamic light scattering and zeta potential data also support differences in structure and mode of binding of N and M DNA. This study highlights that mutations can manifest structural changes in DNA, which may influence the binding efficacy of the drugs. New generation of drugs can be designed which recognize the difference in DNA structure in the cancerous cells instead of their biochemical manifestation.
Highlights
Improvement in therapeutic activity and selectivity is a major goal in the development of anticancer agents
For both the drugs examined the Isothermal titration calorimetry (ITC) thermograms showed negative heat deflection, consistent with exothermic binding to both types of DNA. These thermograms from the built in software fitted best with sequential binding model
In such processes bonds are broken to bring higher disorder or openness (B to A transition) in the structure in order to accommodate a rather complex intercalation with bulky group binding in the minor groove with release of water from binding interface to the bulk and stabilized by hydrophobic forces [13,43]. This state (+ve DH and +ve DS) is not observed in mutated DNA (M-DNA) as the DNA adapts partial B to A transition due to mutation and further intercalation does not bring about significant conformational changes. These structural changes are evidenced by appearance of new peaks in Raman spectra in N-DNA drug complexes, which are representative of A form DNA (Table 2)
Summary
Improvement in therapeutic activity and selectivity is a major goal in the development of anticancer agents. The genetic differences between the normal cells and cancerous cells are exploited by several molecular targeted drugs like imatinib and trastuzumab, which show promising therapeutic activity and low toxic side effects [1,2]. Current gene targeting therapeutic strategies still face significant challenges owing to acquired drug resistance and genomic instability of cancer cells [3,4,5]. The multiple genetic alterations (mutations) disturb the DNA structure in cancer cells and can be considered as therapeutic target instead of biochemical manifestations. Such alterations in DNA structure were identified in myeloid leukemic cells (K562), where a partial conformational change from B to A form was reported by us [6]
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