Rent expense was $41,000 for each of the three months ended March 31, 2021 and 2020.

On May 22, 2019, the Company entered into a sublease agreement for office space of 4,677 square feet in San Diego, California which expired on March 31, 2021. On March 17, 2021, the Company entered into a lease directly with the landlord for the same facility (the “San Diego Lease”) which expires on May 31, 2022. Base rent under the San Diego Lease is approximately $184,000 annually and the monthly rent expense is being recognized on a straight-line basis over the term of the lease.

The San Diego Lease is included in the accompanying condensed consolidated balance sheet at the present value of the lease payments. As the San Diego Lease does not have an implicit interest rate, the present value reflects a 10.0% discount rate which is the estimated rate of interest that the Company would have to pay in order to borrow an amount equal to the lease payments on a collateralized basis over a similar term and in a similar economic environment. The Company recognized a net operating lease right-of-use asset and an aggregate lease liability of $204,000 as of March 31, 2021, in the accompanying condensed consolidated balance sheets. The weighted average remaining lease term was 1.2 years.

Maturities of the lease liability due under this lease agreement as of March 31, 2021, are as follows (in thousands):

Maturity of lease liability	Operating Lease
2021	$	138
2022		77
Total lease payments		215
Less imputed interest		(11	)
Total operating lease liabilities		204
Less current portion of lease liability		(173	)
Lease liability	$	31

Effective in September 2019, the Company and Shanghai Pharmaceutical (USA) Inc. (“SPH USA”), the Company’s largest stockholder and an affiliate of two of the Company’s directors entered into a Materials and Supply and Services Agreement (“SPH USA Services Agreement”). Pursuant to the SPH USA Services Agreement, the Company and SPH USA will execute various statements of work for the transfer to SPH USA of key reagents and other materials, and for the supply of certain services by the Company to SPH USA, as contemplated under and in furtherance of a license and distribution agreement between the parties (see Note 4). The Company recorded amounts receivable from SPH USA related to statements of work totaling $0.3 million as of March 31, 2021 and December 31, 2020. The Company has an agreement with SPH USA for certain rights to the greater China area (see Note 4).

In connection with the securities purchase agreements and underwritten offerings described in Note 5, other investors included individuals or entities affiliated with David F. Hale, SPH USA, Daniel L. Kisner, Hazel M. Aker, and Michael G. Carter.