# Molecular Impact of Platinum Drugs on the Proteasome and SQSTM1_P62 Complexes_A Paradigm Shift in Resistance

> **NIH VA I01** · OKLAHOMA CITY VA MEDICAL CENTER · 2020 · —

## Abstract

Lung cancer-related death is primarily due to disease recurrence, drug resistance, and metastasis. Platinum
compounds such as cisplatin (CDDP) and carboplatin (CBDCA) and their derivatives are widely used in the
treatment of lung cancer. Although the tumors initially respond to platinum drugs, they adeptly develop
resistance thereby escaping therapy. Therefore, understanding the mechanisms by which cancer cells evade
therapy and develop resistance is essential for developing new therapeutic approaches for lung cancer.
 This application addresses a highly innovative and high-impact area of translational research that focuses on
investigating how platinum-based drugs impact the proteasome and sequestosome (SQSTM1)/P62 function in
cancer cells to produce drug resistance in lung cancer. Further, a nanodelivery approach targeted towards the
proteasome and SQSTM1/P62 in combination with CDDP for overcoming resistance is proposed.
 Our interest in testing the proteasome and SQSTM1/P62 in chemoresistance stems from a serendipitous
observation made in the laboratory. We observed beta 5 (β5) expression, a subunit of the large 26S
proteasome complex was markedly reduced in cisplatin-resistant (CDDPR) cancer cell lines when compared to
its isogenic cisplatin-sensitive (CDDPS) cell lines. β5 is the chymotryptic component of the proteasome that is
required for degrading ubiquitinated proteins and recycling of amino-acids for synthesis of new proteins in the
cell. Associated with reduced β5 expression in the CDDPR cells was the intracellular accumulation of proteins.
Investigation into how the cellular stress induced by intracellular accumulation of proteins is overcome by the
cells revealed a role for SQSTM1/P62. The primary function of SQSTM1/P62, a scaffolding protein that is
activated in response to cellular stress, is to prevent cell death by aggregating intracellular accumulated
polyubiquitinated proteins into aggresomes and directing towards autophagy, thereby promoting cell survival.
Further, analysis for P62 expression in a subset of human lung tumor tissues showed that chemoexperienced
lung tumors had higher P62 expression compared to chemonaive tumors. Although, reduced proteasome
function and increased SQSTM1/P62 expression have previously been reported in cancer cells and in stem
cells, the impact of chemotherapy drugs on these cellular machineries and their role in contributing to
resistance has not been previously investigated and is the basis of this innovative proposal.
Based on our preliminary results, we hypothesize that alterations in the proteasome and SQSTM1/p62 function
in cancer cells contributes to platinum resistance. To test our hypothesis we have identified three specific aims.
Aim 1. Investigate how modulating the proteasome and SQSTM1/P62 in CDDPR and CDDPS cancer cells and
in normal cells alters the therapeutic response to platinum drugs in vitro.
 In this aim, the requirement of beta-5 subunit of the proteasome and SQSTM1/P62 to ...

## Key facts

- **NIH application ID:** 9815313
- **Project number:** 5I01BX003420-03
- **Recipient organization:** OKLAHOMA CITY VA MEDICAL CENTER
- **Principal Investigator:** Rajagopal Ramesh
- **Activity code:** I01 (R01, R21, SBIR, etc.)
- **Funding institute:** VA
- **Fiscal year:** 2020
- **Award amount:** —
- **Award type:** 5
- **Project period:** 2017-04-01 → 2021-09-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9815313

## Citation

> US National Institutes of Health, RePORTER application 9815313, Molecular Impact of Platinum Drugs on the Proteasome and SQSTM1_P62 Complexes_A Paradigm Shift in Resistance (5I01BX003420-03). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9815313. Licensed CC0.

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