"Top Student" LOXO-435 Among FGFR3 Inhibitors

Mutation or abnormal expression of protein tyrosine kinases (PTKs) is one of the main causes of cancer

Figure 1.

Mechanism of action of FGFR inhibitors

The mechanism of action of most receptor tyrosine kinase inhibitors (TKIs) targeted for cancer therapy is that after the drug (inhibitor) diffuses through the cell membrane, it inhibits the binding of ATP to the catalytic domain of tyrosine kinase (TK), thereby blocking the Intracellular signal transduction

FGFRs are composed of 4 receptor subtypes (FGFR1 to FGFR4)

However, dysregulation of FGFR can lead to constitutive activation, which is closely related to the development of several cancers, such as FGFR2 alterations in 10-16% of intrahepatic cholangiocarcinomas and FGFR3 alterations in 20% of advanced urothelial carcinomas, etc.

Figure 2.

FDA-approved FGFR inhibitors

In April 2019, Erdafitinib was approved, becoming the first FGFR-selective compound approved by the FDA for the second-line treatment of metastatic urothelial carcinoma, a potent oral pan-FGFR inhibitor against all FGFR family members (FGFR1 The IC50 values ​​to FGFR4) are all in the low nanomolar range [3]

Pemigatinib (2020) is an oral, potent, selective inhibitor of FGFR1-3, developed by Incyte Biopharmaceuticals, and the first FDA-approved targeted drug for cholangiocarcinoma

The development company of Infigratinib (2021) is QED Therapeutic, which was developed under the license of Novartis and is mainly clinically targeted at FGFR2 fusion cholangiocarcinoma refractory to chemotherapy.

However, in clinical trials, the above three approved FGFR inhibitors (Figure 3) still have some treatment-related adverse events (TRAEs), such as hyperphosphatemia, dry mouth, fatigue, skin changes, nail changes and ocular Department of disease [3] (Figure 4)

Figure 3.

Figure 4.

The development of pan-FGFR inhibitors and FGFR1-3 inhibitors has been successful, but off-target side effects (Figure 4) also point the way for subsequent development

Figure 5.

About Lilly's LOXO-435

All approved and investigational FGFR small-molecule inhibitors have similar potency against FGFR1-3 (Figure 5)

LOXO-435 origin

At the 2021 AACR meeting, Eli Lilly presented some preclinical data for LOXO-435, Figure 5 shows that LOXO-435 is potent and highly selective for FGFR3 and FGFR3 V555M enzymes, while retaining certain FGFR1 and FGFR2 activity

Figure 6.
Comparison of LOXO-435 cell viability data[4]

Figure 7.
Kinase profile data and hERG toxicity data [4]

Figure 8.
LOXO-435 exhibits a broad therapeutic index in vivo [4]

Preclinical data for LOXO-435

The kinase profile data in Figure 7 and subsequent data demonstrating the safety of the compound demonstrate that LOXO-435 is a potent, highly isoform-selective FGFR3 inhibitor with potency against FGFR3 gatekeeper resistance mutations; LOXO -435 can avoid the dose-limiting toxicity caused by inhibition of FGFR1 and FGFR2 - hyperphosphatemia and other adverse events of chronic intolerance
.
LOXO-435 caused significant tumor regression in an FGFR3 mutant in vivo model, and Eli Lilly plans to file an IND in 2022
.

Such amazing data makes people wonder what kind of structure is LOXO-435? But a search of related patents from Eli Lilly and LOXO found no published patents for FGFR3
.
Public data shows that LOXO's early business is mainly joint development with Array BioPharma Inc.
The cooperation began in July 2013 and expanded in November 2013 and April 2014.
According to the agreement, Array will provide LOXO with Compound design, development and conduct of research and preclinical testing services
.
The author searched Array's related patents for FGFR3, and the results obtained are shown in Table 1 below
.

Table 1.
FGFR3 related patents published by Array [6]

Simple Analysis of Patents

Patent WO2020131674 (A1) discloses a class of FGFR3 selective inhibitors of quinoxaline skeleton, including 30 new compounds and some biological activity data, wherein the compound of Example 27, the selectivity of FGFR3 to FGFR1 and FGFR2 in the enzyme activity test, respectively were 5-fold and 6-fold; the selectivity of FGFR3 over FGFR1 in the cell viability assay was 10.
7-fold, respectively, and the selectivity over FGFR2 was not shown
.

Patent WO2020131627 (A1) discloses a class of FGFR3 selective small molecule inhibitors of pyrazolo[1,5-a]pyridine skeleton, including 196 new compounds and almost all biological activity data, enzymatic activity, cell activity selectivity (FGFR3 vs FGFR1 and FGFR2) is almost completely better than the data in the previous patent, wherein the compound of Example 91 has 142-fold and 9.
5-fold selectivity of FGFR3 to FGFR1 and FGFR2 in the enzymatic activity test, respectively; cell activity test The selectivity of FGFR3 over FGFR1 was 22.
7-fold, respectively, and the selectivity over FGFR2 was not shown
.

Although the selectivity of the second patent is excellent enough, it is still far from LOXO-435.
The same test method LOXO-435 has a 361-fold selectivity of enzymatically active FGFR3 to FGFR1, and a 374-fold selectivity of cell-active FGFR3 to FGFR1; Therefore, the patent containing LOXO-435 is probably not yet published, but looking at the above two patents, the fragment of the red structure (a covalently bound fragment of pyrazole to piperidine to an azetidine) seems to be the key effect.
Therefore, it is speculated that the structure of LOXO-435 is likely to be a small molecule after this type of red fragment and black backbone transition
.

Figure 9.
Speculation of the above patented compound design ideas[5]

Speculation on the design ideas of the above FGFR3 selective inhibitors

As shown in Figure 9, according to the discovery process of erdafitinib, compound 1 with a quinoxaline skeleton with a pyrazole fragment was initially screened out from the compound library of VEGFR2 inhibitors, which has good selectivity for FGFR3
.
The right benzene ring fragment of 1 is connected to a m-dimethoxybenzene ring with an amino group to obtain 2, and the dimethoxybenzene ring of compound 2 occupies the hydrophobic pocket in the ATP binding pocket through van der Waals interaction, one of which is a methoxy group.
Formed a hydrogen bond with Asp641, and the subsequent optimization of the flexible amino chain resulted in Erdafitinib
.
However, the pyrazole fragment was extended and continued to optimize the red key pharmacophore fragment in Figure 9, and an inhibitor with FGFR3 selectivity was obtained; the red fragment was retained, the right quinoxaline skeleton was subjected to skeleton transition, and the substituents were optimized.
The group obtained the compound of Example 91 in the patent CN113490666A; the selectivity of FGFR3 to FGFR1 and FGFR2 in the enzyme activity test was 142 times and 9.
5 times, respectively; the selectivity of FGFR3 to FGFR1 in the cell activity test was 22.
7 times, respectively
.

Epilogue

Looking forward to the subsequent disclosure of the structure of LOXO-435, and pharmaceutical companies such as Incyte also have more layouts for FGFR3 selective inhibitors (Table 2).
FGFR3 selective inhibitors can avoid dose-limiting toxicity caused by inhibiting FGFR1 and FGFR2—— Hyperphosphatemia and other chronic intolerance adverse events have high unmet clinical needs, which can provide patients with more safe medication options
.

references:

1.
https://mp.
weixin.
qq.
com/s/uxqk5JlfMnwl7AmDB9XdFQ

2, Amit Mahipal et al;; FGFR Inhibitors in Oncology: Insight on the Management of Toxicities in Clinical Practice; Cancers 2021, 13, 2968.

3.
ZB Zengin et al.
/ Urologic Oncology: Seminars and Original Investigations 00 (2021) 1−12; https://doi.
org/10.
1016/j.
urolonc.
2021.
10.
003.

4.
Loxo Oncology; Preclinical characterization of LOXO-435 (LOX-24350), a potent and highly isoform-selective FGFR3 inhibitor; AACR-NCI-EORTC VIRTUAL INTERNATIONAL CONFERENCE Date: October 7, 2021.

5.
Doflamingo, Yaodu Public Account; Talking about FGFR Inhibitors from the Binding Mode.

6.
Yaodu database.