Brentuximab

Brentuximab verdotin was approved by the U.S. FDA in August 2011 for treatment of Hodgkin’s lymphoma (HL) in patients who have failed autologous stem cell transplant (ASCT) or ASCT ineligible patients who have failed at least two prior chemotherapy regimens, and for second line treatment of systemic anaplastic large cell leukemia (ALCL). Brentuximab verdotin is a chimeric (mouse V region/human C region) CD30 binding monoclonal antibody (cAC10) that is conjugated via cysteine residues to a small molecule comprising a cysteine reactive dipeptide linker moiety and the microtubule polymerization inhibitor monomethyl auristatin E(MMAE). The antibody component of the drug binds to CD30 expressing tumor cells, and the active cytotoxic component, MMAE, is released by proteolytic cleavage of the dipeptide linker moiety.

Seattle Genetics (United States)

Adcetris

Brentuximab vedotin is an antibody drug conjugate that is comprised of an anti-CD30 antibody and the potent tubulin based inhibitor monomethyl auristatin E (MMAE). These two entities are connected together via a linker consisting of a maleimide conjugation handle that includes an enzyme-cleavable valine-citrulline- para-aminobenzylcarbamate group. This conjugation handle releases MMAE after internalization of the conjugate by the cancer cell that recognizes the antibody. Brentuximab vedotin was discovered by Seattle Genetics who co-developed the conjugate with Millenium Pharmaceuticals. Brentuximab vendotin has been approved for the treatment of relapsed or refractory systemic anaplastic large cell lymphoma (ALCL) and relapsed or refractory Hodgkin’s lymphoma. Brentuximab vedotin is also undergoing clinical trials for the treatment of CD30-expressing cutaneous T-cell lymphoma and CD30-positive hematologic malignancies. Although brentuximab vedotin is classified as a biologic, an exception has been made to include it in this year’s review because the small molecule portion of the conjugate was prepared by total synthesis.

The synthesis of brentuximab vedotin and monomethyl auristatin E (MMAE) has only been described on small scale. However, large-scale preparation follows the same strategy described for the total synthesis of dolastatin 10 which was originally described by the Pettit research group at the University of Arizona. MMAE is a pentapeptide that includes two unusual gamma amino acids, dolaproine (Dap) and dolaisoleuine (Dil).The synthetic strategy to enable the preparation of brentuximab vedotin is highly convergent and requires the preparation of a Val-Val-Dil tripeptide, a Dap-norephederine dipeptide and the MalC-Val-Cit-PABA linker. The synthesis of Val-Val-Dil was initiated from Cbz-protected N-methyl-isoleucine 77 by reduction to the corresponding alcohol with borane and subsequent oxidation to Cbz-protected isoleucinal 78 using dimethyl sulfoxide and sulfur trioxide¨Cpyridine complex. This was accomplished in high overall yield for the two steps without epimerization. Aldol condensation of aldehyde 78 with tert-butyl acetate using LDA provided a 4:3 mixture of diastereomers, from which the desired alcohol diastereomer 79 was isolated in 34% yield. Methylation of 79 with trimethyloxonium tetrafluoroborate afforded methyl ether 80 in 87% yield. Hydrogenolysis using 5% palladium on carbon in ethyl acetate/methanol in the presence of hydrogen chloride provided the Dil coupling partner (81) in 63% yield with minimal lactam by-product formation.76 Peptide coupling with Cbz-protected valine 82 using PyBrop provided 83 in 55% yield. After Cbz deprotection under hydrogenolysis to give 84, an additional peptide coupling was performed with Fmoc-protected methyl Val 85 employing diethyl cyanophosphonate (DEPC) as the coupling reagent provided the protected Val-Val-Dil tripeptide 86 in 50% yield.


The synthesis of the Dap-norephederine dipeptide was initiated with a 1,2 addition of cis potassium crotyltrifluoroboronate to Boc protected prolinal 87 in the presence of tetrabutylammonium iodide to give alcohol 88 in 89% yield with a 94:6 diastereomeric ratio. Methylation of the resulting hydroxy group with sodium hydride followed and methyl iodide provided ether 89 in 76% yield, which was followed by oxidative cleavage of the double bond with ruthenium oxide, furnishing Boc protected Dap 90 in 75% yield. Amide coupling to (1S, 2R)-norephederine 91 using DEPC gave rise to the Dap coupling partner 92 in 84% yield.

The synthesis of the MalC-Val-Cit-PABA linker fragment was initiated with condensation of succinate ester Fmoc-Val 93 with citrulline (94) to give protected Val-Cit 95 in 78% yield. EEDQ-mediated coupling to para-aminobenzylalcohol provided protected Val-Cit-PABA 96 in 80% yield. Removal of the Fmoc protecting group with diethylamine delivered free amine 97 which was condensed with the activated ester 98 to provide MalC-Val-Cit-PABA 99 in high yield. Activation of the alcohol with para-nitrophenyl chloroformate afforded the linker coupling partner 100 in 15% yield.

The fully elaborated MalC-Val-Cit-PABC-MMAE linker/payload is prepared as described in the scheme. Tripeptide 86 and dipeptide 92 were combined and treated with trifluoroacetic acid to remove both the t-butyl ester protecting group of 86 and Boc protecting group of 92, then this mixture was further treated with DEPC to produce Fmoc-protected MMAE 101 in 91% yield. Removal of the Fmoc group by treatment with diethylamine produced MMAE which was subsequently coupled to linker 100 in the presence of HOBt to give MalC-Val-Cit-PABC-MMAE 103 in 57% yield.

Potentially hazardous interactions with other drugs
Antifungals: possible increased risk of neutropenia with ketoconazole.
Antipsychotics: avoid with clozapine, increased risk of agranulocytosis.
Cytotoxics: increased risk of pulmonary toxicity with bleomycin - avoid.
Live vaccines: avoid concomitant use.

Brentuximab vedotin consists of a monoclonal antibody conjugated with monomethyl auristatin E (MMAE). Only a small fraction of MMAE released from brentuximab vedotin is metabolised; this metabolism is mainly via oxidation by cytochrome P450 isoenzyme CYP3A4/5. MMAE is eliminated in the faeces (72% unchanged) and urine.