Cellular uptake of metallated cobalamins

Abstract

Cellular uptake of vitamin B12-cisplatin conjugates was estimated via detection of their metal constituents (Co, Pt, and Re) by inductively coupled plasma mass spectrometry (ICP-MS). Vitamin B12 (cyano-cob(iii)alamin) and aquo-cob(iii)alamin [Cbl-OH2](+), which differ in the β-axial ligands (CN(-) and H2O, respectively), were included as control samples. The results indicated that B12 derivatives delivered cisplatin to both cellular cytosol and nuclei with an efficiency of one third compared to the uptake of free cisplatin cis-[Pt(II)Cl2(NH3)2]. In addition, uptake of charged B12 derivatives including [Cbl-OH2](+), [{Co}-CN-{cis-PtCl(NH3)2}](+), [{Re}-{Co}-CN-{cis-PtCl(NH3)2}](+), and [{Co}-CN-{trans-Pt(Cyt)(NH3)2}](2+) (Cyt = cytarabin) was high compared to neutral B12, which implied the existence of an additional internalization pathway for charged B12 vitamin analogs. The affinities of the charged B12 derivatives to the B12 transporters HC, IF and TC were similar to that of native vitamin B12.

Facilitating the Cellular Accumulation of Pt-Based Chemotherapeutic Drugs

“…Various platinum-(II) and platinum-(IV) agents have been loaded/conjugated into a large variety of lipid, polymeric, inorganic nanocarriers, which include liposomes, nanoparticles, and nanotubes [51,52]. Using cisplatin-sensitive Ehrlich ascites tumor cells (EATC) and their cisplatin-resistant counterpart, Ehrlich Lettré ascites cells (ELA), Tran and co-workers tested vitamin B12 (cyano-cob(III)alamin) as a drug carrier for cisplatin [54]. Cisplatin-induced activation of apoptosis, verified by the caspase 3 activity, is almost impaired in ELA cells compared to EATC, partly due to reduced cytosolic/nuclear Pt accumulation [55] and a concomitant reduction in Pt binding to DNA (Figure 3A).…”

“…As tissue B12 accumulation increased 350% upon overdosing of the vitamin [62], the use of B12 as a drug carrier could ensure a certain transport capacity. Constructing a positively charged [{Re}-{Co}-CN-{ cis -PtCl(NH 3 ) 2 }] + complex, consisting of a {fac-Re(CO) 3 } + and a [ cis -PtCl(OH 2 )(NH 3 ) 2 ] + moiety conjugated to the B12 structure (Figure 3C), Tran and co-workers showed that, despite the chemical modification, the compound retained good affinity to all B12 transport proteins [54]. Furthermore, as the metals (Co, Re, Pt) in the B12-drug conjugate could be measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) ( 59 Co, 195 Pt, and 187 Re) it was shown that [{Re}-{Co}-CN-{ cis -PtCl(NH 3 ) 2 }] + not only accumulated in the cytosol/nucleus of EATC, ELA, and human immortalized myelogenous leukemia (K562) cells (Figure 3D), but Pt was also bound to DNA and no substantial Pt was released from the B12 structure to the extracellular compartment [54].…”

“…Constructing a positively charged [{Re}-{Co}-CN-{ cis -PtCl(NH 3 ) 2 }] + complex, consisting of a {fac-Re(CO) 3 } + and a [ cis -PtCl(OH 2 )(NH 3 ) 2 ] + moiety conjugated to the B12 structure (Figure 3C), Tran and co-workers showed that, despite the chemical modification, the compound retained good affinity to all B12 transport proteins [54]. Furthermore, as the metals (Co, Re, Pt) in the B12-drug conjugate could be measured by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) ( 59 Co, 195 Pt, and 187 Re) it was shown that [{Re}-{Co}-CN-{ cis -PtCl(NH 3 ) 2 }] + not only accumulated in the cytosol/nucleus of EATC, ELA, and human immortalized myelogenous leukemia (K562) cells (Figure 3D), but Pt was also bound to DNA and no substantial Pt was released from the B12 structure to the extracellular compartment [54]. It should be noticed that the positively charged [{Re}-{Co}-CN-{ cis -PtCl(NH 3 ) 2 }] + was preferentially taken up as compared to native B12 [54] and that the cytosolic and nuclear Pt accumulation was always 1.6-fold higher than Co (Figure 3D).…”

Vitamin B12–Metal Conjugates for Targeted Chemotherapy and Diagnosis: Current Status and Future Prospects

“…Although this derivative proved promising, low cytotoxicity is still a major drawback, [17,22] owing to the less efficient cell uptake in comparison with cisplatin. [24] On the other hand, conjugate 2 was also shown to be preferentially taken up into cellular compartments in relation to neutral native vitamin B 12 , [24] and this feature can be exploited by attaching additional pharmacophores or radiolabeled scaffolds to the platinum center.…”

“…A possible explanation has recently been proposed; it was based on the fact that the exploitation of vitamin B 12 as a drug carrier may be restrained by decreased cellular loading capacity of the corresponding vitamin B 12 -metal conjugates. The cellular uptake of the vitamin B 12 [24] The new compound 11 (Figure 7) may be regarded as a "prototype" theranostic agent in which vitamin B 12 is used as a carrier both for cisplatin (chemotherapeutic) and for the {fac-Re I (CO) 3 } moiety (a model for Tc and Re radiopharmaceuticals). Results clearly indicated that the affinities of all the three conjugates towards the vitamin B 12 transporters HC, IF, and TCII were similar to that of native cyanocobalamin, and that they were able to deliver cisplatin-like derivatives both to cellular cytosol and to nuclei.…”