# Prospective effect of linkers type on the anticancer activity of pemetrexed-monoclonal antibody (atezolizumab) conjugates

## TL;DR

This study explores how different linkers affect the cancer-fighting ability of a drug-antibody conjugate, showing better results with a new linker.

## Contribution

The novel use of gamma amino butyric acid (GABA) as a linker in a pemetrexed-atezolizumab conjugate is demonstrated for the first time.

## Key findings

- PMX-GABA-AtZ conjugate showed an IC50 of 0.048 µM, significantly lower than PMX alone or PMX-PEG-AtZ.
- GABA linked two PMX molecules per conjugate, while PEG linked only one.
- The conjugate demonstrated dose- and time-dependent anticancer activity against A549 lung cells.

## Abstract

Background: Conventional chemotherapy results in severe toxic side effects due to affecting normal and cancer cells. The conjugation of chemotherapy with mAb will improve the chemotherapy selectivity towards cancer cells and at the same time will potentiate immune system to detect and kill cancer cells. The aim of the study was to prepare atezolizumab-pemetrexed conjugate using two types of linkers (linker conjugated with -NH2 of lysine amino acid in the mAb).

Methods: This study utilizes (for the first time) the mAb atezolizumab (AtZ) to prepare a new, selective conjugate carrier for pemetrexed (PMX) by using gamma amino butyric acid (GABA) as linker for the first time in comparison to the commonly used linker polyethylene glycol (PEG) using carbodiimide (EDC) / N-hydroxysulfosuccinimide (Sulfo-NHS) zero length cross linker. Stepwise evaluation for PMX-linkers linkage as well as mAb conjugates was evaluated by FTIR,
1HNMR, DSC, LC-MS, gel-electrophoresis as well as the anticancer activity against lung cells A549.

Results: The work revealed that two molecules of GABA combined with PMX, which in turn conjugated with an average ratio of 4:1 with mAb, while one molecule of PEG combined with PMX, which in turn conjugated with mAb in the same average ratio. The IC
50 for the prepared PMX-GABA-AtZ conjugate was 0.048 µM, which was much lower than PMX alone, antibody AtZ alone as well as PMX-PEG-AtZ conjugate in a dose and time dependent manner.

Conclusions: The potential use of such conjugate that selectively directed to the overexpressed lung cells antigen in a low dose leading to reduction of serious side effects of PMX and the cost of therapeutically AtZ mAb used.