Rain Plans $100 Million IPO, Phase III Trial for Lead Precision Cancer Therapy

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Newark, California-based cancer company Rain Therapeutics filed Friday for a $100 million IPO to advance its lead MDM2 inhibitor RAIN-32 into Phase III testing. The news comes months after the company closed a $63 million Series B and inlicensed RAIN-32 from Daiichi Sankyo.

Rain licenses and develops precision cancer therapies. The new lead program, RAIN-32, previously completed Phase I testing in patients with solid tumors or lymphomas. The influx of cash will support a pivotal Phase III trial in liposarcoma, which Rain intends to launch this year, plus two more Phase II trials in solid tumors and intimal sarcoma, respectively.

Preclinical data published by independent French researchers last year suggested MDM2 inhibitors had therapeutic potential for treating liposarcomas, where MDM2 amplification is common.

MDM2 is an inhibitor of tumor-suppressive p53, a notoriously challenging drug target. Several companies are developing MDM2 inhibitors to act upstream of p53, with limited success, which Rain attributes to dose-limiting hematological toxicities.

Last year, Roche ended development of its MDM2 inhibitor, idasanutlin, then in Phase II testing for patients with acute myeloid leukemia (AML). The most advanced anti-MDM2 therapy is APG-115, which Ascentage Pharma has in multiple Phase Ib/II trials for solid tumors and hematologic malignancies, plus a Phase II combination trial with checkpoint inhibitor Keytruda (pembrolizumab) for anti-PD-1 refractory or relapsed cancers. At least two other companies–Novartis and Aileron–also have MDM2 inhibitors in early clinical testing for several cancers.

According to Rain, the safety and tolerability data from Daiichi Sankyo’s trial suggest RAIN-32 can be dosed longer than other MDM2-targeting programs in development.

Rain also has a preclinical RAD52 inhibitor program, licensed from Drexel University in August 2020. RAD52 plays a role in DNA damage response and the company is exploring therapies for breast and ovarian cancers characterized by BRCA1/2 mutations. The company is aiming to select a lead clinical RAD52 inhibitor candidate in 2022. There are no known RAD52 inhibitors in clinical trials.

As recently as last year, its previous lead candidate tarloxotinib, licensed from the University of Auckland, was in Phase II testing for patients with EGFR and ErbB Exon 20 insertion mutations in solid tumors.

The company has not announced an end to the trial but tarloxotinib is not named in Rain’s Securities and Exchange Commission (SEC) forms or listed on the company’s website. Rain did not respond to a request for clarification in time for publication.

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