Abstract # 4858
TM
LADR :
A novel linker activated drug release technology for drug delivery
Khalid Abu Ajaj, Stephan David Koester, Friederike Inga Nollmann, Simon Waltzer, Olga Fuchs, André Warnecke and Felix Kratz
CytRx Corporation, Drug Discovery Branch, Engesserstr. 4, 79108 Freiburg, Germany
Introduction
Drug carrier systems in oncology for treating cancer are based on different drug release mechanisms at the tumor site including
hydrolytic, reductive, enzymatic and/or acid-sensitive cleavage. Drug-carrier conjugates that incorporate an acid-sensitive breaking
point exploit the extra- and intracellular acidic environment of the tumor. Important requirements for acid-sensitive bonds are high
stability of the carrier-bound drug in the blood circulation and an effective or sustained release of the active drug in the acidic
tumor interstitium and the endosomes/lysosomes of tumor cells. Moreover, sufficient stability of the acid-sensitive bond aids the
galenic formulation and reconstitution of the drug candidate.
LADRTM TECHNOLOGY PLATFORM
LINKER ACTIVATED DRUG RELEASE
Substituents at the linker core allow to modulate the drug
release and hence the pharmacokinetic profile of the
chemotherapeutic agent.
Rationale
The SAR of aromatic hydrazones has so far not been studied. Hence, we explored novel aromatic hydrazone linkers and finetuned their pH-dependent release profile by substituting the aromatic moiety with electron withdrawing groups.
2
Aromatic maleimides are prone to hydrolyze at
physiological pH in contrast to aliphatic
maleimides, such as EMC.
2
aromatic drug
binding moiety
2
aromatic drug
binding moiety
3
meta
2
para
Thus, the linker library was expanded with
aromatic hydrazones (for more stability at acidic
conditions) bearing an aliphatic maleimide (for
stability towards hydrolysis).
HSA binding moiety
Scheme 1: Synthesis of an aromatic linker library (with X and Y corresponding
to electron withdrawing substituents).
INCREASED ACID STABILITY
DRUG
LADRTM-vinblastine
AROMATIC hydrazone bearing an
ALIPHATIC maleimide
DRUG
DRUG
NEMORUBICIN
AROMATIC hydrazone bearing an
AROMATIC maleimide
DRUG
+
These linkers are part of a universal tool box to create drug carrier
systems such as albumin-binding small molecules (in this case
the aromatic/aliphatic linkers are advantageous) or even ADCs
(here, the pure aromatic linkers are also an option).
HSA
1
Conclusion
2
HSA conjugates of
1a: R1=H,
3a: R1=H,
4a: R1=F,
5a: R1=H,
8a: R1=H,
9a: R1=NO2,
10a: R1=H,
Scheme 2: Synthesis of aromatic hydrazones in combination with an aliphatic maleimide
(with X corresponding to an electron withdrawing substituent).
3
HSA binding moiety
DRUG
HSA binding moiety
LADRTM-nemorubicin
R2 =H
R2=Cl
R2=H
R2=F
R2=CF3
R2=H
R2=NO2
1b:
2b:
3b:
4b:
5b:
6b:
7b:
R1=H,
R1=Cl,
R1=H,
R1=F,
R1=H,
R1=F,
R1=Cl,
Our work led to an innovative and versatile linker technology - LADRTM creating a platform for developing acid-sensitive drug-carrier conjugates
allowing controlled drug release resulting in sustained exposure to
cancer cells.
derivatives
R2 =H
R2=H
R2=Cl
R2=H
R2=F
R2=F
R2=F
Figure 1: Half-life of HSA conjugates of LADRTM-nemorubicin
conjugates at pH 5. Here, the conjugates were pre-formed at
physiological pH with dethiolated HSA. This conjugate solution was
then acidified and the release of the anthracycline was monitiored by
HPLC.
These linkers have proven to be fruitful in the synthesis of various
hydrazones of conventional as well as highly potent drugs. For example,
the gemcitabine-hydrazone DK049 emerged as a lead compound,
demonstrating superior antitumor efficacy versus gemcitabine in human
tumor xenograft models (see also Abstract #2061).
LADRTM-gemcitabine (DK049)
800
Relative Tumor Volume [%]
2
Examples of anticancer drug derivatives
using LADRTM-technology
aromatic drug
binding moiety
Control
700
Gemcitabine 4 x 240 mg/kg
600
DK049 8 x 18 mg/kg
500
400
300
200
100
0
0
10
20 30 40 50 60 70
Days after Randomization
80
90
Figure 2: Evaluation of DK049 versus gemcitabine in the
human tumor xenograft model OVFX899.